Contents

Acknowledgements i-ii

List of Figures iii-vii

List of Tables viii

Chapter 1– Introduction 1-7

1.1 Background information 1-2

1.2 Problem delineation 2-3

1.3 Present status and scope of work 3-5

1.4 Objectives 5

1.5 Implication of work

1.6 Organization of thesis

6

7

Chapter 2– Geology and Stratigraphy of the Marwar Supergroup 8-14

2.1 Introduction 8-9

2.2 Geology and Classification of the Marwar Supergroup 9-11

2.3 Study area: Jodhpur and surrounding areas 11-12

2.4 Marwar Supergroup: age assessment 13-14

Chapter 3 – Methodology 15-22

3.1 (a) Field work 15

(b) Laboratory work 15-16

3.2 Petrography 16

3.2.1 Sandstone section 17-18

3.2.2 Giant Nodule

18-20

3.2.3 Carbonate Investigation 20-21

3.2.4 Nagaur Sandstone 21-22

Chapter 4 – Systematic Palaeontology 23-95

4.1 Palaeontology 23

4.1.1 Animal body fossil from the Jodhpur Group 23-36

a. Five-armed body fossil 23-26

b. Marsonia artiyansis 27-33

c. Hiemalora 34

d. Aspidella 34-35

4.1.2 Plant fossils 37-51

4.1.3 Microbial Mats 52-69

4.1.4 Stromatolites from the Bilara Group 70-72

4.1.5 Trace fossils from the Nagaur Group 73-95

Chapter 5 – Biozonation and Correlation 96-109

5.1 Biozonation 96

A. Body fossils 96-98

B. Organo-sedimentary Structures 99-101

C. Trace fossils 101-103

D. Microfossils 103-104

5.1.1 Discussions 104-105

5.2 Correlation 106-109

Chapter 6- Conclusions 110-114

References 115-126

i 

 

ACKNOWLEDGEMENTS The thesis is the end of journey for obtaining my Ph.D. but heralds the beginning of a new era in the field of research. It is the thesis that builds a passion for getting updated in the field of research and creates enthusiasm for keeping us on track. However, the completion of thesis seems to be partial without the support and encouragement of numerous people including mentor, well-wishers, friends, colleagues and family. So most humbly, I would like to thank all those people who made this thesis possible and an unforgettable experience for me. It is a pleasant task to express my thanks to all those who contributed in many ways to the successful completion of this study and made it an unforgettable moment.

At this moment of accomplishment, I pay respect to Dr. S. Kumar whose guidance, tremendous support, critical analysis of my work, depth of views and continuous encouragement. Due to his incredible guidance and valuable suggestions, I have successfully overcome many hurdles of the thesis work and learned a lot.

I am also extremely indebted to my mentor and supervisor Dr. A.K. Jauhri, to accomplish my research work. I owe his greatness for selecting me as a student at the critical stage of my Ph.D. I warmly thank, for his valuable advice, constructive criticism and his extensive discussions regarding my work.

It feel privileged in acknowledging Dr. Sunil Bajpai, Director, Birbal Sahni Institute of Palaeobotany, Lucknow for his kind support and motivation for my thesis with new and better directions.

It is my humble submission to give regards to Dr. Mukund Sharma, Scientist F, Birbal Sahni Institute of Palaeobotany, Lucknow for his continuous and sincere encouragement and inspiration for my research work and boosting me with proper guidance for research completion.

I pay respectful thanks to Prof. K.K. Agarwal, Head, CAS in Geology, University of Lucknow, Lucknow, for providing me with adequate facility and soothing environment in the department.

I gratefully acknowledge the suggestion and the help received from Dr. Adolf Seilacher, Tübengen University, Germany and Dr. Nigel Hughes, University of California, during the field work.

My sincere thanks are due to Prof. I.B. Singh, Prof. Ashok Sahni and Prof. M.P.Singh for their understanding, encouragement and personal attention for providing valuable ideas for my thesis work. I express my gratitude to Prof. A.R. Bhattacharya, Prof. N.L. Chhabra, Prof D.D. Awasthi, Prof. Vibhuti Rai, Prof. R. Bali, Dr. Ajai Mishra, Dr. D.S. Singh, Dr. S. Sensarma, Dr. Munendra Singh, Dr. A.K. Kulshrestha and Mr. Ajay Arya for their help and cooperation.

I express deep sense of gratitude to Dr. D.M. Banerjee, Delhi University, for valuable guidance in the field. I am also thankful to Dr. Purnima Srivastava, Department of Geology, University of Lucknow for her constant support and valuable suggestion.

I would also like to thank my seniors and colleagues specially Dr. Naval K. Tewari, Dr. Atal B. Shukla, Dr. Ajay P. Singh, Dr. Alok Thakur, Dr. Yogendra Bhadauria, Mrs. Akansha Bhadauria, Dr. Anju Verma, Dr. Biswajeet Thakur, Dr. Anju Saxena, Dr. Amit K. Singh, Dr. Santosh Kumar Pandey, Dr. Vikram Bhardwaj, Dr. S. Nawaz Ali, Dr. Kamlesh K. Verma, Dr. Krishna Gopal Mishra, Dr. Pankaj Sharma, Mr. Sushant Singh, Dr. Amit Awasthi, Mr. Saurabh Rastogi, Mr. Kalyan Krishna, Mr. Ashish Sharma, Mrs. Nivedita Sarkar and Mr. Ankur

ii 

 

Kashyap for help and discussion in compilation of this work. Late Mr. P.K. Joshi who of great help in finalizing the figures during the early days of my research work is thankfully acknowledged.

I would like to express my particular appreciation of Dr. Pranay Vikram Singh for his useful suggestions and constant motivation towards completion of this work. His critical remarks on findings of research work have helped me to improve my work. I am indebted to my friends Mr. Dheerendra Kumar, Mr. Chandra Prakash, Mr. Amit Singh, Mr. Dharmendra Kumar Jigyasu, Mr. Shailendra Kumar Prajapati, Mrs. Droupti Yadav, Ms. Nigar Jahan, Ms. Purnima Sharma, Ms. Shasi Verma, Mr. Rohit Kuvar, Mr. Parijat Mishra, Mr. Gaurav Joshi and Mr. Shakti Yadav for providing stimulating and congenial environment. My warm appreciation is due to Dr. Pawan Govil, Mr. Veeru Kant Singh, Dr. Arjun Singh Rathore, Ms. Bandana Dimri and Mr. Keshav Ram for providing me hospitable research environment. My sincere thanks goes to Mr. Ashok Verma and Mr. Anuj Saxena for his technical support in times of urgent need and requirements.

I take this opportunity to say heartfelt thanks to Late Mr. B.B. Singh and Late Mrs. Sheela Singh for blessings and source of inspiration. Thanks are also due to Mr. Anand Singh Chauhan and Mrs. Mandavi Singh Mr. Vishwajeet Singh for their moral support.

I feel highly indebted to Ms. Arunabha Singh for their unconditional moral support and help me in finalizing my thesis work.

I also wish to thanks all the non-teaching staff of Geology Department for their constant support.

Words fail me to express my gratitude towards my father Late Mr. Abdul Salim who gave me freedom to choose my path and always encouraged me to achieve my goal. He was always beside me during the happy and hard moments to push me and motivate me. This thesis is dream of my father and is fulfilled with the grace of God.

It’s my fortune to gratefully acknowledge the support of my family members My mother Mrs. Afrooz Khatoon, My elder brothers Mr. Javed Ahmad, Mr. Suhail Ahmad and my sisters Ms. Zarina Parveen, Ms. Shahnaaz for their moral support, encouragement all through my work. I owe everything to them.

I take this opportunity to sincerely acknowledge the Department of Science and Technology (DST)(vide letter no SR/S4/ES-348/2008), Government of India, New Delhi, for providing financial assistance in the form of Junior Research Fellowship which buttressed me to perform my work comfortably and later on SRF fellowship awarded by CSIR, New Delhi (Fellowship no. 09/528(0019)/2013 EMR-I).

Besides this, several people have knowingly and unknowingly helped me in the successful completion of this project.

(Shamim Ahmad)

iii  

List of Figures

Page No.

Fig. 1.1 : Generalized geological map of the Marwar Supergroup (redrawn and modified after Pareek, 1981).

3

Fig. 3.1 : Well developed Salt Pseudomorphs of various shapes in shale on the

road side on Bhopalgarh - Dhanapa road. 17

Fig 3.2 : Photomicrograph of Quartz arenite of Jodhpur Sandstone; a and b)

Showing the compact arrangement of quartz grain in cross nicol and PPL respectively; c and d) Quartz grain showing subrounded to rounded in cross nicols.

18

Fig. 3.3 : Giant nodules seen in the Jodhpur Sandstone. There is no lithologic

difference between the host rock and the lithology of the nodule, except the hardness. a. The host rock is seen both at the base as well as at the back of the nodule, in which the nodule is embedded, b. The host rock is also seen associated with the nodule, c. Outer margin of the giant nodule showing parallel differential markings in the sandstone, d. Transverse section of the giant nodule showing clearly marked circular margin and lack of any internal structure; the entire surface looks homogenous, e. and f. Photomicrographs of sandstone forming the nodule and host rock. The sandstones are made up of subangular to subrounded detrital quartz grains cemented together by silica (under crossed nicols). e. Sandstone of the nodule; f. Sandstone of the host rock.

19

Fig. 3.4 : Photomicrograph of Limestone of Bilara Group. a-b) Gotan limestone

showing microcrystalline calcite in cross nicol and PPL respectively. Quartz vein is also observed in the thin section.

21

Fig. 3.5 : Photomicrograph of Quartz arenite of Nagaur Sandstone; a and b)

Showing the compact arrangement of quartz grain in cross nicol and PPL respectively.

21

Fig. 4.1 : Geological and location map of the Marwar Supergroup, western

Rajasthan, showing study area (after Pareek, 1984). 24

Fig. 4.2 : Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Sursagar

mine, western Rajasthan. 25

Fig. 4.3

: Five-armed body fossil on the bedding surface of the Jodhpur Sandstone. A and C) Five-armed body fossil; B) Line diagram of the fossil seen in A and B) Enlarged view of (C) showing a disc-like structure at the centre of the body fossil.

25

Fig. 4.4 : A, Location map of the Jodhpur area, western Rajasthan. B, Geological

map of the Jodhpur area, showing fossil locality, (Redrawn after Raghav et al., 2005).

27

Fig. 4.5 : Detailed geological map of the Artiya Kalan area, Jodhpur District,

Rajasthan showing fossil locality (Redrawn after Raghav et al., 2005). 28

iv  

Fig. 4.6 : Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Artiya Kalan

area, western Rajasthan. 28

Fig. 4.7 : A) Field photograph of the Jodhpur Sandstone; arrow marks the position

of the fossil-bearing horizon; B) Section of the Jodhpur Sandstone (Sonia Sandstone) exposed in a pit near the Artiya Kalan area, district Jodhpur. The lower part is made up of sandstone and the upper part is made up of shale and siltstone which has yielded the fossils; C) Marsonia artiyansis shows wrinkled margin at the outer bell with four radial arms originating from the central part of the medusa, Sample no. SK/AK-1; D) Specimen showing smooth outer margin with elevated central disc up to 2mm in height, Sample no. SK/AK-2 and E) (i) Upper surface of the poorly preserved medusa showing wrinkled outer margin. When sample in E (i) was chipped it yielded a sample E (ii) which on its sole shows marks of the radial arms with negative relief and E (iii) is its counterpart which shows arms in positive relief.

31

Fig. 4.8 : Marsonia artiyansis shows variation in size as well as in the outer

margin from smooth to wrinkled. A) (sample no. SK/AK-21) and B) (sample no. SK/AK-23), Smooth outer margin with dislocated radial arms; C) “a” and “b” are the counter parts of the same specimen; “a” shows raised central part showing central disc with four radial arms; outer margin smooth, sample no. SK/AK-22 a and b. Specimen “b” shows depressed radial arms, D) Specimens “b” is the chipped off part of specimens “a”, showing additional circle in the middle and minute central pit at the central part (specimen “b”), sample no. SK/AK-32 a and b; E) Bead-like structure is seen in photograph marked by arrow, sample no. SK/AK-3 and F) Specimen showing preservation of many wrinkle layers, sample no. SK/AK-16.

32

Fig. 4.9 : Simplified sketch of Marsonia artiyansis. A) Longitudinal section of the

umbrella or bell and B) Oral view of the animal showing gonads and oral arms. The shaded area represents the thinner part of the bell.

33

Fig. 4.10 : Field photographs of Hiemalora from Sursagar mine, Jodhpur

Sandstone. a) Showing the specimen deposited over the ripple marks. b) Radiating arms originating from the centre of the specimen.

34

Fig.4.11 : Field photographs of Aspidella from Sursagar mine, Jodhpur Sandstone.

A) Showing well preserved Aspidella with solid outer rim (marked by an arrow); b) Close up photograph of Aspidella showing the circular morphology.

35

Fig. 4.12 : Field photograph of fossil bearing locality. (1) Showing the horizon

from where the fossils have been collected. (2) Trail marks in fine grain sandstone. (3 and 4) Showing well preserved network of burrows.

36

Fig. 4.13 : Geological and location map of the Jodhpur area, western Rajasthan (after Pareek, 1984).

38

Fig. 4.14 : Litholog of the fossil-bearing horizon, Sursagar mine area, Jodhpur, 39

v  

western Rajasthan. Fig. 4.15 : Plant fossils of the Jodhpur Sandstone, Sursagar area, Jodhpur, western

Rajasthan. A) The holotype of Vendophycus rajasthanensis showing thallus with swollen tips referred as beads; arrow marks the beads; B) Close-up view of (A) showing the swollen part at the tip. C) Development of microbial mat over the thallus of plant fossil on the bedding surface; D) Vendophycus rajasthanensis showing thallus with smooth wall preserved on the top of the rippled surface of the medium grain sandstone. E) Thallus preserved as hollow tube; F, Development of thallus showing fertile structures at their tips as beads. G, Branching pattern of Vendophycus rajasthanensis seen on the bedding surface; H) Figure shows overlapping of thallus as well as splitting tendency of thallus; I) Magnified view of (D) showing well developed fertile structure (oogonia); J) Close up view of (K) showing cf developing synzoospore and K) Figure shows well developed thallus with antheridia and oogonia, marked by arrows “a” and “b” respectively.

42

Fig. 4.16 : Vendophycus sursagarensis reported from the Jodhpur Sandstone,

Sursagar area, Jodhpur, western Rajasthan. A) Photomicrograph showing the contact of the host rock and the thallus of the plant fossil. The dotted line marks the contact; B) Well developed branching pattern in the thallus; C) View of the thallus showing regular pattern of branching; D) Swollen structures at the tip of the thallus; preserved as negative hyporelief; E) Swollen structure seen at the tip of the thallus; F) Elliptical size of the thallus in cross sectional view, preserved in sandstone and G-H) Typical characteristic feature of splitting of the thallus at middle observed in Vendophycus sursagarensis.

45

Fig 4.17 : Plant fossil Indophycus marwarensis reported from the Jodhpur

Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) Indophycus marwarensis showing shrub-like profuse branching with abundance of bead like structure on the thallus preserved on the top of the bedding plane; B) Figure shows hollow depressions in the middle of the thallus, marked by the arrow; C) Excellent preservation of fertile structures (oogonia) closely attached with the thallus; D) Closely attached bead like structure at the wall of thallus with bulbous tip; E) Close up view of the thallus showing closely attached beads making the outer wall serrated which is marked by the arrow; F) Photograph showing development of thallus with well preserved beads as fertile structures. Arrow marks the structures and G, Magnified view of fertile parts of plant; antheridia and oogonia are marked by the arrows “a” and “b” respectively.

47

Fig. 4.18 : Schematic diagrams of Jodhpur plant. A, Vendophycus sursagarensis, B,

Vendophycus rajasthanensis C, Indophycus marwarensis. D, Schematic diagram depicts the mode of occurrence of the Jodhpur plant. The plant is embedded within the microbial mat in the Jodhpur Sandstone.

51

Fig. 4.19 : Geological and location map of the Marwar Supergroup western

Rajasthan, showing study area (after Pareek, 1984). 53

Fig. 4.20 : Litholog of the MISS (Microbially Induced Sedimentary Structures) 54

vi  

bearing horizon of the Jodhpur Group. Fig. 4.21 : Field photograph of Microbially Induced Sedimentary Structures (MISS)

reported from the Jodhpur Sandstone, western Rajasthan. A) Incomplete ripples over microbially flat laminated surface (coin diameter = 2.4 cm); B, C and D) Various types of well preserved sinusoidal, curved and straight wrinkle marks on the bedding surface (coin diameter = 2.4 cm and lens cap diameter = 5.7 cm); E and F) “Bun shaped” microbial structures with positive relief (maximum elevation from the bedding plane = 3.5 cm), the growth of the “bun shaped” structure not effected the ripples (lens cap diameter = 5.7 cm).

57

Fig. 4.22 : A) Well developed cracks in the sandstone (scale = 12cm); B) Cracks

along the ripple crests bounded by sharp ridges (marked by arrows) by both sides of the crack (coin diameter = 2.3cm); C) Inverted flute structure in sandstone illustrates surface pavement in which sand has accumulated forming small drumlin shaped inverted flute cast (coin diameter = 2.4cm); D) Magnified view of Inverted flute Structure (scale bar = 2cm); E) Well preserved Aristophycus around a large sandstone clast showing primary, secondary and tertiary bifurcations (coin diameter = 2.4cm) and F) Close up of Aristophycus: an inorganically formed structure showing well developed bifurcations which is possibly formed by action of water current and microbial mat (coin diameter = 2.4cm).

61

Fig 4.23 : A) Arumberia banski showing presence of small ridges on bedding

surface separated by concave furrows (coin diameter = 2.4cm); B and C) Rameshia rampurensis showing very small mounds or blisters making the entire bedding surface granular (coin diameter = 2.4cm); D) and E) Blisters are arranged in a linear fashion (coin diameter = 2.4cm) and F) Transitional form exhibiting characteristics both Arumberia and Rameshia, (coin diameter = 2.4cm).

65

Fig. 4.24 : A) Rameshia anastomose showing small mound like structure forming

anastomose pattern (coin diameter = 2.3cm); B) Jodhpuria circularis showing ridges forming circular to concentric pattern in the central part while in the outer part it forms petal like arrangement of ridges (marked by arrows), (coin diameter = 2.4cm); C) Close up view of Jodhpuria circularis; D) Old Elephant Skin (OES) textured surface (coin diameter = 2.3cm); E and F) Poorly developed microbial structures on rippled surface (coin diameter = 2.3cm).

69

Fig. 4.25 : Stromatolites of the Bilara Group. A, D and E- Colonnella columnaris;

B- Transverse section of Colonnella. C and F- Coniform stromatolites. 71

Fig. 4.26 : Stromatolites of the Bilara Group. A- Colonnella columnaris B-

Coniform stromatolite C-Transitional form D- Pseudocolumnar form, E and F- New form A (Scale bar = 2 cm).

72

Fig. 4.27 : Geological and location map of the Dulmera area, District Bikaner,

Rajasthan (after Pareek, 1984). 73

Fig. 4.28 : Litholog of the Nagaur Sandstone showing the position of trace fossils, 74

vii  

Dulmera area, Bikaner district, Rajasthan. Fig. 4.29 : Trace fossils reported from the Nagaur sandstone, Dulmera area,

Rajasthan. A) Rusophycus carbonarious; B) Close up view of Rusophycus carbonarious; C and D) Rusophycus didymus; E and F) Cruziana fasiculata (diameter of coin = 2.3cm).

81

Fig. 4.30 : Trace fossils reported from the Nagaur sandstone, Dulmera area,

Rajasthan. A) Cruziana cf salomonis; B) Isopodichnus isp; C) Tasmanadia cachii; D and E) Diplichnites; F) Merostomichnites isp; G) Planolites beverleyensis.

82

Fig. 4.31 : Trace fossils reported from the Nagaur sandstone, Dulmera area,

Rajasthan. A, B and C) Bergaueria aff. Perata; D) Dimorphichnus cf. obliquus; E and F) Monocraterion isp.

85

Fig. 4.32 : Trace fossils reported from the Nagaur sandstone, Dulmera area,

Rajasthan. A) Planolites annularis; B, C, D and E) Scratch marks of arthropods.

87

Fig. 4.33 : Trace fossils reported from the Nagaur sandstone, Dulmera area,

Rajasthan. A) Treptichnus pedum; B) Monomorphichnus isp; C) Small knob like Burrow; D) Chondrites isp. E) Animal escape structure; F) Horizontal burrow.

91

Fig. 4.34 : Trace fossils reported from the Nagaur sandstone, Dulmera area,

Rajasthan. A) Needle like burrow; B) Tubular burrow; C and D) Palaeophycus tubularis; E) Small burrows reported from Tunkliyan; F) Scratch marks reported from Tunkliyan.

95

Fig. 5.1 : The schematic diagram showing the different biozones present in the

various stratigraphic horizons of Marwar Supergroup. The biozone are constructed on the basis of megafossils, microbial mat, trace fossils, stromatolites and microfossils.

99

Fig. 5.2 : Map shows the geographical distribution of Biozones based on the

palaeontological remains of the Marwar Supergroup. 106

Fig. 5.3 : Schematic diagram showing the correlation between the Bhander section of the Vindhyan Basin and Jodhpur section of Marwar Basin. (after Kumar, 2012).

108

Fig. 5.4 : Comparative stratigraphy (idealized) and proposed correlations between

the Marwar Supergroup, the Salt Range (Pakistan), the Krol-Tal (Himalayas) and the Huqf Supergroup of Oman (modified after Davis et al., 2013).

109

viii  

List of Tables

Page No.

Table 1.1 Stratigraphic Succession of the Marwar Supergroup (modified after Pareek, 1984 and Chauhan et al., 2004).

4

Table 2.1 Lithostratigraphic succession of the Marwar Supergroup, western Rajasthan (after Pareek, 1984).

10

Table 5.1 Behavioural pattern of the Ichnofossil from Nagaur Group 102 

1  

Introduction

1.1 Background information

The intracratonic Marwar Supergroup is exposed in Rajasthan in the western of

part of the Peninsular India. Earlier, it was believed that the Marwar Supergroup was the

extension of the Vindhyan Supergroup; hence it was also called the “Trans-Aravalli

Vindhyans” in the older literature. Now the studies have shown that there are many

differences in the lithological facies as well as in the fossil content. The Marwar

Supergroup (MSG) occupies a large area of about ~51,000 km2 in the Jodhpur-Khatu-

Nagaur-Bikaner areas of western Rajasthan (Paliwal, 2007) (Fig. 1.1). It attains a

thickness of about 1000 m (Pareek, 1984). It unconformably overlies the Malani Igneous

Suite which has been dated as 779 to 681 Ma (Roy and Jakhar, 2002). Later on, it was

revised by Gregory et al. (2009) as 771±5 (U-Pb dating). The Marwar Supergroup is

overlain by the Permo-Carboniferous Bap Beds. It is believed that the sedimentation

either ended before the onset of Cambrian or during Lower Cambrian. As stated earlier,

the Marwar Supergroup was considered as unfossiliferous as no body fossil had been

discovered except a report of a brachiopod from the Jodhpur Sandstone published in the

form of an abstract by Khan (1973) which could not be replicated by any other person

since then and hence, it is now ignored. Stromatolites have been recorded from the Bilara

Group (Khilnani, 1964; Barman 1980; 1987) but they were not helpful in suggesting any

age. Recently, the Ediacaran fossils have also been discovered from the Jodhpur

Sandstone (Raghav et al., 2005), but the morphology of the reported fossils is not clearly

discernible and the taxonomic assignment of the reported fossils is somewhat doubtful.

More recently, microfossils have also been discovered from the Bilara Group (Babu et

al., 2009; Mehrotra et al., 2008). The presence of Precambrian-Cambrian boundary

within the middle part of the Marwar Supergroup is speculative as it is based on the

chemical signatures of carbon, strontium and sulfur isotopes of the carbonates of the

Bilara Group (Pandit et al., 2001; Maheshwari et al., 2002; Mazumdar and Strauss,

2006). Recently, Kumar and Pandey (2008) for the first time have discovered the trilobite

trace fossils from the Nagaur Sandstone which constitutes the upper part of the Marwar

2  

Supergroup, and confirmed its Cambrian age. However, it has also been correlated with

the Purple Sandstone of the Salt Range of Pakistan which has been considered Cambrian

in age (Kumar and Pandey, 2010). Kumar et al. (2009) have also noted some possible

Ediacaran forms and a megaplant fossil in the Jodhpur Sandstone. In recent years, much

attention is also given to the algal mat structures in the siliciclastic sediments and their

utility in correlation is now being accepted. Recently, Sarkar et al. (2008) have described

a number of algal mat structures from the Jodhpur Sandstone. Kumar and Pandey, (2009)

also recorded Arumberia banksi from the Jodhpur Sandstone (the Sonia Formation of

Pareek, 1984) which is a characteristic form of Ediacaran age (Kumar and Pandey, 2008;

2009).

The present study envisages establishing a high resolution biozonation based on

megafossils, trace fossils, stromatolites and algal mat structures for the Marwar

Supergroup. Pattern and distribution of the Ediacaran biota are helpful establish

palaeobiogeography and evolution of the earliest multicellular life within the basin. The

present study will be helpful in the correlation and in assigning ages to different

lithostratigraphic units on the basis of biogenic signatures. With the lower group of the

Marwar Supergroup representing Ediacaran age and the younger group representing

Cambrian age, the biozonation will help in establishing Precambrian-Cambrian boundary.

Biozonation will also help in its correlation with homotaxial stratigraphic units of both

the peninsular and the Himalayan regions of India.

1.2 Problem delineation   The Marwar Supergroup attains a huge thickness of about 1000 m and was earlier

considered unfossiliferous. It overlies the Malani Igneous Suite which has been dated as

771±5 (U-Pb dating) by Gregory et al. (2009) and is overlain by the Permo-

Carboniferous Bap Beds. Pareek (1981) subdivided the MSG into three groups’ viz., the

Jodhpur Group, the Bilara Group and the Nagaur Group (Table 1.1). Only in the Bilara

Group, the carbonates are developed, while the Jodhpur and the Nagaur Groups show

siliciclastic sediments dominantly represented by sandstones. In the absence of

3  

radiometric dates, the age of these groups is basically speculative. Presence of fossils and

biogenic structures help to establish the biozones which in turn will help in suggesting

precise age. With age assignment it will be much easier to establish interbasinal

correlation.

Fig 1.1: Generalized geological map of the Marwar Supergroup (redrawn and modified after Pareek, 1981). 1.3 Present status and scope of work:

Recently, much attention has been drawn towards the presence of hydrocarbons in

the Precambrian basins. In the light of this, the Nagaur Basin (the Marwar Supergroup)

has been identified as a potential basin for the presence of hydrocarbon (Banerjee et al.,

4  

1999). For the source of hydrocarbons, there has to be established the presence of organic

matter vis-a-vis the presence of life at the time of deposition of the sediments in a basin

unless the hydrocarbons are migrated from other younger source. Thus, the presence of

fossils or any signature of their presence is very crucial for deciding the potentiality of

the basin for the presence of hydrocarbons.

Table 1.1: Stratigraphic Succession of the Marwar Supergroup (modified after Pareek, 1984 and Chauhan et al., 2004).

Presence of Precambrian-Cambrian (Pc-C) boundary has a global significance as

very important and significant changes in evolution, ocean chemistry and possibly in

composition of atmosphere have taken place during this transition. The Pc-C boundary

has been used with confidence for correlation as well as in suggesting the age. There are

5  

definite chemical signatures for the presence of this boundary within the Bilara Group

(Maheshwari et al., 2002; Mazumdar and Bhattacharya, 2004; Mazumdar and Strauss,

2006) but no fossil evidence has so been far presented. The Ediacaran deposits

underlying Pc-C boundary should also contain Ediacaran assemblages as reported from

most of the coeval deposits of the world. Ediacaran biota has not yet been discovered

from the Marwar sediments.

The Ediacaran fossils in the Jodhpur Sandstone may have a distinctly unique

assemblage because of biogeographic provinciality and may differ from the other known

occurrences such as Ediacara Hill (Australia), Avalon (Newfoundland) and Nama

(Namibia). They may also constitute a different biofacies. There are reports of the

Ediacaran fossils from the Marwar Supergroup (Raghav et al., 2005; Paliwal, 2007) but

both the reports show a very poor quality of material and the biogenicity of the reported

fossils and their taxonomic assignment could not generate a fair degree of confidence

(Kumar and Pandey, 2008). However, there is an excellent preservation of microbial mats

in the siliciclastic sediments of the Jodhpur Group which is of Ediacaran age and in

general the Ediacaran fossils are preserved where microbial mats are developed. The

Ediacaran fossils are unique in nature and their status in the overall evolution of

megascopic life is still not well understood. Any record of these fossils will definitely

give better understanding of the evolution of early life.

1.4 Objectives

The main objectives of the work are as follows:

1. Search and identification of megafossils and trace fossils.

2. Search and description of algal mat structures in the arenaceous facies.

3. Establish a relationship of microbial mat structures and associated Ediacaran

fossils in light of ecological and sedimentological setting.

4. Identification of biozones in the Marwar Supergroup.

5. Correlation of the Marwar Supergroup with other successions of Indian

subcontinent.

6  

1.5 Implication of work

The present work shall have implications with respect to the following points:

A. To establish a high resolution biozones representing megafossils, microbiota

and algal mat textures f and their correlation for the Marwar Supergroup.

B. Detailed field work in Jodhpur, Nagaur, Gotan and the Dulmera areas and

preparation of different lithologs of different fossil-bearing horizons would

enhance the detailed prospective view for biostratigraphy of the basin.

C. Sampling and detailed taxonomic description and petrographical studies of

different stromatolites, megafossils and algal mat structures will help to

understand palaeoecology and depositional environment during the deposition of

sediments through time and space.

D. Detailed biozones could help to establish and describe the different biogenic

facies with in the basin.

E. Interbasinal correlation of the Marwar Basin with the Vindhyan Basin will

help to understand the evolutionary history of two Neoproterozoic basins of

India and adjoining areas.

F. If glacial events are identified in the Jodhpur Group, it will of considerable help in

intrabasinal correlation, age assignment and will give a much better understanding

of the all global events during the Neoproterozoic.

7  

1.6 Organization of thesis

The work has been subdivided into six chapters.

Chapter-1 deals with the outlines of the background information, problem delineation,

present status and scope of work, objectives, implication of work and

organization of thesis.

Chapter-2 focuses on the geology and stratigraphy of the Marwar Supergroup and also

deals with the age assessment of the study area.

Chapter-3 illustrates the present work for which samples of fossils and sedimentary rocks

have been collected and analyzed in laboratory as well as in the field.

Chapter-4 concerned with the systematic palaeontology of the fossils reported from the

study area.

Chapter-5 deals with the biozonation of the Marwar Supergroup and its correlation with

the Vindhyan Supergroup and other coeval succession from other parts of the

world.

Chapter-6 comprises the conclusions of the present study.

A complete list of the various references cited in the text is given at the end of the thesis.

   

8  

Geology and Stratigraphy of the Marwar Supergroup

2.1 Introduction

The rocks of the Marwar Supergroup are exposed in NNW-SSE trending shallow

intracratonic sag basin. The Marwar Basin extends from near Jodhpur to further

northwestward to the Salt Range, Pakistan (Chauhan et al., 2004). The Jodhpur

Sandstone has been considered by earlier workers, namely Blandford (1887) Oldham

(1886) and La Touché (1902) as equivalent to the Vindhyans of Son Valley

(Neoproterozoic to Early Cambrian). Earlier, the workers correlated the Jodhpur

Sandstone with the Purple Sandstone of the Cambrian of Salt Range on the basis of gross

lithology. The association of salt pseudomorphs (Halite casts) and limestone lent support

to the Jodhpur Sandstone as being its equivalent to Cambrian of Salt Range. Heron

(1932) considered the Marwar Supergroup of rocks as the Trans-Aravalli Vindhyans.

According to Barman (1980), the Marwar Basin does not show any link to the Vindhyan

Basin but may possibly represent southerly extension of the Cambrian Basin of Salt

Range. Shrivastava (1971, 1992) proposed rock-stratigraphic nomenclature for the

sediments of western Rajasthan and made studies related to palaeogeography. Virendra

Kumar (1995, 1999) correlated sandstones of the Nagaur Group with the Purple

Sandstone of Salt Range.

The first major attempt to reconstruct the stratigraphy in the study area was

attempted by Pareek (1981, 1984) who drew conclusions on the palaeogeographic set-up

of the western part of this sub-continent. Gupta et al. (1981) have renamed the erstwhile

Trans-Aravalli Vindhyans as the Marwar Supergroup (MSG). The MSG with an

estimated thickness of about 1000m lies unconformably over the basement rocks

comprising either Malani Igneous Suite and/or Delhi metamorphites. Pareek (1984)

divided the Marwar Supergroup into three parts: lower arenaceous (Jodhpur Group),

middle calcareous (Bilara Group) and upper argillaceous/arenaceous (Nagaur Group).

The earlier palaeontological studies made on the sediments of the Marwar Supergroup

revealed that over most part is unfossiliferous except for the stromatolites. Khilnani

(1964, 1968) first drew attention towards the occurrence of the stromatolites in the Bilara

9  

Limestone. Srivastava (1971) mentioned about the occurrence of the algal remains in the

Bilara Limestone. Barman (1980, 1987) also reported stromatolites from other parts of

the Marwar Supergroup. Shrivastava (1971, 1992) worked in Marwar and also in the

Phalodi-Khichan area. The contact of the Igneous Basement and the Marwar Supergroup

(Jodhpur sandstone) is noticed at Mehrangarh Fort. At Jodhpur Fort, the Jodhpur

Sandstone directly overlies the rhyolites, where the contact is sharp and is heterolithic in

nature. 2.2 Geology and Classification of Marwar Supergroup

Pareek (1984) has divided the Marwar Supergroup into the Jodhpur Group, the

Bilara Group and the Nagaur Group. These groups are further subdivided into formations.

In the study area, the Jodhpur Group was subdivided into three units viz. Pokaran Boulder

Bed (lower unit), Sonia Sandstone (middle unit), and Girbhakar Sandstone (upper unit).

The Pokaran boulder bed is dominated by the boulder and overlain by calcrete and

coarse-grained sandstone. The next lithounit is the Sonia Sandstone. The facies of this

lithounit consists of maroon siltstone and shale, creamish sandstone with abundant

sedimentary structures such as salt pseudomorphs, ripple marks, cross-bedding, etc. The

Sonia Sandstone is overlain by the Girbhakar Sandstone. The facies association in this

unit is characterized by the brick-red sandstone, siltstone; sandstone is gritty to pebbly

near the top. The classification of MSG is summarized in table 2.1. Later, Chauhan et al.

(2004) clubbed the Sonia Sandstone and Girbhakar Sandstone into the Jodhpur Sandstone

as they did not find marked variations in the lithological attributes. The MSG

classification given by Chauhan et al. (2004) has been followed in the present work. The

Jodhpur Group is overlain by the carbonate rocks of the Bilara Group. The Bilara Group

(250 to 300 m thick) is subdivided into three units namely Dhanapa, Gotan and Pondlo

formations in ascending order. The Bilara Group conformably overlies the Jodhpur

Group with gradational contact. The contact can be seen at Pichak village near Bilara

town. The Bilara Group shows good development of stromatolites. The Dhanapa

Formation exposed in Dhanapa village is represented by chert beds at the base, followed

upwards by well-bedded and laminated cherty dolomite and massive dolomite. The

dolomites at places contain stromatolites. The stromatolites and biohermal limestone

10  

attain a thickness of about 15 m near Dhanapa village. This formation is also exposed

near Khoaspura, Borunda and Gorawat villages. The Gotan Formation is composed of

dark grayish laminated limestone interbedded with variegated clay beds. Unlike Dhanapa

Formation, the stromatolites are less pronounced in this unit. A good section (5 m to 10 m

thick) of this unit is exposed near Gotan village.

Table 2.1. Lithostratigraphic succession of the Marwar Supergroup, western Rajasthan (after Pareek, 1984).

11  

The Pondlo Formation is composed of dolomite, cherty dolomite, claystone,

siltstone and reddish sandstone. The dolomite is stromatolitic in nature. The section is

best exposed near Pondlo village. The Nagaur Group overlies unconformably the Pondlo

Formation. The Nagaur Group is subdivided into the lower Nagaur and upper Tunklian

formations. The Nagaur Formation is composed of reddish to brownish, coarse to

medium grained sandstone, siltstone and maroon shale. The shale is intercalated with

siltstone and sandstone. The sandstone of the Nagaur Formation is typically ferruginous

and contains clay balls. The sandstone shows profuse development of ripple marks, mud

cracks and cross beddings. The sections are well exposed near Dulmera area in Bikaner

District, Rajasthan. The Tunklian Formation is gritty to pebbly, containing brick red

sandstone, siltstone, pebbles of granite, rhyolite, dolomite, quartzite, etc. as observed near

the Tunklian hill. It is best exposed at the base of Tunklian hill; it comprises reddish to

purplish shale followed upwards by ferruginous gritty to pebbly sandstone beds.

2.3 Study area Jodhpur and surrounding areas

The Marwar Supergroup unconformably rests over the Malani Igneous Suite. The

Malani Igneous Suite is a broad term used to denote Neoproterozoic granites and felsic

volcanics exposed over an area of 54,000 km2 in Rajasthan, India (Gregory et al., 2009). 

Magmatic activity associated with the Malani Igneous Suite is constrained to at least

three distinct phases. The initial phase of igneous activity was characterized by major

felsic and minor mafic flows. This was followed by the emplacement of granitic bodies

into the region. The intrusion of volumetrically minor felsic and mafic dykes represent

the final phase of Malani Igneous activity. The Malani Igneous Suite rests unconformably

over Paleo to Mesoproterozoic metasediments, and basement granitic gneisses and

granodiorite. The Pokaran Boulder Bed is 4 m thick and is developed only in the western

part of the basin around Pokaran where it unconformably overlies the Malani Igneous

Suite. In rest of the area, the Jodhpur Sandstone directly overlies the Malani Igneous

Suite (Pareek, 1981, 1984; Chauhan et al., 2004).The Jodhpur Group holds the important

place in the Marwar stratigraphy; it represents the oldest litho sequence along with

12  

significant age deciphering fossils such as Aspidella, Hiemalora, and Arumberia. It

consists mainly of fine to medium grained, ripple marked sandstone, gritty coarse-grained

sandstone, siltstone and shale. The uneven gritty sandstone is deposited under fluvial

conditions. In the Jodhpur Sandstone, the repetitions of fine to medium grained sandstone

and the coarse-grained gritty/pebbly/conglomeratic sandstone has been observed in the

entire basin. In thin section, fine-grained sandstone of the Jodhpur Group comprises

subangular to subrounded grains of quartz, in good amount, few grains of feldspar, mica,

calcite and opaque iron minerals are present as accessory minerals and the cementing

material is siliceous. The calcareous sandstone contains some amount of micritic calcite.

The outcrops of the Bilara Group are scanty and can be seen only in the southern

part (Kumar, 2012). It contains mostly carbonate rocks. The Bilara Group exhibits

excellent development of biohermal stromatolites. Well-preserved sections can be seen

near Sojat in the south to Phalodi in the west through Rundhia, Bilara, Hariadhana,

Gorawat, Dhanapa, Gotan, Pondlo, etc. The beds are horizontal to subhorizontal. The

Bilara Group has a maximum thickness of 300 m pinching out in the eastern and western

extensions. In the western part of the Marwar Basin, the exposures are absent but the

rocks are present in the subsurface region, as inferred on the basis of the borehole data.

This subsurface deposit is named as the Hanseran Group. It attains a maximum thickness

of 652 m as found in the borehole data near Hanseran (Rastogi et al., 2005). It is

considered to be a facies variation of the Bilara Group developed in the southern part.

The Nagaur Group consists of predominantly red coloured rocks and these

sediments were deposited under very shallow marine conditions and had a very

prolonged aerial exposure for intensive oxidation (Rastogi et al., 2005). The ripple marks

and cross bedding can be seen in the Dulmera area. These sediment associations indicate

a periodical high energy environment within predominant low energy environment of

deposition (Dey, 1991). The younger Tunkliyan Sandstone is developed in Tunkliyan hill

near Gudralli area. It is characterized by brick red claystone, calcareous clay to gritty and

pebbly sandstone. The nature of this Tunkliyan Formation is indicative of somewhat

humid climatic conditions as compared to the arid climatic conditions of the Nagaur

Formation (Dey, 1991).

13  

2.4 Marwar Supergroup

Age assessment

In the present scenario, the Marwar Basin is considered as the repository of

various fossils of different ages ranging from the Ediacaran to the Lower Cambrian. The

Marwar Supergroup was historically classified as Neoproterozoic based upon the

relatively undeformed stratigraphy and the absence of index fossils within the sequence.

The Malani Igneous Suite is well dated to between 750-800 Ma (Torsvik et al., 2001;

Gregory et al. 2009; Van Lente et al., 2009; Pradhan et al., 2010) and therefore provides

a maximum age for the unconformably overlying Marwar sediments. Assuming that the

Neoproterozoic Snowball Earth event was globally distributed, the absence of glacial

deposits within the Marwar Supergroup suggests a post-Marinoan age for the deposits

(i.e. <650 Ma). The Ediacaran fossils collected from the Jodhpur Group, including

Arumberia, Beltanelliformis, Aspidella, and Hiemalora, support a late-Neoproterozoic

age assignment (< ~570 Ma; Kumar and Pandey, 2009; Kumar et al., 2009). Previously,

the Marwar Supergroup was considered as an unfossiliferous basin but Khan (1973)

reported brachiopod, which could not be replicated again. Malone et al. (2008) recently

studied detrital zircon populations from the Jodhpur Sandstones of the Jodhpur Group.

The results yielded a peak detrital zircon age range between 800-900 Ma along with a

smaller subset of 780 Ma zircons. The carbonates of the Bilara Group were the focus of

several chemostratigraphic attempts to constrain the age of the Marwar Supergroup. The

presence of stromatolite assemblage in the carbonate rocks of Marwar Supergroup was

first reported by Khilnani (1964) giving evidence of early life. Later on, Khan (1971) and

Hashimi and Gauri (1972) also reported a few other fossils from the Marwar Supergroup

but the facts are still debatable. A major detailed study was carried out by Barman

(1975), who highlighted the presence of a numerous stromatolite beds associated with the

marked lithofacies changes in a sedimentary sequence adjacent to the western margin of

the Aravalli range. The stromatolitic assemblage completely lacks the typical Riphean

and Vendian forms (Preiss, 1976) such as Conophyton, Baicalia, and Kussiella which are

confined to the eastern side of the Aravalli Range. The stromatolites of the Bilara Group

do not indicate any significant age; however, the form genus Colleniella would point to

14  

the terminal Riphean-Cambrian age (Semikhatov, 1976). Carbon isotope studies suggest

that the Precambrian-Cambrian boundary lies within the Bilara Group based upon

negative δ13C anomalies (<-4.3% PBD and <-6.5% PBD) that correlate with the Nemakit-

Daldynian-Tommotian carbon isotopic evolution curve (Mazumdar and Bhatacharya,

2004). Mazumdar and Strauss (2006) analyzed the δ34S concentrations within trace

sulfates from the Bilara Group carbonates and calcium sulfates from the Hanseran

evaporites and concluded that the data (33.8±3.1% and 32.4±3%) closely matched the

sulfate enrichment patterns from the end-Neoproterozoic. Mazumdar and Strauss (2006)

also examined the Strontium isotopic composition from the Bilara carbonates and

Hanseran Evaporites and found that the results (87Sr/86Sr= 0.70832±0.000354) were

comparable to Post-Varangerian 87Sr/86Sr global seawater curves. The Nagaur Group, the

uppermost unit of the Marwar, yielded trace fossils e.g. Rusophycus, Dimophichnus, and

Cruziana, suggesting an Early Cambrian age for the unit (Kumar and Pandey, 2008,

2010). Recently, McKenzie et al. (2011) studied detrital zircon populations from the

Nagaur Sandstones. The results of this study demonstrate a large concentration of grains

between 700 Ma and 1000 Ma and a small population of young grains with a peak at 540

Ma.

 

 

 

 

 

 

 

 

 

 

 

15  

Methodology

Methodology is the mainstay of the present work in order to achieve the objectives of the study. In the present work, the methodology has been divided into two parts: the first part deals with the field observations, data and sample collections and preparation of detailed lithologs while the second part deals with the laboratory work including the study of fossils, trace fossils, microbial mat structures and the thin section study of rock samples. Schematic diagrams have been prepared wherever needed. Based on the above criteria, the chapter has been divided into two parts:

a) Field work

b) Laboratory work

3.1 a) Field work

The field work has been carried out in different localities of the Marwar Supergroup viz. Sursagar (Jodhpur district), Artiya Kalan (Jodhpur district), Khatu (Nagaur district), Pokaran (Jaisalmer district), along Jodhpur-Jaisalmer highway, Bilara district, Dhanapa-Gotan-Pondlo (Bilara district) and Dulmera village (Bikaner district). The Survey of India (SOI) toposheets no. 45E/12, 45F/3, 45F/6, 45F/12, 45F/14, 45F/10, 44H/11, and 40N/13 based on scale 1:50,000 were used for the study. In the field investigation the different sections were identified and detailed lithologs were prepared. During the field work, the non-carbonaceous megaplant fossils, animal body fossils, MISS (Microbially Induced Sedimentary Structures), trace fossils and stromatolites were searched and studied in the siliciclastic rocks. The geological data as well as samples were collected for the detailed study in the laboratory.

3.1 b) Laboratory work In the laboratory, animal and plant fossils were studied for their biogenic

characters. The thin sections of non-carbonaceous megafossils were studied with the help

of Wild Stereomicroscope. Carbonate thin sections were stained by Alzarine Red S

16  

solution for the identification of calcite and dolomite. Photomicrographs were prepared

with the help of Wild, Leitz Orthoplan and Leica DMRXP microscopes. The thin sections

of the chert have been scanned for the study of microbiota with the help of Leitz

Orthoplan microscope. On the basis of field and laboratory study along with literature

review, the biozones of the Marwar Supergroup have been established. The plant and

animal body fossils, organo-sedimentary structures including MISS and stromatolites,

trace fossils and microfossils were used for biozonation. This chapter also delineates the

sedimentological aspect of the present study based on thin sections.

3.2 Petrography

The petrographical study of sandstone and carbonate rocks has been done. The

grain size analysis of sandstone was carried out to decipher the depositional history. For

the ease of the study, this chapter is further subdivided into sandstone section and

carbonate section, and giant nodules. Sedimentary structures such as medium to large

scale cross bedding and ripple marks are generally associated with the sandstones. The

salt pseudomorphs (Fig. 3.1) with GPS value 26o33.846″ N and 73o44.930″ E are also

found at the upper horizon of the Jodhpur Sandstone on way to Dhanapa village.

17  

Fig 3.1: Well-developed Salt Pseudomorphs of various shapes in shale on the road side on Bhopalgarh-Dhanapa road. 3.2.1 Sandstone Section

For petrographic analysis of the Jodhpur Sandstone, in all, 35 thin sections have been

studied. The rock is mainly constituted of equidimensional, medium sized quartz grains

which constitute more than 95% while the matrix is less than 5% of the rock (Fig. 3.2).

The grains are more compact and closely in contact with each other binded by cementing

material which is made up of silica. The quartz is well sorted and subrounded to rounded.

A few grains of orthoclase and microcline also noted. The authigenic enlargement or

overgrowth on quartz grains is commonly seen. The typical accessory minerals include

only the stable minerals such as zircon, tourmaline and rutile. Texturally, most quartz

sandstone is characterized by thorough sorting. They are usually clean, well washed

sandstone comprising quartz and devoid of silt and clay. Presumably, they are deposited

18  

in stable environments either continental or marine, where deposition was relatively slow

and particles were so winnowed by currents before final burial that the argillaceous

material washed away. At least, few of them are the result of more than one cycle of

erosion and deposition. Under these conditions, the quartz grains tend to become sub-

rounded to well-rounded. It can be classified as quartz arenite.

Fig 3.2: Photomicrograph of Quartz arenite of Jodhpur Sandstone; a and b) Showing the compact arrangement of quartz grain in cross nicol and PPL respectively; c and d) Quartz grain showing subrounded to rounded in cross nicols. 3.2.2 Giant Nodule

In the mines of the Sursagar, Jodhpur district (26˚ 19.70� N and 73˚ 0.12� E), a

number of giant nodules of sandstone are seen within the sandstone beds (Fig. 3.3 A-D).

About 10-20 m thick succession of the middle part of the Jodhpur Sandstone is exposed

in the Sursagar mines and the nodules are mainly exposed approximate 10 m from the

base level of mines.

19  

Fig 3.3: Giant nodules seen in the Jodhpur Sandstone. There is no lithologic difference between the host rock and the lithology of the nodule, except the hardness. a. The host rock is seen both at the base as well as at the back of the nodule, in which the nodule is embedded, b. The host rock is also seen associated with the nodule, c. Outer margin of the giant nodule showing parallel differential markings in the sandstone, d. Transverse section of the giant nodule showing clearly marked circular margin and lack of any internal structure; the entire surface looks homogenous, e. and f. Photomicrographs of sandstone forming the nodule and host rock. The sandstones are made up of subangular to subrounded detrital quartz grains cemented together by silica (under crossed nicols). e. Sandstone of the nodule; f. Sandstone of the host rock.

20  

It appears that the nodules are restricted at a specific stratigraphic horizon. The nodules are spherical whose diameter ranges from 2.0m to 6.0m. The nodules are spherical to slightly distorted. At places two nodules are seen merging with each other. The outer surface is smooth with horizontal parallel marking (Fig. 3.3 C).

Any internal structure including concentric banding is completely lacking as the

cross section of the nodules are homogenous (Fig. 3.3 D). Along with this, no colour

marking or mineralogical differences is noticed. In comparison to the host rock, the

nodules do not show any marked colour difference and nodules are formed due to relative

hardness. The nodules are light reddish brown to light whitish brown in colour with

resemblance to the host rock. The sandstone has been identified as quartz arenite with

silica as the cementing material. There is no marked petrographic difference between the

sandstone of the nodules and the host rock (Fig. 3.3 E and F). It appears that the silica

cement plays an important role in the formation of the nodules and higher concentration

of silica may be responsible for genesis of the same.

3.2.3 Carbonate investigation The carbonate investigation has been carried out for the middle part of the

Marwar Supergroup, i.e. Bilara Group. The contact between the Bilara and Nagaur

Groups is also conformable and is marked by a distinct transitional lithology. The

lithounits of Bilara Group are calcareous in most parts and is represented by limestone,

dolomitic limestone, dolomite and cherty limestone. The observed chert content is

significant in the basal part (Dhanapa Dolomite) but increases in the upper part (Pondlo

Dolomite). The stromatolitic composition is highest in lower, negligible in the middle and

moderate in the upper parts. In field, it is difficult to demarcate the lithological boundary

between Dhanapa, Gotan and Pondlo Formations as they laterally grade into each other.

These three formations are found only in their respective type localities and their

persistence is not discernible. In all 18 thin sections of the carbonate rocks have been

studied. In the petrographic study, it is observed that no microfossils were encountered in

carbonate rocks as well as in the cherts. In thin sections, the rock is essentially fine-

grained calcite (micrite). Infirmly lithified limestones, such aggregates consist of

interlocking anhedral calcite crystals typically less than 20 µm in diameter and they are

21  

generally considered to represent original carbonate mud. In thin section quartz vein is

observed which may be representing the post-depositional event. The quartz vein may be

observed as nearly vertical to the lamina. The thin sections (Fig. 3.4 a and b) show the

laminated nature of limestone. The lamina is being demarcated by the colour variation

and change in textural arrangement. The dark colour band seen at the top of the

photomicrograph is composed entirely of clay-sized material which may be the cemented

material comprising of limestone. Presumably, the carbonate material was deposited

initially as an impalpable mud composed of minute crystals of calcite, which by

cementation and partial recrystallization, was converted to microcrystalline calcite.

Fig 3.4: Photomicrograph of Limestone of Bilara Group. a-b) Gotan limestone showing microcrystalline calcite in cross nicol and PPL respectively. Quartz vein is also observed in the thin section. 3.2.4 Nagaur Sandstone

Fig 3.5: Photomicrograph of Quartz arenite of Nagaur Sandstone; a and b) Showing the compact arrangement of quartz grain in cross nicol and PPL respectively.

22  

For petrography of Nagaur sandstone, the 20 thin sections have been studied. The

rock is mainly comprised of equidimensional, medium sized quartz which constitutes

more than 90% of the host rock with matrix and cementing material less than 10% (Fig.

3.5). Therefore, the rock is classified as quartz arenite. The grains are very compact in

nature and closely in contact amongst themselves. The cementing material is usually

silica but at some instances the presence of iron oxides is also noticed which is indicated

by the reddish-brown colour in thin section. The grains are rounded to sub rounded

indicating the mature stage of the rock in depositional environment. In terms of accessory

minerals hematite, zircon, tourmaline, etc. are also noticed.

 

 

 

 

 

 

 

 

 

 

23  

Systematic Palaeontology

4.1 Palaeontology

The palaeontological investigation has been carried out on the Jodhpur Group, the

Bilara Group and the Nagaur Group of rocks exposed in the different localities of

Jodhpur, Khatu, Barna Mine near Bilara, Dhanapa, Gotan, Pondlo, Bikaner, Nagaur and

Tunkliyan. The lowermost Jodhpur Group yields the fossils of the Late Neoproterozoic

era comprising body fossils, trace fossils, burrows, trail marks, fourteen types of well-

preserved microbial mats and non-vascular megaplant fossils from the Jodhpur

Sandstone. Stromatolites from the carbonate section have been studied. The Nagaur

Group of the Early Cambrian age consists the Nagaur Sandstone and the Tunkliyan

Sandstone. From the Nagaur sandstone, a number of trace fossils, burrows and scratch

marks of arthropods have been studied. The Tunkliyan Sandstone has also yielded some

sort of organic activity in the forms of scratch marks of arthropods and poorly preserved

burrows in the fine-to medium-grained sandstone. The fossils are described in

stratigraphic order.

4.1.1 Animal body fossils from the Jodhpur Group

There are four body fossils recorded from the Jodhpur Sandstone along with one

burrow structure and a few trail marks from the Tunkliyan Sandstone.

a) Five-armed body fossil b) Marsonia artiyansis c) Hiemalora d) Aspidella

a) Five-armed body fossil

The five-armed body fossil has been found on the bedding surface of the light

brown coloured, fine-grained Jodhpur sandstone in a mine at Sursagar with GPS value

26°15.77′N and 73°0.14′E, which is about 7 km NW of Jodhpur city (Figs. 4.1 and 4.2).

The fossil-bearing sandstone is quartz arenite with mean grain size of 0.23 mm. The

fossil is preserved as an epirelief and is characterized by the presence of five unequal,

wavy arms arising from a central circular disc of 1 cm in diameter (Fig. 4.3). Arms are

24  

found radiating away from the disc (Fig. 4.3 D). The angle between the different arms

varies between 30° and 90°, and their length ranges from 12.5 to 22.5 cm, and mean

length is 17 cm. The maximum width of the arms varies from 0.4 to 0.7 cm with mean as

0.56 cm. The margins of these arms are smooth and their distal ends are pointed.

However, no other surface feature could be observed.

Fig 4.1: Geological and location map of the Marwar Supergroup, western Rajasthan, showing study area (after Pareek, 1984).

25  

Fig 4.3: Five-armed body fossil on the bedding surface of the Jodhpur Sandstone. A and C) Five-armed body fossil; B) Line diagram of the fossil seen in A and B) Enlarged view of (C) showing a disc-like structure at the centre of the body fossil.

Fig 4.2: Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Sursagar mine, western Rajasthan. 

26  

The morphology of the structure under description cannot be produced by any

inorganic process, including microbial mat-related sedimentary structures such as

Aristophycus (Häntzschel, 1975) which is characterized by a regular, anastomosing,

raised pattern of branching structures. It is not comparable with Hiemalora stellaris

(Fedonkin, 1982) also; as Hiemalora is characterized by the presence of appendages

(rays) outwardly radiating from a disc generally of the order of disc diameter and rarely

reaching double the diameter of the disc. The appendages are densely packed to

moderately spaced, narrow rays. In the present specimen, there are only five arms and the

ratio of the dimensions of the arms and the disc is between 12.5 and 22.5 cm, whereas it

is never more than 2 cm in Hiemalora. The morphology of the phylum Echinodermata

shows five arms with a central disc and has been known from the Cambrian Period.

Living echinoderms are characterized by extensive water vascular structure and are

pentamerous. Fossil evidence shows that stereon evolved before pentamery, but both

were acquired during the Lower Cambrian. The tests of echinoderms are made up of

calcium carbonate though the present fossil shows no preservation of the nature of the

soft tissues.

Body Fossil from Artiya Kalan

The medusoid form Marsonia artiyansis reported by Raghav et al. (2005) from

the Sonia Sandstone (Jodhpur Sandstone) of the Marwar Supergroup is restudied. For

this, a fresh collection was made in the abandoned mines near Artiya Kalan, about 66 km

northeast from Jodhpur on Jodhpur-Gotan motor road from where Raghav et al. (2005)

had originally described the fossil. The Marwar Supergroup occupies a large area in the

western Rajasthan forming small hillocks in a desert setting (Figs. 4.4 A, B and 4.5). The

sampling for the collection of Marsonia artiyansis has been done from the type locality

which is near Artiya Kalan village in the Jodhpur district, Rajasthan. About seven meters

thick succession is exposed in the pits which are about 1 km east of the village (Fig. 4.7

A and B).

27  

Fig 4.4: A, Location map of the Jodhpur area, western Rajasthan. B, Geological map of the Jodhpur area, showing fossil locality, (Redrawn after Raghav et al., 2005).

b) Marsonia artiyansis The Marsonia has been first evaluated as biogenic structure before attempting its

taxonomic assignment. It occurs as a simple impression on the bedding surfaces of the

shales. It is marked by a circular, disc-shaped structure with well-preserved wrinkle

marks. Occasional presence of beads and arm-like structures within the disc-shaped

structure is very common.

28  

Fig 4.5: Detailed geological map of the Artiya Kalan area, Jodhpur District, Rajasthan showing fossil locality (Redrawn after Raghav et al., 2005).

Fig 4.6: Litholog of the fossil-bearing horizon, Jodhpur Sandstone, Artiya Kalan area, western Rajasthan. 

29  

Phylum Cnidaria

Class Scyphozoa

Family Incertae sedis

Genus Marsonia Raghav et al. 2005

(Fig. 4.7 C- E i-iii; Fig. 4.8 A-F)

Type species: Marsonia artiyansis Raghav et al. 2005

Holotype: Raghav et al. (2005) have identified 4 holotypes for the genus Marsonia which

is not legitimate according to the rules of biological nomenclature. We have selected the

best photograph shown in Fig. 3C of his published paper as Holotype whose sample

number is not available.

Paratype: SK/AK-1, 16, 21, 23, 29, 30, 32.

Diagnosis: It is disc shaped, generally circular to elliptical in outline, marked by

impression on the top of the bed (Fig. 4.7). The diameter ranges from 0.5 to 5.5 cm. The

outer peripheral margin of the disc is smooth (Fig. 4.7 D and Fig. 4.8 A, B, C, D) or

marked by complex wrinkles (Fig. 4.7 C and Fig. 4.8 E, F). Wrinkled margins are slightly

irregular and individual wrinkle could not be traced around the circular outer margin. The

width of wrinkled part of the disc varies from 2 mm to 4 mm. Non-wrinkled part is

marked by uneven surface and also shows small, straight to slightly curved ridges or

arms, which are symmetrically or asymmetrically placed. They taper at the outer margin

of the disc. The arms are originating from the centre but do not continue up to the outer

margin. The maximum length of the arm has been measured as 2 cm. In a few forms, the

arms are placed in such a way as to divide the disc into four more or less symmetrical

parts. In the central part of the disc, a circular mark is preserved both as positive or

negative epirelief with diameter ranging from 1 to 2 mm (Fig. 4.8 C “a” and “b”). The

central part of the disc also shows bead-like structures (Fig. 4.8 E); otherwise it is

uneven. The outer margin of the bell is completely devoid of tentacles.

Remarks: A large variation is seen in the morphology of Marsonia. In some, the central

part is uneven, while in others few arms are missing. In the larger forms, the wrinkle

marks are prominent. The quality of preservation in the smaller forms is relatively better.

It appears that the effect of compression or overloading was less in smaller forms in

30  

comparison to the larger forms. A few forms are embedded in the bed and have three

dimensional preservation. It can be confirmed when small chips of shale is removed from

the top surface of the fossils and some preservation could still be seen on the under

surface suggesting continuity of the fossil body (Fig. 4.7 E i- iii). Differences in the

morphology of the fossil may also be due to the fact that whether the preservation is from

the oral or aboral side of the medusoid.

Discussion: In morphology, the present form resembles Marsonia reported by Raghav et

al. (2005). In their collection, they had only four samples and all were erroneously

described as holotypes (see page 24, Raghav et al., 2005). In the published photographs

of Raghav et al. (2005), the morphology of the fossil can be observed only in fig. 3-A, B,

C, F and G, out of which B, C, F and G are the photographs of the same sample. All the

forms have a diameter of about 1cm. In none of the photographs, the wrinkles are seen

but their presence has been mentioned in the description. Though the diameter is shown

to be ranging from 0.4 to 1 cm, no photograph is given for the smaller range. In fig. 3-A

nothing is visible in the areas marked as ‘b’, ‘c’ and‘d’. In our collection, we could

observe the morphology in the forms with more than 0.5 cm diameter. Hence, the

minimum diameter is taken as 0.5 cm and the maximum diameter is recorded as 5.5 cm,

whereas Raghav et al. (2005) have given this range as from 0.4 to 1 cm. The form is soft

bodied. The presence of arm-like structure, beads, opening in the centre, circular body,

wrinkle marks in the outer margin and absence of hard parts point towards the medusoid

of Scyphozoan affinity. Raghav et al. (2005) have placed Marsonia under phylum

Cnidaria, class Scyphozoa and family Incertae sedis.

Marsonia artiyansis Raghav et al. 2005, emended

(Fig. 4.7 C to F; Fig. 4.8 A to F)

Paratypes: SK/AK-1, 16, 21, 23, 29, 30, 32 a and b

Description: As for the genus.

Discussion: Specimens are characterized by circular to slightly elliptical shape and it is

termed the bell which is an outer body in a jelly fish. The quality of preservation in

smaller form is relatively better in comparison to the larger forms. A notable character is

the smooth outer margin of the bell in the smaller forms and wrinkled in the larger ones.

31  

Concentric rings are discontinuous and none of them make a complete circle around the

disc. This suggests that the outer part of the bell was very soft and thin.

Fig 4.7: A) Field photograph of the Jodhpur Sandstone; arrow marks the position of the fossil-bearing horizon; B) Section of the Jodhpur Sandstone (Sonia Sandstone) exposed in a pit near the Artiya Kalan area, district Jodhpur. The lower part is made up of sandstone and the upper part is made up of shale and siltstone which has yielded the fossils; C) Marsonia artiyansis shows wrinkled margin at the outer bell with four radial arms originating from the central part of the medusa, Sample no. SK/AK-1; D) Specimen showing smooth outer margin with elevated central disc up to 2 mm in height, Sample no. SK/AK-2 and E) (i) Upper surface of the poorly preserved medusa showing wrinkled outer margin. When sample in E (i) was chipped it yielded a sample E (ii) which on its sole shows marks of the radial arms with negative relief and E (iii) is its counterpart which shows arms in positive relief.

32  

Fig 4.8: Marsonia artiyansis shows variation in size as well as in the outer margin from smooth to wrinkled. A) (sample no. SK/AK-21) and B) (sample no. SK/AK-23), Smooth outer margin with dislocated radial arms; C) “a” and “b” are the counter parts of the same specimen; “a” shows raised central part showing central disc with four radial arms; outer margin smooth, sample no. SK/AK-22 a and b. Specimen “b” shows depressed radial arms, D) Specimens “b” is the chipped off part of specimens “a”, showing additional circle in the middle and minute central pit at the central part (specimen “b”), sample no. SK/AK-32 a and b; E) Bead-like structure is seen in photograph marked by arrow, sample no. SK/AK-3 and F) Specimen showing preservation of many wrinkle layers, sample no. SK/AK-16.

33  

The smooth margin in the smaller forms and better preservation may be due to the

fact that central part of the bell-shaped animal was thicker as depicted in the schematic

diagram in fig. 4.9, where the transverse and oral sections of the animal are shown. It

explains the preservation of complete body of the animal in the larger form and only the

nonstippled part in the smaller form. Outer margin of the bell is devoid of tentacles. The

radial arms originating from the central disc may act as gastrovascular system in the

animal (Raghav et al., 2005). A schematic diagram is made to show the transverse

section and oral section of the animal.

Fig 4.9: Simplified sketch of Marsonia artiyansis. A) Longitudinal section of the umbrella or bell and B) Oral view of the animal showing gonads and oral arms. The shaded area represents the thinner part of the bell.

34  

c) Hiemalora

Genus Hiemalora Fedonkin, 1982

(Type Species: Hiemalora stellaris Fedonkin, 1980)

cf. Hiemalora sp.

(Fig. 4.10 a, b)

Sample no: JD-036, 54

Locality: Sursagar Mine, Jodhpur area, Rajasthan

Description: Circular, disc shaped, with numerous radiating, moderately packed rays or

appendages of variable length seen on the bedding surface of sandstone. The diameter of

disc is about 7.5 cm. No internal structure is visible. The appendages are rectilinear to

slightly sinuous with maximum length of 6.5 cm. Generally unbranched but bifid

branching occasionally seen. Tapering is common. The maximum width of the

appendages is 1.5 mm. In all, 42 appendages are counted.

Fig 4.10: Field photographs of Hiemalora from Sursagar mine, Jodhpur Sandstone. a) Showing the specimen deposited over the ripple marks. b) Radiating arms originating from the centre of the specimen.

d) Aspidella

Genus Aspidella Billings, 1872

(Type Species: Aspidella terranovica Billings, 1872)

Aspidella sp.

(Fig. 4.11 a, b)

35  

Sample no: JD-405,406

Locality: Sursagar Mine, Jodhpur area, Rajasthan

Description: Small circular discs on bedding surface with slightly concave to flat relief

showing that varied morphotypes are preserved. In some forms, raised rim is clearly seen

but in others two to several concentric rings are preserved with very low relief. The

diameter ranges 1.5 cm to 2.5 cm. Maximum relief of the ridges is up to 2 mm. (14

samples traced)

Remarks: Aspidella sp. is considered by Hofmann et al. (2008) as taphonomically quite

variable fossil remain and Gehling et al. (2000) have interpreted the discs as casts of the

basal impression of collapsible or hollow bulb-shaped organism.

Fig 4.11: Field photographs of Aspidella from Sursagar mine, Jodhpur Sandstone. a) Showing well preserved Aspidella with solid outer rim (marked by an arrow); b) Close up photograph of Aspidella showing the circular morphology.

Burrow

(Fig. 4.12-3, 4)

Sample no. AK/SK-21/2011 Burrows are unbranched, horizontal to vertical, present on the top of the bedding

plane, preserved as full relief. Burrows are circular in outline depressed at few places,

forming mess-like network and overlapping each other in a few instances. These are

composed of medium grained sandstone. The maximum to minimum length of burrows

are 0.4 to 11 cm with up to 2 mm in diameter.

36  

These burrows show deposition either at beach or nearshore regime of marine

environment with well oxygenated conditions. The presence of biological activity like

trail mark support in interpreting these structures as burrows.

Fig 4.12: Field photograph of fossil bearing locality. (1) Showing the horizon from where the fossils have been collected. (2) Trail marks in fine grain sandstone. (3 and 4) Showing well preserved network of burrows.

Trail marks (Fig.4.12-2)

Sample no. AK/SK-22/2011 11 cm long and 2 mm wide trail mark running parallel on the bedding plane,

branched and shows sigmoidal movement. In lateral view, it shows “U” shape. Specimen

preserved on top of the bedding plane with medium sand.

37  

4.1.2 Plant fossils Kumar et al. (2009) have reported noncarbonaceous, filamentous megaplant

fossils from the Jodhpur Sandstone and compared them with the extant Vaucheria of

Xanthophycean affinity. The only difference between the fossils and Vaucheria is the

size which is 140 times larger in the fossil record. The morphology of these filamentous

structures is evaluated again for their biogenic nature. These structures are preserved on

the bedding planes of the sandstones as epirelief marked by colour difference with the

host rock. They occur as cast and mould and show more or less similar lithology as that

of the host rock which is a quartz arenite but there is a difference in grain size of the plant

fossils and the host rock. In thin section, the plant fossil is made up fine-grained

sandstone, whereas the host rock is made up of medium grained sandstone (Fig. 4.16 A).

It has been argued that if these structures were of inorganic origin, they should either

represent sandstone dykes or some diagenetic structures. In the Sursagar mines, the

transverse sections to the bedding planes can be studied in detail as there are many

available areas and sections for such scrutiny, but nowhere has any evidence for the

presence of sandstone dykes and sills has been noticed. Moreover, the interwoven nature

of the tube like structures at many places rules out the possibility of these structures being

sandstone dykes. These structures are synsedimentary with the formation of the sandstone

and it is inferred from the fact that a thin microbial mat in the form of small blisters

referred to as a microbial mat Rameshia rampurensis (see Kumar and Pandey, 2008) has

also engulfed the tubular structures. This is possible only when the plant already existed

before the development of the microbial mat. Thus, the chances of it is being a primary

inorganic sedimentary structure as well as a diagenetic structure are ruled out. If

biogenic, it has also been evaluated as to whether these structures belong to a plant

kingdom or they represent the body fossils or trace fossils. It is not comparable to any

animal body fossil or trace fossil and its morphology is also not comparable to any

microbial mat induced sedimentary structures (MISS) (see Schieber et al., 2007). But it

has a pattern and consistency comparable to the thallus of nonvascular plants. In support

of its nonvascular plant origin the following points can be cited:

38  

Fig. 4.13: Geological and location map of the Jodhpur area, western Rajasthan (after Pareek, 1984).

I. The structure is represented by a filamentous tube which is comparable to a

thallus of a nonvascular plant. It is nonseptate with smooth margins. In cross

section the thallus is circular, elliptical or compressed. At a few places, it is

preserved as a hollow tube with thin walls.

II. It has tapering ends but the thallus maintains its width for a considerable length.

39  

III. Branching is prominently seen in the thallus.

IV. In the middle part of the thallus, a swelling is seen which looks like an intercalary

sporangia as seen in the living Vaucheria (Fig. 4.15 K).

V. Presence of swelling at the end of the thallus as well as on the thallus is a

prominent feature. It can be compared with oogonium (sporangia) of a living

Vaucheriacean plant.

VI. The hook-shaped structures present at the margins of the thallus can be compared

with the antheridium. The antheridia are curved, sickle-shaped cylindrical tube

generally found along with oogonia in modern-day Vaucherian algae (Robin

South and Whittick, 1987).

All these features support the conclusion that these structures show morphologies

comparable to the nonvascular plants and, hence, it seems that the Jodhpur filamentous

bodies can be assigned to plant kingdom with affinity to the nonvascular plants. The

consistency in the morphology observed at different places also supports this conclusion.

Taxonomy

Two genera and three species of the megaplant fossils have been identified in the

Jodhpur Sandstone. All the species have been assigned to family Incertae sedis as their

true nature could not be deciphered. Their morphology is comparable to the morphology

Fig. 4.14: Litholog of the fossil-bearing horizon,

Sursagar mine area, Jodhpur, western Rajasthan.

40  

of the Vaucheria plant in shape, branching, presence of beads and antheridium but the

dimensions are so dissimilar that it is not possible to compare them. They are megascopic

and Vaucheria is microscopic. The plant fossils are recorded only in the Sursagar area,

near Jodhpur which is about 8 km NNE of Jodhpur city (Fig. 4.13). The fossils can be

studied in the different mine pits where about up to ca. 15 m thick section of the middle

part of the Jodhpur Sandstone is exposed. The GPS value of the fossil-bearing horizon is

N26o20.007' and E72o59.76'. Since the rocks are more or less horizontal, cross bedding

(Fig. 4.14), the bedding planes can be searched for the plant fossils in different mines.

These are preserved as mould and cast on the bedding planes of the light brown coloured,

fine to medium-grained sandstones. The fossils are marked by the relatively darker colour

in comparison to the host rock on the exposed bedding surfaces (Fig. 4.16 D) and the

grain size marking the structure is relatively less in comparison to the host rock. But in

the fresh section they are also of lighter colour. All the samples have been deposited in

the Museum of the Department of Geology, University of Lucknow, Lucknow.

Family: Incertae sedis

Genus: Vendophycus gen. nov.

(Figure. 4.15)

Type Species: Vendophycus rajasthanensis gen. & sp. nov.

Holotype: Sample no. SK-15

Paratype: Sample no. SS/SK-10, 11, 12, 14

Locality: Sursagar mines, Jodhpur area, Rajasthan.

Lithology: Fine to medium grained sandstone.

Stratigraphic horizon: Middle part of the Jodhpur Sandstone (Sonia Sandstone of Pareek,

1984).

Nomenclature: Genus is named after the ‘Vendian’ stage denoting the age of the Jodhpur

Sandstone.

Diagnosis: The plant is generally preserved as cast on the bedding surface. It is

occasionally preserved as mould also. It is represented by filamentous form which is

large in size and made up of nonseptate cylindrical and tubular body, straight to sinuous

41  

with smooth margins (Fig. 4.15 D, G and 4.18 B). It is freely branched with tapering ends

(Fig. 4.15 A, B). Branching generally occurs at acute angles but the branching at obtuse

angle is also noted (Fig. 4.15 F). Interwoven nature of the filaments is also seen. The

width of the filament varies from 0.3 to 5 cm. If the tubular filament is thin, it shows

smooth upper surface and is circular to elliptical in cross-section (Fig. 4.16 F), but in

thicker filaments striations are seen on the surface of the filament wall and it is

compressed or flattened (Fig. 4.15 C). The filaments appear to be hollow with a thin wall

(Fig. 4.15 E). It shows a tendency to break or split with smooth margin in the middle part

of the thallus (Fig. 4.15 D). Overlapping of filament is also observed (Fig. 4.15 H). Tip of

the filaments is either tapering or becomes swollen forming a circular, globular or

elliptical body (Fig. 4.15 I, J). Small, curved bodies noted on the filament can be

compared to the antheridia of a living Vaucheria plant of Xanthophycean affinity (Fig.

4.15 J).

Remarks: The structure under consideration is preserved as mould and cast in which no

trace of organic matter could be recovered. Thus there is no way to confirm the organic

nature of the structure. It is the morphology of the structure which can help in assigning

its affinity. The morphology is comparable to vegetative thallus and the swollen ends as

sporangia of living Vaucheria only in shape. Hence, the structure appears to be closest to

the family Vaucheriaceae under the class Xanthophyceae, order Vaucheriales and

division Xynthophyta. But since the dimensions are so different it is kept under the

family Incertae sedis. The filament is described as thallus, and the swellings beads as

sporangia. The curved structure attached to the thallus has been diagnosed as

antheridium. The present form is megascopic with width as large as 5 cm while in

Vaucheria it is less than 1 mm. Vaucheria like fossils are known since Mesoproterozoic

(see Butterfield, 2004). Figure 4.15 C depicts the development of microbial mat over the

thallus on the rippled bedding surface confirming to the synsedimentary nature of the

thallus.

42  

Fig 4.15: Plant fossils of the Jodhpur Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) The holotype of Vendophycus rajasthanensis showing thallus with swollen tips referred as beads; arrow marks the beads; B) Close-up view of (A) showing the swollen part at the tip. C) Development of microbial mat over the thallus of plant fossil on the bedding surface; D) Vendophycus rajasthanensis showing thallus with smooth wall preserved on the top of the rippled surface of the medium grain sandstone. E) Thallus preserved as hollow tube; F, Development of thallus showing fertile structures at their tips as beads. G, Branching pattern of Vendophycus rajasthanensis seen on the bedding surface; H) Figure shows overlapping of thallus as well as splitting tendency of thallus; I) Magnified view of (D) showing well developed fertile structure (oogonia); J) Close up view of (K) showing cf. developing synzoospore and K) Figure shows well developed thallus with antheridia and oogonia, marked by arrows “a” and “b” respectively.

43  

Vendophycus rajasthanensis gen. & sp. nov.

(Figure. 4.15, 4.18 B)

Holotype: Sample no. SK-15 Paratypes: Sample no. SS/SK-10, 11, 12, 13 Locality: Sursagar mines, Jodhpur. Lithology: Fine grained to medium grained sandstone. Nomenclature: The species is named after the “Rajasthan” state in western India from

where it is being reported for the first time.

Diagnosis: The plant is generally preserved as cast on the bedding surface. It is

occasionally preserved as mould also. It is represented by filamentous form which is

large in size and made up of nonseptate cylindrical and tubular body, straight to sinuous

with smooth margins (Fig. 4.15 D, G and 4.18 B). It is freely branched with tapering

ends. Branching generally makes at obtuse angles also (Fig. 4.15 F). Interwoven nature of

the filaments is also seen. The width of the filament varies from 0.3 to 3.5 cm. If the

tubular filament is thin, it shows smooth upper surface and is circular to elliptical in

cross-section, but in thicker filaments striations are seen on the surface of the filament

wall and it is compressed or flattened (Fig. 4.15 C). The filaments appear to be hollow

with a thin wall (Fig. 4.15 E). It shows a tendency to break or split with smooth margin in

the middle part of the thallus (Fig. 4.15 D). Overlapping of filament is also observed (Fig.

4.15 H). Tip of the filaments is either tapering or swollen forming a circular, globular or

elliptical body (Fig. 4.15 I, J). The mean diameter of the globular bodies is 1.6 cm. Small,

curved bodies noted on the filament are comparable to the antheridia of living Vaucheria

(Fig. 4.15 J).

Remarks: It is characterised by many swellings at the end of the filament tips, whereas

they are very few in V. sursagarensis and swellings are smaller in size.

44  

Vendophycus sursagarensis gen. and sp. nov.

(Figure. 4.16, 4.18 A)

Holotype: Sample no-SS/SK-16 Paratypes: Sample no-VS/C 1-4 Locality: Sursagar mines, Jodhpur. Lithology: Fine to medium grained sandstone. Nomenclature: The species is named after the locality Sursagar, near Jodhpur Township

from where it is reported for the first time. Diagnosis: The plant is generally preserved as cast on the bedding surface. It is

represented by filamentous tube, large in size made up of nonseptate cylindrical and

tubular body, straight to sinuous with smooth margins. It is freely branched (Fig. 4.16 B

and C) with tapering ends. Interwoven nature of the filaments is also seen. The maximum

width of the filament is up to 5 cm. The maximum length recorded is 167 cm. The

filament bifurcates at a mean angle of 56o (N=8). The maximum elevation of the filament

from the bedding surface is 1.4 cm (N=10). Bifurcation on an average is after a length of

35 cm (N=15). If the tubular filament is thin, it shows smooth upper surface and is

circular to elliptical in cross-section (Fig. 4.16 F), but in the thicker thallus it is

compressed or flattened with striation on the surface. The thallus is curved and smooth

walled (Fig. 4.16 F). It shows a tendency to break or split in the middle (Fig. 4.16 G and

H). Very few swollen tips are seen with diameter ranging from 2 to 3 mm (Fig. 4.16 E).

45  

Fig 4.16: Vendophycus sursagarensis reported from the Jodhpur Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) Photomicrograph showing the contact of the host rock and the thallus of the plant fossil. The dotted line marks the contact; B) Well developed branching pattern in the thallus; C) View of the thallus showing regular pattern of branching; D) Swollen structures at the tip of the thallus; preserved as negative hyporelief; E) Swollen structure seen at the tip of the thallus; F) Elliptical size of the thallus in cross sectional view, preserved in sandstone and G-H) Typical characteristic feature of splitting of the thallus at middle observed in Vendophycus sursagarensis.

46  

Remarks: The difference between the two species of the genus Vendophycus is that in the

V. sursagarensis the swollen tips are very few and rare, while in the V. rajasthanensis

they are common and the swellings are relatively larger in size. The frequency of

branching is more in Vendophycus sursagarensis than in V. rajasthanensis.

Family: Incertae sedis

Genus Indophycus gen. nov.

(Type Species: Indophycus marwarensis gen. and sp. nov.)

(Figure. 4.17)

Holotype: Sample no.SS/SK-1 Paratypes: Sample no. SS/SK-2, 3, 4, 6 Locality: Sursagar mines, Jodhpur area. Lithology: Fine to medium grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone (Sonia Sandstone of Pareek,

1984). Nomenclature: Genus is named after India from where it is being reported for the first

time.

Diagnosis: The plant is preserved as cast and rarely as mould on the bedding surface. It is

represented by filamentous tubes with profuse branching (Fig. 4.17 A and B). It is made

up of nonseptate cylindrical and tubular body, straight to sinuous, with smooth to uneven

margins (Fig. 4.17 E). It is freely branched with a tapering end. Interwoven nature of the

filaments is also seen (Fig. 4.17 A). The maximum length recorded is up to 72 cm. The

width of the filament varies from 0.5 to 3 cm. In a few forms, the thallus is marked by a

depression in the middle (Fig. 4.17 B). Tip of some filaments becomes swollen and forms

a circular or elliptical body which is comparable to sporangia of living Vaucheria (Fig.

4.17 F). Size of swollen bodies varies from 0.4 to 1.4 cm. The filaments also show

abundance of bead like bodies attached at the margin of the thallus (Fig. 4.17 D). Even

serrated or cracked margin is quite common (Fig. 4.17 E). Presence of small, curved

bodies or antheridia (male sex organs) (Fig. 4.17 G) on the filament is also noted. The

antheridia are about 1 cm in length and 0.5 cm in width.

47  

Fig 4.17: Plant fossil Indophycus marwarensis reported from the Jodhpur Sandstone, Sursagar area, Jodhpur, western Rajasthan. A) Indophycus marwarensis showing shrub-like profuse branching with abundance of bead like structure on the thallus preserved on the top of the bedding plane; B) Figure shows hollow depressions in the middle of the thallus, marked by the arrow; C) Excellent preservation of fertile structures (oogonia) closely attached with the thallus; D) Closely attached bead like structure at the wall of thallus with bulbous tip; E) Close up view of the thallus showing closely attached beads making the outer wall serrated which is marked by the arrow; F) Photograph showing development of thallus with well preserved beads as fertile structures. Arrow marks the structures and G, Magnified view of fertile parts of plant; antheridia and oogonia are marked by the arrows “a” and “b” respectively.

48  

Remarks: Indophycus differs from Vendophycus in having smaller dimensions, more

profuse branching pattern and abundance of bead-like bodies on the tubular/cylinderical

thallus. The thallus never breaks or splits in the middle as is commonly seen in

Vendophycus. Size is smaller in comparison to Vendophycus and the branching is more

common in Indophycus giving a shrub-like appearance.

Indophycus marwarensis gen. and sp. nov.

(Figure. 4.17, 4.18 C)

Holotype: Sample no.SS/SK-1 Paratypes: Sample no. SS/SK-2, 3, 4, 6 Locality: Sursagar mines, Jodhpur. Lithology: Fine to medium grained sandstone. Stratigraphic horizon: Jodhpur Sandstone (Sonia Sandstone). Nomenclature: The species is named after the Marwar region of the western Rajasthan. Diagnosis: As for the genus. Remarks: As for the genus.

• Proposed model for the development of Jodhpur plants The present plant fossils have been recorded from that part of the Jodhpur

Sandstone where the microbial mat or biomat-related structures are abundantly

developed. The make-up of the microbial community is unknown as they did not leave

any record in the sediment. On the basis of the available information on the modern

microbial mats, it is inferred that it must have been made up of cyanobacterial, bacterial

and algal forms (see Noffke, 2010). Most mats in marine or hypersaline environment are

principally cyanobacterial mats built predominantly by eukaryotic microorganisms and

are cosmopolitan in shallow marine, lacustrine and flowing waters (Ward et al., 1992). It

can be presumed that within the microbial community there must have been competition

both for the nutrients and space for growth. The nutrient supply was through surface

membrane. A few microbial forms started to increase their size for occupying larger

space but retained the physiological characters of the original microscopic size.

49  

Ultimately, some plants could increase their size to the megascopic level. The microbial

community played the most significant role in stabilizing the sand at the sediment-water

interface up to a depth of few millimeters to possibly several tens of centimeters. This

inference can be drawn on the basis of the abundance of microbial related sedimentary

structures which are conspicuously common in the middle part of the Jodhpur Sandstone

(Sarkar et al., 2008), the firm sandy bottom layer is possible only when the sand is made

firm by the development of microbial mat. The microbial mats that developed at the

water/sand interface offered resistance to erosion. In addition, the absence of benthic

animal population which could have produced burrows for living and were sediment

feeders, the microbial mats were not bioturbated and remained stable. Thus, a stabilized

and firm ground was available in sandy substrate for the growth of megaplants. During

the Ediacaran period, the plants were not growing vertically but developed a creeping

mode of growth which followed the sediment/water interface partially embedded within

the microbial mat. The following conditions can be suggested for this change:

i. The Jodhpur plants developed at the microbial mat-water interface partly

embedded within the microbial mat in a shallow water marine setting where sand was

being dominantly deposited in a moderate energy condition. The microbial mat could

develop in the upper few centimeters of sandy substrate.

ii. The increase of the plant size was triggered because of the competition between

the various communities of algae and cyanobacteria and it was facilitated by the

availability of space for the growth on the upper surface of the mat and ambient water.

iii. The embedded nature of the plant within the microbial mat gave stability to the

plant.

iv. Holdfast, if present, could not be preserved or destroyed early.

v. This plant assemblage did not survive in the Cambrian because of the appearance

of animal life which started bioturbating the sediments. It also affected the stability of the

microbial mats. The animals also nourished on the mega plants. With the loss of mats, the

50  

plants lost their habitat. With the loss of habitat and sudden growth of benthic animal life

in the Cambrian the mega plants became extinct.

vi. Fig. 4.18 (A-C) gives the line sketch of the three plant species to highlight the

morphological difference between them. Fig. 4.18 D shows the schematic diagram

showing the development of the Jodhpur plants on the microbial mat. The mat has

stabilized the sand and the plant is embedded within the mat.

51  

Fig 4.18: Schematic diagrams of Jodhpur plant. A, Vendophycus sursagarensis, B, Vendophycus rajasthanensis C, Indophycus marwarensis. D, Schematic diagram depicts the mode of occurrence of the Jodhpur plant. The plant is embedded within the microbial mat in the Jodhpur Sandstone.

52  

4.1.3 Microbial Mats

Description of Microbially Induced Sedimentary Structures

(MISS)

Sarkar et al. (2008) have described a number of mat related morphologies which are

preserved in the Jodhpur Sandstone and considered them simply as the mat-influenced

sedimentary structures. But in the present work, these structures are described under three

headings:

A. Those microbially induced structures which could be compared with the structures

also produced by the inorganic processes.

B. Those structures which have unique morphologies and could not have been produced

by inorganic processes alone.

C. Those structures which could not acquire specific morphologies and can be referred to

as ‘textured morphological surfaces’ in the sense of Gehling and Droser (2009).

Six structures have been described by using binomial nomenclature. These are

described as ‘group’ and ‘form’ as used for the stromatolites instead of ‘genus’ and

‘species’. It is done for the ease of communication, conceding the fact that these

morphologies are not true fossils but are the product of a collective interaction of a

community of micro-organisms with the sediments. It is emphasized that the form and

group are not species and genus in the true sense of palaeontology; for example the

nomenclature is used for describing siliciclastic mat structure Arumberia banksi from the

Arumbera Sandstone, Australia reported originally by Glaessner and Walter (1975) but is

now considered a mat structure (McIlroy and Walter, 1997) and it is not a species but a

‘form’. In all, 12 microbial forms and 2 types of textured morphological surfaces have

been described from the Jodhpur Sandstone which owes their origin to the microbial

activity at the time of the formation of the sandstones. These have been reported from

two areas; one is the Sursagar area near Jodhpur and the other is the Khatu area, about 60

km from Nagaur Township in the western Rajasthan. The samples have been deposited in

the museum of the Centre of Advanced Study in Geology, University of Lucknow,

Lucknow, Uttar Pradesh.

53  

Fig 4.19: Geological and location map of the Marwar Supergroup western Rajasthan, showing study area (after Pareek, 1984).

54  

A. Microbially Induced Sedimentary Structures which also show similarity with the inorganically produced sedimentary structures:

(i) Microbial Flat Laminated Beds (Fig. 4.21 A)

In the Sursagar area, there are many sandstone beds in the Jodhpur Sandstone on

whose bedding surfaces incomplete or isolated ripples are preserved. The thickness of

such beds varies from a few centimeters to tens of centimeters and they are massive

looking. The height of the ripple crest is up to about 4 mm and the distance between the

two crests varies from 1.4 to 3 cm. In most of the cases, the ripples are wave ripples. The

two ripple crests are separated by plane or flat surface. A number of horizons are noted in

the middle part of the Jodhpur Sandstone in the Sursagar mines. Formation of incomplete ripples or isolated ripples over a sandstone bed is

suggestive of a fact the structure is formed only when the basement for the incomplete

ripples was made firm and stable before the formation of these ripples. The incomplete

ripples are formed when there is insufficient supply of sand to cover the entire surface on

the firm bottom and the wave motion or the current action tends to heap the grains or

Fig 4.20: Litholog of the MISS (Microbially Induced Sedimentary Structures) bearing horizon of the Jodhpur Group.

55  

particles into isolated small symmetrical or asymmetrical lenticular bodies (Reineck and

Singh, 1980). Sand being non-cohesive requires presence of microbial community to

make a firm substrate.

In the modern sediments, flat laminated microbial mats rarely form relief above

the horizon but they may extend to some depth below the surface from a few mm to

several meters (Franks and Stolz, 2009). As such, it is very difficult to distinguish these

beds in absence of the preservation of microbial community in siliciclastic sandy

sediments from the beds produced by purely inorganic processes. However, any evidence

which can give clue about the stability and firmness of non-cohesive sandy beds may

help in the identification of microbially formed flat beds.

(ii) Microbial Wrinkle Marks

(Fig. 4.21 B, C and D)

These are represented by small ridges developed on the bedding surface which

vary in height from 1 mm to 17 mm. They are straight to curved, sinuous to irregular. The

ridges can be traced up to 40 cm or more. The ridges are separated by flat to slightly

concave surfaces. They also bifurcate. At few places the ridges are arranged in such a

way to form more or less semicircular pattern. It appears that depending upon the level of

cohesiveness and the available hydrodynamic conditions a variety of morphologies

representing wrinkle marks are produced in the fine to medium grained sandstone. Sarkar

et al. (2008) have described similar structures from these sandstones as mat-layer

wrinkled structures (mlw).

These wrinkle marks are comparable to the wrinkles marks produced in the mud

by inorganic processes. However, in the sandstones their presence is possible only when

the sand is made cohesive by the development of microbial mats due to the presence of

EPS (Extracellular Polymeric Substance). In literature, these are also described as

Runzelmarken and Kinneyia ripples (Reineck and Singh, 1980). There are many places in

the different mine sections around Jodhpur where wrinkle structures are well preserved in

the sandstones.

56  

(iii) Microbial Buns and Mounds

(Fig. 4.21 E and F)

On the bedding surface of the sandstone, the bun or small mound shaped domal

structures are seen on the ripples and non-rippled surfaces which vary in diameter from 4

cm to 20 cm with an average of 8.6 cm (N=10). The maximum height recorded is 3.5 cm.

The surfaces as well as the margins of the buns are smooth. Generally these are circular

but elliptical outline also noted. In cross section no cavity filling or any other internal

structure is seen. These structures have not affected the ripple crests and their continuity

can be traced on these mounds suggesting that these structures were formed after the

formation of the ripples. Noffke (2010) has suggested that the decay of organic matter in

the microbial mat will produce gases which may accumulate under the sediments sealing

the mat. With increasing pressure the gas will lift the microbial mat which may lose

contact with the under lying substrate. It will produce a hallow cavern. But in the present

case no hallow gap is noted which rules out the role of gases in producing the domal

structures. There is also no evidence of the presence of escaping water jet to produce

domal structures. Thus, the chances are fair that these domes are formed by localized

microbial growth.

57  

Fig 4.21: Field photograph of Microbially Induced Sedimentary Structures (MISS) reported from the Jodhpur Sandstone, western Rajasthan. A) Incomplete ripples over microbially flat laminated surface (coin diameter = 2.4 cm); B, C and D) Various types of well preserved sinusoidal, curved and straight wrinkle marks on the bedding surface (coin diameter = 2.4 cm and lens cap diameter = 5.7 cm); E and F) “Bun shaped” microbial structures with positive relief (maximum elevation from the bedding plane = 3.5 cm), the growth of the “bun shaped” structure not effected the ripples (lens cap diameter = 5.7 cm).

58  

(iv) Cracks in Sandstones

(Fig. 4.22 A) At a number of places, the sandstone shows cracks which compare well with the

mud cracks/synaeresis cracks of the argillaceous rocks. The cracks are irregular. The

width varies from 1-2 mm. These cracks join each other and form the polygon whose size

(longest axes) ranges from 0.4 cm to 2.5 cm. The cracks have depth up to several mm.

From the same horizon Sarkar et al. (2008) have described cracks in the sandstone as mat

induced surface cracks (misc).

These cracks in the sandstones are possible only when the sand becomes cohesive

just after its deposition; on drying the mat cracks to form the structure. In the absence of

lithification, the only possible way by which the sand can be made cohesive is by

invoking the role of microbial mats which developed either immediately or shortly after

the deposition at the sand-water interface involving up to few mm or few cm thick

organically produced layer. This layer under drying conditions developed cracks. Some

of these cracks may have subsurface synaeresis origin. The presence of cracks in the

sandstones simply confirms the role of microbial mats.

(v) Cracks along the Ripple Crests

(Fig. 4.22 B)

Some of the ripple crests show cracks which run parallel to the strike of the crests.

Generally, the cracks are not seen at right angle to the crests or in the troughs. The cracks

are 2.4 cm wide and up to 0.6 cm deep. If the ripples are formed and then partly eroded

then the crest should have a planar surface. However, the crests show cracks all along the

strike marked by a depression. It is envisaged that a thin microbial layer was formed after

the formation of the ripple marks which stabilized the ripples. The ripples were

subsequently eroded but instead of producing flat surface at the ripple crest, the crests

show cracks which depict somewhat deeper and marked erosion with preserved thin

margins. Sarkar et al. (2008) have described them as mat-induced cracks along ripple

crests (micr).

59  

(vi) Microbially produced Inverted Flute Cast

(Figs. 4.22 C and D)

These structures look like inverted flute casts arranged parallel to each other on

the top of the sandstone beds. They are steep at one end and flare out at the other. The

maximum recorded length is 2.8 cm and the width is 1.4 cm. They have a positive relief

and are oriented in one direction. The structure is described from both modern beaches

and ancient sediments (Friedman and Sanders, 1974; Sarkar et al. 2008; Chakraborty et

al. 2013). For preservation of this structure, Sarkar et al. (2011) have suggested the role

of microbial mat. For its genesis they have envisaged the role of trapping of wind

deflated sands on the lee sides of moist obstructions of sections in the littoral-supralittoral

depositional setup. These obstructions must have been formed by the even growth on the

microbial mat surface. Sarkar et al. (2008) have reported them as mat protected setulf and

referred to them as mpsf.

B. Microbial Structures which could not have been produced by

inorganic processes alone: Under this heading all such structures are grouped which could not have been

produced by inorganic processes alone and the role of the microbial mat is essential for

their genesis. The structures described in the previous section can be produced by the

inorganic processes in the cohesive sediments but the structures described in this section

cannot be produced without the participation of microbial mats. All the structures have

been given binomial nomenclature for the ease of communication conceding the fact that

they are not true species and genera in the traditional sense of palaeontology. Instead they

are referred to as ‘form’ and ‘group’ as have been done in describing the stromatolites.

60  

(vii) Aristophycus Miller and Dyer 1878 (in Häntzschel, 1975)

(Type form: Aristophycus ramosum Miller and Dyer 1878; in Häntzschel, 1975)

Aristophycus sp.

(Figs. 4.22 E and F)

Sample no: SK/ARI-12/09.

Locality: Khatu area, Nagaur district, Rajasthan; GPS value N27º 8.837’, E74º 19.596’. Lithology: Fine grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone. Description: It is a branching form characterized by anastomizing raised ridges seen on

the top of the sandstone bed. It shows main branch, generally straight to slightly curved

in which secondary, tertiary and quaternary branches develop forming anatomizing raised

structure. The main branch shows maximum width as 1.8 cm. For secondary and tertiary

branches it decreases gradually. The height of the raised structure is 5 mm. Tapering is

quite prominent and it starts from the side of maximum width. The maximum width in

the main branch is seen at the raised part of the bedding plane. The secondary and tertiary

branches bifurcate and rarely trifurcate. The raised ridges show flat or slightly convex

surface. Branches make an angle which ranges from 30o-60o. Area between ridges is

concave to smooth. The margins of the ridges are smooth. The ridges taper off and

merges with the bedding plane at the distal part. The structure is developed around a

raised part made up of sandstone clasts.

Remarks: Aristophycus is a branching structure well developed in the Khatu area in the

northern side of the main hillock at western side of the Khatu Township. It is recorded in

the fine grained light whitish coloured sandstone showing large scale cross bedding. It is

developed around large sized sandstone clasts. The clast shows slightly higher position

with respect to the bedding and there is a slope around the clasts. The structure is

developed with large stem or main branch near the clast and as one moves away from

clast the width decreases. Originally the structure was considered as of inorganic origin

and Häntzschel (1975) included it under the heading ‘Pseudofossils’. Seilacher (2007)

suggested the origin of this structure. He considered Aristophycus as a dewatering

structure. It is formed when water escapes during compaction from the sand and it is

61  

stopped by the overlying biomat. Since the water fails to escape, it dissipates below the

biomat eroding its sole producing a structure resembling a distributary river system.

Subsequently the sand below the mat occupied the eroded space to produce the structure.

Fig 4.22: A) Well developed cracks in the sandstone (scale = 12cm); B) Cracks along the ripple crests bounded by sharp ridges (marked by arrows) by both sides of the crack (coin diameter = 2.3cm); C) Inverted flute structure in sandstone illustrates surface pavement in which sand has accumulated forming small drumlin shaped inverted flute cast (coin diameter = 2.4cm); D) Magnified view of Inverted flute Structure (scale bar = 2cm); E) Well preserved Aristophycus around a large sandstone clast showing primary, secondary and tertiary bifurcations (coin diameter = 2.4cm) and F) Close up of Aristophycus: an inorganically formed structure showing well developed bifurcations which is possibly formed by action of water current and microbial mat (coin diameter = 2.4cm).

62  

(viii) Arumberia banksi Glaessner and Walter 1975

Group: Arumberia Glaessner and Walter 1975 (Type form: Arumberia banksi Glaessner and Walter 1975)

(Fig. 4.23 A) Sample no: Kh0608. Locality: Khatu area, Nagaur district, Rajasthan; GPS value N27º 8.837’, E74º 19.596’. Lithology: Fine-grained sandstone. Stratigraphic horizon: Upper part of the Jodhpur Sandstone. Description: It is marked by the presence of small ridges seen on top of the bedding plane

separated by flat to concave furrows. These are parallel, straight, gently curved and

between 1 to 3 mm wide separated by flat to gently concave furrows of 1 to 4 mm in

width. The relief of the ridges is less than 1 mm and maximum recorded length is 14 cm.

Generally the ridges are parallel but they also bifurcate. It is seen on plane as well as

rippled surface. Remarks: This form was originally described by Kumar and Pandey (2009) from the

same locality. It compares well with Arumberia banksi described by Glaessner and

Walter (1975) from the Arumbera Sandstone, Australia. It also compares with the form

described by Kumar and Pandey (2008) from the Maihar Sandstone, the uppermost

lithostratigraphic unit of the Bhander Group of the Vindhyan Supergroup of the Son

Valley Section. It grades to Rameshia rampurensis with the development of small

mounds/blisters or pustules interspersed and superimposed on the Arumberia banksi (Fig.

4.15-F).

(ix) Rameshia rampurensis (Kumar and Pandey, 2008)

Group: Rameshia Kumar and Pandey, 2008

Type form: Rameshia rampurensis Kumar and Pandey, 2008

(Figs. 4.23 B and C)

63  

Sample no: Kh0808. Locality: Two localities; one is in Khatu area, Nagaur district with GPS value N

27°08.168′; E 74° 18.871′ and the second is in the Sursagar area, Jodhpur district with

GPS value as 26°15.774′ N ; 73°00.148′ E.

Lithology: Fine-grained sandstone. Stratigraphic horizon: Upper part of the Jodhpur Sandstone. Description: It is made up of rounded to elliptical very small mounds/blisters making the

entire surface granular. The size of the blisters ranges from 1 mm to 4 mm. Generally it is

circular to elliptical. It gives a mat texture to the bedding plane. It is seen both on the

rippled surface as well as on the plane bed.

Remarks: Kumar and Pandey (2009) were the first to describe it from the Khatu area. It

compares well with form described from the Maihar Sandstone of the Vindhyan

Supergroup by Kumar and Pandey (2008). In the Sursagar area, there are many horizons

where this structure is seen.

(x) Rameshia linearis New form

(Figs. 4.23 D and E) Sample no: SK/JD08/12. Locality: Two localities; one is in Khatu area, Nagaur district with GPS value N

27°08.168′ ; E 74° 18.871′ and the second is in Sursagar area, Jodhpur district with GPS

value as N 26°15.774′ ; E73°00.148′. Lithology: Fine-grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone. Diagnosis: It is made up of rounded to elliptical very small mounds/blisters arranged in

rows. At places rows are made up of two or more blisters. Diameter of the blisters ranges

from 1 mm to 5 mm. Generally the blisters are circular to elliptical. The rows are straight

to slightly curved. The rows can be traced up to 26 cm. The distance between the two

64  

rows varies from 8 mm to 10 mm. It is seen both on the rippled surface as well as on the

plane bed. Description: As above. Derivation of name: The form is named because the blisters are arranged in rows.

Remarks: In Rameshia rampurensis the blisters cover the entire surface of the bedding

plane, whereas in R. linearis the blisters are linearly arranged in rows. Gerdes (2007) has

suggested the role of gases which are formed by the decay of microbial mats in producing

the structure.

65  

Fig 4.23: A) Arumberia banski showing presence of small ridges on bedding surface separated by concave furrows (coin diameter = 2.4cm); B and C) Rameshia rampurensis showing very small mounds or blisters making the entire bedding surface granular (coin diameter = 2.4cm); D) and E) Blisters are arranged in a linear fashion (coin diameter = 2.4cm) and F) Transitional form exhibiting characteristics both Arumberia and Rameshia, (coin diameter = 2.4cm).

(xi) Rameshia anastomose (New form)

(Fig. 4.24 A)

Sample no: SK/JD09/12. Locality: Sursagar area, Jodhpur district with GPS value as N 26°15.774′; E73°00.148′.

66  

Lithology: Fine grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone. Diagnosis: It is made up of rounded to elliptical very small mounds/blisters arranged in

rows which form irregular pattern. Diameter of the blisters ranges from 1 mm to 4 mm.

Generally the blisters are circular to elliptical. The rows are curved and form different

enclosed patterns. The diameter of the enclosed area varies from 2 cm to 5 cm. Description: As above. Derivation of name: The form is named after the nature of the rows of the blisters which

form irregular enclosed patterns. Remarks: In Rameshia rampurensis the blisters cover the entire surface of the bedding

plane, whereas in R. linearis the blisters are linearly arranged more or less in straight

rows. In the present form the linearly arranged blisters form irregular enclosed patterns.

(xii) Jodhpuria new group

(Type species: Jodhpuria circularis)

(Fig. 4.24 B and C)

Sample no: SK/1108. Locality: Sursagar area, Jodhpur district with GPS value as N 26°15.774′; E73°00.148′. Lithology: Fine-grained sandstone. Stratigraphic horizon: Middle part of the Jodhpur Sandstone.

Diagnosis: It is made up of very thin ridges forming complex colonies in which the

individual colony is formed by a circular flower like pattern. It is made up of a central

body with expanding circular ridges which subsequently interfere with adjacent colonies.

The individual circular outline in general is not continuous but broken to form somewhat

irregular pattern which collectively form expanding flower like pattern. Length of the

ridges varies from 10 cm to 25 cm. Top of the ridge smooth and rounded. Height of the

67  

ridges is less than 1 mm. It is seen both on the rippled surface as well as on the plane

beds.

Derivation of name: The form is named after the town Jodhpur from where it is reported

for the first time.

Remarks: Sarkar et al. (2008) have described it as mat related structures and referred it as

mld (mat-layer discoidal) structure. Banerjee et al. (2010) have compared this structure

with Palaeopascichnus though in no way it is related to this trace fossil.

Jodhpuria circularis new group and form

Jodhpuria circularis

(Fig. 4.24 B and C)

Description: It is made up of very thin ridges forming a pattern of rose petals or flower

like pattern arranged in a circular or concentric manner around a rim which is more or

less circular in outline or having a distorted shape. The expanding pattern of ridges

overlaps the previous ridges and creates a unique pattern. The expanding ridges

subsequently interfere with the adjoining units. The size of the central sub-circular rim is

ca 4.2 cm and the maximum size of the circular pattern is 34 cm (excluding outer petal

like structure marked in Fig. 4.16 B). The width of the ridges varies from 1 mm to 2.4

mm. The entire structure covers an area of about 1 meter. The area between the ridges is

smooth. The concentric rims quite often produce spindle shaped bodies. Sarkar et al.

(2008) have called these patterns as mat-layer discoidal structures (mld).

Remarks: As for the group.

Derivation of name: It is named because of the circular nature of the ridges.

C. Structures which could not acquire specific morphologies and can be referred to

as ‘Textured Morphological Surfaces’:

Textured Organic Surfaces (TOS) are defined as a diverse assemblage of

structures that may have discrete morphological characters but do not have a defined

shape or size that might enable taxonomic description (Gehling and Droser, 2009). On

68  

many bedding surfaces of sandstones, there are features which cannot be given any name

as the morphology of the structures could not attain any specific shape. Though Gehling

and Droser (2009) have identified 9 different forms, only two patterns have been

identified here under this heading. These are:

(I) Old elephant skin weathering pattern

(II) Poorly developed patterns

(I) Old elephant skin weathering pattern

(Fig. 4.24 D)

“Elephant skin” texture occurs as network of reticulate ridges that grade laterally

into more irregular pattern (Gehling, 1999). It is developed in grayish black silty

sandstone. According to Seilacher (2007), the elephant skin texture represents a kind of

load casts on a rather smaller scale. The structure is characterized by reticulate ridges on

the upper bedding surface, or respective impression on lower bedding surface. They also

form polygonal network with a width of 5 to 10 mm. Old elephant skin weathering

pattern is geometrically distinguishable forms other mat-forming structures and easily

recognized by its textured surface.

(II) Poorly developed patterns

(Fig. 4.24 E and F)

Under this heading, all such patterns are included which could not be defined on

the basis of morphology. Such forms could not have formed by only inorganic processes.

There are many records of mat induced structures in the Jodhpur Sandstone which do not

have a specific shape, geometry and pattern which could be given a name but in spite of

that they provide good proxy records of the presence of biomat (microorganisms) in a

shallow marine to sub-tidal environment of the Jodhpur Sandstone.

69  

Fig 4.24: A) Rameshia anastomose showing small mound like structure forming anastomose pattern (coin diameter = 2.3cm); B) Jodhpuria circularis showing ridges forming circular to concentric pattern in the central part while in the outer part it forms petal like arrangement of ridges (marked by arrows), (coin diameter = 2.4cm); C) Close up view of Jodhpuria circularis; D) Old Elephant Skin (OES) textured surface (coin diameter = 2.3cm); E and F) Poorly developed microbial structures on rippled surface (coin diameter = 2.3cm).

70  

4.1.4 Stromatolites from the Bilara Group Only stromatolites have been reported from the Bilara Group. Though the

microbiota has been reported from the black chert by Babu et al. (2009), in the present

work none of the thin section of the chert has yielded any microfossil. Prasad (2010) have

reported fossils from the Bilara Group by using maceration methods. The stromatolites

are restricted to the carbonate rocks of Bilara Group only. The carbonate rocks are

exposed in all the three formation of the group i.e. the Dhanapa Formation, the Gotan

Formation and Pondlo Formation (from lower unit to upper unit). Khilnani (1964) was

the first to notice them in the Bilara Group. The stromatolites exhibit diverse

morphologies from domal to columnar forms but most of them are stratiforms sheets of

low relief. Some of these stromatolites are identified by Barman (1987) as Collenia

pseudocolumnaris Maslov, Colleniella Koroyak. Cryptozoon occidentale Dawson and

Stratifera Korolyuk with occasional Oncolites pia (Barman 1980, Verma and Barman,

1980). According to Barman (1987), these stromatolites are generally stunted in growth

as compared to stromatolites of Aravalli, Delhi, Vindhyan Supergroup. The stromatolites

of the Marwar Supergroup do not have well defined margins. Such stromatolites with ill

formed column margin may be termed the colloform mat structures conforming to

subtidal conditions (Hoffman, 1974). Most of the stromatolites of the Bilara Group show

development of asymmetrical laminations with thicker laminae developed on one side.

The stromatolites assemblage, from the carbonaceous Bilara Group (Marwar Supergroup)

has no form which is distinctive for age determination of the host rocks. However, it is

certain that the Late Riphean and the Vendian forms of stromatolites (Preiss 1976 p, 361)

are not present in the Bilara Group of rocks.

71  

Fig 4.25. Stromatolites of the Bilara Group. A, D and E- Colonnella columnaris; B- Transverse section of Colonnella. C and F- Coniform stromatolites.

72  

Fig 4.26: Stromatolites of the Bilara Group. A- Colonnella columnaris B- Coniform stromatolite C-Transitional form D- Pseudocolumnar form, E and F-New form A (Scale bar = 2 cm).

73  

4.1.5 Trace Fossils from the Nagaur Group Only one body fossil has so far been described by Singh et al. (2013). However,

well-preserved trace fossils are abundantly recorded. Kumar and Pandey (2010) were the

first to describe the trace fossils from the Nagaur Group. In the present study, numerous

trace fossils were identified, out of which six forms are new. Most of these fossils are

seen on the sole of the bedding plane as well as on top of the bedding surface. Lithology

is represented by fine-grained sandstone, siltstone and shale.

Fig 4.27: Geological and location map of the Dulmera area, District Bikaner, Rajasthan (after Pareek, 1984).

74  

Fig 4.28: Litholog of the Nagaur Sandstone showing the position of trace fossils, Dulmera area, Bikaner district, Rajasthan.

Ichnogenus Rusophycus Hall, 1852

Rusophycus carbonarius Dawson, 1864

(Figs. 4.29 A and B)

Repository ref. NG/SK13/1

Material: A single slab of fine grained sandstone showing 35 specimens preserved as

hyporelief on the sole of the bedding plane.

Description: Convex, coffee-bean-shaped hypichnia, 0.5 to 1.5 cm long with mean value

as 1.03 cm (N=35) and 0.4 to 0.9 cm wide with mean value as 0.6 cm (N=35). The

individual lobe is 0.2 to 0.7 cm wide. The two symmetrical lobes are separated by a

distinct furrow. The furrow is 0.1 to 0.2 cm wide. Lobes are parallel, rarely oblique and

0.3 to 0.5 cm in height from the bedding surface. The median furrow runs for through full

length of hypichnion.

75  

Discussion: The specimens do not display the stripes on the lobes which is typical

characteristic of Rusophycus carbonarius (Schlirf et al., 2001). However, Kieghley and

Pickerill (1996) interpreted such specimen as taxonomic variants of R. carbonarius. The

Early Cambrian R. carbonarius was possibly produced by small or juvenile trilobite

(Stachacz, M. 2012). R. carbonarius is believed as a resting trace of tiny arthropod

(Hofmann et al., 2012). Present form is slightly larger in size and closely resembles

ichnospecies R. carbonarius reported from the Holycross Mountain, Poland (Stachacz,

M., 2012).

Rusophycus didymus, Salter 1856

(Figs. 4.29 C and D)

Repository ref. D-108/08

Material: One slab of fine grained sandstone showing two well preserved specimens on

top and nine on the sole of the bedding plane.

Description: Short bilobate, smooth, elliptical in outline, resembling coffee bean,

posteriorly tapering lobes preserved as epirelief on the other side (anterior) making acute

angle (40-45o). The lobes are 0.9 to 3 cm long with mean value as 1.8 cm (N=11) and 0.8

to 2.1 cm wide with mean value as 1.6 cm (N=11), whereas, the individual width of the

lobe varies from 0.4 to 0.9 cm with mean value as 0.6 cm (N=11). The gap between the

lobes varies from 0.2 to 0.7 mm (mean=0.3 cm; N=11). Normally both lobes are parallel

but sometime making an acute angle and median furrow rarely seen. The traces are 2 to 3

mm in height from the bedding surface.

Remarks: Both lobes are smooth devoid of any stripes. Specimen closely resembles

Rusophycus didymus Salter, 1856. This ichnogenus has worldwide occurrence such as

Europe, North America, North Africa, Asia, and the Lower Cambrian of Pakistan

(Moore, 1962). Rusophycus is first described by Salter (1856) and later on by Seilacher

(1953) who interpreted it as a trilobite resting excavation. The specimen is also described

by Kumar and Pandey (2008, 2010) from the same horizon simply as Rusophycus isp.

76  

Ichnogenus Cruziana d’ Orbigny, 1852

Cruziana fasiculata Seilacher, 1970 (Figs. 4.29 E and F)

Repository ref. DL-45, 47, 51, 52, 56, 60, 102, 124, NS-12 and NS-24 Material: Ten slabs of fine-grained sandstone containing more than fifty two specimens

oriented broadly in particular direction or randomly arranged on the sole of the bedding

plane, while four specimens are preserved on the top of the bed. Description: Elongate furrow, herringbone-shaped ridges with sub-equal scratches.

Median furrow runs parallel and divides the structure into two lobes and continues

uninterrupted. The specimens taper at posterior end and broader at anterior end. Genal

spine absent in all specimens. Width varies from 1 to 3 cm with mean value as 1.6 cm

(N=56), length ranges from 1.4 to 30 cm with mean value as 5.8 cm (N=56). The traces

are 0.5 to 1 mm in height. The gap between the two consecutive scratch marks is 1 to 2

mm. The furrow width ranges upto 0.2 cm. Length of median furrow is as per the size of

the specimen. The podial marks on the lobes meet centrally at a furrow making V-shaped

structure with varying angle ranges from 50-60o. Remarks: Scratch marks present on both the lobes are not identical. Each lobe showing

scratch marks in bundles which is comparatively unequal in 1 cm length. The podial

marks are counted as 8 to 10 lines/cm, which indicates the movement of the animal,

faster or slower. Present specimen is very close to ichnogenus Cruziana fasiculata

Seilacher in terms of podial marks. Cruziana is considered a burrow produced by

trilobites (Seilacher 1970). Cruziana fasiculata is also described by Kumar and Pandey,

(2010) from the same horizon simply as Cruziana isp.

Cruziana cf. salomonis Seilacher, 1990

(Fig. 4.30 A)

Repository ref. NG/SK-13/4&5

77  

Material: Two slabs of fine grained sandstone comprising 5 specimens collected from the

Dulmera mine preserved as hyporelief on the sole of the bedding surface.

Description: The form is having typical morphology of Cruziana species. The endopodal

scratches are prominent in the frontal part of furrow. The median furrow has constituent

width all along the trace. The traces are 1.4 to 2.8 cm long with mean value as 3.8 cm

(N=5) and is 2.4 cm wide with mean value as 1.1 cm (N=5). The individual widths of

lobes are 0.9 to 1.3 cm. Both lobes are more or less symmetrical in shape. The continuous

length of furrow up to 1.7 cm is noticed with mean value as 1.5 cm (N=5) along with 0.1

to 0.3 cm wide. The striation joins at the furrow at about 150o to 170o making an obtuse

angle. 10 podial marks are counted in 1 cm length.

Discussion: The present form has close resemblance with the form reported from the

eastern desert of Egypt (Seilacher, 1970) in furrow morphology and obtuse angle

relationship between two sets of podal markings. C. salomonis endorsed to the activities

of small to medium trilobite mostly digging activity within the sand (Hofmann et al.,

2012). The specimen is close to C. salomonis only in terms of angular relationship of

podial marks with respect to median furrow, but differs in lacking 3 to 4 podial marks in

groups.

Ichnogenus Isopodichnus Bornemann 1889

Isopodichnus isp.

(Fig. 4.30 B)

Repository ref. DL-108/106/ 115 and 202 Material: Four slabs of muddy to fine grained sandstone with three specimens preserved

on the top and three on the sole.

Description: Paired ribbon like trail, smooth walls, straight to curved, separated by fine

prominent furrow. There is no marking observed on the wall of track. Trails are 3.4 to 9

cm long and 0.9 to 1.5 cm wide. The furrow runs parallel to the structure and ranges from

0.1 to 0.4 cm in width.

78  

Remarks: Specimen is comparable to Cruziana as far as the morphology and the outline

the trail is concerned but it lacks any type of scratch marks (sensu Fürich, 1974). The

specimen is closely resembles Isopodichnus described by Kumar and Pandey, (2010).

Ichnogenus Tasmanadia, Chapman, 1929

Tasmanadia cachii Durand and Aceñolaza, 1990 (Fig. 4.30 C)

Repository ref. NG/SK-13/21

Material: One slab containing two specimens preserved as positive relief on fine grained

sandstone on the top of the bedding plane. Description: Double rows of prominent ridges forming “bracket”-shaped structure. The

trace is 2.8 cm long and 1.3 cm wide containing total 14 ridges, seven at both sides. The

space between two contiguous ridges is 0.6 cm. Discussion: Morphologically, the present specimen shows close resemblance with the

Tasmanadia cachii Durand and Aceñolaza (1990) and the trace is interpreted as the

trackway produced by an arthropod. The bracket-shaped outline of the trackway indicates

the shape of the body of the animal; it means that animal moves in jumps rather than

walking continuously (Seilacher, et al., 2005). This ichnospecies is being reported for the

first time from the Nagaur Sandstone.

Ichnogenus Diplichnites, Dawson, 1873

Diplichnites gouldi (Bradshaw, 1981)

(Fig. 4.30 D) Repository ref. NG/SK-13/18 Material: Two specimens preserved hyporelief in fine grained sandstone. Description: Trackway consisting two parallel series of fine ridges, oriented

perpendicular to the track axis. Width of the trackway 1.7 cm and length measured up to

79  

5.2 cm. Individual ridge elongate, 0.4 to 0.6 cm in length. Both rows of are 0.6 cm apart.

The gap between the two contiguous ridges is 0.3 cm. Both series are well preserved. Remarks: Specimen shows close resemblance with ichnogenus Diplichnites aenigma

Dawson (1873), which is interpreted as a walking trace of trilobite (Seilacher, 1955;

Radwanski and Roniewicz, 1963; Crimes 1970). Specimen quite differs from

Dimorphicnus in respect of lacking prominent ridges. During the movement, the width of

the trace will depend on the size of the animal and how far its limbs extend outside

(Crimes and Harper, 1970). The specimen shows fine imprints oriented perpendicular to

the midline of the trackway which is similar in Diplichnites gouldi Bradshaw, 1981(see

Minter and Lucas, 2009). Diplichnites are abundantly reported from Cambrian rocks

(Seilacher, 1955). The specimen is comparable with the form described by Kumar and

Pandey (2010).

Ichnogenus Merostomichnites Packard, 1900b

(Type ichnospecies Merostomichnites beecheri Häntzschel, 1962)

Merostomichnites isp. (Figs. 4.30 E and F) Repository ref. NG/SK-12/102 Material: Specimens preserved as epirelief in fine-grained sandstone. Description: Sickle-shaped, prominent and parallel rows of ridges arranged in a pair,

obliquely to midline of trackway. Width of the trackway is 1.5 cm and length varying

from 2.4 to 5.3 cm, individual ridge varies from 2 to 5 mm in width and 8 mm in length

while gap between two consistent ridges is 3 to 4 mm. The series of ridges is 6 mm apart

from each other and gap between the two consistent ridges is 2 mm. The ridges are

crescent in outline. Remarks: The specimen is comparable with the ichnogenus Merostomichnites described

by Häntzschel, 1975. It also shows resemblance with the specimen described by Parcha

80  

and Pandey (2011). Merostomichnites differs from ichnogenus Diplichnites Dawson

(1873) in lacking median grooves and morphology of making podial marks. This

ichnogenus is formed by resting activity of the animal.

Ichnogenus Planolites Nicholson 1873

Planolites beverleyensis, Billings 1862

(Fig. 4.30 G)

Repository ref. NG/SK-13/23 Material: Four specimens preserved as positive hyporelief in fine-grained sandstone. Description: Full relief, unbranched, horizontal to the bedding surface, straight to slightly

curved burrow, partly infilled with host sediments. Individual burrow is 2.0 to 8.5 cm

long and 1 to 3 mm wide.

Remarks: The specimens closely resemble Planolites beverleyensis, Crimes and

Anderson (1985), in unbranched nature of burrows. It is often difficult to distinguish

between Planolites and Palaeophycus Hall, except in non branching nature of burrow.

Planolites beverleyensis has a broad range from Precambrian to Recent.

81  

Fig 4.29: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Rusophycus carbonarious; B) Close up view of Rusophycus carbonarious; C and D) Rusophycus didymus; E and F) Cruziana fasiculata (diameter of coin = 2.3cm).

82  

Fig 4.30: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Cruziana cf. salomonis; B) Isopodichnus isp; C) Tasmanadia cachii; D and E) Diplichnites; F) Merostomichnites isp; G) Planolites beverleyensis.

83  

Ichnogenus Bergaueria Prantl 1945

Bergaueria aff. perata Prantl 1945 (Fig.4. 31 A, B and C)

Repository ref. NG/SK-13/24

Material: Total four specimens preserved in fine-grained sandstone as positive

hyporelief.

Description: Cup-shaped protrusion with smooth walls, wider than deeper, perpendicular

to bedding plane. Circular to sub-circular in outline 2 to 4 cm in diameter and 0.4 to 1.0

cm deep. Lower end rounded, with shallow depression. Outer wall smooth, devoid of any

striations.

Discussion: Bergaueria is interpreted as a domichion or cubichion produced by actinarian

and ceriantharian coelenterates (Fillion and Pickerill, 1990; Bromley, 1996). Bergaueria

is regarded as a dwelling structure, and present specimen shows close resemblance with

Bergaueria perata Prantl (1945). The specimen has global occurrences from Cambrian to

Ordovician strata (Häntzschel, 1975) but most common in Lower Cambrian (Mc Kee,

1945; Seilacher, 1956; Crimes and Anderson, 1985; Gàmez vintaned et al., 2006).

Ichnogenus Dimorphicnus Seilacher, 1955

Dimorphicnus cf. obliquus Seilacher, 1955 (Fig. 4.31 D)

Repository ref. NG/SK-13/29

Material: one slab of fine grained sandstone with two specimens preserved as positive

hyporelief.

Description: A pair of symmetrical trails horizontal to the bedding plane, the length of

the structure is up to 1 cm and width 1mm, and is less than 1 mm apart from each other.

Remarks: The specimen described herein resembles Dimorphicnus cf. obliquus Seilacher

(1955). According to Seilacher (1955), Dimorphicnus is a grazing trace formed by

trilobites while scratching the sea bottom with appendages in search for food. This

ichnogenus also known from the Lower Cambrian succession of Wales (Crimes, 1970),

Lesser Himalaya (Tewari and Parcha, 2006), Zanskar (Parcha and Singh, 2010), western

84  

Rajasthan (Kumar and Pandey, 2008 and 2010), Krol-Tal succession of Lesser Himalaya

(Singh and Rai, 1983).

Ichnogenus: Monocraterion Torell 1870,

Monocraterion isp. (Figs. 4.31 E and F)

Repository ref. NG/SK-13/44

Material: Two specimens collected in situ with full relief within fine-grained sandstone.

Description: Knob-like circular structure projecting downward, perpendicular to the

bedding plane, never branched. The centre of burrow is deep and unornamented; two

circular rings are present; one central and other making the outline of the body. The

diameter of outer ring is 3 to 4.5 cm and up to 1.5 cm deep, while inner circle is 1.8 to 2.3

cm in diameter and up to 0.5 cm deep.

Discussion: The specimen shows close resemblance with the ichnogenus Monocraterion

in terms of its cylindrical burrow and concordant funnel at the top. But present specimen

is not so much deep and it also lacks the well-developed, funnel-like structure, which is a

diagnostic feature of Monocraterion (Häntzschel, 1975). The specimen is also

comparable with the ichnogenus Bergaueria but the presence of circular rings and

absence of any concentric structure on the body completely rules out this idea.

85  

Fig 4.31: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A, B and C) Bergaueria aff. Perata; D) Dimorphichnus cf. obliquus; E and F) Monocraterion isp.

86  

Ichnogenus Planolites Nicholson, 1873

Planolites annularis Walcott, 1890 (Fig. 4.32 A)

Repository ref. NG/SK-13/39

Material: One slab of fine-grained sandstone having ten specimens preserved as positive

hyporelief on the sole of the bedding plane.

Description: Transversely annulated, horizontal burrow, generally straight, slightly

curved, arranged in a back to back pattern. Single scratch varies from 1.0 to 3.9 cm long

and width 2 to 4 mm. The gap between the annulations is normally 1mm. There are 6 to

8 transverse annulations counted per cm.

Discussion: This specimen shows resemblance with Planolites annularis Walcott,

1890.The specimen also shows some resemblance with the Priapulid-like worm reported

from the Nagaur Group (Srivastava, 2012b) only in transverse annulations, but differs in

overall morphology (shape and size).

Scratch marks/Dig marks

(Figs. 4.32; B, C, D and E)

Repository ref. NG/SK-13/42, 42, 44 and 45

Material: Ten specimens of fine grained sandstone collected as positive relief from the

sole of bedding plane.

Description: Even spaced deep imprints, comb shaped, generally straight, sometime

curved with very prominent ridges from 2.0 to 3.5 cm long and 1 mm in width. The

distance between the two consecutive imprints is 2 mm. The finger print like imprints

(Fig. C and E) possessing 4 to 5 division/cm.

Discussion: The structures shown in fig. 4.32 B show close resemblance with the scratch

marks possibly produced by arthropod. These structures are formed by digging activity of

the animal. On the other hand the structures shown in fig. 4.32 C, D and E are termed

here the trilobite fingerprints rather than scratch marks. These structures have been also

described as trilobite finger prints by Seilacher (2007). Possibly, the fingerprints are left

by the tips of the endopodites displaying groupings of claws or setae. These specimens

87  

also show similarity with the dig mark of one lobe produced by trilobite (Crimes and

Harper, 1976).

Fig 4.32: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Planolites annularis; B, C, D and E) Scratch marks of arthropods.

88  

Ichnogenus Treptichnus Miller, 1889

Treptichnus pedum Seilacher, 1955 (Fig. 4.33, A)

Repository ref. NG/SK-12/05

Material: The specimen preserved in situ as positive hyporelief in fine-grained sandstone.

Two slabs having four specimens were collected.

Description: Burrow system with oblique to curved row of segments, arranged alternately

left and right, or in a zig-zag feather-stitch pattern (Häntzschel, 1975), comparable to

ramification of plants. Individual segments are slightly displaced in relation to each other.

Segments are simple or elongated. Length of individual segments is 0.5 to 2 cm and

width up to 4 mm with 3 mm in height. The complete stretch of structure is 13 cm.

Remarks: On the basis of the diagniostic characteristic of feather-stitch like arrangement

of segments the present specimen appears close to ichnogenus Treptichnus Miller, 1889.

The present burrow system Treptichnus is interpreted as fodichnion made by vermiform

animals (Buatois et al., 1998). Parcha and Pandey (2011) considered Treptichnus in

Phylum Annelida. The present form is similar to the ichnogenus Treptichnus pedum

reported from the Nagaur Sandstone (Srivastava, 2012a).

Ichnogenus: Monomorphicnus Dawson, 1873

Monomorphicnus isp.

(Fig. 4.33; B)

Repository ref. NG/SK-13/28

Material: Two specimens preserved as hyporelief in fine-grained sandstone.

Description: Gently curved ridges arranged in a row. The ridge is 5.4 cm long and is 3

mm in width. Ridges are 1 cm apart from each other. The specimen comprises of 4 to 6

curved ridges.

Discussion: The specimen is morphologically close to the Monomorphicnus Crimes,

1970. Monomorphicnus lineatus reported from Paseky Shale of Czech Republic by

Mikulas, R (1995). It is suggested that the structure was formed by the sideways

propagation of the animal.

89  

Small Knob-shaped burrow Form A (Fig. 4.33 C)

Repository ref. NG/SK-13/32

Material: One single slab containing more than 5 specimens preserved as positive relief

in fine-grained sandstone.

Description: Small-knob like burrow, horizontal to the bedding plane. The length is 2 to

4.5 cm and width 0.5 to 0.8 cm, with poorly preserved transverse markings on the wall of

burrow.

Remarks: The burrow and its ornamentation on wall is slightly different from all the

reported burrow forms from the Lower Cambrian.

Ichnogenus Chondrites von Sternberg, 1833

Chondrites isp.

(Fig. 4.33 D)

Repository ref. CH/SK-13/34

Material: Single slab of fine grain sandstone. Specimen preserved on the top of bed.

Description: Dendritic pattern, small tunnel like structure lying parallel to the bedding

plane, asymmetrical traces of biogenic origin. Specimen is 1.0 mm wide while length

varying from 0.4 to 2.0 cm. Width constant throughout the length. The angle of branching

may also be variable between 35º - 40º.

Discussion: The present form of Chondrites resembles in all respect Chondrites von

Sternberg. Chondrites undoubtly belongs to the fodinichnia and is to be regarded as a

feeding structure of animals (Seilacher, 1955; Osgood, 1970) and not a dwelling burrow

of filter feeding annelids (Osgood, 1970).

Animal escape structure Form B

(Fig. 4.33 E)

Repository ref. NG/SK-13/33

Material: Two specimens preserved in fine grained sandstone.

Description: Vertically perpendicular to the bedding plane depicting “U”-shaped

morphology. The burrow structures are 3.8 cm in depth and 1.7 cm in width. There are 7

90  

to 8 concentric “U”-shaped lines in 1 cm. Both limbs of burrow are parallel. Distance

between the limbs at surface is less than 1 cm.

Discussion: The present structure is formed by hideaway activity of the animal during its

life span. The specimen resembles Diplocraterion Torell (1870); but a typical “U” shaped

burrow without any opening structure at the bedding plane, completely rules out the idea

of structure being Diplocraterion. Although the specimen is a “U” shaped burrow, it fails

to show openings at the surface of the bedding plane. It closely resembles the structure

known as animal escape structure reported by Hofmann et al. (2012).

Horizontal Burrow Form C

(Fig. 4.33 F)

Repository ref. NG/SK-13/34

Material: Three slabs with randomly oriented specimens preserved as positive relief in

fine-grained sandstone.

Description: Randomly arranged, horizontal to the bedding plane, varying in size. Length

3 to 4 cm, width up to 0.4 to 0.8 cm. These structures tapering at both ends.

Remarks: The present specimen closely resembles the burrow morphology shown by

Crimes and Harper (1970);( see page for fig. 29 b).

91  

Fig 4.33: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Treptichnus pedum; B) Monomorphichnus isp; C) Small knob like Burrow; D) Chondrites isp. E) Animal escape structure; F) Horizontal burrow.

92  

Needle-like burrow Form D (Fig. 4.34 A)

Repository ref. NG/SK-13/35

Material: The twenty six specimens preserved as hyporelief in fine grained sandstone.

Description: Small, needle-like, uniform, epichinial cast ranging from 0.3 mm to 1.0 cm

in length; 1 mm in width. These structures are randomly arranged.

Discussion: These structures show resemblance with forms reported as exichnial and

hypichnial cast of horizontal burrows by Crimes and Harper (1970); (see page 25 for

Plate I D). These needle-like burrows are very small in shape and size and indicate the

morphology of the animal as well. Present specimen is being reported for the first time

from the Nagaur Sandstone.

Tubular burrow Form E

(Fig. 4.34 B)

Repository ref. NG/SK-13/36

Material: A single slab containing around 60 forms are counted, preserved as positive

relief in fine grained sandstone on the sole of the bedding plane.

Description: Randomly distributed, medium to small worm-like burrow, length ranges

between 0.2 to 1.9 cm, while width varies from 1 to 3 mm; the specimens are 2 mm in

height. Both ends of the structure are curved and rounded. Out of sixty specimens, twenty

five forms are medium while the rest are small.

Discussion: Possibly, this structure could be a burrow formed by worm-like animals.

There are two sets of structures, one large and one small. Both forms are preserved in an

isolated patch. Another possibility is that this structure could be faecal remains of

existing animals as far as the morphology is concerned. However, the size and shape

completely rules out the idea of its being a fecal remain.

93  

Ichnogenus: Palaeophycus Hall, 1847

Palaeophycus tubularis Hall, 1847 (Figs. 4.34 C and D)

Repository ref. NG/SK-13/40

Material: One specimen in situ preserved as full relief on the bedding surface in fine-

grained sandstone.

Description: Horizontal to the bedding plane, cylindrical in outline, solid, infilled with

host rock. Straight to slightly curved, unbranched and smooth body wall. The dimensions

of the structure are 1.6 cm (longer axes) in diameter, 12.5 cm in length. Width varies

from one end to other end, maximum width recorded at the middle part (2.6 cm) and

tapering at posterior end.

Remarks: Morphologically, it resembles with the Palaeophycus Hall, 1847. The structure

is interpreted as the result of dwelling activity of the animal. The present form is quite

larger, bulbous in outline and different from the Palaeophycus Hall, 1847. It is also

similar with the form reported from the Tethys Himalaya by Parcha and Pandey (2011).

Small burrows reported from Tunkliyan

(Fig. 4.34 E)

Material: Six slabs of sandstone comprising twelve specimens preserved as hyporelief on

the sole of bedding plane.

Description: Small tubular burrow, horizontal to the bedding plane, spindle shaped,

smooth wall. Specimens randomly preserved. Burrow width maximum at the middle part

varying from less than 1to 2 mm; 0.4 to 1 cm in length.

Remarks: The present structure depicts the burrow morphology which is similar to forms

reported from the Nagaur Sandstone; however, the only difference is that these forms are

small and straight, whereas the burrow forms reported earlier from the Nagaur Sandstone

are slightly larger and curved in nature.

94  

Scratch marks from Tunkliyan (Fig. 4.34 F)

Repository ref. TNK/SK-12/16

Material: Four specimens collected from Tunkliyan preserved as positive hyporelief.

Description: Specimen shows a large numbers of scratch marks which are randomly

preserved. The width of the scratch mark is 0.4 to 0.7 cm, while individually it is up to 2

mm and length of scratch marks is 2.5 cm. The consecutive gap between the podial marks

is 1 mm.

Discussion: Morphologically, the specimens are close to scratch mark produced by

trilobite. The podial markings are in ascending order. The present specimen is similar to

the scratch marks reported from the Nagaur Group by Kumar and Pandey (2010). The

present specimen is being reported for the first time from the Tunkliyan Sandstone.

95  

Fig 4.34: Trace fossils reported from the Nagaur sandstone, Dulmera area, Rajasthan. A) Needle like burrow; B) Tubular burrow; C and D) Palaeophycus tubularis; E) Small burrows reported from Tunkliyan; F) Scratch marks reported from Tunkliyan.

 

 

96  

Biozonation and Correlation

In the Marwar Supergroup, the fossils are recorded from the Late Neoproterozoic

Jodhpur Sandstone to the Early Cambrian Nagaur Group. Though there are limited

parameters available for defining biozones, the fossil pattern obeys the chronological

order as the lower part of MSG (Marwar Supergroup) consists of fossils of the Ediacaran

age; followed by the middle part, i.e. the Bilara Group comprising stromatolites which

possibly characterized the Pc-C, and the upper part, i.e. the Nagaur Group having fossils

of Early Cambrian age.

5.1 Biozonation The Biozonation of the Marwar Supergroup has been proposed on the basis of the

available fossil records. In all, XIII biozones (fig 5.1) have been recognized in the

Marwar Supergroup on the basis of mega as well as microfossils. The biozones are

categorized under the following headings:

A. Body fossils

B. Organo-sedimentary structures

C. Trace fossils

D. Microfossils

A. BODY FOSSILS: This category includes the plant and animal body fossil

which further subdivides into five respective biozones namely Aspidella-Hiemalora zone,

Marsonia zone, Priapulid zone, Articulated Arthropod Tergites zone and Vendophycus

zone,

Aspidella-Hiemalora zone

This biozone includes the soft bodied ediacaran body fossils viz. Aspidella,

Hiemalora, etc. which have been reported from the Sursagar mine, Golasni mine of the

Jodhpur Group. Aspidella is a circular Ediacaran body fossil which is of worldwide

occurrence during the Ediacaran period and potentially represents a biozone. The other

Ediacaran fossil is a Cnidarian identified as Hiemalora with radiating arms/rays from the

97  

centre portion of the body. It is also reported from the Bhander Group of the Vindhyan

Supergroup, Flinders Ranges South Australia, Newfoundland Canada by Hofmann

(2008), etc.

Marsonia zone

This biozone is located near Artiya Kalan village in Jodhpur district, Rajasthan.

This zone is named after Marsonia artiyansis reported by Raghav et al. (2005) and later

restudied by Kumar and Ahmad (2012). Marsonia is the first known medusoid body

fossil reported from middle part of the Jodhpur Group. The fossil is circular to slightly

elliptical disc, preserved in shale. M. artiyansis comes under the class Scyphozoa. In this

class all the animals are marine, free swimming and have a well developed gastrovascular

cavity with large medusa. The medusoids known from different countries across the

globe including USSR, Canada, New Zealand and Australia (Sokolov and Ivonowski,

1985) represent the phylum Cnidaria. Thus, the Marsonia artiyansis unfolds the

evolutionary facts about the Ediacaran fossils.

Priapulid zone

This biozone includes Priapulid worm like fossil reported by Srivastava (2012b)

from the Nagaur Sandstone which is a body fossil and can constitute a biozone.

Articulated arthropod tergites zone

This biozone is located in the Nagaur Group. The body fossil is reported by Singh

et al. 2013. The fossil is not very convincing as a body fossil of trilobite. The authors

named as “articulated arthropod tergites or trilobite” similar to the fossils reported from

lesser Himalayan region of India. Except the present body fossil, no other body fossil has

been reported from this horizon; although, the horizon is rich in trace fossils.

Vendophycus zone

This biozone includes non-carbonaceous mega plant fossils. This zone exclusively

located in the Sursagar mine of Jodhpur district and stratigraphically comes under the

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Jodhpur Group. The plant fossils are preserved as mould and cast on the bedding surfaces

in a shallow marine setting. The plant fossils are divided into two genera and three

species viz., Vendophycus rajasthanensis, Vendophycus sursagarensis and Indophycus

marwarensis and are described with many morphological features comparable to the

extant Vaucheriaceae family with tube like nonseptate thallus, branching pattern,

presence of swellings at the ends of tubes and on the tubes and also within the tubes; but

the dimensions of the present forms are megascopic. The plants acquired megascopic size

because of competition with other plant communities, availability of space and nutrients

and stability of the habitat. These plants lost their existence in the Cambrian with the loss

of their habitat because of the appearance of the faunal life which bioturbated the

substrate and browsed upon the microbial mats as well as the mega plants. Hence, the

occurrence of this giant sized plant fossil has a great significance in the stratigraphy of

the Marwar Supergroup.

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Fig 5.1: The schematic diagram showing the different biozones present in the various stratigraphic horizons of Marwar Supergroup. The biozone are constructed on the basis of megafossils, microbial mat, trace fossils, stromatolites and microfossils.

B. ORGANO-SEDIMENTARY STRUCTURES: This category is divided into

the following subcategories such as Stromatolites, and Microbially Induced Sedimentary

Structure (MISS). The MISS is further subdivided into Arumberia zone and Ediacaran

Disc zone.

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Collenia-Conophyton zone

The biozone is the assemblage of Stromatolites located in the Bilara Group. The

Stromatolites are predominantly found in the Dhanapa Dolomite, Gotan Limestone and in

few parts of Pondlu Dolomite. The Stromatolites assemblage includes viz. Collenia

columnaris, Conophyton, Collenia pseudocolumnaris, Oncolites, etc. The Collenia

cololumnaris is a columnar form well exposed in the Dhanapa dolomite near Dhanapa

village. The Conophyton is exposed in the block section of Barna mine near Bilara

village. The Oncolites are exposed mainly in the Dhanapa Dolomite and dolomite in the

Moriya locality in Phalodi district. The assemblage is comparable with the stromatolites

of the Chambal valley section of the Vindhyan Supergroup.

Arumberia zone

This biozone is well exposed in the middle (Sursagar mine) and upper parts

(Khatu area) of the Jodhpur Sandstone. It includes different kinds of microbial mats. The

microbial mats include Arumberia banski, Rameshia rampurensis and Aristophycus

exposed in the Khatu section of the Jodhpur Group. Aristophycus is a branching structure

well developed in the Khatu area in the northern side of the main hillock at western side

of the Khatu Township. Seilacher (2007) considers its genesis as due to dewatering. The

middle part of the Jodhpur Sandstone exposed in the Sursagar area, exhibits 12 different

types of microbial mats with 2 poorly preserved structures. Out of these Arumberia

banski and Aristophycus are exposed in the Khatu section. There are three new forms viz.

Rameshia linearis, Rameshia anastamose and Jodhpuria circularis exposed in the fine

grained Jodhpur sandstone. The microbial mats are of value in the intrabasinal and

interbasinal correlations when age marker fossils are absent. The microbial mat provides

base for the preservation of different types of body fossils and other biological signatures.

Without microbial mat, the preservation of soft bodied Ediacaran fossils is not possible in

quartz arenite facies of MSG. These microbial mats are the main source of food for the

metazoans and the animals that may have existed during the Ediacaran period.

Ediacaran Disc zone

This biozone is located in the Sursagar mine of Jodhpur district, which is the

middle part of the Jodhpur sandstone. They are restricted to the Jodhpur Group only as

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they are absent in the Bilara and Nagaur Group. Their size ranges up to a few mm to 75

cm (Srivastava, 2013). Their genesis is under debate. According to Srivastava (2013), it

is a disc of Ediacaran age as its name reveals. These discs are thought to have Cnidarians

affinity in terms of origin. These discoidal discs are similar to the Ediacaran body fossil

Aspidella but they (Ediacaran disc) are bigger in shape and size. The other feature that

differentiates the Ediacaran disc from Aspidella is that in case of Aspidella, there is a

prominent outer rim and elevated inner disc which differs from the Ediacaran disc.

Therefore, it seems reasonable to put this type of structure in separate biozone.

C. TRACE FOSSILS The trace fossils are sub-categorized as trace which further

divided into 3 biozones which are as follows:

Cruziana-Rusophycus zone

It is categorized as a biozone, which includes traces of arthropods, exclusively the

trilobite. The zone falls under the Nagaur Group and it is exposed in the Dulmera village

which is about 65 km from Bikaner district on Bikaner-Sri Ganganagar Highway. In 18

m thick sequence of maroon colour sandstone, shale and siltstone, there are number of

traces of Rusophycus carbonarious, Rusophycus didymus, Cruziana fasiculata, Cruziana

solomonis, Isopodichnus isp and Tasmanadia cachii. This zone is helpful in demarcating

the age of the Nagaur Group as the Lower Cambrian (upper part of Marwar Supergroup).

The general behavioural trend of the trace fossils are shown in the table 5.1. It is based on

the work of Kumar and Pandey (2009) and present findings.

Treptichnus zone

This biozone also exists in the Nagaur Group. It is an important biozone as it

defines the Pc-C boundary in the Marwar Supergroup. The T. pedum is an index fossil of

Lower Cambrian. The lithology is the fine grained sandstone. The dimension of

Treptichnus pedum is 0.5 to 2 cm long and width up to 4 mm with 3 mm in height. The

complete stretch of structure is 13 cm. In the same quarry there is another fossil named

as Priapulid which is a segmented worm. The priapulid-like worm is responsible for

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creating the Treptichnus pedum burrows (Srivastava, 2012a). The present biozone

includes the work of Srivastava, (2012a) and present work.

Trail and burrows

The biozone represents the biogenic activity during the course of the life cycle.

This zone includes the scratch marks, tracks and trail marks, animal escape structure and

well preserved burrows of different dimensions. The scratch marks are possibly produced

by Monomorphicnus linearus which indicates the movement activity of the animal. The

tracks and trail marks are produced by the Diplichnites aenigma, Dimorphichnus

obliquus, Chondrites isp and other arthropods. The animal escape structure is unique

feature as it shows similarity with the “U” shaped burrow. Another important content of

this zone is the burrows. The Bergaueria perata, Palnolites vulgaris, Palaeophycus

tubularis, Merostomichnites isp, Monocraterion isp and some unknown burrows which

are not related with the known burrow forming genera, are named as Form “A”, Form

“B”, Form “C”, Form “D” and Form “E”.

Table 5.1: Behavioural pattern of the Ichnofossil from Nagaur Group

S. No. Ichnogenera Behavioural activity

1 Rusophycus Carbonarious Cubichnia (Resting trace of trilobites)

2 Rusophycus didymus Cubichnia (Resting trace of trilobites)

3 Merostomichnites isp. Cubichnia (Resting trace of trilobites)

4 Tasmanadia cachii Cubichnia (Resting trace of trilobites)

5 Cruziana fasiculata Repichnia (Crawling trace)

6 Cruziana solomonis Repichnia (Crawling trace)

7 Diplichnites aenigma Repichnia (Crawling trace)

8 Isopodichnus isp. Walking trace of trilobites

9 Planolites vulgaris Fodinichnia (Feeding structure)

10 Treptichnus pedum Fodinichnia (Feeding structure)

11 Chondrites isp Fodinichnia (Feeding structure)

12 Planolites annularis Fodinichnia (Feeding structure)

13 Burrows Fodinichnia (Feeding structure)

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14 Bergaueria perata Domichnia (Dwelling Structure)

15 Monocraterion isp. Domichnia (Dwelling Structure)

16 Palaeophycus tubularis Domichnia (Dwelling Structure)

17 Dimorphicnus obliquus Pascichnia (Grazing Trace)

18 Monomorphicnus isp. Pascichnia (Grazing Trace)

19 Scratch marks Pascichnia (Grazing Trace)

The Tunkliyan Sandstone, stratigraphically, the topmost part of the Marwar

Supergroup has also yielded some poorly preserved scratch marks and small burrows.

Before the present study, the particular horizon was untouched and no fossils have been

reported from it.

D. MICROFOSSILS: This category includes the two biozone i.e. Obruchevella zone

and Acritarch zone.

Obruchevella zone

This biozone is recorded with in the Gotan Limestone is based on the thin section

study of black chert lenses by Babu et al. (2009). This microfossil zone includes the

assemblage of various microfossils viz. Obruchevella valdaica Yankauskas et al.;

Polythrichoides lineatus Hermann, Siphonophycus septatum Schopf; Leiosphaeridia

jacutica (Timofeev) Yankauskas et al.; Octosphaeridium truncatum Rudavaskaja;

Echinosphaeridium maximum Yin; Gloeocapsamorpha karauliensis Maithy and Mandal;

Stictosphaeridium, sinapticuliferum Timofeev; Trachysphaeridium laminaritum

(Timofeev) Vidal; Synsphaeridium sorediforme, (Timofeev) Eisenack and

Cymatiosphaera wenlokia Downie.

Acritarch zone

This biozone is reported from the different horizons of the Marwar Supergroup. It

is based on subsurface samples and the fossils are recovered through standard

palynological technique by Prasad et al. (2010). The assemblage includes

Lophosphaeridium spp, along with various species of Leiosphaeridia, suggesting Late

Ediacaran age. Occurrence of small micrhystrids (Asteridium spp.) and appearance of

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Dictyotidium birvetense, Pterospermella solida and Annulum squamaceum in the lower

part of the Bilara Group, suggests Latest Ediacaran to Early Cambrian age. The recorded

acritarch assemblages suggest demarcation of Precambrian-Cambrian boundary within

the lower part of Bilara Group, Marwar Supergroup. The succeeding Upper Carbonate

Sequence of Bilara Group (727-481m) shows abundant Cristallinium randomense,

Cymatiosphaera crameri and Asteridium spp., along with other species of

Cymatiosphaera and Cristallinium, and also includes the Late Cambrian marker forms,

such as Striatotheca loculifera and Dorsenidium (Veryhachium) minutum, suggest Middle

Cambrian to Late Cambrian age. This assemblage also makes a potential biozone in the

Marwar Supergroup. This biozone not only emphasizes the age but has also helped to

understand the palaeoenvironment of the Marwar Supergroup based micropalaeontology.

The age implication based on acritarchs gives somewhat younger age in comparison to

the age inferred on the basis of trace fossils.

5.1.4 Discussions The different assemblages from the Jodhpur Group, Bilara Group and Nagaur Group are

shown in fig 5.4 and categorized under the body fossil, organosedimentary structures,

trace fossils and microfossils. The Aspidella-Hiemalora biozone is a well known

Ichnofossil reported from the Ediacaran period with worldwide occurrences such as

Ediacara Hills (South Australia), Ukraine, Mistaken Point in Newfoundland etc. On the

basis of this zone, the oldest unit i.e. the Jodhpur Group is assigned the Ediacaran age.

Another important biozone is Marsonia artiyansis, a typical medusoid form. The

medusoid forms are global in occurrence during the Ediacaran period. The “Articulated

Arthropod Tergites” zone which is supposed to be a body fossil of trilobite. Opens an

opportunity for searching a more relevant body fossil in the Nagaur Sandstone where

only trace fossils are in abundance. The Vendophycus biozone includes two genera and

three species viz. Vendophycus rajasthanensis, Vendophycus sursagarensis and

Indophycus marwarensis, which are preserved as mould and cast on the bedding surfaces

in a shallow marine setting. The basic concept behind this zone is that they exist in the

Ediacaran period and become extinct near the Cambrian with the loss of their habitat

105  

because of the appearance of the animal life which bioturbated the substrate and browsed

upon microbial mats as well as the mega plants.

The stromatolite assemblage consists of Colleniella Korolyuk (1960), Collenia

Pseudocolumnaris Maslov (1960), Oncolites Pia, (1927). The stromatolites present in the

Marwar basin completely lack the typical Riphean and Vendian forms (Priess, 1976) such

as Baicalia, Kussiella which are confined to eastern side of Aravalli range. The form

genus Colleniella would point to terminal Riphean-Cambrian age (Semikhatov, 1976).

Arumberia zone is very important component in the present study as it has relevance in

terms of time framed occurrences in the Latest Neoproterozoic Era. Ediacaran Disc zone

is well marked in the Jodhpur Sandstone.

The Cruziana-Rusophycus biozone is important because on the basis of this zone

the age of Nagaur Group is bracketed as the Lower Cambrian. Treptichnus pedum is

crucial in delineating the Ediacaran-Cambrian boundary. The Treptichnus pedum is

essential to evaluate the reliability of the Ediacaran-Cambrian (Buatois et al., 2013). The

next important biozone is based on the microfossil Obruchevella zone, which is assigned

the Vendian age. The Acritarchs (Prasad et al., 2010) is also used in establishing the

biozone in the Marwar Supergroup. The geographical distribution of biozones in the

Marwar Supergroup is shown in the figure 5.2.

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Fig 5.2: Map shows the geographical distribution of Biozones based on the palaeontological remains of the Marwar Supergroup. 5.2 Correlation

Regional Correlation The Marwar Supergroup was traditionally considered to be a westward extension

of the upper part of the adjacent Vindhyan sedimentary basin (Heron, 1932; Pandey and

Bahadur, 2009). It was originally referred to as the ‘Trans-Aravalli Vindhyans’. In the

absence of radiometric dates in the Marwar Supergroup, the interbasinal correlation is

possible only with help of biogenic signatures and megafossils. The dating has been done

only in the part of the Bilara Group with the help of Rb/Sr dating (Mazumdar et al.,

2004) and δ13C studies (Pandit et al., 2001) and recently in the Nagaur Sandstone of the

Nagaur Group by McKenzie et al., 2011 (540Ma DZ; LAICPMS). The Marwar

107  

Supergroup has a vast range of fossil assemblages varying from the soft-bodied to the

invertebrate fossils. In this group, the interbasinal correlation is attempted with following

parameters such as microbial mats, stromatolites, body fossils, etc. Here the lower part of

Marwar Supergroup i.e. Jodhpur Group is correlated with the Bhander Group which is

the upper part of the Vindhyan Supergroup (Fig. 5.3). The Jodhpur Group has been

assigned an Ediacaran age on the basis of the presence of Arumberia, Aristophycus,

Rameshia rampurensis, Rameshia linearis, Beltanelliformis, Marsonia artiyansis,

Aspidella and cf. Hiemelora. It unconformably overlies the Malani Igneous suite which

has been dated as 779 ± 5 Ma by U-Pb method (Gregory et al., 2009). The stromatolites

reported in the Marwar Supergroup are different from the assemblages of the Vindhyan

Supergroup at generic level. The Nagaur Sandstone has yielded trilobite trace fossils and

has been assigned the Lower Cambrian age, hence the Bilara Group possibly straddles the

Precambrian-Cambrian boundary. But it is inferred after the discovery of Treptichnus

pedum (Srivastava et al., 2012a) from the Nagaur Group that the possibilities of the

presence of Pc-C boundary below the Nagaur Group or within the Nagaur cannot be ruled

out. Since, no Cambrian fossils are present in the Vindhyan Basin, the youngest horizon

of the Vindhyan Basin, the Maihar Sandstone, which is Ediacaran in age, can be

correlated with the Jodhpur Sandstone of the Marwar Supergroup.

Intercontinental Correlation

The Marwar Basin is located in proximity to basins in Oman, Pakistan, Madagascar

and northern India (Krol-Tal region). Many of these sedimentary sequences show

remarkable similarities and there exist possible correlations between these basins. The

Marwar Supergroup has also been correlated with the other parts of the world such as the

Salt Range, Pakistan, Krol-Tal of Lesser Himalaya, Huqf Supergroup of Oman. The

correlation is based on U-Pb dating and hence, it is concluded that the Marwar

Supergroup developed near the close of the Ediacaran Period and is a part of a larger

group of sedimentary basins which includes the Huqf Supergroup (Oman), the Salt Range

(Pakistan), the Krol-Tal belt (Himalayas) and perhaps the Molo Supergroup

(Madagascar) (Davis et al., 2013). Many of these sedimentary sequences show

108  

remarkable similarities and are here attempted to show possible correlations between

these basins (Fig 5.4).

Fig. 5.3: Schematic diagram showing the correlation between the Bhander section of the Vindhyan Basin and Jodhpur section of Marwar Basin. (after Kumar, 2012).

109  

 

 

 

Fig.

5.4

: C

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and

prop

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cor

rela

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bet

wee

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e M

arw

ar S

uper

grou

p, t

he S

alt

Ran

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he K

rol-T

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imal

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the

Huq

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oup

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, 201

3). 

110  

Conclusions

Based on the available information and present study, the following conclusions have been

drawn and summarized:

1. Marsonia artiyansis, a medusoid by Raghav et al. (2005) reported from the Jodhpur

Sandstone of Ediacaran age has been restudied for its taxonomic affinity. The

conclusions drawn by Raghav et al. (2005) concerning its affinity with a medusoid of

Class Scyphozoa can be accepted on the basis of morphology. It is characterized by a

circular disc-shaped structure with smooth to wrinkled margin and mode of preservation

in a very shallow water lagoonal setting. The animal must have been a planktic soft

body. The major variations in morphology possibly appear to be due to taphonomy and

load-effect of the overlying sediments.

2. The burrows and trail marks in the lower part of the Jodhpur Sandstone from the Artiya

Kalan locality suggest presence of benthic community during deposition of the Jodhpur

Sandstone.

3. One of the important findings of the present study is the record of MISS (Microbially

Induced Sedimentary Structures) in the Jodhpur Sandstone, where there is a complete

range of such structures (MISS) from two poorly defined morphologies to twelve well-

defined structures. The dominance of microbial structures with varied morphologies in

the Jodhpur Sandstone is its unique feature which requires explanation. Near absence of

animal life allowed the microbial community to flourish in a shallow marine setting with

abundance of sunlight and nutrients. The quartz-dominated sand and moderate to high

energy environment allowed growth of the microbial community due to removal of mud

which made the water less turbid. Quartz sand allowed the light to penetrate deeper in

the sediment at sediment-water interface which helped the microbial community to grow

to greater depths, and also to produce varied morphologies on the bedding surfaces. In

the present study, of the reported fourteen microbial mat structures some appear to have

been restricted within a specific time period near the Precambrian-Cambrian boundary

111  

(i.e. the Ediacaran Period). It appears that the different mat morphologies were shaped

by a combination of the microbial community, physical parameters, mineralogy and

textural composition of the sediments. If the physical parameters and the mineralogy of

the sediments of the different stratigraphic horizons are compared, the morphological

variation in the microbial mats can be attributed to the differences in the composition of

the microbial community. Thus, the morphological variations in the microbial mats in a

similar environment may represent the dominance of differing microbial community.

Hence, such morphologies can be identified by their specific characters. The microbial

mats may often leave a proxy record of the microbial community bearing specific

morphologies produced in the sandstones. These are Arumberia banksi, Rameshia

rampurensis and Jodhpuria circularis which have not been reported from the modern

sediments. The origin of Aristophycus is also linked to mats. Its origin is explained by

Seilacher (2007) who suggested that the plant like appearance is linked to water escape

under a strong microbial mat. The water jet could not break the mat but eroded the

underside of the mat which might have later been filled with the sand.

4. The Ediacaran Jodhpur Sandstone shows profuse development of noncarbonaceous

megaplant fossils which are preserved as mould and cast on the bedding surfaces in a

shallow marine environment. The plant fossils have been studied for their taxonomic

assignment and genesis. Two genera and three species viz., Vendophycus rajasthanensis,

Vendophycus sursagarensis and Indophycus marwarensis are described whose

morphological features are compared to the extant Vaucheriaceae family characterized

by tube-like nonseptate thallus, branching pattern, presence of swellings at end of tubes

and on the tubes and also within the tubes but the dimensions of the present forms are

megascopic. The plants acquired megascopic size because of competition with other

plant communities, availability of space and nutrients and stability of the habitat. These

plants lost their existence in the Cambrian when their habitats disappeared with the

appearance of the animals, which bioturbated the substrate and browsed upon the

microbial mats and the mega plants.

112  

5. The presence of stromatolites is noted in the Bilara Group. In the present study,

Colonnella columnaris, Coniform stromatolites, domal stromatolites, stratified forms;

pseudocolumnar forms and a new form simply referred to as Form A have been

reported. The assemblage differs from the stromatolite assemblage of the Bhander

Group of the Vindhyan Basin. No age can be assigned to the stromatolite assemblage.

6. The Marwar Supergroup has yielded twenty five ichnogenera. These are Rusophycus

carbonarious, Cruziana fasiculata, Cruziana solomonis, Isopodichnus isp, Tasmanadia

cachii, Diplichnites aenigma, Bergaueria perata, Monomorphicnus isp, Monocraterion

isp, Planolites vulgaris, Planolites annularis, Merostomichnites isp, Treptichnus pedum,

Dimorphicnus obliquus, Palaeophycus tubularis, Chondrites isp, scratch marks, burrow

forms from the Nagaur Group. These trace fossils in the MSG (Marwar Supergroup)

provide a robust database to throw light on the evolving life in the Precambrian-

Cambrian (Pc-C) time span in the global level.

7. The biogenic proxies in the present study help to establish the detailed biozones in the

studied successions of the study area as well as the entire basin (Marwar Supergroup).

These provide diagnostic age brackets for the Ediacaran to Early Cambrian successions.

The age assignment helps to establish inter-and intra-basinal correlation. The animal

body fossils include the Aspidella, Hiemalora, Marsonia, etc which are helpful in age

determination and in suggesting the age of the Jodhpur Group as the Ediacaran.

8. The evidence of multicellular animal origin on the basis of the five-armed body fossil

can simply be considered to represent a pre-biomineralization stage in the evolution of

echinoiderms during the Ediacaran Period. Along with the participation of biological

systems in the environment of deposition, the sedimentological role was equally

significant in shaping the basinal morphology and for better understanding of the

palaeogeographic evolution and stratigraphic sections in both the Marwar Supergroup

and the Bhander Group (Vindhyan Supergroup). An attempt has been made in respect of

biogenic correlation. The Jodhpur Group of the Marwar Supergroup have been assigned

113  

Ediacaran age on the basis of the presence of Arumberia, Ediacaran body fossils

Marsonia, Aspidella and cf. Hiemalora. The correlation of the lithounits of the Marwar

Supergroup has also been established with the sequences from the other parts of the

world, such as the Salt Range (Pakistan), Krol-Tal of the Lesser Himalaya, Huqf

Supergroup of Oman, this correlation also supports the present findings.

9. The present work has identified 13 biozones in the Marwar Supergroup based on the

biological records. These are categorized under the body fossils, organosedimentary

structures, trace fossils and microfossils. The first category (i.e. body fossil) has been

further subdivided into five biozones. The first biozone is Aspidella-Hiemalora zone

from the study area of the Jodhpur Sandstone which is of global significance in the

Ediacaran period. This biozone is also important as it suggests a definite Ediacaran age

to the oldest group (Jodhpur Group). The second biozone is also from the same group

and it carries the name as Marsonia zone. This biozone is named after the medusoid

fossil called Marsonia artiyansis. The medusoids have worldwide distribution and

provide strong data-base in exploring the evolutionary trends of the Ediacaran life.

Hence, this biozone also supports the Ediacaran age to the Jodhpur Group. The third

biozone is referred to as Priapulid worm biozone. This work is supposed to build the

Treptichnus pedum burrows and is from the Nagaur Group. The fourth biozone is the

body fossil from the Nagaur Group which is suggested by Nigel Hughes to be

“Articulated arthropod tergites”. Therefore, this biozone justifies the age of the Nagaur

Group as Early Cambrian. The fifth biozone represents non-carbonaceous plant

megafossils preserved in the middle part of Jodhpur Sandstone. These plant fossils are

megascopic up to metric level and are interrelated with the modern-day Vaucherian

algae in morphology and its fertile structures and bear much similarity.

10. The next category of biozones is the organo-sedimentary structures which comprise

stromatolites and microbially induced sedimentary structures. In this category, the sixth

biozone is based on stromatolites from the Bilara Group. The important stromatolites are

Colonnella coloumnaris, Conophyton and pseudocolumnar forms including one new

unknown form. This assemblage differs from the stromatolites of the Bhander Group.

114  

Hence, they are not comparable. No definite age can be given to the stromatolite

assemblage.

11. The next subcategory is made up of MISS (Microbially induced sedimentary structures)

which is further sub-classed into two biozones. The seventh biozone is named as

Arumberia zone which belongs to the Jodhpur Group. Arumberia is a typical Ediacaran

microbial mat and its presence indicates the Ediacaran age. In the same manner, the

eighth biozone includes the Ediacaran discs abundantly reported from the Jodhpur

Sandstone and hence it has also been assigned the status of a biozone.

12. The next category for biozonation includes the trace fossils and constitutes ninth, tenth

and eleventh biozones respectively. The ninth biozone includes trace fossils belonging to

the trilobites from the Nagaur Group. This biozone has been assigned the Early

Cambrian age for the Nagaur Group. The tenth biozone described as Treptichnus zone is

the index fossil of the Lower Cambrian age. The demarcation of Pc-C boundary has

been suggested on the basis of Treptichnus pedum. The eleventh biozone has been

established on behalf of the behavioural activity of the arthropods indicating the mode of

life during early phase of evolution.

 

 

 

 

 

 

 

 

 

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References

Babu, R., Singh, V.K., Shukla, M., 2009. Cryptic biocriteria with their significance from

the Gotan Formation of Bilara Group, Marwar Supergroup, Rajasthan. Current

Science 96 (12), 1575-1577.

Banerjee, S., Sarkar, S., Eriksson, P.G., Samanta, P., 2010. Microbially related structures

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