8/16/2019 Indai_cretaceous Phosphorite Facies of the Barmer Basin

1/2

 Joint Workshop on Rapid Environmental/Climate Change

in the Cretaceous Greenhouse World: Ocean-Land Interaction

& Deep Terrestrial Scientific Drilling Project of the Cretaceous Songliao Basin

 August 28-30, 2007, Daqing, China

- 44 -

 

[23]

CRETACEOUS PHOSPHORITE FACIES OF THE BARMER BASIN,WESTERN RAJASTHAN, INDIA : SIGNIFICANCE OF ITS FAUNA

AND MAGNETIC OBJECTS

S. C. Mathur, R. S. Loyal*, S. D. Gour, Shankar Lal and Akashdeep

Department of Geology, Jai Narain Vyas University, Jodhpur 342005, India

* Center of Advanced Study in Geology, Panjab University, Chandigarh, India

The phosphorite facies belonging to the Fatehgarh Formation, exposed in the riftedgraben referred to as Barmer Basin of western Rajasthan, India. Microfacies analysis of the

 phosphorite facies indicate four major types viz: phosphatic sandstone, bone bed, bedded

 phosphorite and gastropod bed. Among these microfacies, the bone bed contains significant

framework elements such as rich assemblage of microvertebrate and vertebrate fauna along

with unusual magnetic objects.

The microvertebrate comprises well-preserved isolate bone, teeth, spines, vertebrae, and

skeletal material. The assemblage represented of cf. Igdabatis sp., Semionotiformes indet.,

Lepisosteus indicus., Enchodontidae indet., Albuloidei indet., and Stephanodus sp. Beside,

fragmentary pictoral and dorsal spines of Siluriformes indet. are also present ( Mathur et al.,

2006).The vertebrate comprises an isolated fragmentary dinosaurian reptilian femur, a small

crocodilian cranium with isolated teeth and vertebrae and well-preserved turtle scute. A

large number of dinosaurian and crocodilian coprolite and dung also form a major portion of

recovered fossils. A Late Cretaceous (Maastrichian) age is suggested from the close faunistic

affinities of Fatehgarh fauna with those from Lameta and intertrapian sequences of India.

As such the phosphorite of the Barmer Basin represents a global Late Cretaceous phospho-

genic event in the northwestern part of the India.

The bone bed also contains some unusual and significant magnetic objects viz: mag-

netic spherules, fine magnetic particles and microbracciated matrix (Mathur et al., 2005a;

Mathur 2005b). To understand the nature of host rock and magnetic objects we used dif-

ferent tools such as conventional petrography, SEM, EDAX, ICPMS, and INAA, Mossbaure

spectroscopy, X ray florescence and XRD. The results reveal that the phosphorite facies

represent anomalies, biostratigraphically, mineralogically and geochemically. The results

also indicate that the Magnetic objects represent a high temperature event either of volcanic

or impact nature (c.f. Cisowski, 1988; O’Keefe and Ahrens, 1989; Bohor and Glass, 1995

and Alvarez, et al., 1980). These high temperature objects along with rich biota occur in a

very thin, disrupted, desiccated and discontinuous layer in the top part of the bone bed indi-

cate some cause and effect relationship that brought significant biological changes perhaps

mortality enmasse of the Fatehgarh biota.

8/16/2019 Indai_cretaceous Phosphorite Facies of the Barmer Basin

2/2

 Joint Workshop on Rapid Environmental/Climate Change

in the Cretaceous Greenhouse World: Ocean-Land Interaction

& Deep Terrestrial Scientific Drilling Project of the Cretaceous Songliao Basin

 August 28-30, 2007, Daqing, China

- 45 -

 

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