221

PERMIAN LIMESTONES OF SURAT THANI PROVINCE, PENINSULAR THAILAND

Fontaine Henri, Hoang Thi Than, Sirot Salyapongse, Varavudh Suteethorn and Daniel Vachard

ABSTRACT

Limestone is widespread in Surat Thani Province. It is locally exposed at ground surface but, more widely, it builds up small to large hills with a spectacular karst topography. Because of its large distribution, it appears interesting from economical points of view. In order to assess its resources, it has been recently studied in the field and laboratories (Harrison et al., 1997; Chaodumrong et al., 1998; Dill et al., 2004). In the past, the stratigraphy of the Surat Thani Province was commonly based on the limestone appearance after observing its colour, the thickness of the beds, the presence of chert nodule or of the elephant skin texture characteristic of the occurrence of dolomite. Fossils were only occasionally mentioned. In fact, they are not in abundance at many places. In addition to that, they are not diverse and locally they have been destroyed by strong dolomitization or recrystallization. However, the samples which have been recently collected from an important number of Permian limestone exposures (samples T7306 to T7485) contain fossils which indicate rather precise ages at some localities and bring also important information on paleogeography. In the following text, other localities are not mentioned because no fossil was found due to dolomitization or recrystallization. Key words: fossil, limestone, southern Thailand PERMIAN FOSSILS A few previous studies have reported Permian fossils in Surat Thani Province. In 1993 in Donsak District, on land and on two islands (Ko Nai Pud and Ko Woa Lap), Ingavat-Helmcke found algae, calcispheres, smaller foraminifers (Sphairionia, Dagmarita, Rectostipulina, Langella and others), Fusulinidae (Minojapanella, Ozawainella, Pseudodoliolina, Chusenella) and corals (Tabulata). A Middle Permian age was suggested. In 1994, Sphairionia and Neomisellina were mentioned at another island, Ko Pha Luai (Fontaine et al., 1994). In 2004, Dill et al. mentioned Hemigordiopsis and Dagmarita in the widespread Um Luk Formation without giving names of precise localities. They gave also lists of Carboniferous and Permian fossils which will be discussed in the following lines.

LOCALITIES WITH HEMIGORDIOPSIS AND/OR SPHAIRIONIA According to our own research, the youngest well-dated Permian limestones of Surat Thani Province contain Hemigordiopsis and Sphairionia. They belong to the Midian, maybe down to a part of the Murgabian. They are exposed in Kanchanadit area and in Donsak area. They are similar to Khao Yoi, a hill south of Ratburi where Hemigordiopsis, Dagmarita and Sphairionia are an important part of the fossil fauna (Fontaine et al., 1998), and to other localities of southern Thailand (Fontaine et al., 1994). The stratigraphic significance of Hemigordiopsis has been discussed by Nestell and

Pronina (1997) while that of Sphairionia has been discussed by Pronina (1996). In Kanchanadit area east of Surat Thani, limestone hills are scattered; they are assigned to the Um Luk Formation (Chaodumrong et al., 1998). Two hills have yielded interesting material: 1 - At Khao Khuha (9°09’09”N, 99°28’26”E; samples T7464 to T7468; pl. I, figs. 1 to 4), a small hill with a cave and a Buddhist Temple, 16 km east of Surat Thani in Kanchanadit area, a grey thickly bedded to massive limestone contains abundant and quite diverse fossils. It is rich in Hemigordiopsis renzi Reichel 1945, associated with calcispheres (Eotuberitina), smaller foraminifers (Sphairionia sikuoides Nguyen 1987, Climacammina, Geinitzina, Endothyra, Pachyphloia, Globivalvulina and Agathammina), rare poorly preserved Fusulinidae, very rare solitary corals, fragments of brachiopods (shells and spines), a few gastropods and crinoids. Sphairionia is rare at Khao Khuha. 2 – At a hill without name (9°08’07”N, 99°28’01”E; samples T7469 to T7471), 2 km south of Khao Khuha, a grey thickly bedded to massive limestone is micstone to wackestone. It contains calcispheres, smaller foraminifers (Sphairionia sikuoides Nguyen, Climacammina, Globivalvulina, Pachyphloia, Eolasiodiscus), rare fusulinidae and rare fragments of solitary Rugosa (Pavastehphyllum). In Donsak area east-northeast of Surat Thani, Sphairionia has been found at localities on land and in the sea. Donsak is 59 km far from Surat Thani town. 1 – At a small hill southeast of Donsak (9°17’18”N, 99°44’07”E; samples T7352 to T7356; pl. I, fig. 6; pl. III, fig. 3), a thickly bedded limestone is wackestone to

GEOTHAI’07 International Conference on Geology of Thailand: Towards Sustainable Development and Sufficiency Economy

222

packstone. It contains poorly preserved algae (Ungdarella), calcispheres (Eotuberitina), smaller foraminifers (Sphairionia sikuoides, Climacammina), scattered Fusulinidae (Parafusulina), common fragments of bryozoans (Fenestellidae), a few brachiopods and rare crinoids.

2 – At Khao Ok, an elongated limestone hill south-southeast of Laem Kula (laem = cape) and 55 km east-northeast of Surat Thani, samples have been collected from two localities of the western side of the hill. The limestone is grey and contains rare chert nodules. Fusulinidae are locally in abundance.

PLATE I Fossil location at Khao Khuha. Figure 1– Hemigordiopsis renzi Reichel, associated with Agathammina, Pachyphloia, Climacammina, Globivalvulina. Sample T7464. Figure 2 – Hemigordiopsis renzi Reichel. Sample T7468. Figures 3 and 4 – Hemigordiopsis renzi Reichel. Sample T7465. Fossil at second locality Khao Ok. Figures 5, 7 and 8 – Sphairionia sikuoides Nguyen. Sample T7318. Fossil location at small hill southeast of Donsak. Figure 6 – Sphairionia sikuoides Nguyen. Sample

T7353. Fossil at first locality, Khao Kho Kwang. Figure 9 – Sphairionia sikuoides Nguyen. Sample T7321.

223

At the first locality (9°17’55”N, 99°44’55”E; samples T7313 to T7315; pl. II, figs. 1 to 5), limestone is wackestone to packstone. It contains Tubiphytes, smaller foraminifers (Geinitzina, Climacammina, Globivalvulina, Pachyphloia, rare Sphairionia and very rare Hemigordiopsis), Fusulinidae, a few fragments of Fenestellidae and rare crinoids. Fusulinidae are locally in abundance and mainly belong to Parafusulina and to at least two species of this genus (see plate II). At the second locality (9°18’03”N, 99°44’54”E; samples T7316 to T7320; pl. I, figs. 5, 7 and 8; pl. II, figs. 6 to 8), limestone is similar to that of the first locality. It contains algae (Ungdarella), Tubiphytes, smaller foraminifers (Climacammina, Geinitzina, Pachyphloia, Tetrataxis, Sphairionia common in sample T7318), Fusulinidae, bryozoans (Fistulipora in abundance in sample T7320) and rare solitary corals. Fusulinidae are again locally in abundance and belong to Parafusulina cf. crassispira Leven and to Pseudodoliolina ozawai Yabe 1932. At a small hill at Laem Kula near the ferry pier (9°19’19”N, 99°44’42”; samples T7306 and T7307), a black bedded limestone is very poor in fossils. The beds are 10 to 50 cm thick and dips 30° towards west. South of Laem Kula, a black bedded limestone (samples T7308 and T7309), is underlain by black shale and minor sandstone; it contains a few fossils (bryozoans, brachiopods, gastropods). At Khao Noi (9°18’07”N, 99°44’31”E; samples T7310 and T7311), a small hill south of Laem Kula and west of Khao Ok, limestone is locally dolomitized. 3 – At Khao Kho Kwang, a hill 2 km southeast of Khao Ok, limestone is dark grey; samples have been collected from two localities of the western side of the hill. At the first locality (9°17’15”N, 99°45’37”E; samples T7321 to T7325; pl. I, fig. 9; pl. III, figs. 1, 5 to 7), the limestone contains small fragments of algae, Tubiphytes, smaller foraminifers (Pachyphloia, Climacammina, Geinitzina, Globivalvulina, Sphairionia common in sample T7321), Fusulinidae (Yangchienia iniqua Lee 1933 in sample T7323), solitary corals (Lophophyllidium 6 mm in diameter, Pavastehphyllum 12 mm in diameter), a poorly preserved massive Rugosa (sample T7325), bryozoans and crinoids. At the second locality (9°16’54”N, 99°45’57”E; samples T7326 to T7331), limestone is bedded, dark grey to black. Beds are 20 to 60 cm thick; they dip towards west. Fossils are few and of a low diversity. They consist of a few solitary corals (Lophophyllidium, Paracaninia), Fenestellidae, fragments of brachiopods and crinoids. The two localities of Khao Kho Kwang maybe do not belong to the same stratigraphic horizon. Few fossils have been obtained from the second locality. LIMESTONE EXPOSURES CONTAINING FUSULINIDAE AND CORALS Some limestones of the Surat Thani Province are grey, thickly bedded to massive, not very different from the limestones containing Hemigordiopsis and Sphairionia. They are locally rich in Fusulinidae and contain a few

corals (Tabulata, solitary, fasciculate and massive Rugosa). However, these fossils are of a low diversity and they are commonly in a poor state of preservation. At Khao Singkhon (9°14’49”N, 99°41’09”E; samples T7348 to T7351), a small hill with a cave and a Buddhist Temple, grey thickly bedded to massive limestone contains calcareous sponges, rare solitary corals, brachiopods, gastropods and crinoids. A fasciculate coral has been collected (sample T7349), but it is almost completely destroyed by recrystallization. At other hills near Khao Singkhon: a small hill without name (9°11’57”N, 99°40’31”E; samples T7341 and T7342), Khao Chong Khok (9°11’47”N, 99°39’51”E; sample T7343) and Khao Wat (9°12’08”N, 99°39’55”E; samples T7344 to T7347), limestone is recrystallized at different degrees; only crinoids have been noticed. At the southern part of Khao Nom Tro (9°01’32”N, 99°34’29”E; samples T7417 to T7423; pl. IV, fig. 8), a large hill, limestone contains diverse fossils: rare debris of algae, Tubiphytes, calcispheres (Eotuberitina), smaller foraminifers (Climacammina), small transported and eroded Fusulinidae (Nankinella sp.), solitary Rugosa, very rare massive Rugosa (Wentzelophyllum), bryozoans (Fistulipora), brachiopods, bivalves, gastropods and crinoids. At Khao Tan (9°16’51”N, 99°46’39”E; samples T7364 to T7369; plate III, figs. 2, 8 and 9), a grey thickly bedded to massive limestone is partly dolomitized, but elsewhere contains Tubiphytes, smaller foraminifers (Pachyphloia, Climacammina, Globivalvulina, Langella), locally abundant Fusulinidae (Yangchienia iniqua Lee 1933 and Parafusulina), small solitary corals (Lophophyllidium, Pavastehphyllum?) and bryozoans. At a Buddhist Temple (9°14’22”N, 99°48’19”E; sample T7375) and at a cave (9°14’15”N, 99°48’15”E; no sample) at Khao Krot, a hill southeast of Khao Tan, limestone displays elephant skin texture and no fossil has been noticed. At Khao Lom (9°03’02”N, 99°47’16”E; samples T7381 to T7385; pl. IV, figs. 1, 2, 4 and 6), a hill 20 km south of Khao Krot, limestone is black, thickly bedded to massive. It contains poorly preserved fragments of algae, calcispheres (Eotuberitina), smaller foraminifers (Climacammina, Deckerella, Langella), Fusulinidae (locally in abundance and belonging mainly to Chusenella crassa Deprat 1913 and maybe to Chusenella navillei Erk 1942), Tabulata (Protomichelinia with corallites 3 to 4 mm in diameter; sample T7385), very rare solitary Rugosa (Pavastehphyllum), bryozoans (Fistulipora), brachiopods, gastropods and ostracods. At Khao Sak (9°03’17”N, 99°47’20”E; samples T7386 to T7388), a hill near and north of Khao Lom, limestone is black, bedded; it is underlain by black shale. It contains fragments of algae, smaller foraminifers (Pachyphloia), very rare fragments of Fusulinidae (impossible to identify), two species of Tabulata belonging to Protomichelinia (corallites 3 to 4 mm in diameter in sample T7387 and 2 to 2.5 mm in sample T7386). At Khao Samna (9°04’06”N, 99°46’12”E; samples T7389 and T7390; pl. IV, fig. 3), 3.5 km northwest of Khao Lom, dark grey limestone is packstone. It contains calcispheres, smaller

224

foraminifers (Climacammina, Deckerella, Langella), Fusulinidae (Chusenella cf. crassa Deprat 1913), very rare solitary corals only noticed in the field

(Pavastehphyllum?), bryozoans, brachiopods gastropods and abundant crinoids.

PLATE II Fossil of first locality at Khao Ok. Figure 1 – Parafusulina sp. (transverse section; on the left) and Parafusulina cf. crassispira Leven 1967 (on the right). Sample T7313. Figures 2 to 4 – Parafusulina sp. and Parafusulina cf. nosonensis Thompson

& Wheeler 1946 (fig. 4, at the center and the bottom). Sample T7314. Figure 5 – Parafusulina sp. (transverse and subaxial sections). Sample T7315 Fossil of second locality at Khao Ok. Figure 6 – Parafusulina sp. (two transverse sections at the top) and Parafusulina cf. crassispira Leven 1967 (subaxial section at the bottom). Sample T7317. Figure 7 – Pseudodoliolina ozawai Yabe 1932. Although only subaxial, this section is well characterized by the number and the type of volutions as well as by the shape of

parachomata and their intervals. Sample T7318. Figure 8 – Chusenellidae indet. (transverse section). Sample T7318.

225

PLATE III Fossil of first locality at Khao Kho Kwang. Figure 1 – Yangchienia cf. iniqua Lee 1933. Several types of sections. Sample T7323. Figure 5 – Yangchienia iniqua Lee 1933. Subaxial section. Sample T7323. Figure 6 – Yangchienia iniqua Lee

1933. Subaxial section. Sample T7323. Figure 7 – Yangchienia cf. iniqua Lee 1933. Subtransverse section. Sample T7323. Fossil at Khao Tan Figure 2 – Parafusulina sp. (the transverse sections) and Parafusulina cf. nosonensis Thompson & Wheeler 1946 (the

two subaxial sections on the right, center and bottom). Sample T7366. Figure 8 – Yangchienia iniqua Lee 1933. This subaxial section is well characterized by the almost rhombic form of the test and the very massive chomata. Sample T7369. Figure 9 –

Yangchienia iniqua Lee 1933. Axial section, also characteristic. Sample T7367. Fossil at small hill southeast of Donsak Figure 3 – Parafusulina sp. (various sections). Sample T7354. Fossil at a small hill near Khao Nam Lai. Figure 4 – Chusenella cf. crassa

Deprat 1913. Various sections. Sample T7370.

226

PLATE IV Fossil at Khao Lom. Figures 1, 2, 4 and 6 – Chusenella crassa Deprat 1913. Various sections. Fig. 6 is a typical section, fig. 4 is more atypical and looks like Chusenella navillei (Erk) sensu Skinner 1969, not Erk 1942. Sample T7381. Fossil at Khao Samna. Figure 3 – Chusenella cf. crassa Deprat 1913. Transverse and subtransverse sections. Sample T7389. Fossil at Khao Phap Pha. Figures 5 and 7 – Chusenella cf. crassa Deprat 1913. Various sections . Sample T7392. Fossil at Khao Nom Tro. Figure

8 – Nankinella sp. Subaxial section. Transported specimen with facets of truncature (bottom). Sample T7420.

227

At Khao Phap Pha (9°10’42”N, 99°41’16”E; samples T7391 to T7394; pl. IV, figs. 5 and 7), 3 km west of an abandoned gypsum mine where gypsum is within a sequence of shale and sandstone, a black bedded limestone dips 20° towards west. It contains smaller foraminifers (Climacammina, Deckerella, Endothyra), locally Fusulinidae (Chusenella cf. crassa Deprat 1913), 2 species of solitary corals belonging to Pavastehphyllum and showing different diameters, bryozoans, brachiopods and crinoids. In this area, Permian and older rocks are apparently exposed; Tentaculites was found in 1991 by S. Salyapongse, A. Lumjuan and T. Thathong at the eastern side of Khao Khuan Reng, the northern end and the southeastern side of Khao Chang Lot, hills east of the gypsum mine; a Devonian age was suggested. At Laem Phap Pha (9°18’30”N, 99°47’14”E; samples T7325 and T7328, T7357 to T7359), a black bedded limestone is rich in Tabulata (Sinopora), reaching up to 50 cm in diameter and associated with smaller foraminifers (Tetrataxis), poorly preserved Fusulinidae, a few solitary Rugosa and gastropods. At Laem Thap, limestone belongs to an important section easy to observe along seashore and already described by Lumjuan (1993). The limestone builds up a cliff at one end of the beach (9°18’57”N, 99°48’16”E; samples T7332 to T7335); it is poor in fossils. It is underlain by a sequence of shale and sandstone containing pebbly mudstone at the other end of the beach (9°18’36”N, 99°48’25”E). Pebbles are commonly less than 5 cm in diameter, rarely 5 to 10 cm in diameter and 20 cm measured in a single sample. South of Laem Thap (9°18’26”N, 99°48’13”E; samples T7337 to T7340), large blocks of shale and limestone are scattered at the foot of a hill. The limestone contains calcispheres, some smaller foraminifers (Geinitzina, Pachyphloia, Endothyra), a few fragments of Fusulinidae, Tabulata with common Sinopora, rare solitary Rugosa and a few gastropods. At the northern end of Khao Nam Lai (9°18’21”N, 99°47’42”E; samples T7360 to T7363), limestone is locally dolomitized; elsewhere, it is very poor in fossils. At a small hill (9°16’08”N, 99°47’29”E; samples T7370 to T7374; pl. III, fig. 4) near and south of Khao Nam Lai, a dark grey to black bedded limestone contains a few fragments of algae, calcispheres, smaller foraminifers (Climacammina, Geinitzina), Fusulinidae (locally in abundance: Chusenella cf. crassa Deprat) and bryozoans. At Khao Nui (9°14’31”N, 99°48’34”E; samples T7376 to T7380), 8 km north of Amphoe Khanom (district southwest of Surat Thani), a black bedded limestone contains smaller foraminifers (Pachyphloia), diverse bryozoans and fragments of brachiopods. Fusulinidae are absent. The stratigraphical range of Pachyphloia is restricted to the Permian. At Khao Maen, 10 km south of the gypsum mine, fossils have been found only at its southern part (9°04’29”N, 99°42’27”E; samples T7401 to 7406) where a black bedded limestone dips 10° towards east and is underlain by sandstone. The fossils consist of fragments of algae, smaller foraminifers (Pachyphloia, Geinitzina), Tabulata

(Sinopora), solitary Rugosa (Pavastehphyllum), bryozoans, bivalves and gastropods. As for Pachyphloia, the stratigraphical range of Geinitzina is restricted to the Permian. At Khao Kun (9°04’04”N, 99°41’42”E; samples T7409 to T7413), limestone contains rare solitary corals (Plerophyllum), bryozoans and locally brachiopods in abundance. At Khao Wang Phut (9°05’47”N, 99°37’22”E; samples T7433 to T7435), a bedded limestone is rich in fragments of diverse shells (brachiopods, bivalves, ammonoids). It displays a peculiar facies. At the eastern side of Khao Yom Doi (9°09’11”N, 99°33’37”E; samples T7449 to T7452), 10 km northwest of Khao Phru Nom Wang and 4 km north of Khao Thung Nang Ling, a dark grey bedded limestone is rich in crinoids associated with a few solitary Rugosa (Paracaninia) and with bryozoans. Khao Thung Nang Ling is a large hill almost 3 km long in a north-south direction. It has been visited at 3 places. In its northern part (9°06’58”N, 99°33’30”E), limestone is poor in fossils which consist of solitary corals and brachiopods. At its western side (9°06’51”N, 99°33’06”E), limestone is rich in crinoids associated with some Fenestellidae. At the southern end of the hill (9°05’44”N, 99°32’59”E; samples T7458 and T7459), limestone contains smaller foraminifers (Geinitzina, Climacammina, Deckerella), Fusulinidae (Chusenella?), bryozoans, brachiopods and crinoids. The localities mentioned up to now in this text belong largely to the Permian and mainly to Middle Permian. They are not rich in diverse assemblages of fossils. Because of that, their study is not easy. Other hills have been visited, but fossils are absent in the collected samples. PROBLEM OF UPPER CARBONIFEROUS AND LOWER PERMIAN Some limestone exposures of Surat Thani Province have been assigned to “Lower to Upper Carboniferous”, to “Upper Carboniferous” and to “Lower Permian” (Dill et al., 2004, p. 66-67). Lists of diverse fossils have been provided and, in conclusion, a stratigraphic extension of the Ratburi Limestone down to the Carboniferous has been proposed. These results have been leading to a new interpretation of the geology of Peninsular Thailand, but they are restricted to the Surat Thani Province and they remain partly questionable. During the last 20 years, many geologists have not observed limestone of Upper Carboniferous age or belonging to the lower part of the Lower Permian in Peninsular Thailand, and to prove the contrary, there is a need of a detailed study of the local stratigraphy and of a discussion about the environmental meaning of the identified fossils. The “Upper Carboniferous” fossils of Dill and his co-authors are smaller foraminifers and ostracodes; the genera are identified, but the species are not precisely known. The identified genera of ostracodes: Holinella and Cavellina have a long stratigraphical range extending to

228

Permian and even Triassic; it is difficult to suggest an Upper Carboniferous age without precise identification of the species. The smaller foraminifers cannot bring more information. The “Lower Permian” age is based on algae and smaller foraminifers with a long stratigraphical range; there is no mention of the Fusulinidae well known in the Lower Permian of northeast and northwest Thailand. Some conodonts are also mentioned. There is no discussion about the different horizons of the Lower Permian.

PALEOGEOGRAPHY The Surat Thani Province does not appear different from the other parts of Peninsular Thailand. Permian limestone is widespread, with an age evidenced by the occurrence of Hemigordiopsis, Sphairionia, Pachyphloia, Geinitzina, some genera of Fusulinidae and of corals. The fossil assemblages are not very diverse and commonly not in great abundance. Genera of large Fusulinidae, such as Sphaeroschwagerina, Pseudoschwagerina, Verbeekina, Neoschwagerina, Yabeina, and others, are easy to notice in the field. They are widespread in central, northeastern and northwestern Thailand, but have not been found in Surat Thani Province as in the other parts of Peninsular Thailand. Corals are not diverse and in abundance in Surat Thani Province; there is no reef. Rugosa are mainly solitary specimens; fasciculate and massive Rugosa are not common. Locally, a species of Tabulata is in abundance, but is not associated with diverse other groups of fossils. The Carboniferous of northeastern and northwestern Thailand contains diverse assemblages of fossils which indicate different stratigraphical horizons. In the Upper Carboniferous or Pennsylvanian, it is easy to recognize Bashkirian, Moscovian, Kasimovian and Gshelian, by the studies of different groups of fossils which lead to the same conclusion. In Peninsular Thailand, the oldest beds of Permian limestone appear to belong to the upper part of Lower Permian, but commonly not to the lower part of Lower Permian. However, a Late Asselian species of conodont has been reported by Dill et al., 2004, p.78; this discovery may suggest a local deposition of calcareous material slightly earlier than elsewhere, but probably, not under a truly warm climate. In conclusion, observations have been made in Peninsular Thailand by many geologists in the past from different points of view. They have shown that the geology of the peninsula is not exactly the same as in the other parts of Thailand. They cannot be changed without very precise studies. A fact easy to observe immediately is that fossils are not in abundance at many localities and they are not very diverse. A succession of the different stages of the Upper Carboniferous has not been found up to now.

REFERENCES Chaodumrong P., P. Bamroongsong and N. Jungyusuk, 1998,

Limestone and dolomite resources map of Ban Pak Nam Tha Thong Sheet or Sheet 4927III of 1:50,000 scale.

Dill H. G., F. W. Luppold, A. Techmer, P. Chaodumrong and S. Phoonphun, 2004, Lithology, micropaleontology and chemical composition of calcareous rocks of Paleozoic through Cenozoic age (Surat Thani Province, central Peninsular Thailand): implications concerning the environment of deposition and the economic potential of limestones. Journ. Asian Earth Sci., 23: 63-89.

Fontaine H., C. Chonglakmani, Ibrahim B. A. and S. Piyasin, 1994, A well-defined biogeographic unit : Peninsular Thailand and northwest Peninsular Malaysia. Journ. Southeast Asian Earth Sci., 9(1-2): 129-151.

Fontaine H., V. Suteethorn and D. Vachard, 1998, Khao Yoi, a Permian limestone hill of the Ratburi area, Peninsular Thailand. CCOP Newsletter, 23(3): 12-14.

Harrison D. J., P. Chaodumrong and M. Charusribandhu, 1997, Assessment of limestones resources from Surat Thani Province, Thailand. Proc. Intern. Conf. Stratigraphy and Tectonic Evolution of Southeast Asia and the Pacific, Bangkok, 640-649.

Ingavat-Helmcke R., 1993, Contribution to the Permian fusulinacean faunas of Peninsular Thailand. Journ. Southeast Asian Earth Sci., 8(1-4): 67-75.

Lumjuan A., 1993, Permo-Carboniferous of northern Nakhon Si Thammarat. Intern. Symposium on Biostratigraphy of Mainland Southeast Asia: Facies and Paleontology, Chiang Mai, vol. 1: 219-224.

Nestell M. K. and G. P. Pronina, 1997, The distribution and age of the Genus Hemigordiopsis. In: Ross C. A., J. R. P. Ross and P. L. Brenckle, 1997 – Late Paleozoic Foraminifera; their biostratigraphy, evolution and palaeoecology; and the Mid-Carboniferous boundary. Cushman Foundation for Foraminiferal Research, Special Publication, 36: 105-110.

Nguyen D. T., 1989, Sphairionia sikuoides gen. et sp. nov., a Permian incertae sedis organism. XIe Congrès International de Stratigraphie et de Géologie du Carbonifère, Beijing 1987, Compte Rendu 3 (1989) : 73-77, 2 pl.

Pronina G. P., 1996, Genus Sphairionia and its stratigraphic significance. Ann. Mus. Civ. Rovereto, Sez.: Arch., St., Sc. Nat., Suppl. Vol. 11 (1995): 105-118.