International Research Journal of Earth Sciences______________________________________ ISSN 2321–2527Vol. 1(4), 31-38, September (2013) Int. Res. Earth Sci. International Science Congress Association 31 Late Pliocene (Piacenzian Stage) Fossil Molluscs from Upper Siwalik Subgroup of Jammu, Jammu and Kashmir, India Kundal Som Nath P.G. Department of Geology, University of Jammu, Jammu-180006, INDIAAvailable online at: www.isca.in Received 7th July 2013, revised 23rd July 2013, accepted 22nd August 2013 AbstractFive species of gastropods and two of bivalves are being reported, and described from the mudstone horizon immediately underlying geochronologically dated (2.8±0.56m.y.) bentonitized tuff band exposed at Barakhetar village in a stream cutting section. The reported fauna comprises Gastropods: Gastrocopta sp., Gyraulus sp. indet., Viviparus bengalensis, Viviparus sp., Bellamya celispiralis and Bivalves: Lamellidens lewisi, Oxynaia sp. indet. Stratigraphically, the fossil (gastropod and bivalve) bearing mudstone horizon belongs to the Nagrota Formation of Upper Siwalik Subgroup of Jammu Province, Jammu and Kashmir, India and located about 30km east of Jammu city. A brief account of the age and palaeoecology of the recovered taxa have also been discussed in the present paper. Keywords: Late Pliocene, Molluscs, Palaeoecology, Age, Nagrota Formation, Upper Siwalik Subgroup, Jammu, IntroductionSiwalik Group is the southernmost part of the Himalayan foreland basin containing rich assemblage of Neogene fossils. It occurs all along the length of the Himalayan arc from the Indus River in the northwest to Brahmaputra in the east. Most of the type sections of the Siwalik Group occur in Pakistan; a few occur in India and reference sections that yield fossils are known from both India and Nepal. Bhatia and Mathur have reported eleven taxa of bivalves and twenty two of gastropods from the Late Pleistocene of Punjab. Takayasu et al. recovered freshwater Moicene – Pliocene molluscan fossils from the Churia Group (equivalent to the Siwalik Group) of Nepal. The recovered bivalve fauna comprises Lamellidens arungensis, Lamellidens longiformis, Indonaia narayani, Indonaia jimuriensis, Indonaia tenella, Parreysia binaiensis, Parreysia zigzagicostata and Physunio chitwanensis. Mathur described four taxa of gastropods and six of bivalves from the Middle and Upper Siwalik deposits (Late Miocene-Pleistocene) of Kangra (H.P.), Ambala (Harayana), and Ropar (Punjab) districts. This fauna is represented by Amnicola Alocinma) sp., cf. A. A.) sistanica, Sitala sp. indet. (Upper Siwalik Pinjor Formation) and Hydrobioides avarix and Indoplanorbis exustus from terrace deposits. The bivalves are represented by Parreysia sp., cf. . edwini (Gupta), P. sp. indet., Lamellidens sp. indet. A, L. sp. indet. B, Oxynaia sp. indet. (Pinjor) and Corbicula sp. from the Boulder Conglomerate Formation (Upper Siwalik). Mathurmade an attempt to synthesise the sporadic records of charophytes from the Siwalik Group and to build up a molluscan biostratigraphy and concluding that the Lamellidens prashadi is of the proposed Lower Zone (Chinji) and L. jammuensis of the proposed Upper Zone (DhokPathan – Pinjor). Within L. jammuensis Zone, L. subparallelus-Parreysia Parreysia) tatrotensis assemblage represents the Lower Sub Zone (DhokPathan – Tatrot) and Pisidium Afropisidium) sivalensis represents Upper Sub Zone (Pinjor). Gurungcollected freshwater fossil molluscan fauna from the Siwalik Group of Nepal which is represented by gastropods belonging to the families Viviparidae, Ampullariidae, Bithyniidae, Thiaridae and bivalves belonging to the families Unionidae, Corbiculidae and Pisidiidae. Of these four new species viz. Angulyagra schiddarthai, Brotia dobataensis Paludomus suraiensis and Parreysia chureii have also been described. The Siwalik succession of Jammu Hills, the eastern extension of Potwar Plateau and lying in a linear belt between the Line of Control and Ravi River, is relatively least studied area from invertebrate and micro- paleontological points of view. No reports have been published on gastropods and bivalves of this area until now except that of Prashad and Parmar . Prashad collected two specimens of unionid shells from the Upper Siwalik beds near Nagrota, Jammu and one shell from Nawapet, Hydrabad, and Deccan India. The unionid fauna comprises of Lammellidens jammuensis,Indonaia mittali, and Indnaia pascoei. Parmar recovered a few species of molluscan fauna comprises of Mesogastropoda incertae sedis, Lamellidens indet., Thiaridae sp. Parreysia tatrotensis from the Lower Siwalik deposits of Jammu region. The present collection of bivalve and gastropod specimens have been recovered from the mudstone horizon immediately underlying the geochronologically dated bentonitized tuff band (2.8±0.56m.y.) exposed at Barakhetar village in the Nagrota Formation, Upper Siwalik Subgroup of Jammu region. Repository: The recovered specimens have been lodged in the Department of Geology, Paleontology Laboratory, Jammu University under catalogue numbers DG/PL/JU/1-8. International Research Journal of Earth Sciences____________________________________________________ ISSN 2321–2527Vol. 1(4), 31-38, September (2013) Int. Res. J. Earth Sci. International Science Congress Association 32 Figure 1 A. Map of India; B. Map of Jammu and Kashmir; C. Locality map of gastropods and bivalves bearing mudstone horizon (Reference Google earth) and D. Litho-Log of Barakhetar section showing position of fossil yielding horizon Stratigraphy: From a long time many geoscientists Falconer, Lydekkar, Colbert, Lewis10, Wadia11, Opdyke12 Azzaroli and Napoleone13, Johnson14 have classified the Siwalik Group of rocks on the basis of one or more of lithology, fauna and flora, magnetostratigraphy and satellite imagery analysis. But the standard stratigraphy of the Siwalik rocks was provided by Pilgrim15 on the basis of the fauna recovered from Siwalik Hills. He divided the “Siwalik Series” into three units which could have subdivided into seven stages. i.e. Lower Siwalik ( Kamlial Stage, Chinji Stage), Middle Siwalik (Nagri Stage, Dhok Pathan Stage) and Upper Siwalik (Tatrot Stage, Pinjor Stage and Boulder Conglomerate Stage) and these assigned an age ranging from Middle Miocene to Lower Pleistocene for the Siwalik Series. This classification is more or less followed till date. All these above stages are named on the basis of type sections in undivided India, but after the division of India most of the stages occurr in different localities in Pakistan, except Pinjor and Boulder Conglomerate, which occur in India. The Siwalik Group of Jammu division is exposed in outcrops that occupy an intermediate position between the type sections on the west and Siwalik Hills of Chandpur in east having type localities Pinjor and Boulder Conglomerate. Various lithostratigraphic units starting from Chinji Formation to Boulder Conglomerate Formation have been delineated in this area16. The Upper Siwalik Subgroup of rocks of Jammu region has been divided into Parmandal Sandstone, Nagrota Formation, and Boulder Conglomerate17. Agarwal18 adopted these stratigraphic divisions and subdivided Nagrota Formation into three members i.e. Nagrota-A, Nagrota-B, and Nagrota-C. Gupta and Verma19 classified the Siwalik Group of Jammu into Mansar Formation (Lower Siwalik Subgroup); Dewal Formation (=Nagri), Mohargarh Formation (=Dhok Pathan) (Middle Siwalik Subgroup); and Uttarbehani Formation, Dughor Formation (=Boulder Conglomerate) (Upper Siwalik Subgroup). Gupta20 further modified the latter classification and divided the Mansar Formation into Dodenal Member and Ramnagar Member and Uttarbehani Formation into Labli Member (=Tatrot) and Marikhui Member (=Pinjore). The comparative classification of Siwalik group of Jammu is given by various workers is reproduced in the table-1. Systematic Description Phylum Mollusca Class Gastropoda Order Caenogastropoda Family Viviparidae Genus Viviparus Viviparus bengalensis: Referred Material: DG/PL/JU/01, one shell. Stratigraphic Position: Mudstone horizon immediately underlying the geochronologically dated (2.8 ±0.56 m.y.) International Research Journal of Earth Sciences____________________________________________________ ISSN 2321–2527Vol. 1(4), 31-38, September (2013) Int. Res. J. Earth Sci. International Science Congress Association 33 bentonitized tuff band exposed at BaraKhetar, Jammu. Locality: In a stream cutting, 0.375 km northwest of Barakhetar village, Jammu district, Jammu and Kashmir, India. Description: Shell short and broad, conical spire, four whorls, whorls swollen, dextrally coiled increase in size gradually and evenly, body whorl larger than the spire, suture linear and impressed, surface of whorls convexly flattened, aperture subspherical, ventral surface of the body whorl convex, surface smooth. Remarks:The present forms approach the morphology of Viviparus bengalensis, which has so far been recorded from the Pleistocene deposits of Narmada valley21 and Pinjor Formation near Chandigarh 22 and Saketi. It has also been documented from the freshwater lakes of Jammu region23 and has a wide spread occurrence in the Indian subcontinent. Viviparus sp.: Referred Material: DG/PL/JU/02, one shell. Description: Shell small, medium-sized, slightly inflated, short conical, apex blunt, three whorls, whorls increase in size gradually and evenly, body whorl higher than spire, whorls moderately convex, sutures linear and depressed, aperture ovoidal in shape, ventral surface of body whorl convex, dextrally coiled, a low prominent ridge along the basal periphery of ultimate whorl, surface with fine longitudinal striae. Remarks: The specimens under discussion differ from those of V. bengalensis in having adpressed sutures, less inflated whorls, and ovoidal aperature. Although in general appearance, the present specimen resembles Sitala sp. indet. from Pinjor Formation near Chandigarh, is elongate conical and the number of whorls are5 ˝ , the spire is relatively high and the apical angle is low. Order Mesogastropoda Genus Bellamya Bellamya celsipiralis: Referred Material:DG/PL/JU/03, one specimen. Description: Shell elongated turbinate in shape, moderately solid, spire elevated, long, equal or slightly larger than the body whorl. Shell consisting of four whorls, gradually and regularly increase in size. The whorls are rounded and separated by impressed suture. Aperture partially preserved, body whorl not greatly enlarged in size. Shell surface marked with coarse and fine striate or growth lines. Aperture broadly ovate, small, thinly lipped, inner lip is thicker than the outer lip. Remarks: The specimen under study compares well with Bellamya celsipiralis described by Gurung24 from the Churia (Siwalik) Group of Tinau (Nepal). Genus Gyraulus Gyraulus sp. indet.: Referred Material: DG/PL/JU/05, one specimen. Description: Shell small in size, 2-4 mm in diameter, discoidal, thin and dextrally coiled; all the whorls are visible from above. Large apical part can be observed but adapical part cannot be seen because of the breakage of the specimens. Whorls increasing in diameter rapidly and consist of two and half whorls. Body whorl larger and a little expanded around the aperture. Remarks:The specimens under study campare with those of Gyraulus reported by Bhatia25 from the Karewa deposits of Kashmir. However, breakage of the specimens from adapical side made their identification at species level difficult. Order Stylommatophora Family Chondrinidae Genus Gastrocopta Gastrocopta sp.: Referred Material:DG/PL/JU/06, one specimen. Description:Shell elongated cylindrical in outline, five whorls, whorls increase in size gradually and evenly, and moderately convex, spire higher than body whorl or nearly equal to it, apex blunt, sutures linear and impressed, aperture sub-quadrate in outline, ventral surface of body whorl convex, surface with fine longitudinal striae, apertural folds are indistinct due to matrix filling. Remarks: Gastrocopta is known by Gastrocoptakashmirensisfrom the Karewa Formation of Kashmir26, Gastrocoptanaidui 27and Gastrocopta (Gastrocopta) prashadi22 from the terrace deposits near Chandigarh. More recently, Mathur described additional molluscan fauna and revised earlier described ones from the Siwalik Group and terrace deposits of Himachal Pradesh, Haryana, and Punjab and provided a comprehensive account of apertural characters that can be successfully used in taxonomic classification. In overall appearance, the specimen from the Upper Siwalik beds of Jammu is comparable to Gastrocoptakashmirensis. Because of the indistinct nature of apertural characteristics and paucity of material, assignment of present material to G. kashmiriensis is avoided. Class Bivalvia Order Unionoida Family Unionidae Genus Oxynaia Oxynaia sp. Indet: Referred Material: DG/PL/JU/07, single specimen with both valve. Description: The specimen is transversly ovate in outline, anterior margin broadly rounded with an antero-dorsal notch, posteriorly cuneate, dorsal gradually sloping, ventral feebly arched, convex, broadly rounded anterior end, nearly acutely pointed posterior end, antero-dorsal notch, shell moderatelly inflated, umbo slightly inflated, strongly inequilaterial, umbo sculpture indistinct.Dimensions: Length = 7 mm, Width = 4 mm. Remarks: The present specimen is camparable to Oxynaia sp. indet. earlier described by Mathur from the Chhoti Parch, near Chandigarh, Pinjor Formation. This species is restricted to the Pinjor Formation. Genus Lamellidens