CALCAREOUS NANNOFOSSILS OF ALBIAN AGE FROM TANOT WELL1, JAISALMER BASIN, RAJASTHAN AND ITS PALAEOBIOGEOGRAPHIC SIGNIFICANCE

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1 Journal of the Palaeontological Society of India Volume 58(1), June 2013: ISSN CALCAREOUS NANNOFOSSILS OF ALBIAN AGE FROM TANOT WELL1, JAISALMER BASIN, RAJASTHAN AND ITS PALAEOBIOGEOGRAPHIC SIGNIFICANCE ABSTRACT JYOTSANA RAI 1, ABHA SINGH 1 and RAHUL GARG 2 1 BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY; 53, UNIVERSITY ROAD, LUCKNOW CAS GEOLOGY, UNIVERSITY OF LUCKNOW, LUCKNOW jyotsana_rai@yahoo.com The present paper deals with the record of well preserved and diverse early-middle Albian nannofossils recovered from Tanot # 1 (Oil India Limited), drilled in the Jaisalmer Basin, Rajasthan, western India. Early Cretaceous (Aptian-Albian) marine sediments are known from the western (Jaisalmer and Kachchh basins) and the eastern continental margins (Mahanadi, Krishna-Godavari, Palar and Cauvery basins) of the Indian Plate. Early-middle Albian nannofossils are known from sandy, fossil-fauna depleted; Upper Member of Bhuj Formation in Kachchh (Biswas, 1977). Aptian to Turonian nannofossils are recorded from fossiliferous Cauvery Basin, southern India. The Tanot #1 samples are available from m depth; however, only a part of the interval between depths 1899m-1596m is studied herein. The occurrence of Tranolithus orionatus from the oldest sample (1899m) upwards is used here to assign it to CC8 Zone (Sissingh, 1978) and NC8 Zone (Roth, 1978) of middle Albian age. FAD of T. orionatus is a middle Albian marker both in the Tethyan and the Boreal provinces in various zonation schemes. FAD of Axopodorhabdus albianus at 1656m marks base of NC9 Zone (Roth, 1978) in the section as well. The dominance of Nannoconus spp. suggests shallow water environment and nearness to shore. Keywords: Nannofossils, Albian, Cretaceous, Tanot, Jaisalmer Basin INTRODUCTION Early Cretaceous marine sediments are widespread in the western (Jaisalmer and Kachchh basins) and eastern continental margins (Mahanadi, Krishna-Godavari, Palar and Cauvery basins) of the Indian Plate. Records of calcareous nannofossils from these deposits are, however, scarce and are known only from the Kachchh (Rai, 2006) and Cauvery basins (Jafar and Rai, 1989; Kale and Phansalkar, 1992a, 1992b; Venkatchalapathy and Hari Kiran, 1993; Kale et al., 2000). Rai (2006) documented early-middle Albian nannofossil assemblage from sandy, megafauna lacking; upper part of the Upper Member of the Bhuj Formation, Kachchh Basin (Biswas, 1977). In the Cauvery Basin, late Aptian-early Turonian nannofossil assemblages are documented from the fossiliferous Dalmiapuram and Uttatur formations (Jafar and Rai, 1989; Kale and Phansalkar, 1992a, 1992b). The early Cretaceous succession (Pariwar Formation) exposed in the Jaisalmer basin is poorly fossiliferous containing only plant fossils (Maheshwari and Singh, 1974), although the predominantly sandy succession contains several profusely bioturbated horizons. Calcareous nannofossils have recently been documented from the calcareous shale partings from the Pariwar Formation exposed near Pariwar Village, Jaisalmer (Rai et al., 2009) providing evidence for its age and marine character. In the present paper, well-preserved, rich and diverse assemblages of calcareous nannofossils of early-middle Albian age are documented from the subsurface succession encountered in the Tanot #1 (27 28 N and E) drilled by Oil India Limited in the Jaisalmer Basin, Rajasthan, western India. Only foraminifera and ostracodes have been recorded till date (Singh, 1996; Kalia and Kintso, 2006; Andreu et al., 2007; Bhandari, 2008) and calcareous nannofossils are being documented for the first time from the subsurface Cretaceous successions of the Jaisalmer Basin. GEOLOGICAL SETTING In the Jaisalmer Basin, marine Jurassic-early Cretaceous rocks are extensively exposed and have been investigated in detail by several workers (Das Gupta, 1974, 1975; Kachhara and Jodhawat, 1981; Kalia and Chowdhury, 1983; Dave and Chatterjee, 1996; Singh, 1996). The lithostratigraphic classification proposed by Das Gupta (1975) for subsurface and surface successions is followed herein. Samples for the present study were obtained from 1899 m-1596 m interval from the Tanot 1 located northwest of Jaisalmer near Tanot Village (27 28 N and E). Tanot #1 lies in the Kishangarh subbasin of the Jaisalmer Basin (Fig. 1). The studied subsurface interval belongs to the Pariwar Formation. The exposures of lower Cretaceous Pariwar Formation though widespread but are mostly covered by aeolian deposits. Fossil mega-fauna are not found in the Pariwar Formation but fossil wood and plant leaf impressions have been documented (Maheshwari and Singh, 1974). However, in the subsurface, rich microfossil Fig. 1. Map showing location of the study area (modified after Misra et al., 1993).

2 68 JYOTSANA RAI, ABHA SINGH AND RAHUL GARG assemblages viz. arenaceous foraminifera with rare calcareous benthic foraminifers (Singh, 1997), ostracodes (Singh, 1997; Bhandari, 1999; Andreu et al., 2007) and palynomorphs (Venkatachala, 1966) have been recorded and used for age determination. In the absence of any age-diagnostic marine fauna, lower Cretaceous (Neocomian) age is broadly assigned based on plant fossil evidences and stratigraphic criterion, as the outcropping Pariwar Formation is sandwiched between datable ammonite-bearing Bhadasar Formation (Late Tithonian) and Habur Formation (Late Aptian-Early Albian). However, in the subsurface, the Pariwar Formation is overlain by predominantly shaly succession (Goru Formation) which is Albian- Cenomanian in age and the ammonite rich coquina limestone characteristic of the Habur Formation is not encountered. The Goru Formation is overlain by the Parh Formation (Turonian- Santonian). Thus, in the subsurface more complete and thick Early Cretaceous succession has been encountered as compared to the exposed surface deposits (Das Gupta, 1975; Pareek, 1981; Singh, 1996). CALCAREOUS NANNOFOSSIL RECORDS FROM JAISALMER BASIN Calcareous nannofossils from the Jaisalmer Basin are known from the Jurassic (Jaisalmer Formation) and Cretaceous (Pariwar Formation) successions. Rich and well-preserved Callovian nannofossil assemblages are documented and calibrated with ammonite zones from the Kuldhar Member, Jaisalmer Formation (Kalia and Roy, 1986; Rai and Garg, 2007; Jain, 2008; Rai, 2009). Besides, the Bada Bagh Member (Jaisalmer Formation) and Rupsi Member (Baisakhi Formation) have also shown nannofossil productivity (Rai personal observation). Only recently, precisely datable early Albian nannofossil assemblage is recorded from the surface samples of the Pariwar Formation providing precise early-middle Albian age (Rai et al., 2009). The nannofossil data thus suggests that in part, the Pariwar Formation may be lateral facies equivalent of the well-dated ammonite-containing Habur Formation, although till date no such evidence from surface exposures is available. The contact of the Pariwar and Habur formations is not discernible due to the desert alluvium cover. In the present study, fairly rich, diverse and datable Cretaceous nannofossil assemblages are documented from the subsurface Pariwar Formation encountered in the studied interval of the Tanot #1 (1899m-1596m). METHODOLOGY Conventional method of preparation of slides for nannofossil study is used. A small fraction of sample is soaked in neutral distilled water in a clean and dried porcelain crucible. A homogenous suspension is formed by finger tip. The material is allowed to settle for a while. Few drops of the turbid suspension are evenly spread over a clean slide. Duplicate slides of each sample, one containing fine and the other having comparatively coarse fraction is spread as thin film and allowed to dry over a hot plate. The slides are then mounted in the Canada balsam. The nannofossils are studied using Leitz polarizing microscope under 100/0.32 oil immersion objective both under normal (using single polarized) and crossed polarized illumination with gypsum plate. The slides are deposited in the museum of Birbal Sahni Institute of Palaeobotany (BSIP museum numbers ). RESULTS AND DISCUSSION Age of nannofossil assemblages Fifty-five species of calcareous nannofossils are identified in the assemblages recorded between 1899m to 1596m depth interval from the Tanot #1 (Fig. 2). In the lower part of the succession (1731m-1899m), nannofossil assemblages show predominance of large-sized specimens, while in the upper part (1596m-1728m) relatively smaller forms predominate. In general, preservation of nannofossils is moderate to good in the studied interval. Stratigraphic distribution of nannofossils in Tanot #1 is given in Fig 2. Last occurrence of B. stenorhetha at m depth interval may suggest the presence of Albian-Cenomanian Boundary as the nannofossil assemblages in the overlying samples (1590m-1593m) show absence of this species. In the underlying succession, the nannofossil assemblages are rich and diversified dominated by species characteristic of Middle- Late Albian known from the different parts of the world (Roth and Berger, 1975; Thierstein, 1976; Verbeek, 1977; Roth, 1978; Roth and Bowdler, 1981; Roth and Krumbach, 1986; Crux, 1991; Erba, 1992; Bown, 1998; Lees, 2002; Kulhanek and Wise, 2006). Common occurrences of A. albianus, B. africana, E. gorkae, E. turriseifelli, R. angustus and T. orinatus suggest placement of the assemblages within the Middle-Late Albian time slice. FAD of T. orionatus is considered to be a cosmopolitan age marker in both Tethyan and Boreal provinces (Bown et al., 1998) and its FAD lies within CC8 Zone (Sissingh, 1978) and NC8 Zone (Roth, 1978) of Middle Albian age. Successive appearances of A. albianus (1656m) and E. turriseifelli (1647m) further indicate assignment to NC9 Zone of late Middle to Upper Albian age (Fig. 3). The nannofossil assemblages recorded within 1899 m to 1596 m interval are, therefore, assigned to CC8 (part) to CC9 Zones of Middle to Late Albian age. Reworking from the older Early Cretaceous sediments is also suggested due to the occurrence of C. oblongata. During Aptian-Albian times, the epeiric seas encroached upon both western and eastern margins of India, imprints of which are present in the form of coeval nannofossil assemblages in Kachchh and Rajasthan in western India and Cauvery and other east coast basins. Palaeobiogeographic Remarks The Albian time is known for extensive marine transgressions in Africa and America enabling faunas and floras to use either African-S. American or African-Australian seaway (Barron, 1987). Abundance of braarudosphaerids and nannoconids is indicative of shallow neritic, warm water conditions of deposition (Perch-Nielsen, 1979 Erba, 1987; Mutterlose, 1991; Erba et al., 1992; Mutterlose and Kessels, 1992; Erba, 1994; Aguado et al., 2000). R. asper is another species characteristic of warm water conditions having moderate productivity with pronounced abundance in a tropical-subtropical assemblage than subarctic-subantarctic assemblages. Presence of R. asper in the assemblage is indicative of favourable warm conditions; however, its abundance never exceeds that of W. barnesae. Occurrence of reworked C. oblongata suggests deposition of nannofossil rich pre-albian Early Cretaceous sediments in the Jaisalmer Basin, which have not been encountered in the studied section of Tanot #1. However, thick Early Cretaceous age succession containing plant leaf impressions and arenaceous forams is

3 CALCAREOUS NANNOFOSSILS OF ALBIAN AGE FROM JAISALMER BASIN, RAJASTHAN Fig. 2 Distribution of calcareous nannofossil from Tanot #1. 69

4 70 JYOTSANA RAI, ABHA SINGH AND RAHUL GARG Fig. 3. Composite figure showing nannofossil events in present study and its comparison with NC Zone (Roth, 1978) and CC Zones (Sissingh, 1978) along with age and lithology. documented in other wells drilled for hydrocarbon exploration in Jaisalmer (Das Gupta, 1975; Singh, 1996). Record of high abundance of Nannoconus spp. in Tanot #1 is indicative of influx of warm water nannoflora from the Tethys during transgressive phases in early Cretaceous. Distribution of Nannoconus spp. rich assemblage is controlled by palaeogeographical setting and warm climate (Roth and Bowdler, 1981; Roth and Krumbach, 1986; Mutterlose and Kessels, 1992; Lees, 2002). However, nannoconids are also widely reported from the Southern Ocean. Occurrence of Serebiscutum primitivum, a cold water form in the Jaisalmer basin indicates influx of cold water currents in the region. The present nannofossil assemblage indicates a mixed Tethyan affinity. In recent years, Cretaceous nannofossil palaeobiogeography has been dealt by several workers (Mutterlose and Kessels, 2000; Street and Bown, 2000; Lees, 2002). The Jaisalmer Basin was at ~35 S palaeolatitude in Late Albian (~l00 Ma) and it was in the Temperate PBZ zone of Lees (2002) (Fig. 4). The predominance of Austral/mixed Austral species is striking in the present assemblages. The most abundant to common Austral/mixed Austral forms recorded in this time slice are A. albianus, T. orionatus, W. barnesae, E. moratus, R. surirella, R. angustus, R. asper, S. crux, Z. erectus and Z. scutula. Record of Seribiscutum primitivum, in the present assemblage in few numbers (1 specimen per ten fields of view) with dominance of W. barnease indicates low fertility regime (Roth and Krumbach, 1986; Erba et al., 1992). S. primitivum is considered to be characteristic of high-latitude with bipolar distribution (Wise, 1983; Roth and Krumbach, 1986; Mutterlose and Wise, 1990; Mutterlose, 1992; Herrle and Mutterlose, 2003; Kulhanek and Wise, 2006). There appears mixing of warm and cold water currents in western part of the Indian Plate during Albian time. The recorded nannofossil assemblage from Tanot #1 is indicative of mixed Austral-Tethyan affinity. Checklist of Taxa Axopodorhabdus albianus (Black, 1967) Wind and Wise in Wise and Wind, 1977 Biscutum melaniae (Górka, 1957) Burnett, 1997 Braarudosphaera africana Stradner, 1961 Braarudosphaera stenorhetha Hill, 1976 Broinsonia enormis (Shumenko, 1968) Manivit 1971 Bukrylithus ambiguous Black 1971 Calcicalathina oblongata (Worsley, 1971) Thierstein, 1971 Calculites obscurus (Deflandre, 1959) Prins and Sissingh in Sissingh, 1977 Calculites percenis Jeremiah, 1996 Chiastozygus litterarius (Górka, 1957) Manivit, 1971 Corollithion? madagaskarensis Perch-Nielsen, 1973 Cretarhabdus crenulatus Bramlette and Martini, 1964 Cribrosphaerella ehrenbergii (Arkhangelsky, 1912) Deflandre in Piveteau, 1952 Cyclogelosphaera rotaclypeata Bukry, 1969 Cylindralithus nudus Bukry, 1969 Eiffellithus gorkae Reinhardt, 1965

5 Journal of the CALCAREOUS Palaeontological Society of India NANNOFOSSILS Volume 58(1), June 2013 OF ALBIAN AGE FROM JAISALMER BASIN, RAJASTHAN 71 Plate I RAI, SINGH AND GARG EXPLANATION OF PLATE I All the microphotographs are taken in the direction of orientation using gypsum plate both under normal and crossed nicols. The scale bar in each photograph indicates 5µm. 1. Axopodorhabdus albianus (Black, 1967) Wind and Wise in Wise and Wind, 1977, 2. Biscutum melaniae (Górka, 1957) Burnett, 1997, 3. Braarudosphaera africana Stradner, 1961, 4. Braarudosphaera stenorhetha Hill, 1976, 5. Broinsonia enormis (Shumenko, 1968) Manivit Bukrylithus ambiguous Black 1971, 7. Calcicalathina oblongata (Worsley, 1971) Thierstein, 1971, 8. Calculites obscurus (Deflandre, 1959) Prins and Sissingh in Sissingh, 1977, 9. Calculites percenis Jeremiah, 1996, 10. Chiastozygus litterarius (Górka, 1957) Manivit, 1971, 11. Corollithion? madagaskarensis Perch-Nielsen, 1973, 12. Cretarhabdus crenulatus Bramlette and Martini, 1964, 13. Cribrosphaerella ehrenbergii (Arkhangelsky, 1912) Deflandre in Piveteau, 1952, 14. Cyclogelosphaera rotaclypeata Bukry, 1969, 15. Cylindralithus nudus Bukry, 1969, 16. Eiffellithus gorkae Reinhardt, 1965, 17. Eiffellithus turriseiffelii (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965, 18. Eprolithus floralis (Stradner, 1962) Stover, 1966, 19. Helenea chiastia Worsley, 1971, 20. Helicolithus cf. H. anceps (Górka, 1957) Noël, 1970, 21. Helicolithus trabeculatus (Górka, 1957) Verbeek, 1977, 22. Isocrystallithus compactus Verbeek, 1976, 23. Munarinus cf. M. lesliae Risatti, 1973, 24. Nannoconus circularis Deres and Achéritéguy, 1980, 25. Nannoconus sp. 1, 26. Nannoconus sp.2, 27. Nannoconus sp. 3, 28. Nannoconus truitti Brönnimann, 1955, 29. Nannoconus truitti frequens Deres and Achéritéguy, 1980, 30. Nannoconus truitti rectangularis Deres and Achéritéguy, 1980, 31a-b. Owenia hilli Crux, 1991, 32. Prediscosphaera columnata (Stover, 1966) Perch-Nielsen, 1984, 33. Prediscosphaera spinosa (Bramlette and Martini, 1964) Gartner, 1968, 34. Radiolithus planus Stover, 1966, 35. Repagulum parvidentatum (Deflandre and Fert, 1954) Forchheimer, 1972, 36. Retecapsa crenulata (Bramlette and Martini, 1964) Grün in Grün and Allemann, 1975, 37. Retecapsa ficula (Stover, 1966) Burnett, 1998, 38. Retecapsa surirella (Deflandre and Fert, 1954) Grün in Grün and Allemann, 1975, 39. Rhagodiscus achlyostaurion (Hill, 1976) Doeven, Rhagodiscus angustus (Stradner, 1963) Reinhardt, 1971, 41. Rhagodiscus asper (Stradner, 1963) Reinhardt, 1967, 42. Rhagodiscus gallagheri Rutledge and Bown, 1996, 43. Rhagodiscus splendens (Deflandre, 1953) Verbeek, 1977, 44. Seribiscutum primitivum (Thierstein, 1974) Filewicz et al. in Wise and Wind, 1977, 45. Stradneria crenulata (Bramlette and Martini, 1964) Noël, 1970, 46. Tetrapodorhabdus decorus (Deflandre in Deflandre and Fert, 1954) Wind and Wise in Wise and Wind, 1977, 47. Tranolithus orionatus (Reinhardt, 1966) Reinhardt, 1966, 48. Watznaueria barnesae (Black, 1959) Perch-Nielsen, 1968 Reinhardt, 1965, 49. Watznaueria ovata Bukry, 1969, 50. Zeugrhabdotus bicrescenticus (Stover, 1966) Burnett in Gale et. al., 1996, 51. Zeugrhabdotus biperforatus (Gartner, 1968) Burnett, 1998, 52. Zeugrhabdotus erectus (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965, 53. Zeugrhabdotus noeliae Rood et. al., 1971, 54. Zeugrhabdotus scutula (Bergen, 1994) Rutledge and Bown, 1996, 55. Thoracosphaera operculata Bramlette and Martini, 1964

6 72 JYOTSANA RAI, ABHA SINGH AND RAHUL GARG Zeugrhabdotus bicrescenticus (Stover, 1966) Burnett in Gale et. al., 1996 Zeugrhabdotus biperforatus (Gartner, 1968) Burnett, 1998 Zeugrhabdotus erectus (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965 Zeugrhabdotus noeliae Rood et. al., 1971 Zeugrhabdotus scutula (Bergen, 1994) Rutledge and Bown, 1996 Thoracosphaera operculata Bramlette and Martini, 1964 Fig. 4. Late Albian Palaeogeographic position of India and nannofossil assemblage (after Lees, 2002). Eiffellithus turriseiffelii (Deflandre in Deflandre and Fert, 1954) Reinhardt, Eprolithus floralis (Stradner, 1962) Stover, 1966 Helenea chiastia Worsley, 1971 Helicolithus cf. H. anceps (Górka, 1957) Noël, 1970 Helicolithus trabeculatus (Górka, 1957) Verbeek, 1977 Isocrystallithus compactus Verbeek, 1976 Munarinus cf. M. lesliae Risatti, 1973 Nannoconus circularis Deres and Achéritéguy, 1980 Nannoconus sp. 1 Nannoconus sp. 2 Nannoconus sp. 3 Nannoconus truitti Brönnimann, 1955 Nannoconus truitti frequens Deres and Achéritéguy, 1980 Nannoconus truitti rectangularis Deres and Achéritéguy, 1980 Owenia hilli Crux, 1991 Prediscosphaera columnata (Stover, 1966) Perch-Nielsen, 1984 Prediscosphaera spinosa (Bramlette and Martini, 1964) Gartner, 1968 Radiolithus planus Stover, 1966 Repagulum parvidentatum (Deflandre and Fert, 1954) Forchheimer, 1972 Retecapsa crenulata (Bramlette and Martini, 1964) Grün in Grün and Allemann, 1975 Retecapsa ficula (Stover, 1966) Burnett, 1998 Retecapsa surirella (Deflandre and Fert, 1954) Grün in Grün and Allemann, 1975 Rhagodiscus achlyostaurion (Hill, 1976) Doeven, 1983 Rhagodiscus angustus (Stradner, 1963) Reinhardt, 1971 Rhagodiscus asper (Stradner, 1963) Reinhardt, 1967 Rhagodiscus gallagheri Rutledge and Bown, 1996 Rhagodiscus splendens (Deflandre, 1953) Verbeek, 1977 Seribiscutum primitivum (Thierstein, 1974) Filewicz et al. in Wise and Wind, 1977 Stradneria crenulata (Bramlette and Martini, 1964) Noël, 1970 Tetrapodorhabdus decorus (Deflandre in Deflandre and Fert, 1954) Wind and Wise in Wise and Wind, 1977 Tranolithus orionatus (Reinhardt, 1966) Reinhardt, 1966 Watznaueria barnesae (Black, 1959) Perch-Nielsen, 1968 Reinhardt, 1965 Watznaueria ovata Bukry, 1969 ACKNOWLEDGEMENTS Thanks are extended to Director, Birbal Sahni Institute of Palaeobotany, Lucknow for working facilities. 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H.), Cushman Foundation for Foraminiferal Research Special Publication, 13. Roth, P. H. and Bowdler, J. L Middle Cretaceous calcareous nannoplankton biogeography and oceanography of the Atlantic Ocean. Society of Economic Palaeontologist and Mineralogist Special Publication, 32: Roth, P. H. and Krumbach, K. R Middle Cretaceous calcareous nannofossil biogeography and preservation in the Atlantic and Indian Oceans: implications for palaeoceanography. Marine Micropaleontology, 10: Singh, N. P Mesozoic-Tertiary biostratigraphy and biogeochronological datum planes in Jaisalmer Basin, Rajasthan. XVI Indian Colloquium on Micropalaeontology and Stratigraphy: Singh, P Ostracoda from the subsurface Cretaceous strata of Manhera Tibba well-a and Shahgarh well-b, Jaisalmer Basin, Rajasthan, India with special remarks on foraminiferids. Geoscience Journal, 18(1): Sissingh, W Microfossil biostratigraphy and stage-startotypes of the Cretaceous. Geologie en Mijnbouw, 57(3): Street, C. and Bown, P. R Palaeobiogeography of Early Cretaceous (Berriasian-Barremian) calcareous nannoplankton. Marine Micropaleontology, 39: Thierstein, H. R Mesozoic calcareous nannoplankton biostratigraphy of marine sediments. Marine micropalaeontology, 1: Venkatachala, B. S Mesozoic Operculate pollen and their morphology. The Palaeobotanist, 15(1 and 2): Venkatachalapathy, V. and HariKiran, M Albian nannofossils from Melarasur, Tiruchirapalli, Tamil Nadu, India. INA Newsletter, 15(2): 99 (Abstract). Verbeek, J. W Calcareous nannoplankton biostratigraphy of Middle and Upper Cretaceous deposits in Tunisia, southern Spain and France. Utrecht Micropaleontological Bulletins, 16: Wise S. W., Jr Mesozoic and Cenozoic Calcareous Nannofossils recovered by Deep Sea Drilling project Leg 71 in the Falkland Plateau Region South West Atlantic Ocean. Initial Report of Deep Sea Drilling Project, 71: Manuscript accepted February 2013

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