Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

A. D. Singh ¹, M. S. Srinivasan ²

Affiliations
1 Marine Geology Division, School of Marine Sciences, Cochin University of Science and Technology, Cochin 682016, IN
2 Departrnent of Geology, Banaras Hindu University, Varanasi 221005, IN

Abstract

Qualitative and quantitative planktic foraminif∼raal nalyses of the Central Indim Ocean DSDP Sites 237 and 238 provided 34 important events during the Neogene. A comparison of the chronoIogica1 succession of ihese planktic foraminiferal events, with the other tropical Indian Ocean and Southwest Pacific DSDP Sites reveals remarkable similarity. Therefore, these Neogene foraminiferai events [First Appearance (FA) and Last Appearance (LA)] are considered as synchronous within the tropical Indo-Pacific except Gq. dehiscens LAD, Gr. margaritae FAD, range of Gr. tumidaflexuosa, Gr. crassaformis FAD, Gr. truncatulinoides FAD, and Gs. obliquusLAD, which are diachronous reflecting their paleobiogeographic control. Stratigraphic ranges of planktic foraminifera enabled recognition of 20 zones from the late Early Miocene to Pleistocene.

Two hiatuses (NH3 at Site 238 and NH4 at Site 237) associated with severe carbonate dissolution were identified. These hiatuses havealsobeen recordedatabout the same stratigraphic intervals in several deep sea sections in the Pacific and represent an important oceanographic event, useful for inreroceanic correlation.

Keywords

Micropalaeonloiogy, Planktic Foraminifera, Central Indian Ocean, Neogene.

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A. D. Singh ¹

Affiliations
1 Marine Geology Division, School of Marine Sciences, Cochin University of Science and Technology, Cochin-682016, IN

Abstract

The evolutionary gradation and ancestor-descendant relationship within planktic foraminiferal lineages Neogloboquadrina, Pulleniatina and Sphaeroidinellopsis-Sphaeroidinella, from DSDP sites 214, 219 and 237 (Northern Indian Ocean) are discussed. The study suggests that the evolutionary diversification among these lineages are closely linked with the major oceanographic changes during the Neogene. The phyletic lineages are placed within chronologie framework in order to find out the reliability of vital taxa of these bioseries for biostratigraphic correlation.

Keywords

Planktic Foraminifera, Micropaleontology, Northern Indian Ocean.

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A. D. Singh ¹

Affiliations
1 Department of Marine Geology and Geophysics, Cochin University of Science and Technology, Cochin-682016, IN

Abstract

Planktic foraminifera and pteropods were analysed qualitatively and quantitatively from two gravity cores recovered from the shelf off northern Kerala representing the past - 23 Ka record. Based on the temporal variation in the composition of faunal assemblages, oceanographic and climatic changes during late Quaternary are interpreted. A time-series of the monsoonal-upwelling indices suggests that between - 23 to 18 Ka BP minimum upwelling and weaker monsoon occurred. This period was followed by a gradual increase in the intensity of upwelling and monsoonal strength during - 18 to 15 Ka BP. After a breif interval of weak monsoon, it intensified again from -12 to 10 Ka BP. The southwest monsoon was weaker from - 5 Ka BP with minor fluctuations in its strength. The study also reveals that pteropod shells made up of aragonite (highly solution susceptible) are found in different states of preservation in response to oceanographic changes during the Quaternary. Three kinds of shells subjected to different modes of preservation occur in the cores: (i) transparent shells (excellent preservation), (ii) opaque-white shells and (iii) molds with original shells (corrosion and dissolution). The preservation of aragonite shells was excellent between - 23 to 18 Ka BP. Aragonite dissolution is recorded with its maximum from - 17 to 15 Ka BP. The pteropod shells are well preserved during Holocene.

Keywords

Micropaleontology, Planktic Foraminifera, Pteropods, Quaternary, Paleoceanography, Arabian Sea.

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A. D. Singh ¹, N. R. Nisha ¹, K. K. Ramchandran ²

Affiliations
1 Department of Marine Geology and Geophysics, Cochin University of Science and Technology, Cochin-682016, IN
2 Centre for Earth Science Studies, Akkulam, Trivandrum -695031, IN

Abstract

Four gravity cores from the shelf off the southwest coast of India were studied in detail for various microfaunal and sedimentological parameters The study enabled to establish chronostratigraphic subdivisisons in two late Quaternary outershelf sediment cores using stable oxygen isotopes foraminifera and pteropod records and Iithological characteristics combined with the radiocarbon dates The Innershelf cores display two distinct benthic foraminiferal biofacies and corresponding hthofacies representing the late Pleistocene and the Holocene periods The investigation indicates that the planktic forarninifera/ benthic foraminifera ratio, pteropods/planktic foraminifera ratio, absolute abundance, species diversity and epifaunal/infaunal ratio In benthic foraminifera1 population can be potential criteria for biostratigraphic subdivisions in shelf sedimentary records which are mainly expressions of past changes in sea level and environmental condlt~onsD own-core vanatlon in benthic foramin~ferarle cordsreflects changes In bathymetry and environmental conditions associated with sea level variation and glacial interglacial boundary conditions in the last 23 kyr Foraminiferal and sedimentological records further indicate a probable existence of paleoestuary In the study area.

Keywords

Quaternary, Foraminifera, Paleoenvironment, North Kerala coast.

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A. D. Singh , D. Kroon , R. S. Ganeshram

Abstract

No Abstract.

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A. D. Singh ¹, D. Kroon ², R. S. Ganeshram ³

Affiliations
1 Department of Marine Geology and Geophysics, Cochin University of Science & Technology, Kochi 682 016, IN
2 Institute of Earth Sciences, Free University de Boelelaan 1085 HV Amsterdam The Netherlands, NL
3 School of Geosciences, University of Edinburgh, Edinburgh EH9 3JW, Scotland, GB

Abstract

We studied high -resolution microfaunal (absolute abundances of planktic foraminifera and pteropods and relative abundance of G bulloides) and geochemical(C_org wt %) proxy records in a well-dated core (SK-17) from the present day Oxygen Minimurn Zone (OMZ)) In the Indian margin off Goa, to infer the varabi1tty of productivitya nd OMZ intensity in the last 30 ka The microfaunal and geochernical proxy records indicate three distinct regimes of monsoon-related varablility, viz, thelate glacial, the deglacial and the Holocene The late glacial records exhbit millennial scale changes, for e g , low productivity duribg the cold Heinrich Events, which can be llnked with a weaker SW monsoon Our record demonstrates a generally low productivlty during the deglacia1 period from Termination IA to the beginning of the Holocene The biological productivity was higher in the Late Holocene as evidenced by the well larninated sediments with high contents of C_org and planktic foraminifera The record of preservation and loss of aragontic pteropod shells In core SK 17 1s linked with vanations in the OMZ intenstty and Aragonite Compensation Depth (ACD) The core site appears to have remained below the ACD since 7 ka The pteropod abundance maxima of the Heinrich periods and the Younger Dryas (YD) suggest a weaker OMZ and deeper ACD during these periods The chronology of these millennial scale cycles indicates that they are synchronous with nsuch events recorded in the western Arabian Sea.

Keywords

Late Quaternary, Eastern Arablan Sea, Monsoon, Productivity, Oxygen Minimum Zone.

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A. D. Singh ¹

Affiliations
1 Department of Marine Geology and Geophysics, Cochin University of Science and Technology, Kochi - 682 016, IN

Abstract

No Abstract.

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A. D. Singh ¹

Affiliations
1 Dept. of Geology, A. D. SINGH Banaras Hindu University, Varanasi - 221 005, IN

Abstract

No Abstract.

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A. D. Singh ¹

Affiliations
1 Department of Marine Geology and Geophysics, Cochin University of Science and Technology, Cochin - 682 016, IN

Abstract

Praeorbulina glomerosa (Blow), Praeorbulina sicana (de Stefani), Globigerinoides diminutus Bolli are recorded for the first time from the Quilon Formation in a subsurface section at Quilon. These planktic foraminifera are considered as diagnostic forms of the Early-Middle Miocene. Two biostratigraphic subdivisions were established based on the detailed qualitative analysis of planktic foraminiferal assemblages. The co-occurrence of Gs. diminutus and Gs. alttapertura Bolli and the absence of Praeorbulina Olsson in the assemblages of the lower portion of the section suggest this part to be referable to Globigerinatella insueta Zone of Bolli (1966), which is of late Early Miocene age. The assemblages from the upper part of the section are characterised by the presence of Praeorbulina glomerosa, P. Sicana and Gs. diminutus, representing early Middle Miocene Praeorbulina glomerosa Zone of Srinivasan (1989). The Praeorbulina glomerosa Zone (=Zone N8) lies within the European Langhian Stage, whereas the Globigerinatella insueta Zone (=Zone N7) corresponds to the upper part of the Burdigalian Stage. Thus, the stratigraphic age of the Quilon Formation is late Early Miocene to the earliest Middle Miocene (upper Burdigalian to lower Langhian) and not Burdigalian as previously inferred by many workers.

Keywords

Micropalaeontology, Planktic Foraminifera, Quilon Formation, Kerala.

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