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

Ashish Sarkar ¹, Asit K. Guha ¹

Affiliations
1 Department of Geology and Geophysics, IIT, Kharagpur - 721302, IN

Abstract

Paleontologic Time Series (PTS) analysis in both time and frequency domains on eight series of abundance data of Globorotalia menardii and total planktonic foraminifera from top core sections of DSDP Sites 219, 220 and 241 of Northern Indian Ocean depict cyclic variation presumably due to fluctuations in the Pleistocene paleo-temperature. At these sites, the relative dominance of planktonic foraminifera and G. menardii, uniform effect of post-mortem transport on foraminiferal tests of different sizes and differential sediment accumulation rate are revealed from the nature of energy distribution in the spectra, identical nature of major peaks and varying cycle lengths respectively.

Keywords

Paleontologic Time Series (PTS), Deep Sea Drilling Project (DSDP), Pleistocene, Planktonic Foraminifera.

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Asit K. Guha ¹, T. J. Mukhopadhyay ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur - 721 302, IN

Abstract

Nine types of Standard Microfacies (SMF) are identified in the Cretaceous-Paleocene carbonate sequences of the Ariyalur-Vridhachalam of Tamil Nadu and the Pondicherry areas. Of these four SMFs occur frequently.

The recurrence of SMF types within FZ 7 in successive fonnations of varying thickness indicates multiple transgressive - regressive episodes of unequal areal extent and time interval. A gradual decrease in the number of microfacies types in carbonate lithologies younger than the Turonian suggests progressive stabilization of the shelf. Presence of similar SMF in younger carbonate layers belonging to different areas and ages point to their being time-transgressive lithologic units. The carbonates are of low-Mg calcite variety. Significant depletion of Sr and Na and enrichment of Ba, K and Mn took place due to prolonged diagenetic alteration by meteoric water.

Keywords

Carbonate Rocks, Cretaceous, Paleocene, Ariyalur, Vridhachalam, Pondicherry.

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Ashish Sarkar ¹, Asit K. Guha ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur-721302, IN

Abstract

The Quaternary planktonic foraminiferal assemblages from DSDP Sites 219,220 and 241 in Northern Indian Ocean have been analysed in terms of diversity changes along the depth of each core. For an understanding of the population dynamics in the region and its relation to the paleoclimatic events (Ericson zones), relative abundance at family and species levels have been studied. Different indices of diversity viz., S, D, Hand E have been worked out and correlated with that of the oscillation in paleoclimatic record, which is based on the fluctuation in abundance of Globorotalia menardii along the depth of the core. It has been noted that during the Quaternary, relative abundance of different species and changes in diversity indices match well with that of the Ericson paleoclimatic zonation, enabling recognition of different stages of glacial and interglacial episodes in Northern Indian Ocean.

Keywords

Palaeontology, Foraminifera, Palaeoclimate, Quaternary, Northern Indian Ocean.

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Asit K. Guha ¹, K. Gopikrishna ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur - 721 302, IN

Abstract

Five new fossil species, three of the family Steginoporellidae Hincks (Labioporella bassleri, Labioporella hariparensis and Steginoporella bhujensis) and two of the family Schizoporellidae Jullien (Schizoporella sowerbyi and Therenia indica), from the Tertiary sequences of western Kachchh Gujarat are described and illustrated. Significance of the evolutionary, biogeographical and paleoecological aspects of some of these taxa is added.

Keywords

Bryozoa, Cheilostomata, Tertiary, Biogeographical Distribution, Kachchh, Gujarat.

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Asit K. Guha ¹, K. Gopikrishna ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, IN

Abstract

Seven bryozoan species belonging to six genera in five families under the Order Cyclostomata are described and illustrated for the first time from the Harudi Formation (Lutetian) of wcstern Kachchh, Gujarat. They are Stornutoporu illiesae n. sp., Voigtopora reticulata n .sp., Discosparsa lakhpatensis n. sp., ldmindronea sp.,Oncousoecia narediensis n.sp.,' proboscina' sp. and Plagioecia taylori n. sp. Of these five are new to science.

Keywords

Bryozoa, Cyclostomata, Harudi Formation, Lutetian Epoch, species, Kachchh, Gujarat.

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Asit K. Guha ¹, K. Gopikrishna ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur -721302

Abstract

Eight cheilostomate bryozoan species (Aplousina sp., Copidozourzt feddeni n, sp., Crassimarginatella blanfordi n. sp., C. ukirensis n. sp., Marginaria sengrrptai n. sp., Planicellaria kharaiertsis n. sp., P. naliyaensis n. sp. and Reptoporina chhasraensis n. sp. belonging to the family Calloporidae Norman, 1903 are described and jllustsated for the first time from the Tertiary (Lutetian to Aquitanian) sequences of western Kachchh, Gujarat. In the Tertiary bryozoan assemblages of this area, tRis family has the highest generic diversity.

Keywords

Bryozoa, Cheilostomata, Calloporidae, Tertiary, Diversity, Kachchh, Gujarat.

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Asit K. Guha ¹

Affiliations
1 Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur - 721302, IN

Abstract

No Abstract.

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