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

Arun Kumar ¹

Affiliations
1 Palynologist, P. T. Corelab Indonesia, 303, Cilandak Commercial Estate, Jalan Cilandak KKO, Jakarta 12560, ID

Abstract

A list of dinocysts is provided for the Jhura Dome Section (Jhurio Formation of Upper Bathonian to Callovian age) and Khari Nadi Section (Middle Member of the Jhuran Formation of Lower Kimmerdgian to Tithonian age) of Kachchh. These dinocyst assemblages are compared with the assemblages of dinocysts of equivalent age described from different parts of the world. A new dinocyst Forma-A is described from the Jhura Dome section.

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Pratul Kumar Saraswati ¹, Arun Kumar ²

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076
2 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076, IN

Abstract

Analysis of an Indo-Pacific species, Lepidocyclina (Nephrolepidina) sumatrensis shows that the protoconch diameter varies with latitude. The data plotted on the reconstructed continental positions for the Miocene epoch shows that forms away from the equator are characterised by progressively larger protoconch diameter. An average value of protoconch diameter >200μ is seen to occur from 15° to 30° latitude while those with <200μ are confined within 15° latitude. This observation can have potential use in inferring the climate of the geological past.

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Arun Kumar ¹, Pratul Kumar Saraswati ¹

Affiliations
1 Dept. of Earth Sciences, Indian Institute of Technology, Powai, Bombay-400076, IN

Abstract

Electron microscopic studies are carried out to examine wall structure, stolon and canal system of Heterostegina, Operculina and Spiroclypeus from the Late Oligocene section of Kutch. Walls are made of preferentially oriented prismatic crystals of calcium carbonate while septa contain randomly oriented polygonal crystals. Heterostegina and Spiroclypeus are characterised by Y-shaped radial stolons in the median plane. Canal system, comprising of marginal, septal and secondary septal canals are described and illustrated.

Keywords

Nummulitidae, Oligocene, Kutch, Gujarat.

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D. S. N. Raju ¹, B. C. Jaiprakash ¹, Arun Kumar ¹, R. K. Saxena ¹, Alok Dave ¹, T. K. Chatterjee ¹, C. M. Mishra ¹

Affiliations
1 Geological Laboratories, KDM Institute of Petroleum Exploration, ONGC, Kaulagarh Road, Dehra Dun - 248195, IN

Abstract

The latest Paleontological data suggest that the duration of Deccan trap eruption in Krishna-Godavari basin varies from place to place and could be anywhere between <0.5 Ma and 6 Maacross KTB. Three groups of fossils viz., Planktic foraminifera, Nannoplanktics and Dinoflagellate cysts suggest that the initiation of volcanism was during latest Maastrichtian within the upper part of Abathomphalus mayaroensis Zone, Micula murus Zone and Triblastula utinensis Zone between 67 and 66.5 Ma. There are conflicting evidences in dating the upper age limit of the volcanics probably due to diverse methods employed in calibration of forarniniferal and nannoplanktic scales or selective retrieval of very small sized planktics of zones P0 and P1 in well cuttings.

Keywords

Micropalaeotogy, Deccan Volcanism, Age, Krishna-Godawari Basin.

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Arun Kumar ¹, D. S. Ratha ², Partha Nandy ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Bombay - 400 076, IN
2 Centre of Studies in Resource Engineering, Indian Institute of Technology, Bombay - 400 076, IN

Abstract

Tertiary carbonates from Kutch have been analysed for chemical constituents such as Ca, Mg, Mn, Fe, Sr, Ba and insoluble residue. Vertical distribution of these elements shows a gradual decrease in Ca and Sr and increase in Mn, Fe, Ba and insoluble residue from older to younger beds. R-mode factor analysis of chemical data is interpreted. The first factor loaded on IR-Mn-Fe-Ba is considered to be the effect of clastic deposition, chemical co-precipitation and adsorption by clay minerals. The second factor loaded on Ca, Sr, Ba and Mg explains their syndeposition, leading to the formation of limestones.

Keywords

Carbonates, Sedimentology, Statistical Geology, Kutch, Gujarat.

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