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R. K. Saxena ¹, Syed A. Jafar ²

Affiliations
1 Palynology Laboratory, Geology Division, KDMIPE, ONGC, Dehradun-248195, IN
2 5B Whispering Meadows, Haralur Road, Off Sarjapur Road, Bangalore-560034, IN

Abstract

Late Bathoman - Callovian - Oxfordian - Early Kimmendgian siliciclastic sediments of some prominent sections of Kachchh Mainland Jumara, Basal Jumara, Ler, Kanthkot, including Kuldhar Member of Jaisalmer Basin, contain discrete succession of Calcareous Nannofossil assemblage encompassing Standard Jurassic Zones NJ12 Ansulasphaera helvetica, NJ13 Stephanohthion bigotu bigotu, NJ14 Stephanolithion bigoti maximum and NJ15 Cyclagelosphaera margerelu. The Calcareous Nannofossil Zones and Events are tied to Boreal and Indian part of Tethyan Ammonite zonation 33 species of Calcareous Nannofossils were documented from the Bositra (=Posidonia) bearing basal dark grey shales of Jumara (=Chan) Formation exposed at the type area of Jumara Dome.

Keywords

Calcareous Nannofossils, Late Bathoman-Early Kimmendgian Biostratigraphy, Kachchh-Jaisalmer Basins.

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Suhas Shetye ¹, Rahul Mohan ¹, Syed A. Jafar ¹, Abhilash Nair ¹, Shramik Patil ¹, Shridhar Jawak ¹, Rajesh Asthana ², Sahina Gazi ¹

Affiliations
1 National Centre for Antarctic and Ocean Research, Headland Sada, Goa 403 804, IN
2 Geological Survey of India, Faridabad 121 001, IN

Abstract

Earlier studies have documented the role of diatoms in reducing the diversity and abundance of other silicadependent organisms, such as radiolaria. Here we hypothesize that diatom burst-driven depletion of dissolved silica (Dsi) in the Antarctic under sea-ice waters affects other silica-biomineralizing organisms. We found intense diatom-dominated, ice-edge phytoplankton bloom in the Enderby basin resulting in severe depletion of Dsi (<5 μM) under the sea ice. We also found siliceous sponge spicules within the surface sediment collected from under the Antarctic sea ice. Dominance of small style spicules (170 spicules/g sediment) under the sea ice along with dissolution seen on them, suggests DSi deficiency in the Antarctic waters. We, therefore, conclude that there is a rapid depletion of DSi due to seasonal diatom blooms under sea ice in the Antarctic waters.

Keywords

Diatoms, Dissolved Silica, Sea Ice, Sponge Spicules.

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