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Neogene Silicoflagellates from Deep Water Sediments of Mahanadi Basin and Their Significance in Hydrocarbon Exploration

Anand Gupta
Palynology Division, Oil and Natural Gas Corporation Limited, Dehradun, India

Silicoflagellates are the marine unicellular algae with characteristic flagella, and commonly preserved in Upper Cretaceous to Holocene sediments. Studies of silicoflagellates are very useful in dating of sediments where particularly other microfossils are absent. In addition, silicoflagellates are the best indicators of sea water temperature and thus provide a tool to infer paleotempratures.

Mahanadi Basin is one of the five passive margin sedimentary basins situated along the east coast of India. The early drift stage of the basin was marked by the deposition of Late Cretaceous clastics over the volcanic sequences. The late drift stage is represented by Paleogene and Neogene carbonate / clastics sequences which are unconformably overlying on the early drift sequences.

The recovered silicoflagellates from the deep water Neogene sediments in a well Mahanadi Offshore-A, consist of two age-marker taxa, viz, Dictyocha and Distephanus with thirteen species. The taxa recorded between 1465-1530m depth intervals are Distephanus speculum patulus, Distephanus speculum pentagonus, Dictyocha flexatella, D. hessii, D. perlaevis, D. pulchella, D. aspera D. pumila, D. perlaevis, D. longa, D. fibula and D. longa paxilla. The assemblage closely compares with the D. pulchella Zone of Middle to Late Miocene.

General paleotemperature trends of silicoflagellates can be assessed by the relative abundances of warm-water Dictyocha and cool-water Distephanus. Most of the species/subspecies recorded belong to the genus Dictyocha, suggesting warm waters realm. The technique of paleotemperature analysis based on silicoflagellates and the study of both the paleogeothermal gradient and porosity-depth relationships in a basin make possible interpretation of hydrocarbon pools in the exploration area.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery