Agglutinated Foraminiferal Proxies to Identify Organic Rich Sediment Facies in the Krishna-Godavari Basin, India
Addula N. Reddy1, Kotha Yadagiri2, B. C. Jaipraksh3, and L. Chidambaram1
1Regional Laboratory, ONGC, Chennai, India
2Geology Division, ONGC, Rajahmundry, India
3Forward base, ONGC, Karaikal, India
The study analyses Early-Middle Eocene sediments to build biostratigraphic framework and elucidate possible relationship between faunal assemblages vis-à-vis organic flux at four well sections in the East Godavari subbasin of the Krishna-Godavari Basin.
Agglutinated foraminiferal assemblage dominated by a single genus Cyclammina. It occurs in Early to Middle Eocene sediments in four well sections in the East Godavari subbasin. Stratigraphically, Cyclammina abundance is associated with planktic foraminifera: Morozovella aragonensis, Globigerina lozanoi, Acarinina pentacamerata, A.soldadoensis, Turborotalia cerroazulensis and Truncorotaloides rohri of P9-P11 planktic zones. The estimated TOC values range from 2-4.5% in these sediments.
The frequency of agglutinated foraminifera varies from site to site and also within planktic zones. The abundance of agglutinated benthic foraminifera exhibits close relationship with relatively high TOC values. This possibly suggests that high organic flux has a bearing on the distribution of agglutinated foraminifera. High organic flux rates (TOC >2%) may be attributed to relative rise in sea-level during Early-Middle Eocene. As a result, the increased surface organic productivity has facilitated the flourishing of Cyclammina. The black color and pyritised nature of agglutinated tests also reflect oxygen minimum conditions at sediment/ water interface. The low oxygen content might be another factor in association with high organic flux that constrained the abundance of agglutinated taxa.
The study establishes a close relationship between agglutinated foraminiferal abundance and the TOC content of the sediment. This characteristic can serve as reliable proxy to delineate organic rich facies in the absence of experimental TOC data.
Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery