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A. Nallapa Reddy ¹, K. Satyanarayana ¹, K. V. Bhaktavatsala ¹, K. Narasimha ¹, M. Nagaraj ¹

Affiliations
1 Regional Laboratory, ONGC Ltd., N.H. Road, Chennai - 600 034, IN

Abstract

Detailed chronostratigraphic biodatums and lithofacies in combination with correlative seismic horizons recognized two 3^rd order depositional sequences designated as Sequence 1 and Sequence 2 in stratigraphic order within Miocene in KD field. The biostratigraphic correlation has brought out that the Sequence 1 in shelf well GS-AD is sandrich and bounded by unconformable sequence boundaries, whereas coeval sequence in slope wells KDA and KDB, bounded by correlative conformities are dominated by clay rich system deposited during highstand sea-levels in earlymiddle Miocene. The clays are planar bedded with glauconite and pyrite nuggets with abundant deepwater benthics in association with shelf derived foraminifera, inferring that these clays were derived into intraslope basins mainly as debris flow/slump process. The Sequence 2 in wells KDA and KDB is represented by multiple sands with mudstone alternations, deposited during lowstand Sea-Levels. Biofacies are mixed with dominantly shelf derived benthics and the tests are commonly broken, abraded and occasionally ferruginised, suggesting reworking into intraslope basins as a result of relative Sea-Level fall during middle and late Miocene. The occurrence of abundant Paleocene to early Miocene dinoflageIlate cyst assemblage are also suggesting reworking process into upper slope by network of active channel system and were redeposited by Gravity-Flow processes into intraslope basins. The present study indicates each intraslope basin acting as an independent petroleum system and matured organic rich Paleogene beds lying at the bottom are contributing hydrocarbons to middle Miocene reservoirs through active growth fault system.

Keywords

KD-Structure, Sequence Stratigraphy, Systems Tracts, Depositional Setting, Krishna-Godavari Basin.

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R. Nagendra ¹, G. Nagendran ¹, K. Narasimha ², B. C. JaiPrakash ³, A. Nallapa Reddy ²

Affiliations
1 Centre for Geosciencc and Engineering, Anna University, Chennai - 600 025, IN
2 Regional Geology Laboratory, Oil & Natural Gas Corporation Ltd., Chennai - 600 034, IN
3 Geology Division, ONGC, Tripura project, Badarghat complex, Agartala - 799 014, IN

Abstract

A sequence stratigraphic framework is worked out for the first time for the Dalmiapuram Formation exposed in Kallakudi quarry near Kallakudi village in Tiruchirapalli District. Thc complete lithological succession of this formation is designated as 'Dalmiapuram Sequence' of latest Albian - Cenomanian age and consists of grey shale, coral/algal limestone and bedded biostromal limestone and marl in ascending order. Grey shale rests unconformably ovcr thc Archaean basement. This contact forms the lower sequencc boundary of Dalmiapuram Sequence. The middle lithounit, the coral algal limestone rests ovcr grey shale. This unit abruptly grades into bedded limestone/marl alternations. This abrupt termination of coral algal limestone may be due to relative sea level rise and possibly this surface represents 'drowning unconformity'. The upper lithounit, which has alternating bands of biostromal limcstonc and marl, might indicatc cyclic carbonate precipitation (?Milankovich cycles). This unit is unconformably overlain by Neogene Cuddalore sandstone. This unconformity surface represents the upper boundary of the sequencc. The entire Dalmiapuram Sequence appears to have been deposited as Transgressive Systems Tract (TST) dcposit and got exposed as a result of basinal rise.

Keywords

Sequence Stratigraphy, Dalmiapuram Sequence, Albian-Cenomanian, Kallakudi, Tamil Nadu.

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