ABSTRACT: Source Rock Sequence Stratigraphy - A Test for Lake Basin Connectivity in an Active Rift System

Lomando, A.J.¹, S. Teerman¹, R. Bate², R. Wang¹, J. Dahl¹, S. Sundararaman¹, M. Schoell¹
(1) Chevron Overseas Petroleum Inc, San Ramon, CA
(2) Lacustrine Basin Research Ltd, United Kingdom

Significant issues arise when source rock systems are related and correlated within complex lacustrine active rift settings that may contain multiple subbasins. A question for stratigraphy and source rock risk assessment is determining when a lacustrine system behaves as one basin/lake system and when does it behave as segmented or compartmentalized subbasin systems. Lithofacies based regional correlation can be tricky. This is due to differential subsidence from subbasin to subbasin, which influences lake depth and drainage basin configuration and therefor variations in accumulation rates and the stability of anoxic conditions. This most often occurs when major fault transfer zones are crossed. Suboxic to anoxic changes that impact quality and composition of organic matter appear to be cyclic in continuous well data sets. These characteristics can be related to a number of factors usually focusing on climate, and variations in subsidence history between subbasins through a sequence stratigraphic approach. High quality/high resolution biostratigraphic data allows geochemical data sets (TOC, Rock Eval S2, etc.) to be placed in a time-stratigraphic framework. Construction of Wheeler (time-stratigraphic) charts from geochemical cycle data permits comparisons within and between subbasins. The time relationship between cycles, duration of cycles, accumulation rates and components of basin history can then be evaluated and compared from subbasin to subbasin.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia