New Perspectives on the Stratigraphy of the Andaman Trough, offshore North Sumatra, Indonesia. Utilising Modern Quantitative Biostratigraphical Analysis, Integrated with Newly Acquired 3D Multi Client Seismic Data

Abstract

The Andaman Trough, located offshore North Sumatra is currently defined as an emerging basin for exploration. Its location primarily in a remote deep-water environment has resulted in limited well data being acquired to date and although there has historically been abundant seismic data, imaging of pre-Miocene stratigraphy has been poor. New seismic data, including the regional PGS NSMC3D and proprietary and multi-client 2D reprocessed data, combined with high resolution biostratigraphical analysis, has enabled extrapolation of the stratigraphy from the well explored and established shelfal areas down into the deep-water areas. To establish the high-resolution stratigraphic framework, paleo-environment, and paleo-climate for the well penetrations in the Andaman Trough, re-evaluation of quantitative and semi-quantitative abundance charts based on nannofossil, micropaleontology, and palynology zonation and sequences was conducted. Integration of this updated biostratigraphic analysis with interpretation from the modern regional seismic datasets enabled the identification of and confirmation of sequence boundaries and flooding surfaces across the Andaman Trough. Insights into timing of rifting, uplift, and erosion were made, as well as an interpretation of depositional environments, paleo-bathymetry and paleo-climate throughout the Andaman Trough. Significant findings include the chronostratigraphic separation of Late Oligocene Parapat fluvialtile deposits from the overlying Bampo marine turbidites, absent or incomplete Bampo Formation penetrated by some wells, as well as the delineation of a previously unidentified Eocene unconformity and revised timing of basin formation. Further insights into source rock development for the Eocene stratigraphic package were also developed.