Reconstruction of the gross depositional environment evolution in the northern Malay Basin, Malaysia-Thailand joint development area (MTJDA)

Abstract

This paper provides new insight on the complex interactions between regional tectonic evolution, differential subsidence across the basin, and variation in sediment supply based on a reconstruction of the gross depositional environment in the northern part of Malay Basin. In addition, the variation in sedimentary facies, established from an integrated analysis based on seismic interpretation, well-log analysis, and core evaluation, are used to establish the gross depositional environment for key surfaces within the Oligocene to Miocene succession.The basin fill comprises Oligocene syn-rift and Miocene post-rift successions. The syn-rift successions are Syn-Rift Unconformity (SRU)-Base of Syn-Rift (BSR), and Base Chattian Unconformity (BCU)-Syn-Rift Unconformity (SRU) sequences. Whereas, the post-rift successions represent by Intra-Aquitanian MFS (IAM)-Base Chattian Unconformity (BCU), Intra-Burdigalian MFS (IBM)-Intra-Aquitanian MFS (IAM), Miocene Transgressive-Regressive (MTR)-Intra-Burdigalian MFS (IBM), Intra-Serravalian MFS (ISM)-Miocene Transgressive-Regressive (MTR), and Intra-Tortonian (ITM)-Intra-Serravalian MFS (ISM) sequences.The Oligocene-early Miocene syn-rift succession in the study area is characterized by aggradational stacking patterns, with an indication of retrogradation in individual sand packages for SRU-BSR, and BCU-SRU intervals, whereas an overall aggradational stacking pattern can be observed within the IAM-BCU sequence. The depositional environment of the syn-rift succession is mainly deltaic, fluvial, alluvial fan, shallow and deep lacustrine at the basin center.The early-middle Miocene post-rift succession is characterized by mostly aggradational and fining upwards stacking within the IBM-IAM sequence. This gradually changed to a retrogradational pattern in the MTR-ISM sequence. Depositional environments for this succession consist of an alternation between fluvio-marine and sub-tidal to marine sedimentation. Depositional environments for the overlying late Miocene Intra-Tortonian to Intra-Serravalian (ITM-ISM) was estuarine or tidally-influenced environments comprising fluvial channel, tidal or distributary channel, tidal sand flat, and tidal flat deposition. This interval mainly consists of coarsening upward units that gradually changed to a stacked higher-order fining upwards package. The deeper stratigraphic units are generally more continental (non-marine) in character, but fluvio-tidally influenced marine environments became more dominant in the shallower sequences.