Seismic Geomorphology of Fluvial Systems, Pattani Basin, Gulf of Thailand

Abstract

During the last decade seismic geomorphology has become a key tool for the analysis of a wide spectrum of depositional settings from fluvial to deepwater environments. This study uses a seismic geomorphology interpretation of a shallow 3-D seismic data set in the southern Pattani Basin, Gulf of Thailand to analyse the fluvial dominant Recent to Upper Miocene succession. This shallow section has been interpreted in previous studies to have similar depositional geometries to the deeper fluvial reservoirs in the prospective Middle to Lower Miocene section within this basin. Fluvial geomorphologic features are well imaged in the seismic data and the objective of this study is to document the distribution and depositional architecture of these fluvial systems in order to better understand the controlling factors on sand body geometries. Wide variations in fluvial style were found, from interpreted distributary channel and estuarine deposits in marginal marine environments in the Upper Miocene section to lowstand incised valley dominant systems in the Pleistocene. In this younger section large meandering river systems develop in relatively confined incised valleys with well developed point bars deposited within this physiographic setting. Associated tributary valleys down cut into broad pre-existing fluvial plains. Controls on channel style in these systems are predominantly related to changes in fluvial discharge rate associated with climate change in the Pleistocene which is linked to the high frequency, high amplitude sea level changes during this time. The question is, are these fluvial systems and their controls representative of the deeper Middle to Lower Miocene prospective section? In contrast, sea level changes in the Upper Miocene were relatively minor and marginal marine fluvial features such as estuarine and distributary channel geometries are well preserved and more evident. During this time, low amplitude relative sea level changes are interpreted to be the main control on fluvial accommodation space and incised valleys are less prominent. Broad coastal plains with unconfined fluvial systems are more prevalent. We interpret these conditions to be more representative of the factors controlling reservoir geometries in the prospective Middle to Lower Miocene. The fluvial systems in the shallow section of this study are not good analogues for deeper prospective fluvial systems in the Pattani Basin as previously suggested.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015