Zhi-Qiang Feng1, TR Astin2, PWM Corbett3
(1) Research Institute of Daqing Oilfield, N/A, China
(2) Reading university
(3) Heriot-Watt University
ABSTRACT: Characteristics of the Quaternary sequences and channels in the Gulf of Thailand
Three dimensional sequences of Quaternary river channels and point bars can be clearly seen in high quality boomer seismic profiles, engineering boreholes, and three-dimensional seismic data from the Gulf of Thailand. The geometry, stacking patterns and in some cases the internal geometry of sandbodies can be mapped over an area of about 2000 km2. Eight stratigraphic sequences, identified in earlier studies, have been mapped. A typical Quaternary sequence in the Gulf of Thailand is about 13 m thickness. Each sequence has lasted about 100-ky, and is composed of lowstand incised valley fills, marine transgression muds, highstand progradation marine shelf wedges and aggradational floodplain deposits.
Only small (normally less than 100 m wide) channels were identified in the highstand floodplain deposits, which may relate to small meandering, or anastomosing rivers. All large channels, or valleys, incised into previous sequences, are related to relative sea level fall and lowstand, during which, deposition of sediments (including point bars) was restricted to within incised valleys. The lowstand channels evolve from small, tributary drainage systems to large, regular, meandering channels, and no associated levee, or crevasse splay, and only one ox-bow lake, was identified. The lowstand point bars remain isolated from each other. Their volume within the last five Quaternary sequences averages three percent. This volume varies widely from sequence to sequence because of a) variation in the duration of lowstand, and b) the location of major rivers relative to the study area. Lack of more complex channel pattern may due to the duration of lowstand limiting the development of river channel evolution. Channel density and position tend to reflect tectonic subsidence pattern.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado