Tectonic Control of Channel Morphology and Orientation in the Gulf of Thailand
Lambiase, Joseph; Ahmad, Naseer; Wainuson, Parichat; Paramita, Dini; Thongsang, Pongthep; Priyanto, Bagus
Six tectono-stratigraphic units ranging in age from early Oligocene to Pliocene that represent the syn-rift, post-rift and transitional phases of two distinct rifting events were identified in each of two separate basins in the Gulf of Thailand. The units vary considerably with respect to subsidence rates, basin-scale paleo-geography and the style of faulting at the time of deposition. Syn-rift units occur within rapidly subsiding, fault-bounded half-grabens with internal block faulting. Transitional units also occur within half-grabens but subsidence rates are substantially lower and nearly all the extension and subsidence are focused along one dominant basin-bounding fault. Faults persist into the early post-rift succession which forms basin-scale sags, while the late post-rift is not faulted and has a down to the southeast, regional subsidence geometry.
It has long been recognized that the strongly non-marine stratigraphic succession includes a large number of fluvial channels and, more recently, they have been successfully imaged with advanced seismic imaging techniques. The present study used seismic inversion, spectral decomposition and seismic attribute analysis to image channel size, shape and orientation in numerous stratal slices. Seismic inversion and full spectrum seismic attribute analysis could only image channel geometries for relatively shallow depths (up to1500 m), whereas spectral decomposition techniques successfully imaged channel systems at greater depths.
Channel width, sinuosity and orientation vary considerably, yet preliminary results indicate a relationship between basin evolution and channel geometry. Generally, syn-rift channels are relatively small with low sinuosity and are oriented approximately parallel to the basin axis, reflecting structural control by block faulting and relatively high stream gradients. Conversely, channels tend to be relatively wide and highly sinuous in transitional and, especially, post-rift units because of lower subsidence rates. Most channels are basin-parallel in units without syn-depositional faulting, although the proportion of basin-oblique and basin-perpendicular channels is higher than in the syn-rift. The orientation of some post-rift channels coincides with regional drainage patterns and others indicate internal drainage associated with basin-scale sags. Relatively wide, straight channels with flared downstream ends suggest minor marine influence in specific stratigraphic intervals.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013