Seismic Geomorphology and High-Resolution Seismic Stratigraphy of Inner Shelf Fluvial, Deltaic, and Marine Sequences, Gulf of Thailand
Pleistocene fluvial, estuarine, marine, and deltaic depositional systems were identified in the uppermost 120 m of the central Gulf of Thailand modern continental shelf, situated at ~70 meters below sea level. Integration of offshore 3D seismic reflection data, high-resolution, shallow-penetration 2D seismic reflection sparker and boomer profiles, and 1D shallow geotechnical borehole measurements enabled the identification of seven depositional sequences.
3D plan-view images at successive time slices exhibit single meandering channels (up to 900 m wide) and channel belts (up to 10 km wide) deposited on the shelf during times of subaerial exposure. Additional geomorphic features imaged include incised valleys, interfluves, oxbow lakes, neck and chute cut-offs, and point-bar meander scrolls showing evidence of expansion and translation. The high-resolution 2D profiles with a tuning thickness of ~25 cm, enabled the discrimination of high frequency stratigraphic discontinuities (sequence boundaries) and allowed a detailed bed-scale seismic facies characterization of fluvial point bars, deltaic clinoforms, estuarine, and marine deposits within a sequence stratigraphic context. The complete succession shows that most fluvial systems lie within incised valleys in the lower portions of each depositional sequence, channel belts cut into older sequences, and there is no evidence of multi-storey fluvial aggradation; overall aggradation is limited to hemipelagic sedimentation during marine incursions. Such features are described both in plan view as well as in section view.
A shallow (< 35 m) single-storey, incised valley was described in detail, placing particular emphasis on the recognition criteria, and the controls on valley formation and preservation potential of different systems tracts in an inner shelf location. Evidence of tidal influence in the downstream portion of the valley suggests the presence of a nearby paleo-shoreline.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009