Zhi-Qiang Feng¹, P Corbett², T Astin³

(1) Research Institute of Daqing oilfield, N/A, China
(2) Heriot-Watt University
(3) Reading university

ABSTRACT: Shelf slope, an important control on river channel evolution: comparison of Quaternary river channel in the Gulf of Thailand and in the Gulf of Mexico

Both in the Gulf of Thailand and in the Gulf of Mexico, within the top 100-m sediments, the internal architecture of Quaternary sequences and river channels can be seen in high resolution seismic profiles (about 800-4000 Hz) and time slices (about 10 to 100Hz) over large areas. In both sites, a typical sequence, is about 10 m thick and is composed of lowstand incised valley fills, marine transgression muds and highstand aggradational floodplain deposits. The sequence construction is primarily controlled by relative sea level changes (100-ky Milankvitch cycles). Although both have large quantities of meander channels and point bars, channel evolution is different from each other.

In the Gulf of Thailand, all large channels, or valleys, incise into previous sequences, which were developed during lowstand, and which evolve from small, tributary drainage systems to large, regular, meandering channels. Channel patterns remain simple and point bars are isolated from each other. On contrast, in the Gulf of Mexico, large meandering channel present both within the highstand and lowstand deposits. There are fewer undeveloped drainage systems and meandering channels are more developed and associated with more ammelgrated point bars.

The differences are interpreted as caused by the difference in shelf slope. The shelf slope in the Gulf of Mexico (about 0.0013) is 6.5 times higher than in the Gulf of Thailand (about 0.0002). During highstand, with low shelf slope large rivers may disperse to fine-grained anastomosing rivers, whereas, with high shelf slope large rivers may keep pace with the retreated shoreline. During lowstand, the former has a significant lag time for forming large rivers and deliver coarse-grained sediments across the shelf, whereas, the latter not.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado