Sediment dispersal and tectonic accommodation in the Gaoping Slope, Southwestern Taiwan

The Gaoping Slope offshore southwestern Taiwan is a tectonically active fold-and-thrust belt where numerous mud diapirs and submarine canyons have developed. Several types of contractional basins are formed due to regional convergent tectonics and mud diapirs, namely slope basin, piggy-back basin and intraslope basin. Most of the sediments discharged from the Taiwan mountain belt were transported to deep sea by large submarine canyons, such as the Gaoping Canyon, and the rest are deposited on the Gaoping Shelf and Gaoping Slope. The complex system of faults, basins, canyons and diapirs form different accommodations in the Gaoping Slope region. Active tectonic activities and sediment feeding by submarine channels are influencing factors in sediment dispersal as well. This study attempts to examine the linkage between accommodations of tectonic and sedimentary processes in the Gaoping Slope, using seismic facies analyses, acoustic images, and high resolution bathymetric data. Previous studies have shown that about 80-90% discharged sediments were transported to deep-sea through the Gaoping Canyon, only about 10-20% discharged sediments were deposited on the shelf and slope area. Four seismic facies have been recognized in the Gaoping Slope basin strata which suggest that filling-and-spilling is a key process during slope development. Because of the competition between regional tectonism and the sediment routing distance from provenance to depository, deposition rate in the southern part of the Gaoping Slope is slower than that of basin subsidence. In this way, most under-filled basins occur in the southern Gaoping Slope, while the basins in the northern part of the Gaoping Slope are overfilled or “healed”. Morphologically, the Gaoping Canyon delimits these two different types of accommodations spatially. Submarine channels also affect the accommodation space of the Gaoping Slope. They are generally confined in the unfilled basins, producing knickpoint incision, channel meandering and levees overfilling. In this kind of buried paleo-channel system, deposits contain a considerable amount of sand could form good gas hydrate reservoir in the Gaoping Slope area.