Tectonic features and BSR distribution off SW Taiwan
Speaker: Tsung-Yu Shih
Abstract
Offshore southwest Taiwan, a west-advancing orogenic wedge has obliquely impinged on the northern continental slope of South China Sea margin. Therefore, the collision between accretionary wedge and continental slope form many complex tectonic features offshore SW Taiwan. Authors use the multichannel seismic data from 2002 to 2005 which are collected by R/V OR1 and other seismic data which are collected by different research vessels to interpret the tectonic features and BSR distribution.
In western half of continental slope, a series of Paleogene rift structures are buried by 3-4 km thick sediments. Seismic data show that the Miocene sediments beneath the shelf have a series of normal faults which are related to two post-breakup extensional events. The Pliocene-Pleistocene succession exhibits progradation and aggradation on upper succession and aggradation on lower succession. The BSR distribution is less in this region because of absent deep-cutting fault. The gas migrates mainly by diffusion. In eastern half, the major features are a deep-cutting listric normal fault and tilted hangingwall beds. The BSR distribution is abundant more than western half because of the deep-cutting normal fault. Gas can migrate upward along decollement and tilted beds.
In accretionary wedge, it can divide into upper slope, rear segment and frontal segment. Upper slope exhibits more gentle relief and exists many mud diapiric structures because of higher sedimentation rate. Many emergent thrust faults and blind faults which form anticlines and homoclines are discovered in rear segment. In frontal segment, only blind faults and anticlines are found. The BSR distribution in rear segment is more than frontal segment due to the emergent thrust fault and canyon cutting. Deeper thermogas and shallow biogas can migrate along the fracture zone to GHSZ only in rear segment. And many canyons cut across the frontal segment, the biogas may leak through the erosional gullies.
Reference
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Lin, C.-C., Lin, A.T., Liu, C.-S., Chen, G.-Y., Liao, W.-Z., Schnurle, P., 2009. Geological controls on BSR occurrences in the incipient arc-continent collision zone off southwest Taiwan. Mar. Geol. 26, 1118-1131.