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DEVELOPMENT OF PLEISTOCENE LIMESTONE ON A MUD-DIAPIR, OFFSHORE SW TAIWAN
Seismic survey off southwestern Taiwan reveals numerous N-S and NW trending submarine ridges and mud diapirs originated from subduction of the Eurasian plate beneath the Philippine Sea plate.
LCH is situated on the only offshore diapir that has reached the surface, therefore serves as an excellent location for observing the development of limestone over an accretionary wedge.
With a sharp contact, the highly deformed mudstone is overlain by a carbonate conglomerate bed several 10's of cm (up to 1 m) in thickness. The conglomerate bed is composed of rounded coral fragments and other limestone intraclasts. This indicates that some early limestone patches had developed on the shoaling mudstone, thereby provided carbonate gravels that were later dispersed on the mudstone.
The carbonate conglomerate bed is overlain by carbonate sandstone about 0.5 m in thickness. Large-scale trough cross-beds are common. In some places the sandstone is densely occupied with Ophiomorpha and Thalassinoides. This lithofacies suggests lateral transportation of the carbonate sands by strong currents, as well as intense bioturbation within the sands.
Rhodolith layer up to 1 m thick overlies the carbonate sandstone, which implies that currents had turned around the algal balls periodically, and that little detrital carbonate sediments were generated at this stage.
A coral limestone bed 10-13 m in thickness covers all the above lithofacies, indicating that by then the foundation was steady enough for the reef to build up. Finally, a red mudstone bed 0.5 m in thickness tops the section.
The vertical transition of lithofacies in LCH described above clearly shows the following sequence of evolution: Diapiring of the Plio-Pleistocene mudstone, carbonate sedimentation, and subaerial exposure.