From Passive Continental Margin to ForelandBasin in Southwestern Taiwan: Using Stratigraphic Analyses.

Liang, Shen-hsiung

Abstract

The plain and foothill belt in Southwestern Taiwan were from the passive continental margin to the foreland basin. Further, the compressional stress influenced the formation of the fold-thrust belt in this area. In addition, there were thick depositions in the region. Therefore, southwestern Taiwan is a key to interpret the relationships between the basin evolution, faults growth and the interactions of extension and compressional stress.

This provides a good opportunity to observe the process of the foreland basin evolution and the faulting activities by the stratigraphic analyses, including outcrop columns, the borehole columns and seismic stratigraphy.

Using the results of the stratigraphic analyses, and then mapped out 6 isopach maps. The isopach maps of the Chunglun, Niaotsui, Yunshuihsi, Liuchunghsi, Kanhsialiao and the Erhchunghsi formations in southwestern Taiwan were constructed. The trend of the sediment thickness was from east to west displayed in the isopach map of the Kanhsialiao formation, but others were from the north to south.

The A-fault had been acted or even earlier in the isopach map of the Chunglun formation. The basin was from the passive continental margin to the foreland basin in this period. Because Peikang high was near the northern area, the the sediments in northern area were thinner then south in the isopach map of the Niaotsui formation. The type of the piggy basin was developed in the isopach map of the Yunshuihsi formation. In the isopach map of the Liuchunghsi formation, the basin had returned to the rapid subsidence of the typical foreland basin. It was showed that the basin was high-speed uplift in the form of the piggy basin in the isopach map of the Kanhsialiao formation. It was implied that the Sedimentary center of the basin moving to the western in the isopach map of the Erhchunghsi formation. Finally, the center was relocated offshore southwestern Taiwan.