The Tectonic Implication of Stratigraphy Architecture in the Foreland Basin, Western Taiwan

Kenn-Ming Yang, Jong-Chang Wu, Wen-Rong Chi, and Hsin-Hsiu Ting

Different models for the development of a foreland basin predict distinct stratigraphic architecture across the basin. Sequence stratigraphy and time-spatial variation in lithofacies patterns and subsidence histories in the distal part of a foreland basin are the most crucial indicators to infer the mode of tectonic evolution of the basin.

The western Taiwan can be characterized by a foreland basin that is bordered by a westward moving fold-and-thrust belt to its east. The foreland basin has been developing on a previously uplifted margin of an extensional basin of which the width and extension increase toward the east. Rapid subsidence following the uplifting indicates the onset of development of the foreland basin. The characteristics of stratigraphy architecture are: 1) westward onlapping of the sequences in the distal part of the basin, associated with initial rapid subsidence stepwise younging toward the craton, 2) unconformities that punctuate the onlapping of the sequences and also are younging to the west, 3) several later phases of rapid subsidence recognized across the entire area and immediately succeeding th unconformities to the west, and 4) submarine truncation followed by deposition of coarsening-upward sequences during each phase of the rapid subsidence. These stratigraphic features cannot be explained by eustatic sea-level fluctuation but rather should be related to eastward migration of forebulge during episodic westward movement of the fold-and-thrust belt and later progradation of deposition toward the craton.

Migration rate of the distal part of the foreland basin was slower in the early stage but higher in the final stage than that derived from the previously proposed kinematic model for the steady migration of the orogenic belt. This implies that the pre-collision extensional tectonics might have caused weaker lithosphere beneath the foreland basin and that once the foreland basin migrated onto the less stretched lithosphere the basin would expand rapidly into the craton.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California