TENG, LOUIS S., NENG-TI. YU, and C. H. PENG
Institute of Geology, National Taiwan University, Taipei, Taiwan, R.O.C.

Abstract: Sequence Stratigraphy of Quaternary Alluvial-Lacustrine-Estuarine Deposits of the Taipei Basin, Taiwan

To test the validity of the sequence stratigraphic models developed for non-marine systems, the facies sequences of Quaternary alluvial-lacustrine-estuarine deposits of the Taipei Basin in northern Taiwan have been carefully investigated. The Taipei Basin is located 12 km inland from the coastline and is connected with the ocean through the effluent Tanshui River. Two 5th-order sequences can be recognized in the Taipei Basin deposits, which date back to about 220 Ka. Each sequence is based on an erosional unconformity marked by the sharp contact between the floodplain muds and the overlying alluvial fan gravels or between the estuarine muds and overlying channel pebbles. Trangressive surfaces can be recognized by the sharp facies change from the alluvial fan gravels to fluvial sands or pebbles. Maximum flooding surfaces are identified by the muddy distal floodplain deposits in the southeast and central Basin and by the estuarine muds in the northwest. In terms of these boundaries and surfaces, each sequence can be divided into low-stand, transgressive, and high-stand systems tracts, which can be correlated among boreholes. Tied to the pollen stratigraphic sequence and radiometric datings, the sequence variations clearly reflect the sea level changes induced by the glacial cycles. Each sequence begins with an erosion surface developed during the falling sea level, which is followed by alluvial fan and fluvial gravels accumulated during the late low-stand. As the sea level rises, the basin is filled with floodplain and estuarine deposits that dominate the transgressive systems tracts. During the highstand, the basin is dominated by prograding fluvial deposits which, however, are often eroded away during the next sea level fall.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas