A Preliminary Study of Seismic Stratigraphy of the Late Cenozoic Sequences in the Tainan Basin off Southwestern Taiwan

Abstract

This study investigates the late Cenozoic strata in the Tainan b in o south­ west Taiwan. The nature and development· history of late Cenozoic sequences are discussed in terms of seismic stratigaphy. Multichannel seismic profiles more than 330 km long were acquired and processed; including 4 dip profiles and 3 strike lines. The quality of the seismic profiles range from fair to good.
Seismic profiles show that late Cenozoic strata are relatively conformable stratigraphic successions from which Pletocene and Pliocene seismic sequences are defined. The seismic reflection configurations of the late Cenozoic sequences are characterized by parallel, subparallel and divergent patterns. The parallel pattern suggests that sediments accumulated at a relatively uniform rate on a shallow shelf within the study ea. The divergent reflection pattern and the external wedge­ shape of the sequences indicate lateral changes in deposition rates and progressive tilting of the shelf facies. Seismic facies analysis indicates that late Cenozoic sed­iments were deposited mainly in the Huvia nearshore environments. The regional trends of the Pliocene and Pleistocene sequences represent relatively smooth parts of the shelf without the characteristic shelf-slope breaks. The shelf breaks in the Pliocene and Pleistocene sequences are probably situated farther seaward than to­day's she edge.
Velocity models indicate an interval velocity ranging from 1,800 m/s to 4,000 m/s suggesting that the late Cenozoic sequence composed mainly of sands and shales. Vertical distribution of the inter velocity shows that the velocity of the sequences increases with depth a result of compaction (i.e. depth of burial).
Analyses of seismic sequences, seismic facies and velocity suggest that the Pleistocene and Pliocene sequences developed into a clastic wedge. The sequence form parts of the South China continental m gin which h undergone tilting and subsiding during the past ten or more milion years.

Read 826 times