| dc.description.abstract | The Tainan Formation dominating the Chianan Plain is the best source material for studying Holocene tectonics and paleo-earthquakes. Definition, age, thickness, depositional environment and deformation features are discussed in this study. These may form a basis for further study of neotectonics and paleo-seismology in southwestern Taiwan.
Data come from two different sources, one is a NSC trenching report in year 2000, the other is some research wells and engineering drill logs in southwestern Taiwan. The reports on paper were digitized, sorted, checked and input into a database system for profile analysis, trend surface analysis, Kriging analysis and geologic explanation.
The result shows that the Tainan Formation at the trench site can be separate into five members. The last four members can be correlated with that being defined by Lin (1963). Tainan Formation directly contact with basement on the tableland. Out of the tableland and in the surrounding area, the five members of the Tainan Formation conformably contact with older Holocene formation. Holocene transgression started in Chianan Plain region 11,000 years ago. But the oldest age of the Tainan Formation at the tableland is only about six thousand years old. That may indicate the Tainan Region had been a high land at six thousand years ago. The high land maybe brought about mud diapir or a diapiric fold. Recognizing from the similar dipping angle of every member of the Tainan Formation and the conformable beds without onlap, the Tainan Formation should be folded after deposition. Also, the younger Tawan Formation is onlapping on the Tainan Formation and presenting a lower dip angle, the folding process should be immediately after deposition of the Tainan Formation and during the deposition of the Tawan Formation. According to the fold shape and fracture pattern in the Tainan Formation, the Tainan Anticline may be fitted to a fault-propagation fold model with the fault-plane dipping about fifty degrees. The so-called “Houchiali fault” may be just a back-folding or a blind back-thrust. This east vergence structure follows the development of the Tainan Anticline. The main active phase of this structure should be after the deposition of the Tainan Formation, and is continue to the present time. | en_US |