台南層遍佈嘉南平原，為研究全新世構造活動及古地震的極佳素材。本研究針對台南層之界定、年代、地層厚度、沈積環境及其褶皺形貌進行研究與討論，作為進一步研究台灣西南部地區新期構造及古地震之基礎。資料來源一為國科會八十九年度計畫之研究成果，另一為西南部地區水井及工程鑽井資料。將紙面報告進行數位化、資料整理及資料庫建置，進行地層剖面分析、趨勢面分析、克力金分析，並進行地質解釋。研究結果發現，台南台地周緣槽溝位置之台南層可分為五段，後四段可對比林朝棨(1963)定義之台南層的四個段。在台地上，台南層直接與基盤接觸。在台地以外之地區，台南層的五個段之下尚整合接續了更老之全新世地層。全新世的海進沈積作用在台南台地以外的嘉南平原地區始自11000年前，但台南台地之台南層最老約六千多年前。此可能代表了六千餘年以前，台南地區已經是一個高地，這個高地有可能是泥岩衝頂或衝頂褶皺造成。由於槽溝內台南層各段的傾斜角度相近，地層整合良好，無超覆之情形，故可推論在台南層的沈積結束之後褶皺作用才開始。由更年輕的大灣層超覆在台南層之上之現象，可知台南層結束沈積之後隨即開始褶皺作用。由褶皺形貌及破裂機制觀之，全新世台南層所形成之台南背斜比較符合一斷層面傾斜約50度的斷層擴展褶皺模型。所謂之「後甲里斷層」可能只是一向西傾斜的背扭褶皺或背衝盲斷層。此構造隨同台南背斜的發育，其主要活動期應在台南層形成之後，並一直持續至今。 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.
