| 摘要: | TCDP-A井的連續岩心(台灣車籠埔斷層計畫岩心，總深度2003公尺)獲得了台灣中部地區，上新世至更新世台灣前陸盆地的層序。TCDP-A井岩心記錄著台灣前陸盆地淺海沉積環境的演化過程，由形成初期(桂竹林層，1300-1710公尺)，經過發育期(錦水頁岩，1013-1300公尺)，進入成熟期(卓蘭層，0-1013公尺、1710-2003公尺)的這些階段。 經由岩心完整岩性與地球物理電測資料的結合，使得這些連續的岩心紀錄提供了我們一個獨一無二的機會，來研究一個逐漸發育形成之海洋前陸盆地的岩石地層與沉積作用演化過程。我們描述岩心的岩性、顆粒度變化、沉積構造、生物擾動指數、生痕化石、岩層間的接觸關係與特殊岩層(如貝類化石富集帶、泥塊或是小礫石富集帶、碳層、結核等特徵)。由上述的岩相特徵，可將研究岩心分出濱海海岸沉積體系及淺海大陸棚沉積體系。利用上述所建立的基礎，可分別定義出15種岩相與12種生痕化石相。結合相鄰與相關的岩相可辨認出8種岩相組合，分別為外遠濱相、內遠濱相、下濱面相、上濱面相、障壁島相、潮坪相、潟湖相及沼澤相。經由這些岩相組合的建立，使我們得知台灣前陸盆地的環境由淺變深再由深變淺的演化過程。 The continuous coring of the TCDP-A (Taiwan Chelungpu-Fault Drilling Project-A, 2003 m in drill depth) borehole recovered a Pliocene-Pleistocene Taiwan foreland sequence in central Taiwan. The drilled interval records the shallow marine sedimentation of an evolving foreland basin from its inception (i.e., the Kueichulin Formation, 1300m-1710m) through the under-filled stage (i.e., the Chinshui Shale, 1013m-1300m) into the mature/over-filled stage (i.e., the Cholan Formation, 0m-1013m, 1710m-2003m). The continuous cores provide us a unique opportunity to decipher the sedimentology and lithology of an evolving marine foreland basin through an integrated study of core lithofacies and geophysical wireline logs. Fifteen lithofacies and 12 trace-fossil assemblages were recognized from the TCDP-A cores on the basis of the lithology, grain size, sedimentary structure, degree of bioturbation, trace fossils, and fossils content. Genetically related lithofacies were then combined into 8 facies associations. These facies associations are deposits accumulated in environments of outer offshore, inner offshore, lower shoreface, upper shoreface, barrier complex, tidal flat, lagoon, and swamp, respectively. The vertical change of paleo-environments documents the Taiwan foreland basin evolving from an early overall transgressive phase(i.e., the Kueichulin Formation and Chinshui Shale) into a late regressive phase(i.e., the Cholan Formation). |
