| 摘要: | 本研究利用台灣西北部，沿大漢溪流域出露的三鶯剖面、大漢溪剖面共2400公尺厚，以及由工研院鑽探的三鶯一號井岩心300公尺鑽厚，研究並描述自南莊層上部至楊梅層的岩相及沉積相分析，解釋沉積環境演化。並研究大漢溪剖面的超微化石，在THC-11及THC-12之間辨認出R. Pseudoumbilica的滅絕面，為NN15及NN16的介面，同時也是錦水頁岩及卓蘭層的交界。 根據岩相分析，可區分出21種岩相，包含5種泥岩相、2種砂泥互層相、13種砂岩相與1種泥礫相；根據不同的岩相組成的岩相組合，指示出14種沉積相，可細分為遠濱、下濱面、上濱面、入潮道/堰洲島、入潮三角洲、砂質及泥質中央盆地、潮汐水道、潮坪、草澤、河道砂洲、自然堤、潰堤扇、泛濫平原及砂質辮狀河等沉積次環境；根據不同的沉積相，可區分出3種沉積環境，包括波浪及潮汐影響的開放性淺海環境、以波浪為主且受潮汐影響的河口灣環境，以及陸相的曲流河及砂質辮狀河環境。 堆積南莊層時仍為被動大陸邊緣時期，沉積環境以陸相河道及河口灣環境為主；堆積桂竹林層時開始形成前陸盆地，並因盆地沉降使環境由淺變深，環境以河口灣及濱面環境為主；堆積錦水頁岩時期環境達到最深，為遠濱環境；而後前陸盆地逐漸被沉積物填滿，使環境由深變淺，堆積卓蘭層時為海岸的河口灣環境，楊梅層則以陸相的曲流河及砂質辮狀河為主。因此台灣西北部大漢溪剖面的環境演化，大體來說為由淺變深之後，再由深變淺。 由東南-西北對比可知從濱海進入麓山帶，岩層厚度具漸漸變厚的趨勢；由南北對比，可知大漢溪剖面的楊梅層，可向南對比至新竹-關西地區的楊梅層照鏡段，向北可對比至林口地區的大南灣層寶斗厝段；而TY-07井的大茅埔礫岩，可向南對比至新竹-關西地區的大茅埔礫岩，向北可對比至林口地區的林口層。 This study investigated the facies characteristics of the upper Nanchuang to Yangmei formations by examing San-Ying section, Dahan River section, and San-Ying borehole in northwestern Taiwan. I recognized 21 lithofacies, including 5 mudstone facies, 2 mudstone & sandstone interbedded facies, 13 sandstone facies, and 1 mudclast facies. On the basis of different combination of lithofacies, I recognized 14 lithofacies associations, including offshore, lower shoreface, upper shoreface, tidal inlets/barrier islands, tidal flood delta, sandy & muddy central basin, tidal channel, tidal flat, marsh, channel sand bar, levee, crevasse splay, flood plain and sandy braided river. These lithofacies associations occurred in 3 major sedimentary environments: (1) wave- and tidal-inflenced open marine, (2) wave-dominated estuaries, and (3) meandering and sandy braided rivers. In late Miocene, the sedimentary environments were fluvial and wave-dominated estuaries for the Nanchuang Formation, pertaining to a passive-margin setting. During the initiation of foreland basin, the basin started to subside and the environments became deeper to wave-dominated estuaries and wave- and tidal-inflenced open marine system when sediments of the Kueichulin Formation accumulated. During Chinshui Shale stage, the environments deepened into offshore, which was the deepest environment for the studied sequence. The foreland basin was filled up by subsequent deposits and the environments became shallower as wave-dominated estuaries during Cholan Formation stage and later became meandering and sandy braided rivers during Yangmei Formation stage. In summary, the trend of the sedimentary evolution for the studied sequence shows a deepening then shallowing upward trend. Sediment thickness thicken toward the east as revealed from stratigraphic correlation. The Yangmei Formation along the Dahan River section can be correlated southwardly to the Chaochin Member of Yangmei Formation in the Hsinchu-Kuanhsi area and northwardly to the Paotoutso Member of the Tananwan Formation in the Linkou area. In addition, the Tamaopu Conglomerates of TY-07 borehole can be correlated to the Tamaopu Conglomerate in Hsinchu-Kuanhsi area and Linkou Formation in the north. |
