臺灣新生代大陸邊緣盆地的構造演化與油氣儲積關係

Tectonic Evolution and Hydrocarbon Accumulation of the Cenozoic Continent Margin Basins in Taiwan

黃富文(F. W. Frank Huang) ； 丁信修(Hsin-Hsiu Ting)

《臺灣鑛業》 70卷3期 (2018/09) Pp. 1-14

摘要

臺灣新生代大陸邊緣盆地在臺灣海峽中部有內盆地如東引島、南日島及澎湖等盆地，在鄰近臺灣西部平原有外盆地如東引島、南日島及澎湖等盆地。根據盆地型式、新生代地層對比和大地構造特性，本研究探討了這些盆地的構造演化和油氣儲積之關係。這些位在歐亞大陸邊緣的新生代沉積盆地，由於具火山活動及地震等地質活動特徵，應屬聚合的大陸邊緣。內盆地的古第三紀地層由東北西南方向雁行排列的同向組合之半地塹系所組成。井下資料顯示，這些盆地的發展始於晚白堊紀的張裂活動。盆地早期沉降快速，並伴著斷裂活動，沉積物則以粗粒碎屑岩為主，後期沉降速率放緩，且斷裂活動減弱或停止，顯示出新第三紀漥陷沉積作用的特徵。臺灣海域外盆地的盆地架構較為複雜，古第三紀震測地層學的研究顯示，南澎佳嶼及臺西盆地最初的發育是同期同向半地塹組合，以後又受到不同期構造運動的影響。臺南盆地則更受到南海運動影響成階梯狀下陷。這些盆地的構造演化及經歷過的沉積作用，與內盆地雷同，在臺灣陸上地區則另外經歷了晚中新世至上新世早期的菲律賓海板塊的擠壓，臺灣海岸山脈碰撞的蓬萊運動造成盆地反轉上升，沉積來自盆地反轉侵蝕的沉積物。臺灣海域盆地的構造演化，主要受到西太平洋板塊活動影響，這點與東海盆地類似，但它還受到印度板塊移動所造成南海運動的影響。晚侏儸紀到早白堊紀，發生西太平洋海板塊的隱沒活動，乃至於晚白堊紀的斜向隱沒，及中新世晚期以後臺灣陸上的海岸山脈碰撞和擠壓作用。臺灣臺南盆地，有晚白堊紀到漸新世的拉張，在中新世以降則持續地以階梯型式下陷，形成今日的地質形貌。半地塹盆地早期的張裂，沉積了湖相始新世和早漸新世之生油岩。晚漸新世以降的漥陷作用沉積了淺海煤系生油岩。臺灣陸地因蓬萊運動造成盆地反轉上升，深層油氣因而向上排移聚存在上層封閉內。未受蓬萊運動影響的盆地，其油氣仍儲存於半地塹盆地封閉中，此可以北港古高區相隔區分為陸塊內河湖相油氣田和大陸邊緣河海相油氣田，這些地區的油氣探勘策略及目標應不盡相同。

關鍵字

臺灣 ； 新生代 ； 沉積盆地 ； 構造演化 ； 油氣儲積

並列摘要

The continental margin in Taiwan area during the Cenozoic, there are inner basins in the central part of the Taiwan Strait such as Dongyindao, Nanridao and Penghu and outer basins adjacent to the western plains of Taiwan such as Nanpangjiayu, Taixi and Tainan. Based on the basin types, stratigraphic correlation of the Cenozoic strata and the tectonic characteristics, the study aims to understand the relation between the tectonic evolution and its hydrocarbon accumulation. These Cenozoic sedimentary basins in the margin of the Eurasian continent should be classified as the convergent continental margin ones as they are characteristic of geological movements such as volcanic activity and earthquakes. The Paleogene strata in the inner basins are composed of en echelon-arranged, half graben systems, in which the boundary faults run Northeast and Southwest. Well data shows that the development of these basins began with the rifting in the Late Cretaceous. In the early stage, the basins are characterized by rapid basin subsidence, active faulting and coarse clastic sediments. In the later stage, these basins are characterized by the reduced sedimentation rate, the weakened or ceased fault activities, and the depression deposition in the Neogene stable environment. The frameworks of the outer basins are more complicated. Study from the seismic stratigraphy of the Paleogene strata in the Nanpangjiayu and Taixi basins shows that the set of half grabens has developed at the same period with the same direction and later is affected by tectonic movements in different periods. The Tainan Basin is affected by the South China Sea movement in advance and becomes a stepped subsidence. These basins experienced the same sedimentary process as the inner basins. Besides, the basins in the land region of Taiwan experienced a squeezing by the Philippine Sea plate, and the Penglai movement by the collision of the Taiwan Coastal Range from the late Miocene to the early Pliocene, which caused a reversal of the basin that accumulated the sediments from the erosion of the structure highs from the late Pliocene until now. The tectonic evolution of Taiwan offshore basins, mainly affected by the subduction movement of the West Pacific sea plate, is similar to that of the East China Sea basins in northern Taiwan except that the former is also affected by the South China Sea movement caused by the movement of the Indian plate. The subduction movements of the West Pacific sea plate to these basins were transtension from the late Jurassic to early Cretaceous, oblique subduction from the late Cretaceous to Oligocene, and the collision and compression of the Coastal range to the land of Taiwan after the late Miocene. In the Tainan offshore basin, there was a late-Cretaceous to Oligocene extension and a continuous step-like subsidence after the early Miocene, forming present geological features. In early stage of rifting of these half grabens, the lacustrine Eocene and early Oligocene source rocks were deposited and hydrocarbon is accumulated. After the late Oligocene, the depression of these basins formed shallow sea, the coal-bearing hydrocarbon source rock was thus deposited. In the onshore Taiwan, the Penglai movement caused a reversal of the basin and hydrocarbon migrated from deep to the shallow, while the offshore basin, not affected by the Penglai movement, the hydrocarbon was still preserved in the deep closure of these basins. Besides, the Penghu- Peikang high can divide these basins into the inland river-lake oil and gas field area and the continental marginal river-sea oil and gas field area. In that case, the strategies and targets of the oil and gas exploration should be different.

並列關鍵字

Taiwan ； Cenozoic ； Sedimentary Basin ； Tectonic Evolution ； hydrocarbon accumulation