由層序地層學原理探討台灣西部麓山帶低水位體系域地層封閉之潛能

Using Sequence Stratigraphic Concepts to Evaluate the Stratigraphic Trap Potential of Lowstand Systems Tracts in the Western Foothill Area of Taiwan

黃進達(Chin-Da Huang) ； 李通藝(Tung-Yi Lee) ； 邱宇平(Yu-Ping Chiu) ； 曹嘉修(Chia-Hsiu Tsao) ； 吳榮章(Jong-Chang Wu) ； 葉孟宛(Meng-Wan Yeh)

《臺灣鑛業》 62卷2期 (2010/06) Pp. 15-32

https://doi.org/10.30014/TMI.201006.0004

摘要

台灣西部平原的第三紀地層，其沉積環境都偏在大陸棚以上。而台灣中油公司在2003年於苗栗大湖地區鑽探栗林一號井之後，推測有海底扇之存在；但由有孔蟲紀錄判斷此海底扇發育於淺水環境，其沉積和相關之構造意義皆十分特殊。本研究利用層序地層學原理，藉由野外露頭考察、井下電測資料、及震測剖面來探討台灣西部（接近麓山帶）地區可能存在之低水位體系域（lowstand systems tract, LST）中較深水部分之重要單元，並評估其地層封閉潛能。研究結果發現，其成因很可能和前陸盆地形成初期之演化有關：關刀山砂岩沉積時，弧－陸碰撞使被動大陸邊緣的上部地殼彎曲伸展，於出磺坑和細道邦之間因生長斷層的發育而形成構造低區，使沉積坡度突然增大，形成一侷限環境之淺水海底扇。因此此淺水扇的發育可代表台灣前陸盆地發育之肇始；而桂竹林層開始沉積的時間（約9Ma），當可視為台灣西部前陸盆地開始的時期；這一點，亦可由台灣地區火成活動之紀錄得到印證。另外，海底扇與其他低水位體系域深水部分重要單元的分布，可視為一個單獨生油、儲油、封閉體系，藉由層序地層學原理來評估可能之生油、儲油、移棲和蓋層的組合，可做為區域探勘的參考依據。

關鍵字

層序地層學 ； 低水位體系域 ； 淺水海底扇

並列摘要

The depositional environments of Tertiary strata in the western Taiwan are mainly above the shelf. After the CPC (CPC Corporation, Taiwan) drilled the LLN-1 well at Dahu area of Miaoli in 2003, submarine fan was reported to have been identified from the subsurface data. However, it is highly possible that the submarine fan was deposited in a shallow marine environment according to the foraminifer record. This finding would imply a special tectonic setting for the deposition of this shallow marine fan. This study used outcrop, well data, and seismic sections to analyze lowstand systems tract (LST) in the western Taiwan foothill area by sequence stratigraphic concepts, and focused on the deeper parts of the LST in order to evaluate the stratigraphic trap potential. We concluded that the formation of the shallow marine fan may be correlated with the initiation of the foreland basin. That is when the Kuantaoshan sandstone was deposited, the approaching Luzon Arc made the upper crust of the Eurasian passive continental margin bent and stretched, produced the growth fault system. In the hanging-wall side of the growth fault, a structural low shaped between Chuhuangkeng and Hsitaopang, and also induced a sudden increase of the depositional slope which enabled the formation of the shallow marine fan in this area. Therefore, the development of the shallow marine fan could be used to indicate the commencement of the foreland basin. Furthermore, the timing of deposition of Kueichoulin formation (about 9 Ma) can be considered as the starting point for western Taiwan foreland basin. The notion can be further proved by the cessation of volcanic activities in Taiwan (also around 9 Ma). In addition, the distribution of the shallow submarine fan and the other units in the LST can be considered as a complete hydrocarbon system which has source, reservoir, and trap all in one place. In general, sequence stratigraphic analysis provides a good tool for hydrocarbon play assessments.

並列關鍵字

Sequence stratigraphy ； lowstand systems tract (LST) ； and shallow marine fan