臺灣西部前陸盆地前凸起遷移與潮汕凹陷的震測相分析與其在南海北部大陸邊緣盆地演化之意涵

Forebulge Migration in the Western Taiwan Foreland Basin and seismic facies analyses in the Chaoshan Depression: implications for basin evolution of the northern continental margin, South China Sea

張日新(Jih-Hsin Chang)

指導教授 ： 俞何興

國立臺灣大學/理學院/海洋研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.00478

摘要

本文利用震測剖面資料，研究台灣西部前陸盆地前凸起遷移與潮汕凹陷同張裂層序之震測相，討論南海北部大陸邊緣盆地演化的含義。橫跨台灣西部前陸盆地前凸起之震測剖面的地層特徵指出，台灣西部前陸盆地基底上有連續向西跨踏(overstepping)的不整合面，說明了台灣西部前陸盆地在晚中新世形成後，前凸起持續向西遷移，至少有兩次遷移事件。潮汕凹陷的同張裂層序中可辨識出震測相I(平行－次平行)、震測相II(混沌)、震測相III(超覆狀)及震測相IV(丘狀)四種震測相。平行－次平行及混沌震測相可解釋為張裂初期的沈積物堆積，超覆狀震測相可解釋為張裂盛期的沈積物堆積，而丘狀震測相可解釋為後張裂初期的沈積物堆積。震測相I代表湖沼相的沈積，平行－次平行的反射說明了沈積時為一低能量的沈積環境；震測相II代表的河流相及湖沼相沈積，混沌反射說明了沈積環境側向的不連續；震測相III可解釋為濱海相的沈積環境，超覆狀的反射可能與三角洲沈積體的進覆積(progradation)有關；震測相IV為下部陸坡到深海盆底的沈積環境，丘狀反射可能為海底扇的沈積葉體。

台灣西部前陸盆地與潮汕凹陷張裂盆地的時空分佈可闡釋南海北部大陸邊緣盆地演化的含義。在古第三紀時南海北部大陸邊緣發育了一系列東北－西南走向的張裂盆地，包含潮汕凹陷與台南盆地。自中新世起時南海北部大陸邊緣進入了後張裂時期，潮汕凹陷堆積後張裂層序(中新世－現代)。自上新世起，呂宋島弧與中國大陸邊緣斜向碰撞形成台灣造山帶，造山荷重與板塊撓曲影響了晚中新世後台灣西部前陸盆地與台南盆地的發育。台灣西部前陸盆地接受大量的台灣造山帶沈積物堆積，發育為成熟(mature)的前陸盆地；台南盆地亦受到板塊撓曲的影響，造成撓曲下陷，僅接受少量的台灣造山帶沈積物堆積，發育了未成熟(immature)的前陸盆地(更新世至今)。潮汕凹陷未受到板塊撓曲的影響，至今仍維持張裂盆地的原貌，具有張裂層序與後張裂層序。台灣西部前陸盆地、台南盆地以及潮汕凹陷在中新世之後盆地框架上的差異，說明了南海北部大陸邊緣盆地之發育為被動大陸邊緣受到板塊撓曲沈降之影響，並由南而北呈現了南海北部被動大陸邊緣之後張裂盆地、受呂宋島弧－中國大陸邊緣初始碰撞影響但尚未被完全充填之未成熟前陸盆地、以及受板塊撓曲沈降影響且已被完全充填之成熟前陸盆地等不同階段之漸變的過程。

關鍵字

台灣西部前陸盆地 ； 前凸起 ； 張裂盆地 ； 潮汕凹陷

並列摘要

Using reflection seismic profiles, this study investigates the forebulge migration in the Western Taiwan Foreland Basin (WTFB), the seismic facies of the synrift sequences of the Chaoshan Depresion, and discusses their implications for basin evolution of northern continental margin, South China Sea. The seismic characteristics in the sections across the forebulge of the WTFB displays a series of westwards overstepping unconformities, suggesting that the forebulge of the WTFB has migrated westwards since the Late Miocene. There are at least two episodes of migration of the forebulge of the WTFB. Four seismic facies are identified in the synrift sequences of the Chaoshan Depression: the Seismic Facies I (parallel-subparallel), the Seismic Facies II (chaotic), the Seismic Facies III (offlap), and the Seismic Facies IV (mounded). The Seismic Facies I and the Seismic Facies II are interpreted as the deposits formed during rift initiation of the Chaoshan rifting basin. The Seismic Facies III is interpreted as the deposits formed during rift climax of the rift basin. The Seismic Facies IV is interpreted as the deposits formed during immediate post rift of the rift basin. The parallel-subparallel reflectors in the Seismic Facies I may represent the deposits of a lacustrine environment and the chaotic reflectors in the Seismic Facies II may represent the lateral discontinuity of the sediments. Offlap reflections in the Seismic Facies III may
represent the progradation of deltaic sedimentary sequences in a marginal marine environment. Mounded reflectors in the Seismic Facies IV may represent the sedimentary lobes of a deep sea fan, deposited in a lower slope-basin floor environment.

The spatial-temporal distributions of the WTFB and the Chaoshan Depression provide implications for basin evolution of northern continental margin of the South China Sea. In the Paleogene, a series of rifting basins with a NE-SW trend occurred on the northern continental margin of the South China Sea, including the Chaoshan Depression and the Tainan Basin. The rifting of these basins has ceased at the Early Miocene, and following post-rift sedimentary sequences are deposited onto the rifting sequence of these basins. Since the Pliocene, the oblique collision between the Luzon arc and the Chinese continental margin has formed the Taiwan orogenic belt at the
northernmost part of the Northern continental margin of the South China Sea. The load of the Taiwan orogenic belt and the flexure of the Eurasian Plate resulted in the development of the WTFB and had influence on the development of the Tainan Basin since the Late Miocene. The central part of the WTFB has become a "mature" foreland basin and has received sediments derived from the Taiwan orogenic belt. On the other hand, the Kaoping Slope(SW Taiwan) and the Tainan Basin are currently considered to be "immature" foreland basins which are suffered from less tectonic(flexural) influence by orogenic load. Southwards, the Chaoshan Depression is not influenced by the load of the Taiwan orogenic belt, and preserves the configuration of a post-rift basin. The variations in tectono-stratigraphic characteristics of the basins (ie., the WTFB, the Tainan Basin, and the Chaoshan Depression) along the northern continental margin of the South China Sea suggest that the development of these basins are influenced by the
flexure of the Eurasian Plate in the Taiwan region. The progressive changes of basin configurations from a post-rift basin on the Chinese passive margin (the Chaoshan Depression), in transition to an "immature" underfilled foreland basin (the Tainan Basin), to a "mature" filled foreland basin (the WTFB) are reflected by the accompanying progressive changes from rifting in transition to initial collision and to arc-continent collision in Taiwan.

並列關鍵字

Western Taiwan Foreland Basin ； forebulge ； rifting basin ； Chaoshan Depression

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