南中國海東北部晚期第四紀濁流岩研究;A study on late Quaternary turbidites in the northeastern South China Sea

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题名:	南中國海東北部晚期第四紀濁流岩研究;A study on late Quaternary turbidites in the northeastern South China Sea
作者:	俞舜文;Yu, Shun-Wen
贡献者:	應用地質研究所
关键词:	濁流岩;南中國海東北部
日期:	2019-07-24
上传时间:	2019-09-03 16:59:28 (UTC+8)
出版者:	國立中央大學
摘要:	南中國海為世界上沉積速率最快的陸緣海，其東北部由具有狹窄陸棚的活動大陸邊緣與具有寬廣陸棚的被動大陸邊緣組成，每年約有176萬噸的台灣河流沉積物匯入於此。過去對於探討具有寬廣陸棚但受到大量陸源沉積物輸入的深海環境的層序地層發育之控制因子甚少，本研究藉由比較相鄰但地體環境不同的岩心的濁流紀錄的異同，探討南中國海大陸斜坡這種環境獨特的層序地層控制因子。結果顯示，在南中國海東北部無論是活動大陸邊緣或被動大陸邊緣，濁流發生頻率的變化相似，頻繁的濁流除了發生在全球海平面低水位至早期海進時期(約21~15 kyr BP)外，晚期海進至高水位時期(約10 kyr BP~現在)亦有頻繁的濁流發生。此一現象與早期提出的在被動大陸邊緣深海的層序地層模型相異，暗示著控制南中國海東北部的深海地層層序並非僅以海水面變化為主。再進一步與鄰近區域的氣候紀錄進行比對後發現，控制南中國海東北部深海環境地層層序變化，氣候亦為一重要的因子，且並非僅與氣候變遷造成的沉積物供應量變化有關，亦可能與氣候變遷所造成的颱風發生頻率變化有關；換言之，在建置深海地層模型時，即使是具有廣闊陸棚之沉積系統，氣候變遷亦為重要的控制因子，應納入考量。;Turbidity currents are the major agents for transporting sediments from the continents into the deep sea. Thickly-bedded turbidites commonly serve as good hydrocarbon reservoirs and are the major target for deep water hydrocarbon exploration. The South China Sea is the largest sink in the world for fluvial sediments (around 1,600 million metric tons) among marginal seas, and the northeastern South China Sea is where the passive continental margin meets Taiwan orogenic wedge and the Manila subduction zone. Therefore, the northeastern South China Sea is an ideal place to compare and contrast the turbidite development in the neighboring rifted continental margin and orogenic wedge. We used 3 giant piston cores (MD3291, MD3266, and MD3264) recovered onboardR/V Marion Dufresne in 2010 along the rifted continental margin and Taiwan orogenic wedge to reconstruct the depositional history late Quaternary turbidites by sedimentologic study and AMS 14C dating. Our results reveal frequent turbidity currents occurred during ~21 kyr to 15 kyr BP and ~10 kyr BP to the present day in the study area. The correlation among turbidite occurrence and changes in eustasy, climate, and rainfall intensity in southern Taiwan reveal that the frequency of turbidity currents is most likely related to sea level and climatic changes, even for the cases that canyon heads and river mouths are separated by a wide shelf.
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