Difference in full-filled time and its controlling factors in the central canyon of the Qiongdongnan Basin
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Difference in full-filled time and its controlling factors in the Central Canyon of the Qiongdongnan Basin SHANG Zhilei1, XIE Xinong1*, LI Xushen2, ZHANG Daojun2, HE Yunlong1, YANG Xing3, CUI Mingzhe4 1 Key Laboratory of Tectonics & Petroleum Resources of Ministry of Education, China University of Geosciences,
Wuhan 430074, China 2 Zhanjiang Branch of China National Offshore Oil Corporation (CNOOC) Limited, Zhanjiang 524057, China 3 Hubei Shale Gas Development Co., Ltd., Wuhan 430070, China 4 Bohai Oilfield Research Institute, Tianjin Branch of CNOOC Limited, Tianjin 300452, China
Received 25 June 2014; accepted 18 January 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015
Abstract
Based on the interpretation of high resolution 2D/3D seismic data, sedimentary filling characteristics and fullfilled time of the Central Canyon in different segments in the Qiongdongnan Basin of northwestern South China Sea have been studied. The research results indicate that the initial formation age of the Central Canyon is traced back to 11.6 Ma (T40), at which the canyon began to develop due to the scouring of turbidity currents from west to east. During the period of 11.6–8.2 Ma (T40–T31), strong downcutting by gravity flow occurred, which led to the formation of the canyon. The canyon fillings began to form since 8.2 Ma (T31) and were dominated by turbidite deposits, which constituted of lateral migration and vertical superposition of turbidity channels during the time of 8.2–5.5 Ma. The interbeds of turbidity currents deposits and mass transport deposits (MTDs) were developed in the period of 5.5–3.8 Ma (T30–T28). After then, the canyon fillings were primarily made up of large scale MTDs, interrupted by small scale turbidity channels and thin pelagic mudstones. The Central Canyon can be divided into three types according to the main controlling factors, geomorphology-controlled, fault-controlled and intrusionmodified canyons. Among them, the geomorphology-controlled canyon is developed at the Ledong, Lingshui, Songnan and western Baodao Depressions, situated in a confined basin center between the northern slope and the South Uplift Belt along the Central Depression Belt. The fault-controlled canyon is developed mainly along the deep-seated faults in the Changchang Depression and eastern Baodao Depression. Intrusion-modified canyon is only occurred in the Songnan Low Uplift, which is still mainly controlled by geomorphology, the intrusion just modified seabed morphology. The full-filled time of the Central Canyon differs from west to east, displaying a tendency of being successively late eastward. The geomorphology-controlled canyon was completely filled before 3.8 Ma (T28), but that in intrusion-modified canyon was delayed to 2.4 Ma (T27) because of the uplifted southern canyon wall. To the Changchang Depression, the complete filling time was successively late eastward, and the canyon in eastern Changchang Depression is still not fully filled up to today. Difference in full-filled time in the
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