MORPHOLOGICAL FEATURES AND FORMATION MECHANISM OF CENTRAL CANYON IN THE QIONGDONGNAN BASIN, NORTHERN SOUTH CHINA SEA
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摘要: 琼东南盆地中央峡谷平面上呈"S "型、NE向展布,西起莺歌海盆地中央凹陷带,经乐东凹陷、陵水凹陷、松南凹陷、宝岛凹陷、长昌凹陷,向东延伸进入西沙海槽。剖面形态上存在" V"型、"W "型、" U"型和复合型等4种类型。通过不同区域峡谷下切底界面的形态变化及充填特征,将中央峡谷划分为东段、西段和转换段3个区段,转换段与琼东南盆地的构造转换段相一致,即以西地区控凹断裂为NE向,而以东地区控凹断裂渐变为NEE或EW向。琼东南盆地中央峡谷的成因与构造作用和深水沉积作用关系密切,峡谷东段主要受构造作用控制,特别是深部隆起的存在为黄流期中央峡谷的形成提供了"限制性"作用,并且为后期中央峡谷的发育提供了"限制性通道";西段则受深水沉积作用的控制,重力流沉积为中央峡谷的下切和充填提供了来源。每期中央峡谷的形成均稍早于或与该时期陆坡的发育同期,最早形成于盆地东部,并随陆坡的持续向西迁移表现为不断向西上溯,下切能力逐渐减弱。Abstract: The Central Canyon in the Qiongdongnan basin,northern South China Sea,with an "S-shaped" geometry,trends NE across the Ledong-Lingshui,Songnan,Baodao and Changchang depressions.According to the morphology,filling and stratigraphic architectures,the Central Canyon can be divided into 4 types in shape:V U,W,and complex types,and 3 segments in area:eastern,western and transfer segments.The transfer segment that goes consistent with the tectonic transfer zone of the Qiongdongnan basin,has depression-controlling faults to the west of it strike in NE direction and those to the east of it turn into NEE or EW direction.The formation and development of the Central Canyon were a result from the tectonic activity and deep-water deposition.Eastern segment was controlled by submarine uplift,which limited the generation of Central Canyon in Huangliu Formation but formed a restricted channel for the later canyon.The western segemnt was associated with the deep-water deposition.The origin of the filling in the Central Canyon can be ascribed to the gravity sediment.At each stage,the generation of the Central Canyon was simultaneous to or a little earlier than that of synchronous slope.It can be proposed that the canyon formed initially at the east of Qiongdongnan basin and spread westwards gradually.
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Key words:
- morphological characteristics /
- Central Canyon /
- Miocene /
- Qiongdongnan basin
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