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Sedimentary architecture and provenance analysis of a sublacustrine fan system in a half-graben rift depression of the South China Sea
Sedimentary Geology ( IF 2.8 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.sedgeo.2020.105781
Entao Liu , Hua Wang , Yuexing Feng , Songqi Pan , Zhenhua Jing , Qinglin Ma , Huajun Gan , Jian-xin Zhao

Abstract Research on the sedimentary architecture and provenance of sublacustrine fans is crucial not only to better understand the gravity flow evolution in lacustrine basins but to successfully locate hydrocarbon reservoirs. This study targets at a sublacustrine fan with a large petroleum reserve that has been revealed by drilling within an Eocene lacustrine succession in the Fushan Depression, northern South China Sea. The sedimentary architecture of the sublacustrine fan was investigated through the integration of core, well logs and 3D seismic data, and its provenance was identified by detrital zircon U Pb dating. The examination of 117 m long continuous drilling core reveals four major lithofacies in the sublacustrine fan deposits, which are interpreted as deposits of two types of gravity flows (cohesive debris flows and turbidity currents). The cohesive debris flows developed in the lower section are mainly composed of massive gravelly mudstones with various floating clasts and high clay content, whereas the turbidity currents in the upper section are characterized by parallel to ripple bedding and normal graded bedding. These observations reflect a transformation from cohesive debrites to turbidites from deep to shallow water environments. In addition, provenance analysis of 648 detrital zircon U Pb ages yield a well-defined relationship between potential provenance areas and sublacustrine fan deposits in the deep lake. The U Pb age pattern of the fan is similar to that of northern fan delta deposits, but different from sediments from the western and southern deltas, suggesting that the sublacustrine fan was sourced from the north. Therefore, a deep-lacustrine depositional model is proposed for the sublacustrine fan, showing a gravity-driven evolution process from fan delta front in the northern slope into cohesive debrites and then turbidites in the lake center. This was mainly controlled by fault-related topography and sediment supply. This study highlights the effective use of the detrital zircon U Pb dating method to identify the provenance direction of sublacustrine fans, and the proposed depositional model may be applicable to reservoir prediction in other lacustrine basins.

中文翻译:

南海半地堑裂陷坳陷湖底扇系统沉积构型及物源分析

摘要 研究湖底扇的沉积构造和物源不仅对更好地理解湖盆重力流演化和成功定位油气藏具有重要意义。本研究的目标是在南海北部富山坳陷始新世湖相系列中钻探发现的具有大量石油储量的湖底扇。通过岩心、测井和3D地震资料的整合研究了湖底扇的沉积构造,并通过碎屑锆石U Pb定年确定了其物源。对 117 m 长连续钻孔岩心的检查揭示了湖底扇形沉积物中的四种主要岩相,它们被解释为两种重力流沉积物(粘性碎屑流和浊流)。下段发育的粘性泥石流主要为块状砾质泥岩,漂浮碎屑种类繁多,粘土含量高,而上段浊流则以平行波纹层理和正常梯度层理为特征。这些观察结果反映了从深水环境到浅水环境从粘性碎屑到浊流的转变。此外,对 648 个碎屑锆石 U Pb 年龄的物源分析产生了潜在物源区与深湖湖底扇沉积之间明确定义的关系。该扇的U Pb年龄格局与北部扇三角洲沉积物相似,但不同于西部和南部三角洲的沉积物,表明湖底扇起源于北部。所以,提出了湖底扇深湖沉积模型,显示了重力驱动的演化过程,从北坡的扇三角洲前缘到粘性碎屑岩,然后是湖中心的浊积岩。这主要受断层相关地形和沉积物供应控制。本研究突出了碎屑锆石U Pb定年方法在确定湖底扇物源方向方面的有效应用,所提出的沉积模型可能适用于其他湖盆盆地的储层预测。
更新日期:2020-11-01
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