林理娥,卓海腾,冯进,等. 南海北部陆架早—中中新世古珠江河道发育特征及汇流冲刷模式[J]. 海洋地质与第四纪地质,2023,43(2): 31-44. doi: 10.16562/j.cnki.0256-1492.2022090601
引用本文: 林理娥,卓海腾,冯进,等. 南海北部陆架早—中中新世古珠江河道发育特征及汇流冲刷模式[J]. 海洋地质与第四纪地质,2023,43(2): 31-44. doi: 10.16562/j.cnki.0256-1492.2022090601
LIN Li’e,ZHUO Haiteng,FENG Jin,et al. Seismic sedimentary characteristics of the Ancient Pearl River system and its depositional model of confluence scours, northern shelf of the South China Sea in Early-Mid Miocene[J]. Marine Geology & Quaternary Geology,2023,43(2):31-44. doi: 10.16562/j.cnki.0256-1492.2022090601
Citation: LIN Li’e,ZHUO Haiteng,FENG Jin,et al. Seismic sedimentary characteristics of the Ancient Pearl River system and its depositional model of confluence scours, northern shelf of the South China Sea in Early-Mid Miocene[J]. Marine Geology & Quaternary Geology,2023,43(2):31-44. doi: 10.16562/j.cnki.0256-1492.2022090601

南海北部陆架早—中中新世古珠江河道发育特征及汇流冲刷模式

Seismic sedimentary characteristics of the Ancient Pearl River system and its depositional model of confluence scours, northern shelf of the South China Sea in Early-Mid Miocene

  • 摘要: 河道体系是侵蚀和沉积物搬运的重要通道,控制了大陆边缘源汇体系中砂体总体的输送和分布格局,并可有效指示古代构造活动、物源供给、气候变迁和海平面变化等丰富地质信息。研究基于高分辨率的三维地震、钻测井资料,结合层序划分方法和地震沉积学综合分析手段,揭示了南海北部珠一坳陷早—中中新世古珠江分流河道体系的类型和展布特征,并且以典型层序为例精细揭示了海平面变化控制下河道类型由辫状向曲流的转换。同时,在研究区地震剖面上识别到多处异常下切现象,经研究可解释为辫状河道内的汇流冲刷,其典型特征为:① 下切深度局部增大;② 平面近似圆形或椭圆形;③ 内部为砂质充填。虽然汇流冲刷结构在地震剖面特征上与“传统”意义的下切谷极易混淆,但在沉积特征和成因上存在较大差别,因此,对它的识别有助于避免层序界面的错误判别,并且其后期充填的河道砂体具有局限分布的特点,易于在后期海侵泥岩的覆盖下形成潜在的岩性圈闭新类型。

     

    Abstract: The river channel system is an important passage for erosion and sediment transport, which controls the overall transport and distribution pattern of sand bodies in the source-sink system of the continental margin, which indicates effectively the tectonic subsidence, sediment supply, climate change, and sea level change of the ancient sedimentary environment. Based on the high-resolution 3D seismic data, well logging and coring data, the types and distributions of the fluvial system in the Early-Mid Miocene of the Zhu I Depression in the ancient Pearl River Delta, northern South China Sea were studied in combination of the classification of the sequence stratigraphy and comprehensive seismic-sedimentary analysis. Furthermore, representative sequences were used to analyze the transition mechanism of fluvial types controlled by sea-level change. Abnormal incisions in large numbers were identified from the high-resolution seismic profiles of the study area, which can be interpreted as confluence scour in a braided channel. The typical characteristics are as follows: (1) showing local increase of cutting depth; (2) being approximately circular or elliptical in plan view; and (3) the interior being filled with sand. Although the confluence scour structure is easily confused with the incised valley in seismic profile, it is quite different in sedimentary characteristics and genesis. Therefore, the identification of confluence scour could help avoid wrong interpretation of sequence boundary, and they are filled with sediments carried by later fluvial channels, which is easy to form a new type of potential lithologic trap under the cover of the later transgressive mudstone. The confluence scours facilitated the access to the reservoirs and connected the stacked fluvial sandstones, which effectively enhanced the internal connectivity of sandstone reservoirs.

     

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