珠江口盆地惠州凹陷恩平组浅水辫状河三角洲沉积

SHALLOW BRAIDED DELTAIC SYSTEM IN ENPING FORMATION OF HUIZHOU DEPRESSION,PEARL RIVER MOUTH

  • 摘要: 珠江口盆地惠州凹陷恩平组广泛发育浅水湖泊,然而长期被认为是断陷湖盆的沉积充填模式。通过岩性组合、地球物理响应特征、古生物组合、地球化学指标、砂岩粒度特征等方面的综合分析,论证了在惠州凹陷恩平组沉积时期湖盆广阔平缓,湖泊淤浅,陆源供应充足,证实了在这种沉积背景下,发育浅水辫状河三角洲沉积体系。该体系具有三角洲平原、辫状河道极其发育,而河口坝等反旋回序列不发育等特征,该体系的提出揭示了研究区断拗转换期湖盆广、薄煤层发育、砂体分布广、沉降速率高、碎屑颗粒粗等沉积特色,与前人探讨的惠州凹陷恩平组的沉积面貌完全不同,为惠州凹陷古近系的勘探提供了新的理论和思路。

     

    Abstract: Shallow lacustrine deposits are widely distributed in the Enping Formation of the Huizhou depression of the Pearl River Mouth Basin,and has long been considered as a kind of infilling of a faulted basin.Through the study of lithology,geophysical responses,paleontology,geochemical proxies,and grain size distribution,this paper confirms that a special delta,shallow braided river delta,was developed in the Enping Formation of the Huizhou depression in a broad shallow flat lake,with sufficient terrigenous deposits.And this system is characterized by a well-developed delta plain,an undeveloped coarsening-upwards sequence of a mouth bar,and a well-developed braided stream.Depositional features of shallow braided delta are widely observed,such as the lacustrine deposits formed in the fault-sag transition stage,wide-spread thin coal seam,high sedimentation rate,widely distributed sand body,and coarse deposits in the research area,totally different with the depositional features of the infilling deposits in a faulted lake.The new model may help exploration in the Eogene of the Huizhou depression.

     

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