Transgression Model of Restricted Epicontinental Sea
摘要: 突发性海侵是受限陆表海的特征之一,受海平面升降引起的峡口启闭控制,多发生在板块的活动边缘。突发性海侵常有相序缺失,常见海陆相交互层;海相层在大范围内分布稳定,无明显相变,具有良好的等时性,可以作为区域对比的标志层。受限陆表海的突发性海浸,有利于油气的生成和聚集。Abstract: The restricted epicontinental sea lies on the edge of a continent and surrounded by islands as a sill. The sedimentation there is characterized by the episodic sea water invasion which takes place in short period and rapidly covers a wide area. As a consequence, there always occur discontinuous depositional sequence and frequently alternation of marine and nonmarine deposits.The transgression is controlled by the openning and closing of the gateway between islands due to the sea level fluctuation.lt is the defined event transgression or episodic transgression by the authors. In view of the plate tectonics, the back-arc basins arround active margin are typical epicontinental sea, so episodic transgression happens quite often. The episodic transgressive beds are magnafacies as well as parvafacies (isochronous).Therefore they can be used as a marker of stratigraphic correlation. The Mediterranean sea had repeatedly dried at the end of Miocene due to the openning and closing of the Strait of Gibratar which caused the alternation of deep sea and Sabkha sedimentation.lt provides a good example of episodic trasgression.The East China Sea was a typical epicontinental sea in Cenozoic. the sea level fluctuation resulted from climatic change caused many times of episodic transgression and interruption of marine sedimentation and resulted in a sequence consiting of interbeded marine and non-marine deposits. We can go far back to the Carboniferous deposits in northern China where the marine beds of limestone can be traced in a wide area even though they are very thin, the fauna assemblage indicates that they are formed in a normal marine environment. No transitional sequence could be found.The boundaries between the limestone and the terrigenous deposits are always abrupt. The Late Permian deposits in Sichuan Basin are characterized by the interbedding of pelagic carbonates and coal beds.They can only be interpreted by the model of episodic transgression. The depositional characteristics of the restricted epicontinental sea depends mainly on their tectonic-topographic pattern. Such an environments is demonstrated benifit to the formation of coal and hydrocarbons.lt can be ear ted that the depositional features would be useful oil and gas survey in both different stages.
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