Characteristics of Fluvial Deposits in Permian, Shanxi

Ke Baojia; Chen Zhiming; Huang Jiakuan; Chen Changming; Wang Shousong; Chen Anning

The Permian System of Western Shanxi has now recognized that it mainly consists of fluvial sediments, and the ancient rivers in this area can be divided into three main types as meandering, braided and anastomosed. The depositional sequences of meandering river are typified by the development of point bars, flood plains and crevasse-splays. Lower and upper point bars with erosive contacts between them have been found in the Permian.In extreme circumstances deposits of crevasse-splays can be found as many as 11 layers within a single depositional sequence of the meandering river which indicates a very frequent occurrence of floods.Possible sand dune deposits have been suggested in some of the meandering rives. The depositional sequences that are rich in sandstones are believed to form in braided rivers.Flood plain sediments are much thinner than the channel's and their thickness is in the ratio of 0.25-0.5.The sequences are normally poor in crevasse-splays and levee deposits. Braided-meandering rivers are proposed the environment for those depositional sequences which are both rich in channel and flood plain sediments, but lack of natural levee and crevasse-splay deposits.Various scales of trough cross bedding prevail in channel sediments in these sequences. The repeatedly overlapping of channel sand bodies and the development of coal in marshes or bogs are used as the evidences of asastomosed river in the area. While the sediments overlaying just above coastal deposits, indicate the once existed flat plain when anastomosed channel was developing.

1. Institute of geology, Chinese Academy of Sciences;

2. Institute of Petroleum Exploration and Development, Changqing Oilfield

Received Date: 1989-02-28

Publish Date: 1991-03-10

Abstract: The Permian System of Western Shanxi has now recognized that it mainly consists of fluvial sediments, and the ancient rivers in this area can be divided into three main types as meandering, braided and anastomosed. The depositional sequences of meandering river are typified by the development of point bars, flood plains and crevasse-splays. Lower and upper point bars with erosive contacts between them have been found in the Permian.In extreme circumstances deposits of crevasse-splays can be found as many as 11 layers within a single depositional sequence of the meandering river which indicates a very frequent occurrence of floods.Possible sand dune deposits have been suggested in some of the meandering rives. The depositional sequences that are rich in sandstones are believed to form in braided rivers.Flood plain sediments are much thinner than the channel's and their thickness is in the ratio of 0.25-0.5.The sequences are normally poor in crevasse-splays and levee deposits. Braided-meandering rivers are proposed the environment for those depositional sequences which are both rich in channel and flood plain sediments, but lack of natural levee and crevasse-splay deposits.Various scales of trough cross bedding prevail in channel sediments in these sequences. The repeatedly overlapping of channel sand bodies and the development of coal in marshes or bogs are used as the evidences of asastomosed river in the area. While the sediments overlaying just above coastal deposits, indicate the once existed flat plain when anastomosed channel was developing.

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Reference (1)

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Characteristics of Fluvial Deposits in Permian, Shanxi

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