Study on Silurian Turbidite System in Bajiaokou Area, Shaanxi

Meng Qingren

The lower to middle Silurian strata are well exposed in Bajiaokou area, which is geologically located in the southern part of the Qinling orogenic belt. This sequence has been intensely studied by means of biostratigraphy in recent years, but less effort was made to address its lithofacies problems.As a result, this study is earned out to approach the facies analyses and paleoenvironmental interpretation of this sequence. The interpretation of the strata as a deep-water turbidite system is based on the following lines of evidence: the strata show typical sedimentary features of sediment gravity flows, mainly turbidity current, and the turbidite facies A to G (Mutti and Ricci Lucchi, 1972) are recognized; there are no phenomina of wave reworking; fossils are exclusively graptolites and no shallow-water benthic fossils are found; trace fossils also indicate deep water settings.The turbidite facies can be grouped into sevaral distinct facies associations indicative of different depositional elements of this turbidite system, those that are discussed in detail include: basin plain facies assiciation. lobe fringe facies association, sandstone lobe facies association, channel-lobe transition facies association, channel-levee complex facies association, and basinal slope facies association. To identify the diverse turbidite facies and facies associations, some new criteria are employed, such as different sorts of scours, and the channel-lobe transition element is particularly stressed because its importance was ignored in the previous work.The turbidite system is divided into four stages, and the developmental trend is form basin plain deposit to proximal deposit. It is concluded that this turbidite system was developed in an immature passive continental margin and quite similar to the slope apron turbidite deposit because of the absence of major channel fill of inner fan deposit.

Xi' an College of Geology

Received Date: 1987-07-20

Publish Date: 1991-03-10

Abstract: The lower to middle Silurian strata are well exposed in Bajiaokou area, which is geologically located in the southern part of the Qinling orogenic belt. This sequence has been intensely studied by means of biostratigraphy in recent years, but less effort was made to address its lithofacies problems.As a result, this study is earned out to approach the facies analyses and paleoenvironmental interpretation of this sequence. The interpretation of the strata as a deep-water turbidite system is based on the following lines of evidence: the strata show typical sedimentary features of sediment gravity flows, mainly turbidity current, and the turbidite facies A to G (Mutti and Ricci Lucchi, 1972) are recognized; there are no phenomina of wave reworking; fossils are exclusively graptolites and no shallow-water benthic fossils are found; trace fossils also indicate deep water settings.The turbidite facies can be grouped into sevaral distinct facies associations indicative of different depositional elements of this turbidite system, those that are discussed in detail include: basin plain facies assiciation. lobe fringe facies association, sandstone lobe facies association, channel-lobe transition facies association, channel-levee complex facies association, and basinal slope facies association. To identify the diverse turbidite facies and facies associations, some new criteria are employed, such as different sorts of scours, and the channel-lobe transition element is particularly stressed because its importance was ignored in the previous work.The turbidite system is divided into four stages, and the developmental trend is form basin plain deposit to proximal deposit. It is concluded that this turbidite system was developed in an immature passive continental margin and quite similar to the slope apron turbidite deposit because of the absence of major channel fill of inner fan deposit.

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Study on Silurian Turbidite System in Bajiaokou Area, Shaanxi

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