Study on Silurian Turbidite System in Bajiaokou Area, Shaanxi
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摘要: 本文从浊积岩相、相组合以及组合序列等分析方法入手对芭蕉口志留纪浊积岩系进行了研究。根据目前古代浊积岩研究中的一些新思想,在识别不同浊积岩相和相组合时使用了新的鉴定标志,并且强调了以前曾被忽视了的水道-舌体过渡带沉积。研究结果证明,此浊积岩系共由六个相结合构成,即盆地平原相组合、舌体边缘相组合、舌体相组合、水道-舌体过渡带相组合、水道-漫滩相组合以及盆地斜坡相组合.(?)个浊积岩系是在一种不成熟的被动大陆边缘环境下形成,并类似于斜坡裙浊流沉积。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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