The Application of Punctuated Aggradational Cycles sequences to the Analysis of the Micro-strata of the Visean Heshilafu Formation, SW Tarim Basin, NW China
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摘要: 近年来,点断加积旋回理论作为微地层分析的一种重要手段受到越来越多的沉积学家和地层学家的重视(Goodwin,P.W.&Anderson.E.J,1985)。本文通过对塔里木盆地西南缘下石炭统和什拉甫组的做相分析及古生态分析,从中识别出71个点断加积旋回(PACS)。据其垂向叠加规律,建立该地区维宪期多级次高频旋回的叠加模式及层序地层格架。Abstract: The study materials of this paper were collected from the Lower Carboniferous of Damusi section, Shache County, SW Tarim Basin. The hypothesis of Punctuated Aggradational CyCles sequences (Goodwin,P. W. Anderson, E. J., 1985) is applied to the analysis of the micro-strata of the Visean (Early Carboniferous) Heshilafu Formation. Five types micro-factes are also recognized from the above micro-strata.Based on the micro-factes and palaeoecological analysis, 71 PACs (Punctuated Aggradational Cycles sequence) are identified from the 2nd and 3rd Member of the Heshilafu Formation. Among them, 36 PACs recorded in the 2nd Member of the Heshilafu Formation form the Transgressive System Tracts (TST) and Highstand System Tracts (HST) of Sequence I, the other 35 PACs consist of Sequence II standing for the 3rd cycles. The above forcro-strata analysis indicates the characters of frequent high-frequency sea-level changes and cycles within cycles (Miall, A. D., 1985) in the southwestern sea of Tarim during Visean time.Those mutiple cycles can be classified to 4 orders cycles at least corresponding to 4 orders sea-level changes.The above 71 basic high-frequency cycles controlled by 11 fourth order cycles consist of two 3rd order cycles standing for sequences, which are also controlled by a 2nd order cycle standing for supersequence. Every high-frequency sea level rising corresponds to large diversity of brachiopods. The maxium flooding surface of depositional sequence corresponds to the greatest value of the diversity of brachiopods.
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