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首页> 外文期刊>Acta Geologica Sinica >From Basin Black Shales to Platform Carbonate Rocks: A Study on Sequence Stratigraphy for the Lower Cambrian of the Upper-Yangtze Region in South China
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From Basin Black Shales to Platform Carbonate Rocks: A Study on Sequence Stratigraphy for the Lower Cambrian of the Upper-Yangtze Region in South China

机译:从盆地黑色页岩到台地碳酸盐岩:华南长江上游地区下寒武统层序地层研究

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In the Upper-Yangtze region, especially in Guizhou Province and its adjacent areas, the Lower Cambrian is well developed and is marked by a succession from black shales of the basin facies to carbonate rocks of the platform facies. The drowning event of the platform occurring at the turn from Sinian to Cambrian resulted in a set of black shales, i.e. the Niutitang Formation, which makes up the bottom part of the Lower Cambrian. With the shoaling of the sedimentary environment, a set of carbonate rocks, i.e. the Qingxudong Formation, was formed in the top part of the Lower Cambrian. Thus, the Lower Cambrian in the study area makes up one second-order sequence that can be further subdivided into five third-order sequences, and forms a regularly cyclic succession of transgression-regression. There is a regularly vertical stacking pattern for the third-order sequences in the second-order sequence. From bottom to top, the succession of the "CS (condensed section) +HST (high-stand system tract)" of the third-order sequences is changed into the succession of the "TST (transgressive system tract)+CS+HST". Correspondingly, the drowning-type sequence boundary is changed into the exposure-type one. Therefore, both the second-order and the third-order sequences have similar sedimentary-facies architectures. A concomitant with these temporal changes, the Lower Cambrian with a thickness of 1000 m that contains five third-order sequences is changed into a condensed succession that cannot identify third-order sequences toward the southeast with the deepening of the sedimentary environment. According to the elementary features of the third-order sequences, i.e. the regularity o sedimentary-facies successions in space and the synchronism of sedimentary-environment changes in time, the detailed division of the third-order sequences at main logged sections in different paleogeographical background becomes the basis to establish the sequence-stratigraphic framework that can demonstrate two types of facies-changing surface and two types of diachronism in the stratigraphic records. This sequence-stratigraphic framework shows a growing process of the carbonate platform from the base of the condensed succession formed by black shales of basin facies. Resulting from the rapid transgression at the turn from Sinian to Cambrian the ecological space became open, which formed the antecedent condition of paleogeographical setting for "the Cambrian Biological Explosion". Ultimately, the genetic relationship between the depositional events and the biological-diversity events is very complex and there remain lots of problems that need further research in the future.
机译:在上扬子地区,尤其是贵州省及其邻近地区,下寒武统发育良好,其特征是盆地相的黑色页岩到台地相的碳酸盐岩。在从震旦纪到寒武纪转弯时发生的平台溺水事件导致了一组黑色页岩,即牛下塘组,它构成了下寒武统的底部。在沉积环境的带动下,下寒武统顶部形成了一套碳酸盐岩,即清徐洞组。因此,研究区的下寒武统构成了一个二阶序列,该二阶序列可以进一步细分为五个三阶序列,并构成了海侵回归的规则循环序列。二阶序列中的三阶序列存在规则的垂直堆叠模式。从下至上,将三阶序列的“ CS(压缩截面)+ HST(高位系统域)”的序列更改为“ TST(侵略性系统域)+ CS + HST”的序列。相应地,淹没型序列边界变为暴露型边界。因此,二阶和三阶序列都具有相似的沉积相构造。与这些时间变化相伴的是,厚度为1000 m的包含五个三阶序列的下寒武统被转变成一个密集的序列,随着沉积环境的加深,该序列无法识别出东南向的三阶序列。根据三阶层序的基本特征,即空间上的沉积相序的规律性和沉积-环境变化的时间同步性,对不同古地理背景下主要测井剖面的三层层序进行了详细划分。成为建立层序-地层学框架的基础,可以在地层记录中显示两种类型的相变表面和两种历时。该层序地层学框架显示了碳酸盐台地从盆地相黑色页岩形成的稠密演替的基础上的生长过程。由于从震旦纪到寒武纪转变的快速侵袭,生态空间变得开放,形成了“寒武纪生物爆炸”的古地理环境的先决条件。最终,沉积事件与生物多样性事件之间的遗传关系非常复杂,并且仍有许多问题需要在未来进行进一步研究。

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