Abstract

The article characterizes some geochemical proxies of endo- and exospheric processes in sedimentary sequences and analyzes their average values in Upper Precambrian clayey rocks in the South Urals. It is shown that a gradual decrease of the Th/Sc_aver value in Lower Riphean (Mesoproterozoic) ~1750–1300 Ma ago rocks correlates to a certain extent with the assembly and disintegration of the Columbia/Nuna supercontinent. The assembly of Rodinia corresponds to two peaks (Biryan Member and Min’yar Formation) of relatively high Th/Sc_aver values. However, they are separated by rocks with Th/Sc_aver values comparable with those typical of the fine-grained clastic rocks of the Mashak plume episode (~1380 Ma). Variations of Th/Cr_aver in the Lower–Middle Riphean clayey rocks also correlate quite well with the assembly of Columbia/Nuna, whereas the Upper Riphean–Vendian (Neoproterozoic) interval does not show any significant variation in Th/Cr_aver values. Hence, the assembly and disintegration of Rodinia and the associated changes in rock composition in the provenance did not have any notable effect on the fine-grained aluminosilicate rocks of the Riphean stratotype. The Middle–Upper Riphean sequences were also formed at relatively constant values of T_DM and ε_Nd(T). Hence, the Grenvillian events did not make significant contribution to the formation of rocks of the Yurmatau and Karatau groups. Average values of indicators of the redox parameters of water in the Late Precambrian basins, which existed in the eastern part (in modern coordinates) of the East European Platform, indicate that their sedimentary infilling was deposited predominantly under oxidizing or similar conditions. This conclusion contrasts markedly with the notion of the prevalence of ferruginous and euxinic environments in the World Ocean during the Late Precambrian. Comparison of variations in the mean EF_Ni and EF_Zn values in clayey rocks of the South Urals, as well as other paleoproductivity proxies, does not reveal any definite relationship of their excursions with the Late Precambrian global and subglobal, endo- and exospheric events. In the Early–Middle Riphean succession, the P₂O₅ values, slightly higher than in PAAS, correspond approximately to the period of Columbia/Nuna supercontinent existence. Lower values are typical for the clayey rocks formed during its disintegration, although the volume of mafic igneous rocks (main sources of phosphorus) in the provenances at that time should be larger. During the existence of Rodinia, the Upper Riphean clayey rocks were characterized by P₂O_5aver values both higher and lower than the PAAS. The same is true for its disintegration period. These facts suggest that the global and subglobal, endo- and exospheric processes did not significantly affect the formation of the Riphean–Vendian sedimentary sequences in the South Urals. More important here is the role of local factors.

中文翻译：

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南乌拉尔沉积序列和上前寒武纪剖面内外圈过程的地球化学代理

摘要

本文描述了沉积序列中内外圈过程的一些地球化学代理，并分析了南乌拉尔上寒武统上层黏土岩石的平均值。结果表明，所述的Th / Sc组成的逐渐降低_AVER在Lower里菲（中元）值〜一七五〇年至1300年马前岩石相关因素在一定程度上与哥伦比亚/努娜超大陆的组装和解体。罗迪尼亚对应的相对高的Th / Sc组成的两个峰（Biryan会员和Min'yar形成）的组件，_AVER值。然而，它们是由岩石的Th / SC分离_AVER与那些典型的Mashak羽情节（〜1380马）的细颗粒碎屑岩可比值。Th / Cr_平均值的变化在中下的里菲粘土岩相关成分也相当好与装配哥伦比亚/努娜的，而上部里菲-Vendian（新元）间隔不显示的Th / Cr的任何显著变化_AVER值。因此，罗迪尼亚的组装和解体以及相应的岩石成分变化对里菲亚平流型细粒硅铝酸盐岩石没有显着影响。也形成在T的相对恒定的值中，上里菲序列_DM和ε_的Nd（T）。因此，格伦维尔事件并未对尤尔马套和卡拉陶组的岩石形成做出重大贡献。东欧平台东部（现代坐标）中存在的前寒武纪盆地水的氧化还原参数指标的平均值表明，它们的沉积充填物主要是在氧化或类似条件下沉积的。该结论与前寒武纪晚期世界海洋中铁质和富余环境的流行趋势形成鲜明对比。平均EF _Ni和EF _Zn变化的比较南乌拉尔粘土质岩石中的数值，以及其他古生产力代理，并未揭示其偏移与前寒武纪晚期全球和亚全球，内外圈外事件的任何明确关系。在里菲亚早中期演替中，P ₂ O ₅值略高于PAAS中的值，大致对应于哥伦比亚/努纳河超大陆存在的时期。崩解过程中形成的黏土岩石通常具有较低的值，尽管当时物源中的镁铁质火成岩（磷的主要来源）的体积应较大。在Rodinia存在期间，上里菲安粘土岩石的特征是P ₂ O _5aver值高于和低于PAAS。其崩解期也是如此。这些事实表明，全球和亚全球，圈内和圈外的过程并没有显着影响南乌拉尔的里菲安-文迪安沉积序列的形成。这里更重要的是本地因素的作用。