Abstract

This work considers for the first time mineralogical features of the Lower Cambrian (Tommotian) glauconite collected from terrigenous–carbonate rocks of the Kessyusa Group (upper part of the Mattaia Formation and lower part of the Chuskuna Formation), as well as from basal beds of the overlying limestones of the Erkeket Formation. Samples were taken from three sections on the northwestern slope of the Olenek Uplift, North Siberia. Their stratigraphic assignment is given on the basis of recent data (Nagovitsin et al., 2015 and others). Grains of the layer silicates are made up of the mixed layer mica–smectite phases with relatively low (<10%) and higher (10–20%) contents of expandable layers (unit cell parameter b = 9.06–9.12 Å). Micaceous minerals form a series from glauconite to Al-glauconite (Al index K_Al = ^VIAl/(^VIFe³⁺ + ^VIAl) is 0.11–0.47 and 0.60, respectively), with the K₂O content varying from 6.80 to 8.54%. Detailed lithological-mineralogical characteristics is given for the first time for the glauconite-bearing rocks, the primary sediments of which were accumulated in the prefrontal beach zone and transitional beach–shelf zone in the Siberian epicontinental marine paleobasin (Marusin, 2016). Origin of the studied grains (authigenic, allothigenic) is discussed and their secondary alterations at different stages of lithogenesis are considered (rewashing, phosphatization, pyritization, calcitization, ferrugination, and others). It is shown that the obtained preliminary Rb–Sr dates (450–320 Ma) are “rejuvenated” and do not correspond to the age value of 541.0 Ma accepted for the Vendian–Lower Cambrian boundary (Gradstein et al., 2012). This can be related to diverse secondary alterations of the glauconite grains during the rewashing, transportation, and different stages of diagenesis of primary sediments after their redeposition, as well as at stages of catagenesis and hypergenesis of the glauconite-bearing rocks.

中文翻译：

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北西伯利亚Olenek隆起的下寒武统陆相碳酸盐岩中的青灰石

摘要

这项工作首次考虑了从Kessyusa组（Mattaia组的上部和Chuskuna组的下部）的陆源碳酸盐岩中收集的下寒武统（Tommotian）青绿岩的矿物学特征。 Erkeket组上覆的石灰岩。样品取自北西伯利亚Olenek隆起西北斜坡的三个部分。根据最近的数据给出了它们的地层分配（Nagovitsin等，2015等）。硅酸盐层的晶粒由云母-蒙脱石混合相组成，可膨胀层含量相对较低（<10％）而较高（10-20％）（晶胞参数b = 9.06-9.12Å）。云母状矿物形成了从青绿岩到铝青绿岩（Al指数）的系列。K _Al = ^VI Al /（^VI Fe ³⁺ + ^VI Al）分别为0.11-0.47和0.60），其中K ₂O含量在6.80至8.54％之间。首次给出了含青石岩的岩石的岩石-矿物学特征，其主要沉积物聚集在西伯利亚陆陆海洋古盆地的前额滩区和过渡滩-陆架区（Marusin，2016）。讨论了所研究谷物的来源（自生的，异源的），并考虑了它们在成岩作用的不同阶段的二次变化（重新洗涤，磷化，黄铁矿化，钙化，铁素化等）。结果表明，获得的Rb-Sr初步日期（450-320 Ma）是“充满活力的”，并且与Vendian-Cambrian下界接受的541.0 Ma年龄值不对应（Gradstein等，2012）。