Nodular carbonates in the Lower Carboniferous, Cementstone Group of the Tweed Embayment, Berwickshire: evidence for a former sulphate evaporite facies
Nodular carbonates in the Lower Carboniferous, Cementstone Group of the Tweed Embayment, Berwickshire: evidence for a former sulphate evaporite facies
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贝里克郡特威德湾水泥岩群下石炭统的球状碳酸盐：前硫酸盐蒸发岩相的证据
DOI：
10.1144/sjg22030325
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发表时间：
1986
影响因子：
0.7
通讯作者：
W. B. Scott
中科院分区：
文献类型：
--
作者：
W. B. Scott
在特威德地区的下石炭统水泥岩群中，有少量粗晶的方解石和白云石结核状碳酸盐层夹在湖相沉积物中。结构和矿物学特征表明，它们代表了以前的结节状硬石膏层，这些硬石膏层发育在湖边缘的萨布哈斯。这些替换的硫酸盐与水泥石床（细晶碳酸盐岩）的密切联系有利于水泥石结晶化的sabkha模型，其中硫酸盐沉淀有助于促进结晶化盐水中所需的Mg/Ca比。两个主要阶段的成岩作用，每个占主导地位的矿物置换，似乎已经影响了硫酸盐相后，其形成：最初的硬石膏进行部分石膏化，然后，在后期阶段的成岩作用，白云石和方解石的硫酸盐发生更换。
Synopsis A small number of coarsely crystalline nodular carbonate beds of calcite and dolomite are intercalated within lacustrine sediments in the Lower Carboniferous Cementstone Group of the Tweed area. Textural and mineralogical features indicate that they represent former nodular anhydrite beds which developed in lake marginal sabkhas. The close association of these replaced sulphates with beds of cementstone (finely crystalline dolomites) favours a sabkha model for cementstone dolomitisation in which sulphate precipitation helps to promote the requisite Mg/Ca ratios in the dolomitising brines. Two main stages of diagenesis, each dominated by mineral replacement, appear to have affected the sulphate facies subsequent to its formation: initially the anhydrite was subject to partial gypsification and then, at a later stage of diagenesis, dolomite and calcite replacements of sulphate occurred.