Geochemical and stable isotope patterns of calcite cementation in the Upper Cretaceous Chalk, Uk: Direct evidence from calcite-filled vugs in brachiopods
Geochemical and stable isotope patterns of calcite cementation in the Upper Cretaceous Chalk, Uk: Direct evidence from calcite-filled vugs in brachiopods
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英国上白垩纪白垩中方解石胶结物的地球化学和稳定同位素模式：来自腕足动物中充满方解石的孔洞的直接证据
DOI：
10.2478/v10263-012-0007-x
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发表时间：
2012
影响因子：
1.1
通讯作者：
T. Dickson
中科院分区：
文献类型：
--
作者：
Xiufang Hu;C. Jeans;T. Dickson
回顾了英国上白垩统白垩胶结作用的研究历史。通过阴极发光成像、染色、电子显微探针和稳定同位素分析，对来自英格兰东部塞诺曼白垩的长足类腕足动物壳腔内的方解石填充孔洞进行了研究。这首次对白垩水泥的地球化学进行了详细分析。公认的有两个水泥系列：低氧和缺氧。两者均以富镁方解石开始，具有正 δ13C 值，被认为是在受好氧氨化影响的有氧条件下沉淀的。低氧系列的特点是 δ13C 值为正，随着胶结作用的进展，δ13C 值变得越来越大，达到 3.5‰ 的值。锰是早期水泥中的主要微量元素，铁是后期水泥中的主要微量元素。锰和铁还原微生物影响水泥沉淀以及微量元素和 δ13C 模式。缺氧系列的特点是 δ13C 值随着胶结的进展而变得越来越负，达到 –6.5‰ 的值。微量元素以铁、锰为主。硫酸盐还原微生物影响水泥沉淀以及微量元素和 δ13C 模式。这两个胶结物系列都与白垩区域硬化之前的岩相和早期岩化密切相关。低氧系列出现在不断沉积的白垩中，含有赤铁矿颜料和有限的有机物。缺氧系列与最初含有赤铁矿颜料但不再含有的粉笔的缓慢沉积和硬地发育以及有机物供应的增加有关。
the history of research into the cementation of the Upper Cretaceous Chalk of the UK is reviewed. Calcitefilled vugs within the shell cavities of terebratulid brachiopods from the Cenomanian Chalk of eastern england have been investigated by cathodoluminesence imaging, staining, electron microprobe and stable isotope analysis. this has provided the first detailed analysis of the geochemistry of the Chalk’s cement. two cement series, suboxic and anoxic, are recognized. both start with a Mg-rich calcite with positive δ13C values considered to have been precipitated under oxic conditions influenced by aerobic ammonification. the suboxic series is characterized by positive δ13C values that became increasingly so as cementation progressed, reaching values of 3.5‰. Manganese is the dominant trace element in the earlier cement, iron in the later cement. Mnand fe-reducing microbes influenced cement precipitation and the trace element and δ13C patterns. the anoxic series is characterized by δ13C values that became increasingly negative as cementation progressed, reaching values of –6.5‰. trace elements are dominated by iron and manganese. sulphate-reducing microbes influenced cement precipitation and the trace element and δ13C patterns. both cement series are related closely to lithofacies and early lithification pre-dating the regional hardening of the Chalk. the suboxic series occurs in chalk which was continuously deposited and contained hematite pigment and limited organic matter. the anoxic series was associated with slow to nil deposition and hardground development in chalks that originally contained hematite pigment but no longer do so, and an enhanced supply of organic matter.