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首页> 外文期刊>Anais da Academia Brasileira de Ciencias >Carbon and oxygen isotope geochemistry of Ediacaran outer platform carbonates, Paraguay Belt, central Brazil
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Carbon and oxygen isotope geochemistry of Ediacaran outer platform carbonates, Paraguay Belt, central Brazil

机译：巴西中部巴拉圭带Ediacaran外层碳酸盐岩的碳氧同位素地球化学

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摘要

After the late Cryogenian glaciation the central region of Brazil was the site of extensive deposition of platformal carbonates of the Araras Group. This group includes a basal cap carbonate sequence succeeded by transgressive, deep platform deposits of bituminous lime mudstone and shale. Facies and stratigraphic data combined with carbon and oxygen isotopic analyses of the most complete section of the transgressive deposits, exposed in the Guia syncline, were used to evaluate the depositional paleoenvironment and to test the correlation of these deposits along the belt and with other units worldwide. The studied succession consists of 150 m thick tabular beds of black to grey lime mudstone and shale with predominantly negative delta13C PDB values around -2.5 to -1‰ . The delta13C PDB profile of Guia syncline shows a clear correlation with the upper portion of Guia Formation in the Cáceres region, about 200 km to the southwest. The delta13C PDB profile of the Araras Group is comparable with delta13C PDB profiles of Ediacaran units of the southern Paraguay Belt, western Canada, and the Congo and Kalahari cratons. Moreover, facies distribution, stratigraphy and the carbon isotopic profile of the Araras Group match the middle Tsumeb Subgroup in Namibia, which reinforces the Ediacaran age assigned to the Araras Group.
机译：低温冰期晚期冰川之后，巴西的中部地区是Araras集团平台性碳酸盐岩大量沉积的地点。该组包括一个基性盖层碳酸盐岩层序，其次是海侵石灰岩泥岩和页岩的深海平台沉积。在Guia向斜中暴露的海相沉积的最完整部分的相和地层数据与碳和氧同位素分析相结合，用于评估沉积古环境，并测试这些沉积物沿地带和世界其他地区的相关性。研究的演替包括150m厚的黑色至灰色石灰泥岩和页岩的板状床，主要δ13CPDB值为-2.5至-1‰负。圭亚那向斜线的delta13C PDB剖面显示与卡塞雷斯地区（距西南约200公里）的圭亚那组上部明显相关。 Araras集团的delta13C PDB分布图与南部巴拉圭带，加拿大西部，刚果和卡拉哈里克拉通的Ediacaran单位的delta13C PDB分布图相当。此外，阿拉拉斯组的相分布，地层学和碳同位素特征与纳米比亚中部的楚梅布次组相匹配，这增强了阿拉拉斯组的埃迪卡拉安时代。

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