Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China
Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China
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DOI：
10.1017/s0016756819000293
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发表时间：
2019-11-01
影响因子：
2.3
通讯作者：
Kaufman, Alan J.
中科院分区：
文献类型：
--
作者：
Cui, Huan;Xiao, Shuhai;Kaufman, Alan J.
Ediacaran Dengying Formation（c. 551.1-538.8 Ma）是埃迪卡拉类大型化石与骨骼化石、两侧动物遗迹一起沿着保存于碳酸盐相的两个层序之一。鉴于在不到1230万年的时间内沉积的含碳酸盐岩地层的显著厚度，灯影组具有构建埃迪卡拉纪末期相对连续的化学地层剖面的潜力。本文对陕西宁强高家山剖面灯影组进行了详细的沉积学和化学地层学（δ 13 C（carb）、δ O-18（carb）、δ C-13（org）、δ S-34（黄铁矿）和Sr-87/Sr-86）研究。沉积学结果显示，总体上为浅海沉积环境。灯影组藻白云岩段中普遍存在碳酸盐角砾岩、充填空洞的葡萄状沉淀物和文石晶体扇，表明潮缘相曾多次岩溶作用。岩溶作用的时间可能是早期的，可能是在白云岩沉积物沉积后不久。自生文石胶结物的存在表明埃迪卡拉纪末期海洋具有高碱度。微钻样品的地球化学分析表明，不同的组合物登记在不同的碳酸盐相，这应该被考虑时，建设化学地层剖面代表海水化学的真实时间变化。综合化学地层学数据表明，有机碳和黄铁矿的埋藏增强，以及广泛的海洋缺氧的发生（至少在高家山段）。在海水碱度升高和黄铁矿埋藏速率增加的时期，盆地快速沉降和碳酸盐积累可能促进了早期生物矿化后生动物的进化创新。
The terminal Ediacaran Dengying Formation (c. 551.1-538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for construction of a relatively continuous chemostratigraphic profile for the terminal Ediacaran Period. In this study, a detailed sedimentological and chemostratigraphic (delta 13C(carb), delta O-18(carb), delta C-13(org), delta S-34(pyrite), and Sr-87/Sr-86) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow-marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.