Chemo- and biostratigraphy of the Gaojiashan section (northern Yangtze platform, South China): a new Pc-C boundary section
Chemo- and biostratigraphy of the Gaojiashan section (northern Yangtze platform, South China): a new Pc-C boundary section
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DOI：
10.5194/fr-18-105-2015
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发表时间：
2015-06
期刊：
影响因子：
1.4
通讯作者：
A. Gamper;U. Struck;F. Ohnemueller;C. Heubeck;S. Hohl
中科院分区：
文献类型：
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作者：
A. Gamper;U. Struck;F. Ohnemueller;C. Heubeck;S. Hohl
抽象的。华南埃迪卡拉纪末期灯影组（~ 551-~ 542 Ma）广泛分布，是地球历史上碳酸盐碳同位素负偏移最显著的时期之一，对全球前寒武纪-寒武纪界线的对比具有重要意义。灯影组主要是碳酸盐岩地层的研究，主要是因为他们独特的保存其终端埃迪卡拉动物群，但其地球化学背景知之甚少。首次获得了陕西高家山剖面钙质硅质岩浅水沉积物的高分辨率稳定同位素（δ 13 C，δ 18 O）记录。该剖面自下而上包括灯影组藻白云岩段、高家山段和北湾段。在高家山段最上部记录到一个δ 13 C负偏移至-6 ‰的主要数据，其形状和幅度与全球前寒武纪-寒武纪界线的δ 13 C负偏移相当。我们的数据集是一致的“浅水缺氧”的情况下，这被认为是有助于“寒武纪大爆发”。Cloudina的地层产出和δ 13 C的大幅度负偏移表明，前寒武纪-寒武纪界线位于高家山段顶部附近，因此，北湾段上覆的碳酸盐岩和碳酸盐岩的时代最早为寒武纪。因此，高家山剖面可能代表了一个新的跨越前寒武系-寒武系界线的浅水剖面。虽然生物和化学地层学数据支持这种新的解释，我们不能排除的可能性，关键的游览可能代表一个局部扰动，表明一个限制盆地环境。
Abstract. The widespread, terminal Ediacaran Dengying Formation (~ 551–~ 542 Ma) of South China hosts one of the most prominent negative carbonate carbon isotope excursions in Earth's history and thus bears on the correlation of the Precambrian–Cambrian boundary worldwide. The dominantly carbonate strata of the Dengying Formation are largely studied for their unique preservation of its terminal Ediacaran fauna but their geochemical context is poorly known. This study presents the first high-resolution stable isotope record (δ13C, δ18O) of calcareous siliciclastic shallow-water deposits of the Gaojiashan section (Shaanxi Province). The section includes (in ascending order) the Algal Dolomite Member, the Gaojiashan Member and the Beiwan Member of the Dengying Formation. Our data record a major δ13Ccarb negative excursion to −6 ‰ in the uppermost Gaojiashan Member which is comparable in shape and magnitude to the global Precambrian–Cambrian boundary negative δ13C excursion. Our data set is consistent with a "shallow-water anoxia" scenario which is thought to contribute to the "Cambrian explosion". The stratigraphic occurrence of Cloudina and a large negative δ13C excursion suggest that the Precambrian–Cambrian boundary is located near the top of the Gaojiashan Member and, consequently, that overlying carbonates and dolomites of the Beiwan Member are of earliest Cambrian age. Thus the Gaojiashan section may represent a new shallow-water section spanning the Precambrian–Cambrian boundary. Although bio- and chemostratigraphic data support this novel interpretation, we cannot exclude the possibility that the key excursions may represent a local perturbation indicating a restricted-basin environment.