Cambrian small skeletal fossil and carbon isotope records of the southern Huangling Anticline, Hubei (China) and implications for chemostratigraphy of the Yangtze Platform
Cambrian small skeletal fossil and carbon isotope records of the southern Huangling Anticline, Hubei (China) and implications for chemostratigraphy of the Yangtze Platform
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DOI：
10.1016/j.palaeo.2020.109817
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发表时间：
2020-09
期刊：
影响因子：
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通讯作者：
M. Steiner;Ben Yang;S. Hohl;Lei Zhang;Shan Chang
中科院分区：
文献类型：
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作者：
M. Steiner;Ben Yang;S. Hohl;Lei Zhang;Shan Chang
黄陵背斜南部岩家河组和天柱山段发育了丰富的小型骨骼化石组合。Anabarites trisulcatus- Protohertzina anabarica组合带在岩家河组中上部识别出小Skeleton化石1带，而最上部的薄层砾岩灰岩单元产生了混合组合，这是小Skeleton化石1 - 3带的源物质改造和再沉积的结果（包括Anabarites trisulcatus、Protohertzina anabarica、P. unguliformis、Watsonella crosbyi、Aldanella attleborensis、Anabarella plana）。通过生物地层对比，发现严家河组以及严家河组与水井沱组之间存在较长的间断。本文所测得的δ ~（13）C_（carb）值与前人报道的值有一定的偏差。基于新的生物地层对比，δ 13 C碳趋势记录值在上部Anabarites trisulcatus - Protohertzina anabarica组合带的-3到+4.4‰之间波动，这在扬子地台中是不寻常的。滇东岩家河组上部和大海段δ 13 C碳值为正值的区间反映了局部水相的影响。此外，在这里认为，选择一个碳同位素峰值作为主要的指标工具，在老林剖面定义寒武纪第二阶段必须谨慎对待，因为这种同位素偏移的影响，区域性的水团，并不反映一个开放的海洋海水签名，强调其他技术和理论问题的一般应用化学地层学在寒武系浅水碳酸盐岩台地。总体而言，我们认为，化学地层对比需要支持生物地层工具。
Rich small skeletal fossil assemblages are described from the Yanjiahe Formation and Tianzhushan Member of southern Huangling Anticline. TheAnabarites trisulcatus– Protohertzina anabaricaAssemblage Zone (Small Skeletal Fossil Zone 1) is recognized in the middle to upper Yanjiahe Formation, while the thin topmost conglomeratic limestone unit yielded a mixed assemblage resulting from reworking and redeposition of source material of Small Skeletal Fossil Zones 1 to 3 (includingAnabarites trisulcatus, Protohertzina anabarica, P. unguliformis, Watsonella crosbyi, Aldanella attleborensis, Anabarella plana). Our revised biostratigraphic correlation indicates the existence of longer hiatuses in the Yanjiahe Formation and between the Yanjiahe and Shuijingtuo formations. The obtained δ13Ccarbvalues in our profile deviate in some details from those of some previous reports. Based on the new biostratigraphic correlation, the δ13Ccarbtrend records values oscillating between −3 to +4.4‰ in the upperAnabarites trisulcatus - Protohertzina anabaricaAssemblage Zone, which is unusual for the Yangtze Platform. This interval of positive δ13Ccarbvalues in the upper Yanjiahe Formation and the Dahai Member of eastern Yunnan are here interpreted to reflect the impact of a local aquafacies. Moreover, it is here argued that the selection of a carbon isotope peak as a primary index tool in the Laolin section for defining the Cambrian Stage 2 must be treated with caution, as this isotope excursion is influenced by a regional water mass and does not reflect an open marine seawater signature, underlining other technical and theoretic concerns on the general application of chemostratigraphy in Cambrian shallow-water carbonate platforms. Overall we suggest that chemostratigraphic correlations need to be supported by biostratigraphic tools.