The anomalous Ca cycle in the Ediacaran ocean: Evidence from Ca isotopes preserved in carbonates in the Three Gorges area, South China
The anomalous Ca cycle in the Ediacaran ocean: Evidence from Ca isotopes preserved in carbonates in the Three Gorges area, South China
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埃迪卡拉纪海洋的异常Ca循环：来自华南三峡地区碳酸盐岩中Ca同位素的证据
DOI：
10.1016/j.gr.2013.03.008
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发表时间：
2014-04
影响因子：
6.1
通讯作者：
Degan Shu
中科院分区：
文献类型：
--
作者：
Takafumi Hirata;Shigenori Maruyama;Jian Han;Degan Shu
埃迪卡拉-寒武纪是生命进化最重要的时期之一。最近的研究提供了详细的化学地层学，揭示了环境表面环境变化与生物进化之间的联系。埃迪卡拉系岩石中骨骼化石的出现表明，钙生物矿化可能开始于新元古代晚期。分子钟还预测了新元古代含有碳酸钙针状体的动物的出现。因此，估算海水中钙循环的转变具有重要意义。根据碳酸盐岩的钙同位素组成估计了海洋中古代钙旋回。然而，由于缺乏连续的埃迪卡拉纪钙同位素数据，使得钙旋回无法确定。华南地区几乎连续出露的埃迪卡拉系和寒武系地层以碳酸盐岩为主，下部为黑色页岩和砂岩，含大量化石，适合研究环境和生物变化。为了获得连续的、新鲜的、无表面蚀变和氧化的样品，我们在三峡地区的4个地点进行了从连沱、南沱、陡山沱、灯影和鄢家河到水井沱组的钻探。利用多收集器-电感耦合等离子体质谱仪（MC-ICP-MS）对碳酸盐岩中的44ca /42Ca比值进行了分析。所得δ44/42Ca比值曲线光滑。δ44/42Ca值相对显生宙异常高，在埃迪卡拉纪末期δ44/42Ca值逐渐降低。新的钙同位素化学地层学表明，埃迪卡拉纪存在一个不同的钙旋回。长期的高δ44/42Ca不能简单地用温度变化、碳酸盐矿物学差异或Ca向海洋输入/输出通量的变化来解释。对于埃迪卡拉纪观测到的高δ44/42Ca比值，我们提出了三种可能的解释：高δ44/42Ca比值的Ca输入，低δ44/42Ca值的潜在未发现的Ca汇，以及碳酸盐岩与海水之间可以忽略的同位素分异；我们认为这些因素中的一个或所有因素都导致了较高的δ44/42Ca比值。其中，我们更倾向于小的同位素分异，这表明海水中的Ca浓度在埃迪卡拉纪早期开始较低，并在整个时期增加。
The Ediacaran–Cambrian was one of the most important periods for the evolution of life. Recent studies have provided detailed chemostratigraphies that decipher the linkages between ambient surface environmental changes and biological evolution. The occurrence of skeletal fossils in Ediacaran rocks suggests that the possible onset of Ca-biomineralization started in the latest Neoproterozoic. Molecular clocks also predict the emergence of animals containing Ca-carbonate spicules in the Neoproterozoic. Therefore, it is important to estimate the transition of the Ca cycle in seawater. Ancient Ca cycles in the oceans are estimated from the calcium isotopic compositions of carbonate rocks. However, the lack of continuous Ca isotopic data in the Ediacaran leaves the Ca cycle unresolved.The almost continuously exposed, Ediacaran and Cambrian strata in South China mainly comprise carbonate rocks with subordinate black shales and sandstones, which contain many fossils, suitable for the study of environmental and biological changes. We conducted drilling from the Liantuo,viathe Nantuo, Doushantuo, Dengying and Yanjiahe to the Shuijingtuo formation at four sites in the Three Gorges area in order to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed44Ca/42Ca ratios in carbonate rocks with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) screened for diagenetic alteration.The resultant δ44/42Ca ratios exhibit a smooth curve. The values of δ44/42Ca are anomalously high relative to those in the Phanerozoic, and they gradually decrease towards the end of the Ediacaran. Our new Ca isotope chemostratigraphy suggests that a different Ca cycle had existed during the Ediacaran. The long-term, high δ44/42Ca is not simply explicable by changes in temperature, differences in carbonate mineralogy, or changes in the input/output fluxes of Ca to the ocean. We propose three possible explanations for the observed high δ44/42Ca ratios in the Ediacaran: high δ44/42Ca ratios of Ca inputs, potential undiscovered sinks of Ca with low δ44/42Ca values, and negligible isotope fractionation between carbonate and seawater; we consider that one or all of these contributed to the high δ44/42Ca ratios. Of these, we prefer the small isotope fractionation, which implies that the Ca concentration in seawater was initially low in the early Ediacaran and increased throughout that period.
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DOI：
--
发表时间：
2005
期刊：
--
影响因子：
--
作者：
F. Böhm;A. Eisenhauer;A. Heuser;W. Kiessling;K. Wallmann
通讯作者：
F. Böhm;A. Eisenhauer;A. Heuser;W. Kiessling;K. Wallmann
DOI：
10.1073/pnas.0503660102
发表时间：
2005-07-05
影响因子：
11.1
作者：
Peterson, KJ;Butterfield, NJ
通讯作者：
Butterfield, NJ
DOI：
10.1017/s0022336000058108
发表时间：
2009-01
期刊：
--
影响因子：
--
作者：
Lin Dong;S. Xiao;B. Shen;Chuanming Zhou;Guoxiang Li;Jinxian Yao
通讯作者：
Lin Dong;S. Xiao;B. Shen;Chuanming Zhou;Guoxiang Li;Jinxian Yao
DOI：
10.1016/j.palaeo.2007.02.028
发表时间：
2007-12-06
影响因子：
3
作者：
Halverson, Galen P.;Dudas, Francis O.;Bowring, Samuel A.
通讯作者：
Bowring, Samuel A.
DOI：
10.1111/j.1755-6724.1922.mp11-4008.x
发表时间：
2009-05
期刊：
Bulletin of The Geological Society of China
影响因子：
--
作者：
A. W. Grabau
通讯作者：
A. W. Grabau