Constraining the onset and environmental setting of metazoan biomineralization: The Ediacaran Nama Group of the Tsaus Mountains, Namibia
Constraining the onset and environmental setting of metazoan biomineralization: The Ediacaran Nama Group of the Tsaus Mountains, Namibia
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DOI：
10.1016/j.epsl.2023.118336
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发表时间：
2023-08-17
影响因子：
5.3
通讯作者：
Wood, Rachel A.
中科院分区：
文献类型：
--
作者：
Bowyer, Fred T.;Uahengo, Collen-Issia;Wood, Rachel A.
动物（后生动物）生物矿化的出现标志着地球历史上的一个根本性转变，促进了新的身体计划的多样化以及碳酸盐沉积物生产的生物控制，导致全球碳循环的永久性重组。已知最古老的骨骼后生动物，管状的“cloudinids”，例如，Cloudina，出现在终端埃迪卡拉纪的纳马组，纳米比亚，但正是在何时，何地，以及为什么后生动物第一次获得了生物矿化的能力和他们的时间相对于区域的三角洲; 13 Ccarb配置文件是无证的。因此，评估这一关键事件可能的环境触发因素需要准确的年龄，古环境背景和最早期云顶的地球化学背景的约束。在这里，我们提出了新的地层学，沉积学和地球化学（13 Ccarb和18 Ocarb）数据从最古老的地层（达比斯组）的Nama组从Witputs次盆地，暴露在Tsau Khaeb国家公园（原Sperrgebiet）的Tsaus山脉。这限制了最古老的确认发生的Cloudina石灰岩较低的Kliphoek成员，约。551-550 Ma，横向沉积，相当于更近端的含矿Kliphoek石英岩。这些石灰岩主要是负的&三角洲; 13 Ccarb值，立即恢复从基础纳玛负&三角洲; 13 Ccarb偏移（BANE），并在浅水沃茨沉积后，从半限制，碳酸盐岩，开放的海洋碳酸盐岩设置的过渡。区域相关性表明，Cloudina首先出现在一个时间间隔的主要是低氧和不稳定的，区域海洋氧化还原条件。我们的结论是，数据不支持长期转向更稳定的，含氧的条件作为驱动程序的第一次出现在后生动物的tenonization，但确实表明，开放的海洋碳酸盐设置高碳酸盐过饱和度，以支持钙化Cloudina。在Nama组，Cloudina的出现也明显与一个主要的海平面低水位相吻合，我们假设这可能使这些更远的设置的氧合。因此，浅海氧气的这种扩张可能为不需要代谢成本的创新提供了进化驱动力，例如Cloudina生物矿化的开始。© 2023作者。由Elsevier B. V.发布。这是CC BY许可下的开放获取文章（http：//creativecommons.org/licenses/by/4.0/）。
The advent of animal (metazoan) biomineralization marks a fundamental transition in Earth's history, facilitating the diversification of novel body plans as well as the biological control of carbonate sediment production, resulting in a permanent restructuring of the global carbon cycle. The oldest known skeletal metazoans, the tubular 'cloudinids' e.g., Cloudina, appeared during the terminal Ediacaran of the Nama Group, Namibia, but precisely when, where, and why metazoans first acquired the ability to biomineralize and their timing relative to the regional & delta;13Ccarb profile is undocumented. Assessing possible environmental triggers for this key event therefore requires accurate constraint of the age, paleoenvironmental setting and the geochemical context of the earliest cloudinids. Here we present new stratigraphic, sedimentological, and geochemical (& delta;13Ccarb and & delta;18Ocarb) data from the oldest strata (Dabis Formation) of the Nama Group from the Witputs Sub-basin, exposed in the Tsaus Mountains of the Tsau Khaeb National Park (formerly Sperrgebiet). This constrains the oldest confirmed occurrence of Cloudina to limestones of the lower Kliphoek Member, ca. 551-550 Ma, that were deposited laterally-equivalent to the more proximal fossiliferous Kliphoek quartzite. These limestones have dominantly negative & delta;13Ccarb values that immediately precede recovery from the basal Nama negative & delta;13Ccarb excursion (BANE), and were deposited in shallow waters after a transition from semi-restricted, evaporitive-dolomitic to open marine carbonate settings. Regional correlation shows that Cloudina first appeared during an interval of dominantly low oxygen and unstable, regional marine redox conditions. We conclude that data do not support a long-term shift towards more stable, oxygenated conditions as a driver for the first appearance of skeletonization in metazoans, but do suggest that open marine carbonate settings with high carbonate supersaturation were required to support the calcifying Cloudina. In the Nama Group, the appearance of Cloudina also notably coincided with a major sea level lowstand, which we hypothesise may have enabled oxygenation of these more distal settings. Such an expansion of shallow marine oxygen may therefore have provided an evolutionary driver for innovations that were not metabolically costly, such as the onset of Cloudina biomineralization. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/).