Carbon, oxygen and strontium isotopic and elemental characteristics of the Cambrian Longwangmiao Formation in South China: Paleoenvironmental significance and implications for carbon isotope excursions
Carbon, oxygen and strontium isotopic and elemental characteristics of the Cambrian Longwangmiao Formation in South China: Paleoenvironmental significance and implications for carbon isotope excursions
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华南寒武系龙王庙组碳、氧、锶同位素及元素特征：古环境意义及碳同位素偏移的意义
DOI：
10.1016/j.gr.2022.01.008
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发表时间：
2022-01
影响因子：
6.1
通讯作者：
Chenxi Zhu
中科院分区：
文献类型：
--
作者：
Pengyuan Zhang;Yongli Wang;Xiaojun Zhang;Zhifu Wei;Gen Wang;Ting Zhang;He Ma;Jingyi Wei;Wei He;Xueyun Ma;Chenxi Zhu
在新元古代-早寒武世，生物圈经历了阶段性的扰动，伴随着碳循环的大波动。然而，与埃迪卡拉-早寒武世相比，寒武纪丰田阶（龙王庙）的地球化学记录很少，其中包含显着的Redlichiid-Olenellid灭绝碳同位素漂移（ROECE）。为了解决这一数据缺口，我们进行了碳，氧，锶同位素和元素含量的连续系列的碳酸盐岩样品的HS 2井龙王庙组，位于中国南方四川盆地中部。我们的具体目标是重建古环境和确定ROECE的起源。严格的样品筛选，以确保同位素和元素不受成岩作用。HS 2井和其他地点的87 Sr/86 Sr值表明，海平面在寒武纪Toyonian阶段逐渐下降。此外，晚Toyonian显著的负δ 13 C偏移与全球范围内的ROECE有关，这被广泛认为是由海侵引起的反射造成的。但在HS 2井的87 Sr/86 Sr剖面上没有发现海侵现象，这可能是由于频繁的区域海退造成的局部岩溶作用和侵蚀作用的结果。多个古环境指标之间的相互关系表明，大陆风化受气候控制，影响陆源碎屑的供应，碳酸盐台地是半限制的。此外，配置文件的古环境代理表明，环境温暖潮湿，有利于高生物生产力和多样性在间隔I（早期Toyonian），并逐渐变得寒冷和干燥的间隔II（中期Toyonian）。我们认为，由间隔III（晚Toyonian）的时间，一个寒冷和干旱的环境的不利影响叠加在海侵，触发ROECE。我们的研究结果为其他碳同位素漂移事件提供了参考和可能的解释。
The biosphere experienced episodic perturbations during the Neoproterozoic–early Cambrian, accompanied by major fluctuations of the carbon cycle. However, compared to the Ediacaran–early Cambrian, geochemical records of the Cambrian Toyonian Stage (Longwangmiao), which contains the significant Redlichiid–Olenellid Extinction Carbon Isotope Excursion (ROECE), are scarce. To address this data gap, we conducted measurements of carbon, oxygen and strontium isotopes and element contents of a continuous series of carbonate samples from the Longwangmiao Formation of Well HS2, located in the central Sichuan Basin of South China. Our specific aims were to reconstruct the paleoenvironment and to determine the origin of the ROECE. Strict sample screening was used to ensure that the isotopes and elements were not affected by diagenesis. The87Sr/86Sr values of Well HS2, and for sites elsewhere, show that sea level gradually decreased during the Cambrian Toyonian Stage. Additionally, the pronounced negative δ13C excursion in the late Toyonian is globally associated with the ROECE, which is widely thought to have resulted from extinctions caused by a transgression. However, a transgression is not shown in the87Sr/86Sr profile of Well HS2, which we attribute to local karst formation and erosion caused by frequent regional regressions. The interrelationships among several paleoenvironmental proxies show that continental weathering was climatically controlled, which affected the supply of terrigenous detritus, and that the carbonate platform was semi–restricted. Furthermore, profiles of paleoenvironmental proxies indicate that the environment was warm and humid, favoring high biological productivity and diversity during Interval I (early Toyonian), and that it gradually became colder and drier during Interval II (middle Toyonian). We suggest that by the time of Interval III (late Toyonian), the adverse effects of a cold and arid environment were superimposed on the transgression, triggering the ROECE. Our results provide a reference and possible interpretation for other carbon isotope excursion events.
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