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Local paleoenvironmental controls on the carbon-isotope record defining the Bitter Springs Anomaly.
Geobiology ( IF 3.7 ) Pub Date : 2016-10-08 , DOI: 10.1111/gbi.12217
R M Klaebe 1 , M J Kennedy 2 , A J M Jarrett 3 , J J Brocks 3
Affiliation  

Large magnitude (>10‰) carbon‐isotope (δ13C) excursions recorded in carbonate‐bearing sediments are increasingly used to monitor environmental change and constrain the chronology of the critical interval in the Neoproterozoic stratigraphic record that is timed with the first appearance and radiation of metazoan life. The ~10‰ Bitter Springs Anomaly preserved in Tonian‐aged (1000–720 Ma) carbonate rocks in the Amadeus Basin of central Australia has been offered as one of the best preserved examples of a primary marine δ13C excursion because it is regionally reproducible and δ13C values covary in organic and carbonate carbon arguing against diagenetic exchange. However, here we show that δ13C values defining the excursion coincide with abrupt lithofacies changes between regularly cyclic grainstone and microbial carbonates, and desiccated red bed mudstones with interbedded evaporite and dolomite deposits, recording local environmental shifts from restricted marine conditions to alkaline lacustrine and playa settings that preserve negative (−4‰) and positive (+6‰) δ13C values, respectively. The stratigraphic δ13C pattern in both organic and carbonate carbon recurs within the basin in a similar way to associated sedimentary facies, reflecting the linkage of local paleoenvironmental conditions and δ13C values. These local excursions may be time transgressive or record a relative sea‐level influence manifest through exposure of sub‐basins isolated by sea‐level fall below shallow sills, but are independent of secular seawater variation. As the shallow intracratonic setting of the Bitter Springs Formation is typical of other Neoproterozoic carbonate successions used to construct the present δ13C seawater record, it identifies the potential for local influences on δ13C excursions that are neither diagenetic nor representative of the global exogenic cycle.

中文翻译:

碳同位素记录上的局部古环境控制定义了苦泉异常。

大的幅度(> 10‰)的碳-同位素(δ 13 C)记录在碳酸轴承沉积物偏移被越来越多地用于监测环境的变化和限制的临界时间间隔的时间顺序在被定时与所述第一外观的新元地层记录和辐射的后生生活。在〜10‰苦泉异常保存在Tonian老化(1000-720马)碳酸酯在澳大利亚中部的Amadeus的盆地岩石已被提供作为一个主海洋δ保存最好的例子之一13 Ç偏移,因为它是可重复的区域和δ 13 C值在共变针对成岩交换有机和碳酸盐碳争论。不过,在这里我们表明δ 13定义偏移的C值与规则循环的花岗石和微生物碳酸盐以及带有层状蒸发岩和白云岩沉积物的干燥红层泥岩之间的岩相突然变化相吻合,记录了局部环境从受限海洋条件到碱性湖相和Playa设置的环境变化,这些变化保留了负值(−4 ‰)和阳性(+ 6‰)δ 13个C值,分别。地层δ 13中以类似的方式,以相关联的沉积相盆地内有机和碳酸盐碳复发模式C,反映当地古环境条件的联系和δ 13C值。这些局部漂移可能是时间跨度的,或者通过暴露于浅海底下的海平面所隔离的子流域而记录了相对的海平面影响,但与世俗的海水变化无关。作为苦泉形成的浅通内设置是典型用于构建本δ其他新元碳酸盐继承的13 Ç海水记录,它识别在δ为本地的影响的潜力13 Ç偏移既不成岩也不代表全球外生的循环。
更新日期:2016-10-08
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