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Fingerprinting local controls on the Neoproterozoic carbon cycle with the isotopic record of Cryogenian carbonates in the Panamint Range, California
Earth and Planetary Science Letters ( IF 4.8 ) Pub Date : 2021-04-29 , DOI: 10.1016/j.epsl.2021.116956
Lyle L. Nelson , Anne-Sofie C. Ahm , Francis A. Macdonald , John A. Higgins , Emily F. Smith

Neoproterozoic carbon isotope excursions are commonly attributed to changes in the global fraction of organic carbon burial associated with climate instability and/or oxygenation. Here we show that carbonate sediment deposited during the ca. 661 – <651 Ma Cryogenian non-glacial interlude between the Sturtian and Marinoan glaciations exhibit lateral offsets in carbonate-carbon isotope values from coeval units by as much as 10‰. Within the Thorndike submember of the Cryogenian succession in the Panamint Range, California, USA, carbonate-carbon isotope values can be linked to a laterally discontinuous dolomitization front: limestones exhibit δ13Ccarb values of ∼+4 to +9‰, whereas values of stratigraphically equivalent dolostones are consistently lower, between ∼-4 and +4‰. Field observations and analyses of clasts from the overlying Marinoan glacial diamictite show that the offset in δ13Ccarb values resulted from pre- to syn-Marinoan dolomitization. Further, δ44/40Ca and δ26Mg data indicate that this isotopic variability resulted from sediment-buffered diagenesis. We propose that extremely positive δ13Ccarb values record local primary productivity within restricted platform surface waters and/or oxygenated pore fluids and negative values reflect anaerobic remineralization of organic carbon within sediment pore waters. In this scenario, neither the original calcite/aragonite nor subsequent dolomite precipitates of the Thorndike submember record δ13Ccarb values that are representative of global Cryogenian seawater, and instead they archive the evolution of local dissolved inorganic carbon pools.



中文翻译:

用加利福尼亚州Panamint山脉的低温碳酸盐碳酸盐同位素记录指纹识别新元古代碳循环的局部控制

新元古代碳同位素漂移通常归因于与气候不稳定和/或充氧有关的全球有机碳埋藏比例的变化。在这里,我们显示了碳酸盐沉积物在ca期间沉积。661 – <651 Ma Sturtian和Marinoan冰河之间的冰河系非冰川夹层显示,碳酸盐-碳同位素值与同代单位的横向偏移量高达10‰。在美国加利福尼亚州Panamint山脉的深冷层演替的Thorndike子成员中,碳酸盐-碳同位素值可与侧向不连续的白云石化锋面相关:石灰岩表现出δ13C carb值约为+4至+ 9‰,而地层等效白云岩的值始终较低,约为-4至+ 4‰。实地观测和对上覆的Marinoan冰河白铁矿碎屑的分析表明,δ13C碳水化合物的价值是由Marinoan的白云石化前到合成的白云石化引起的。更多,δ44/40钙和 δ26镁数据表明这种同位素变异性是由沉积物缓冲的成岩作用引起的。我们建议,非常积极δ13C碳水化合物值记录了受限平台地表水和/或充氧孔隙流体中的局部初级生产力,负值反映了沉积物孔隙水中有机碳的厌氧再矿化。在这种情况下,Thorndike子成员记录的原始方解石/文石或随后的白云石均不会析出δ13代表全球低温冰冻海水的C碳水化合物值,而是归档了局部溶解的无机碳库的演变。

更新日期:2021-04-30
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