It has been proposed that isotopically light inorganic carbon precipitated diagenetically in clastic sediments can explain the large carbon isotopic excursions recorded in Neoproterozoic carbonates. To date, however, the data needed to test this hypothesis have been limited. Here we report the analysis of ca. 540 clastic sedimentary rocks, including shales, siltstones, sandstones and tillites, that span the second half of the Neoproterozoic Era. A diagenetic carbon isotopic overprint does indeed occur in many of the samples; however, when we include our analyses in a carbon isotope mass balance model, they produce only a small effect on mass balance model results. Thus, clastic sedimentary rocks were not a major sink for 13C-depleted carbonate during the Neoproterozoic Era. These results do, however, produce a more accurate carbon mass balance, pointing to a high proportion of total organic carbon burial, compared to total carbon burial, during the late Tonian, Cryogenian, and late Ediacaran Periods. This result suggests a vigorous release of oxygen to the atmosphere. The clastic carbonate record also offers a chemostratigraphic tool. For example, we observe an isotope trend in clastic-hosted carbonates of the Isaac Formation, Windermere Supergroup, that strongly resembles the Shuram-Wonoka isotope anomaly, allowing us to place this previously undated section in a temporal context. We also find isotope trends in the fossiliferous and radiometrically well-dated sedimentary rocks of the Avalon Peninsula, Newfoundland, that may also reflect the Shuram-Wonoka anomaly. If correct, this constrains the timing of the Shuram event, suggesting that it began after 571 Ma and ended before 562 Ma, with the most extreme isotopic values lying well within those bounds.

中文翻译：

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碎屑岩中的碳同位素与新元古代碳循环

有人提出，碎屑沉积物中成岩沉积的同位素轻无机碳可以解释新元古代碳酸盐中记录的大量碳同位素偏移。然而，迄今为止，检验这一假设所需的数据是有限的。在这里，我们报告了 ca 的分析。540 种碎屑沉积岩，包括页岩、粉砂岩、砂岩和黑土，跨越新元古代后半期。许多样品中确实存在成岩碳同位素叠加；然而，当我们将我们的分析包含在碳同位素质量平衡模型中时，它们对质量平衡模型结果的影响很小。因此，碎屑沉积岩在新元古代并不是 13C 贫化碳酸盐的主要汇。然而，这些结果确实产生了更准确的碳质量平衡，表明在托尼阶晚期、低温纪和埃迪卡拉纪晚期，有机碳埋藏占总有机碳埋藏的比例较高。这一结果表明氧气向大气中大量释放。碎屑碳酸盐记录还提供了化学地层学工具。例如，我们观察到 Isaac 组的碎屑岩碳酸盐岩中的同位素趋势，温德米尔超群，与 Shuram-Wonoka 同位素异常非常相似，使我们能够将这个先前未注明日期的部分置于时间背景中。我们还在纽芬兰阿瓦隆半岛的含化石和放射性测年良好的沉积岩中发现同位素趋势，这也可能反映了 Shuram-Wonoka 异常。如果正确，这将限制舒兰事件发生的时间，表明它在 571 Ma 之后开始并在 562 Ma 之前结束，