Are Proterozoic cap carbonates and isotopic excursions a record of gas hydrate destabilization following Earth's coldest intervals?
Are Proterozoic cap carbonates and isotopic excursions a record of gas hydrate destabilization following Earth's coldest intervals?
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DOI：
10.1130/0091-7613(2001)029
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发表时间：
2001-05-01
期刊：
影响因子：
5.8
通讯作者：
Sohl, LE
中科院分区：
文献类型：
--
作者：
Kennedy, MJ;Christie-Blick, N;Sohl, LE
区域性持久的薄层碳酸盐岩直接普遍地覆盖在几乎每个大陆的元古代冰川沉积物上，通常被称为帽碳酸盐岩。它们不寻常的相、地层突变的基底和上部接触以及强负碳同位素特征（δ C-13 值在大约千分之 0 和 -5 之间）表明化学海洋学起源，其细节尚未解决。在这里，我们提出，这些神秘的沉积物与冰后快速变暖和广泛暴露的大陆架和内部盆地的洪水之后陆地永久冻土中天然气水合物的不稳定有关。支持这一假设的证据包括（1）不寻常结构的盖碳酸盐中常见，类似于冷甲烷渗漏产生的碳酸盐； (2) 碳同位素偏移的独特时间演化表明同位素贫化碳脉冲添加到海洋-大气系统中； (3)水合物失稳释放的碳与埋藏在盖帽碳酸盐中的碳的质量平衡估计之间的一致性。我们推断，在新元古代特征的低纬度冰川时期，天然气水合物的含量可能比地球历史上任何其他时期都要丰富。
Regionally persistent, thin intervals of carbonate rock directly and ubiquitously overlie Proterozoic glacial deposits on almost every continent, and are commonly referred to as cap carbonates, Their unusual facies, stratigraphically abrupt basal and upper contacts, and strongly negative carbon isotopic signature (delta C-13 values between similar to0 parts per thousand and -5 parts per thousand) suggest a chemical oceanographic origin, the details of which remain unresolved. Here we propose that these enigmatic deposits are related to the destabilization of gas hydrate in terrestrial permafrost following rapid postglacial warming and flooding of widely exposed continental shelves and interior basins, Supporting evidence for this hypothesis includes (1) the common occurrence within the cap carbonates of unusual fabrics, similar to those produced by cold methane seeps; (2) a distinctive time evolution for the carbon isotopic excursions indicative of a pulse addition of isotopically depleted carbon to the ocean-atmosphere system; and (3) agreement between mass-balance estimates of carbon released by hydrate destabilization and carbon buried in the cap carbonate. We infer that during times of low-latitude glaciation, characteristic of the Neoproterozoic, gas hydrates may have been in greater abundance than at any other time in Earth history.