The rise of oxygen and siderite oxidation during the Lomagundi Event
The rise of oxygen and siderite oxidation during the Lomagundi Event
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DOI：
10.1073/pnas.1422319112
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发表时间：
2015-05-26
影响因子：
11.1
通讯作者：
Kump, Lee R.
中科院分区：
文献类型：
--
作者：
Bachan, Aviv;Kump, Lee R.
古元古代洛马芒迪事件的时间间隔为1.3亿-2.5亿年，距今约23亿-21亿年，全球均有异常富含碳-13(>；10ppm)的石灰岩和白云岩。正的三角洲C-13值暗示了高水平的有机碳埋藏，表明产生了大量的O-2，以及需要极低水平的风化的碱度失衡。硫化物的氧化被认为是一种能够改善这些失衡的机制：它是O-2的有效汇，也是酸度的来源。然而，硫化物氧化消耗的O-2超过了它提供的二氧化碳，导致了碳和氧之间难以克服的失衡。相比之下，菱铁矿(FeCO3本身以及其他含Fe2+的碳酸盐矿物)的氧化产生的二氧化碳是消耗O2的4倍，是太古宙和早元古代沉积序列的常见成分，但往往被忽视。在这里，我们认为，随着大气中O-2的最初上升，菱铁矿的氧化为硫化物的继续氧化、有机碳的埋藏以及最重要的是游离O-2的积累提供了必要的碳。洛马芒迪事件的持续时间和强度取决于先前存在的太古宙菱铁矿储集层的大小，该储集层被氧化风化所消耗。我们的建议有助于解决一个长期存在的难题，并促进我们对大气O-2地质历史的理解。
The Paleoproterozoic Lomagundi Event is an interval of 130-250 million years, ca. 2.3-2.1 billion years ago, in which extraordinarily C-13 enriched (>10 parts per thousand) limestones and dolostones occur globally. The high levels of organic carbon burial implied by the positive delta C-13 values suggest the production of vast quantities of O-2 as well as an alkalinity imbalance demanding extremely low levels of weathering. The oxidation of sulfides has been proposed as a mechanism capable of ameliorating these imbalances: It is a potent sink for O-2 as well as a source of acidity. However, sulfide oxidation consumes more O-2 than it can supply CO2, leading to insurmountable imbalances in both carbon and oxygen. In contrast, the oxidation of siderite (FeCO3 proper, as well as other Fe2+-bearing carbonate minerals), produces 4 times more CO2 than it consumes O-2 and is a common-although often overlooked-constituent of Archean and Early Proterozoic sedimentary successions. Here we propose that following the initial rise of O-2 in the atmosphere, oxidation of siderite provided the necessary carbon for the continued oxidation of sulfides, burial of organic carbon, and, most importantly, accumulation of free O-2. The duration and magnitude of the Lomagundi Event were determined by the size of the preexisting Archean siderite reservoir, which was consumed through oxidative weathering. Our proposal helps resolve a long-standing conundrum and advances our understanding of the geologic history of atmospheric O-2.