Pyrite-enhanced chemical weathering in Kärkevagge, Swedish Lapland
Pyrite-enhanced chemical weathering in Kärkevagge, Swedish Lapland
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瑞典拉普兰 Kärkevagge 的黄铁矿增强化学风化作用
DOI：
10.1130/b26228.1
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发表时间：
2007
影响因子：
4.9
通讯作者：
J. Dixon
中科院分区：
文献类型：
--
作者：
R. Darmody;C. E. Thorn;J. Dixon
传统观点曾经认为，寒冷气候下的风化绝大多数是由于物理过程。然而，该公约受到挑战时，化学风化被确定，但无法解释，作为主要的景观剥蚀过程中Karkevagge，在瑞典拉普地区的高山峡谷。这里报告的研究涉及扫描电子显微镜和岩石涂层的能量色散X射线荧光，以调查Karkevagge的化学风化。分析表明，与山谷崖面上的溪流有关的白色涂层通常是无定形的羟基硫酸铝，如基铝矿[Al4（SO4）（OH）10 ·H2 O]。河道中季节性植被的风化表明这是一个活跃的过程。白色涂层化学没有表现出系统的空间模式沿着山谷轴或与悬崖面上的位置。虽然这些白色涂层不是结晶的，也不含明显数量的铁或钙，但在谷底巨石之间的遮蔽悬垂物中，还有其他结晶良好的次生硫酸盐矿物，通常与黄铁矿氧化有关，包括石膏、黄钾铁矾和无定形铁化合物。这种差异可能是由于相关沃茨的pH值，因为Fe化合物仅在pH 5时倾向于沉淀，这是溪流水的pH值。黄铁矿氧化可能是一个重要的早期风化过程中，这种环境和许多其他环境。然而，它在很大程度上没有得到承认，因为它在地质意义上发生得相对较快，通常只在最近与采矿或其他大规模土方活动有关的扰动景观中被发现。Karkevagge证明，亚北极条件并不排除条件有利的强烈化学风化，但它并没有确定强烈的化学风化是亚北极条件的普遍属性。
Conventional wisdom once held that weathering in cold climates was overwhelmingly due to physical processes. However, that convention was challenged when chemical weathering was identified, but unexplained, as the dominant landscape denudation process in Karkevagge, an alpine valley in Swedish Lap-land. The research reported here involved scanning electron microscopy and energy dispersive X-ray fluorescence of rock coatings to investigate chemical weathering in Karkevagge. Analyses revealed that white coatings associated with streams emerging on the valley cliff face are commonly an amorphous aluminum oxyhydroxide sulfate such as basaluminite [Al 4 (SO 4 )(OH) 10 ·H 2 O]. Efflorescence on seasonal vegetation in stream channels demonstrates that this is an active process. The white coating chemistry exhibited no systematic spatial patterns along the valley axis or with position on the cliff face. Although the white coatings were not crystalline and did not contain appreciable amounts of Fe or Ca, in sheltered overhangs among boulders on the valley floor there were other well-crystallized secondary sulfate minerals commonly associated with pyrite oxidation, including gypsum, jarosite, and amorphous Fe compounds. This difference is due presumably to the pH of the associated waters, because Fe compounds tend to precipitate only at pH 5, which is the pH of the stream water. Pyrite oxidation may be an important early weathering process in this and in many other environments. However, it largely goes unrecognized because it occurs relatively rapidly in a geological sense and typically is only identified in recently disturbed landscapes associated with mining or other large-scale earth-moving activities. Karkevagge demonstrates that subarctic conditions do not preclude intense chemical weathering where conditions are favorable, but it does not establish that strong chemical weathering is a widespread attribute of subarctic conditions.