The Relationship Between Topography, Bedrock Weathering, and Water Storage Across a Sequence of Ridges and Valleys
The Relationship Between Topography, Bedrock Weathering, and Water Storage Across a Sequence of Ridges and Valleys
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DOI：
10.1029/2020jf005848
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发表时间：
2021-03
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影响因子：
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通讯作者：
M. Pedrazas;W. Hahm;Mong‐Han Huang;D. Dralle;M. Nelson;Rachel E. Breunig;K. Fauria;A. Bryk;W. Dietrich;D. Rempe
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作者：
M. Pedrazas;W. Hahm;Mong‐Han Huang;D. Dralle;M. Nelson;Rachel E. Breunig;K. Fauria;A. Bryk;W. Dietrich;D. Rempe
基岩风化调节养分的流动、水的储存和土壤的产生。相对于移动的土层，地形和基岩风化之间的关系知之甚少。在这里，我们确定了一个共同的模式，风化和水存储在一个序列的三个山脊和山谷的沉积大峡谷序列在北方加州，共享一个构造和气候的历史。深钻、井下测井以及化学和孔隙度的表征揭示了两个风化锋。较浅的前缘在所有三个山坡的山脊处深2.7m，标志着黄铁矿和有机碳的普遍断裂和氧化的程度。更深的风化锋标志着开放性断裂和变色的程度。这一前缘在两个脊谷间距相似的脊下深11米，但在一个脊谷间距近两倍的脊下深17.5米。因此，在山脊顶部，山坡起伏的一部分，是风化规模与山坡长度。在所有三个山坡中，在第二风化锋以下，闭合的裂缝和未风化的基岩延伸到邻近河道上方约一半的山顶高程。中子探针调查显示，季节性动态水分存储到大约相同的深度作为浅风化锋。在限制我们研究山坡的通道下，两个风化锋重合，并发生在地表厘米范围内。我们的研究结果提供了证据之间的反馈侵蚀和风化的山地景观，导致系统的地下结构和水路由。
Bedrock weathering regulates nutrient mobilization, water storage, and soil production. Relative to the mobile soil layer, little is known about the relationship between topography and bedrock weathering. Here, we identify a common pattern of weathering and water storage across a sequence of three ridges and valleys in the sedimentary Great Valley Sequence in Northern California that share a tectonic and climate history. Deep drilling, downhole logging, and characterization of chemistry and porosity reveal two weathering fronts. The shallower front is ∼7 m deep at the ridge of all three hillslopes, and marks the extent of pervasive fracturing and oxidation of pyrite and organic carbon. A deeper weathering front marks the extent of open fractures and discoloration. This front is 11 m deep under two ridges of similar ridge‐valley spacing, but 17.5 m deep under a ridge with nearly twice the ridge‐valley spacing. Hence, at ridge tops, the fraction of the hillslope relief that is weathered scales with hillslope length. In all three hillslopes, below this second weathering front, closed fractures and unweathered bedrock extend about one‐half the hilltop elevation above the adjacent channels. Neutron probe surveys reveal that seasonally dynamic moisture is stored to approximately the same depth as the shallow weathering front. Under the channels that bound our study hillslopes, the two weathering fronts coincide and occur within centimeters of the ground surface. Our findings provide evidence for feedbacks between erosion and weathering in mountainous landscapes that result in systematic subsurface structuring and water routing.