The role of peri‐glacial active layer development in determining soil‐regolith thickness across a Triassic sandstone outcrop in the UK
The role of peri‐glacial active layer development in determining soil‐regolith thickness across a Triassic sandstone outcrop in the UK
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冰周活动层发育在确定英国三叠纪砂岩露头土壤风化层厚度中的作用
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
A. Milodowski
中科院分区：
文献类型：
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作者：
A. Tye;S. Kemp;R. Murray Lark;A. Milodowski
本文研究了英国诺丁汉郡三叠纪舍伍德砂岩群露头（750平方公里）的风化过程，这些风化过程共同产生了土壤风化层（SR）厚度的分布。从露头采集的存档钻孔日志（n = 282）显示SR厚度的平均深度和中值深度分别约为1.8 m和1.5 m。岩心取自森林覆盖区，深度约3 m，用于地球化学分析。在该地点，SR厚度约为1.7 m。使用质量平衡计算（τ）对元素损失进行分析，并与基岩进行比较，结果表明，所有方解石和石膏胶结物已被清除到>3 m的深度。因此，SR和下面的腐泥土之间的主要区别是前者作为松散的沙子而不是半耐用的岩石存在。岩心样品的扫描电子显微镜（SEM）分析表明，非耐久性岩石或腐泥土具有更大的粘土颗粒胶结作用。我们建议，通过该机制的粘土水泥（和其他联锁粮食债券）被缓解除了是通过冻融过程与夏季“活跃层发展（ALD）”在英国的末次冰期活动。我们测试了这个理论的基础上开发一个简化版本的Stefan方程的Monte Carlo模拟。获得了目前北极地区的空气和地面温度数据集，为输入变量提供了合理的起始条件。这些数据与已知的舍伍德砂岩风化层的热导率、体积密度和含水量数据相结合。SR厚度分布的模型预测（n = 1000）准确地反映了从钻孔测井中观察到的分布厚度。这有力地证明了冻融和ALD过程是决定该露头SR厚度的主要因素。英国地质调查局© NERC 2012
This paper examines the weathering processes that have combined to produce the distribution of soil‐regolith (SR) thickness across the Triassic Sherwood Sandstone Group outcrop (750 km2) in Nottinghamshire, UK. Archive borehole logs (n = 282) taken across the outcrop showed that SR thickness had mean and median depths of ~1·8 and 1·5 m, respectively. Cores were taken from a forested site to depths ~3 m for geochemical analysis. At this site the SR thickness was ~1·7 m. Analysis of the loss of elements, compared to bedrock using mass balance calculations (τ) showed that all the calcite and gypsum cement had been removed to depths of >3 m. Thus the major difference between the SR and the underlying saprolite was that the former exists as loose sand as opposed to a semi‐durable rock. Scanning electron microscopy (SEM) analysis of core samples suggested that the non‐durable rock or saprolite had greater cementation of clay particles. We propose that the mechanism through which the clay cement (and other interlocking grain bonds) was eased apart was through freeze–thaw processes associated with the summer ‘active layer development (ALD)’ during the last glacial activity in the UK. We tested this theory by developing a Monte Carlo simulation based on a simplified version of the Stefan equation. Current Arctic datasets of air and ground temperatures were obtained to provide reasonable starting conditions for input variables. These were combined with known data for thermal conductivity, bulk density and moisture content of the Sherwood Sandstone regolith. Model predictions (n = 1000) of the distribution of SR thickness accurately reflect the observed distribution thickness from the borehole logs. This is strong evidence that freeze–thaw and ‘ALD’ processes are major factors in determining the thickness of SR across this outcrop. British Geological Survey © NERC 2012
DOI：
10.5194/tc-4-269-2010
发表时间：
2009-11
期刊：
The Cryosphere
影响因子：
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作者：
U. Wollschläger;H. Gerhards;Qihao Yu;K. Roth
通讯作者：
U. Wollschläger;H. Gerhards;Qihao Yu;K. Roth