Physical, chemical, and biological investigation of an unconformity between limestone and sandstone in a coastal area: Iriomote Island case study
Physical, chemical, and biological investigation of an unconformity between limestone and sandstone in a coastal area: Iriomote Island case study
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对沿海地区石灰岩和砂岩不整合面进行物理、化学和生物研究：西表岛案例研究
DOI：
10.1016/j.catena.2018.07.013
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发表时间：
2018
期刊：
影响因子：
6.2
通讯作者：
H. Matsubara
中科院分区：
文献类型：
--
作者：
Hirotaka Sakiyama;H. Matsubara
虽然经常在露头中观察到地下水和/或风流引起的物理和化学风化，但对这些过程的地质机制尚未完全了解。在日本西表岛的北方沿海地区，已观察到由更新世石灰岩和中新世砂岩之间的不整合面风化引起的岩石崩塌。边界的特征是砂岩中独特的柱状结构，可能是由沿着干燥诱导裂缝的优先风化引起的。我们发现，这些柱体的形成过程可能与岩石崩塌密切相关。在这项研究中，更新世琉球群和中新世八重山群之间的不整合层进行了调查，以确定所涉及的地质过程，如形成，风化机制，化学和物理性质的变化。因此，宏观和微观的几何形状，抗压强度，和矿物组成的柱状结构被确定。碳稳定同位素分析表明，微生物固化现象可能参与了柱的形成。随后提出了一个形成方案的列，我们发现，过去的分层过程的基础上的化学和生物反应与干燥裂缝桑迪土壤直接影响现代动态岩石塌陷。
Although physical and chemical weathering due to groundwater and/or wind flow is frequently observed in outcrops, the geological mechanism responsible for these processes is not fully understood. In the northern coastal area of Iriomote Island, Japan, rock collapse caused by weathering of an unconformity between Pleistocene limestones and Miocene sandstones has been observed. The boundary is characterised by distinctive columnar structures in the sandstone, possibly induced by preferential weathering along desiccation-induced fractures. We found that the formation processes of the columns may be closely related to the rock collapse. In this study, the unconformable layer between the Pleistocene Ryukyu Group and the Miocene Yaeyama Group was investigated to determine the geological processes involved, such as the formation, weathering mechanisms, and alteration of chemical and physical properties. Consequently, the macroscopic and microscopic geometric forms, compressive strength, and mineral composition of the columnar structures were determined. Carbon stable isotopic analysis of the columns indicated that microbial solidification phenomena might have been involved in column formation. A formation scenario for the columns has subsequently been proposed, and we found that past stratification processes based on chemical and biological reactions with desiccation cracks on sandy soil directly influenced the modern dynamic rock collapse.