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>Downwearing rates on shore platforms of different calcareous lithotypes
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Downwearing rates on shore platforms of different calcareous lithotypes
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机译：不同钙质岩性的岸上平台的磨损率
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摘要
Vertical lowering (downwearing) of shore platform surfaces is a very important mechanism in their morphological evolution albeit much remains incompletely understood. The efficacy of mechanical and chemical weathering acting on a given substrate, together with erosional processes, influences downwearing rates. In order to determine the relationship between lithotypes and downwearing rates, data collected from a Transverse Micro-erosion Meter were obtained for shore platforms of three different calcareous lithotypes(biocalcarenite, calcarenite and carbonated siltstone) along the central Algarve coast (Southern Portugal).Downwearing rates ranged between 0.096 mm year−1 and 1.676 mm year−1 in biocalcarenite and weakly cemented calcarenite, respectively. In addition, physical properties of the rocks comprising the platforms were measured, including uniaxial compressive strength (as determined by the Point Load Test), porosity, and calcium carbonate content. The results show that downwearing depends primarily on the intrinsic properties of the substrate. Porosity, in particular, acts in two ways: (i) it tends to weaken the substrate; and, (ii) it controls the downward extent of the water percolation and therefore the depth of the weathering mantle subject to erosion by waves and currents.
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机译：海岸平台表面的垂直下降（磨损）是它们形态演变的一个非常重要的机制，尽管还没有完全了解。机械和化学风化作用在给定基材上的功效以及腐蚀过程会影响磨损率。为了确定岩石类型与磨损率之间的关系，从横向微侵蚀仪获得了沿阿尔加维中部海岸（葡萄牙南部）三种钙质岩石类型（生物钙钙石，钙钙石和碳酸盐粉砂岩）的海岸平台收集的数据。生物钙钙石和弱胶结钙钙石的成矿速率分别在0.096 mm year-1和1.676 mm year-1之间。另外，测量了组成平台的岩石的物理性质，包括单轴抗压强度（由点载荷试验确定），孔隙率和碳酸钙含量。结果表明，磨耗主要取决于基材的固有特性。孔隙率尤其以两种方式起作用：（i）它倾向于削弱基材； （ii）它控制了渗水的向下程度，从而控制了受到波浪和水流侵蚀的风化地幔的深度。
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