ANALYSIS OF SCARP PROFILES - EVALUATION OF ERRORS IN MORPHOLOGIC DATING
ANALYSIS OF SCARP PROFILES - EVALUATION OF ERRORS IN MORPHOLOGIC DATING
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DOI：
10.1029/92jb01962
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发表时间：
1993-04-10
影响因子：
3.9
通讯作者：
AVOUAC, JP
中科院分区：
文献类型：
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作者：
AVOUAC, JP
陡坎退化的形态学分析可以定量地确定在相同气候条件下无粘性物质中形成的不同陡坎的相对年龄。构造成因的陡坎以及波切或河切阶地可被视为地形脉动，其被地表侵蚀过程衰减。这种形态演变可以模拟为初始形状与侵蚀（或退化）函数的卷积，其宽度随时间增加。这种模型适用于高度小于10米的陡崖，形成于未固结的fanglomerates。为了更好地近似，退化函数是高斯函数，其方差测量初始形状的舍入程度。该几何参数可称为退化系数。合成实验表明，通过垂直于陡坎的水平剖面的最小二乘拟合，可以得到退化系数。通过假设无粘性材料休止角（30度-35度）处的初始陡坎坡度来解释自由面的重力塌陷。测量曲线的不确定性导致降解系数的不确定性，可以用图形进行评估。由于退化系数对区域坡度和三维过程（冲沟、黄土堆积、河流下切）敏感。等等），可靠和准确地确定退化系数需要跨越同一陡崖的几个长剖面。陡坎退化的线性扩散模型是一个高斯模型，其中退化系数与数值年龄成正比。在这种情况下，绝对定年只需要确定比例常数，称为质量扩散常数。对于几米高的全新世陡崖，在松散的冲积层和气候条件下，质量扩散系数常数一般在1和6平方米/千年之间。地貌分析是比较同一地区不同陡崖年龄的可靠方法，它可以提供全新世陡崖地貌的近似绝对年龄。
Morphologic analysis of scarp degradation can be used quantitatively to determine relative ages of different scarps formed in cohesionless materials, under the same climatic conditions. Scarps of tectonic origin as well as wavecut or rivercut terraces can be treated as topographic impulses that are attenuated by surface erosional processes. This morphological evolution can be modelled as the convolution of the initial shape with erosion (or degradation) function whose width increases with time. Such modelling applies well to scarps less than 10m high, formed in unconsolidated fanglomerates. To a good approximation, the degradation function is Gaussian with a variance measuring the degree of rounding of the initial shape. This geometric parameter can be called the degradation coefficient. A synthetic experiment shows that the degradation coefficient can be obtained by least squares fitting of profiles levelled perpendicular to the scarp. Gravitational collapse of the free face is accounted for by assuming initial scarp slopes at the angle of repose of the cohesionless materials (30-degrees-35-degrees). Uncertainties in the measured profiles result in an uncertainty in degradation coefficient that can be evaluated graphically. Because the degradation coefficient is sensitive to the regional slope and to three-dimensional processes (gullying, loess accumulation, stream incision. etc.), a reliable and accurate determination of degradation coefficient requires several long profiles across the same scarp. The linear diffusion model of scarp degradation is a Gaussian model in which the degradation coefficient is proportional to numerical age. In that case, absolute dating requires only determination of the propotionality constant, called the mass diffusivity constant. For Holocene scarps a few meters high, in loose alluvium under and climatic conditions, mass diffusivity constants generally range between 1 and 6 m2/kyr. Morphologic analysis is a reliable method to compare ages of different scarps in a given area, and it can provide approximate absolute ages of Holocene scarplike landforms.