USING IN-SITU PRODUCED COSMOGENIC ISOTOPES TO ESTIMATE RATES OF LANDSCAPE EVOLUTION - A REVIEW FROM THE GEOMORPHIC PERSPECTIVE
USING IN-SITU PRODUCED COSMOGENIC ISOTOPES TO ESTIMATE RATES OF LANDSCAPE EVOLUTION - A REVIEW FROM THE GEOMORPHIC PERSPECTIVE
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DOI：
10.1029/94jb00459
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发表时间：
1994-07-10
影响因子：
3.9
通讯作者：
BIERMAN, PR
中科院分区：
文献类型：
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作者：
BIERMAN, PR
在过去的十年中，应用原位产生的宇宙成因同位素在地貌学问题中迅速增加。自20世纪80年代中期以来，至少发表了57篇论文和许多摘要，当时首次对地球产生的宇宙成因同位素进行了质谱测量。从表面上看，这些研究提供了定量信息的景观演变和地貌年龄的速度，然而，计算的侵蚀速率和暴露年龄的意义在很大程度上取决于用于解释同位素数据的模型，这些模型固有的假设的有效性，以及地质环境中收集的样品。本文试图把宇宙成因同位素研究的地貌背景下，通过审查的基本原理的方法和评估的有效性的假设下，这些数据已被解释。目前，建立高精度的，基于宇宙成因的冰川和冲积年表受到地貌表面的演变，岩石样品的岩石侵蚀，同位素遗传的潜力，从以前的曝光，和同位素测量的不确定性。同位素生产率的不确定性和个别地貌表面暴露年龄的变化限制了宇宙成因年龄与其他技术获得的年龄可靠相关的置信度。对地貌上单个点的侵蚀速率进行估算，可以提供有用的小尺度信息。外推这些速率在更长的时间和更大的空间尺度是不太确定的，最有可能偏向于较低的侵蚀速率的无意中选择的耐样品的网站。然而，由于目前侵蚀速率受到的限制很差，即使是在2倍之内的估计也可能对地貌学家和构造学家具有重要价值。
The application of in-situ produced cosmogenic isotopes to problems in geomorphology has increased rapidly over the past decade. At least 57 papers and numerous abstracts have been published since the mid-1980s when the first mass-spectrometric measurements of terrestrially produced cosmogenic isotopes were made. Taken at face value, these studies provide quantitative information about rates of landscape evolution and landform age; however, the significance of calculated erosion rates and exposure ages depends strongly on the models used to interpret isotopic data, the validity of assumptions inherent to these models, and the geologic surroundings in which the samples were collected. This paper attempts to place cosmogenic isotope studies in a geomorphic context by reviewing fundamentals of the method and evaluating the validity of assumptions under which these data have been interpreted. At present, the establishment of high-precision, cosmogenically based glacial and alluvial chronologies is stymied by the evolution of geomorphic surfaces, the erosion of rock from sampled boulders, the potential for isotope inheritance from previous exposure, and the uncertainty of isotopic measurements. Uncertainties in isotope production rates and die observed variability of exposure ages on individual geomorphic surfaces limit the confidence with which cosmogenic ages can be correlated reliably with those obtained by other techniques. Estimation of erosion rates at single points on the landscape gives useful small-scale information. Extrapolation of these rates over longer time and larger spatial scales is less sure and most likely biased toward lower erosion rates by the inadvertent selection of resistant sample sites. However, because erosion rates are so poorly constrained at present, even estimates to within a factor of 2 may be of significant value to geomorphologists and tectonicists.