Estimating the Age of Abandoned Alluvial Surfaces Using Morphologic Dating of Gully Incision

Abstract

The age of abandoned alluvial surfaces is a key component in quantifying landscape evolution processes, tectonic activity, and paleoclimate. However, limited resources, restricted field accessibility, lacking dating material and analytical constraints are often encountered when dating such landforms. To help mitigate these limitations, we propose a new and complementary surface dating approach that is based on calculating the duration of gully incision into a surface since its abandonment using a locally calibrated landscape evolution model. The approach consists of calibration of incision model parameters for abandoned alluvial surfaces with known age and then using the calibrated model to calculate the time required for gully profiles to form on nearby undated alluvial surfaces as a proxy for surface abandonment. The approach was tested on previously dated late Pleistocene (34 and 70 ka) alluvial terraces in the hyper-arid Negev desert (Israel). Calibrated model parameters were within the range reported for incision models in arid regions worldwide and late Pleistocene surface abandonment ages were recovered to within 10% accuracy. In contrast, modeled durations for gully incision into an older mid-Pleistocene surface previously dated to 230–549 ka were grossly underestimated at <120 ka. Field observations and approach tests indeed indicated that late Pleistocene model parameters should not be extrapolated as-is to model gully incision farther back through geologic time. Because the validity of the proposed ages depends on extrapolating the locally calibrated parameters of the incision model, we recommend that such dating be conducted with care and where assumptions will probably be valid.