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Unraveling natural and human-accelerated erosional and weathering processes in the past: The new "comminution dating" approach based on uranium isotope analyses applied on a lake sediment record

揭示过去自然和人为加速的侵蚀和风化过程：基于铀同位素分析的新“粉碎测年”方法应用于湖泊沉积物记录

基本信息

批准号：
324893917
负责人：
Dr. Alexander Francke
金额：
--
依托单位：
Wollongong Isotope Geochronology Laboratory (WIGL)
依托单位国家：
德国
项目类别：
Research Fellowships
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/324893917?language=en
关键词：
Unraveling natural human accelerated erosional

项目摘要

Erosion and weathering are predominately controlled by tectonic uplift and climate conditions and are therefore affected by natural variations. Rapid anthropogenic induced climate warming can trigger distinct modifications in these processes in the near future. Furthermore, anthropogenic wood clearance and agricultural land use can accelerate the erosion in the terrestrial realm. Although a profound understanding of how erosion and weathering form landscapes are fundamentally important for future predictions, appropriate analytical methods for linking the history of erosion and weathering to paleoenviromntal and -climatic proxy data in the geological history are sparse. A new promising method to close this gap of knowledge is the application of uranium isotope analyses on clastic sediment material, which enables the determination of the so-called comminution age, i.e. the time that has elapsed since a detrital grain was formed by weathering. By comparing the comminution age with the depositional age in a sedimentary basin, erosional processes and catchment dynamics can be quantified. A long residence time of clastic material in the weathering horizon (long regolith residence time) suggests slow removal of topsoil material by sheet wash, whereas a short regolith residence time points to an intensification and deepening of the denudation by gully erosion. This relatively new method shall be applied on a lacustrine sediment succession from Lake Ohrid (Macedonia, Albania). The paleoclimatic and -environmental history of Lake Ohrid is already well studied by using sedimentologic, (bio-)geochemical, isotope (O, C), and pollen data. This information will be combined with the uranium isotope data in order to investigate the link between climate, environment and erosion. Thereby, particular focus will be drawn on the human impact on the landscape evolution by wood clearance and agricultural land-use during the Late Holocene period. Since uranium isotope analysis as a proxy for past landscape evolution is a relatively new approach and was not applied to lake sediment successions until today, the proposed research project also encompasses a calibration and evaluation of the method. Chemical pre-treatment methods will be tested for their applicability on lake sediments, and the conceptual model of sheet wash versus gully erosion will be studied on (sub-)recent sediments from Darwin Harbor (Northern Territory, Australia). Erosional processes in the catchment area of Darwin Harbor can geographically be separated into two endmembers, characterized by sheet wash and gully erosion, respectively. This study enables a detailed examination if the signal of these two erosion types can be detected in the Darwin Harbor sediments by means of uranium isotope analyses.

侵蚀和风化主要受构造隆升和气候条件控制，因此受自然变化的影响。在不久的将来，人为引起的快速气候变暖可能引发这些过程的明显变化。此外，人为砍伐木材和农业用地会加速陆地领域的侵蚀。尽管对侵蚀和风化如何形成景观的深刻理解对未来的预测至关重要，但将侵蚀和风化的历史与地质历史中的古环境和气候代理数据联系起来的适当分析方法却很少。一种有望填补这一知识空白的新方法是将铀同位素分析应用于碎屑沉积物材料，它可以确定所谓的粉碎年龄，即碎屑颗粒经过风化作用形成的时间。通过比较沉积盆地的粉碎年龄和沉积年龄，可以量化侵蚀过程和流域动力学。碎屑物质在风化层中的停留时间较长（风化层停留时间较长）表明表层土壤物质被薄层冲刷带走的速度较慢，而风化层停留时间较短则表明沟壑侵蚀加剧和加深了剥蚀。这种相对较新的方法将应用于奥赫里德湖（马其顿，阿尔巴尼亚）的湖泊沉积物演替。利用沉积学、（生物）地球化学、同位素（O， C）和花粉等资料对奥赫里德湖的古气候和环境历史进行了较好的研究。这些资料将与铀同位素数据结合起来，以便调查气候、环境和侵蚀之间的联系。因此，我们将特别关注全新世晚期人类对景观演变的影响，包括砍伐树木和农业土地利用。由于铀同位素分析作为过去景观演变的代表是一种相对较新的方法，并且直到今天才应用于湖泊沉积物演替，因此拟议的研究项目还包括对该方法的校准和评估。将测试化学预处理方法对湖泊沉积物的适用性，并将研究来自达尔文港（澳大利亚北领地）的（亚）近期沉积物的薄片冲刷与沟槽侵蚀的概念模型。达尔文港集水区的侵蚀过程在地理上可分为两个端段，分别以片冲和沟冲为特征。这项研究可以通过铀同位素分析的方法来详细检查达尔文港沉积物中是否可以检测到这两种侵蚀类型的信号。