Evolution of the western Namibian drainage systems since Eocene times - a multi-methodical approach

规划的项目旨在利用近期河流及其前体的沉积物重建流域长期演变和大面积分布。由于始新世以来的侵蚀率一直很低，始新世到最近的河流地层的遗迹保存得非常完好，而且缺乏精确的年龄测定，因此选择纳米比亚西部的排水系统作为工作区。为了获得单个阶地层的精确年龄，并检测沉积物物源的变化，本研究首次使用U-Th-Pb和Lu-Hf同位素与单颗粒形态计量学相结合的方法，将石英和碎屑锆石年代学中常用的陆地宇宙成因核素（TCN） 10Be、21Ne和26Al结合起来。除了这些方法外，我们还计划对全新的先进测年技术进行可行性研究，包括方解石中的26Al和36Cl以及磁铁矿中的36Cl， 41Ca和53Mn的交叉校准。无论成功与否，这个相当偶然的目标的科学结果都不会危及上述主要目标。根据常规使用的TCN精确确定的年龄和从锆石中获得的独特的高分辨率物源分析，我们将能够确定阶地形成事件的时间，从而得出地质和古地理方面的进一步结论（构造隆起，切口事件，汇水区的变异性）。沉积物还将提供数据，有助于重建沉积物通量、源汇动力学、河流古环境和一些古气候条件（如供水和排水）的潜在变化。因此，这一建议与绝大多数早期研究相反，这些研究通常局限于小区域和/或短时间，旨在古地理和/或地质重建或了解古气候条件。最后，两个机构的合作，拥有设备齐全的最先进的实验室，加上先进的经验，使这个项目非常独特和经济。

The planned project aims to the reconstruction of drainage basin evolution over a long period of time and large areal distribution using sediments of the recent rivers and their precursors. With respect to the constantly very low erosion rates since Eocene times, exceptionally well-preserved remnants of Eocene to recent fluvial strata and a lack of precise age determinations, the western Namibian drainage system was chosen as working area. In order to obtain precise ages of the single terrace levels and to detect changes in the provenance of the sediments, this is the first study coupling the routinely used terrestrial cosmogenic nuclides (TCN) 10Be, 21Ne and 26Al from quartz and detrital zircon geochronology using U-Th-Pb and Lu-Hf isotopics complemented by single grain morphometrics. In addition to these methods, we plan a feasability study of entirely new and advanced dating techniques including cross-calibration of 26Al and 36Cl in calcite, as well as 36Cl, 41Ca, and 53Mn in magnetite. Succeeding or not, the scientific outcome of this rather chancy objective will not put the above mentioned primary objective at risk. Based on precise age determinations from routinely used TCN and uniquely high-resolution provenance analyses obtained from zircon we will be able to establish the timing of terrace forming events, and, therefore draw further conclusions like aspects of geology and palaeogeography (tectonic uplift, incision events, variability of catchment areas). The sediments will also provide data that will facilitate the reconstruction of potential changes in the sediment fluxes, source to sink dynamics, fluvial palaeoenvironment and some palaeoclimatic conditions, like water supply and discharge. Hence, this proposal is in contrast to the vast majority of all earlier studies, which are generally limited to small areas and/or short periods of time and aim either at palaeogeographic and/or geologic reconstructions or at the understanding of palaeoclimatic conditions. Finally, the cooperation of two institutions with fully-equipped state-of-the-art laboratories accompanied with advanced experience makes this project quite unique and economical.