TY - JOUR A1 - Margirier, Audrey A1 - Braun, Jean A1 - Gautheron, Cecile A1 - Carcaillet, Julien A1 - Schwartz, Stephane A1 - Jamme, Rosella Pinna A1 - Stanley, Jessica T1 - Climate control on Early Cenozoic denudation of the Namibian margin as deduced from new thermochronological constraints JF - Earth & planetary science letters N2 - The processes that control long term landscape evolution in continental interiors and, in particular, along passive margins such as in southern Africa, are still the subject of much debate (e.g. Braun, 2018). Although today the Namibian margin is characterized by an arid climate, it has experienced climatic fluctuations during the Cenozoic and, yet, to date no study has documented the potential role of climate on its erosion history. In western Namibia, the Brandberg Massif, an erosional remnant or inselberg, provides a good opportunity to document the Cenozoic denudation history of the margin using the relationship between rock cooling or exhumation ages and their elevation. Here we provide new apatite (UThSm)/He dates on the Brandberg Inselberg that range from 151 +/- 12 to 30 +/- 2 Ma. Combined with existing apatite fission track data, they yield new constraints on the denudation history of the margin. These data document two main cooling phases since continental break-up 130 Myr ago, a rapid one (similar to 10 degrees C/Myr) following break-up and a slower one (similar to 12 degrees C/Myr) between 65 and 35 Ma. We interpret them respectively to be related to escarpment erosion following rifting and continental break-up and as a phase of enhanced denudation during the Early Eocene Climatic Optimum. We propose that during the Early Eocene Climatic Optimum chemical weathering was important and contributed significantly to the denudation of the Namibian margin and the formation of a pediplain around the Brandberg and enhanced valley incision within the massif. Additionally, aridification of the region since 35 Ma has resulted in negligible denudation rates since that time. (C) 2019 Elsevier B.V. All rights reserved. KW - climate KW - Early Eocene Climatic Optimum KW - apatite (U-Th-Sm)/He thermochronology KW - denudation KW - weathering KW - Namibian passive margin Y1 - 2019 U6 - https://doi.org/10.1016/j.epsl.2019.115779 SN - 0012-821X SN - 1385-013X VL - 527 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Genderjahn, Steffi A1 - Lewin, Simon A1 - Horn, Fabian A1 - Schleicher, Anja M. A1 - Mangelsdorf, Kai A1 - Wagner, Dirk T1 - Living lithic and sublithic bacterial communities in Namibian drylands JF - Microorganisms : open access journal N2 - Dryland xeric conditions exert a deterministic effect on microbial communities, forcing life into refuge niches. Deposited rocks can form a lithic niche for microorganisms in desert regions. Mineral weathering is a key process in soil formation and the importance of microbial-driven mineral weathering for nutrient extraction is increasingly accepted. Advances in geobiology provide insight into the interactions between microorganisms and minerals that play an important role in weathering processes. In this study, we present the examination of the microbial diversity in dryland rocks from the Tsauchab River banks in Namibia. We paired culture-independent 16S rRNA gene amplicon sequencing with culture-dependent (isolation of bacteria) techniques to assess the community structure and diversity patterns. Bacteria isolated from dryland rocks are typical of xeric environments and are described as being involved in rock weathering processes. For the first time, we extracted extra- and intracellular DNA from rocks to enhance our understanding of potentially rock-weathering microorganisms. We compared the microbial community structure in different rock types (limestone, quartz-rich sandstone and quartz-rich shale) with adjacent soils below the rocks. Our results indicate differences in the living lithic and sublithic microbial communities. KW - lithobiont KW - intracellular DNA KW - extracellular DNA KW - weathering KW - dryland KW - rock Y1 - 2021 U6 - https://doi.org/10.3390/microorganisms9020235 SN - 2076-2607 VL - 9 IS - 2 PB - MDPI CY - Basel ER - TY - JOUR A1 - Korges, Maximilian A1 - Junge, Malte A1 - Borg, Gregor A1 - Oberthür, Thomas T1 - Supergene mobilization and redistribution of platinum-group elements in the Merensky Reef, eastern Bushveld Complex, South Africa JF - The Canadian mineralogist N2 - Near-surface supergene ores of the Merensky Reef in the Bushveld Complex, South Africa, contain economic grades of platinum-group elements, however, these are currently uneconomic due to low recovery rates. This is the first study that investigates the variation in platinum-group elements in pristine and supergene samples of the Merensky Reef from five drill cores from the eastern Bushveld. The samples from the Richmond and Twickenham farms show different degrees of weathering. The whole-rock platinum-group element distribution was studied by inductively coupled plasma-mass spectrometry and the platinum-group minerals were investigated by reflected-light microscopy, scanning electron microscopy, and electron microprobe analysis.
In pristine ("fresh") Merensky Reef samples, platinum-group elements occur mainly as discrete platinum-group minerals, such as platinum-group element-sulfides (cooperite-braggite) and laurite as well as subordinate platinum-group elementbismuthotellurides and platinum-group element-arsenides, and also in solid solution in sulfides (especially Pd in pentlandite). During weathering, Pd and S were removed, resulting in a platinum-group mineral mineralogy in the supergene Merensky Reef that mainly consists of relict platinum-group minerals, Pt-Fe alloys, and Pt-oxides/hydroxides. Additional proportions of platinum-group elements are hosted by Fe-hydroxides and secondary hydrosilicates (e.g., serpentine group minerals and chlorite).
In supergene ores, only low recovery rates (ca. 40%) are achieved due to the polymodal and complex platinum-group element distribution. To achieve higher recovery rates for the platinum-group elements, hydrometallurgical or pyrometallurgical processing of the bulk ore would be required, which is not economically viable with existing technology. KW - Bushveld Complex KW - Merensky Reef KW - PGE KW - PGM KW - supergene ores KW - weathering Y1 - 2021 U6 - https://doi.org/10.3749/canmin.2100023 SN - 1499-1276 VL - 59 IS - 6 SP - 1381 EP - 1396 PB - Mineralogical Association of Canada CY - Ottawa ER -