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 -