Interdisciplinary studies on Rock Varnish
This work is a study of rock varnishes collected from different locations worldwide and from several environments. The focus was set on the microanalytical investigation of i) the geochemistry of different varnishes and adjacent collected mineral dust, ii) the structures of different varnishes, and...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Johannes Gutenberg-Universität Mainz
2017
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| Online Access: | https://openscience.ub.uni-mainz.de/handle/20.500.12030/1732 https://hdl.handle.net/20.500.12030/1732 https://doi.org/10.25358/openscience-1730 |
| Summary: | This work is a study of rock varnishes collected from different locations worldwide and from several environments. The focus was set on the microanalytical investigation of i) the geochemistry of different varnishes and adjacent collected mineral dust, ii) the structures of different varnishes, and iii) signs for a definite proof for a biogenic compound necessary for the formation of rock varnish. To this end, a combination of different cutting-edge analytical techniques was utilized to investigate the rock varnishes. Rock varnish is a black, micrometer thin, sedimentary crust on top of rock surfaces. It occurs on almost all lithologies and can be found for instance in deserts, in caves, on mountains and plateaus, in large cities, Antarctica, at waterfronts, and possibly even on Mars. Rock varnish consists of a mixture of dust grains as its main component, and a Mn-rich matrix material as cement component. A biogenic contribution to the genesis has been suggested. Rock varnish is a phenomenon that has defied more than 200 years of intermittent scientific examination. Methods and instruments used in this study were amongst others fs/ns LA-ICP-MS, fs LA-MC-ICP-MS, solution ICP-MS, portable XRF, stationary XRF, EPMA, NanoSIMS, FIB- and Microtome-slicing, STXM-NEXAFS, SEM, Raman spectroscopy, EDX, XRD, and TEM. More than 150 individual rock samples were investigated for their chemical composition by fs LA-ICP-MS, and on each sample about 10-30 measurements were conducted to obtain enough statistical accuracy since the crusts are very inhomogeneous. On the basis of the results, several samples were selected that were additionally investigated by other methods mentioned above, to receive further information about, e.g., nano- and microstructures, element distributions, in-situ oxidation state distributions, and isotope ratios. Mineral dust samples were collected and investigated by fs LA-ICP-MS and XRD, due to their role as potential element and material source for rock varnish. Additionally, STXM-NEXAFS measurements, ... |
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