Characterization and differentiation of rock varnish types from different environments by microanalytical techniques
| Autor: | Bettina Weber, Meinrat O. Andreae, Markus Weigand, Ulrike Weis, Denis Scholz, Christopher Pöhlker, Brigitte Stoll, Abdullah Al-Amri, Manabu Shiraiwa, Andrea M. Arangio, A. L. D. Kilcoyne, Dorothea S. Macholdt, Jan-David Förster, Gerald H. Haug, Michael Kappl, Klaus Peter Jochum, Maren Müller |
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| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
Geochemistry & Geophysics
010504 meteorology & atmospheric sciences Scanning electron microscope Varnish Analytical chemistry Mineralogy fs LA-ICP-MS Rock varnish 010502 geochemistry & geophysics Mass spectrometry 01 natural sciences Focused ion beam Physical Geography and Environmental Geoscience Geochemistry and Petrology Spectroscopy 0105 earth and related environmental sciences Rare-earth element Desert varnish STXM-NEXAFS Varnish types Geology Characterization (materials science) Geochemistry Categorization visual_art SEM visual_art.visual_art_medium EPR |
| Zdroj: | Macholdt, DS; Jochum, KP; Pöhlker, C; Arangio, A; Förster, JD; Stoll, B; et al.(2017). Characterization and differentiation of rock varnish types from different environments by microanalytical techniques. Chemical Geology, 459, 91-118. doi: 10.1016/j.chemgeo.2017.04.009. Lawrence Berkeley National Laboratory: Retrieved from: http://www.escholarship.org/uc/item/3nw8g0pg |
| DOI: | 10.1016/j.chemgeo.2017.04.009. |
| Popis: | © 2017 Elsevier B.V. We investigated rock varnishes collected from several locations and environments worldwide by a broad range of microanalytical techniques. These techniques were selected to address the challenges posed by the chemical and structural complexity within the micrometer- to nanometer-sized structures in these geological materials. Femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS), scanning transmission X-ray microscopy-near edge X-ray adsorption fine structure spectroscopy (STXM-NEXAFS) in combination with scanning electron microscopy (SEM) of focused ion beam (FIB) ultra-thin (100–200 nm) sections, conventional and polarization microscopy, as well as electron paramagnetic resonance (EPR) measurements were used to obtain information about these rock varnishes. Rock varnishes from different environments, which cannot readily be distinguished based on their macroscopic appearance, differ significantly in their constituent elemental mass fractions, e.g., of Mn, Fe, Ni, Co, Ba, and Pb, and their rare earth element (REE) patterns. Structural characteristics such as the particle sizes of embedded dust grains, internal structures such as layers of Mn-, Fe-, and Ca -rich material, and structures such as cavities varied between varnishes from different environments and regions in the world. The EPR spectra were consistent with aged biogenic Mn oxides in all samples, but showed subtle differences between samples of different origin. Our observations allow us to separate rock varnishes into different types, with differences that might be indicators of distinct geneses. Five different types of rock varnish could be distinguished, Type I–V, of which only Type I might be used as potential paleoclimate archive. Each varnish type has specific characteristics in terms of their elemental composition, element distribution, and structures. The combination of element ratios (Mn/Ba, Al/Ni, Mn/REY, Mn/Ce, Mn/Pb, LaN/YbN, and Ce/Ce*), total REE contents, and structures can be used to separate the different types of rock varnish from each other. |
| Databáze: | OpenAIRE |
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