Title: Characterization and differentiation of rock varnish types from different environments by microanalytical techniques

Abstract

We investigated rock varnishes collected from several locations and environments worldwide by a wide 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. Ourmore » 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, La N /Yb N , and Ce/Ce*), total REE contents, and structures can be used to separate the different types of rock varnish from each other.« less

Authors:

Macholdt, D. S. ^[1]; Jochum, K. P. ^[1]; Pöhlker, C. ^[1]; Arangio, A. ^[1]; Förster, J. -D. ^[1]; Stoll, B. ^[1]; Weis, U. ^[1]; Weber, B. ^[1]; Müller, M. ^[2]; Kappl, M. ^[2]; Shiraiwa, M. ^[1]; Kilcoyne, A. L. D. ^[3]; Weigand, M. ^[4]; Scholz, D. ^[5]; Haug, G. H. ^[1]; Al-Amri, A. ^[6]; Andreae, M. O. ^[7]

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+ Show Author Affiliations

1. Max Planck Society, Mainz (Germany). Max Planck Inst. for Chemistry
2. Max Planck Inst. for Polymer Research, Mainz (Germany)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
4. Max Planck Inst. for Intelligent Systems, Stuttgart (Germany)
5. Johannes Gutenberg Univ., Mainz (Germany)
6. King Saud Univ., Riyadh (Saudi Arabia)
7. Max Planck Society, Mainz (Germany). Max Planck Inst. for Chemistry; King Saud Univ., Riyadh (Saudi Arabia)

Publication Date:

Thu Apr 13 00:00:00 EDT 2017

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1393236

Alternate Identifier(s):

OSTI ID: 1413374

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Chemical Geology

Additional Journal Information:

Journal Volume: 459; Journal Issue: C; Journal ID: ISSN 0009-2541

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES