Microbial activity records in Marinoan Snowball Earth postglacial transition layers connecting diamictite with cap carbonate (Otavi Group, NW-Namibia)

Abstract

This study concerns the microbial mat formation in postglacial layers of the Marinoan Snowball Earth glaciation. A high resolution investigation was carried out on the transition layers of Ghaub to Maieberg Formation (start of Keilberg Member) of the Otavi Group in NW-Namibia (Neoproterozoic). Macroscopic characterization, optical rock microscopy, XRD mineralogy, Raman spectroscopy investigations were done and geochemical (major and trace element content) as well as carbonate carbon isotopic data were collected. Three types of microbial contributions were determined: (1) primary, synsedimentary Fe-rich biomats; (2) secondary biomats from biodegradation of Fe-bearing minerals (pyrite, chlorite); and (3) pseudo-secondary structures coating on clasts. These microbial mats of iron-oxidizing bacteria consumed iron from different sources, such as hydrothermal solutions or ironbearing minerals. On the basis of the morphology of Fe-biomats, and the mineralogical and geochemical signatures, we suggest that the Marinoan postglacial transition layers (Ghaub-Maieberg boundary) formed under neutral, suboxic conditions in brackish water at the studied locality.____________________________________________________________________________________

Asteroid impact effects on Snowball Earth

“…However, we note that so far no direct geological or geochemical evidence of a large‐scale impact near the Snowball period has yet been found (Gyollai et al. , ; Peucker‐Ehrenbrink et al. ).…”

“…The data of Bodiselitsch et al (2005), originally intended to constrain the duration of the Marinoan glaciation, can also be interpreted to indicate the presence of a possible impact-related meteoritic component. However, we note that so far no direct geological or geochemical evidence of a large-scale impact near the Snowball period has yet been found (Gyollai et al 2014(Gyollai et al , 2017Peucker-Ehrenbrink et al 2016).…”

Impact of iron‐rich scale in service lines on lead release to water

“…Raman analyses revealed the presence of Fe(III) oxyhydoxides (lepidocrocite and goethite) and magnetite on the inner surface of R1 (Figure 4). Comparison of the pipe spectra with spectra of standards available in the laboratory and spectra in Das and Hendry (2011), Drahota et al (2018), and Gyollai et al (2017) reveals that the pipe samples tend to have broad peaks indicative of low crystallinity. Other than the light brown main mass, the scale of R1 (Figure 2) had patches of white crusts and black spherical particles.…”

“…Labels L, G, M, and H indicate the bands of lepidocrocite (γ‐FeOOH (s) ), goethite (α‐FeOOH (s) ), magnetite (Fe 3 O 4(s) ), and hydrocerussite, respectively. Databases for peak positions for iron oxides were obtained from several different literature sources (Das & Hendry, 2011; Drahota et al, 2018; Gyollai et al, 2017), as well as spectra of laboratory standards and those of the RRUFF Project (RRUFF, n.d.). The peak position labeled hydrocerussite was determined by Raman analysis of synthetic hydrocerussite powder confirmed by X‐ray diffraction.…”

“…The labels L, G, M, and H indicate the bands for lepidocrocite (γ‐FeOOH (s) ), goethite, magnetite (Fe 3 O 4(s) ), and hydrocerussite, respectively. Comparison data for each compound's spectrum were obtained from several studies (Das & Hendry, 2011; Drahota et al, 2018; Gyollai et al, 2017), our own laboratory standards, and the RRUFF Project (RRUFF, n.d.). Figure S5.…”