Microbially-driven formation of Cenozoic siderite and calcite concretions from eastern Austria

Autor(en)

Lydia M. F. Baumann, Daniel Birgel, Michael Wagreich, Joern Peckmann

Abstrakt

Carbonate concretions from two distinct settings have been studied for their petrography, carbon and oxygen stable isotope patterns, and lipid biomarker inventories. Siderite concretions are enclosed in a Paleocene-Eocene deep-marine succession with sandy to silty turbidites and marl layers from the Gosau Basin of Gams in northern Styria. Septarian calcite concretions of the southern Vienna Basin from the sandpit of Steinbrunn (Burgenland) are embedded in Upper Miocene brackish sediments, represented by calcareous sands, silts, and clays. Neither for the siderite, nor for the calcite concretions a petrographic, mineralogical, or stable isotope trend from the center to the margin of the concretions was observed, implying that the concretions grew pervasively. The δ

¹³C values of the Gams siderite concretions (-11.1 to -7.5%) point to microbial respiration of organic carbon and the d18O values (-3.5 to +2.2%) are in accordance with a marine depositional environment. The low δ

¹³C values (-6.8 to -4.2%) of the Steinbrunn calcite concretions most likely reflect a combination of bacterial organic matter oxidation and input of marine biodetrital carbonate. The corresponding δ

¹⁸O values (-8.8 to -7.9%) agree with carbonate precipitation in a meteoric environment or fractionation in the course of bacterial sulfate reduction. Lipid biomarkers have been extracted before and after decalcification of the concretions in order to assess pristine signatures and to exclude secondary contamination. The siderite concretions did not yield indigenous biomarkers due to their high thermal maturity. The calcite concretions comprise abundant plant wax-derived long-chain n-alkanes, reflecting high terrestrial input. Bacterial-derived, terminally-branched fatty acids and hopanoids were found, but with overall low contents. The presence of framboidal pyrite, the moderately low δ

¹³C values, and the biomarker inventory indicate that bacterial sulfate reduction contributed to the formation of the calcite concretions in a brackish environment. The low δ

¹³C values of the siderite concretions, on the other hand, are best explained by bacterial iron reduction, since sulfate reduction and resultant hydrogen sulfide production would have inhibited siderite precipitation. This study documents a new example for an exception from the common pattern that siderite concretions preferentially precipitate in freshwater environments. The Gams siderite concretions formed within marine sediments, whereas the Steinbrunn calcite concretions formed in freshwater to brackish sediments.

Organisation(en)

Institut für Geologie

Externe Organisation(en)

Universität Hamburg

Journal

Austrian Journal of Earth Sciences

Band

109

Seiten

211-232

ISSN

0251-7493

DOI

https://doi.org/10.17738/ajes.2016.0016

Publikationsdatum

2016

Peer-reviewed

Ja

ÖFOS 2012

105106 Geodynamik

Schlagwörter

ASJC Scopus Sachgebiete

Geology, Palaeontology, Stratigraphy

Sustainable Development Goals

SDG 14 – Leben unter Wasser

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/microbiallydriven-formation-of-cenozoic-siderite-and-calcite-concretions-from-eastern-austria(1ceb4a97-2000-4fef-8c73-e9429bf5e13f).html