Preserved organic matter in a fossil Ocean Continent Transition in the Alps: the example of Totalp, SE Switzerland

Abstract

Evidence from ultraslow spreading mid-ocean ridges and both fossil and present-day Ocean-Continent Transitions (OCT) demonstrates that mantle serpentinization resulting from the interaction of mantle rock and water during tectonic exhumation is widespread. Observations at white smokers in modern ocean settings suggest that methane produced by serpentinization can support methanotrophic bio-systems, which use methane as the only source of carbon. An important question is whether such bio-systems are more generally pervasive in their association with serpentinized mantle in the subsurface. In this study, we examined whether there is evidence for such a methanotrophic system in exhumed serpentinized mantle at a magma-poor rifted continental margin, by probing for characteristic biological markers in these and associated sedimentary rocks in the Totalp unit of SE Switzerland. This unit represents a remnant of the former OCT of the southern Alpine Tethyan margin and was chosen because of its mild Alpine tectonic and low-grade metamorphic overprint during Alpine orogeny, hence giving potential for the preservation of indigenous organic matter (OM). Totalp samples are characterized by low organic carbon contents of 11-647 ppm. The majority of the samples contain hydrocarbons in the form of n-alkanes in the range C 17 -C 36 . Some sediments contain isoprenoids, for example pristane and phytane and a suite of steranes that are consistent with a marine origin for the OM preserved in the rocks. Traces of marine planktonic and bacterial OM are preserved in the serpentinized mantle and overlying sediments of this ancient Tethyan OCT, but there is no evidence that the OM has been generated from methanotrophic bio-systems.

New Perspectives on Abiotic Organic Synthesis and Processing during Hydrothermal Alteration of the Oceanic Lithosphere

“…Based on the presence of biomarkers (e.g. pristane, phytane, squalane, hopanes, and steranes) or higher relative abundances of n-C 16 to n-C 20 alkanes, 26,54 amino acids, and long-chain n-alkanes 53 identified in the solvent-extracted fraction, they all concluded that the organic carbon was of biological origin, as supported by TOC isotopic analysis of the oceanic rocks. 25,28 However, biological contamination may have overprinted any possible abiotic geochemical signatures, 26 since these oceanic basement rocks have been affected by long-lived hydrothermal alteration and present-day microbial ecosystems.…”

“…More recently, three studies characterized by bulk molecular approaches (1) serpentinized peridotites and gabbroic rocks recovered at the Atlantis Massif (30 N MAR) at both the Lost City hydrothermal field and Hole U1309D (Expeditions 304/305, Integrated Ocean Drilling Program (IODP)), 26 (2) peridotites from the Ashadze (12 58ʹN) and Logatchev hydrothermal sites along the MAR, 53 and (3) the fossil ocean-continent transition recorded in the Swiss Alps. 54 All of these studies used gas chromatography and/or gas chromatography-mass spectrometry. Based on the presence of biomarkers (e.g.…”

Characterization and Pollution Profile of the Tanning Industry by Distance in Gandong River, Indonesia

“…Water color can be observed with the naked eye (directly) or measured using the platinum cobalt scale (in PtCo units), comparing the color of the water sample and the standard color [20]. The difference in colour values obtained may be due to the presence of different amounts of organic substances or the geology of the stream [21].…”