Geochemical evidence for the link between sulfate reduction, sulfide oxidation and phosphate accumulation in a Late Cretaceous upwelling system

Heiko Alsenz; Peter Illner; Sarit Ashckenazi-Polivoda; Aaron Meilijson; Sigal Abramovich; Shimon Feinstein; Ahuva Almogi-Labin; Zsolt Berner; Wilhelm Püttmann

doi:10.1186/s12932-015-0017-1

Geochemical evidence for the link between sulfate reduction, sulfide oxidation and phosphate accumulation in a Late Cretaceous upwelling system

Geochem Trans. 2015 Apr 10:16:2. doi: 10.1186/s12932-015-0017-1. eCollection 2015.

Authors

Heiko Alsenz¹, Peter Illner², Sarit Ashckenazi-Polivoda³, Aaron Meilijson⁴, Sigal Abramovich⁴, Shimon Feinstein⁴, Ahuva Almogi-Labin⁵, Zsolt Berner², Wilhelm Püttmann¹

Affiliations

¹ Department of Environmental Analytical Chemistry, Goethe-University, Institute of Atmospheric and Environmental Sciences, Altenhoeferallee 1, 60438 Frankfurt am Main, Germany.
² Institute for Mineralogy and Geochemistry, Karlsruhe University, 76131 Karlsruhe, Germany.
³ Dead Sea and Arava Science Center, Neve Zohar, Dead Sea Mobile Post, Neve Zohar, 86910 Israel.
⁴ Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, POB 653, Beer Sheva, 84105 Israel.
⁵ Geological Survey of Israel, Jerusalem, 95501 Israel.

Abstract

Background: On Late Cretaceous Tethyan upwelling sediments from the Mishash/Ghareb Formation (Negev, Israel), bulk geochemical and biomarker analyses were performed to explain the high proportion of phosphates in the lower part and of organic matter (OM) preserved in upper parts of the studied section. The profile is composed of three facies types; the underlying Phosphate Member (PM), the Oil Shale Member (OSM) and the overlying Marl Member (MM).

Results: Total organic carbon (TOC) contents are highly variable over the whole profile reaching from 0.6% in the MM, to 24.5% in the OSM. Total iron (TFe) varies from 0.1% in the PM to 3.3% in the OSM. Total sulfur (TS) ranges between 0.1% in the MM and 3.4% in the OSM, resulting in a high C/S ratio of 6.5 in the OSM section. A mean proportion of 11.5% total phosphorus (TP) in the PM changed abruptly with the facies to a mean value of only 0.9% in the OSM and the MM. The TOC/TOCOR ratios argue for a high bacterial sulfate reduction activity and in addition, results from fatty acid analyses indicate that the activity of sulfide-oxidizing activity of bacteria was high during deposition of the PM, while decreasing during the deposition of the OSM.

Conclusions: The upwelling conditions effected a high primary productivity and consequently the presence of abundant OM. This, in combination with high sulfate availability in the sediments of the PM resulted in a higher sulfide production due to the activity of sulfate-reducing bacteria. Iron availability was a limiting factor during the deposition of the whole section, affecting the incorporation of S into OM. This resulted in the preservation of a substantial part of OM against microbial degradation due to naturally-occurring sulfurization processes expressed by the high C/S ratio of 6.5 in the OSM. Further, the abundant sulfide in the pore water supported the growth of sulfide-oxidizing bacteria promoting the deposition of P, which amounted to as much as 15% in the PM. These conditions changed drastically from the PM to the OSM, resulting in a significant reduction of the apatite precipitation and a high concentration of reactive S species reacting with the OM.

Keywords: Cretaceous; Ghareb formation; Lipid biomarkers; Negev/Israel; Phosphate deposition; Sulfate-reducing bacteria; Sulfide-oxidizing bacteria.