Document Type

Article

Publication Date

7-5-2025

Journal / Book Title

Marine and Petroleum Geology

Abstract

The Messinian Salinity Crisis (MSC) generated extensive anoxic sediments under the evaporitic deposits in marginal Mediterranean basins. In an interdisciplinary approach combining field work with multiple laboratory techniques, the oil source rock potential and biomarkers of pre-evaporitic Messinian sediments from the Caltanissetta Basin (Sicily) were evaluated using Rock-Eval pyrolysis, gas chromatography-mass spectrometry, isotopic analysis and optical and electron microscopy. Organic-rich samples from the 45 m Serra Pirciata section consist of cycles of diatomaceous and carbonate layers alternating with organic shales of variable TOC. The organic matter is mostly optically amorphous, increasing in content upwards in the section. Of the 43 samples analyzed within the section, an especially organic- and sulfur-rich interval shows TOC values up to 10%, and oil generation potential (Rock-Eval S2) up to 75 mg HC/g rock. Samples show Rock-Eval Hydrogen Indices (HI) up to ca. 800 mg HC/g TOC, but most fall in the range of 300-600 mg HC/ g TOC, indicating type II kerogen. Within this section, a specific interval is especially remarkable for its unusual biomarker assemblage, having abundant sulfur compounds including isoprenoid, steroid, and hopanoid thiophenes and thiolanes, as well as microscopic sponge fossils. We propose that this organic-rich interval with its distinctive biomarkers represents an initial episode of basin restriction and, based on cyclostratigraphic interpretations, constitutes a non-evaporitic record of the onset of the MSC in the deeper part of the Caltanissetta Basin, where gypsum deposits were initially absent. If the depocenter of the Caltanissetta Basin is an analog for the deep Mediterranean basin, these results suggest that a large volume of organic matter of bacterial origin accumulated in the deep Mediterranean prior to evaporitic deposition.

Comments

From the conclusions:

An organic-rich interval of 5 m with a TOC up to 10% occurs in the middle of the studied section associated with paper shale and dolostone beds. This interval was deposited prior or during the onset of the MSC during a period of major productivity, anoxia and increasing salinity prior to halite saturation and deposition of salt in Caltanissetta Basin. At Serra Pirciata, the detected geochemical markers clearly herald the initiation of the Messinian Salinity Crisis. Based on these novel insights gleaned from our results, we propose a chemostratigraphic approach for determining MSC onset as a supplement to the cyclo-, litho- and biostratigraphic approaches, in sections where the euxinic deeper water facies has been preserved and remains thermally immature. At candidate intervals in which geochemical screening detects high values of TOC, sulfur, Rock-Eval S2 and the Hydrogen Index, samples should be chosen for biomarker analysis. If this reveals the unusual assemblage including the aforementioned isoprenoids, hopanoids, and – most importantly – the various thiophenes and thiolanes, this could signal that the MSC onset level will be found in directly superjacent strata. Our hope is that this concept will be put to the test at other field sites around the Mediterranean region, particularly where litho- or biostratigraphical indications are inconclusive.

This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by- nc/4.0/).

DOI

10.1016/j.marpetgeo.2025.107532

Publisher

Elsevier

Journal ISSN / Book ISBN

0264-8172

Published Citation

Permanyer, A., Kruge, M.A., Gibert, L. (2025) Onset of the Messinian Salinity Crisis: Insights from molecular organic geochemistry. Marine and Petroleum Geology, 181:107532. https://doi.org/10.1016/j.marpetgeo.2025.107532

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