Suboxic conditions prevailed during the Toarcian Oceanic Anoxic Event in the Alpine-Mediterranean Tethys: The Sogno Core pelagic record (Lombardy Basin, northern Italy)

Gabriele Gambacorta, Liyenne Cavalheiro, H.-J. Brumsack, Alexander J. Dickson, Hugh C. Jenkyns, Bernhard Schnetger, Thomas Wagner, Elisabetta Erba

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

The Sogno Core represents one of the deepest pelagic records of the Toarcian Oceanic Anoxic Event (T-OAE) in the Alpine-Mediterranean Tethys. New sedimentological, elemental, Rock-Eval, and biomarker data are presented here, with the aim of reconstructing the depositional conditions that characterized the sedimentation of this succession during the broad positive carbon-isotope excursion of the T-OAE, and its negative isotopic anomaly (Jenkyns Event). Higher Mnxs concentrations, inversely correlated with the δ18O curve, were observed starting slightly below the onset level of the Jenkyns Event up to the lowermost part of the negative carbon-isotope anomaly, reflecting a combination of a gradual warming and a progressive increase in fresh waters delivered by runoff. Increased weathering intensity was accompanied by enhanced detrital input with higher concentrations in lithogenic elements, and by a relative increase in palaeoproductivity, consistently with higher Sixs concentrations and changes in calcareous nannoplankton assemblages. The enhanced fresh-water input favored water-column stratification, less efficient deep-water circulation and oxygen depletion. Except for two discrete black shales characterized by anoxic pore waters, redox conditions at Sogno turned at maximum suboxic, as indicated by rare to absent bioturbation, limited enrichments in redox-sensitive elements, and molecular biomarkers. The Sogno Core record shows that dominant oxic–suboxic conditions were present also at bathyal depths in the Alpine-Mediterranean Tethys during the Jenkyns Event, thereby contrasting with the anoxic–euxinic environments present both in the shallower water basins and sub-basins of epicontinental northern Europe and, locally, in the relatively deep-water areas of the Alpine Tethys.
Original languageEnglish
Article number104089
JournalGlobal and Planetary Change
Volume223
Early online date15 Mar 2023
DOIs
Publication statusPublished - Apr 2023

Keywords

  • Biomarkers
  • Black shale
  • Fish Level
  • Jurassic
  • OAEs
  • Trace metals

ASJC Scopus subject areas

  • Oceanography
  • Global and Planetary Change

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