Bottom water redox dynamics during the Early Cretaceous Weissert Event in ODP Hole 692B (Weddell Sea, Antarctica) reconstructed from the benthic foraminiferal assemblages

Benthic foraminifera at Ocean Drilling Program (ODP) Hole 692B were studied to understand variations in oxygen and organic-matter fluxes in bottom waters during the Early Cretaceous. The upper Berriasian to lower Barremian black shales, characterized by high concentrations of total organic carbon (TOC) ranging between 1.3 and 18%, were deposited in an outer neritic-upper bathyal environment (~200–500 m) according to benthic foraminifera assemblages. A new high-resolution record of benthic foraminiferal assemblages of high-latitude, dominated by infaunal taxa (Citharina, Eoguttulina, Laevidentalina, Lagena, Lenticulina, Marginulina, Nodosaria, Planularia, Saracenaria, and Vaginulinopsis), is described in depleted‑oxygen and high organic‑carbon flux conditions.

Extremely dysoxic conditions are recorded at the onset of the carbon isotope excursion (CIE) marking the Weissert Event (late Valanginian), followed by a period of anoxic conditions in bottom waters. A repopulation event of benthic foraminifera, linked to an increase in oxygen concentrations, coincided with the global cooling episode that characterized the late part of the Weissert Event.

Subsequently, there were short periods in the late Valanginian and the late early Hauterivian when the bottom waters experienced increased oxygen concentrations. Possibly, bottom currents related to the influx of Southern Ocean waters favored short-term pulses of ventilation under constant increased organic‑carbon flux during the late Valanginian and late Hauterivian.