Bottom current activity and sediment redistribution during Ocean Anoxic Event 1d revealed from late-Albian black shales and carbonates

This study is based on understanding the potential role of bottom currents in sediment redistribution during the late Albian Ocean Anoxic Event 1d (OAE1d). The current knowledge on the influence of bottom currents during this event remains poorly understood due to limited research. During our study, field samples from the Pialli Level black shales and interbedded carbonates (Scaglia Bianca Formation–Umbria Marche Basin, Central Italy) were studied under scanning electron microscopy (SEM), revealing evidence of reworked sediments by bottom currents with dipping cross laminations, transported intraclasts, and micro-scale truncations among thin beds. Petrographic microscopy further identified texturally variable laminations, fine truncations, bioturbation and abundant detrital lithics suggesting shifts in the depositional regime, possibly triggered due to changes in sediment sources, and/or sediment flow dynamics. Mineralogically, the presence of disseminated barite (BaSO4) suggests a redox boundary within the shallow sediments, lying beneath the sediment–water interface (rather than at the surface) likely resulting from episodic influxes of relatively oxygenated, slow-moving bottom currents disrupting the anoxia. Thus, our sediment analysis indicates the prevalence of bottom currents activity as a decisive process operating alongside the suspension settling within the pelagic–hemipelagic ocean realm during OAE1d. The knowledge on bottom currents sediment transport from this study will reshape the sediment dynamics-related research and broaden understanding on organic matter burial, hydrocarbon reservoir characterization, oceanic response to climatic and geochemical modifications during ocean anoxic events in the Earth’s history.