A Redox-Based Model for Carbonate Platform Drowning and Ocean Anoxic Events

Abstract

The deposition of marine carbonate rocks is influenced by climate and seawater chemistry. Carbonate platforms usually keep pace with subsidence and sea level rise but "platform drowning" occurs when carbonate sedimentation slows or when siliciclastics replace carbonates. Identifying specific mechanism(s) behind platform drowning is critical for understanding global environmental changes such as Ocean Anoxic Events (OAEs). We developed a model for OAEs which couples ocean basin redox processes to rates of carbonate sedimentation. Well-oxygenated oceans have steep gradients in saturation state such that deep-ocean dissolution is balanced by carbonate "overproduction" in shallow water. Through anaerobic metabolisms, deep-ocean anoxia reduces both dissolution and overproduction, leading to slower accumulation rates in shallow-water environments. This quasi-steady state response links carbonate sedimentation with longer timescales associated with redox changes. Redox-based drowning may have acted alongside other mechanisms to create spatially diverse patterns of platform drowning during Mesozoic OAEs and other Phanerozoic hyperthermal events.

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