The Coniacian-Santonian Oceanic Anoxic Event OAE3 - global correlation of subevents

The Coniacian-Santonian was a time of strong differentiation in marine sedimentation, characterized by organic carbon-rich black shales and dark carbonates interpreted as the last oceanic anoxic event, OAE3, versus organic carbon-poor white/reddish limestones, chalk and claystones known as Cretaceous Oceanic Red Beds (CORBs). Based on compiled geochemical and isotope proxy data, two high-resolution global carbon isotope curves for carbonate and organic matter were reconstructed based on statistical analysis. Three main levels of short amplitude (around 0.5‰) carbon isotope excursions were identified. These excursions, each some 0.4 to 0.7 Ma in duration, were characterized by regionally restricted benthic anoxia and sea-level highstands that controlled regional organic matter accumulation during the OAE3 subevents defined herein as OAE3a (late mid-Coniacian, ca. 86.9 Ma, Kingsdown Event), OAE3b (late mid-Santonian, ca. 85.0 Ma, Horseshoe Bay Event), and OAE3c (late Santonian to Santonian-Campanian Boundary Event, ca. 83.5 Ma). Based on a compilation oxygen isotope temperature data and reconstructed pCO₂ trends, the Coniacian-Santonian was characterized by: 1) a steady state phase of warm greenhouse climate during the Coniacian, followed by (2) a hot greenhouse during the early Santonian that might be consistent with activation of the Central Kerguelen large igneous province, and (3) a longer-term cooling of the warm greenhouse climate from the mid-Santonian onwards. Organic matter-rich deposition is largely restricted to the low-latitude Atlantic and adjacent epeiric and shelf seas. Areas of enhanced oceanic circulation systems with a westwards directed Tethyan current and regional eddies of water mass flow had a negative feedback resulted in well-developed water column oxygen content within the Tethys.