POTENTIAL LINKS BETWEEN OCEAN PLATEAU VOLCANISM AND GLOBAL OCEAN ANOXIA AT THE CENOMANIAN-TURONIAN BOUNDARY

The Cenomanian-Turonian boundary is marked globally by the extinction of marine invertebrates and an increase in the accumulation and preser vation of organic carbon-rich sediments (black shales). The timing of this boundary also coincides with large-scale volcanism from at least three large igneous provinces: the Caribbean and Ontong-Java plateaus and the Madagascar flood basalts. In this paper, we assess the possibi lity that hydrothermalism associated with large-scale submarine magmat ism was responsible for the reduction of dissolved O-2 in the oceans. We investigate two potential mechanisms; the oxidation of reduced mate rial in hydrothermal effluents and the stimulation of primary producti vity in the water column due to the injection of hydrothermal Fe into surface waters. With the first mechanism, we find that a 10,000-km(3) submarine basalt eruption (three orders of magnitude larger than recen t midocean ridge eruptions) could release enough reduced hydrothermal material to consume at least 6 percent of the dissolved O-2 in seawate r in a well-ventilated ocean (such as the present ocean). With the sec ond mechanism, we calculate that even a small percentage of the hydrot hermal Fe released from a single large flow could have led to a signif icant increase in primary productivity in areas where Fe was the bioli miting nutrient (such as open-ocean areas in the Pacific). The potenti al impact of both of these O-2-reducing mechanisms at the Cenomanian-T uromian boundary would have been significantly greater if Cretaceous o ceans were less well ventilated than the present oceans.