HR: 15:10h
AN: PP42C-06    [PDF]
TI: Hydrothermal Links Between the Caribbean Plateau and OAE2
AU: * Duncan, R A
EM: rduncan@coas.oregonstate.edu
AF: College of Oceanic and Atmopsheric Sciences, Oregon State University, Corvallis, OR 97331 United States
AU: Snow, L J
EM: lsnow@coas.oregonstate.edu
AF: College of Oceanic and Atmopsheric Sciences, Oregon State University, Corvallis, OR 97331 United States
AB: A popular current model for the sporadic occurrence of ocean anoxic events (OAEs) in the Cretaceous ties hydrothermally-induced changes in ocean chemistry (bio-limiting trace metals) during ocean plateau (LIP) volcanism to increased surface productivity, followed by mid-to-deep water oxygen depletion and accumulation of organic-rich sediments. This proposed connection is far from accepted, and important unresolved aspects include the timing of events and yet-to-be-proved synchroneity of volcanism and OAEs, the sensitivity of phytoplankton to bio-limiting (and toxic) trace metals, the difference in biotic responses at various OAEs, and the source of the hydrothermal inputs (sea floor spreading centers or ocean plateaus). To test this hypothesis we have measured the distribution of major, minor and trace element abundances in five pelagic carbonate and black shale sequences that bracket the OAE2, defined by a prominent positive excursion in the global seawater d13C record. Sedimentary sections at Rock Creek Canyon (Pueblo, CO), ODP Site 1138 (Kerguelen Plateau), Bass River (NJ), Totuma well (Venezuela) and Baranca el Canyon (Mexico) were chosen to examine potential trace metal patterns and gradients around the proposed source of hydrothermal inputs - the Caribbean Plateau, whose initial volcanic activity has been dated at 93-89 Ma. ICP-AES and ICP-MS elemental abundances from whole rock samples are normalized to Zr to remove the effect of terrestrial inputs. We find prominent trace metal "spikes" (up to 50 times background) for elements known to be concentrated in volatile degassing of magmas and in hydrothermal plumes resulting from seawater-rock reactions. These anomalies begin at the onset and continue well into the d13C excusion at all five sites. Furthermore, the magnitude of the anomalies decreases with distance from the Caribbean region, and the pattern of elements shifts from a wide range of metals near-source to predominantly long residence time metals far "downstream".
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4267 Paleoceanography
DE: 4271 Physical and chemical properties of seawater
DE: 4875 Trace elements
DE: 8424 Hydrothermal systems (8135)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting