T238 Marine Redox Evolution: Controls and Consequences I

Wednesday, 3 November 2010
8:00 AM - 12:00 PM
Room 203

THE IREVIKEN EVENT: A SILURIAN OAE

Paper number: T238-9
Program: Technical Sessions
Time: 10:10 AM – 10:25 AM

Authors

Abstract

The Silurian Ireviken Event near the Llandovery/Wenlock boundary is interpreted as a time of environmental, biotic and isotopic perturbations of the paleo-ocean. Eight discreet extinction datums comprise this event. While conditions responsible for the extinctions remain poorly understood, several researchers have proposed that water-column anoxia had a significant role.

Chemical analyses of conodonts, brachiopods, and micritic carbonate from a section in Gotland, Sweden through the Ireviken Event detected systematic changes in the abundance of redox sensitive elements. Ce*, Eu*, U/Th and other element concentrations indicate conditions become increasingly reducing through the event. Short-lived, signatures of anoxia occur at datums 1-3. At datum 4 these signatures reach maxima that persist through the remainder of the event. Increased REE, Fe, and Mn contents during anoxic episodes are best explained by the transfer of elements released by dissolution of oxy-hydroxides in sediments to the water column. This interpretation is consistent with changes from red to green shale to gray-black pyritic shale through this event in eastern North America and elsewhere. The temporal correlation between indicators of anoxia with extinction datums at several locations and the global δ13C excursion are evidence that the anoxia was global in extent.