2006 Philadelphia Annual Meeting (2225 October 2006)
Paper No. 211-9
Presentation Time: 3:30 PM-3:45 PM

CAUSAL MECHANISMS FOR OAE'S III: THE ROLE OF PHOSPHOROUS?

FLAUM, Jason A., Geological Sciences, Northwestern Univ, 1850 Campus Dr, Evanston, IL 60202, j-flaum2@northwestern.edu, SAGEMAN, Bradley B., Northwestern Univ, Locy Hall 1850 Campus Drive, Evanston, IL 60208-2150, MEYERS, Stephen R., Department of Geological Sciences, University of North Carolina at Chapel Hill, 213 Mitchell Hall, CB # 3315, Chapel Hill, NC 27599-3315, and HURTGEN, Matthew T., Department of Geological Sciences, Northwestern University, 1850 Campus Dr, Evanston, IL 60208

Increased rates of marine primary production due to enhanced nutrient flux is one of the favored mechanisms proposed to account for the initiation of Cretaceous Oceanic Anoxic Events. Among the possible candidates phosphorus (P) is believed to be important because of arguments that it is the key biolimiting nutrient on geologic timescales. What remains unclear in this hypothesis is the mechanism by which P delivery to surface waters might have been enhanced. Did the terrigenous P flux increase due to a change in chemical weathering rates? Or did the proportion of P recycled from decomposing marine organic matter change due to a shift in early diagenetic conditions. In this study a sequential extraction procedure (SEDEX) is used to separate 5 phases of P known to occur in modern marine sediments from strata spanning the Cenomanian Turonian (C-T) OAE II. The study area is the Western Interior Basin (WIB) of North America, where a terrigenous P signal, if present, should be readily detectable. Sampled localities represent a number of sites representing different depositional environments. The sample interval begins in strata representing open marine, but intermittently strongly stratified conditions on sub-orbital timescales that preceded OAE II and extends through the deeper marine OAE II period during which mixed and stratified conditions oscillated on orbital timescales. Development of a new timescale integrating radiometric and orbital components allows concentration data to be converted to accumulation rates. The WIB P data demonstrates a significant increase in the accumulation rates of both detrital and authigenic phases immediately prior to OAE II. The increase in detrital P suggests a change in the P budget related to an increase in the weathering flux of P. A comparison of detrital P accumulation rates in a distal proximal transect supports the conclusion that the detrital phase is not overestimated authigenic phase as has been suggested. Once OAE II initiates, however, accumulation rates of both phases drop to between 20 50% of pre-OAE II values. This suggests a major change in the P burial rate and provides a possible source of the excess P that maintained increased primary production during OAE II. This talk will conclude by considering the relationship between reactive Fe availability and P burial rate.

2006 Philadelphia Annual Meeting (2225 October 2006)
General Information for this Meeting
Session No. 211
Paleoclimatology/Paleoceanography II: Proxy Reconstructions
Pennsylvania Convention Center: 107 AB
1:30 PM-5:30 PM, Wednesday, 25 October 2006

Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 513

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