--> Climate, Circulation, and Anoxia in the Mid-Cretaceous Western Interior Seaway of North America, by R. L. Slingerland, L. R. Kump, M. A. Arthur, E. J. Barron, and B. B. Sagemen; #90986 (1994).

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Abstract: Climate, Circulation, and Anoxia in the Mid-Cretaceous Western Interior Seaway of North America

Rudy L. Slingerland, L. R. Kump, M. A. Arthur, E. J. Barron, B. B. Sagemen

As at many sites worldwide, the Cenomanian/Turonian boundary in the Western Interior Cretaceous Seaway (WIKS) of North America is marked by an ocean anoxic event (OAE) with organic-rich strata, a pronounced carbon isotope excursion, and significant loss of marine taxa. To understand the necessary conditions for this event in the Western Interior we have used GENESIS, an NCAR community climate model, to drive a three-dimensional, turbulent flow, coastal ocean model that includes dynamic formulations for the biogeochemical cycles of organic carbon, nutrients, and dissolved oxygen. Circulation and chemical evolution of WIKS waters are computed under the following initial and boundary conditions: (1) paleobathymetry according to a new interpretation of the litho- and bio-stratigraphy; (2) temperatures and salinities of the Boreal and Tethys Oceans based on atmospheric temperatures and precipitation-evaporation magnitudes computed by GENESIS; and (3) mean annual and dally wind stresses over WIKS computed by GENESIS. The first series of experiments explores thermohaline circulation in the absence of wind stresses by allowing an initially vertical East-West oceanic front in Colorado separating 27 ^sgrt Boreal water from 25 ^sgrt Tethys waters to evolve dynamically. Results show that for a variety of frontal geometries and density differences, flows are sufficient to mix the water column over much of the seaway, thereby effectively precluding development of anoxic bottom waters. In the second series of experiments, flows in an initially and variably stra ified WIKS are driven by the GENESIS wind fields. Again, for a two-layer stratified seaway where ^sgrt = 2, mixing is practically complete after 2 years. These results arise because of the extreme width and length to depth ratios of the seaway and its platform and bathymetric irregularities. We conclude that the origin of the WIKS Cenomanian/Turonian OAE requires quite unique oceanographic conditions, two possibilities of which are caballing due to Boreal and Tethys water masses of equal density or a surface fresh water influx of remarkable proportions.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994