Abstract: The Cretaceous Western Interior Seaway Drilling Project: An Overview

Walter E. Dean, Michael A. Arthur

This project is a multidisciplinary study of Cretaceous strata in cores from bore holes along a transect across the Cretaceous Western Interior Seaway, which extended from the Gulf of Mexico to the Arctic Ocean during maximum marine transgressions. Funding for the project was provided by the U.S. Geological Survey, Department of Energy, and Amoco. The project is focused on, in ascending order, the Graneros Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation, and the lower part of the Pierre Shale in cores from sites in western Kansas, southeastern Colorado, and eastern Utah. The rocks grade from pelagic carbonates that contain organic-carbon rich source rocks for hydrocarbons at the eastern end of the transect to nearshore coal-bearing strata at the western end. The project ombines biostratigraphic, paleoecologic, geochemical, mineralogical, and high-resolution geophysical logging studies being conducted by about 24 scientists from the U. S. Geological Survey, Amoco, and seven universities.

Results of these studies to be presented in this poster symposium include: (1) the effects of organic-matter enrichment on the geochemical characteristics of the sediments; (3) the effects of burial depth on the geochemical characteristics of the sediments and their contained organic matter; (4) use of variations of faunal and floral components and sedimentary structures to evaluate the extent and intensity of oxygen deficiency in bottom waters; (5) documentation of rates and timing of biotic extinction and evolution; (6) construction of a high-resolution chronostratigraphy using the highly diverse faunal and floral assemblages, together with radiometric dating of volcanic ash layers; and (7) use of this unique high-resolution chronology to calculate rates and timing of supply of sedi ent components, organic productivity, and changes in water-mass characteristics that contribute to the sedimentary expression of Milankovitch orbital cycles.

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