A PLANKTONIC FORAMINIFERAL DERIVED MODEL OF THE LATEST CENOMANIAN WESTERN INTERIOR CIRCULATION

Early field researchers suggested that planktonic foraminifera construct less dense shells (more porous) in warmer and less saline waters. (Bé, 1968; Scott, 1972; Frerichs et al., 1972; and Bé et al., 1973, 1976; and Kennett, 1976). Bijma et al. (1990) verified this relationship in the laboratory. Many methods have been used to interpret the oceanic circulation of the late Cenomanian Western Interior Seaway. Within sample porosity variations of the planktonic foraminifera Hedbergella delrioensis are being used to reconstruct the water column structure of the time-slice lying above the latest Cenomanian B bentonite in the Western Interior Seaway. Variations in porosity indicate that the water column in which Hedbergella delrioensis grew were stratified and varied in density from west to east and north to south across the seaway. The most-dense waters at the Hedbergella delrioensis habitat occurred in the north and along the eastern margin of the sea. The least-dense waters reside over the four-corner area. Areas of closely spaced porosity contours indicate areas of strong current flow. Porosity contours rise near the margins of the seaway, indicating the potential for water mass mixing. Previously reported anomalously depleted oxygen isotopic values in the Western Interior Seaway suggest that much of the water in the Western Interior Sea may have been manufactured internally, and were unique to the seaway. The porosity-based oceanographic model is compared to foraminiferal and calcareous nannofossil data collected on the B bentonite, as well as, published biotic and sedimentologic data. Much of the data is in close agreement to the porosity based oceanographic conditions.