Spatial characterization of cretaceous Western Interior Seaway paleoceanography using foraminifera, fuzzy sets and Dempster–Shafer theory

Abstract

The spatial paleoceanography of the entire Western Interior Seaway (WIS) during the Cenomanian-Turonian Oceanic Anoxic Event (OAE2) has been reconstructed quantitatively for the first time using Geographic Information Systems. Models of foraminiferal occurrences—derived from Dempster–Shafer theory and driven by fuzzy sets of stratigraphic and spatial data—reflect water mass distributions during a brief period of rapid biotic turnover and oceanographic changes in a greenhouse world. Locality data for four benthic and one planktic foraminiferal species and lithologic and geochemical data from sites distributed throughout the WIS were compiled from four ammonoid biozones of the upper Cenomanian and lower Turonian stages. Of the 14 environmental parameters included in the dataset, percent silt, percent total carbonate, and depositional environment (essentially water depth) were associated with foraminiferal occurrences. The inductive Dempster–Shafer belief models for foraminiferal occurrences reveal the positions of northern and southern water masses consistent with the oceanographic gyre circulation pattern that dominated in the seaway during the Cenomanian/Turonian Boundary Event. The water-mixing interface in the southwestern part of the WIS was mostly restricted to the Four Corners region of the US, while the zone of overlap of northern and southern waters encompassed a much larger area along the eastern margin, where southern waters occasionally entered from the tropics. In addition to its paleospatial significance, this study introduces a rigorous, quantitative methodology with which to analyze paleontological occurrence data, assess the degree of uncertainty and prioritize regions for additional data collection.