Previously established stratigraphic framework and gross depositional history have permitted analysis of nature and distribution of trace fossil assemblages from western margin to basin center for upper Albian to lower Maestrichtian deposits of the western interior sea. Cluster analysis of trace variety and density reveals distribution patterns which represent habitats similar to those determined previously for mollusks. Trace fossil "habitats" were, however, controlled more closely by substrate nature and events related directly to sedimentation than were the habitats determined by body fossil analysis. Changes in sediment type, depositional rate, and early diagenetic phenomena were recorded with greater accuracy by these groups of trace-makers, which may be used to eluc date the more detailed history of the study interval. The analytical method was applied to several bioturbated carbonate beds of the Greenhorn Limestone that are traceable over large areas of the basin. Bed-by-bed analysis suggests that subtle changes in depositional parameters and/or nature of overlying water column were imparted to certain beds with distinct and characteristic trace fossil assemblages. Basin-wide analysis and mapping of trace fossil assemblages from such beds can be used to improve environmental resolution of this part of the Upper Cretaceous.

Despite great utility of these trace fossil assemblages for environmental analysis, gross interpretations (e.g., water depth) based on trace fossil assemblages alone, must be made with caution. Traces from "deep-water" Upper Cretaceous carbonate rocks are compared to traces in texturally similar but clearly shallow-water Illinois basin Mississippian carbonate rocks. Environmental parameters such as salinity or oxygen availability, that are less readily suggested by lithology, may be largely responsible for such trace fossil assemblage similarities.

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