PROCESS ICHNOLOGICAL ANALYSIS OF THE LOWER CRETACEOUS BLUESKY FORMATION, ALBERTA

The process ichnological methodology was applied to a core dataset from the late Aptian to early Albian Bluesky Formation in northwest Alberta to identify the ichnological characteristics of ancient, marginal marine environments. Process ichnology utilizes trace fossils as biogenic sedimentary structures and provides a framework in which various physico-chemical stresses can be interpreted. This methodology has proven effective in recognizing the response of trace making organisms to such stresses in modern environments, but its application to ancient deposits is less established. Several previous studies of the Bluesky Formation have identified a wide range of environmental affinities. However, few of these studies have focused on the detailed combination of ichnologic criteria outlined within the process ichnological framework. In order to assess the effectiveness of the process ichnological framework to the rock record, high resolution, systematic ichnological characteristics were recorded and combined with sedimentologic data from nine wells containing core from within the Bluesky Formation. These ichnological characteristics included: 1) burrow distribution; 2) maximum burrow diameter; 3) burrow deformation; 4) burrow lining; 5) bioturbation intensity; 6) characteristic ichnogenera, and; 6) size diversity index. These characteristics led to the identification of several inferred physico-chemical stresses within the dataset showing an overall evolution from high energy, tidally influenced brackish water deposition to a low energy, wave influenced embayment setting. This study contributes to the well established brackish-water ichnological model and, in addition, helps establish the utility of the process ichnological methodology in the recognition of physico-chemical stresses in ancient environments.