SIGNIFICANCE OF PALEOCOMMUNITY ANALYSIS FOR INTERPRETING THE ECOLOGY AND GEOLOGY OF THE DEVONIAN WATERWAYS FORMATION, NORTHEASTERN ALBERTA, CANADA (Invited Presentation)

Community paleoecology reveals factors that control ancient ecosystems, but also is applicable to other types of geological inquiry. Herein, we explore the communities in the Devonian Waterways Formation of northeastern Alberta, a structurally complex carbonate and shale unit that has an influence on the thickness distribution of overlying oilsand deposits and on regional fluid flow. We utilize paleocommunity data to reveal (a) the controls on spatial and stratigraphic distribution of fossil communities; (b) the use of paleocommunities in interpreting regressive phases; (c) the high-resolution stratigraphic correlation in a structurally complex area; and (d) the prediction of reservoir properties based on paleocommunity types.

Two predominantly limestone members (Calumet and Moberly) of the Waterways Formation form the regressive phases of two basin-wide sequences. Using the abundances of 22 genera from 20 bedding planes, we analyzed community patterns using Bray-Curtis and NMDS ordination. Both ordinations reveal two clusters: (a) diverse assemblages dominated by atrypides, especially Radiatrypa, and to a lesser extent, Schizophoria (most Calumet and higher Moberly beds); and (b) a moderately diverse assemblage characterized by Eleutherokomma and other small brachiopods, including productides (lowermost Moberly). One outlier sample contained abundant large Strophodonta and large Schizophoria in an assemblage of average richness and low evenness (lower Calumet). This paleocommunity outlier is similar to Strophodonta-rich faunas recovered in basinal argillaceous floatstones in core.

We reconstruct a shallowing-upward succession of (1) a paleoecosystem dominated by concavo-convex strophomenides through (2) one of moderate diversity, characterized by Eleutherokomma and culminating with (3) a rich assemblage containing abundant atrypides. Deeper water communities tend to be found in “tight” limestones; shallow water communities are more typical of porous limestones. These communities are traceable throughout the study area, and facilitate correlation of limestone beds in a zone of structural collapse and karst. In this study, paleocommunity analysis allows for a greater precision of stratigraphic correlation than through index fossils alone.