Coeval deposition of transgressive and normal regressive stratal packages in a structurally controlled area of the Viking Formation, central Alberta, Canada

Abstract

Variability in accommodation and sedimentation rates within a basin generates significant deviations in the along‐strike stratal stacking patterns of systems tracts. This variability can lead to coeval depositional units that record the juxtaposition of transgressive (retrogradational) and regressive (progradational) stratal stacking patterns. In scenarios where transgressive and regressive units are deposited concurrently, challenges arise when attempting to correlate and place systems tracts into a sequence stratigraphic framework. In these scenarios, the maximum flooding surface records a high level of diachroneity, with the position of the surface variable throughout the stratigraphic column. In this study, Viking Formation (late Albian) deposits in the Western Canada Sedimentary Basin, central Alberta, Canada, preserve significant along‐strike variability of palaeoshorelines that developed in response to autogenic processes as well as allogenic controls that were active during deposition. Specifically, structural reactivation of Precambrian basement structures during Viking deposition led to significant variability in depositional environments along the palaeoshoreline. The incremental basement reactivation of the Precambrian Snowbird Tectonic Zone influenced sedimentation patterns and the creation of anomalous zones of accommodation in localized areas of the basin. Across fault boundaries and within the anomalously thick strata, both progradational and retrogradational stacking patterns occur within broadly contemporaneous deposits, complicating the correlation of stratigraphic units. While the concomitant deposition of transgressive and regressive units has been documented in a number of modern marine analogues, the concept is rarely applied to ancient successions. By identifying along‐strike variabilities in shoreline geometries and incorporating the autogenic and allogenic controls that were active during deposition, a more accurate sequence stratigraphic framework can be proposed.

Benthic Foraminiferal Morphogroups and Trace Fossils From Albian Shallow-Marine Mudstone Facies of the Viking Formation, Western Interior Seaway, Canada

“…Owing to its economic significance as a hydrocarbon-bearing interval and the abundance of available cores for analysis, the Viking Formation has been studied extensively over the last 60 years and has become a natural laboratory for evaluating sequence stratigraphy, sedimentology, depositional processes, and trace fossil analysis. Several classic trace fossil publications (e.g., MacEachern and Pemberton 1994; MacEachern et al 1998, 1999a; Dafoe et al 2010) and numerous pertinent sedimentological papers (e.g., Boreen and Walker 1991; Pattison 1991; Pattison and Walker 1994, 1998; Walker and Wiseman 1995; Burton and Walker 1999; Schultz et al 2019, 2020) have characterized a wide range of paralic depositional environments associated with the Viking sandstone, mudstone, and shale facies.…”