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Facies and Facies Architecture of Allomembers D and E, Upper Cretaceous Horseshoe Canyon Formation, Drumheller, Alberta, Canada

Montgomery, Adam; Dashtgard, Shahin E.; MacEachern, James A.; Ainsworth, Bruce; Ricci, Liam

Extensive outcrop exposures of the lower Horseshoe Canyon Fm near Drumheller, Alberta provide an excellent opportunity to study facies variability in a mixed-influence marginal-marine system, with the aim to improve our understanding of reservoir architecture. In the study area, continuous outcrops extend for 15 km in the paleo-depositional-dip direction (NW-SE) and 3.5 km parallel to paleo-depositional strike (SW-NE). High-resolution sedimentological and ichnological data from 30 sections through allomembers D and E (T-R sequences) are integrated with data from 4 cored wells and 75 wireline logs. Facies are characterized and interpreted on the basis of the relative proportions of the depositional processes (i.e., fluvial, wave, and tidal) responsible for their deposition.

Allomember D contains three discrete Element Complexes (EC). EC-D1 comprises a 1-6 m thick fining-upward succession, interpreted as a Tf-Tidal Flat EC. Sandstones in EC-D1 are current rippled and trough-cross bedded and are commonly draped by rhythmic laminae of mudstone and carbonaceous material. The rhythmic mud laminae are considered evidence of tidal deposition. Bioturbation intensities range from BI 0-1, probably due to stresses imposed by freshwater (fluvial) and high sedimentation rates (fluvial and tidal). EC-D2 is dominated by carbonaceous-rich, mud-dominated heterolithic facies that accumulated within a >6 m deep Tf-Channel EC. Marine palynomorphs present within EC-D2 indicate that saltwater was present in the channel during deposition. EC-D3 constitutes sediment deposited in a 5.5 m deep, Ft-Channel EC that is filled mainly with trough cross-bedded sandstones with mudstone drapes.

Allomember E comprises three ECs. EC-E1 depicts a coarsening-upward Wt-Beach EC with hummocky cross-stratified, trough cross-bedded, plane-bedded sandstones and common mudstone drapes. BI values range from 0-4, with a trace fossil suite is consistent with the Skolithos Ichnofacies. EC-E2 forms a 1-4.5 m thick fining-upward succession of sandstones and mudstones, interpreted as a Tfw-Tidal Flat EC broadly similar to that of EC-D1. EC-E3 comprises a 6.5 m deep Ft-Channel EC filled with inclined heterolithic stratification (IHS). BI values range from 0-1, containing trace fossils consistent with the brackish-water ichnological model. The presence of both IHS and a brackish-water trace-fossil suite is evidence of both tidal and fluvial influence, consistent with an estuarine channel interpretation.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013