--> Abstract: Along-Strike Facies Variations in a Mixed Wave- and River-Influenced Delta Lobe, Upper Cretaceous Basal Belly River Formation, Ferrybank and Eastern Pembina Fields, Central Alberta, by Cindy D. Hansen; #90039 (2005)

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Along-Strike Facies Variations in a Mixed Wave- and River-Influenced Delta Lobe, Upper Cretaceous Basal Belly River Formation, Ferrybank and Eastern Pembina Fields, Central Alberta

Cindy D. Hansen
Simon Fraser University, Burnaby, BC

The early to mid-Campanian Basal Belly River Formation of central Alberta reflects a mixed wave- and river-influenced delta lobe with strong storm overprinting. Prodelta deposits consist of mud-dominated heterolithic successions characterized by a low abundance yet moderately diverse trace fossil suite attributable to a "stressed" expression of the Cruziana ichnofacies. Thin tempestites and rare sediment-gravity flow event beds display top-downward bioturbation with bioturbation index (BI) values of 1-3. Proximal prodelta to distal delta front intervals comprise interbedded sandy siltstones and very fine- to fine-grained sandstones exhibiting convolute bedding that are weakly and sporadically burrowed (BI 0-2). Distal delta front deposits coarsen upwards into fine- to medium-grained sandstones of the proximal delta front. High-energy conditions, coupled with strong storm influences, resulted in erosional amalgamation of tempestites, and led to sporadic distribution of ichnogenera. Proximal delta front intervals are weakly bioturbated (BI 0-2). Suites are characterized by low abundances and low to moderate diversities of predominantly deposit-feeding structures that reflect a "stressed" expression of the mixed Skolithos-Cruziana ichnofacies.

Preliminary analysis of more than fifty cored wells from the Ferrybank and eastern Pembina fields reveal prodelta and delta front deposits that vary markedly along depositional strike. Continued research seeks to delineate delta lobe asymmetry and concomitant along-strike facies variations, both attributable to longshore drift and deflection of river-induced stresses downdrift of distributary channel mouths. Trace fossil diversities, abundances, and ethological preferences are exceedingly sensitive to fluvial influences and thus, their mapped distributions may serve as a predictive tool for determining distributary channel proximity.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005