--> Abstract: An Integrated Ichnological-Sedimentological Model for a Mixed Wave- and River-Influenced Asymmetric Delta Lobe, Upper Cretaceous Basal Belly River Formation, Central Alberta, by Cindy D. Hansen and James A. MacEachern; #90078 (2008)

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An Integrated Ichnological-Sedimentological Model for a Mixed Wave- and River-Influenced Asymmetric Delta Lobe, Upper Cretaceous Basal Belly River Formation, Central Alberta

Cindy D. Hansen and James A. MacEachern
Earth Sciences, Simon Fraser University, Burnaby, BC, Canada

Cycle G of the Campanian Belly River Formation is differentiated into two mappable facies associations (FA1 and FA2). FA1 forms uniformly coarsening-upward successions with abundant wave- and storm-generated sedimentary structures, subordinate syneresis cracks, convolute bedding, and claystone drapes. Trace fossils are sporadically distributed in low- to moderate-abundance and moderate-diversity suites, recording stressed expressions of the Cruziana Ichnofacies. FA2 comprises coarsening-upwards successions with pronounced facies variability. Facies are highly heterolithic, with abundant current-generated sedimentary structures, normally graded beds, structureless siltstones, claystone drapes, convolute bedding, and syneresis cracks. Some event beds record hyperpycnal emplacement. FA2 also includes distributary channel/mouth-bar complexes. FA2 yields sporadically distributed, low-intensity bioturbation, and very low- to moderate-diversity trace fossil suites. Dominant ichnogenera correspond to strongly facies-crossing deposit-feeding structures, attributable to highly stressed expressions of the Cruziana Ichnofacies.

FA1 and FA2 are interpreted to record distal prodelta through proximal delta-front deposits, representing the progradation of a mixed river-, wave- and storm-influenced delta lobe. The spatial distributions of FA1 and FA2 delineate a predictable along-strike variation in facies character. FA1 records conditions consistent with positions lying updrift of distributary channel discharge. FA2, in contrast, records conditions reflecting positions downdrift of active distributaries and a more fluvially dominated character. The integration of ichnological and sedimentological facies characteristics, coupled with the spatial distribution of the facies associations demonstrates that this cycle of the Belly River Formation corresponds to an asymmetric delta.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas