--> Abstract: Shelf and Shoreline Clastic Reservoirs of the Triassic Halfway-Doig Formation, Western Canada Sedimentary Basin, by T. F. Moslow, J. Wittenberg, A. Willis, M. Caplan, and H. D. Munroe; #91012 (1992).

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ABSTRACT: Shelf and Shoreline Clastic Reservoirs of the Triassic Halfway-Doig Formation, Western Canada Sedimentary Basin

MOSLOW, THOMAS F., J. WITTENBERG, A. WILLIS, and M. CAPLAN, University of Alberta, Edmonton, Alberta, Canada, and H. D. MUNROE, IGC, Ltd., Calgary, Alberta, Canada

Siliciclastic and bioclastic sandstone facies of the mid-to-late Triassic (Ladinian-Carnian) Halfway-Doig Formation comprise a parasequence set deposited in highstand and transgressive systems tracts as a product of cyclic shallow marine sedimentation in a continental margin setting. The main reservoir facies are concentrated along north-south-oriented shoreline and shelf margin trends that extend approximately 300 km from central Alberta to northeastern British Columbia. The commonly proposed regional unconformity between the Halfway and Doig formations is not recognized. However, numerous subregional disconformities can be attributed to truncation from lateral tidal inlet migration, shoreface ravinement, and/or marine flooding surfaces.

The barrier island depositional system in the Halfway interval is characterized by coarsening-upward sequences of lower through upper shoreface facies that are discontinuous along the paleostrandline owing to truncation and reworking from the lateral migration of tidal inlets. Inlet fill sequences fine upwards, are comprised of either bioclastic sandstone or sublitharenite, and are the facies of greatest reservoir quality. Variations in the sand body geometry, vertical stacking, and sedimentary characteristics of inlet fill sequences have provided for the recognition of relative changes in paleo wave energy and tidal range from north to south in the study area. Backbarrier facies include washover fan and flood-tidal delta sandstones that thin or pinch out updip and are significant str tigraphic traps. Dolomitic shales and evaporites, deposited in hypersaline lagoons, are common hydrocarbon seals.

Siliciclastic facies of the Doig interval were deposited in a continental shelf environment subject to sea floor instability, mass wasting, and sediment gravity flows. Reservoir sandstones are up to 30 m thick and form strike-linear trends extending for tens of kilometers, interpreted to define the paleo shelf-margin. Predominant sedimentary characteristics include oversteepened bedding, soft sediment deformation, and a severely restricted trace fossil assemblage within finely laminated, normally graded beds. The differential compaction of Doig sandstones and shales has influenced the orientation and distribution of younger (Halfway) tidal inlet-fill sequences.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)