Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Geology

Supervisor

Dr. A. Guy Plint

Abstract

Strata of the Late Albian Lower Colorado Group are widely distributed in subsurface and outcrop in the Western Canada Foreland Basin. The rocks represent depositional environments ranging from alluvial to offshore marine. The Lower Colorado Group comprises, in ascending stratigraphic order, the Joli Fou, Viking, Westgate, and Fish Scales formations. Mudrocks of the Joli Fou Formation record a time when the interior of North America was flooded by a shallow sea that led to the connection of the Polar Ocean and the Gulf of Mexico. Ensuing sea-level fall and regression led to deposition of Viking Formation sandstone across much of the basin. This regression was terminated by a flooding event leading represented in the rock record by Westgate Formation mudstones. The Joli Fou and Viking alloformations were correlated throughout a study area of 56,000 km2 in south central Alberta and adjacent Saskatchewan using 1626 well logs and 118 cores. The Joli Fou alloformation is equivalent to the Lower Paddy alloformation, the latter recording active subsidence in NW Alberta, whereas in the study area, the Joli Fou is relatively sheet-like. Sediments deposited during early to mid-Viking time are also approximately sheet-like, reflecting little to no regional flexural subsidence. Minor thickening to the SW probably reflects the development of local deltaic depocentres. During mid-Viking time, subtle uplift and erosion in NW Alberta and adjacent British Columbia led to the deposition of lowstand shorefaces, some of which are oil and gas rich. These sandstone bodies are sharp-based, onlap towards the south, and are concentrated along a NW-SE trending hinge-line. During late Viking time, stacked and shingled deltaic sandstones, up to 40 m thick, prograded from the south and SW, and onlapped north-eastward onto the flexural hinge. The hinge is inferred to overlie a deep-seated fault that underwent episodic reactivation, possibly related to activity in the orogen. Sandstone distribution maps show dramatic shifts in the locus of sediment delivery, possibly related to tectonic reorganization of river systems. Regional stratal geometry and U/Pb zircon dating from bentonites show that transgressiveregressive events in the Joli Fou and Viking alloformations took place on a 104-105 yr timescale and were possibly influenced by eustatic cycles attributable to the growth and decay of small Antarctic ice sheets modulated by Milankovitch cyclicity.

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