--> Abstract: Tectonic and Eustatic Controls on Deposition of the Harmon, Cadotte and Paddy Members of the Albian Peace River Formation, Alberta and British Columbia, Canada, by Robin A. Buckley and Guy Plint; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Tectonic and Eustatic Controls on Deposition of the Harmon, Cadotte and Paddy Members of the Albian Peace River Formation, Alberta and British Columbia, Canada

Robin A. Buckley1; Guy Plint1

(1) Earth Sciences, University of Western Ontario, London, ON, Canada.

The Middle to Upper Albian Peace River Formation was deposited in the Western Canada Foreland Basin and consists of three members: the Harmon Member is a broadly transgressive marine mudstone that is overlain by broadly regressive shoreface sandstones of the Cadotte Member. Sandstones of the Cadotte are capped by a subaerial unconformity that defines the base of the Paddy Member. This regional study is based on detailed correlation of 17 allomembers using over 800 geophysical well logs, 15 outcrop sections and 21 cores covering an area of over 38,000 km2.

Changing patterns and rates of flexural subsidence during deposition of the Peace River Formation are indicated by progressive changes in stratal geometry within depocentres, and by spatial changes in depocentre location and orientation. Flexural subsidence during deposition of the Harmon Member resulted in a wedge-shaped body of rock that thins over 250 km from 108 m in the foredeep to 2 m near the forebulge. In contrast, the Cadotte Member has an almost tabular geometry that thins from 58 to 13 m across the basin, and was deposited during a phase of minimal differential subsidence, possibly related to limited thrust activity, and/or erosional unloading in the adjacent sector of the fold and thrust belt. Lower Paddy allomembers are wedge-shaped and imply deposition during a time of more rapid flexural subsidence; in contrast, upper Paddy allomembers are much more tabular, suggesting deposition during another phase of relative tectonic quiescence.

High frequency (~100 ky) sea-level fluctuations, indicated by regionally-mappable flooding surfaces, provided accommodation for a succession of at least three stacked, progradational shoreface sandstones within the Cadotte Member. These sea-level changes, probably attributable to eustasy, also resulted in stacked shallow marine and lagoonal sequences in the Paddy Member.

The Cadotte and most of the Paddy are composed of chert-rich lithic arenite of Cordilleran provenance. In the eastern part of the basin however, parts of the Paddy consist of essentially chert-free quartz arenite, typically comprising very well-rounded quartz sand. It seems likely that the quartz arenites were derived from erosion of Lower Cretaceous strata in eastern Alberta, that ultimately were of cratonic provenance. Erosion in the east may indicate forebulge uplift, dynamically linked to a phase of flexural subsidence in the west that generated accommodation for the entire Paddy wedge.