Facies Architecture and Sequence Stratigraphy of the Lower and Middle Triassic of Western Canada Sedimentary Basin

Abstract

The Lower and Middle Triassic of Western Canada consist of the Montney, Sunset Prairie, Doig and Halfway Formations. Historically, these intervals have been considered to represent three major transgressive-regressive third- or fourth- order cycles (Edwards et al., 1994, Davies, 1997). More recently, four third-order sequence stratigraphic sequences have been interpreted within the Lower and Middle Triassic (Crombez et al., 2016). However, these models do not incorporate the newly identified Sunset Prairie Formation (Anisian, Middle Triassic) (Furlong et al., in press). A reevaluation of the Triassic sequence stratigraphic framework is needed to include the formation into a large-scale basin evolution model.

The Sunset Prairie Formation is an unconformity bound interval restricted to the western-most portion of the Peace River Embayment. Through the analysis of 5 core within the Fort St John Graben System, the thickest portion of the Sunset Prairie Formation can be evaluated for sedimentological and ichnological characteristics. From this facies analysis, a stratigraphic architecture and sequence stratigraphic framework can be formulated between wells. Seven facies are present within the formation and are interpreted to represent offshore, offshore transition and lower shoreface facies associations. Facies stacking and well log signatures depict at least three progradational parasequence sets present in the western-most wells.

The base and top contacts of the Sunset Prairie Formation are marked by a Glossifungites demarcated discontinuity surface (burrowed firmground) and/or thinly bedded conglomerate (lag deposit). Both represent major sequence stratigraphic surface, with the unit being bound by a sequence boundary at the base and a maximum regressive surface at the top. Overall, the Sunset Prairie Formation preserves deposits that were deposited within a lowstand system tract, with highstand system tract deposits of the Upper Montney below and transgressive system tract deposits of the Doig phosphate zone above. Investigating the Upper Montney, Sunset Prairie and Doig phosphate zone demonstrates the stratigraphic response of proximal and distal marine depositional environments along a Triassic ramp margin.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018