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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 66 (2018), No. 1. (March), Pages 93-127

Palaeogeographic Setting, Lithostratigraphy, and Sedimentary Framework of the Lower Triassic Montney Formation of Western Alberta and Northeastern British Columbia

John-Paul Zonneveld, Thomas F. Moslow

Abstract

The subsurface Montney Formation records deposition through the Lower Triassic interval on the northwestern margin of the North American craton. Various evidence, including stratigraphic architecture, the presence of late Paleozoic and Mesozoic zircons and sediment geochemistry support the contention that the Montney is a product of deposition in a collisional retro-foreland basin setting.

The Montney is formally divided into eight regionally extensive members on the basis of lithology, mineralogy and well log character. Three of these, the Lower Montney Member, Middle Montney Member and Upper Montney Member are similar to informal units used by industry geoscientists. The boundaries of these units coincide with major stage boundaries (Dienerian-Smithian and Smithian-Spathian). Three new members are provided for carbonate-dominated units in the Montney Formation. The Pocketknife Member, formerly referred to as the Claraia zone), consists of bituminous, planar-laminated siltstone with abundant thin-shelled bivalves and thin bioclastic packstone beds. It occurs interbedded with the Lower Montney Member. The Anten Coquina Member (formerly the informal coquinal dolomite middle member) occurs in the eastern part of the Montney basin (near the subcrop limit) and consists of bioclastic grainstone dominated by fragmentary, disarticulated bivalves, gastropods and lingulide brachiopods that occurs coincident with the Dienerian-Smithian boundary. The Altares Member consists of interbeds of bioclastic packstone and grainstone with bituminous dolomitic siltstone and occurs interbedded with the upper part of the Middle Montney Member in the west-central part of the basin. Two sandstone-dominated members are also named. The Calais Sandstone Member occurs near the base of the Montney and consists of well-sorted cross-stratified fine-grained sandstone. The LaGlace Sandstone Member occurs near the base of the Middle Montney Member. Both sandstone members are of turbidite origin and occur primarily within the Peace River embayment (sensu stricto) area.

Dominated by subangular to subrounded quartz silt and a low overall proportion of clay and high proportion of detrital dolomite and feldspar, the Montney is compositionally and texturally unique in Western Canada. Although fine-grained siliciclastic sediment dominates, dolomite occurs throughout the Montney Formation and several regionally extensive bioclastic packstone and grainstone horizons occur. Montney deposition records a low-relief clastic ramp succession deposited in an arid coastal setting and includes units deposited in a variety of shallow marine and turbidite lobe / channel settings. The Montney’s unique mineralogical and textural composition is a function of both the demise of Palaeozoic carbonate-secreting organisms and deposition in an arid coastal setting fed by rare perennial, and abundant ephemeral, fluvial systems.


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