Palynostratigraphy, lithostratigraphy and thermal maturity of the Lower Triassic Toad and Grayling, and Montney formations of western Canada, and comparisons with coeval rocks of the Sverdrup Basin, Nunavut

Abstract

In western Canada samples obtained from outcrops of the Lower Triassic Toad and Grayling formations and core samples from coeval subsurface sections of the Montney Formation contain well-preserved palynofloras. These are generally dominated by taeniate bisaccate (e.g. Lunatisporites noviaulensis) and polyplicate gymnosperm pollen (e.g. Ephedripites steevesiae). Acanthomorph acritarchs (e.g. Filisphaeridium sp. cf. F. deunffii, Micrhystridium breve, M. setasessitante, Wilsonastrum colonicum) are often common to abundant. In addition, the stratigraphically and environmentally significant alga(?) Chordecystia chalasta occurs. These western Canadian Lower Triassic assemblages correlate with the Griesbachian Chordecystia chalasta-Striatoabieites richteri Assemblage Zone of the Sverdrup Basin, Canadian Arctic Archipelago, Nunavut.The environment of deposition, based on the abundance of pollen and spores and common occurrence of acanthomorph acritarchs, is near-shore marine. At a few horizons in the Montney Formation acritarchs are dominant, and this may indicate deeper water facies. Trace fossils in core and outcrop, lithofacies and sedimentary structures indicate fully marine, proximal offshore to lower and upper shoreface settings. The paleoclimate at the site of plant growth, based on the dominance of taeniate bisaccate pollen and polyplicate pollen, was probably arid.The Lower Triassic samples commonly include reworked Middle and Upper Devonian spores and less common Lower Carboniferous spores, demonstrating that significant erosion of Paleozoic rocks took place in early Triassic time in this area; recognition of such erosional events is relevant to sequence stratigraphic reconstructions.The thermal maturity of the in situ organic matter in the study areas is generally low (close to the threshold or within the "oil window"). This, along with the abundant amorphous and common exinous material, suggests a potential for the generation of liquid hydrocarbons. At one locality in southeast Yukon within the deformation belt the thermal maturity is high, suggesting some potential for dry gas generation. Reworked material generally has a slightly higher maturity, a fact that should be taken into consideration when assessing other thermal maturity indicators such as vitrinite reflectance. RÉSUMÉDans l'ouest du Canada, des échantillons provenant des affleurements des formations du Grayling d'âge du Triasique inférieur, ainsi que des échantillons de carottes provenant de sections contemporaines du sous-sol de la Formation de Montney, contiennent des palynoflores en bon état de conservation. Ils sont généralement dominés par des taénites bisaques (ex. Lunatisporites noviaulensis) et des pollens de polyplicates gymnospermes (ex. Ephedripites steevesiae). Des acritarches acanthomorphes (ex. Filisphaeridium sp. cf. F. deunffii, Micrhystridium breve, M. setasessitante, Wilsonastrum

Anomalously diverse Early Triassic ichnofossil assemblages in northwest Pangea: A case for a shallow-marine habitable zone

“…Induan (Griesbachian-Dienerian) sedimentary successions range from ~100 m in Alberta to >450 m in the Canadian arctic. Conodonts (see GSA Data Repository Table DR1 1 ) provide biostratigraphic control for the studied stratigraphic sections (Henderson, 1997;Henderson and Baud, 1997;Beatty et al, 2006;Hays et al, 2007) and palynological data supplement these results (Utting et al, 2005).…”

Provenance of North American Triassic strata from west-central and southeastern Yukon: correlations with coeval strata in the Western Canada Sedimentary Basin and Canadian Arctic Islands

“…2; L. Lane, personal communication, 2009). Utting et al (2005) concluded Toad Formation strata in an adjacent map area contain Griesbachian (early Induan) palynomorphs. Preliminary palynomorph collections from this section suggest it may be as old as Middle Permian (L. Lane and J. Utting, personal communication, 2009).…”

Classification and characteristics of tight oil plays

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