Correlation of physical surfaces, bentonites, and biozones in the Cretaceous Colorado Group from the Alberta Foothills to southwest Saskatchewan, and a revision of the Belle Fourche - Second White Specks formational boundary

Abstract

New allostratigraphic correlations in west-central Alberta show that flooding surfaces in the Sunkay and basal Vimy members of the Blackstone Formation can be traced eastward from Burnt Timber Creek for >500 km to western Saskatchewan, and for 350 km northward into the Dunvegan and Kaskapau formations. At Burnt Timber Creek, a Miliammina manitobensis microfauna in the lowest 1 m of the Sunkay Member indicates equivalence to the Westgate Formation, and an overlying 70 cm conglomerate is correlative with the Fish Scales Formation. Overlying mudstones contain foraminifera of the Verneuilinoides perplexus Zone, indicative of the middle Cenomanian Belle Fourche Formation. The base of the Second White Specks Formation, as currently defined in core in eastern Alberta, equates in outcrop with the lower part of the Sunkay, rather than the base of the Vimy Member as previously thought. The base of the Second White Specks Formation should be placed about 35 m higher in the stratotype core. A bentonite located 9.3 m above the base of the Sunkay Member at Burnt Timber Creek lies near the highest occurrence of Evolutinella sp. aff. E. apricarius, indicating proximity to the "X" bentonite, recognized across the prairies and traceable north into allomember C of the Dunvegan alloformation. A thick bentonite 93.2 m above the base of the Burnt Timber Creek section lies 4 m above the base of the Vimy Member; this bentonite, traceable from northern British Columbia to New Mexico, lies a few metres below the Cenomanian–Turonian boundary and is here formally named the Bighorn River Bentonite.

Migration and stratigraphic fill of an underfilled foreland basin: Middle–Late Cenomanian Belle Fourche Formation in southern Alberta, Canada

“…3,4). Allomember A and allomembers B-E can be correlated with the Middle Cenomanian lower Belle Fourche Formation and Late Cenomanian upper Belle Fourche Formation in central Alberta, respectively (Tyagi et al, 2007). It was suggested that the Middle Cenomanian Dunvegan Formation in northwestern Alberta was deposited in the foredeep zone (Plint, 2000;Plint et al, 2001) and Allomember A (lower Belle Fourche Formation) in southern Alberta in the forebulge and backbulge zones (Yang and Miall, 2009) (Figs.…”

“…Rice (1984) interpreted that the sandstones were transported by waves and geostrophic currents from the Middle Cenomanian Dunvegan delta in northwestern Alberta and deposited over an ancestral tectonic paleo-high. However, no time-equivalent lower and upper Belle Fourche sandstones have been documented in central Alberta, and the Late Cenomanian upper Belle Fourche Formation and the Middle Cenomanian Dunvegan Formation are not contemporaneous strata (Tyagi et al, 2007) (Fig. 3).…”

“…The middle and late Cenomanian Belle Fourche Formation consists mainly of shale and siltstone in the subsurface of southern and central Alberta (Leckie et al, 2000;Tyagi et al, 2007;Yang and Miall, 2009). In the southern Alberta Foothills, the middle and late Cenomanian strata contain offshore marine shale interbedded with siltstone and fine-grained sandstone (Stott, 1963;Leckie et al, 2000).…”

“…Nomenclature in northeastern British Columbia and northwestern Alberta are based onPlint (2000). Nomenclature in southern Alberta are based onBloch et al (1993),Tyagi et al (2007).…”

Biostratigraphy and Inoceramus survival across the Cenomanian–Turonian (Cretaceous) boundary in the Ram River section, Alberta, Canada

“…The Sunkay Member contains abundant diffuse pyrite and weathers a rusty orange, with white sulphate efflorescence. A few bentonite beds are present in the succession, the most prominent of which is the Bighorn River Bentonite (Tyagi et al 2007), which at the Ram River is about 30 cm thick. This bentonite has been traced from Alberta to New Mexico (Stott 1963(Stott , 1967Elder 1988;Tyagi et al 2007), and was dated to 94.29± 0.13 Ma by Barker et al (2011) using the U/Pb method on single zircon crystals.…”