An allostratigraphic and paleogeographic framework for the Joli Fou and Pelican formations and contiguous strata (Late Albian, Early Cretaceous) in central Alberta

Abstract An allostratigraphic approach was used to investigate the stratigraphy of the Late Albian Joli Fou and Pelican formations across 77 000 km2 of east-central Alberta. Although the Pelican Formation is known to be broadly equivalent to the Viking Formation to the south, its internal stratigraphy and precise allostratigraphic relationship to the Viking and Paddy alloformations to the south and west have not been established. The Joli Fou alloformation is bounded below by transgressive surface JE0 and above by the basal surface VE0 of the Viking alloformation. Within the study area, the Joli Fou comprises marine mudstone that thins from approximately 20 m in the SE to a pinch-out in the NW where it onlaps against a NE-SW-trending topographic high dubbed the ‘Smoky River Ridge’. The Pelican alloformation comprises four regionally mappable, upward shoaling allomembers PeA to PeD, each bounded by a marine flooding surface. Collectively, allomembers PeA and PeB are bounded by Viking surfaces VE0 and VE1 and hence are temporally equivalent to Viking allomember VA. PeC and PeD are bounded by VE1 and VE3 and are equivalent to Viking VB. To the west, allomembers PeA and PeB merge laterally with the upper Paddy alloformation, but allomembers PeC and PeD toplap against VE3, with the margin of PeD offset to the SE relative to PeC. Pelican allomembers form sandier-upward successions, typically 5–10 m thick, and can show marked lateral changes in thickness. Where exposed on the Athabasca River, Pelican sandstones are dominated by dm-scale, uni- or bi-directional cross-bedding, with cross-sets capped by wave ripples and thick mudstone drapes; evidence for storm wave processes (e.g. hummocky and swaley cross-stratification) appears to be scarce. The successions are interpreted to represent river- and/or tide-dominated delta systems. Pelican sandstones are distinctive quartz arenites that collectively thicken to the NE, strongly suggesting provenance from the Canadian Shield. In the vicinity of Peace River town, the Paddy alloformation comprises chert-rich litharenites of Cordilleran provenance interstratified with quartz arenites. This observation implies that rivers from the Shield had constructed a delta system across the entire 400–500 km width of the Joli Fou Sea, in order to deliver sediment to the Paddy depocentre to the west of the Smoky River Ridge. Sandstone bodies in each Pelican allomember form south-facing lobes, interpreted to have formed on the south side of the delta complex where they were protected from storm waves from the north. In contrast, the north-facing margin of the Paddy depocentre in the west forms a linear strandplain, reflecting strong wave influence from the open sea to the north. The southern entrance to the Joli Fou Seaway, formed by a topographic ridge in Kansas, is known to have closed in late Joli Fou-Skull Creek time. Closure of the northern entrance by the Pelican delta system probably led to a slow decrease in salinity of the landlocked sea, and may explain the absence of fully marine macrofauna from the Viking, Bow Island, Muddy Sandstone and equivalent formations throughout the length of the Seaway.

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