Tectonic and eustatic controls on the allostratigraphy and depositional environments of the Lower Colorado Group (Upper Albian) central foothills and adjacent plains of Alberta, Western Canada foreland basin

The Lower Colorado allogroup of the Western Canada foreland basin is a mudstone-dominated unit that consists of marine, estuarine and coastal plain rocks deposited during two Late Albian transgressions and the intervening regression of the Western Interior Seaway. In the subsurface of west-central Alberta, the Lower Colorado allogroup has an overall tabular geometry with a mean thickness of 80 m, and connects two Upper Albian depocenters located directly adjacent to the northern and southern segments of the Canadian Cordillera. Late Albian relative sea-level oscillations generated discontinuities of regional and local extent that allow the division of the allogroup into the Joli Fou, Viking, Westgate, and Fish Scales alloformations and their component allomembers. Correlation of regional discontinuities using well-log, core and outcrop data has shown that the Lower Colorado allogroup is equivalent to the uppermost strata of the Paddy Member and most of the overlying Shaftesbury Formation in the North, as well as the uppermost rocks of the Mountain Park Member of the Gates Formation in the central Foothills.; The establishment of a regional chronostratigraphic framework has allowed the reconstruction of paleogeographic evolution, and the interpretation of allogenic controls on accommodation patterns in space and time. The early Late Albian transgression of the Skull Creek Sea, which represented the inception of the Western Interior Seaway as the Tethian and Boreal oceans connected, was mainly eustatically-driven. Middle Late Albian regression ensued with the southward progradation of shallow marine depositional systems supplied from the North. Eustatic fall coupled with tectonic tilting to the East contributed to the subsequent incision of a widespread system of paleovalleys. Renewed transgression from the North in late Late Albian was largely tectonically-induced, with flexure leading to the encroachment of the Mowry Sea. Simultaneously, the source area shifted to the South, from which direction a limited volume of coarse sediment was supplied. Southward transgression was enhanced by gradual eustatic rise, although pulses of flexure continued in the North. Connection of the northern and southern marine embayments reestablished the Western Interior Seaway and led to salinity stratification, triggering a widespread event of bottom-water anoxia near the end of the Albian.; Keywords: Lower Colorado Group, Viking Formation, Allostratigraphy, Tectonics and eustasy, Western Canada foreland basin...