The Application of High-Resolution Chemostratigraphy to Differentiate between Low Accommodation Incised Valley Systems in a Foreland Basin Setting: The Lower Cretaceous Basal Colorado and Basal Quartz of the Western Canadian Sedimentary Basin

Amelia Wright¹, Brian Zaitlin², and Ken Ratcliffe^3
1 Chemostrat Inc, Houston, TX
² Suncor Energy Inc, Calgary, Cape Verde
³ Chemostrat Ltd, Llanfyllin, United Kingdom

The Lower Cretaceous Basal Quartz (BQ) and Basal Colorado (BCS) sequences are prolific hydrocarbon producers within the Western Canadian Sedimentary Basin. Due to the low accommodation and predominantly fluvial nature of these incised valley system (IVS) deposits, traditional stratigraphic characterization and correlation of the reservoir sequences is problematic. Whole rock geochemistry is used here to characterize between: 1) the IVS fill sequences of the BQ and BCS; 2) between internal units of the BQ IVS (Horsefly, BAT and Ellerslie); and 3) between BCS and Upper Mannville deposits.

The Basal Quartz system is chemically differentiated from the BCS system by changing Na/K and Cs/Al values within silty-claystone lithologies, indicating that the two depositional systems were sourced from different provenances, and deposited under differing palaeoclimate conditions.

Within the BQ three lithostratigraphic units are identified, and are differentiated by changes in clay mineralogy, heavy mineralogy, feldspar contents and the degree of volcanogenic input, all of which can be geochemically modeled. The component units of the BCS are differentiated by changes in Ti/Nb and K/Na ratio values that indicate the Lower Basal Colorado and Upper Basal Colorado IVS sandstones were derived from different provenances.

With the greater understanding of the component units of the IVS sequences afforded by combining chemostratigraphy with heavy mineral analysis, it is possible the better to explore for and exploit these types of reservoirs.