Stratigraphy, maturation and source rock potential of cretaceous strata in the Chilcotin-Nechako region of British Columbia

The Chilcotin-Nechako region lies within the Intermontane Belt of British Columbia on the western edge of Stikinia and includes the Tyaughton Basin. Exposed within the region are Early Albian to Cenomanian sediments of the Skeena, Taylor Creek, Jackass Mountain and Battlement Ridge groups plus unnamed sediments of similar age and lithology. These sediments were deposited in one large, initially marine, basin (Nazko Basin) and are separated from older sediments by a major hiatus (Barremian to Aptian in the south and Berriasian to Valanginian in the north). Marine conditions persisted in the northern Chilcotin-Nechako region until at least Cenomanian time, and until the Maastrichtian in the central Chilcotin-Nechako region. In southern Chilcotin-Nechako region, marine conditions ceased in mid Albian time with the deposition of the Silverquick formation. Latest Albian - Cenomanian time marks the transition from a dominantly sedimentary to volcanic province. Volcanism was widespread throughout the Chilcotin-Nechako region until at least the Santonian (Kasalka and upper Kingsvale groups, Powell Creek formation, unnamed volcanics and possibly the Brian Boni Formation). In Central Chilcotin-Nechako region volcanism was succeeded by marine sedimentation in the Santonian which continued until Maastrichtian time, indicating marine conditions persisted on the mainland of British Columbia well beyond the previously documented Albian limit. Sediments in the Nazko Basin were sourced from the Omineca Belt and the Cache Creek Terrane to the east and the Insular Terrane to the west. In the southern region detritus was also provided by the Bridge River Terrane. New data from this study indicate mid to Late Cretaceous sediments within the Chilcotin-Nechako region are zeolite facies. This low grade of metamorphism isprobably due to comparatively low heat flow in the Chilcotin-Nechako region. When compared to equivalent strata exposed to the north, sediments within the Nazko Basin have markedly lower maturation values even though they have experienced the same amount of burial. Sediments with zeolite grade metamorphism have the potential to lie within the oil window and thus may contain significant hydrocarbon reserves. However, Rock-Eval pyrolysis and TOC analyses of outcrop and well samples indicate the overall hydrocarbon potential of the Chilcotin-Nechako region is low.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat