Structural Evolution of the Firebag Basin and Stratigraphic Architecture of its Cretaceous Fill, Athabasca Oil Sands Region, Alberta, Canada. The Firebag Composite Pull-Apart/Karst Basin

Abstract

Located 60 km northeast of the city of Fort McMurray, Alberta, Canada, the Firebag Basin is host to bitumen saturated siliciclastics of the Aptian McMurray Formation. These deposits form a portion of Suncor Energy's resource at the Firebag Steam-Assisted Gravity Drainage (SAGD) Project. Although rooted in Precambrian basement rocks, the Firebag Basin is most prominently expressed at the sub-Cretaceous unconformity (SCU). Negative relief on this surface is upwards of 50m, and defines a nearly equidimensional rhombic basin with sharp margins. The overall surface area of the basin is upwards of 45 km², and its shape is reflected in all underlying geologic surfaces. Regional potential field data sets highlight a major 100 km long, NNW-SSE linear discontinuity transecting the Firebag SAGD Project that is interpreted to be a fault at the level of the Precambrian basement. Higher resolution aeromagnetic data coupled with 3D seismic suggest the fault is strike-slip in nature, locally segmented and contains both paired bend and bypass structures. The structural history of the Firebag Basin is subdivided into four distinct phases: 1- Paleoproterozoic (Taltson-Thelon orogeny), 2- Early-Middle Devonian (extension associated with uplift of the Peace River-Athabasca Arch and Antler orogeny), 3- Middle Jurassic to Early Cretaceous (Columbian orogeny), 4- Early Cretaceous (Columbian-early Laramide orogenies). Paleozoic compressional events are interpreted to have preferentially activated this regional strike-slip fault in a dextral sense, promoting both extensional and contractional regimes within the study area. The Firebag Basin formed in the extensional zone developed around the northern releasing bend. The corresponding contractional zone formed around the southern restraining bend is defined by basement uplift and erosion. Mesozoic basement fault activation is interpreted to have significantly accelerated and focused the episodic dissolution of Middle Devonian evaporite. The Firebag Basin is described here as a composite pull-apart/karst basin that owes its origin to sub-regionally unique extensional responses to regional compressional tectonics, and non-unique multi-phase evaporite dissolution-collapse. Part II of this study focuses on the stratigraphic architecture of the basin fill, and highlights a unique piece of sand-rich McMurray Formation stratigraphy (supra-lower McMurray, sub-middle McMurray) that forms the primary reservoir at the Firebag SAGD Project.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016