Technical Luncheons
Phanerozoic Structural Evolution of Eagle Plain, Yukon
Speaker:
Larry Lane,
Geological Survey of Canada
Date/Time: Tuesday, February 23, 2010 - 11:30am
Location: Telus Convention Centre - Calgary, Alberta
The cut-off date for ticket sales is 1:00 pm, Thursday, February 18, 2010.*
CSPG Member Ticket Price: $38.00 + GST.
NON-MEMBER Ticket PRICE: $45.00 + GST.
Each CSPG Technical Luncheon session is 1 APEGGA PDH Credit.
*Please note: Due to the popularity of talks, we strongly suggest purchasing tickets early, as we cannot guarantee seats will be available on the cut-off date.
ABSTRACT
As a northern Cordilleran "intermontane" basin, Eagle Plain (northern Yukon) was shaped by multiple tectonic events throughout its Phanerozoic history. This structural history is fundamental to our understanding of the basin's petroleum potential. Of 35 wells drilled in the basin, all but three were spudded between 1957 and 1978, most on large surface structures. Known oil and gas reserves are concentrated in the Chance and Birch Fields, in its southern part. In the past 20 years, major advances have been made in defining the basin's regional architecture and structural evolution, and their impact on the basin's petroleum prospectivity.
With the breakup of Rodinia in Late Neoproterozoic time, the Franklinian (Arctic) margin formed in the north and the paleo-Pacific margin formed in the south. Eagle Plain sits atop a continental promontory that was left behind at the junction of the two margins. This promontory remained subaerial until Early Cambrian time, when the Richardson Trough, a north-facing rift basin commonly identified as an aulacogen, was initiated, separating Eagle Plain from the Mackenzie Platform to the east. Richardson Trough, having developed as a fundamental crustal scale rift structure in the early Paleozoic, would be reactivated periodically throughout Phanerozoic time.
Ellesmerian tectonism encroached southward into the region in the Late Devonian and Early Carboniferous, shedding clastic debris southward and south-westward across Eagle Plain and depositing some two to four kilometres of potential source rock. As Ellesmerian detached folding progressed southward into Eagle Plain, shale and sandstone of the Imperial Formation were deformed into generally east-trending folds. These structures represent an untested petroleum play.
The tectonic record for Eagle Plain in the late Paleozoic and early Mesozoic is poorly defined locally. Regionally, collision of continental fragments and magmatic arcs on the paleo-Pacific margin initiated early phases of Cordilleran orogenesis, culminating in the collapse of the Selwyn Basin into fold and thrust belts, followed by emplacement of mid-Cretaceous granitic plutons that plug regional structures. These southern ranges (Ogilvie and Wernecke mountains) shed clastic debris northward across the area through Late Cretaceous time, comprising sand and shale of the Eagle Plain Group, accumulating up to two kilometres of strata deposited unconformably across Jurassic to Early Cretaceous rocks.
To the north, initial rifting of the nascent Canada Basin (Arctic Ocean) was underway by the Middle Jurassic. In northern Yukon, rifting culminated in Albian time with the development and infill of massive fault-bounded graben systems such as Kugmallit and Blow troughs. Less well preserved are the coeval Sharp Mountain and Kandik basins. These basins were probably kinematically and possibly physically linked. Several grabens are imaged seismically in the northern part of Eagle Plain, and probably date from the early stages of rifting. Some grabens locally preserve potential reservoir rocks of unknown age beneath local unconformities.
Tertiary development of the northern Yukon fold complex and adjacent north-eastern Brooks Range shaped the present Eagle Plain basin and produced broad north-trending folds, detached on décollements in the Proterozoic succession. In the western side of the basin, deformation is more intense and the structures are predominantly thrust faults. Most of the early wells were drilled on Tertiary anticlines, and the Chance field lies in the hanging wall of a small thrust fault. Tertiary folds and thrust faults have thickened both the late Paleozoic succession (locally four kilometres thick) as well as the Cretaceous succession up to two kilometres thick, providing mechanisms for local burial of source rocks as well as trap formation. Tertiary triangle zones marginal to the basin remain untested for hydrocarbon resources.
BIOGRAPHY
Larry Lane is a Research Scientist with the Geological Survey of Canada and leader of the Yukon Basins Project, in the Geo-Mapping for Energy and Minerals (GEM) Program. Lane is a structural geologist with over thirty years' experience in bedrock mapping, and structural and tectonic synthesis in the Canadian Cordillera, northern Yukon, Beaufort-Mackenzie Basin and circum-Arctic region. Since joining the GSC in 1986 he has also led major projects under the Frontier Geoscience Program and NATMAP.
