Geology and assessment of undiscovered oil and gas resources of the Franklinian Shelf Province, Arctic Canada and North Greenland, 2008

Abstract

In 2008, the U.S. Geological Survey assessed the potential for undiscovered oil and gas resources of the Franklinian Shelf Province of northern Canada and Greenland as part of the U.S. Geological Survey Circum-Arctic Resource Appraisal Program. The Franklinian Shelf Province lies along the northernmost edge of the North American craton in Greenland and Canada. It encompasses a Cambrian through Middle Devonian passive margin sequence deposited on the margin of an ocean formed by rifting and seafloor spreading that began in latest Precambrian time and continued into Ordovician time. In the Canadian part of the province, the passive margin sequence is overlain by a thick succession of Devonian clastic strata shed from uplifts produced by the Caledonian collision between Laurentia and Baltica that closed Iapetus Ocean. The late Silurian to Early Devonian Boothia-Cornwallis uplifts within the region, apparently a distal effect of earlier phases of the Caledonian collision, were local sources of clastic wedges within the predominantly carbonate shelf sequence. Much of the northern part of the province was subjected to folding and thrusting during Late Devonian to earliest Carboniferous Ellesmerian deformation, followed by a prolonged period of erosion. The eastern part of the province again experienced transpressive and compressive deformation as Greenland converged with North America during the early Tertiary Eurekan orogeny. Potential source rocks include Ordovician to Lower Devonian shales that contain abundant oil-prone organic matter, deposited on the outer continental shelf and slope. The most likely source rocks are Silurian strata, deposited as the continental shelf was drowned by a marine transgression caused by regional subsidence most likely associated with thrust loading. Potential source rocks in Greenland also may include organic-rich Cambrian shales deposited on the continental shelf. Rapid burial by thick Caledonian-derived strata in Late Devonian time abruptly matured the source rocks and generated oil; continued rapid burial may have cracked much of the accumulated oil to gas. In North Greenland, oil generation may have resulted from burial by now-eroded Devonian strata or from burial by Ellesmerian thrust sheets. Widespread bitumen in outcrops and in exploration wells appears to confirm that oil was indeed generated. Potential reservoirs include Cambrian nearshore clastic strata, Cambrian to Silurian carbonate bank strata, and Silurian to Middle Devonian reef buildups on the drowned shelf. Because Ellesmerian deformation postdated migration, only stratigraphic traps are likely, except in the area of the Boothia-Cornwallis uplift, a north-trending, structurally elevated zone, where structural traps formed by late Silurian to Early Devonian deformation are possible. It is unlikely that any large accumulations survived subsequent deformation or uplift and erosion. Three assessment units were defined: the Western Franklinian Shelf, the Boothia-Cornwallis Uplift, and the Eastern Franklinian Shelf Assessment Units. These assessment units were not quantitatively assessed, mostly because of the high risk to timing and preservation.