Structures Associated with Evaporite Diapirs on Ellef Ringnes Island, NE Sverdrup Basin

Carol Evenchick
Natural Resources Canada, Geological Survey of Canada, Vancouver, BC, Canada.

The objectives of new bedrock mapping on Ellef Ringnes Island are to apply current stratigraphic terminology, map the distribution of stratigraphic units, gain an understanding of structures associated with evaporite domes, and integrate surface and subsurface well and seismic data. Four weeks of fieldwork were supplemented by extensive use of oblique aerial photographs and satellite imagery to produce a preliminary new map of the island, and interpret structures. Cretaceous clastic rocks of the Sverdrup Basin underlie much of the island. Evaporites, intrusive rocks, and Jurassic clastics are minor. The Lower Cretaceous Isachsen Formation is subdivided into its Paterson Island, Rondon, and Walker Island members by recognizing the marine shale of the Rondon Member that separates the overlying and underlying sandy units. The overlying Christopher Formation is locally subdivided into the Invincible Point and Macdougall Point members. The Lower and Upper Cretaceous Hassel Formation, largely sandy, includes a locally mappable marine shale. Distribution of the Upper Cretaceous Kanguk Formation and Eureka Sound Group is largely as previously mapped. The large-scale structural geometry of the southern and central island is dominated by 7 evaporite diapirs. Bedding on the flanks of the diapirs is steep to overturned, and decreases in dip away from the diapers, to subhorizontal. Folds distant from the domes are commonly gentle (interlimb angles between 120° and 180°), with wavelengths of >5 km. The major folds trend north northwest and are intersected by less continuous folds that trend west northwest. Thrust faults have minor displacement. The most common structures are apparent strike-slip faults of a range of scales, in units surrounding the evaporite domes. Many of these probably originated as extensional faults that formed during deposition of the Cretaceous units. Deformation associated with diapiric movement of evaporite and contractional deformation subsequently rotated the faults to their current position, presenting an apparent strike-slip offset. The faults are most common in Christopher Formation. On the flank of Dumbells Dome 700 m of apparent offset of the Isachsen-Christopher contact represents 600 m of syn-Christopher dip-slip if the fault is extensional. North Ellef Ringnes Island is underlain by Lower Jurassic, Middle Jurassic, Upper Jurassic, and lowest Cretaceous clastic units. These strata are intruded by a swarm of ring dykes and sills. Faults in the north commonly strike north northeast. Their orientation may be inherited from basement faults formed during early basin rifting, and/or related to Canada Basin rifting. The possibility of previously unrecognized hydrocarbon traps is being investigated. These include evaporite flanges and overhangs on the margins of the diapirs, and domal structures resulting from intersection of folds.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.