Orogeny and the collapse of the Devonian Prairie Evaporite karst in Western Canada: impact on the overlying Cretaceous Athabasca Oil Sands
Paul L. Broughton, 2018. "Orogeny and the collapse of the Devonian Prairie Evaporite karst in Western Canada: impact on the overlying Cretaceous Athabasca Oil Sands", Advances in Karst Research: Theory, Fieldwork and Applications, M. Parise, F. Gabrovsek, G. Kaufmann, N. Ravbar
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The Middle Devonian Prairie Evaporite Formation accumulated up to 200 m of halite-dominated beds across Western Canada in a salt basin extending from northern Alberta southeastwards into southern Saskatchewan and western North Dakota. A 1000 km long salt dissolution trend along the eastern basin margin resulted in the removal of 100–150 m of halite–anhydrite beds. A second salt dissolution trend removed up to 200 m of section across southern Saskatchewan. The removal of the halite-dominated beds and the collapse of the overlying strata responded to regional aquifer and vertical water flows driven by compaction up-structure to the NE towards the eastern margins of the foreland Alberta and intracratonic Williston constituent basins of the Western Canadian Sedimentary Basin. Flows resulting in dissolution trends in the deepening Alberta foreland basin were responses to Middle Jurassic–Early Cretaceous Columbian orogenic tectonism, in contrast with the multiple Paleozoic and Mesozoic dissolution stages across the southern Saskatchewan area of the northern Williston basin. Water flows along the Devonian Keg River strata migrated into the overlying Prairie Evaporite salt beds. The dissolution fronts advanced along multi-kilometre long NW- and NE-oriented sets of fault–fracture lineaments resulting from orogenic Precambrian block movements propagated into the overlying Devonian strata. The Athabasca Oil Sands accumulated above a 300 km long segment of the dissolution trend along the eastern margin of the evaporite basin. An unusually low 1:2 thickness ratio of removed salt beds to overlying strata resulted in significant structural controls on the deposition of the overlying Cretaceous McMurray Formation point bar complexes. Fluvial point bars up to 6 km long and tens of metres thick collinearly aligned along fairways tens of kilometres long, following the halite dissolution trends 200 m below. These sand reservoirs trapped Laramide oil migration into the area. Biodegradation followed, resulting in a trillion barrel resource. A final stage of salt removal occurred with the influx of subglacial meltwaters, rejuvenating 10 km2 Cretaceous collapses across southern Saskatchewan.
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Karst landscapes and karst aquifers are composed of a variety of soluble rocks, such as salt, gypsum, anhydrite, limestone, dolomite and quartzite. They are fascinating areas of exploration, study and research. As karst rocks are abundant on the Earth’s surface, the fast evolution of karst landscapes and the rapid flow of water through karst aquifers present many challenges from a number of different perspectives. This collection of 25 papers deals with different aspects of these challenges, including karst geology, geomorphology and speleogenesis, karst hydrogeology, karst modelling, and karst hazards and management. Together these papers provide a state-of-the-art review of the current challenges and solutions we face in describing karst from a scientific perspective, while at the same time providing useful data and information for managing karst territories to land planners, developers, and managers of show caves, natural parks and reserves in karst terrains.