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Variation of Rivers and Their Paleo-Drainages in Mesozoic Foreland Basins of North America

Abstract

Estimates of water and sediment paleodischarge, paleo-drainage area, and sediment budgets are calculated for a number of Mesozoic systems, from western North America. Extensive outcrop and subsurface data allow the largest trunk rivers to be identified, typically within incised valleys. Thickness, grain size, and sedimentary structures can be used to infer slope and flow velocities, and using width estimations, water and sediment paleodischarge can be calculated. River paleoslope can also be independently measured from stratigraphic-geometric considerations. Paleodischarge in turn is used to estimate the size of the catchment source area. Paleodischarge of rivers can also be estimated independently by integrating estimates of catchment source area, for example by using detrital zircons integrated with paleoclimate and regional paleogeographic/paleotectonic reconstructions. The catchment areas of North America evolved significantly during the late Mesozoic. During the Jurassic-Early Cretaceous, fluvial systems consisting of continental-scale low-slope (S=10-4), axially-drained rivers, formed the 40-m-deep channels in the Mannville Group in Canada, which now host the supergiant heavy-oil-sands reserves. During times of maximum transgression of the Cretaceous Seaway, such as the Turonian and Campanian the western North American foreland basin was characterized by smaller-scale (typically 10-m deep), steeper gradient (S=10-3) sand and gravel bed load rivers, dominated by transverse drainages in the rising Cordillera. This created a number of smaller river-delta systems along the coast, such as the Dunvegan, Ferron, Frontier, Lance and Cardium formations. As the Laramide Orogeny progressed, the Western Interior Seaway receded, and by the Paleocene the modern continental-scale drainage of North America was largely established with a major continental divide separating south-flowing Mississippi drainages that fed into the Gulf of Mexico, from north-flowing systems that drained into the Artic Ocean or Hudson's Bay, Canada. This approach shows that the tectono-paleogeograhic evolution of the foreland basin fill alternates from axial to tranversely drained rivers, that ranged from continental-scale rivers to smaller scale systems. The S2S analysis predicts the size and scale of fluvial systems and associated downstream depositional systems, which host much of the hydrocarbon in these prolific basins.