Paleodrainage for the Mannville Group, Eastern Margins of the Alberta Foreland Basin System

Abstract

The Aptian McMurray Formation, eastern Alberta foreland basin, consists of basal fluvial deposits that become increasingly marine-influenced upwards. This presentation examines the McMurray drainage area and sediment-routing system within the context of the evolving foreland basin. Detrital zircon (DZ) data indicate the McMurray was the axial stream for a drainage sourced in the Appalachian Cordillera of the SE US through eastern Canada, which served as the divide between the Gulf of Mexico-Atlantic and the Boreal Sea. This continental-scale drainage, the Mississippi or Amazon of its time, was routed through the US midcontinent to the Assiniboia paleovalley, and was a contributive system, joined by shield-derived tributaries from the east, but remained separate from Western Cordillera-derived fluvial systems that dominate McMurray-equivalent strata in the foredeep farther west. The position of the McMurray axial drainage is consistent with the broad low-relief backbulge of the Cordilleran foreland basin, with the forebulge represented by the area of thin McMurray deposition to the west. The McMurray paleodrainage is interpreted to represent the last vestiges of continental-scale east-to-west sediment transfer that resulted from development of the Paleozoic Appalachian Cordillera along the eastern margin of North America. Prior to development of the Mesozoic Western Cordillera, this drainage routed sediments to the western North America passive margin, then, with development of eastward-propagating foreland flexural topography, the axial drainage was routed to the northwest Throughout this reconstructed drainage, Lower McMurray fluvial channel-belt sands rest on the sub-Cretaceous unconformity, which cuts sedimentary rocks of Jurassic to Devonian age. These relationships are consistent with what geomorphologists refer to as mixed bedrock-alluvial valleys. In the modern world, mixed bedrock-alluvial valleys (a) dominate the low-relief, erosional continental interiors, (b) require net rock uplift, (c) deepen and widen over long periods of time (≫10^6 yrs) by lateral migration and channel-belt deposition, punctuated by periods of bedrock valley incision and terrace formation, and (d) are contributory. One possible interpretation would be that plate-scale geodynamic processes drove net rock uplift and bedrock incision throughout the drainage basin, while the superimposed, eastward-propagating flexural signal steered drainage to the north and the Boreal Sea.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016