--> Abstract: The Early Cretaceous Cadomin and Gething Formations of the Deep Basin Area, Western Canada: Cordilleran Tectonics and Alluvial Sedimentation in a Retroarc Foreland Basin, by Michael F. Johnson and Robert W. Dalrymple; #90039 (2005)

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The Early Cretaceous Cadomin and Gething Formations of the Deep Basin Area, Western Canada: Cordilleran Tectonics and Alluvial Sedimentation in a Retroarc Foreland Basin

Michael F. Johnson and Robert W. Dalrymple
Dept. of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON

Until the last decade, it was assumed that orogenic (i.e., isostatic) loading dominated retroarc foreland-basin development. Since then, it has been demonstrated that dynamic subsidence, caused by flow in the asthenosphere associated with slab subduction, is also responsible for large-scale vertical movements of the lithosphere. A growing understanding of the growth of the Canadian Cordillera allows us to make a first-order decoupling of these factors.

The initial Early Cretaceous deposits in west-central Alberta consist of the Cadomin Conglomerate, a thin, fluvially terraced apron of coarse-grained detritus that was shed far into the Western Canada Sedimentary Basin. This unit accumulated over approximately 15 million years, during which time accommodation was very low and even negative. It was followed, apparently abruptly, by deposition of the Gething Formation, which consists predominantly of muddy floodplain facies with minor channel deposits. Gething sequence boundaries display little incision, despite the local presence of coarse sand and gravel, indicating a high rate of subsidence.

During Cadomin time, there appears to have been a hiatus in subduction, as indicated by a lack of volcanic rocks of that age within the Canadian Cordillera. This resulted in uplift of both isostatic and dynamic origins (erosional unloading and reduced mantle flow, respectively). During Gething time, rates of terrane accretion were very slow, suggesting that the foreland development was minor and that Gething subsidence was not due to isostatic loading. However, there was considerable volcanism in the Cordillera, implying active subduction. Therefore, the subsidence was primarily of dynamic origin.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005