A Sand-Filled Meandering Channel, Upper Horseshoe Canyon Formation (Upper Cretaceous), Drumheller, Alberta

Abstract

<p>Three fluvial channels of the Upper Cretaceous Horseshoe Canyon Formation are exposed at Drumheller Alberta. The channels are isolated lenticular bodies and are separated by abundant fine- grained sediment.</p> <p>One channel appears to be filled to the top with sand and contains large, concave upward surfaces. The other channels contain well defined lateral accretion surfaces and large scale trough cross-bedding. Associated with the channel sands are levee, crevasse splay and distal over bank deposits. These channels are interpreted as high sinuosity, suspended lad, meandering channels. </p> <p>Paleoflow directions measured in the cross-bedded sands indicate paleoflow directions towards the east.</p> <p>Grain size distribution plots for the sandstones commonly lack a coarse population of grains transported by traction. Flow calculations show that the channels were competent to move grain sizes much larger than those present within the channels . This leads to the conclusion that the characteristics of the traction population were strongly dependant on the supply of coarse material. Shear velocities in the channels were calulated to range from 3.1 to 9 cm s -1.</p> <p>The proposeed mechanism for the sand filling of a meandering channel is through gradual abandonment by chute cutoff. Maintenance of flow conditions, capable of transporting sand, due to the decrease of depth with discharge, allowed the continued deposition of sand within the channel. Evidence of scoured surfaces within the channel indicate that any fines that may have been deposited were eroded away during flood stages when the meander loop was reoccupied.</p>