Benjamin A. Sheets¹, Chris Paola¹, Thomas A. Hickson¹
(1) University of Minnesota, Minneapolis, MN

Abstract: Experimental tests of alluvial basin filling models

Theoretical models of the architecture of alluvial stratigraphy typically predict the stacking patterns of sand bodies as a function of the sedimentation rate, as well as the frequency and style of avulsion. Unfortunately any model of these processes is limited by our poor understanding of the controls on avulsion. In an attempt to bridge the gap between theoretical models and field observations of alluvial architecture, we investigated the role of aggradational controls on channel-scale alluvial architecture in the Experimental Earthscape facility ("Jurassic Tank"), which can simulate variable subsidence rates and patterns, sea-level change, and variations in sediment flux. We performed an experiment in which a braided fluvial system was allowed to aggrade through four separate phases of subsidence. In particular, we investigated the influences of a cross-stream basement fault, lateral subsidence variation, downstream rigid-beam subsidence, four-fold change in the subsidence rate, and two-fold change in the water discharge to sediment discharge ratio. Throughout each phase, the volumetric sediment discharge of a coal and sand mixture was matched with the accommodation rate, with the lower density coal simulating fine sediments, and the higher density sand simulating channel deposits. The meter-thick sedimentary package was sliced vertically and imaged perpendicular to the mean flow direction. The slices were compared to images of the surface flow pattern to analyze the architecture of the deposit. This poster summarizes the preliminary results from this experiment and discusses their implications with respect to the amalgamation of sand bodies, and the resultant sandstone/shale ratio variation through the section.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana