Paleo-channel reconstruction and grain size variability in fluvial deposits, Ferron Sandstone, Notom Delta, Hanksville, Utah

Abstract

Planform meanderbelt exposures display the evolution of the channel which leads to better understanding of three dimensional architecture of the fluvial deposit. Due to the paucity of extensive plan-view exposures in rock record, reconstruction of paleo channels from plan form exposures has been hardly studied. This study combines closely spaced paleocurrent and grain size data from plan-view exposures of point bar deposits in the delta plain deposits of the Cretaceous Ferron Sandstone near Hanksville, Utah, USA. Airborne Light Detection and Ranging (LiDAR) was used to create hillshade images in which numerous crescent shaped sandstone ridges were identified. These are dominated by unidirectional paleocurrent and thus they are interpreted as scroll bars associated with four distinct meander loops. The loops show a combination of growth by lateral expansion and downstream translation. Cross-cutting relationships allow us to decipher the order of loop formation. Paleocurrent directions closely follow the shape of individual scroll bars. Plan-view grain size distributions show a coarsening trend toward the bend apex on individual scroll bars. However, at the scale of an entire meander loop, this trend is less prominent. Paleohydraulic estimates show that these channels have low sinuosity (1.3–1.7) and have an average discharge ranging from 42.1 to 66.4m3/s. Comparison with larger sandbodies in underlying valley systems suggests that the studied channels represent the upper delta plain distributary channels and indicate an overall backstep with respect to channels in the immediately underlying incised valley.