Paleo Channel Reconstruction and Grain Size Variability in Fluvial Deposits in the Cretaceous Ferron Sandstone, Utah

Abstract:

Paleocurrents are significant in predicting heterogeneity in ancient point bar deposits but have been mostly studied from vertical exposures. Changes in channel orientation could be misinterpreted in cross-sectional studies. In this study, we combined closely spaced paleocurrent and grain size data, collected in field, with airborne LiDAR survey (Light Detection and Ranging) to evaluate the paleocurrent geometry in ancient point bar deposits in Cretaceous Ferron Sandstone near Hanksville, Utah. In LiDAR hillshade images, derived from LiDAR digital terrain models, numerous crescent shaped sandstone ridges, dominated by unidirectional paleocurrents, are interpreted as scroll bars. Migration patterns of these scroll bars and their cross-cutting relationships have been interpreted from their distribution in plan view as seen in the hillshade images. Paleocurrent directions, measured in the field, closely follow the shape of these scroll bars. Planview grain size distribution shows a coarsening trend toward the bend apex on an individual point bar. However, on the whole channel bend scale this trend is less prominent. Two sets of cross cutting scroll bars, with different orientations, have been identified in the field area. Paleoflow directions are perpendicular in these scroll bars. A significant change in grain size has been observed at the edge, indicating where the younger scroll bars cut into the older one. These two set of scroll bars are identified as two channel belts built by migration of the bars. However, lack of vertical exposures in the field area limits our understanding of the complete three dimensional geometry, paleohydraulics and the temporal evolution of the channel. Future work will involve integration of our current data set with GPR (Ground Penetrating Radar) which will allow reconstruction of the three dimensional architecture of this deposit.