Plan-view Paleochannel Reconstruction and Paleocurrent Field of Meanderbelts, Cretaceous Ferron Sandstone, Henry Mountain Region, Utah



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Plan view and cliff exposures of an ancient meander belt in the Cretaceous Ferron Sandstone member, Mancos Shale Formation, Utah, allow us to evaluate numerical models of facies variability in meander belts. These models predict that grain size and vertical facies associations vary as a function of the style of bar migration as well as position within a bar (upstream vs. downstream). This project integrates measured sections and bedding diagrams of cliff exposures with areal mapping of grain-size and paleocurrent variability to investigate the plan view variations in grain size as a function of paleoflow. Three channel stories are identified. Lateral amalgamation of many point bars suggests the dominance of a meandering river style. Compound braid bars built by overlapping unit bars constitute the youngest channel deposits. The Red River is a proper modern analogue to the Ferron river deposits in study area. The youngest channel is 2.0 m in depth, 90m in width, 435m in meander amplitude, and has a sinuosity of 2.9. The middle one is 3.1m in depth, 1083m in meander amplitude, and has a sinuosity of 1.2. The Ferron rivers are small to medium scale according to calculated paleohydraulic parameters (Qw = 135~225m3/sec). Topographic roughness is documented to be associated with sinuosity of channel deposits. Grain size coarsens towards the bend apex along the bend axis and fines downstream within some meander scrolls. Independent measurement of meander wavelength based on plan view exposures is close to the results from empirical equations.



Paleocurrent, Plan view