Paleoflow Characteristics of a Late Cretaceous River in Utah from Analysis of Sedimentary Structures in the Ferron Sandstone

Abstract

ABSTRACT Interpretation of sedimentary structures and detailed stratigraphic relations of the fluvial facies of the Upper Cretaceous Ferron Sandstone in the Castle Valley in east-central Utah permits reasonable reconstruction of many parameters of a Late Cretaceous alluvial system. After the width and depth of flow of the ancient Ferron river have been estimated from the geometry of preserved sedimentary structures, and the type of sediment transported by the river has been determined by study of the sandstone texture, various relationships of modern streams empirically derived by Schumm are used to estimate channel sinuosity, meander length, mean annual discharge, mean annual flood, channel slope, and flow velocity. Values derived for the slope and velocity are supported by other indirect met ods based on the Manning equation. It appears likely that the Late Cretaceous Ferron river was about 300 feet wide and 25 feet deep, and that it was highly sinuous, with meander lengths of 2,500 to 4,100 feet. As the 200-mile-long river drained an area to the southwest of 6,000 to 8,000 square miles, it had a mean annual discharge of approximately 6,000 to 7,000 cubic feet per second and a mean annual flood of about 22,000 cubic feet per second. Although only 2 percent of the total river load was bedload, the flow velocity of between 2.0 and 4.6 feet per second in the upper part of the lower flow regime caused the fine- to medium-grained sand to be in a dune bed configuration. Some caution is advised in using this approach because of unresolved questions of applying modern stream relations to pre-Quaternary deposits and because of uncertainties in determining the cross-sectional shape and sediment texture of the ancient Ferron river.