Coarse-grained meandering distributive fluvial system of the basal Cedar Mountain Formation, U.S.A.

ABSTRACT The analysis of downstream changes in ancient fluvial systems can better inform depositional models for foreland-basin systems. Herein we analyze the basal deposits Early Cretaceous Cedar Mountain Formation Utah to understand variety present and develop a model Sevier foreland basin. We also evaluate long-held interpretation braided origin these document numerous examples point-bar deposition highly sinuous meandering rivers by large (20 60 km2) plan-view exposures. These exposures allow comparisons between planform cross-sectional geometries. study utilizes outcrop data, virtual models, satellite imagery facies architecture channel bodies Buckhorn Conglomerate Poison Strip Sandstone Formation. (west east) decreases lateral migration, sinuosity, amalgamation, grain size, percent (conglomerate sandstone). Fluvial occur arranged into larger stratal bodies: multistory–multilateral that are dominantly composed clast-supported conglomerate west mix multistory, multilateral, isolated matrix-supported east. median width point bars is similar across field area (344 m 477 m), but inclusion narrower (median = 174 low-sinuosity bar elements east indicates an overall reduction migration sinuosity downstream. Net-to-gross values range from 100% much western outcrops as low 38% Paleocurrent reveals transverse paleoflow interval merges with axial (south–north) near Utah–Colorado state line. estimate 104 m3/s-scale discharge 106 kilometer-scale drainage based on paleohydraulic which represents significant part continental-scale drainage. observed trends net-to-gross consistent expected single-thread distributive Jurassic Morrison Medial (Buckhorn Conglomerate) distal (Poison Sandstone) zones preserved span forebulge backbulge depozones system. Postulated proximal system have been removed during erosion foredeep depozone. easternmost coeval Burro Canyon represent at western-sourced end. Distributive dominate modern basins, this suggests they may constitute proportion successions.