Synorogenic Sedimentation of Upper Cretaceous Frontier Formation Conglomerates and Associated Strata, Wyoming-Idaho-Utah Thrust Belt

Abstract

The Dry Hollow Member of the Upper Cretaceous (Turonian) Frontier Formation in the Wyoming-Idaho-Utah thrust belt is comprised predominantly of fluvial deposits. In northeastern Utah, these strata include massive cobble conglomerates, horizontally-stratified very coarse sandstones, planar cross-stratified pebbly sandstones, and rare siltstones. Farther eastward in southwestern Wyoming, the Dry Hollow Member contains sandstone lenses which possess basal conglomeratic (pebble) lenses and fine upward to medium-grained, trough cross­ stratified sandstones interbedded shales, coals, and thin, fine-grained, ripple-drift cross-laminated sandstones account for much of the Dry Hollow Member. Regional variations in stratification styles, grain size, and geometry of the sandstone units are interpreted as a consequence of downslope variations in channel pattern. These variations represent a change from near-source braided streams in northeastern Utah to distal meandering streams in southwestern Wyoming.