Lanterna Rally

Author: Henry W. Roehler

Publisher:

Published: 1990

Total Pages: 20

ISBN-13:

Two freshwater shorelines are present in the Scheggs Bed of the Tipton Tongue of the Green River Formation along Hardgrove Rim in the Sand Wash basin. The shorelines are part of Lake Gosiute, which occupied southwest Wyoming, northeast Utah, and northwest Colorado during the Eocene Epoch. The rocks comprising the shorelines range in thickness from about 40 feet to 275 feet. They are composed of thick beds of resistant quartzose sandstone, and interbed- ded thin, less resistant conglomerate, siltstone, shale, oil shale, carbonaceous shale, and coal. The shorelines are vertically and horizontally divisible into fluvial channel, mud- flat, swamp, strandline, nearshore, and offshore lithofacies, which are defined by their characteristic lithologies, their sedimentary structures, or both. Each lithofacies can be identified and correlated in the outcrops along Hardgrove Rim. The term shoreline in this report refers to all of the subaerial and subaqueous margins of a lake. The investigations have revealed that the shorelines ·of the Scheggs Bed prograded extensively and that they were entirely wave dominated. They had maximum widths of about 10 miles and probably sloped less than 1 o from back shore areas lakeward to water depths below wave base. Three different environments were present along the shorelines at the land-water interface: (1) strandlines, where there were sand beaches with swash zones; (2) swamps, where vegetation grew in backshore areas out into the lake; and (3) mudflats, where wave erosion caused flooding of parts of the backshore. A columnar section illustrates freshwater lacustrine shoreline deposits that are typical of the Scheggs Bed of the Tipton Tongue and of other tongues and members of the Green River Formation.