- GeoRef, Copyright 2006, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Experiments are being conducted in flumes designed to simulate conditions of deposition (1) through stream current action, and (2) by slumping into a standing body of water. Previous experiments, made in a wind tunnel with dry sand, formed deposits (1) by wind currents and (2) by avalanching down steep slopes. Stratification, or cross-stratification, was developed under each of the four environments of deposition. The type of deposit formed depends upon such factors as speed of current, depth of water, size of grain, degree of sorting. Significant observations from the experiments include: (1) Foreset beds develop without bottomset beds where sorting is good and clay minerals are absent or sparse. (2) Topset beds commonly are eliminated in delta-front deposits through lowering of the water level. (3) Wind-deposited sand on the lee sides of dunes forms strata with dips that consistently are several degrees greater than those of foreset slopes in water-deposited sand of corresponding grain size and texture. (4) Channel profiles tend to be U-shaped where formed by streams flowing down the channel bottoms, semicircular where formed by currents in a standing body of water that fills the channels. (5) Cross-stratification that appears to be upside down, consisting of festoons that are convex upward, can be formed by coalescing lobes at the front of an advancing delta; strata in channel-fills, including "festoon" types, vary from those that curve in conformity with the channel to those that are nearly flat-lying as a result of differences in position of water level at or above the channel rims during deposition.