Relation of Grain Size to Sedimentary Processes: ABSTRACT

Abstract

Sand samples from known environments of deposition along the Gulf and East Coasts of the United States were collected to determine the effects of provenance, tidal range, average wave height, and sand supply on grain-size distributions. More than 300 samples were collected along profiles across 26 different tidal inlets, bays, and beaches. Samples were taken from the dune ridge to the plunge point, and in many places beyond the breaker zone. Additional samples were analyzed from the mouth of Southwest Pass of the Mississippi River. At each sample locality information was collected on (1) the beach profile, (2) sedimentary structures, (3) tidal cycle, (4) average breaker height, and (5) relation to sources of sediment supply. The information gathered was compared with log-probability plots of the size distributions. Probability plots of similar form were grouped to determine how different physical conditions affected the size distribution, and to determine the presence of genetic associations. Specific aspects of the grain-size distributions were found to be uniquely associated with differing depositional environments. The dune, swash zone, plunge zone, and wave-rippled sands exhibit characteristic size distributions even though they included samples from widely divergent provenance, energy, and tidal conditions. Grain-size distributions of samples collected from both the Gulf and East Coasts illustrate the environmental and provenance variations. Localities with high wave energy and limited supply include Cape Hatteras, North Carolina, Long Beach, North Carolina, and Pensacola Beach, Florida. These three areas show a limited fine fraction and a large coarse fraction. Other beaches close to a major source of supply and of lower average breaker height include Folly Beach, North Carolina, Forest Beach, South Carolina, Indian Beach, Florida, and Grand Isle, Louisiana. These show a large fine fraction and little coarse material. End_of_Article - Last_Page 484------------