Grain-size analysis of Jacksonian sediments of Mississippi and adjacent areas

Abstract The Jacksonian sediments concerned in this study crop out in east Texas, Louisiana, Mississippi, and western Alabama for about seven hundred miles in a narrow strip which is approximately parallel to the strand line of the Mississippi embayment. According to the nomenclature of Shepard (1954), the predominant types of sediments are sand, clayey silt, clayey sand, and sand-silt-clay. The less common types are silty sand, clay, sandy clay, sandy silt, and silty clay. There is no silt. The environment of deposition ranges from outer shelf, inner shelf, channels, bays near narrows, and deltaic, to beach sand. Most of the sediments are predominant in fine admixtures, and are normal-sorted. Well-sorted and poorly-sorted sediments are common. The subdivision of the Jacksonian sediments of Louisiana cannot be made according to their size composition. However, it is possible to subdivide the Jacksonian sediments of Mississippi according to their size composition. The transgression of the Jacksonian sea is interpreted by the change of grain size of the sediments.