Origin of Patterns of Quartz Sand Types on the Southeastern United States Continental Shelf and Implications on Contemporary Shelf Sedimentation--Fourier Grain Shape Analysis

Abstract

ABSTRACT Quartz sands in the fine sand range were found to form areally discrete zones with different shape characteristics on the continental shelf from Charleston Harbor, South Carolina northward to Cape Fear, North Carolina. The nature and location of these sand zones can be used to gain insights into the past and present hydrodynamic history of the continental margin during the Pleistocene-Holocene. Fourier grain shape analysis of 95 samples indicates that the shelf surface in this area is characterized by coast-perpendicular bands of sand containing alternating high and low percentages of highly abraded (smooth) quartz grains. The bands containing high proportions of smooth grains are interpreted to be of coastal plain origin. The bands containing high proportions of quartz grains of irregular outline represent traces of pre-Holocene alluvial drainages on the exposed shelf during sea level lowstands. This interpretation is greatly strengthened by the fact that all three shelf bands of irregular sand exactly coincide at their landward ends with the coastal positions of Pleistocene courses of the three major Piedmont drainages in the region. The presence and preservation of these coast perpendicular bands emphasize the relict character of the fine sand on the shelf surface as well as the inability of bottom currents to produce significant shore-parallel net transport in this area.