3.4 Summary

Despite being primarily composed of eroded geologic units that provide a fragmented record, the Grand Strand geologic framework contains a wealth of information about the long- and short-term evolution of the region.  The framework components illustrate how geologic, oceanographic, and fluvial processes have influenced its development. The present coast has been shaped by the cumulative effect of these processes, which have acted over very different spatial and temporal scales.  In this report, the scales of these interrelated processes are placed into three broad categories: margin, platform, and coastal. 

At the margin scale, the Grand Strand has been predisposed to sediment limitation over millions of years due to its location within the structural configuration of the U.S. Atlantic continental margin.  At the platform scale, widely fluctuating sea levels between the Late Pliocene and present have caused alternating periods of subaerial and marine erosion.  At the coastal scale, nearshore-marine processes have forced the southwestward migration of the Pee Dee River; this shift diminished its role as the dominant source of regional sediment supply.  As coastal processes continued to shape the region during the Holocene, erosion of shoreline and inner-shelf deposits became the more important mode of regional sediment supply.  Driven by coastal wave and current energy, predominant southwestward sediment transport has generally prevented significant deposition along the northern and central portions of the Grand Strand and caused concentrated deposition in the southwestern part of the region.  Differential erosion across the geologic framework has influenced the distribution and extent of coastal features and the overall shape of the shoreline.  The geologic framework continues to control coastal evolution as sea level slowly rises, and coastal processes continue to erode sediments along the coast and inner shelf.

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