Frank W. Stapor

History and sand budgets of the barrier island system in the Panama City, Florida, region

Abstract Shell Island and Crooked Island peninsulas comprise the Holocene barrier system in the Panama City, Florida, region. Both of these peninsulas have experienced a history of integration-fragmentation-integration superimposed on a net shoreward migration since 1779. Catastrophic events such as hurricanes are most probably responsible for the pass cutting which has fragmented these barriers. Both barrier peninsulas have very nearly segmented St. Andrew Sound into an eastern and western portion. This segmentation has been achieved through natural causes in the eastern or Crooked Island region, but an alternation in the tidal return pattern, effected by the cutting of a canal across Shell Island, is probably responsible for the ongoing segmentation of the western portion. Rates of erosion/deposition, determined by comparing bathymetries charted in 1877, 1930, and 1946, demand that these two peninsulas receive material by eastward transport. Furthermore, the long shore drift of both peninsulas is bidirectional, northwesterly and southeasterly. These two drift components are very nearly equal in magnitude immediately west of Shell Island; net easterly drift occurs on Shell Island peninsula. Crooked Island experiences net westerly and easterly drift; the easterly drift terminates in the Bell Shoal area and does not reach the adjacent St. Joe Spit.

Sediment budgets on a compartmented low-to-moderate energy coast in northwest Florida

Abstract Sediment budgets for portions of the Franklin and Gulf County, Florida, coasts have been determined through comparison of old (1860s–1940s) U.S. Hydrographic Office smooth sheets. Rate of erosion and deposition and, significantly, minimum distances of transport were computed. This coast is divided into at least six individual compartments (or longshore drift cells) which most probably experience minimal communication; in each instance erosion and deposition are nearly balanced. This compartmentalization is effected by the low-to-moderate wave energy and the offshore bathymetry of the region.

Higher-than-present Holocene sea-level events recorded in wave-cut terraces and scarps: Old Island, Beaufort County, South Carolina

Abstract Wave-cut terraces and scarps record at least two higher-than-present Holocene sea-level events in coastal South Carolina. The higher event reached 110 cm and the lower 80 cm above local, mean spring high water (MSHW). These events occurred subsequent to the formation of the Holocene Old Island barrier island and prior to Wilmington aboriginal occupation 1600 years ago. Shell middens are located on the terrace surfaces. These wave-cut features were formed in a marsh-filled lagoon sheltered from the open ocean by seaward barrier islands. These terraces and scarps are evidence supporting the higher-than-present sea-level events predicted for this region by the Clark et al. (1978) geophysical model of Holocene sea-level recovery. In addition, they support a Fairbridge (1961)-type Holocene sea-level curve, one characterized by oscillations above and below present position. Holocene sea-level fluctuations probably were a prime factor in the episodic progradation of this area, given that in this vicinity the nearshore region is the primary sand source.

Progradation of a Beach Ridge Plain between 5000 and 4000 Years BP Inferred from Luminescence Dating, Coquimbo Bay, Chile

ABSTRACT Hart, E.A.; Stapor, F.W.; Enrique Novoa Jerez, J., and Sutherland, C.J., 2017. Progradation of a beach ridge plain between 5000 and 4000 years BP inferred from luminescence dating, Coquimbo Bay, Chile. Luminescence dating was carried out to determine the depositional history of a 2-km-wide, shore-parallel, beach ridge sequence at Coquimbo Bay, Chile, for which no direct dating had previously been done. The beach ridge plain at Coquimbo Bay represents one of the most extensive Holocene depositional features preserved along the Pacific Coast of South America. Both optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) dates indicate a rapid period of beach ridge progradation lasting approximately 1000 years at an average rate of 2 m y−1. However, based on previously reported luminescence deficiencies of geologically “young” quartz, it is proposed that IRSL dates are more representative of the actual depositional age of the beach ridges. These IRSL ages indicate that the beach ridge plain at Coquimbo Bay was formed between ca. 5000 and 4000 years BP, after the hiatus of eustatic sea-level rise in the mid-Holocene, and that a relatively stable shoreline location has likely prevailed over the last 4000 yrs. The height of beach ridges 8 to 10 m above modern sea level is difficult to interpret but is likely the result of several factors, including the build-up of an eolian cap on each beach ridge at the time of its formation, the height of wave runup, and tectonic uplift. Although uncertain, the cumulative effect of all three of these factors appears to be insufficient to account for all of the present beach ridge elevation, and thus a fall in sea level after the mid-Holocene at this location cannot be ruled out. Archaeological and geomorphic evidence support the idea of a mid-Holocene sea-level high stand and a 1 to 2 m mid-Holocene high stand is well established at many other circum-Pacific, far-field locations.