Keen, T. .
1987.
The Comparative Sedimentology of Two Stranded Bars, and Implications for their Origin..
Geology. Tallahassee, Florida State University.
The 1985 hurricane season saw the deposition of two stranded bars at Carrabelle Beach, Florida. These bars are characterized by convex-up concentric bedding and discrete heavy mineral lamination. The bar deposited by Hurricane Elena contained only these internal structures whereas the Hurricane Kate bar revealed a multistage depositional history with the earliest phase resulting in migrating break-point bar construction. The different paths of these two hurricanes, and local physiographic factors, worked in combination to produce different degrees of sediment reworking for these two events. The "Elena" bar was deposited from an evolving sediment pool and shows a temporal decrease in sample means and standard deviations as well as greater variability .The "Kate " bar was constructed from mature sediment which exhibited little variation. Erosion during the early phases of these storms removed large volumes of sand from the beach to offshore, there reworking it until the wave energy decreased sufficiently for bar growth to commence. This process concentrated heavy minerals to very high levels before moving them ashore. During shoreward transport these sediments were progressively sorted and the two storm sand populations acquired their terminal characteristics. Consideration of the storm surge history and sediment characteristics leads to the conclusion that heavy mineral lamination resulted from wave breaking seaward of the bar whereas the thicker bedding seen in the lower part of the "Elena" bar was due to waves breaking shoreward of the bar. The extent of individual beds and laminae parallel to shore was tens of meters, reflecting the length of unbroken wave crests. This paper tentatively identifies the sedimentary processes responsible for the deposition of these bars and their unique sedimentary characteristics. Further mathematical analysis of these processes is indicated, using suspended sediment concentrations and :general physical principles.