Growth Rates of Beach Ridges on Sanibel Island, Florida: ABSTRACT

Abstract

Sanibel Island, a barrier island located approximately 100 mi south of Tampa along the southwest Florida coast, is about 13 mi long with a curved axis, and comprises a land area of about 18 sq mi with a convex shore facing seaward. At least 7 distinct sets of beach ridges are present on the island. These are separated by lines of truncation causing the older sets to intersect younger sets at angles ranging from nearly 90°to about 10°. The sets consist of varying numbers of individual subparallel-beach ridges with the total number in a set ranging from 10 to over 80. Elevation of the beach ridges differs with regard to comparison of whole sets and individual ridges differ systematically within each set. Mangrove peat and intertidal marsh cover the oldest sets, which were deposited at an elevation below present mean sea level. The highest beach ridges occur in the Wulfert Ridge set, which has maximum elevations near 10 ft above present mean sea level. The second highest ridge set has a radiocarbon age of 2,375 ± 75 years, and the Wulfert Ridge set has an average age of 2,131 ± 100 years. Other radiocarbon dates show the chronologic depositional history of the island and rates of sedimentation. The geometry and elevation of the Wulfert Ridge set indicate a possible higher stand of sea level 2,000 years ago. End_of_Article - Last_Page 1834------------