ABSTRACT

Sanibel Island is one in a series of barrier islands located approximately 100 miles south of Tampa along the southwest Florida coast. The island is about 13 miles long with a curved axis. It comprises a land area of about 18 square miles and has a convex shore facing seaward.

At least seven distinct sets of beach ridges exist on Sanibel Island. These beach ridge sets are separated by truncation lines causing the older sets to intersect with younger sets at angles varying from nearly 90 degrees to about 10 degrees. The sets contain varying numbers of individual subparallel beach ridges with the total number in a set ranging from 10-15 to about 80.

The elevation of the beach ridges varies with regard to comparison of whole sets and individual ridges vary systematically within each set. Mangrove peat and intertidal marsh covers the oldest set(s), which was deposited at an elevation below present mean sea level. The highest beach ridges on Sanibel occur in the Wulfert Ridge Set, which has maximum elevations Near 10 feet above present mean sea level.

Radiocarbon dates indicate that the second oldest ridge set has an age of 2375±75 years B.P. and the Wulfert Ridge Set has an age of 2131±100 years B.P. Several other radiocarbon dates reveal the chronologic depositional history of the island with some sedimentation rates given.

The geometry and elevation of the Wulfert Ridge Set indicate a possible higher stand of sea level some 2000 years ago.