Pleistocene and Plio-Pleistocene sediments in northern Florida have been studied to detect tectonic displacement. Previous studies in southeastern Georgia defined six prominent former coastlines which are essentially horizontal and have altitudes (oldest to youngest) of 95-100 ft, 70-75 ft, 40-45 ft, and approximately 24, 13, and 4.5 ft above present sea level. The heights of the former sea levels were determined from the upper limit of littoral trace fossils and the altitude of salt-marsh sediments associated with each coastline. Each coastline is marked by a series of barrier-island deposits consisting of well-sorted, fine-grained, angular sand, and by lagoonal salt-marsh sediments of fine-grained sand, silt, and clay which accumulated landward of the barriers.

The former coastlines have been traced southward from Georgia into northern Florida where the lagoonal salt-marsh sediments of the Wicomico Formation (sea level 95-100 ft in Georgia) are found at progressively higher altitudes. Maximum uplift is east of Starke along the northeast flank of the Ocala uplift where salt-marsh sediments have an altitude of approximately 166 ft or 65-70 ft higher than those in Georgia. The Penholoway salt-marsh sediments (sea level 70-75 ft in Georgia) reach an altitude of 95 ft in Florida. The Talbot salt-marsh sediments (sea level 40-45 ft in Georgia) are not well preserved but appear to be displaced 5-10 ft in the area of maximum uplift in Florida. Pamlico salt-marsh sediments (sea level approximately 24 ft in Georgia) are as high as 32 ft south of St. A gustine; thus, there is progressively less warping of the lower, younger coastlines. South of the Ocala uplift the five lower Pleistocene coastlines are approximately the same altitudes that they are in Georgia. The oldest coastline, which may be of either Pliocene or Pleistocene age, maintains an altitude of 140-150 ft for more than 150 mi south of the area of maximum uplift.

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