Stratigraphy of Tidal Sand Ridges, Southwest Florida Shelf

Richard A. Davis, Jr., Jonathan M. Klay

Tidal sand ridges on the inner shelf off southwest Florida represent a likely analog to numerous linear sand bodies in the rock record that have been interpreted as having their origins in a continental shelf or cratonic sea environment. These ridges are approximately 10 km in length and 1 km wide and rise 3-4 m above the surrounding shelf. They are asymmetric in profile, and the crests are subparallel. The tide-dominated nature of this shelf system has been well documented by tidal current and side-scan sonar records. These ridges are small and low-energy analogs to the tidal ridges of the North Sea.

Over 40 vibracores have been taken from the ridges and adjacent shelf. These cores range from 2 to 9 m in length, and the longer ones include the entire Holocene record. The stratigraphy of the area shows four lithofacies. In stratigraphic order, they are (1) oxidized, clayey quartz sand (Pleistocene), (2) shelly, clayey sand with carbonate lithoclasts, (3) well-bedded, very shelly quartz sand, and (4) sorted and cross-stratified quartz sand. The ridges themselves are comprised of the upper two lithofacies.

The general stratigraphy and chronology of the tidal ridge sequence are similar to that reported for the adjacent Ten Thousand Islands area and reflect a change in rate of Holocene transgression prior to the development of the ridges. These ridges have developed after sea level rise slowed and sediment supply increased no more than 3,500 years ago. The present ridges appear to be in a state of dynamic equilibrium, with the current supply of sediment being bypassed and deposited in Gullivan Bay between the ridges and the Ten Thousand Islands mainland coast.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.