An unconformity within this formation that represents a hiatus of at least 2 million years is indicated in the Old Pump Road core. In two cores, Collier-Seminole and Old Pump Road, the uppermost sediments of the unnamed formation are not dated by strontium isotopes, and, based on the fossils present, these sediments could be as young as Pliocene. Map of Collier and Monroe Counties, southwestern Florida, showing locations of the corehole sites. The Tamiami Formation overlies the unnamed formation throughout the study area and is represented by the Ochopee Limestone Member. Undifferentiated sands overlie the Pliocene limestones in two cores in the southern part of the study area.
Artificial fill occurs at the top of most of the cores.
The hydrologic confining units penetrated by these cores are different in different parts of the study area. To the west, a hard tightly cemented dolostone forms the first major confining unit below the water table. In the eastern part of the study area, confinement is more difficult to determine. A tightly cemented sandstone, much younger than the dolostones to the west and probably not laterally connected to them, forms a slight confining unit in one core. The age and sedimentologic observations suggest a complex compartmentalization of the surficial aquifer system in southwestern Florida.