Post-Miocene subtropical karst evolution, lower Suwannee River basin, Florida

Morphometric characteristics of similar to 25 000 karstic depressions sugge st that the last phase of the post-Miocene karstic evolution within the low er Suwannee River basin of Florida has been controlled by the lower sea-lev el stands of the Pleistocene and the formation of the Suwannee River. Durin g the Pleistocene, as interglacial seas retreated, marine terraces formed b y sequential sea-level lowstands and the time period of subaerial exposure diminished toward the sea. Consequently, geomorphologically younger karst l andforms formed as the elevation of marine terraces decreased. The evolutio nary geomorphological development of this heavily karstified region produce d more frequent and/or larger and more complex depressions at higher elevat ions. A. geographic information system analysis of morphometric and spatial distribution parameters of the karstic depressions within the lower Suwann ee River basin reveals that the Florida karst is represented by broad, shal low depressions with an average density of 6.07/km(2) and an average pittin g index of 14.5. Morphometric and spatial distribution parameters of karsti c depressions show a great variation within the lower Suwannee River area a nd thus preclude a simple morphoclimatic classification of karst landforms. The Tertiary carbonate rocks of the subtropical Florida karst have relativ ely less joint frequency and significant primary porosity, and do not produ ce the extreme karst landforms observed in the massive limestones of the tr opics.