CHARACTERISTICS AND DEVELOPMENT OF SHALLOW SOLUTION FEATURES IN THINLY MANTLED KARST, ALACHUA COUNTY, FLORIDA

Numerous karst features are present in western Alachua County, Florida and new karst features are uncovered during excavation or are exposed by sudden subsidence. Open and filled shafts (solution pipes), karst windows, subsidence dolines, residual chert boulders, and closed-contour depressions are found throughout the karst plain of the Western Valley.

We identified characteristics that suggested that karst features had formed at several different times as the landscape evolved. Many small (<5 m diameter) sediment-filled solution features penetrate the upper 5 to 8 m of the limestone, but analogous depressions are not evident on unexcavated landscape of adjacent properties. Most are conical and irregular in profile and many have coalesced into small compound solution depressions. In contrast, a smaller number of discrete, shallow solution pipes exhibit a well-formed, smooth-walled, elliptical morphology that may indicate more recent development. Where visible, shallow solution features terminate in a zone of horizontal solution cavities and solution widening is present only above and within the zone of horizontal cavities. Larger, deeper coalesced dolines and solution-widened fractures appeared to interfere, in some locations, with development of the shallow horizontal solution cavities. The deeper coalesced dolines typically penetrate below the depth of excavation, are much larger, and are comparatively widely spaced.

Upchurch (2002) described evidence of vertical conduits carrying surface drainage from upland terrains into the Floridan aquifer at the Cody scarp. The widely spaced, larger, coalesced dolines may be remnants of that process. We interpret the karst features in western Alachua County as a record of episodic development influenced initially by allogenic recharge from the siliciclastic uplands bounded by the retreating Cody scarp followed by more recent development of horizontal cavities and shallow solution pipes in a zone of transition between the scarp and a mature karst plain. Smaller solution pipes that terminate in or above the horizontal cavities appear to be more recently developed.

Upchurch, S.B., 2002, Hydrogeochemistry of a Karst Escarpment, in Martin, J.B., Wicks, C.M., and Sasowsky, I.D., eds, Hydrogeology and Biology of Post-Paleozoic Carbonate Aquifers: Karst Waters Institute SP 7, p. 205-211.