Evolution of karst in the Suwannee River Basin, Florida.

摘要

This study represents an application of Geographic Information Systems to examine the morphometric and spatial distribution of karstic depressions and the factors controlling the karst development in the Suwannee River basin. Analysis of the morphometric and spatial distribution parameters of karstic depressions such as area, length-width ratio, circularity, nearest neighbor distance, depression density, reveals that the Florida karst is represented by broad, shallow depressions with an average density of 6.07 and an average pitting index of 14.5. A simple morphoclimatic classification of karst landforms is precluded by the great variation of morphometric and spatial distribution parameters of karstic depressions within the Suwannee River basin.; Comparison of morphometric and spatial distribution parameters of depressions with geologic and hydrogeologic factors such as potentiometric level fluctuation of the Floridan aquifer, thickness of overburden material above the Floridan aquifer, depth to water table, soil type, and the vadose zone lithology suggests that all of the factors examined in this study collectively affect the morphometric characteristics and spatial distribution of karstic depressions. Analysis of depression major axis orientations does not show a structural control on the karst development. Application of the mass flux technique to available data indicates that the best estimate of the net karstic dissolution rate in the Lower Suwannee River basin is 34.3 m{dollar}sp3{dollar}/km{dollar}sp2{dollar}/year. This is equal to a denudation rate of 34.3 mm/1000 years.; Morphometric and spatial distribution characteristics of karstic depressions suggest that the last phase of the post-Miocene karstic evolution within the Suwannee River basin has been controlled by the retreat of the Pleistocene sea level stands. During the Pleistocene, as interglacial seas retreated, marine terraces were formed by sequential sea level lowstands and the total period of subaerial exposure diminished towards the sea. Consequently, geomorphologically younger karst landforms formed as the elevation of marine terraces decreased. This evolutionary pattern of karst landforms has resulted in the development of more frequent and/or larger and more complex depressions at higher elevations.