Paper No. 2
Presentation Time: 2:00 PM
ORIGIN AND DEVELOPMENT OF KARST VALLEYS IN SOUTHEAST FLORIDA, USA
The origin of valleys in karst terrains is usually from geological processes other than dissolution of limestone. Southeast Florida Transverse Glades are valleys developed by karst processes. Six stages of karst valley development are recognized and documented: 1. Solution pipes and surface depressions formed along lineaments by downward moving water. Cavernous zones formed along stratigraphic contacts providing ground water (GW) conduits. Epikarst processes created the Everglades Basin. 2. Karst features expand in size and collapse dolines form expanding into blind valleys. 3. Blind valleys expand forming irregular valleys. Valley walls expand laterally by collapse of the upper limestone strata and the development of hanging valleys. Up to this time Everglades Basin drainage is primarily by GW. 4. Upper valley walls expand laterally forming terraces and escarpments leaving remnants of the original surface limestone. A second terrace and escarpment forms as dolines and hanging valleys expand to form blind and continuous valleys in the lower strata also leaving behind remnants. The Everglades Basin fills with marl soil and begins to store water. Downward water movement decreases and is replaced by horizontal GW flow because now the limestone surface is close to the water table and the Everglades begins to drain by surface discharge through the karst valleys. Reduced GW discharge continues as most conduits have collapsed. 5. The second limestone strata continuous to collapse widening the valley, decreasing the size of the upper terrace and leaving pillars and remnants closely associated with their precursors. The rising water table associated with rising sea level decreases vertical GW movement but increases surface water discharge and horizontal groundwater discharge. 6. Valley floor fills with marl and residual quartz sand and downward water movement is decreased further. Valley walls expand to margins of subsurface cavernous zones, which is complete in the most mature karst valleys.
Karst valleys developed from vertical, changing to horizontal karst development with Holocene Transgression untill surface drainage became the dominate process. This suggests a relatively unique history that resulted in true karst valleys.