INDIRECT RESPONSE OF THE PEACE RIVER, FLORIDA, TO EPISODIC SEA-LEVEL CHANGE

Rivers must respond to base-level change but the timing, nature, and l ocation of the response varies with the river. This response includes incision and aggradation as recorded in the flood-plain sediment and B oil and calibrated by radiocarbon dates. Stream response to sea-level variations in a karst terrain is identified along the Peace River in c entral Florida. Incision and aggradation of this small river, more tha n 35 km upvalley from its mouth, primarily respond to changes in water -table elevation. This elevation in turn responds to both sea-level an d climate changes. As a consequence, river response to sea-level chang e is indirect and nonsynchronous with sealevel variations and with tha t of other non-karat streams that respond more directly to sea-level f luctuation. Incision of the Peace River occurred prior to 22 ka, durin g the initial decline of sea level and dry climate associated with the late Wisconsin glacial stage. These conditions caused the depression of the water table and hence the potential incision for the Peace Rive r. As the river incised, upstream fluvial and eolian erosion of dry up land surfaces increased sediment load and subsequently caused aggradat ion of the Peace River, despite a declining sea level. The present inc ision of the river occurred within the Last few millennia when sea lev el was at or near its present high stand and the climate was humid, th us resulting in a shallow water table. The wet vegetated ground surfac e restricted erosion therefore reducing sediment load of the Peace Riv er, which then began to incise during a sea-level maximum.