NEW TERTIARY STRATIGRAPHY FOR THE FLORIDA KEYS AND SOUTHERN PENINSULAOF FLORIDA

Seven lithologic formations, ranging in age from Oligocene to Pleistoc ene, were recently penetrated by core holes in southernmost Florida, F rom bottom to top, they are the early Oligocene Suwannee Limestone; la te-early Oligocene-to-Miocene Arcadia Formation, basal Hawthorn Group; late Miocene Peace River Formation, upper Hawthorn Group; newly propo sed late Miocene-to-Pliocene Long Key and Stock Island Formations; and Pleistocene Key Large and Miami Limestones, The rocks of the Suwannee Limestone form a third-order sequence, Although the entire thickness was not penetrated, 96 m of Suwannee core from one well contains at le ast 50 vertically stacked, exposure-capped Limestone cycles, presumabl y related to rapid eustatic fluctuations while experiencing tropical t o subtropical conditions, The Arcadia Formation is a composite sequenc e containing four high-frequency sequences composed of multiple vertic ally stacked carbonate cycles, Most cycles do not show evidence of sub aerial exposure and were deposited under more temperate conditions, re lative to the Suwannee Limestone. The Arcadia Formation in southernmos t Florida is bounded by regional unconformities representing third-ord er sequence boundaries. Post-Arcadia transgression produced a major ba ckstepping of sediment accumulation above the upper sequence boundary of the Arcadia Formation, The Peace River Formation, composed of diato maceous mudstones, has been identified only beneath the Florida penins ula and is not present beneath the Florida Keys, Deposition occurred d uring marine transgressive to high-stand conditions and a local phosph atization event (recorded in northeast Florida). The transgression is possibly related to a global rise in sea level, which resulted in upwe lling of relatively cooler, relatively nutrient-rich water masses onto the Florida Platform. It is proposed that the absence of Peace River sediments beneath the Keys is due to sediment bypass of the upper surf ace of the Arcadia, a result of sediment sweeping by an ancestral Flor ida current. During late Miocene to Pliocene time in the Florida Keys, siliciclastics of the Long Key Formation and fine-grained carbonates of the Stock Island Formation prograded toward the southern edge of th e Florida Platform and downlapped onto the regional unconformity at th e top of the Arcadia, Shallow-marine Pleistocene Limestones (Key Large and Miami Limestones), deposited during tropical to subtropical condi tions, drape over accretionary successions of the Long Key and Stock I sland Formations.