LATE HOLOCENE EROSIONAL SHOREFACE RETREAT WITHIN A SILICICLASTIC-TO-CARBONATE TRANSITION ZONE, EAST-CENTRAL FLORIDA, USA

This study has reconstructed the late Holocene evolution of a section of the North American Atlantic coast barrier-island system in a silici clastic-to-carbonate transition zone. A transgressive stratigraphy, an alogous to that recognized beneath the siliciclastic barriers of the e mbayed Atlantic and Gulf coasts, was identified in the study area and generated by erosional shoreface retreat of the barrier island during Holocene sea-level rise. Vibracores from the backbarrier revealed the preservation of a thin (< 3.5 m) Holocene sediment succession consisti ng of muddy skeletal sand overlain by intercalations of clean skeletal sand and muddy skeletal sand capped by fibrous peat. In the foreshore , the fibrous peat is compressed and abruptly overlain by coarse shell hash grading upward into skeletal sand. The entire Holocene section r ests unconformably upon a thin (< 0.25 m) quartz sand and featureless, gently seaward-dipping Pleistocene limestone surface. Sedimentologic, paleontologic, stratigraphic, and radiocarbon data suggest that this sequence is transgressive and was generated during erosional shoreface retreat of a wave-dominated, microtidal barrier-island system. The ba sal, muddy skeletal sand is interpreted to have been deposited in a sh allow (3 m) backbarrier lagoon. These sediments were buried during ove rwash events that transported skeletal sand across the barrier and int o the lagoon. Repeated overwash generated a shallowing-upward sequence capped by organic-rich tidal-wetland sediment. Radiocarbon dates sugg est that wetland sedimentation started between 1200 and 1960 yr B.P. L andward retreat of the barrier is indicated by the foreshore unconform ity (ravinement surface) that now truncates the fibrous peat. The pres ervation potential of the entire Holocene paralic section is probably low, given the lack of significant antecedent topographic relief and r elatively slow rate of sea-level rise. The preservation potential shou ld increase seaward, however, because the older paralic environments w ould have been subjected to faster sea-level rise.