Late Quaternary stratigraphy, sea-level history, and paleoclimatology of the southeast Florida outer continental shelf

A submerged, massive fossil reef tract, located seaward of the Florida Keys continental shelf, was investigated using seismic reflection profiles, drilled cores, high-precision thermal ionization mass spectrometric (TIMS) {dollar}sp{lcub}234{rcub}{dollar}U/{dollar}sp{lcub}230{rcub}{dollar}Th dating, and stable isotopic analyses. Multiple late Pleistocene and early Holocene reef generations and one major unconformity were documented within two end-member transects of the Outlier Reef tract. These in situ coral reefs, on the tectonically stable Florida platform, provided the ideal setting to determine sea-level elevations during oxygen isotope substage 5a, and a previously undocumented portion of the early Holocene transgression. Paleo-sea surface temperatures were calculated from coral-derived stable {dollar}deltasp{lcub}18{rcub}{dollar}O for the late Pleistocene and early Holocene episodes of reef development. Late Quaternary geologic history of the southeast Florida margin was reconstructed in terms of sea-level fluctuations, paleoclimate, and orbital forcing.; High-precision TIMS U-Th dating of Florida Outlier Reef corals defined a late Pleistocene sequence of substage 5c reef at 106 ka, and a substage 5b/5a reef section from 94-80 ka. Sea level reached a maximum of {dollar}-{dollar}9.0 to {dollar}-{dollar}6.8 m MSL at {dollar}approx{dollar}83 ka. Speleothem from the Bahamas precisely bracket high sea-level timing and elevation from reefs, detailing a history of substage 5c reef growth at 106 ka, subaerial exposure above {dollar}-{dollar}15 m MSL from 100-95 ka, substage 5b reef growth up to {dollar}-{dollar}16 m MSL from 95-90 ka, and substage 5a reef growth from 86 to 80 ka. Insolation forcing of sea-level change occurred consistently through late stage 5 with little or no lag in sea-level response. Sea level fell to {dollar}-{dollar}17 m at 79 ka as insolation decreased. Pleistocene reefs were subaerially exposed during the last glaciation, and recolonized during the Holocene transgression.; Substage 5a reef was disconformably overlain by early Holocene reef ranging in age from 8.9-5.0 ka. Dated Outlier Reef corals fill a former gap in the sea-level record which was attributed to catastrophic rates of sea-level rise and reef drowning. Moderate rates of sea-level rise documented by Outlier Reef data allowed reefs to keep pace throughout the dated interval. Insolation/orbital forcing of sea-level rise from 17 to 9 ka continued past the insolation maximum from 10-9 ka.; Late Pleistocene and early Holocene Montastrea annularis were analyzed for stable isotopic composition to reconstruct paleo-SSTs using the standard paleotemperature equation and a calibrated equation for M. annularis from Florida Keys waters. Paleo-seawater {dollar}deltasp{lcub}18{rcub}{dollar}O was reconstructed using the calibration of Fairbanks and Matthews (1978) and sea levels determined in this study. Paleo-SSTs for substage 5a were indistinguishable from those of the modern reef tract, reflecting the insolation peak at 82 ka. Paleo-SSTs for the early Holocene were slightly higher than those of the modern reef system, including one or more episodes of thermal stress and coral bleaching. Higher temperatures 7-8 kyrs ago are consistent with the insolation maximum at 10 ka.