Key Largo Limestone Revisited; Pleistocene Shelf-edge Facies, Florida Keys, USA

Multer, H.; Gischler, Eberhard; Lundberg, Joyce; Simmons, Kathleen; Shinn, Eugene

New dates and analysis of 12 deep and 57 shallow cores allow a more detailed interpretation of the Pleistocene shelf edge of the Florida Platform as found in various facies of the Key Largo Limestone beneath the Florida Keys. In this study a three-phase evolution of the Quaternary units (QJ -Q5) of the Key Largo is presented with new subdivision of the Q5. (1) In the first phase, the Q1 and Q2 (perhaps deposited during oxygen-isotope stage 11) deep-water quartz-rich environment evolved into a shallow carbonate phase. (2) Subsequently, a.Q3 (presumably corresponding to oxygen-isotope stage 9) flourishing reef and productive high platform sediment phase developed. (3) Finally, a Q4 and Q5 (corresponding to oxygenisotope stages 7 and 5) stabilization phase occurred with reefs and leeward productive lagoons, followed by lower sea levels presenting a sequence of younger (isotope substages 5c, Sa) shelf-margin wedges, sediment veneers and outlier reefs. The Key Largo Limestone provides an accessible model of a carbonate shelf edge with fluctuating water depth, bordering a deep seaward basin for a period of at least 300 ka. During this time, at least four onlaps/offlaps, often separated by periods of karst development with associated diagenetic alterations, took place.