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The Influence of Morphology on Sinkhole Sedimentation at Little Salt Spring, Florida

ABSTRACT Gregory, B.R.B.; Reinhardt, E.G., and Gifford, J.A., 2017. The influence of morphology on sinkhole sedimentation at Little Salt Spring, Florida. Sedimentary processes are important for understanding sinkhole records of climate and sea-level change. This study examines Little Salt Spring (LSS), an hourglass-shaped sinkhole near the SW coast of Florida, to determine the influence of sinkhole morphology on sedimentation. An 8.27-m core recovered from LSS was subsampled at 2-cm intervals for particle-size, loss-on-ignition, and stable-isotope analyses (δ13C, δ15N, and C:N ratios). Nineteen radiocarbon dates provide chronology and sediment accumulation rates over the past approximately 13,500 cal. YBP. Particle size shows alternating periods of coarse and fine sediment from 6600 to 13,500 cal. YBP and coarser sediment from 0 to 6600 cal. YBP. Organic matter (OM) and carbonate content (CC) are initially low (<5%) but increase after about 10,000 cal. YBP to 60 and 15%, respectively. High C:N ratios (∼35), low δ15N (7.5‰), and low δ13C (−25‰) values were found between approximately 9000 and 13,500 cal. YBP but decreased afterward. Based on these sedimentary characteristics, sedimentation is classified into two phases. In Phase 1 (8000–13,500 cal. YBP), water level is low, with sedimentation dominated by input of allochthonous clastic sediment from surrounding areas. In Phase 2 (present–8000 cal. YBP), a higher water level and an increasingly sunlit open water area encouraged productivity, resulting in deposition of autochthonous, organic-rich sediment. Comparisons between the LSS site and an idealized model of sinkhole sedimentation forced solely by water level shows that both water level and karst basin physiography in LSS have influenced deposition.