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Table 6. Data and assumptions used to infer youngest possible age of upper-slope terrace off the Florida Keys. Older part of table modified from Lidz et al., 2003. By inference from dates and depths of corals in the Sand Key outlier reef and from proxy sea-level curve data (Fig. 37A, 37B), the latest possible time the terrace could have been formed (at ~190 ka) was during the post-195-ka regression. This time is 20 ka earlier than the time previously inferred from the same data without the marine-isotope δ¹⁸O curve (Lidz et al., 2003). If the terrace is ~190 ka and given a mean outlier-reef relief of 29 m and the 21.7-m-thick dated interval in the Sand Key outlier reef, a reasonable deduction is that the initial 7.3 m of outlier-reef growth accrued during the next post-190-ka rise in sea level that reached and exceeded elevation of the upper-slope terrace. That transgression occurred during the Stage-6/5 transition that culminated in deposition of the 125-ka Key Largo and Miami Limestone of the Florida Keys. Without reference to any particular coral species or growth rate, it is clear from the thickness (~8 m, Perkins, 1977, his plate 3) of the post-Q3-Unit section in the Big Pine Key core that there was ample time for a comparable 7.3 m of Stage-6/5 (substage-5e) coral framework to accumulate at the base of the outlier reefs. That said, the upper-slope terrace could be older than 190 ka. The only way to verify its age is to core and date the material at and below its surface, an unlikely procedure given the water depths and strong currents of the offshore setting. Authors cited listed in References. For more information, contact Barbara Lidz.

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Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751