Strontium isotope stratigraphy and age estimates for the Leisey Shell Pit faunas, Hillsborough County, Florida

The vertebrate fauna of the Leisey Shell Pit near Tampa Bay, Florida, represents one of the more significant lrvingtonian mammalian faunas of North America. The fossil vertebrates occur in thin bone beds bounded above and below by massive shell beds containing a rich invertebrate ( chiefly molluscan) fauna. Debate has arisen concerning the precise age of the faunas at Leisey. Although generally agreed to be Pleistocene, estimates based upon vertebrate biostratigraphy suggest a somewhat older age than do estimates based upon molluscan biostratigraphy. To help resolve this controvefliy, 87SrJ86Sr ratios were determined on molluscan shells throughout the section. These ratios were then correlated to the global sea water 87Srf86Sr curve for age detennination. The Sr isotopes support an early Pleistocene age for the vertebrate fauna and suggest a complex history for the shell accumulations.