Early Miocene land mammals and chronology of the Belgrade Formation, eastern North Carolina

Abstract Early Miocene land mammals from eastern North America are exceedingly rare. Over the past several decades a small, but significant, vertebrate fauna has been recovered by paleontologists and citizen scientists from the Belgrade Formation at the Martin Marietta Belgrade Quarry in eastern North Carolina. This assemblage has 12 land mammal taxa, including beaver (Castoridae), stem lagomorph, carnivorans (Mustelidae, Ailuridae), horses (Equidae), rhinoceros (Rhinocerotidae), tapir (Tapiridae), peccary (Tayassuidae), anthracothere (Anthracotheriidae), entelodont (Entelodontidae), and protoceratid (Protoceratidae). Taken together, the biochronology of this Maysville Local Fauna indicates a late Arikareean (Ar3/Ar4) to early Hemingfordian (He1) North American Land Mammal Age (NALMA). This interval, which includes the Runningwater Chronofauna, documents numerous important Holarctic immigrants, including Amphictis , Craterogale , and cf. Menoceras found at this locality. Strontium isotope stratigraphy (SIS) of shark teeth collected in situ from the Belgrade Formation yield an age of 21.4 ± 0.13 Ma, which validates the age of interbedded land mammals within this unit. It also is consistent with the late Arikareean (Ar3/Ar4) biochronology and Aquitanian Neogene marine stage. New SIS analyses of oysters ( Striostrea gigantissima ) and clams ( Chione ) from this mine, previously assigned to late Oligocene or Late Miocene, are significantly older (28.0 ± 0.22 Ma and 27.6 ± 0.26 Ma, respectively) than the land mammals. Depending upon stratigraphic interpretations, these may confirm an older marine facies within the Belgrade Formation. This locality is important because of its marine and terrestrial tie-ins that facilitate intercalibration of both NALMAs and Cenozoic marine stages.