Sr concentrations and 87Sr/86Sr data used to determine the Sr-chronostratigraphic age of sirenian fossils on Santa Rosa Island, Channel Islands National Park, California, USA

Publication Date

2022-08-26

Start Date

2018

End Date

2021

Paces, J.B., 2022, Sr concentrations and 87Sr/86Sr data used to determine the Sr-chronostratigraphic age of sirenian fossils on Santa Rosa Island, Channel Islands National Park, California, USA: U.S. Geological Survey data release, https://doi.org/10.5066/P9GG6NB5.

Type: Related Primary Publication

Fossils of marine mammals belonging to the order Sirenia (families Dugongidae or Trichechidae) recently discovered in Tertiary marine sedimentary rocks on Santa Rosa Island, part of the Channel Islands National Park in southern California, are important because they provide a rare evolutionary link both temporally and spatially. Stratigraphic assignment of the sedimentary rocks hosting the fossils remain uncertain, having characteristics of both the mostly Late Oligocene Vaqueros Sandstone and the Early Miocene Rincon Claystone observed on the nearby coastal mainland. To provide a more precise age estimate of the sirenian specimens, fossil marine invertebrate shells were collected from the same exposures for chronostratigraphic assessment using their Sr-isotope compositions and the well-calibrated seawater-Sr evolution curve. Available shells specimens of bivalve mollusks (oysters and scallops) and crustaceans (barnacles) show a wide range of both Sr concentrations and 87Sr/86Sr values indicating that materials experienced varying degrees of diagenetic modification of their original Sr compositions. Combined Sr concentrations and 87Sr/86Sr compositions, both determined by thermal-ionization mass spectrometry, were used in the associated interpretive report to evaluate the extent of diagenetic modification and assess the original seawater-Sr 87Sr/86Sr composition for the purpose of determining a robust Sr-chronostratigraphic age.

• USGS Data Release Products