CLAY MINERALOGY AND BULK GEOCHEMISTRY OF UPPER ORDOVICIAN JUNIATA FORMATION PALEOSOLS AT POTTERS MILLS, PA

The Uppermost Ordovician Juniata Formation preserves multiple stacked paleosol deposits. The Juniata Fm. marks the Ordovician-Silurian boundary, and grades conformably into the Lowermost Silurian Tuscarora Formation. This study relied on an outcrop along Rt. 322 near Potters Mills, PA where several hundred meters of Juniata Fm. is exposed. This study looks at multiple paleosol deposits at the top of this formation with systematic high-resolution sampling for analysis and classification of these sediments. These paleosols are preserved within fining upward successions with occasional drab halo mottling from organic matter and occasional calcium carbonate nodules. Burrows also occur within these deposits, previously described as Scoyenia (Retallack, 2001) or Skolithos (Davies et al., 2010).

The goal of this study is to determine any changes in landscape and paleoclimate conditions as these paleosols form through time. Multiple samples were taken from each B-horizon of these paleosols and processed for clay mineralogy analysis using X-Ray diffraction. These samples are analyzed for bulk geochemistry using inductively coupled plasma optical emission spectroscopy. Bulk geochemistry provides an estimation and interpretation of paleodrainage (Ba/Sr), paleoprecipitation (chemical index of alteration) and paleotemperature (salinization).

The Upper Ordovician is of particular interest because a large climatic cooling shift is evidenced globally and associated with a global extinction event. The Juniata Fm. has been previously described as near-shore marine. The transition to more terrestrial conditions at this location represents a possible drop in sea level associated with the cooling event. Our study highlights that this landscape likely experienced stabilization with drying, and enhanced drainage as base-level drops from this global shift in climate.