LITHOSTRATIGRAPHY AND CLAY MINERALOGY OF PETM SEDIMENTS AT NEW WILSON LAKE, NJ COREHOLE

Wilson Lake hole B was drilled in May 2011 in the New Jersey Coastal Plain, recovering the basal Eocene boundary sediments of the Marlboro Clay. The Marlboro Clay represents a unique lithologic unit within the Mid-Atlantic Coastal Plain. Bulk δ¹³C data show that the deposition of the Marlboro Clay began at the first major δ¹³C decrease associated with the Paleocene-Eocene Thermal Maximum and Carbon Isotope Excursion (CIE). The top of the Marlboro Clay is still within the CIE and truncated by an unconformity. The underlying Vincentown Formation silts were deposited near wavebase (~30m) as indicated by cross bedding and benthic foraminifera. The Marlboro Clay was deposited in deeper water; many estimates place it over 100m, though other studies suggest it was only ~50m. Our lithologic studies provide a broader stratigraphic context, indicating that this clayey silt provides a record of shelf deposition during the CIE and that deposition was associated with a sea-level rise of 10’s m. We examine clay mineralogy, grain size, and elemental composition from XRF analyses to characterize the homogeneous, light gray clay unit. Particle sizes determined with a laser diffraction analyzer positively identify the observed lithologic change at the base of the Marlboro Clay and confirm the vertical consistency of the clayey (<45% clay) silt (>50%). Mineral assemblages determined by XRD show a significant substitution of increased kaolinite over illite and smectite at the base of the Marlboro Clay peaking near 50% total assemblage and decreasing upsection in concert with increasing bulk δ¹³C values. Numerous ~2 cm thick beds are separated by thin (~1 mm) expanding clay laminae. The source of the expanding clay is unclear. Smectite (~15%) and vermiculite (~5%) noted in the clay fraction may be the source of the expanding clay. A representative section (60 cm) of the Wilson Lake B core was scanned by XRF to produce geochemical profiles with hopes of identifying the 1 mm-thick laminations. High resolution XRD analyses and XRF scanning are being used to evaluate whether there are higher frequency signals.