QUARTZ PROVENANCE ACROSS THE K-PG BOUNDARY IN MONMOUTH COUNTY, NEW JERSEY

Landman et al. (2007) identified the Cretaceous-Paleogene (K-Pg) boundary near the top of the Upper Tinton Formation in the Manasquan Basin in New Jersey. Above the iridium spike associated with the bolide impact is a 20-30 cm thick fossilferous layer called the Pinna Layer interpreted by Landman et al. (2007) as a post-impact survivor community. O’Dea et al (2008) investigated the provenance of quartz grains in the Pinna Layer using an SEM equipped with a cathodoluminescent arm, finding that more than half of the quartz in the layer showed CL signatures typical of authigenic quartz. The authigenic grains were often in clusters and typically 0.5-1mm in diameter. According to O’Dea et al (2008) the detrital grains showed no signs of post-depositional solution and could not have been the source of quartz for the authigenic grains. O’Dea suggested the quartz formed from the dissolution of siliceous plankton, suggesting that post-impact diatom blooms were the source and that precipitation of this readily mobilized silica produced the authigenic quartz grains. This study seeks to expand on these findings by analyzing ratios of detrital and authigenic quartz in the layers above and below the Pinna Layer. These layers are described by Landman et al. (2007) and include Tinton Fm proper (below the Pinna Layer), the Pinna Layer, the Burrowed Unit at the base of the Hornerstown Fm, the and lower Hornerstown Fm. Quartz grains were analyzed from each section using a Hitachi S-4700 SEM with a GatanMono cathodoluminescence arm. All samples were carbon coated to prevent electron charging. Comparisons between polished thin-sections and whole grains using both the panchromatic and monochromatic settings returned substantially similar results so clean, unpolished, carbon coated grains were used. Findings suggest that the ratio of authigenic to detrital quartz increases upsection, reaching over 70% in the Hornerstown Fm. While the Hornerstown Fm is associated with a depositional lag, it has a much higher ratio of authigenic quartz, suggesting that the post-impact diatom blooms persisted into the Early Paleogene. Hollis et al (1995) found similar evidence for post-impact diatomaceous blooms off the coast of New Zealand.