X-RAY FLUORESCENCE TRENDS ACROSS THE K-PG BOUNDARY, RANCOCAS CREEK, NEW JERSEY: IMPLICATIONS FOR EVENT STRATIGRAPHY AND ICHNOLOGY

New geochemical analyses corroborate the recent textural and low-field magnetic susceptibility trends across the heavily bioturbated, glauconite-rich, marine K-Pg succession at the Rancocas Creek outcrop, New Jersey. The lithologic shift ~15 cm was proposed as a more accurate contact between the Navesink (NF) and Hornerstown (HF) Formations traditionally placed at an observable change from chocolate brown to rich olive green (color change = 0 reference point). Point sampling of Thalassinoides isp. burrow fill and surrounding matrix, was performed at 5 cm intervals across the NF/HF boundary. Using a portable Niton X-ray Fluorescence (XRF) analyzer, samples were assayed to determine the geochemical variations across the depositional gradient. Whereas previous granulometric trends show a lithologic shift 15 cm above the current placement of the NF/HF boundary, the analysis of the same samples reveals a number of changes in elemental composition 10 cm above the color change: 4% increase in iron, 26% increase in potassium, 93% decrease in sulfur, and 29% decrease in aluminum content. These geochemical shifts, combined with the associated textural trends support a refined placement of the lithologic contact of the NF and HF somewhere within the 10-15 cm interval above the observable color change. Future research at other along-strike sites will test the current boundary placement through lithostratigraphic, ichnological, and geochemical correlations. The dynamic changes in geochemistry across the K-Pg boundary succession, complimented with recent ichnological and textural studies, provide key insights to the complex depositional history exposed along Rancocas Creek. This study has major implications for the placement of the NF/HF formational contact, as well as its relationship to the K-Pg event boundary, the Main Fossiliferous Layer, and the nature of the extinction interval in a marine setting.