NOT JUST FOOL'S GOLD: XRF AND SEM ANALYSIS OF THE EFFECTS OF PYRITE ON A BIOTURBATED K-PG OUTCROP

Recent low-field magnetic susceptibility (MS) studies have revealed substantial shifts across the contact between the Late Cretaceous Navesink Formation (NF) and the Early Paleogene Hornerstown Formation (HF) at Rancocas Creek, New Jersey. These MS shifts accompanied changes in lithology across an intensely bioturbated marine glauconite-rich succession and also to estimate glauconite maturity. In addition to lithologically driven susceptibility trends, high concentrations of diagenetic pyrite on Pycnodonte sp. oysters have yielded anomalously high values of 800-2500 mSI. Pyrite was also found to be coating the low-paramagnetic glauconite grains of the HF, causing heightened levels of MS. The new effort focuses on the abundance and effects of microscopic pyrite crystals on glauconite grains across the NF/HF contact boundary. SEM scans of grain mounts reveal ~6 mm pyrite crystals growing on glauconite grains. XRF analysis across the section revealed high content of iron and sulfur at the top of the NF. In the lower HF, the sulfur content drops 93% and iron increases by 4%. Tracking changes in iron concentration and the amount and distribution of pyrite has major contributions to future MS applications in K-Pg research. Spikes in MS can be associated with iron-rich horizons or concentrations of pyrite-coated grains. Future SEM analyses will focus on image scan maps of individual grains that can provide clues to glauconite zoning and aid in quantifying the contribution of highly paramagnetic pyrite. Our findings have broader implications to redox chemistry along the seafloor during an important extinction interval and to differential diagenetic effects on body fossils and thalassinid burrow fill and matrix.