NEW JERSEY AS A MICROCOSM OF THE CRETACEOUS/PALEOGENE BOUNDARY EVENT: MASS EXTINCTION, RECOVERY AND MOBILE IRIDIUM

The radiation of 3 surviving planktonic foraminiferal species into a diverse Paleocene fauna following the Cretaceous/Paleogene (K/Pg) boundary event took over 3 million years and is associated with a significant perturbation in the oceanic carbon cycle, recorded as a collapse in vertical water column δ¹³C gradient. Though these events have been linked to the Chicxulub impact through a large Iridium (Ir) anomaly, recent studies in New Jersey (NJ) have suggested that extinction of Cretaceous macrofossils may have post-dated the Ir anomaly (Landman et al., 2007). We cored 7 localities in NJ and measured Ir across the K/Pg boundary to test the link between the mass extinction horizon and the Ir. We observed a direct link between the Ir enrichments and the mass extinction of marine plankton, though apparent post-depositional remobilization of Ir is also seen in two localities. At Meirs Farm, Buck Pit, and Search Farm coreholes Ir anomalies correlate with the extinction horizon. The large Ir anomaly of 2.5 ppb at Bass River at the base of the 6 cm thick spherule layer and the modest Ir anomaly of 0.5 ppb at Tighe Park situated below a 20 cm thick sandy Pinna bed are interpreted as resulting from remobilization of Ir down section by 6 cm and 20 cm, respectively. We propose that Ir is in place (i.e. correlatable with the extinction level) in clay-rich sections and displaced in sandier sections, likely a result of post-depositional changes in redox conditions. At Inversand Pit a small Ir concentration of 0.28 ppb is seen in the middle of the 40 cm thick Main Fossiliferous Layer, which is a concentrated, basal Paleocene fossil bed containing in situ and reworked vertebrate and invertebrate fossils. Biostratigraphic studies document that Fort Monmouth and Double Trouble coreholes also recovered the K/Pg boundary; Ir results will be presented for these cores. Foraminiferal δ¹³C data from Bass River show a collapse of export production at the K/Pg, and gradual recovery of vertical structure of shallow, intermediate, and deep dwellers over 3 million years. Future work will include measuring redox sensitive trace elements through the sections to further test our interpretation of remobilization of Ir in NJ strata.