ANALYZING THE THREE-DIMENSIONAL DISTRIBUTION OF A SHALLOW-MARINE BONEBED IN THE LOWER HORNERSTOWN FORMATION AT EDELMAN FOSSIL PARK, NJ

The Jean and Ric Edelman Fossil Park in Mantua Township, NJ, is significant in that it is one of the few sites on Earth where a mass death assemblage can be traced directly to the K-Pg bolide impact. Our excavations of a 1m x 1m x 0.6m deep area crossing the K-Pg boundary in the lower Hornerstown and upper Navesink formations yielded over 1,300 specimens with three-dimensional data. Previous research has identified two distinct layers within this span: an “Oyster Layer” with 80-90% incidence of Pycnodonte dissmiliaris; and the Main Fossiliferous Layer (MFL) about 30cm above the contact with the underlying Navesink Formation, with a Simpson Diversity Index roughly twice that of the “Oyster Layer.” However, such 2D analysis was limited, as it was impossible to discern three-dimensional distribution patterns of faunal diversity. We used ArcGIS Pro to map every specimen. Diversity, occurrence, and spatial patterns were explored through minimum bounding volumes via concave hulls. Transparent boxes around the formerly-defined MFL and oyster layer displayed possible heights where definitions could be modified to accommodate new 3D information. Concave meshes, grouped by taxon, were used to illustrate overlapping distributions, as well as spatial variability between taxa occurrences. A four-quadrant system was also implemented to better visualize the length-width dimensions of fossil distributions in 3D space. Such information allows for greater detailed description of the MFL and “Oyster Layer” within the Hornerstown Formation, as well as the ability to investigate the geometry of the MFL within the Formation. This analysis suggests that the bonebed slopes higher in our northwest quadrant, with greater faunal diversity of the MFL 33-39 cm above the Navesink Formation. However, a sloped geometry does not match sedimentological understanding of this area as massive suspension fallout, and it also does not align spatially with anomalous quartz pebble distribution. Enhanced understanding of the spatial preservation of fossils within the MFL may thus be used to further paleontological and geological understanding of the K-Pg impact event and the mechanics of the infamous mass-death event which followed.