Paper No. 8
Presentation Time: 9:00 AM-6:00 PM
A WHITE LAYER AT THE K/PG BOUNDARY IN MONMOUTH COUNTY NEW JERSEY - IMPACT RELATED OR POST-DEPOSTIONAL DIAGENISIS?
The K/Pg boundary is well exposed within the Crosswicks Creek basin in southern Monmouth County, New Jersey. It is represented by the uppermost Maastrichtian New Egypt Formation and Danian Hornerstown Formation. The New Egypt is composed of a chocolate brown micaceous glauconitic mud and is overlain by a sharp but bioturbated contact with the green glauconitic muddy sand of the Hornerstown Formation. A fossil concentration known as the main fossiliferous layer (MFL) is located within the bottom 30 cm of the Hornerstown. The process related to the formation of the MFL has been debated for many years. Obasi (et al. 20102) and Gallagher (2003) have proposed continuous sedimentation across the New Egypt/Hornerstown contact with the MFL being emplaced in situ. Landman (et al. 2007) suggest that the MFL is a fossil concentration due to a transgressive lag related to a diastem at the boundary. Within the Crosswicks Basin, there appears to be a discontinuous white layer at the top of the MFL. It consists of non-consolidated to crystalline lenses. The lenses are a few mms to up to 20 cms thick and can be as much as 2 meters wide. They are composed of scattered glauconite grains within a white matrix. The matrix, which makes up over 90% of the composition of the white layer, was determined by XRD analysis to be siderite. Two possible hypotheses for the formation of this white layer are examined. The first relates it to the impact and events associated with the K/Pg bolide impact. The second suggests post-depositional diagenitic processes related to concretion formation. The fact that it is not universal and only occurs locally, forms lens shapes of mostly siderite and is stratigraphically positioned at a permeability change suggest that the process of formation was diagenetic concretion formation possibly related to microbial activity leading to reducing conditions not directly related to the impact event at the end of the Cretaceous.