PALEOSOLS AND PEDOGENESIS OF THE POTOMAC FORMATION IN DELAWARE AND NEW JERSEY

The Potomac Formation is a thick succession (10-100s of meters) of interbedded fluvial channel sands and paleosol deposits, and represents the major depositional package of non-marine coastal plain strata along the eastern margin of North America during the Early to Late Cretaceous (Aptian, Albian and Cenomanian stages). This study uses five continuous cores from the southern New Jersey and northern Delaware coastal plain to evaluate the Potomac Formation, focusing on the paleosols because they provide a proxy record of climate, environment and surface stability conditions during their formation.

The use of multiple cores provides both a temporal and spatial record to evaluate this landscape during this period of global change. The studied paleosols offer a record of the evolution of terrestrial coastal plain environments in a greenhouse climate. Paleosols from these five cores were identified and described; the described morphology (color, horizonation, clay fabrics, root/burrow traces), clay mineralogy, and crystallinity is a function of their pedogenic development and surface environment (redox, base-level, drainage conditions). Each core contains multiple paleosols, ranging in thickness of cm to m scale, and varying in pedogenic rate from compound to composite and cumulative soils. Maturity level was either very mature Ultisol-equivalent paleosols, with strongly hued mottles of reds and purples, or less mature Inceptisol/Entisol-equivalent paleosols that offer only weakly defined features. The hydromorphic conditions within the coastal plain can be assessed not only by paleosol maturity but other observed features including the micromorphology varying between soils with high birefringence, sepic plasmic clay fabrics indicative of periods of wetting and drying, to those soils having weak birefringence, randomly oriented clay fabrics often formed in continuously saturated conditions.

This project provides part of a multidisciplinary study utilizing geophysical logs, biostratigraphy, and isotope stratigraphy towards a more complete understanding of the facies relationships on the coastal plain, as well as providing insight into the connectivity of buried strata within the Potomac Formation.