THE PROVENANCE OF EXOTIC FOSSILIFEROUS PALEOZOIC BOULDERS EMBEDDED IN QUATERNARY SEDIMENTS OF THE NEW JERSEY ATLANTIC COASTAL PLAIN

A field of more than 200 exotic boulders scattered over an area of 150 hectares, was discovered in a suburban residential area in Southwestern New Jersey, USA on the unconsolidated Quaternary deposits of the Atlantic Coastal Plain (ACP). Half of the boulders are overtly fossiliferous, harboring tentatively identified Devonian fossils dominated by Plantae, Archaeopteris and Psilophyton but include vertebrates; Antiarch placoderms cf. Pterichthes, Ostracoderm cf. Cephalaspis, invertebrates; gastropod cf. Pleurotomaria tuboides and ichnofossils; Chondrites fabrics and Helicodromites correlative with formations in southcentral New York State. Observed boulder dispersal was eight clasts per hectare but Ground Penetrating Radar (GPR) reconnaissance revealed higher density in the subsurface. Borehole stratigraphy failed to reveal the suspected Pleistocene boulder-bearing stratum. The boulders exhibit faceted, plate and block shapes, some with polished faces and striations, suggesting glacial derivation even though the field is more than 150 kilometers south of the terminal moraines of Pleistocene glaciation crossing the northern part of the state. Comparison of generally accepted fluvial with glacial transport modes concludes that the boulders were ice-rafted into the study area and deposited as melt out dropstones during a sea level highstand when the regional lithosphere was glacioisostatically depressed below the eustatic drop in sea level associated with glacial epochs. The age of the host sediments indicates emplacement during the Middle Pleistocene. These observations have important implications for continental glaciology particularly in areas proximate to sea coasts.