GEOCHEMISTRY OF SEDIMENTARY ROCKS AFFECTED BY CONTACT METAMORPHISM FROM THE INTRUSION OF THE PALISADES SILL

An outcrop of the contact between the base of the Palisades Sill and the Stockton Formation of the Newark Basin sedimentary sequence has been exposed by recent construction at North Bergen, NJ. We have collected samples from several transects through the metamorphic aureole from close to the contact with the sill, into unaltered sedimentary rocks. Previous studies have concluded that there has been Na-metasomatism in rocks in contact with the Palisades Sill, and that this has resulted in the mobilization of other elements, including rare earth elements. However, none have investigated a full suite of major, trace and rare earth elements in small contiguous transects from the contact into unaltered sedimentary rock. This locality provides the perfect field site for such an investigation.

Field investigations also revealed some interesting structures within the altered sedimentary rocks at this site. While in some places the original sedimentary structures, such as channel deposits, are clearly visible right up to the contact, at other locations the sediments have clearly been remobilized as the sill was intruded. This has resulted in the formation of at least one clastic dike. Analysis of major, trace and rare earth elements reveal changes resulting from the metamorphism, while mineralogical changes are interpreted from thin sections. Sedimentary logging during sample collection in the field, allows us to separate variations due to metamorphism from sedimentological variation within the Lockatong Formation, and to compare the sections where there has been sediment remobilization with those where there has not.