The rifting of Pangaea during the Late Triassic and Early Jurassic produced a series of rift basins along the eastern margin of North America. These basins were filled with cyclic, continental lacustrine sediments and intruded by a series of tholeiitic basalt sills. One of the best-known basins is the Newark Basin.

Over the past several years we have been collecting gravity and magnetic data in east-central Pennsylvania for the purpose of interpreting subsurface structures. Gravity data were collected along traverses as well as on a quarter-mile grid. Data were reduced to simple Bouguer values. Total-field magnetic measurements were also taken.

The first goal in collecting these data was to model the subsurface structure of the Coffman Hill and Quakertown sills (Malinconico et al., 1999). Once that was completed, we expanded the geophysical coverage to include the northern margins of the Newark Basin. Since the intrusions fall close to the basin margin, we are now working to separate the effects of the intrusion from the margin structure. We will present maps documenting the spatial relationship between the geophysical (gravity and magnetic) anomalies and the known surficial structure as well as models of the subsurface structure of the sill and basin margin.