BEST OF AAPG: LONG LIVED EXHUMATION ON THE “PASSIVE MARGIN” OF EASTERN NORTH AMERICA: RESULTS FROM SONIC TRANSIT-TIME AND VITRINITE-REFLECTANCE ANALYSES IN THE NEWARK RIFT BASIN (Invited Presentation)

Many of the world's prospective hydrocarbon basins have undergone significant exhumation after their formation. Exhumation can significantly alter the petroleum potential of these basins by influencing the timing of source-rock maturation and hydrocarbon migration, by modifying reservoir quality, and by altering the integrity of hydrocarbon traps. Compaction-based studies using compressional sonic-log data in shales are important for the prediction of pore-pressure during drilling. These shale compaction trends can also shed light on the burial history of normally-pressured sedimentary basins. In this study, we use sonic transit-time analyses to estimate the magnitude of uplift and erosion of the Late Triassic-Early Jurassic Newark rift basin, one of the largest rift basins preserved on the passive margin of eastern North America. We compare these results with exhumation estimates from a basin-wide vitrinite-reflectance study. Results of sonic transit-time analyses from 11 wells show significant exhumation and erosion of syn-rift sedimentary rocks throughout the Newark basin. These exhumation and erosion estimates compare remarkably well with published estimates calculated from downhole vitrinite-reflectance data using the Dow (1977) method. The least exhumation (~1 to 2 km) occurred adjacent to the border-fault system in the northwestern part of the basin. The greatest exhumation (~4 to 6 km) occurred along the eastern hanging-wall side and throughout the southern half of the basin, exposing thick, high-TOC, black shales of the Lockatong Formation. Exhumation and northwest tilting likely began slightly before or during the rift-drift transition during the Early Jurassic. It ended before the deposition of Cretaceous coastal-plain sediments on the eroded rift basin. The eroded material likely contributed to infilling of the adjacent, subsiding post-rift Baltimore Canyon trough, which contains up to 13 km of sedimentary rock, 9 km of which is Jurassic. Both approaches for estimating exhumation, when used together, contribute to recognizing a more complete tectonic history for the Newark rift basin, and more importantly, to better understanding the post-rift evolution of the passive margin of eastern North America and other passive margins.