RIFT-BASIN DEVELOPMENT: NEWARK RIFT BASIN, EASTERN NORTH AMERICA

We have interpreted and restored seismic line NB-1 through the Newark rift basin of eastern North America. Our seismic interpretation, together with well and field data, show that the rift basin is asymmetric, bordered on the northwest by a low-angle, SE-dipping normal-fault zone. Our restoration suggests that the Newark basin, like other rift basins, underwent four distinct stages of development: rift-basin initiation (Stage 1), widening (Stage 2), dissection (Stage 3), and post-depositional tilting and erosion (Stage 4). During Stage 1 (Late Triassic), regional NW-SE extension reactivated a pre-existing compressional fabric to form the low-angle, border-fault zone. During Stage 1, the embryonic rift basin was relatively narrow, and the synrift strata noticeably thickened toward the border-fault zone. Displacement on the border-fault zone exceeded 4 km. During Stage 2 (Late Triassic), the rift basin became much wider, and the synrift strata gradually thickened toward the border-fault zone. Without a regional perspective, these synrift strata could be mistaken for postrift strata because of their very gradual thickening toward the border-fault zone. Despite this seeming lack of growth, however, displacement on the border-fault zone exceeded 7 km during Stage 2. During Stage 3 (mostly Early Jurassic), several kilometers of additional synrift strata and volcanics filled the rift basin, deeply burying and compacting the older synrift strata. Additionally, several large intrabasin normal faults dissected the rift basin. At the end of Stage 3, the cumulative displacement on the border-fault zone exceeded 22 km. During Stage 4, the synrift strata were tilted 10 to 15 degrees toward the border-fault zone. Although large-magnitude synrift extension could produce the tilting and uplift, experimental models of basin inversion indicate that postrift shortening also could produce this deformation.