Stratigraphy and structure of the Hopewell fault block,
Newark basin, NJ: Climatic and structural controls on sedimentation
Abstract--The Hopewell fault, which generally strikes northeast
and dips to the southeast, is a predominantly normal fault with a dip separation
of 2-3 km located in the Newark rift basin of New Jersey. In order to define
the geometry of the Hopewell fault and its associated structures as well
as the extent to which those structures influenced sedimentation, a 14-km-wide
area of the Hopewell fault and its hanging wall block was mapped. The deposits
in this area belong mostly to the middle part of the Late Triassic-age
Passaic Formation and have been continuously cored in the Titusville and
Rutgers drill sites. As seen in core and outcrop, the middle Passaic Formation
consists predominantly of red mudstone and minor sandstone (playa lacustrine
deposits) cyclically alternating with purple, gray and black shale (deeper-water
lacustrine deposits). The cyclical alternations were produced by fluctuating
lake levels driven by climatic changes with Milankovitch periodicities.
The non-red units are traceable across much of the study area, and their
distribution within the hanging wall block of the Hopewell fault reveals
three well-defined synclines separated by poorly defined anticlines, all
of which plunge gently to the northwest (toward the Hopewell fault). The
amplitude of folding decreases away from the fault, suggesting that the
folds may have been at least partially controlled by the Hopewell fault.
Some of the gray units are not laterally continuous across the entire mapped
area, and many display along-strike facies and color changes, suggesting
structural control on sedimentation. If so, faulting and perhaps folding
were coeval with sedimentation. Minor faults within the Hopewell fault
block strike northerly and east-southeasterly; the relative motion along
these faults is uncertain. The most prominent extensional joint set in
the mapped area strikes 040, while a secondary set strikes 010.