A model for the structural evolution of the Newark
basin
Abstract--The Newark basin of N.Y., N.J., and Pa. is an eroded early
Mesozoic half-graben formed during the rifting phase of the breakup of
Pangea. The border fault system, active during sedimentation, consists
of reactivated Paleozoic thrust faults. The basin can be divided into three
subbasins with different styles of deformation and sedimentary record.
The Delaware River subbasin contains the smallest volume of Jurassic sedimentary
rock and is cut by the Flemington and Hopewell faults, twice repeating
the stratigraphic section. Extension was partly taken up on the border
fault and partly on the Flemington and Hopewell faults, resulting in less
basin subsidence and smallest preservation of Jurassic sedimentary rocks.
In contrast, extension was almost exclusively taken up on the border fault
in the New Jersey subbasin, resulting in greater basin subsidence and greater
preservation of Jurassic sedimentary rocks. The Flemington and Hopewell
faults probably originated in the E. Jurassic [note: now thought to be
L. Triassic] as splays of the border fault because of the shallow (or shallowing)
dip of the border fault and/or variations in fault geometry at depth. The
Chalfont transfer fault separates the Delaware River and Pennsylvania subbasins
and accommodates variations in strain between them. The basin strata generally
dip toward the border fault, with younger strata dipping the least and
progressively onlapping the hanging wall basement block. Balanced cross-section
construction which obeys the above constraints indicates that (1) the border
faults of the Newark basin either shallow with depth or were part of a
series of parallel, planar faults which rotated domino style during extension
[note: this view no longer prevails; see Schlische, 1992, GSA Bulletin];
and (2) the Flemington and Hopewell faults were not reactivated Paleozoic
faults. The high extensions required of the domino model make this end-member
unlikely. The extension direction for the L. Triassic-E. Jurassic was parallel
to the Chalfont transfer fault, i.e., east-southeasterly.