Post-Paleozoic activity - Lamont-Doherty Earth Observatory ...

W. Manspeizer and Others
OKM 50 100 150 200 250
kORGES1 BANK ' BASIN'
I
LINE# 19 LINE#[
Figure 5. Cross section of Georges Bank basin, along USGS seismic line 19. Magnetic anomaly profile is
shown across the top. Ages of sedimentary units are indicated by standard abbreviations. Magnetic
depth estimates to basement are shown, as are the locations of the COST G-1 and COST G-2 wells, the
rift and post-rift stratigraphic sequences, and the post-rift unconformity (from Klitgord and Hutchinson,
1985), with alternative interpretation of the basin, based on palynomorphs extracted from the COST
G-2 cores shown in red. The COST G-2 well, drilled to a depth of 6,667 m, is 1,769 m deeper than the
COST G-1 well and bottoms in Late Triassic salt, which is underlain by synrift strata that we speculate
include rocks of Permian (?) to Triassic age.
on a transitional crust of eastward-dipping, thrust-imbricated
ramps of Precambrian Grenville basement and younger metased-
iments. The bedrock geologic map of Massachusetts (Zen and
others, 1983) depicts the eastern border of the Hartford-Deerfield
basin as a reactivated west-dipping listric normal fault that, ac-
cording to MacFayden and others (1978), was a high-angle re-
verse fault of possible late Paleozoic age. Bain (1932), more than
50 years ago, suggested that the eastern border fault of the Hart-
ford basin was a pre-Triassic thrust.
In like manner, the western border fault of the Newark basin
(Fig. 6) lies along an older, gently dipping stack of imbricate
thrust slices (Ratcliffe and Burton, 1985). The narrow corridor or
neck connecting the Newark and Gettysburg basins occurs along
a major east-west lineament (Figs. 1, 3; Plate 5) that includes
the N40°-Kelvi lineament (Van Houten, 1977; Manspeizer,
1980; the Transylvania continental fracture zone of Root and
Hoskins, 1977), the sinistral Chalfont fault (Fig. 6; Sanders,
1963), and the prominent east-west deflection of the basement
hinge zone (Fig. 5; Hutchinson and Klitgord, 1988). Struc-
turally paried basins with listric faults and outward-dipping strata
of the Long Island platform (e.g., the Newark-New York Bight,
Nantucket-Atlantis [Fig. 71 and Long Island basins [Fig. 81) also
occur along the lineament, suggesting that they may have formed
as extensional or transtensional basins along east-west-trending
transforms, similar to those depicted by Bally (1 98 1, Figs. 21 -24;
and Plate 5A).
In the central and southern Appalachians, reflection seismic
studies of the Culpeper basin indicate that the basement consists
of stacked thrust sheets of Proterozoic and early Paleozoic age
(see discussion by Costain and others later in this chapter).
Deeply inclined reflectors also occur beneath the Norfolk basin
(Fig. 9), which lies on the passive margin east of the Culpeper
basin. The Richmond-Taylorsville, Roanoke, Farmville, and
Scotsburg basins of North Carolina and Virginia seem to occur
along a wrench-fault complex that is superimposed over a reacti-
vated Alleghanian thrust belt, including the Hylas fracture zone
(Glover and others, 1980; Bobyarchick, 1981; Ressetar and Tay-
lor, 1988; and Venkatakrishnan and Lutz, 1988). The Chatham-
Stony Ridge fault zone of North Carolina, the dominant
pre-Mesozoic structural control for the development of the Dan-
ville basin (Thayer and others, 1970; Glover and others, 1980),
may extend south into the Davie County basin and perhaps north
into the Scottsville and Culpeper basins (Swanson, 1986). Seis-
mic reflection profiles indicate that the Riddleville basin, which
lies beneath the Coastal Plain cover of Georgia, is bound by a
listric normal fault (the Magruder fault) that dips east and merges
in the subsurface with the Augusta thrust fault of late Paleozoic
age (Cook and others, 1981; Peterson and others, 1984). It is
tempting to project the Augusta fault zone north to the Dunbar-
ton basin (Marine and Siple, 1974) and south to the main South
Georgia basin (Daniels and others, 1983), and to speculate that
these basins were activated along a Paleozoic suture (see Thomas,
1988; Chowns and Williams, 1983; and Nelson and others,
1985).
STRUCTURE
Most Atlantic margin rift basins containing Newark Super-
group strata are asymmetric, bounded on one side by a system of
major high-angle normal faults and on the other side by a gently
sloping basement with sedimentary overlap and/or by secondary
normal faults. The exposed basins are aligned with right-stepping