New York Bight Apex: Geologic Setting
Early investigations of the subsurface structure of the continental shelf off the
New York-New Jersey metropolitan area were seismic-refraction studies by Ewing
and others (1950; 1963) and Brown and others (1961). These studies identified
a large basin off the coast of New Jersey adjacent to a shallow buried platform
south of Long Island, latter named the Baltimore canyon Trough and the Long
Island Platform, respectively (Fig. 1).
|Figure 1. Index map showing the major regional geologic features of the study areas (modified from Uchupi and others, 2001).
seismic-reflection investigations of the sedimentary sequences in the Long Island
Platform and Baltimore Canyon Trough (Robertson, 1964; Emery and Uchupi, 1965;
Uchupi and Emery, 1967; Garrison, 1970; Schlee and others, 1976) identified
acoustic reflectors within the upper Late Jurassic-Cenozoic strata of the Baltimore
Canyon Trough and Long Island Platform. They allowed for a rudimentary reconstruction
of the effects of post-Triassic rift sea-level oscillations on stratigraphic
evolution of the shelf and identification of five regional acoustic horizons
within the upper sedimentary units of the Long Island Platform. A major fault,
the New York Bight Fault, trends along the western margin of a Mesozoic rift
basin on the western edge of the Long Island Platform (Hutchinson and Grow,
1984). There is no evidence for disruption or internal deformation associated
with the New York Bight Fault within the overlying Quaternary sedimentary deposit
(Schwab and others, 1997a).
seismic-reflection data were collected in 1968 to help evaluate potential aggregate
resources off the south shore of Long Island (Williams, 1976). Although these
profiles were located approximately 1.5 km apart and are of relatively poor
quality compared to present standards of digitally acquired data, Williams (1976)
was able to create a rudimentary description of the inner-shelf sedimentary
sequences. Williams (1976) indicated that upper-Cretaceous coastal plain strata
are unconformably overlain by Pleistocene sediments south of Long Island, with
no preservation of Tertiary sedimentary units. This regional unconformity, first
identified by Emery and Uchupi (1965), is believed to have been created initially
during mid-Oligocene and is correlative with the Atlantic Coastal Plain Reflector
of Poag (1978) and Hutchinson and Grow (1984). The unconformity also has been
identified as a contact between late Cretaceous to early Tertiary strata and
overlying Pleistocene sediment under the adjacent subaerial areas of New Jersey
and Long Island, New York using well-log data (Suter and others, 1949; Enright,
1970). In many areas on the inner-continental shelf, the Pleistocene sediment
cover is thin or missing and the late Cretaceous to early Tertiary Coastal Plain
strata crop out on the sea floor (Williams and Duane, 1974; Williams, 1976;
Schwab and others, 1997a, 1997b, 2000).
|Figure 2. Map of the inferred positions of the proglacial lakes formed in the late Wisconsin; glacial stage 2 during period of Laurentide ice sheet retreat (modified from Brighham-Grette, 1988).
Quaternary stratigraphy of the New York Bight continental shelf was strongly
impacted by Pleistocene glaciation. The area was situated in front of the terminus
of the Wisconsinan Laurentide continental ice sheet (Fig. 2). Thus, it was affected
by glacial isostatic rebound, forebuldge collapse, and re-emergence (Dillon
and Oldale, 1978) and was characterized by global sea-level fluctuations described
by Shackleton and others (1988). The repeated emergence and submergence of the
continental shelf led to the dissection of the Cretaceous to early Tertiary
coastal plain strata and Quaternary section by subaerial fluvial incision during
the regression and shoreface ravinement during the transgression. This has resulted
in Wisconsinan glacial outwash-plain and modern barrier-island complexes resting
unconformably over a sequence of pre-Wisconsinan Pleistocene glaciofluvial and
shallow marine units (Suter and others, 1949; Soren, 1978; Oldale and Coleman,
1992). These processes have left a lithologically complex Quaternary stratigraphic
record composed of age-mixed deposits resulting from similar physical processes
but differing widely in the time of genesis.
170-km-long Hudson Shelf Valley, the
largest physiographic feature on the continental shelf, bisects the New York
Bight region (Fig. 3). The Hudson Shelf Valley is the submerged seaward extension
of the ancestral Hudson River drainage system that, unlike most incised valleys
on the Atlantic shelf, has not been infilled with sediment.
|Figure 3. Index map showing the location of depositional lobes thought to be the result of catastrophic drainage of glacial lakes 12,000 - 14,000 yrBP (modified from Uchupi and others, 2001).
The valley head is located in a broad shallow basin (Christiansen Basin) and
extends offshore 20-40 m below the shelf surface to a seaward terminus at a
shelf-edge delta (Ewing and others, 1963; Emery and Uchupi, 1972; Uchupi and
others, 2001). The ancestral Hudson River is hypothesized to have begun to develop
in the Late Cretaceous when post-Atlantic rifting caused continued uplift and
tilting of the margin, resulting in landward erosion and marginal seaward growth
that continued into the Tertiary (Weiss, 1974). The Hudson Shelf Valley is thought
to have been repeatedly downcut during periods of Pleistocene marine regression
(Suter and others, 1949; Weiss, 1974). This downcutting possibly was amplified
by the proposed catastrophic drainage of late Wisconsinan glacial lakes 12,000
- 14,000 yrBP (Newman and others, 1969; Uchupi and others, 2001). The shoreline
was located approximately at the 60 m isobath at this time (Thieler and others,
1999). At 12,000 - 14,000 yr BP, the large glacial lakes north of the New York
Bight are thought to have breached the moraine front at the Verrazano Narrows
and other locations in New Jersey and New York (Newman and others, 1969; Soren,
1971; Lovegreen,, 1974). Boring data at the Verrazano Narrows indicate that
more than 100 m of Pleistocene and Cretaceous sedimentary material was eroded
as a result of this breaching event(s), along with most of the lacustrine sediment
deposited the previous 8,000 yr (Newman and others, 1969). Uchupi and others
(2001) recently proposed that late Wisconsin erosion of the Hudson Shelf Valley
and deposition of sediment lobes on the outer shelf (catastrophic flood morphologies)
were a consequence of this catastrophic drainage of glacial lakes. Further insight
into the age and origin of these lobe deposits remains speculative without sediment
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