This part of the U.S. Atlantic margin is well suited for the study of sea-level changes during the Oligocene to Holocene "Icehouse" interval for several reasons:
2.Good biostratigraphic control is ensured by the mid-latitude setting (Poag, 1985; Olsson and Wise, 1987; Poore and Bybell, 1988; Greenlee et al., 1992). Upper Eocene-Miocene sediments of this region have adequate carbonate to utilize strontium-isotope correlation techniques (Sugarman et al., 1993; Miller et al., 1991b, 1994, 1995; Miller and Sugarman, 1995). Pleistocene stratigraphic control afforded by integration of nannofossil and physical properties data is also excellent (better than 20 k.y. resolution; Mountain, Miller, Blum et al., 1994).
3.Tectonic subsidence has been slow (<10 m/m.y.) and well defined throughout the Cenozoic (Steckler and Watts, 1982); a situation that favors the preservation and identification of glacial-eustatic fluctuations in the stratigraphic record (Vail et al., 1977).
4.There is little seismic or outcrop evidence to suggest major faulting, rotation, or other medium-to-large scale disturbances of the Cenozoic section (Poag, 1985), although some differential subsidence may have occurred between the Delmarva Peninsula (Deleware/Maryland/Virginia) and New Jersey (Owens and Gohn, 1985).
5.A substantial body of useful data, including seismic profiles (collected at various
frequencies) and data derived from boreholes and submarine outcrop collected by DSV
Alvin, already exists for this margin (Fig. 1; Hathaway et al., 1976; Ryan and Miller, 1981;
Poag, 1978, 1980, 1985; Poag, Watts et al., 1987; Kidwell, 1984, 1988; Olsson et al.,
1987; Greenlee et al., 1988, 1992; among others). This includes data from Deep Sea
Drilling Project (DSDP) Legs 93 and 95 (e.g., Site 612, Fig. 1), which represent an attempt
to synthesize the overall stratigraphy and structure of the New Jersey margin (van Hinte,
Wise et al., 1987; Poag, Watts et al., 1987). However, the shallowest site (Site 612) was
drilled at a water depth of 1400 m, and it proved to be poorly located for sampling
Oligocene-Miocene strata (Miller et al., 1987). Nonetheless, these earlier legs set the stage
for more detailed studies, such as the MAT, where the objectives are to improve the dating
resolution of unconformity surfaces and to do so at sites where the water depths are
shallow enough to be sensitive to eustatic variations.
Leg 150 (June-July, 1993; Mountain, Miller, Blum, et al., 1994) capitalized on the Ewing shelf-to
slope imaging and drilled four locations on the slope (Sites 902-904 and 906) at water depths of
between 445 and 1134 meters below sea level (mbsl) (Fig. 1). These sites document the age and
facies of sediments associated with a total of 22 lower Eocene to mid-Pleistocene reflecting
surfaces tentatively interpreted as, or correlated landward with, sequence boundaries (see Fig. 5 for
a synthesis of Oligocene-Miocene results). Integrated bio-, magneto-, and strontium-isotopic
stratigraphy yield temporal resolution approaching several hundred thousand years (Miller et al.,
1995). In most cases, interpreted sequence boundaries are associated with little or no temporal
hiatus; many are expressed by a slight coarsening of sediment transported to the slope, it was
presumed, during low stands of sea level.
To complement the Leg 150 results, MAT proponents launched a land-based drilling program with support from ODP, the National Science Foundation (NSF), and the U.S. and State of New Jersey geological surveys (Miller et al., 1994). Primary objectives of these onshore boreholes (Leg 150X and related; Fig. 1) have been to date Late Cretaceous to Cenozoic sequences, including the Paleocene-Eocene "Doubthouse" section, and to evaluate facies arrangements in an updip setting. Thus far, four holes have been cored and logged, all at sites close to the modern shoreline (Fig. 1). Oligocene to middle Miocene sequence boundaries in both onshore and Leg 150 boreholes appear to correlate with prominent d18O increases, consistent with the hypothesis that these surfaces developed during global lowering of sea level (Mountain, Miller, Blum, et al., 1994; Miller, Mountain et al., 1996a, b). The ages of these sequence boundaries also compare well with the timing of the Haq et al. (1987) "global" boundaries (Miller et al., 1996a,b). Recently completed drilling at Bass River, New Jersey (to be designated Leg 174AX) has recovered a complete Cretaceous/Tertiary boundary section (K.G. Miller, per. com., 1996).
Facies successions onshore are generally well developed for the Paleocene through middle Miocene, with a transgressive shell bed or glauconite sand at the base of each sequence and quartz sand at the top (upper part of the highstand systems tract; Miller et al., 1994). Onshore drilling has, thus, provided important data for regional profiles, but all of the boreholes are landward of the Oligocene-Miocene clinoforms imaged in seismic reflection data beneath the shelf (Figs. 2 and 3). The shelf sites, to be tackled for the first time as the focus of Leg 174A, are the ones most critical for estimating amplitudes of sea-level change during the "Icehouse" interval (see below).
The New Jersey margin is one of two study areas recently selected by the U.S. Office of Naval Research (ONR) for a multiyear initiative it has termed "Strata Formation on Margins" (STRATAFORM). Together with studies of the contrasting margin off Northern California, the goal is to understand the range of factors affecting the deposition and preservation of shelf and slope stratigraphy (Nittrouer and Kravitz, 1995). Off New Jersey, the missions of STRATAFORM and MAT coincide.
As a result, both ONR and JOI supported a consortium of investigators from the University of Texas Institute for Geophysics (UTIG), Lamont Doherty Earth Observatory (LDEO), and Rutgers University to collect, analyze, and interpret high-resolution MCS data on the New Jersey shelf and upper slope in support of proposed drilling in summer 1995 (Fig. 1). These data, which include a series of detailed "hazards" seismic grids mandated by ODP (Fig. 4), augmented a substantial set of regional geophysical and geological data that includes (Fig. 1): (1) 60-fold MCS profiles collected by the R/V Maurice Ewing from the inner shelf to the rise (see Fig. 3 and MAT-13 Site Summary); (2) 2D and 3D single-channel seismic (SCS) seismic grids (using a Huntec deep towed system) and associated vibracores collected by UTIG in 1989 and 1993; (3) commercial MCS profiles collected during the 1970's in a dense grid (~2.5 km line spacing) across the outer shelf and upper slope (Fulthorpe and Austin, in press); and (4) multibeam bathymetry/backscatter coverage of the whole area using a commercial Simrad EM-1000 system (Goff et al., 1996).
The 1995 MCS survey consisted of two interwoven track plans and missions: (1) hazards-type survey grids at eight proposed shelf sites to meet MAT goals set by the JOIDES Pollution Prevention and Safety Panel (hazards surveying was funded by both JOI and ONR); Sites MAT 8B and -9B (Fig. 4) were approved for drilling by both JOIDES and ODP/TAMU safety panels in September 1996; and (2) a regional grid (Fig. 1) across the outer shelf and upper slope (funded by ONR), to achieve both STRATAFORM objectives and MAT goals by tying Leg 150 sites to the shallower shelf stratigraphy to be sampled by Leg 174A.
In conjunction with the earlier seismic data (Fig. 1), these profiles will allow us to: (1) determine
the configuration of buried stratal surfaces and their accompanying acoustic characteristics across a
wide range of depositional environments; (2) establish links among the various elements of the
STRATAFORM initiative; and (3) tie well-dated Leg 150 sequences and other upper slope data to
coeval shelf (Leg 174A) and onshore (Legs 150X/174AX and related) sections.
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