This chapter is the site report for the third continuously cored and logged borehole drilled onshore as part of the New Jersey Sea Level Transect. The geological background and scientific justification for the Transect are provided by Miller and Mountain (1994). The Transect is an integration of Ocean Drilling Program Leg 150 slope and rise drilling (Mountain, Miller, Blum, et al., 1994; Mountain, Miller, Blum, Poag, and Twichell, 1996), future shelf, and onshore Leg 150X drilling (Miller et al., 1994a, 1994b, this chapter). The Transect is intended to document the response of passive continental margin sedimentation to glacioeustatic changes during the Oligocene to recent "Icehouse World," a time when glacio-eustasy was clearly operating, and to document the ages and nature of Eocene and older "Doubthouse" sequences, a time when mechanisms for sea-level change are poorly understood (Miller et al., 1991b).
Determining relative sea level and evaluating the timing and facies changes within sequences requires the integration of studies from nearshore to deep-sea environments (e.g., Miller and Mountain, 1994). The goal of onshore drilling is to recover updip counterparts of well-developed sequences imaged on the continental shelf (Greenlee et al., 1988, 1992; Miller and Mountain, 1994). The Cenozoic shelf sequences have only been sampled by a few industry wells (Greenlee et al., 1992) and a few boreholes with discontinuous recovery (Hathaway et al., 1976); thus, the ages of the sequences were poorly constrained (1 m.y. or worse; Greenlee et al., 1992). These shelf sequences were traced on seismic profiles to the continental slope; Leg 150 (Mountain, Miller, Blum, et al., 1994; Mountain, Miller, Blum, Poag, and Twichell, 1996) drilled and dated the sequences on the slope, improving on preliminary dates provided by Deep Sea Drilling Program slope and rise drilling (Legs 93 and 95; Poag, Watts, et al., 1987; Van Hinte, Wise, et al., 1987). Although the slope-rise sites may be used to date shelf sequences, they yield little facies information. In contrast, drilling onshore not only provides another setting in which to date the sequences but also provides shallow-water (neritic and shallower) facies information that allows evaluation of sequence stratigraphic models (e.g., Posamentier et al., 1988).
The onshore drilling program was sponsored by the National Science Foundation, Earth Science Division, Continental Dynamics, and Ocean Drilling Program. Onshore drilling is a collaborative effort among Rutgers University, Lamont-Doherty Earth Observatory, the U.S. Geological Survey, and the New Jersey State Geological Survey. The JOIDES planning committee endorsed the onshore drilling as an ODP-related activity that was designated Leg 150X.
We drilled two boreholes in 1993 at Island Beach State Park (TD = 1223 ft [373 m] in Maastrichtian) and Atlantic City (TD = 1452 ft [443 m] in upper middle Eocene); preliminary results from these boreholes were published as Miller et al. (1994a, 1994b). The third borehole was drilled in March and April 1994 at Cape May (TD = 1500 ft [457 m] in upper Eocene). The onshore sites were located downdip, close to the present-day shoreline, to maximize the thickness (and minimize the number of hiatuses) of the Oligocene to middle Miocene section and to be close to offshore multichannel seismic ties (Fig. 1). The sites were chosen to maximize recovery of different portions of the section. The Cape May borehole recovered the most complete and thickest Miocene section because of its downdip location; boreholes to the north (updip) penetrated progressively older portions of the Paleogene. This strategy was successful in assembling a mosaic of coastal plain sequences that record uppermost Cretaceous to Holocene relative sea-level changes.
The Leg 150X Cape May borehole was selected to optimize recovery of the upper middle Miocene section (e.g., East Coast Diatom Zones 5-6 and younger), which isopach maps (fig. 3d in Sugarman et al., 1993) show attains maximum thickness in the Cape May peninsula. The only continuously cored coastal plain borehole to sample this section was updip at Belleplain State Park, New Jersey (Sugarman et al., 1993); the upper middle Miocene section is truncated north of Belleplain (Fig. 1). In addition, the Cape May borehole was selected for its thick Oligocene section (Olsson et al., 1980), the possibility of recovering upper Eocene strata (reported by Brown et al., 1972; Poag, 1985), and the proximity of MCS seismic ties obtained in Delaware Bay (Fig. 1). A rotary test well drilled on the western side of the Cape May peninsula by Anchor Dickinson Gas (AD#1 well; Brown et al., 1972) yielded reasonably well-preserved Oligocene foraminifers below about 1000 ft (305 m) (Olsson et al., 1980). Eocene strata below 1450 ft (442 m) yielded silicified microfossils, and we decided to limit penetration at Cape May to 1500 ft (457 m). The location chosen at the Coast Guard base in Cape May is downdip of the AD#1 well and is the most downdip (basinward) location drillable onshore in New Jersey. Rotary drilling 33 km (20 mi) across Delaware Bay at Lewes, Delaware (Oh25-02; Fig. 1) provided deep-water Oligocene successions below ~1220 ft (372 ft) (Benson, 1990). Our results show the Oligocene to Holocene sections are comparable (see below).
At all three Leg 150X coastal plain boreholes, unconformities were identified on the basis of physical stratigraphy (see below) and paraconformities inferred from biostratigraphic and/or Sr-isotopic breaks. Recognition of these surfaces allows identification of sequences. In general, the sequences recovered are shallowing-upward transgressive-regressive cycles, with well-developed erosional surfaces at their bases.
Facies changes within sequences (systems tracts) follow general patterns in the New Jersey coastal plain (Owens and Sohl, 1969; Owens and Gohn, 1985; Sugarman et al., 1993). A shell bed or glauconite sand at the base (= condensed section of Loutit et al., 1988; = late transgressive systems tract [TST] of Posamentier et al., 1988) is overlain by a silt, with a quartz sand at the top (= highstand systems tract [HST]; Sugarman et al., 1993). This results in a distinct gamma log signature with "hot" zones at the base and low values at the top (Sugarman et al., 1993). At Island Beach, we noted that Miocene sequences consist of clay-confining units at the base with quartz sand aquifers at the top (Miller et al., 1994b). The Oligocene to Miocene sequences at Atlantic City are similar, but they are more marine than at Island Beach; their bases are often marked by shell beds (Miller et al., 1994a). At the Cape May borehole, we encountered shell beds at the base and sands (often indurated) at top of Miocene sequences. At both the Atlantic City and Cape May boreholes, Oligocene sequences contain glauconite throughout; glauconite in the medial silts and upper sands is probably recycled from Eocene and older strata (Pekar and Miller, 1994). These successions represent shallowing-upward environments, with transgressive deposits at the base and regressive sands at the top.
These classic transgressive (TST) to regressive (HST) sequences have been recognized in the middle Atlantic coastal plain since the 1960s (e.g., Owens and Sohl, 1969). Lowstand systems tracts (LST) are apparently not represented in the coastal plain. Although flooding surfaces can be identified in the New Jersey coastal plain, it is often not clear where the maximum flooding surfaces (MFS) lies: it may be at the base, within, or at the top of the basal glauconite sands (Sugarman et al., 1995). If the MFS lies at the base of the glauconite sands, merging with the unconformity, then sequences are also parasequences (packages of sediments bounded by flooding surfaces; van Wagoner et al., 1990).
This report presents the lithostratigraphic, biostratigraphic, and Sr-isotopic data on which preliminary sequence stratigraphic studies of the Cape May borehole are based. Scientific results from the Island Beach, Atlantic City, and Cape May boreholes will appear in the Leg 150X Scientific Results volume in 1997.