BACKGROUND AND OBJECTIVES

This chapter is the site report for the fifth continuously cored and logged borehole drilled onshore as part of the New Jersey Sea Level Transect. The first three sites (Fig. F1) were drilled at Island Beach (March-April 1993), Atlantic City (June-August 1993), and Cape May (March-April 1994) as part of ODP Leg 150X (Miller et al., 1994a, 1994b, 1996), the landward continuation of slope drilling by ODP Leg 150 (Mountain, Miller, Blum, et al., 1994). ODP Leg 174A continued the transect by drilling on the shelf (Austin, Christie-Blick, Malone, et al., 1998), whereas drilling at Bass River (ODP Leg 174AX; Miller, Sugarman, Browning, et al., 1998) continued the onshore transect by drilling deeper into Upper Cretaceous strata. The Ancora borehole was designed to sample updip equivalents of Upper Cretaceous strata sampled at Bass River and to push further into the middle Cretaceous section. The Planning Committee endorsed onshore drilling as an ODP-related activity and designated drilling at Bass River, Ancora, and Ocean View (Fig. F1) as ODP Leg 174AX. Onshore drilling of the Leg 150X and 174AX boreholes was sponsored by the National Science Foundation, Earth Science Division, Continental Dynamics and Ocean Drilling Programs, and the New Jersey Geological Survey (NJGS).

The geologic background and scientific justification for the New Jersey Sea Level Transect are provided by Miller and Mountain (1994). The Transect is intended to document the response of passive continental margin sedimentation to glacioeustatic changes during the Oligocene to Holocene "Icehouse World," a time when glacioeustasy was clearly operating, and to document the ages and nature of Eocene and older "Greenhouse" sequences, a time when mechanisms for sea-level change are poorly understood (Miller et al., 1991). The Ancora borehole sampled Upper Cretaceous to lower Eocene "Greenhouse" sequences, an interval thought to have been ice free. Our objective was to date these sequences and compare them with other proxies of global sea-level change (e.g., ¹⁸O changes and Haq et al.'s record [1987]; see Browning et al. [1997b]). This is a particularly intriguing task, because onshore sequence stratigraphic studies in New Jersey and elsewhere provide evidence for large, rapid sea-level changes in this supposedly ice-free world, although the only known mechanism for such large, rapid sea-level variations is glacioeustasy (Pitman and Golovchenko, 1983).

The Ancora borehole was specifically located to sample critical events in Earth history, specifically the LPTM, the K/T boundary, and the Cenomanian/Turonian (C/T) boundary. Based on updip drilling at Clayton, New Jersey (Gibson et al., 1993), and downdip sections at Bass River (Cramer et al., in press), we expected that the section representing the LPTM at Ancora would be one of the most complete representations of this abrupt climatic event. Drilling at Ancora recovered two penetrations of a thick LPTM section.

The Ancora site was also selected to optimize recovery of the K/T boundary section. This section at Bass River provided an unprecedented coastal plain view of K/T boundary events, establishing that ballistic ejecta from the Chicxulub impact was associated with the marine mass extinction event (Olsson et al., 1997). Although drilling at Bass River recovered an excellent K/T boundary succession, there are several issues that required recovery of an additional New Jersey section, where we predicted that the boundary would be continuous, including:

What paleobathymetric changes were associated with the impact, and what is the relationship (if any) of the impact to sea-
level changes and sequences?
What was the response of marine organisms to the impact? Various studies show a global pattern of planktonic response (e.g., Smit, 1982). In contrast, studies show benthic foraminifers experienced few extinctions (e.g., Beckmann, 1960). At Bass River, we failed to recover Subzone P1b, hindering our evaluation of the recovery of marine plankton to the extinction event. We initially planned to drill an updip section at Parvin, New Jersey, to address these issues. We had the opportunity to take a 2-ft core spanning the K/T boundary at Parvin in 1997 and determined that the spherule bed was missing, although a clay clast bed was present as it was at Bass River. We, thus, shifted our proposed drilling from Parvin along strike to Ancora where we managed two penetrations of the K/T boundary, one of which included spherules (see below). In addition, the Ancora borehole recovered two samplings of a thick, relatively complete lower Paleocene section that will allow evaluation of the response and recovery of marine organisms to the K/T event.

The Ancora, Bass River, and planned Ocean View boreholes had another major objective: to evaluate the stratigraphic continuity and hydrogeological potential of aquifers and confining units, particularly those of Cretaceous age. The NJGS funded direct drilling costs for Bass River and partially funded Ancora and Ocean View, targeting Cretaceous aquifers in the Mount Laurel, Englishtown, and Potomac-Raritan-Magothy (PRM) Formations (see Zapecza [1989] for discussion of these aquifers). Continuous coring in the New Jersey Coastal Plain has shown that aquifer-confining couplets are sequences bounded by unconformities (Sugarman and Miller, 1997). Thus, sequence stratigraphy provides a means to predict the continuity and regional distribution of aquifer-confining units (Sugarman and Miller, 1997). However, the updip-downdip relationships of aquifer-confining units is not clear in many cases. For example, the Magothy aquifer displays complex updip-downdip relationships (Miller, Sugarman, Browning, et al., 1998). The Ancora borehole was specifically located to sample these Cretaceous aquifers and to answer outstanding questions about Cenozoic aquifers. In the latter case, the sequence stratigraphy and hydrostratigraphic distribution of the units confining the "Atlantic City 800-ft Sand" aquifer and the regional distribution and significance of the "Piney Point" aquifer are very poorly known in the vicinity of Ancora.

Drilling at Ancora, New Jersey, met "Greenhouse," global event, and aquifer objectives by obtaining remarkable recovery of mid-Cretaceous to Holocene sediments.