Passive continental margins such as those along the East and Gulf coasts of the U.S. contain thick sediment archives that record global sea level, depositional environments, regional/local tectonics, and global/regional climate changes in unconformity-bounded packages termed sequences (Mitchum et al., 1977; Christie-Blick and Driscoll, 1995). Deciphering these archives in a systematic manner has proven to be a challenge. Outcrops provided most of the information for early models of continental margin sedimentation, but these are often thin, weathered, poorly fossiliferous, and discontinuous on passive margins. Thicker sections are available in the subsurface downdip toward the submerged continental shelf, but subsurface sections have been mostly discontinuously sampled by oil or water wells. Continuous coring provides a direct means to sample the subsurface, although it is costly and complicated by unconsolidated nature of coastal plain strata. Advances in coring technology in the 1980's, particularly with extended bits (e.g., the Christensen bit and ODP's extended core barrel), has dramatically improved recovery rates and allowed recovery of undisturbed layers of strata to improve our information archives for passive margins.
In order to understand continental margin processes, passive continental margin studies require sampling from outcrops onshore to regions far offshore. Sampling onshore to offshore in transects (i.e., along dip profiles) or in arrays (i.e., transects with along-strike components) has proven programmatically challenging because it requires the interaction of organizations with distinctly different mandates (e.g., ODP and the International Continental Drilling Program [ICDP]). The Earth Science and Ocean Science Divisions of the National Science Foundation (NSF) recognized and met this challenge when they funded onshore drilling in the NJ Coastal Plain, which has been directly integrated with offshore efforts by ODP Legs 150 and 174A.
Coastal plain drilling by ODP began in 1993 with Leg 150X as part of the NJ/Mid-Atlantic Sea-Level Transect (Fig. F1) (Miller and Mountain, 1994). The primary goal of the transect was 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 (Miller and Mountain, 1994). During Leg 150 four sites were drilled on the NJ continental slope, providing a sequence chronology for the Oligocene-Miocene of the region (Mountain, Miller, Blum, et al., 1994). Concurrent with and subsequent to Leg 150, a complementary drilling program designated Leg 150X was undertaken to core coeval strata onshore in NJ. This drilling was designed not only to provide additional constraints on Oligocene-Holocene sequences but also to address an important goal not resolvable by shelf and slope drilling: to document the ages and nature of middle Eocene and older "greenhouse" sequences, a time when mechanisms for sea-level change are poorly understood (Miller et al., 1991). Sites were drilled at Island Beach (March-April, 1993), Atlantic City (June-August, 1993), and Cape May (March-April, 1994) (Miller et al., 1994, 1996a; Miller and Snyder, 1997) (Fig. F1). Together, Legs 150 and 150X were extremely successful in dating Eocene-Miocene sequences, correlating them to the 
18O proxy for glacioeustasy, and causally relating sequence boundaries to glacioeustatic fall (Miller et al., 1996b, 1998a; Browning et al., 1996). Little information was garnered on Paleocene and older sequences during these legs, with only one lower Eocene-Maastrichtian section sampled at Island Beach.
ODP Leg 174A continued the Mid-Atlantic Transect by drilling between previous slope and onshore sites, targeting the NJ continental shelf (Austin, Christie-Blick, Malone, et al., 1998). The Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES) planning committee endorsed a subsequent phase of onshore drilling as an ODP-related activity and designated the program ODP Leg 174AX. As part of this leg, sites were drilled at
The U.S. Geological Survey (USGS) Eastern Earth Surface Processes Team drilled the Ancora, Ocean View, and Bethany Beach boreholes, whereas a commercial driller, Boart Longyear, drilled Bass River. Full suites of downhole geophysical logs were obtained at Ocean View and Bethany Beach by the DE Geological Survey (DGS) and gamma logs to TD were obtained at Bass River and Ancora by the NJ Geological Survey (NJGS). The excellent recovery overall (5409 ft recovered from 6172 ft drilled; recovery = 88%) is testimony to the skill of the drillers in coring the difficult to recover coastal plain strata.
Onshore drilling during Leg 174AX has provided new insights into greenhouse sequences and added a third-dimensional, along-strike view of Oligocene-Miocene sequences, allowing the evaluation of the effects of tectonics and sediment supply on sequence stratigraphic architecture. This paper summarizes the objectives and accomplishments of onshore drilling during Leg 174AX and provides a brief prospectus for the future of drilling integrated arrays of boreholes on passive continental margins.
This chapter differs from a typical Initial Reports summary chapter in that it is not only a companion to the four site chapters reproduced on CD-ROM, it also summarizes publications and papers. The Bass River Site Report was published in paper form in 1998 and bound with the Leg 174A Initial Reports as Leg 174AX (Miller et al., 1998b). The Ancora (Chap. 1, this volume), Ocean View (Chap. 2, this volume) and Bethany Beach (Chap. 3, this volume) Site Reports are published on the World Wide Web and in this volume on CD-ROM as Leg 174AXS. Because drilling of Leg 174AX spanned 5 yr (1996-2000, inclusive), we summarize the scientific results of a significant body of published, in press, and submitted works. Ongoing studies will be published in 2004 in a Scientific Results volume.
