The holes drilled on the New Jersey continental shelf and slope on Leg 174A form part of a transect of holes from the slope (ODP Leg 150) to coastal outcrops (150X and 174AX) that constitute the Mid-Atlantic Sea-level Transect. The primary goals of the transect were as follows:

1. Date sequence boundaries of Oligocene to Holocene age and compare this stratigraphic record with the timing of glacial-eustatic changes inferred from deep-sea delta18O variations.
Four prominent seismically imaged unconformity surfaces of middle Miocene to Pliocene Pleistocene age are probably related to times of falling sea level. Best estimates of ages for these surfaces, from shipboard paleontology and paleomagnetics are: < 0.5 Ma [pp3(s)], >1.1-<7.4 Ma [pp4(s)], 7.4-11.2 Ma [m0.5(s)], and >11.4 Ma [m1(s)]. Higher order cyclicity is most likely present but not resolved with existing seismic reflection data. The precision of ages will improve with postcruise studies, which will include techniques not available on the ship as well as the analysis of additional samples. Older Miocene and Oligocene sequence boundaries were intersected at the slope site, Site 1073, but in an area of marked condensation. Attempts to date these surfaces at geometrically optimal locations on the shelf (Sites 1071 and 1072) were not successful because off the difficulty of maintaining hole stability in unconsolidated sandy sediments in the upper 400 m of the section.

2. Place constraints on the amplitudes and rates of sea-level change that may have been responsible for unconformity development.
In the case of the late-middle Miocene to Pleistocene surfaces that were intersected at the shelf sites [pp3(s), pp4(s), m0.5(s) and m1(s)], the water depth fell to close to zero at a point 100 km seaward of the present shoreline. This is indicated by (1) the prominence of offlap (stratal truncation) at these surfaces; (2) the presence of several tens of meters of highstand sand in the vicinity of clinoform breakpoints/rollovers (points at which the gradient of the shallow paleoshelf steepens seaward from about 0.1° to a slope of about 4-5°), suggesting very shallow-water conditions [m0.5(s) and m1(s)]; and (3) the recovery of probable estuarine/lagoonal sediments in the vicinty of m0.5(s), only 3 km landward of its breakpoint/rollover (Hole 1071F). Sea level probably did not fall significantly below the level of these breakpoints/rollovers. This is indicated primarily by the lack of significant incision/downcutting by rivers at unconformity surfaces (less than 5 m). Lowstand sediments that might have been derived in part by this process are also thin to absent in the vicinity of clinoform toes, although lowstand deposits may be present in deeper water in the vicinity of the continental slope/rise. Lowstand units have been imaged in deep shelf seismic reflection data for several of the older Miocene surfaces. Evidence from benthic foraminifers indicate maximum water depths on the shallow shelf during times of high sea level were around 50-100 m. This implies changes in water depth of ~50-100 m, a figure that can be used to estimate amplitudes of global sea-level change once the local effects of sediment accumulation, compaction, and loading are taken into account.

3. Assess the relationships between depositional facies and sequence architecture.
One of the surprises of Leg 174A was the discovery of an unusual distribution of sediment types between unconformity surfaces related to times of sea-level fall. The shallow shelf for each sedimentary unit between these surfaces is dominated by sediments that accumulated during overall flooding ("transgressive" deposits). Seaward of breakpoints/rollovers, the deeper shelf is dominated by sediments that accumulated during spans in which the shelf was building seaward ("highstand" deposits). One explanation for this arrangement is that the space available for sediment to accumulate was efficiently filled during times of sea-level rise as a result of an abundant supply of sediment during the past 12 million years. The observed distribution departs from the standard conceptual model, widely used in petroleum exploration, in which highstand sediments extend well landward of associated transgressive ones.

4. Provide a baseline for future scientific ocean drilling that will address the effects and timing of sea-level changes on this and other passive margins.
For the first time in almost 30 years, scientific ocean drilling attempted to sample a thickly sedimented continental margin in water less than 150 m deep. In challenging drilling conditions, sediments as old as middle Miocene (~12.5 Ma) were sampled on the shelf, and late Eocene (~35 Ma) on the upper slope. A full suite of geophysical logs (including logging while drilling) was obtained from one site on the shelf (Site 1072). Logging data were also acquired in available time at slope Site 1073, including both sonic log and VSP data. The data obtained on Leg 174A represent an important step toward completion of the Mid-Atlantic Sea-level Transect, and they also provide valuable information about the technology that will be needed to drill, core, and log unconsolidated sandy sediments expected beneath the middle and inner shelf.

5. Relationship between sea-level fluctuations and interstitial-water chemistry: an unexpected result.
Analyses of interstitial water resulted in two discoveries relevant to the overall sea level and climatic themes of Leg 174A. First, salinity variations with depth observed in pore waters from the shelf are consistent with alternate exposure of the shelf during the Pliocene-Pleistocene and then renewed flooding by seawater. Second, changes in alkalinity and phosphate observed in samples from the thick, late Pleistocene succession of the slope are consistent with variations in the amount or type of buried organic matter, apparently with a periodicity of close to 100,000 yr, and consistent with the time scale of astronomically forced climate change during the Pleistocene.

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