Leg 150

The New Jersey Sealevel

Leg 150 operations off New Jersey comprise part of an integrated program of boreholes drilled, and planned to be drilled, in the U.S. mid-Atlantic region. The primary objective of Leg 150 was to date the Oligocene to Holocene unconformities and to evaluate their correlation with the glacioeustatic age estimates obtained from the d18O record, to determine the ages of major middle to late Eocene "Doubthouse" unconformities, and the relative importance of along-slope vs. downslope sediment transport on the continental rise and their relationship to eustatic variations.

During Leg 150, four sites were drilled on the continental slope (Site 902 to Site 904, and Site 906) and one on the continental rise (Site 905). Sequence boundaries traced from beneath the shelf to the slope were recognized as stratal surfaces and were dated at the slope sites. Several Oligocene-Miocene and other informal and newly identified reflectors were traced from the continental shelf to the slope. One sequence boundary, firmly dated for the first time during Leg 150, marks a fundamental change in depositional regime from Eocene chalks to Oligocene and younger siliciclastic sediments.

Drilling also documented a buried middle Miocene slope canyon, several times wider and more nearly flat-floored than Pleistocene canyons in this same region. The canyon formed between 15 and 12.5 Ma, during an event possibly correlating with an inferred glacioeustatic lowering that is part of the middle Miocene d180 increase. The canyon floor was soon covered with debris from its walls and turbidites, not found at Leg 150 sites outside this canyon, demonstrating that slope incisions enable turbidity currents to largely by-pass the slope environment, leaving very little sediment behind. The end of the canyon phase was marked by rapid infilling with laminated mud, representing an unusual interval of low bottom-water oxygen.

Three separate mass flow units were documented on the continental rise. Each unit was deposited during the Pleistocene and is composed of clasts derived from the adjacent continental slope. Some of the transported fragments reveal previous soft and brittle deformation, attesting to multiple mass wasting events. Physical properties data provide good correlations to the Pleistocene SPECMAP time scale (a complete record from 474 to 122 ka) and present evidence that Pleistocene mass wasting events may correlate with transitions from interglacials to glacials, times of glacioeustatic lowerings.