Gregory Mountain, 1905. "CENOZOIC MARGIN CONSTRUCTION AND DESTRUCTION OFFSHORE NEW JERSEY", Timing and Depositional History of Eustatic Sequences: Constraints on Seismic Stratigraphy, Charles A. Ross, Drew Haman
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Seismic reflection profiles have been correlated to eleven wells drilled between the upper continental slope and upper continental rise in a 2100 km2 grid, offshore New Jersey. This high density of publicly available data represents a unique opportunity for examining processes that control the buildup and erosion of passive continental margins. The conclusions drawn from this study have implications relating to the formation of submarine canyons, mechanisms of down-slope sediment transport, and the validity of interpreting seismic sequence boundaries along continental slopes as evidence of past sea-level changes.
One Upper Cretaceous and four Paleogene episodes of slope failure, slumping, and infilling have been documented. Each event is concentrated in broad, channel-like depressions beneath today's middle and lower slope. Though a hiatus of from one to several million years is associated with most episodes, very little shallow water debris rests on each erosional surface. In general, the channels are partly filled and smoothed by locally derived slumps. A common origin for all of these channels is strongly implied by the fact that each is stacked above the preceding one. It is proposed that these unconformities resulted from slope failure during episodic collapse of the underlying Mesozoic carbonate margin. Headward erosion may have lengthened many channels, but none reached a major source of shallow-water clastic sediment.
Three events occurred during or shortly after the Oligocene that influenced the nature of subsequent margin processes. First, the slope was cut landward between 5 and 25 km, interrupting the stacked arrangement of channels that had been maintained throughout the Paleogene, and this allowed a new pattern of subsequent slope failures to develop. Second, biogenic carbonate and siliceous sedimentation was replaced by detrital accumulation; these younger sediments experienced less early diagensis and more readily failed on gently dipping slopes. Lastly, the polar regions entered into the first of numerous ice-dominated climates. Consequently, oscillatory changes of global sea level became especially rapid, and contributed to the transport of large volumes of clastic sediment to the heads of pre-existing slump scars indenting the shelf edge.
Unfortunately, drill core data available for this study cannot provide information relating to the history of the margin from Oligocene to late middle Miocene time. Seismic profiles show that sediment accumulated in a thick deposit off the mid-Atlantic states during this interval, but any canyons through which these sediments may have been transported from the New Jersey margin are not within the study area.
An era of significant slope erosion and sediment by-pass occurred between 11.7 and 9.5 MY when a narrow canyon was cut directly beneath DSDP Site 612. During this interval a variety of shallow-water and reworked debris by-passed the slope and accumulated on the upper rise.
Pliocene sediments at the foot of the slope were particularly unstable because of layers of glauconite-rich sand. These unconsolidated layers served as detachment surfaces for large Pleistocene debris flows that came down off the slope and spread out onto the upper rise.
At present, the lower and middle slope offshore New Jersey continues to be a zone of sediment failure. Much of the material detached from this region is deposited by debris flows on the upper rise; a few major canyon systems provide channels for turbidity currents to continue beyond the 2500 m isobath. Most of these especially lengthy canyons are incised into the upper slope as well, and consequently are capable of delivering shelf-edge sediment to the deep basin.