--> ABSTRACT: Late Pliocene-Holocene Depositional Systems on the Middle United States Atlantic Continental Rise, by S. D. Locker and E. P. Laine; #91030 (2010)

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Late Pliocene-Holocene Depositional Systems on the Middle United States Atlantic Continental Rise

S. D. Locker, E. P. Laine

Late Pliocene to Holocene depositional systems and their growth patterns are delineated on the middle United States Atlantic continental rise seaward of the Norfolk to Wilmington canyon systems. Earlier patterns of along-slope deposition controlled by geostrophic bottom currents became overrun by down-slope sediment transport in the form of widespread mass-wasting, leveed fan-channel systems, and ponded turbidites during this time. Three depositional sequences, Q1, Q2, and Q3, were mapped and can be correlated with seismic sequences and unconformities recognized by DSDP drilling along the New Jersey transect. Rise morphology is a major control on stratigraphic development and fan system growth patterns, while sea level appears to control the timing and rate of sediment input. Contour currents are most effective along areas of steeper gradients and appear to influence depositional sequence geometry more through erosion rather than contourite facies deposition.

In the late Pliocene, the Norfolk-to-Wilmington channel systems were directed south by the Chesapeake drift. Following the early Pleistocene(?) formation of the Wilmington gorge, a mid-to-lower fan depocenter developed from this point source in an intra-rise basin landward of the Hatteras outer ridge (HOR) near DSDP Site 603. Shifting depocenters in this basin primarily reflect sources from the Hudson and Wilmington fan systems.

Throughout most of the Pleistocene, distinct and separate thickness trends and depocenters are delineated for the Norfolk-Washington and Wilmington fan systems. The principal lower rise depocenter of the Norfolk-Washington system is not within the Wilmington-Hudson basin but across a high area to the south that includes the central HOR proper and upper region of the Hatteras transverse canyon. In contrast to the northern HOR dominated by current-controlled sediment wave deposition, the axial area of the central HOR exhibits upbuilding of conformable strata, truncated seaward of the HOR crest by along-slope bottom currents. This merger of the Norfolk-Washington fan system with the HOR indicates gravity flow deposits may be a significant depositional facies within a current-dominated ou er ridge system.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.