New geophysical constraints on the stratigraphy and structure of the southern New England continental margin

A number of factors influence the evolution of continental slopes including changes in sediment supply, base level and energy flux. Slopes can be categorized as either constructional or destructional depending on the balance between erosion and deposition. The southern New England continental slope represents one of few regions of the U.S. Atlantic margin that maintains constructional form: the slope is ~50 km wide, has convex curvature that gradually increases in gradient from the shelf down to the lower slope, and contains relatively few, widely spaced canyons. Enhanced preservation of slope sedimentary sequences offers a unique opportunity to examine the interplay between sediment delivery, downslope transport and basin physiography. Also, examining these relationships helps understand the geohazards along this section of the U.S. Atlantic margin. We present results from recent seismic reflection surveys conducted along this section of the margin, offshore southern New England and Hudson Canyon in water depths between 500 to 2500 meters. More than 820-km of 2-D seismic reflection data were collected in 2010 and 2011 with a 6 KJ sparker source and a 48-64 channel digital streamer (6.25-m group interval). Seismic horizons are imaged more than 1-sec (two-way travel) below the seafloor, with frequencies between 40-650 Hz, providing up to 2-m vertical resolution. The processed data have been integrated with swath bathymetry and reflection profiles collected by the USGS in the 1970's to examine the relationship between shallow Pleistocene deposits with underlying Tertiary and Cretaceous strata. Despite its constructional form and lack of canyons, the northeastern section of the study region contains pervasive landslides that truncate the upper rise and the slope. We observe a thick, base-of-slope Pleistocene sedimentary wedge that infills steep lower-slope paleo-relief. Based on stratal geometry, the wedge appears to consist of stacked, upslope migrating sediment wave deposits that onlap a regional unconformity. Higher gradient and relief across the lower-slope appears to be limiting upper and middle slope progradation of Pleistocene sequences. Closer to Hudson Canyon, the lower-slope has a relaxed gradient, less relief and the base-of-slope unconformity is more subtle. Pleistocene beds are concordant from the upper slope to the rise. Here, a graded slope profile, a slope in equilibrium, has developed possibly because slope failure of the upper slope appears to be balanced by deposition and aggradation of the lower slope, allowing overall progradation to occur. The southern New England slope also contains evidence for faulting and fluid/gas expulsion extending from irregular, high-amplitude Cretaceous(?) beds through the overlying unconsolidated Pleistocene section. In some instances these features are coincident with large-scale landslide features.