Oligocene to Holocene Mass-Transport Deposits of the New Jersey Continental Margin and Their Correlation to Sequence Boundaries

Abstract

The styles of soft-sediment deformation, mineralogy, and biostratigraphy of mass-transport deposits recovered from Leg 150 drill sites (902-906) provide important new information on the erosional and sedimentary history of the New Jersey continental slope and rise, and on the relationship of mass-wasting processes to changes in relative sea level. Nine distinct sedimentary facies are recognized within these mass-transport deposits, which mainly represent muddy slumps and debris flows, and to a lesser extent, sandy mass flows. These sedimentary facies, coupled with the ages of their clast and matrix material, reveal source areas, transport mechanisms, and depositional processes, and the relative contribution of downslope transport to the evolution of the continental rise.Mass-wasting deposits compose 10%-15% of the total sediment recovered beneath the continental slope at Sites 902, 903, and 904. Upper Miocene and Pleistocene debris flows and slumps frequently correlate to sequence boundaries beneath the upper paleoslope at Site 903, and to a lesser extent, beneath the middle paleoslope at Sites 902 and 904. In contrast, upper Oligocene to upper Miocene sands and sandy mass flows correlate to sequence boundaries beneath the middle paleoslope at Sites 902 and 904 and not beneath the upper paleoslope at Site 903. Mass flows at these sites document shelf and coastal plain erosion and sediment transport to the basin during glacioeustatic lowering. These observations suggest a correlation between mass-transport deposits and sequence boundaries. However, this correlation is complex because preservation of mass-wasting deposits appears to have been significantly influenced by the morphology and gradient of the existing paleoslope. In addition, mass-transport deposits also occur within sequences especially during the upper Miocene and Pleistocene.Site 906 was drilled in the floor of modern Berkeley submarine canyon. The sedimentary facies recovered from the middle Miocene section document an episode of canyon excavation and infilling. The Berkeley and middle Miocene canyon fill facies are different from the mass-transport deposits that characterize intercanyon regions of the slope (they contain debris flows with clasts of diverse ages and multiple turbidites). The middle Miocene canyon cutting event apparently occurred very rapidly (~l.l m.y.) during a single third-order sea-level cycle (13.5-12.4 Ma) and the mass-transport deposits at the base of the canyon fill rest upon a Type I sequence boundary, which forms the canyon floor.Downslope transport of sediment via mass movements has episodically contributed to the evolution of the upper continental rise. At Site 905 on the continental rise, approximately 30 m of mass-transport deposits were accumulated during the middle Miocene. Benthic foraminifer assemblages indicate that some deposits originated in the upper slope. The lithology of the clasts in these deposits indicates they were derived from canyon excavation on the continental slope and the age of the matrix...

Bedrock erosion by sedimentary flows in submarine canyons

“…McHugh et al (2002) characterized the sediments recovered at ODP Sites 902-906; at Site 905, in the continental rise, they described muddy debrites and slump deposits forming intervals of 30 m in the middle Miocene and 215 m in the early Pleistocene stratigraphy. According to McHugh et al (1996), clasts within the Pleistocene mass transport deposits are of varied age (middle and late Eocene, Pliocene, and Pleistocene) and contain benthic foraminifera assemblages that could have originated from water depths of <200 m to 2000 m. Clast lithologies are varied but include Eocene biosiliceous chalk. McHugh et al (2002) interpreted these deposits as having originated from slope failure in the adjacent continental slope.…”

Early carbonate diagenesis in slope sequences and at their boundaries, Cenozoic, offshore New Jersey (ODP Leg 150)

“…With the help of lithologic change, biostratigraphy, and borehole log characteristics, the disconformities found in the cores were correlated to unconformities (mostly truncation surfaces) in the seismic record (Shipboard Scientific Party 1994a,b). Slumps and turbiditic sands overlie several sequence boundaries, including the major ones (McHugh et al 1996), and submarine gravitative erosion is thought to be one of the main processes during the formation of sequence boundaries on the slope (Fulthorpe et al 1996). However, the origin of several reflectors remained unclear because the changes in density and sonic velocity between the rocks above and below several boundaries are insufficient to explain their strength (Lorenzo and Hesselbo 1996).…”

Effects of relative sea-level changes on the diagenesis of Eocene sediment: New Jersey slope and coastal plain

“…Blum, et al, 1994). Clays associated with the upper Eocene are mixed illite/smectite (70%) and illite (30%; McHugh et al, 1996a). However, adjacent to the unconformity at 684 mbsf, there is kaolinite (10%; McHugh et al, 1996a).…”

“…However, adjacent to the unconformity at 684 mbsf, there is kaolinite (10%; McHugh et al, 1996a). The upper Oligocene above the unconformity contains illite (50%), kaolinite (30%), and mixed illite/smectite (20%; McHugh et al, 1996a).…”

“…Lower calcium carbonate values than the Eocene are typical for the Oligocene. The dominant clays for the upper Oligocene are illite, kaolinite, and minor smectite (McHugh et al, 1996a).…”