HR: 1330h
AN: OS52B-0904    [PDF]
TI: Enigmatic Shallow Subsurface Stratigraphy on the New Jersey Mid-Outer Shelf: Catastrophic Erosion or Diagenesis?
AU: * Fulthorpe, C S
EM: craig@ig.utexas.edu
AF: University of Texas Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759 United States
AU: Goff, J A
AF: University of Texas Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759 United States
AU: Austin, J A
AF: University of Texas Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759 United States
AU: Gulick, S P
AF: University of Texas Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759 United States
AU: Nordfjord, S
AF: University of Texas Institute for Geophysics, John A. and Katherine G. Jackson School of Geosciences, 4412 Spicewood Springs Road, Bldg. 600, Austin, TX 78759 United States
AU: Nordfjord, S
AF: University of Texas at Austin, Department of Geological Sciences, John A. and Katherine G. Jackson School of Geosciences, 1 University Station C1100, Austin, TX 78712 United States
AU: Alexander, C
AF: Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA 31411 United States
AU: Sommerfield, C
AF: College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958 United States
AU: Christensen, B
AF: Department of Geology, Georgia State University, 340 Kell Hall, Atlanta, GA 30303 United States
AU: Schock, S
AF: Department of Ocean Engineering, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431 United States
AU: Nielson, D L
AF: DOSECC, Inc., 675 South Arapeen Drive, Suite 201, Salt Lake City, UT 84108 United States
AB: High-resolution (1-15 kHz), shallow-penetration ($\sim$50 m), deep-towed chirp seismic profiles on the New Jersey mid- and outer-shelf have been collected in support of ONR's Geoclutter program. Geoclutter goals are to understand and predict acoustic scattering from the seafloor and the shallow sub-seafloor in order to distinguish man-made objects from naturally occurring features ("geological clutter") on sonar returns. Area 2 of the chirp survey covers 8.6 $\times$ 10.2 km, mostly surveyed at 50 m line spacing. Three shallowly buried, dendritic and meandering channel systems, $\sim$2-4 km apart, are oriented E to NE. Channel flanks are truncated by the seafloor and seismic stratigraphy suggests multiple stages of incision and filling. The northernmost channel system, which is best constrained, is mainly V-shaped, up to 350 m wide and 12 m deep. This scale is among the smallest in the entire Geoclutter survey area. Sampling using an active-heave-compensated AHC-800 rig supplied by DOSECC reveals a sand and mud channel fill with, at its base, a burrowed contact with underlying mud that correlates well with the seismic interpretation. A prominent, vertical, seismic facies change occurs throughout Area 2: stratified material is overlain by up to $\sim$20 m of seismically transparent material, within which the younger, dendritic channels are incised. These two facies are separated by an irregular boundary. In places, the boundary resembles steep-sided (commonly $50\deg$-$90\deg$) incisions which truncate underlying reflections. Mapping of the boundary reveals that its irregularities are not random. Some align to form predominantly NE- and E-trending "channels" that may converge to the SW. Rare "blocks" of stratified material within the transparent facies, along with more numerous smaller, isolated reflections, may correspond to clasts of stiff clay recovered in a 35-cm core. We suggest that the seismically transparent material contains such clasts, of a wide range of sizes, derived from the underlying, presumably clay-rich, stratified material. If the facies boundary represents an erosion surface, the steep flanks suggest that the stratified material was consolidated at the time its erosion. To preserve these flanks, burial must have immediately followed erosion, pointing to erosion and re-deposition during a single, perhaps catastrophic event. One possibility is that widespread erosion accompanied sheet flow across the shelf, following breaching of glacial lake dams in southern New England $\sim$17-15 ka, perhaps partially confined by an outer-shelf flexural bulge which has since relaxed. However, chirp profiles off North Carolina image a similar seismic facies contrast which could preclude an origin related to the collapse of glacial lakes. A second possibility is some form of diagenetic front, but testing this hypothesis will require further sampling.
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 4219 Continental shelf processes
DE: 4556 Sea level variations
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting