Back to Fall 1999 AGU abstract list.
Back to the News
|
Icebergs off New Jersey! Latest Quaternary Seafloor Morphology and Shallow Stratigraphy of the Outer Continental Shelf, Southern Hudson Apron Catherine Schuur Duncan 1,2 (512-471-6156; laurie@utig.ig.utexas.edu) John A. Goff 2 James A. Austin Jr. 2 Hilary C. Olson 2 1Univ. of Texas Inst. for Geophysics, 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759-8500, United States 2Dept. of Geological Sciences, University of Texas at Austin, C1100, Austin, TX 78701, United States Seafloor morphology on the southern Hudson apron shelf records the effects of the last eustatic sea level lowstand on the Mid-Atlantic outer continental shelf and modification during the last transgression. Our study area is a $\sim$600 km$^{2}$ portion of the New Jersey outer shelf bounded landward by the Franklin paleo-shore, a $\sim$10-15 m bathymetric step at the $\sim$100 m isobath, and seaward by the shelf edge at the $\sim$140 m isobath. The study area encompasses the southern half of the Hudson Apron. We use Simrad EM1000 high-resolution, 95 kHz swath sonar maps to investigate detailed bathymetry and acoustic backscatter patterns. Vibracores provide some constraints on the upper $\sim$$<$10 m of sediment, and 3.5 kHz echosounder profiles show shallow sub-seafloor structure. We interpret sinuous gouges $\sim$$<$100 m to $\sim$400 m wide, and kilometers long, as keel marks created by floating icebergs. Generations of keel marks truncate one another, creating distinctive rough topography that suggests several episodes of iceberg rafting under changing oceanographic conditions. The gouges, presumably created by ice detached from the Laurentide ice sheet, end abruptly at the Franklin paleo-shore. Oblique ridges, which resemble modern ridges formed in a near-shore environment, appear to overlie the keel marks proximal to the Franklin shore. Gouges cut into ridges near the shelf edge. Packets of flow-transverse subaqueous dunes are the most recent outer shelf bedforms. According to global and regional studies of the last eustatic cycle, the regressing shoreline moved past the $\sim$100 m isobath $\sim$25 kyrs B.P., reached its maximum lowstand position at the $\sim$127 m isobath $\sim$22 kyrs. B.P., and trangressed back to the Franklin paleo-shoreline $\sim$15.7 kyrs B.P. The ridge features near the shelf edge may be part of the shore zone developed at the glacial maximum. The keel marks must therefore be younger than the maximum lowstand shore, and older than the oblique ridges which overly them. They also appear to have been active during, or shortly after, the period when the shoreline occupied the Franklin shore since several large gouges terminate at the bathymetric escarpment. Stiff clays sampled on the Hudson Apron may explain the preservation of the keel marks since the earliest part of the Holocene transgression. |
Meeting: Meeting Section: Special Session: Index Terms: Theme: |
Last Modified: October 8, 1999
Comments: UTIG webmaster