Back to Fall 2000 AGU abstract list.
Back to the News
From AGU's website.The UNIVERSITY of TEXAS at AUSTIN
INSTITUTE FOR GEOPHYSICS
NewsHR: 1330h
AB: Seafloor morphology and shallow stratigraphy record shoreline migration, subaerial exposure and Holocene transgression of the New Jersey inner shelf during the last eustatic cycle (~120 kyrs B.P. to Present). In a dip-oriented, ~275 km2 corridor on the inner and middle shelf between ~30 m and ~50 m water depths, we used Simrad EM1000 high-resolution, 95 kHz swath sonar data to map detailed bathymetry and acoustic backscatter patterns. A ~400 line-km chirp sonar survey provides very high-resolution (1-6 kHz) profiles of the upper ~30 m of stratigraphy. We also collected ~300 grab samples within the corridor; grain size and lithologic analyses provide some ground truth for the geophysical images. During the chirp sonar survey, we duplicated Huntec (1-3.5 kHz) single-channel seismic profiles on the middle shelf; we correlated inner shelf stratigraphy with previous interpretations of middle shelf strata. These new data resolve a stratigraphic succession developed during Wisconsinan glaciation and subsequent Pleistocene-Holocene sea level rise. We observe, from oldest to youngest by superposition: (1) "paleo-Hudson valley," a buried NW-SE trending truncation surface described in previous studies, (2) "Channels", incisions interpreted as fluvial erosion during the glacial maximum, (3) channel-fill, non-marine to marine sediments filling "Channels" during the last transgression, (4) "T", a surface that truncates "Channels" and channel fill, and forms the base of sandy Holocene surficial units, (5) mid-shelf wedge, a lobate deposit composed of internal backstepping wedges that overlies "T", (6) mid-shelf scarp, a ~15 m escarpment at 37-52 m water depth, and (7) oblique ridges and transverse dunes, palimpsest bedforms created by recent and modern shallow-shelf reworking of surficial sands. Samples confirm that well-sorted, winnowed sands comprise a surficial sheet. A single sample of very large ($>$6 cm), rounded cobbles indicates deposition of coarse-grained material during periods of lowered sea level. We do not observe the regressive erosion surface "R" on the New Jersey inner shelf, in contrast with earlier interpretations of inner shelf stratigraphy. According to global and regional studies of the last eustatic cycle, the regressing shoreline moved across the inner shelf corridor (~30 m to ~50 m below present sea level) between ~100 kyrs B.P. and ~45 kyrs B.P. (14C). Continuing sea level fall exposed the inner shelf, until the transgressing shoreline returned to the ~50 m isobath ~11.5 kyrs B.P. We suggest that "Channels" was carved during subaerial exposure. Incisions filled with upward-deepening sediments beginning at the late Wisconsinan lowstand. "T" is a transgressive ravinement cut by the advancing shoreline beginning ~11.5 kyrs B.P. We interpret the mid-shelf wedge as a sandy, wave-dominated delta deposited during the transgression, perhaps as the result of rapid sediment release from collapse of dams holding impounded glacial lakes to the north and east. The mid-shelf scarp, previously interpreted as a paleo-shoreline, is the depositional front of the mid-shelf wedge. We also observe a change in orientation between "Channels" drainage and the modern Hudson shelf valley. This implies that lowstand drainage was not aligned along the present Hudson system axis.
AN: OS62A-04
TI: Chirp Seismic and Swath Sonar Investigation of Latest Quaternary Stratigraphy, New Jersey Inner Continental Shelf
AU: * Duncan, C S
EM: laurie@ig.utexas.edu
AF: Univ. of Texas Inst. for Geophys., 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759-8500 United States
AU: * Duncan, C S
EM: laurie@ig.utexas.edu
AF: Dept. of Geol. Sciences, Univ. of Texas at Austin C1100, Austin, TX 78712 United States
AU: Goff, J A
AF: Univ. of Texas Inst. for Geophys., 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759-8500 United States
AU: Austin, J A
AF: Univ. of Texas Inst. for Geophys., 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759-8500 United States
AU: Driscoll, N W
AF: Woods Hole Ocean. Inst., Dept. of Geol. and Geophys. MS #22, Woods Hole, MA 02543-1541 United States
AU: Olson, H C
AF: Univ. of Texas Inst. for Geophys., 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759-8500 United States
DE: 9604 Cenozoic
DE: 4556 Sea level variations
DE: 3025 Marine seismics (0935)
DE: 3045 Seafloor morphology and bottom photography
DE: 4219 Continental shelf processes
SC: OS
MN: Fall Meeting 2000
UTIG | About | News | Research | Staff | Students | Search
UTIG Address and Phone
Comments to: www.ig.utexas.edu