HR: 1330h
AB: The Eel River Basin is a tectonically active forearc basin, affected by eastward subduction of the Gorda plate beneath the North America Plate and northward migration of the Mendocino Triple Junction (MTJ), located just to the south. Rapid sediment input from the Eel and Mad rivers has produced a ~3 km Neogene-Quaternary section beneath the continental shelf, which records deformation and associated erosion by many competing processes, including folding, faulting, sea-level fluctuations/fluvial incision, sediment loading, and bottom currents. As a result, multichannel seismic (MCS) data collected offshore in 1996 (R/V Wecoma cruise \#9605B) as part of the Office of Naval Research STRATAFORM initiative image numerous unconformities and deformational features beneath the Eel River shelf. Two of the most prominent unconformities are dated at ~1.0 Ma and ~500 ka, based on correlations with industry wells and onshore outcrops. This age control allows us to estimate the timing of structures and other seismically imaged unconformities. Broad folding occurs north of the offshore extension of the Table Bluff Anticline (TBA); this folding ended in the South Bay area before formation of the ~1.0 Ma unconformity. Little Salmon Fault (LSF) deformation began in conjunction with folding in the South Bay area prior to 1.0 Ma; this deformation ended ~730 ka on the shelf, but has propagated seaward over time and remains active on the upper slope today. After LSF-related deformation ended on the shelf, the resultant anticline was a topographic high until buried by overlying sequences. Faulting in this area continues to the Present, although most seismically imaged faults have minimal offsets, in contrast to those observed onshore. Subsidence north of the LSF began ~830 ka, forming the Freshwater Syncline (FWS), and ended ~580 ka. Uplift north of the FWS began ~830 ka, and has continued intermittently to the Present. In the Eel River Syncline at the southern end of the Eel River Basin, prominent south-southwest-trending channel incision began abruptly after formation of the ~500 ka unconformity, possibly reflecting initiation of the Eel Canyon. The TBA also began to form soon after channel incision began; only the oldest channel clearly drained areas north of the cross-shelf trend of the anticline. Offsets of features across the TBA suggest that right-lateral motion has occurred due to fold-related faulting; thinning of the most recent seismic sequence over the anticline indicates that TBA-related deformation continues today. Both the TBA and channel incisions may reflect uplift and crustal shortening associated with the northward-migrating MTJ. Sedimentation patterns on the shelf have gradually shifted over the past ~1.0 Ma, from a depocenter associated with the FWS to a depocenter beneath the southern shelf today. We suggest this shift was caused in part by changes in structuring of the basin, but it may also indicate a shift in relative influences of the Mad and Eel rivers as sediment sources since ~1.0 Ma.
AN: OS62A-02
TI: Mid-Pleistocene to Present Structural Deformation and Sedimentation Patterns in the Offshore Eel River Basin, Northern California
AU: * Burger, R L
EM: rburger@utig.ig.utexas.edu
AF: University of Texas-Austin Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759-8500 United States
AU: * Burger, R L
EM: rburger@utig.ig.utexas.edu
AF: University of Texas-Austin Department of Geological Sciences, C1100, Austin, TX 78712-1101 United States
AU: Fulthorpe, C S
EM: craig@utig.ig.utexas.edu
AF: University of Texas-Austin Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759-8500 United States
AU: Austin, J A
EM: jamie@utig.ig.utexas.edu
AF: University of Texas-Austin Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759-8500 United States
AU: Gulick, S P
EM: sean@utig.ig.utexas.edu
AF: University of Texas-Austin Institute for Geophysics, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759-8500 United States
DE: 8005 Folds and folding
DE: 4558 Sediment transport
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: OS
MN: Fall Meeting 2000