HR: 0800h
AN: OS41D-0522    [Abstracts]
TI: Transgressive Sequence Development on the Northern California Continental Shelf
AU: * Fenwick, R A
EM: rfenwick@ucsd.edu
AF: UCSD, SIO, MC- 0208, La Jolla, CA 92093 United States
AU: Driscoll, N W
EM: ndriscoll@ucsd.edu
AF: UCSD, SIO, MC- 0208, La Jolla, CA 92093 United States
AU: Babcock, J M
EM: jbabcock@ucsd.edu
AF: UCSD, SIO, MC- 0225, La Jolla, CA 92093 United States
AB: It has long been recognized that stratigraphic patterns and associated facies on continental margins are controlled by three independent variables: eustatic sea level fluctuations, tectonic subsidence/uplift (rate and distribution), and sediment supply. In addition to this triad of processes, climate (e.g., transport and dispersal) and physiography of the margin also play an important role in controlling the resultant geometry of stratigraphic sequences. Numerous attempts have been made to understand how changes in these variables affect the stratigraphic record; that is, trying to define the link between process and product. Despite these efforts controversy remains regarding the importance of tectonics versus eustatic sea-level fluctuations in controlling sequence architecture. The Eel Basin in Northern California is an ideal location to tease out the influence of tectonics versus eustasy because the margin is undergoing shore-perpendicular tectonic deformation in response to the northward propagation of the Mendocino Triple Junction. This northeast-southwest oriented compression is inducing folds and high-angle reverse faults and thrusts with their fold/fault axis oriented northwest-southeast at a high angle to the shoreline. This configuration creates a tectonic signal with varying sign and amplitude parallel to the coastline and provides the ideal opportunity to examine how tectonic deformation affects stratigraphic architecture and facies assemblages. High resolution chirp data acquired in the region during multiple cruises (1998, 1999, 2000) indicate that the bathymetry and subsurface structure are not well correlated. For example, the thickness of the Holocene sediment varies along strike in the Eel Basin from less than 2 m across the crest of the Little Salmon Anticline to greater than 30 m toward the Eel River Syncline. In the Freshwater and Eel River synclines, which also control the location of Mad and Eel rivers, there is greater sediment input and the depositional events have a greater propensity for being preserved due to the rapid subsidence (up to 4 mm/yr in Eel River Syncline). The onlapping reflectors in the syncline diverge and exhibit increasing dip with depth implying that sedimentation is concomitant with tectonic deformation. Using modern tectonic uplift and subsidence rates determined from beach terraces and applying these rates for the Holocene reveals that the relief observed across the transgressive surface and differential Holocene sediment thickness can be explained predominantly by tectonic deformation. In addition to seismic and core data, we will present three-dimensional visualization to illustrate the contributions of tectonics versus eustasy for the Eel Basin.
DE: 8005 Folds and folding
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 3045 Seafloor morphology and bottom photography
DE: 1724 Ocean sciences
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting