HR: 11:50h
AN: OS32A-07 INVITED    [Abstracts]
TI: Controls on Coarse-Grained Sediment Delivery and Distribution in the Holocene Santa Monica Basin, California: Implications for Evaluating Source-to-Sink Flux at Millennial Time Scales in a Deep-Marine Basin
AU: * Romans, B W
EM: bromans@pangea.stanford.edu
AF: Stanford University Dept. of Geological & Env. Sciences, 450 Serra Mall Bldg 320, Stanford, CA 94305, United States
AU: Normark, W R
EM: wnormark@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: McGann, M M
EM: mmcgann@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Covault, J A
EM: jcovault@stanford.edu
AF: Stanford University Dept. of Geological & Env. Sciences, 450 Serra Mall Bldg 320, Stanford, CA 94305, United States
AU: Graham, S A
EM: graham@pangea.stanford.edu
AF: Stanford University Dept. of Geological & Env. Sciences, 450 Serra Mall Bldg 320, Stanford, CA 94305, United States
AB: Accumulations of terrigenous sediment in deep-marine basins commonly represent the terminal position for source-to-sink sediment flux across a continental margin. The sedimentary succession in the sink records the interactions of external, or allogenic, controls (e.g., eustasy, climatic conditions, tectonic activity) and intrinsic, or autogenic, dynamics (e.g., sediment gravity flow processes and development of depositional relief). Analyzing terrigenous sediment from a sink to determine the relative contributions and thus, the history of external controls has been difficult owing to limited knowledge of event timing. In this study, six new radiocarbon (¹⁴C) dates are integrated with five previously published, but recalibrated, dates from a 12.5 meter-thick turbidite section from ODP Site 1015 in Santa Monica Basin, offshore southern California (33°42.925"N; 118°49.185"W; water depth = 900 m). This borehole is tied to high-resolution seismic-reflection profiles that cover a 1,000 km² area of the middle and lower Hueneme submarine fan and most of the basin plain. This regional stratigraphic framework provides the highest temporal resolution to date for a thick-bedded Holocene turbidite succession, permitting an evaluation of source-to-sink controls at millennial (10³ yr) scales. The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity current events is relatively constant (300-360 yrs), but the volume of sediment deposited on the fan and in the basin plain has increased by a factor of two during this period. Moreover, the amount of sand per event (i.e., thickness of turbidite bed) on the basin plain during the same interval increased by a factor of six. Maps of sediment distribution derived from correlation of seismic-reflection profiles indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., lobe progradation). The observed variability in sediment accumulation rates is thus mainly controlled by allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of ENSO events from approximately 2 ka to present; (2) decreasing rates of sea-level rise (i.e., sea level reaches present stand approximately 7 ka); and (3) an apparent change in routing of coarse-grained sediment within the staging area at approximately 2-3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon). The Holocene history of the Santa Clara River-Santa Monica Basin source-to-sink system demonstrates how the interaction of varying sediment flux and changes in dispersal pathways affects the basinal stratigraphic record.
DE: 3022 Marine sediments: processes and transport
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8106 Continental margins: transform
DE: 8169 Sedimentary basin processes
DE: 8177 Tectonics and climatic interactions
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting