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Orbital-Scale Cyclicity in Seismic Reflections and Sediment Character as a Climate Proxy in the Plio-Pleistocene Middle Pico Formation, Santa Barbara, California

C. D. Peterson1, R. J. Behl1, C. Nicholson2, L. E. Lisiecki2, and C. C. Sorlien2
1California State University, Long Beach, CA, [email protected], [email protected]
2University of California, Santa Barbara, CA, [email protected], [email protected], [email protected]

New seismic reflection records from the Santa Barbara Channel suggest that large parts of the Plio-Pleistocene Pico Formation record climate variability on orbital to sub-orbital scales with remarkable sensitivity, much like the well-studied sediments of the last glacial period (ODP Site 893). We propose that acoustic impedance responds to variations in physical properties of the sediment resulting from oscillations in composition and fabric produced by climatic forcing during deposition.

Where it crops out along the northern shelf of the central Santa Barbara Channel, the middle Pico (~1.8-1.2 Ma) is a bathyal hemipelagic mudstone with remarkably rhythmic planar bedding, finely laminated fabric, and well-preserved foraminifera, none of which have been significantly altered, destroyed or obscured by subsequent post-depositional diagenesis or tectonic deformation. Unlike the coarser, turbiditic successions in the Ventura and Los Angeles basins, this sequence has the potential to record late Pliocene-Quaternary global climate change at high resolution. Seismic reflection data (towed chirp) collected on the R/V Melville 2008 Cruise (MV08) image a ~1 km-thick succession of south-dipping seismic reflectors in the middle Pico at a resolution of 10's of centimeters, penetrating 10's of meters below seafloor. The amplitude of these reflectors may be used as a proxy for global climate oscillations and our preliminary analyses suggest that their periodicity falls within the Milankovitch band. Cores collected from the northern shelf on the MV08 Cruise cross these strong reflectors, and will be analyzed for chemical and physical properties, including TOC, CaCO3, and density (gamma ray attenuation) to understand the relationship between climate forcing, sediment material properties and seismic character.

If Milankovitch cyclicity in the sequence is unequivocally established, it will demonstrate that the Pico Formation is a faithful recorder of global climate change. This cyclicity, together with high-resolution seismic data, could also provide a dating tool exceeding the resolution of biostratigraphy.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009