HR: 0830h
AN: PP21C-1188    [PDF]
TI: Using Milankovitch Cyclicity as a High-Resolution Dating and Correlation Tool to Understand the Stratigraphic Evolution of the Late Neogene Central California Margin
AU: * Hill, P S
EM: hillps2002@yahoo.com
AF: California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840 United States
AU: Behl, R J
EM: behl@csulb.edu
AF: California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840 United States
AB: Natural gamma ray logs from Ocean Drilling Program (ODP) sites off the Central California margin and from oil wells on the outer continental shelf show cyclical variation at Milankovitch periodicities in the Neogene upper-Monterey and Sisquoc Formations and their offshore equivalents. The well-dated ODP Site 1016, 150 km offshore of Point Conception, provides the basis for development of an orbital cyclicity-refined age/depth scale that can be applied to the mid-latitude North American margin region. We correlate silica-rich/detritus-rich cycles in logs from this site to cycles in more proximal offshore and onshore oil wells in a transect across the Santa Maria Basin, thereby helping to refine dating of these rapidly-accumulated, biostratigraphically-impoverished, fine-grained sediments, which are otherwise difficult to date. The higher resolution, orbitally-based age-depth scale provides refined dating of oil well logs, revision of the numerical age range of biostratigraphic markers, recognition and quantification of changes in sedimentation rates over time and in space, and identification of generalized climatic/sedimentation trends along the Alta-Baja California margin. For example: the new age model indicates that regional age ranges of some radiolarian biostratigraphic markers extend later than previously documented in other regions. Linear sedimentation rates decrease by an order of magnitude from 45-75 cm/ky to 7-8.5 cm/ky between proximal offshore locations and the distal Site 1016A. Analysis of the frequency modulation of the major harmonic in the frequency spectrum of the gamma ray vs. depth curve reveals the presence of condensed sections between ~4.4-4.8 Ma and ~5.3-5.6 Ma at Site 1016A. These two intervals may be associated with Neogene Hiatus 7 of Keller and Barron (1983). Natural gamma ray logs from deep-sea sites of ODP Leg 167 and the proximal Santa Maria basin wells show a similarity in gross secular trends along a 1300 km stretch of the Alta-Baja California margin, during the late Miocene to early Pliocene (~7.0 to 3.5 Ma). Gamma ray count--inferred to reflect terrigenous detrital content--corresponds roughly with the broad rise and fall of eustatic sea level.
DE: 0915 Downhole methods
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 9355 Pacific Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting