HR: 0800h
AN: GP21A-0012    [Abstracts]
TI: Upper and Lower Jaramillo Polarity Transitions Recorded in North Atlantic Sediments From IODP Exp. 303
AU: * Mazaud, A
EM: mazaud@lsce.cnrs-gif.fr
AF: LSCE CEA-CNRS, Domaine du CNRS, Avenue de la Terrasse, Gif-sur-Yvette, 91198 France
AU: Channell, J E
EM: jetc@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Stoner, J S
EM: jstoner@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331 United States
AB: Sediments collected during Integrated Ocean Drilling Program (IODP) Expedition 303, conducted in the North Atlantic, offer the opportunity to investigate polarity transitions and geomagnetic excursions at a high resolution. Here we examine the top and bottom transitions of the Jaramillo subchronozone recorded at Site 1305, located at the limits of the Eirik Drift (south of Greenland) at a water depth of 3459 m. These polarity transitions were studied with u-channels at Gif-sur-Yvette, using a small access 2G pass-through magnetometer. Progressive alternating field (AF) demagnetization revealed strong magnetizations, with mid-destruction fields and coercivity spectra consistent with magnetite as the dominant carrier of the natural remanent magnetization (NRM). Directions of the characteristic remanent magnetization were determined each centimeter by principal components analysis. Declinations were adjusted according to the shipboard Tensor Multishot orientation tool, or by a rotation so that the mean declination of stable polarity was aligned to 0° or 180°. Polarity transitions are characterized by low relative paleointensities. The Upper Jaramillo VGP path exhibits a loop over the Americas that is similar to the records obtained at ODP Site 983 (ODP Leg 162). The Lower Jaramillo transition is more complex, with a marked cluster over South America reminiscent of features observed in some volcanic records of reversals. Pre-transitional fluctuations in NRM directions are observed at the base of the Jaramillo Subchronozone. The possibe implications of these high-resolution records for the behavior of the geodynamo during polarity transitions will be discussed.
DE: 1521 Paleointensity
DE: 1530 Rapid time variations
DE: 1535 Reversals: process, timescale, magnetostratigraphy
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005