11. Paleomagnetic Records of Stage 3 Excursions, Leg 172¹

Steve P. Lund,² Gary D. Acton,³ Brad Clement,⁴ Makoto Okada,⁵ and Trevor Williams⁶

ABSTRACT

Shipboard long-core paleomagnetic measurements made during Ocean Drilling Program Leg 172 identified a reproducible pattern of directional secular variation between ~15,000 and 45,000 k.y. that could be correlated between Sites 1061, 1062, and 1063, which span a distance of more than 1200 km. Two intervals of excursional paleomagnetic directions were identified at all three sites and were labeled as excursions 3 and 3. New analysis of excursions 3 and 3, based on reassessment of the shipboard measurements, new U-channel paleomagnetic records of the excursions, and independently published discrete sample paleomagnetic records of the same intervals all indicate that excursion 3 is not real; its directional variability is less than originally estimated and not excursional. Excursion 3 is real and easily identified in both U-channel and discrete sample measurements. Excursion 3 is the Laschamp Excursion noted in previous published studies. The best U-channel record of excursion 3 from Hole 1063C is almost identical to the best discrete sample paleomagnetic records. The U-channel records from Holes 1061B and 1061C are similar to one another but somewhat different from the other records (more smoothed). We attribute that difference to systematic biases in the U-channel measurement process when large-amplitude, fast directional changes occur.

¹Lund, S.P., Acton, G.D., Clement, B., Okada, M., and Williams, T., 2001. Paleomagnetic records of Stage 3 excursions, Leg 172. In Keigwin, L.D., Rio, D., Acton, G.D., and Arnold, E. (Eds.), Proc. ODP, Sci. Results, 172 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/172_SR/chap_11/chap_11.htm> [Cited YYYY-MM-DD]

²Department of Earth Sciences, University of Southern California, University Park, Los Angeles CA 90089, USA. slund@usc.edu

³Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station TX 77845-9547, USA.

⁴Department of Geology, PC344, Florida International University, University Park, Miami FL 33199, USA.

⁵Department of Environmental Sciences, Ibaraki University, Bunkyo 2-1-1, Mito 310, Japan.

⁶Department of Geology, University of Leicester, Leicester LE1 7RH, United Kingdom.

Initial receipt: 24 November 1999
Acceptance: 18 January 2001
Web publication: 6 June 2001
Ms 172-217