A sixty thousand year paleomagnetic record from Gulf of California sediments: secular variation, late Quaternary excursions and geomagnetic implications

Details A sixty thousand year paleomagnetic record from Gulf of California sediments: secular variation, late Quaternary excursions and geomagnetic implications A sixty thousand year paleomagnetic record from Gulf of California sediments: secular variation, late Quaternary excursions and geomagnetic implications

Mar 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989e%26psl..92..219l&link_type=abstract

Earth and Planetary Science Letters, Volume 92, Issue 2, p. 219-233.

Computer Science

34

Scientific paper

A unique inclination record of geomagnetic secular variation for the past 60,000 years (60 ka) has been obtained from continuously deposited sediments in the Gulf of California, recovered during Deep Sea Drilling Project (DSDP) Leg 64 by hydraulic piston coring at Site 480. The chronology of Hole 480 was determined by δ18O stratigraphy and varve counts, indicating sedimentation rates approaching 1 m/ka. The paleomagnetic results of the upper 49 m show: (1) The average inclination over this interval is identical to the geocentric axial dipole value at the sampling site. (2) Excursion directions occur between about 53 and 22 ka before present (BP). During this time, the geomagnetic field was generally ``noisier'' than in the overlying and underlying sections, with greater dispersion of the inclination. (3) The Laschamp excursion was apparently recorded at Hole 480 between about 51 and 49 ka BP and the Mono Lake excursion between about 29 and 26 ka BP. In addition, a narrow 0.3-0.4 m zone near 23 ka BP has a very similar paleomagnetic signature as the excursion observed at Summer Lake, Oregon [1], and we suggest that the Summer Lake is distinct from and younger than the Mono Lake excursion by 3-5 ka and of considerably shorter duration, lasting no more than a few hundred years. (4) Recurring inclination fluctuations were identified at Site 480, characterized by end points with steep inclinations and shallow intermediate value(s), as compared with the geocentric axial dipole. The inclination cycles are particularly apparent from 54 to 24 ka BP with a characteristic period of about 4.4 ka. (5) The ``noisier'' inclination record between 54 and 24 ka BP might be related to the generally reduced dipole moment between about 20 and 50 ka, and particularly low paleointensities for the Laschamp and Mono Lake excursions.

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