A detailed record of paleomagnetic field change from Searles Lake, California: 1. Long‐term secular variation bounding the Gauss/Matuyama polarity reversal

Abstract

Clement, 1992] intimates that the field may commonly show signs of early instability. This precursory event is actually one of a sequence of oscillations (in inclination and intensity) preceding the transition. That these fluctuations occur at roughly 4 kyr intervals leading up to the reversal (which also appears at this same interval) strongly suggests that an oscillatory disturbance in the core, active over at least 15 kyr prior to the transition, had eventually triggered the reversal. In addition, that these waveforms are absent from the postransitional record suggests the reversal process actively rejuvenates and stabilizes the field.

Geomagnetic field reversals: Main results and basic problems

“…In other words, no dipole field could exist during the fairly long time of the pole switching. This view offered by S. I. Braginskii agrees with the conclusions advanced by Gurarii [1988], Clement [2004], and other authors, and is of great interest in terms of the physical nature of the dipole and nondipole field.…”

“…[10] The analysis of the paleointensity data variation during and in the vicinity of the reversals showed that the average decline of the magnetic field during its reversals had been as high as seven times [Gurarii, 1988]. This estimate was obtained for the reversals of the last 15 million years, using the data published prior to 1986.…”

“…[12] As follows from the estimates of most of the authors, the time interval of some low M existence was notably longer than the time of the magnetic field reversal. The modal values of the Late Cenozoic reversals, estimated from the data available prior to 1986, suggested the average duration of the reversals to be 7-8 thousand years (the individual estimates varying from 4 to 25 thousand years), the time interval of the declining magnetic moment being 1.5 to 2.0 time longer, that is, embraced a time interval of up to 16 thousand years [Gurarii, 1988]. Merrill and McFadden [1999] estimated the time necessary for a complete reversal to be 1 to 8 thousand years.…”

The Complexity of Reversals

“…Figure 6 shows another complex, high-resolution record of a different reversal, the Gauss/Matuyama transition recorded in a core of lacustrine sediment from eastern California [Glen et al, 1999b]. Based on detailed magnetostratigraphy, the average deposition rate was about 22 cm/kyr during late-Gauss and early Matuyama time, almost twice that of the previous example, and the lithololgy is uniform [Liddicoat, 1982;Glen et al, 1999a]. The core was sampled continuously at 1-cm spacing through a 2.1 m stratigraphic interval centered on the transition, with two or three 1-cm cubic specimens measured at each level.…”

Decay‐rate dependence of anhysteretic remanence: Fundamental origin and paleomagnetic applications

“…Optimum demagnetization is tuned to eliminating viscous overprints without rendering the signal unmeasurably weak. In recent studies, a wide variety of fields and temperatures were used: 10 mT [ Peck et al , 1996; Yamazaki et al , 1995], 15 mT [ Verosub et al , 1996; Yamazaki and Ioka , 1994], 17.5 mT [ Tauxe and Hartl , 1997], 20 mT [ Clement and Kent , 1991; Meynadier et al , 1994, 1995; Tric et al , 1992; Valet et al , 1994; Yamazaki and Oda , 2001, 2002], 25 mT [ Roberts et al , 1997], 30 mT [ Haag , 2000; Pan et al , 2001], 40 mT, [ Glen et al , 1999], averages of more than two steps [ Brachfeld and Banerjee , 2000; Channell et al , 2002; Dinares‐Turell et al , 2002; Guyodo et al , 2001; Meynadier et al , 1992], and thermal demagnetization to 420°C [ Laj et al , 1996]. …”