A possible lacustrine paleomagnetic record of the Blake episode from Pringle Falls, Oregon, U.S.A.

Details A possible lacustrine paleomagnetic record of the Blake episode from Pringle Falls, Oregon, U.S.A. A possible lacustrine paleomagnetic record of the Blake episode from Pringle Falls, Oregon, U.S.A.

Jul 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989pepi...56..112h&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 56, Issue 1-2, p. 112-123.

Physics

31

Scientific paper

We have studied a high-resolution paleomagnetic record of a magnetic polarity episode recovered from a 20-m section of diatomaceous lacustrine sediments from Pringle Falls near La Pine, Oregon (43.7° N, 238.6° E). A total of 474 samples (982 specimens) were collected at about 5-cm intervals from the 20-m section. The age of this record is at present constrained between 0.6 MA and 18 000 yr based upon a pollen date from the older part of the lakebed sequence and the age of the younger glacial deposits that overlie the lakebeds. The characteristic magnetization of the samples was determined by alternating field (AF) demagnetization to 15 mT. The average normal polarity stable declination and inclination of the non-magnetic polarity episode sampled section (61° α95 = 2.6°) is statistically equivalent to that expected at this site for a geocentric axial dipole (62°). The record provides a Virtual Geomagnetic Pole (VGP) path that identifies a well-defined clockwise NE-SW loop with a radius of 60°, followed by a second younger feature that traces out a counter-clockwise loop 15° in radius, residing in the NE quadrant, and characterized by low latitudes. Interpretation of the natural remanent magnetization/anhysteretic remanent magnetization (NRM/ARM) ratios for the samples indicates that the field intensity may have fallen and then increased above the average dipole field intensity. The low-intensity interval ends before the onset of the polarity episode as defined by directions and may suggest that the episode is a result of an unstable regeneration of the field after a significant lowering of overall field intensity. These two characteristic features are similar to the two features present in the Blake geomagnetic polarity episode at 114 000 and 105 000 yr BP observed in different parts of the world.

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