Geology topics

Research about Arizona, California, Colorado, Idaho, New Mexico, Nevada, Oregon, Utah, Washington

Source-linked reports with geographic coverage including Arizona, California, Colorado, Idaho, New Mexico, Nevada, Oregon, Utah, Washington.

2 recordsLinked to original sources

USGS2010

Archeomagnetic dating in western North America: An updated reference curve based on paleomagnetic and archeomagnetic data sets

[1] A robust database of paleomagnetic (PM) and archeomagnetic (AM) data for western North America covering the past 4 millennia is assembled from three data sets: (1) published PM data for dated lava flows, (2) recently published AM data generated by R. L. DuBois, and (3) published AM data generated by J. L. Eighmy. Chronologic information for the AM data sets has been reassessed, and the data points have been assigned to age ranges depending on their archeological contexts. We have selected the computer program ArcheoCourbe, available from M. Le Goff (http://www.ipgp.fr/∼legoff) or the auxiliary material (see also http://EarthRef.org), to construct AM reference curves and to quantitatively estimate AM dates for archeological and geological samples. The updated curve provides a more detailed record of prehistoric secular variation for western North America than was previously available and shows a short interval of rapid secular variation (SV) in the 10th or 11th centuries at near-excursional rates. Similar and coeval features in the Hawaiian and, to a lesser extent, Arkansan SV data sets possibly indicate a rapid amplitudinal shift in the regional nondipole field at that time.

Arizona, California, Colorado, Idaho, New Mexico, ↗

USGS2002

A Holocene paleosecular variation from 14C-dated volcanic rocks in western North America

A paleosecular variation (PSV) curve for western North America is presented on the basis of 94 virtual geomagnetic poles (VGPs) from dated volcanic rocks sampled at 446 sites. Approximately 60% of the paleomagnetic database has been previously published. A curve defined by “spherical smoothed splines” is fitted to the VGPs, ranked by the quality of the age determinations, where the data density is highest between 3690 and −30 years before present (B.P.) (A.D. 1950), between 7800 and 7050 years B.P., and between 14,060 and 12,700 years B.P. The younger segments of the curve derived from volcanic rocks are similar but less complex than other high-resolution PSV curves derived from lacustrine sediments, particularly the record at Fish Lake, Oregon. The PSV record from lava flows (PSVL), however, is perhaps more reliable in its general shape and chronology because of the higher fidelity of volcanic rocks as magnetic field recorders and because of the greater density of 14 C dates. The new PSVL record provides a partial Holocene master curve for western North America and will be of particular value in dating geological and archeological materials using paleomagnetic directions.

Arizona, California, Colorado, Idaho, New Mexico, ↗