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2015
Cromwell, G, Tauxe L, Halldorsson SA.  2015.  New paleointensity results from rapidly cooled Icelandic lavas: Implications for Arctic geomagnetic field strength. Journal of Geophysical Research-Solid Earth. 120:2913-2934.   10.1002/2014jb011828   AbstractWebsite

The Earth's magnetic field is assumed to be a geocentric axial dipole (GAD) when averaged over sufficient time (10(5)-10(6)years). Recent investigations of global paleosecular variation and time-averaged field behavior on million year timescales generally support a predominantly dipole field in the Northern Hemisphere, but unique field structures at high southern latitudes suggest the presence of a substantial (g) over bar (0)(2) quadrupolar component. Average paleointensity results from Antarctica are approximately half the value predicted by a GAD field; this behavior has not been sufficiently investigated because there is a paucity of absolute paleointensity data from the high latitudes of the Arctic and Antarctic, so no adequate comparisons have been made between the two regions. We collected glassy volcanic material from 129 subaerial and subglacial volcanic units in Iceland in order to provide a suitable intensity data set at high northern latitudes. Forty-four sites met our very strict specimen and site level selection criteria. Four Holocene sites have a median intensity value of 55.8 +/- 15.6 mu T (virtual axial dipole moment=78.1 +/- 22.0ZAm(2)), consistent with the present-day field. Thirty-seven sites are between 11ka and 3.35Ma with a median intensity of 33.1 +/- 8.3 mu T (47.0 +/- 11.6ZAm(2)). This median intensity is indistinguishable from some long-term global field strength estimates. Reevaluation of existing high-latitude data suggests a general agreement with our Iceland results, but there are still too few Antarctic sites to adequately compare Arctic and Antarctic field behaviors.

2011
Shaar, R, Ben-Yosef E, Ron H, Tauxe L, Agnon A, Kessel R.  2011.  Geomagnetic field intensity: How high can it get? How fast can it change? Constraints from Iron Age copper slag Earth and Planetary Science Letters. 301:297-306.   10.1016/j.epsl.2010.11.013   AbstractWebsite

The intensity of the geomagnetic field varies over different time scales. Yet, constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record. The purpose of this study is to place firm limits on these fundamental properties by constructing a high-resolution archaeointensity record of the Levant from the 11th century to the early 9th century BCE, a period over which the geomagnetic field reached its maximum intensity in Eurasia over the past 50,000 years. We investigate a (14)C-dated sequence of ten layers of slag material, which accumulated within an ancient industrial waste mound of an Iron Age copper-smelting site in southern Israel. Depositional stratigraphy constrains relative ages of samples analyzed for paleointensity, and (14)C dates from different horizons of the mound constrain the age of the whole sequence. The analysis yielded 35 paleointenisty data points with accuracy better than 94% and precision better than 6%, covering a period of less than 350 years, most probably 200 years. We construct a new high-resolution quasi-continuous archaeointensity curve of the Levant that displays two dramatic spikes in geomagnetic intensity, each corresponding to virtual axial dipole moment (VADM) in excess of 200 ZAm(2). The geomagnetic spikes rise and fall over a period of less than 30 years and are associated with VADM fluctuations of at least 70 ZAm2. Thus, the Levantine archaeomagnetic record places new constraints on maximum geomagnetic intensity as well as for its rate of change. Yet, it is not clear whether the geomagnetic spikes are local non-dipolar features or a geomagnetic dipolar phenomenon. (C) 2010 Elsevier B.V. All rights reserved.

2009
Ben-Yosef, E, Tauxe L, Levy TE, Shaar R, Ron H, Najjar M.  2009.  Geomagnetic intensity spike recorded in high resolution slag deposit in Southern Jordan. Earth and Planetary Science Letters. 287:529-539.   10.1016/j.epsl.2009.09.001   AbstractWebsite

In paleomagnetism, periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals. Hence, questions such as how strong the field can get and how fast changes occur are still open. In this paper we report on data obtained from an archaeometallurgical excavation in the Middle East, designed specifically for archaeomagnetic sampling. We measured 342 specimens from 72 samples collected from a 6.1 m mound of well stratified copper production debris at the early Iron Age (12th-9th centuries BCE) site of Khirbat en-Nahas in Southern Jordan. Seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values. The results display a remarkable spike in field strength, with sample mean values of over 120 mu T (compared to the current field strength of 44 mu T). A suite of 13 radiocarbon dates intimately associated with our samples, tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities. (C) 2009 Elsevier B.V. All rights reserved.

Lawrence, KP, Tauxe L, Staudigel H, Constable CG, Koppers A, McIntosh W, Johnson CL.  2009.  Paleomagnetic field properties at high southern latitude. Geochemistry Geophysics Geosystems. 10   10.1029/2008gc002072   AbstractWebsite

Statistical analyses of paleomagnetic data from lava flows are used to study geomagnetic field behavior on million year timescales. Previous paleomagnetic studies have lacked high-latitude measurements necessary to investigate the persistence of geomagnetic anomalies observed in the recent and historical field and replicated in some numerical geodynamo simulations. These simulations suggest that reduced convective flow inside the tangent cylinder may affect the magnetic field at high latitude, whereas lower-latitude observations are expressions of columnar/helical flow outside the tangent cylinder. This paper presents new paleointensity and paleodirectional data from 100 volcanic sites in the Erebus Volcanic Province (EVP), Antarctica, and 21 new age determinations by the (40)Ar/(39)Ar incremental heating method. The new EVP data are combined with previously published paleomagnetic and geochronological results, providing 133 sites, 91 having radioisotopic dates. Modified Thellier-Thellier paleointensity estimates are reported for 47 sites (37 have dates). Ages for the combined data set span 0.03 to 13.42 Ma. The 125 high-quality EVP directional data selected from the merged data set have a non-Fisherian distribution and a mean direction with an inclination anomaly of similar to 3 degrees, but 95% confidence limits include the prediction from a geocentric axial dipole. Virtual geomagnetic pole (VGP) dispersions for Brunhes, Matuyama, and the combined 0-5 Ma data set are consistently high compared with values from middle-to low-latitude regions regardless of the criterion used to determine transitional fields. With VGP latitude cut off at 45 degrees, the dispersion (23.9 +/-2.1 degrees) for the combined 0-5 Ma EVP data set is consistent with earlier high-latitude data and paleosecular variation (PSV) in Model G but not with some more recent statistical PSV models. Mean EVP paleointensity of 31.5 +/-2.4 mu T, derived from 41 high-quality sites, is about half the current value at McMurdo (similar to 63 mu T). The result is essentially independent of data selection criteria. High VGP dispersion and low-intensity values support the global observation of anticorrelation between directional variability and field strength. Simulations of time-varying dipole strength show that uneven temporal sampling may bias the mean EVP intensity estimate, but the possibility of persistently anomalous field behavior at high latitude cannot be excluded.

Sbarbori, E, Tauxe L, Goguitchaichvili A, Urrutia-Fucugauchi J, Bohrson WA.  2009.  Paleomagnetic behavior of volcanic rocks from Isla Socorro, Mexico. Earth Planets and Space. 61:191-204. AbstractWebsite

The direction and magnitude of the geomagnetic field vary both spatially and temporally and undergo significant departures from that of a geocentric axial dipole. In order to properly characterize persistent behaviors, time-averaged field models must be based oil the highest quality data. Here we present full-vector paleomagnetic data for volcanic units exposed in the southeast quadrant of the island of Socorro, Mexico. We carried out a joint expedition between the Scripps Institution of Oceanography and the Universidad Nacional Autonoma Mexico to Isla Socorro in January of 2005 during which we collected oriented paleomagnetic samples from 21 sites, representing as many as 10 different volcanic units (the oldest of which is similar to 540 ka). We subjected over 100 specimens to the most up-to-date paleointensity methods, and included the standard reliability checks. In all earlier study, Bohrson et al. (1996) proposed a series of widespread eruptive events, based on similarities of argon/argon dates. Paleointensity from specimens that conform to the strictest acceptance criteria are available from both the (unoriented) original sample collection and our fully oriented (but as yet undated) new collection. Correlation between the two collections is however problematic. The time-averaged direction from Socorro is consistent with that expected from a geocentric axial dipole, and the time-averaged intensity is 30.0 +/- 7.1 mu T, equivalent to a virtual axial dipole moment (VADM) of 67.6 +/- 16.0 ZAm(2).

2008
Ben-Yosef, E, Tauxe L, Ron H, Agnon A, Avner U, Najjar M, Levy TE.  2008.  A new approach for geomagnetic archaeointensity research: insights on ancient metallurgy in the Southern Levant. Journal of Archaeological Science. 35:2863-2879.   10.1016/j.jas.2008.05.016   AbstractWebsite

We present results from an archaeointensity investigation based on a relatively unexploited recording medium, copper slag deposits. Together with a recently improved experimental design for the archaeointensity experiment, we demonstrate the applicability of this medium, as well as other archaeometallurgical artifacts, for the study of the ancient geomagnetic field intensity. In addition to archaeointensity data from well-dated archaeological contexts, we obtained reliable archaeointensity results from poorly dated or contentious archaeometallurgical sites in the Southern Levant. These results shed new light on the dating of these sites, among them the copper smelting installation of Timna 39b a site that has important implications for the beginning of metallurgy during the fifth millennium BCE. The paper also aims to introduce archaeointensity research to the archaeologist scholar, and to encourage further collaboration between the disciplines in future research. (C) 2008 Elsevier Ltd. All rights reserved.

He, HY, Pan YX, Tauxe L, Qin HF, Zhu RX.  2008.  Toward age determination of the M0r (Barremian-Aptian boundary) of the Early Cretaceous. Physics of the Earth and Planetary Interiors. 169:41-48.   10.1016/j.pepi.2008.07.014   AbstractWebsite

We carried out integrated paleomagnetic and geochronologic investigations on Cretaceous lava flows at the Mashenmiao-Zhuanchengzi (MZ) section in Yixian, Liaoning Province, northeast China in seeking to understand the onset of the magnetic polarity chron M0r and the associated Barremian-Aptian boundary (BAB), which has been reported to be 125.0 +/- 1.0 Ma [Ogg, J.G., Agternerg, F.P., Gradstein, F.M., 2004. The Cretaceous period. In: Gradstein, F.M., Ogg, J.G., Smith, A.G. (Eds.). A Geologic Time Scale. Cambridge University Press, UK, pp. 344-383]. Stepwise thermal or alternating field demagnetization indicates that all lava flows in the studied section were reversely magnetized. Ar-40/Ar-39 ages obtained from three lava flows are 121.2 +/- 1.3 Ma, 120.2 +/- 1.5 Ma and 122.0 +/- 13 Ma, respectively, with a weighted mean age of 121.2 +/- 0.5 Ma (2 sigma). In combination with previous studies, we argue that these lavas are M0r in age, which therefore is probably some 4 Myr younger than estimated in the 125 Ma of the most recent geologic time scale. (C) 2008 Elsevier B.V. All rights reserved.

2007
Granot, R, Tauxe L, Gee JS, Ron H.  2007.  A view into the Cretaceous geomagnetic field from analysis of gabbros and submarine glasses. Earth and Planetary Science Letters. 256:1-11.   10.1016/j.epsl.2006.12.028   AbstractWebsite

The nature of the geomagnetic field during the Cretaceous normal polarity superchron (CNS) has been a matter of debate for several decades. Numerical geodynamo simulations predict higher intensities, but comparable variability, during times of few reversals than times with frequent reversals. Published geomagnetic paleointensity data from the CNS are highly scattered suggesting that additional studies are required. Here we present new paleointensity results from 18 sites collected from the lower oceanic crust of the Troodos ophiolite, Cyprus (92.1 Ma old). Together with recently published data from the Troodos upper crust we obtain three independent palcointensity time-series. These sequences reveal quasi-cyclic variations of intensities about a mean value of 54 +/- 20 Z Am(2), providing insight into the fluctuating nature of the Cretaceous magnetic field. Our data suggest the CNS field was both weaker and more variable than predicted by geodynamo simulations. The large amplitudes of these variations may explain the wide range of dipole moments previously determined from the CNS. (c) 2007 Elsevier B.V. All rights reserved.

2006
Tauxe, L.  2006.  Long-term trends in paleointensity: The contribution of DSDP/ODP submarine basaltic glass collections. Physics of the Earth and Planetary Interiors. 156:223-241.   10.1016/j.pepi.2005.03.022   AbstractWebsite

The Deep Sea Drilling Project and the Ocean Drilling Program have been collecting fresh appearing submarine basaltic glass from the world's oceans for over three decades. This glass has proved nearly ideal for estimating paleointensity variations of the Earth's magnetic field. We compile here data for 726 paleointensity experiments from six publications on paleointensity using DSDP/ODP glass. We also include new data for an additional 225 specimens. These were obtained through the so-called "IZZI" paleointensity experiment of [Tauxe, L., Staudigel, H., 2004. Strength of the geomagnetic field in the cretaceous normal superchron: new data from submarine basaltic glass of the troodos ophiolite. Geochem. Geophys. Geosyst. 5 (2), Q02H06, doi: 10.1029/2003GCO00635] whereby infield-zerofield steps are alternated with the zerofield-infield steps to enhance quality assessment of the resulting data. The entire collection of data from 951 experiments was prepared for uploading to the MagIC data base (http://earthref.org), including original measurements, interpretations, and useful metadata. Excellent results were obtained throughout the depth (> 1400 mbsf) and age (0-160 Ma) range sampled. DSDP/ODP glass data are compared with published paleointensity data meeting minimal acceptance criteria from the time interval 1-160 Ma. Paleolatitudes were estimated for all cooling units in a self-consistent manner for use in calculating virtual axial dipole moments. We conclude: (1) There is about a 20% difference in mean values between the SBG and the lava flow data (48 +/- 36 and 57 +/- 29 ZAm(2) respectively). The difference is caused by the fact that there are more higher values in the lava flow data than in the SBG data set rather than a difference in the minimum values. Lava flows cooling over a periods of days to months can account for the discrepancy. (2) The positive relationship between polarity interval length and average paleofield intensity first hypothesized by [Cox, A.V, 1968. Lengths of geomagnetic polarity intervals. J. Geophys. Res. 73, 3247-3260] is supported by data compiled here. The Brunhes data (for which we have only a minimum estimate for polarity interval length) are consistent with a long polarity interval, suggesting that instead of racing toward reversal [Hulot, G., Eymin, C., Langlais, B., Mandea, M., Olsen, N., 2002. Small-scale structure of the geodynamo inferred from oersted and magsat satellite data. Nature 416, 620-623], we could instead be in the midst of a long stable polarity interval. (3) Because the average value appears to be a function of polarity interval length, it is probably not useful to calculate a mean value. Nonetheless, it appears that most of the time (apart from the Brunhes and the longest polarity intervals), the average dipole moment is substantially less than the present day value as suggested by [Juarez, T., Tauxe, L., Gee, J.S., Pick, T., 1998. The intensity of the earth's magnetic field over the past 160 million years. Nature 394, 878-881]. (c) 2006 Published by Elsevier B.V.

Krijgsman, W, Tauxe L.  2006.  E/I corrected paleolatitudes for the sedimentary rocks of the Baja British Columbia hypothesis. Earth and Planetary Science Letters. 242:205-216.   10.1016/j.epsl.2005.11.052   AbstractWebsite

Paleomagnetic inclinations from sediments of the western terranes of Canada are consistently too shallow for their reconstructed paleogeographic positions. Two contradicting explanations for these discrepancies are: (1) terranes have been displaced northward with respect to the stable American craton by several thousands of kilometres between the Late Cretaceous (similar to 75 Ma) and the Eocene (similar to 50 Ma) and (2) sedimentary inclination error has caused a shallow bias in the paleomagnetic directions. Here, we apply the elongation/inclination (E/I) method to paleomagnetie data sets from sedimentary rocks of supposedly allochtonous terranes of Nvestem North America to correct for inclination flattening. Our results indicate that the paleomagnetic directions from the continental Silverquick sediments (95-92 Ma) of southern British Colombia are not seriously affected by inclination error, because the magnetic signal most likely concerns a chemical remanent magnetisation (CRM). In contrast, the marine sediments of the Nanaimo Group (84-72 Ma) of Vancouver Island region appear seriously affected by inclination flattening (f=0.7) and the EA corrected mean inclinations are about 9 degrees steeper than the original data. We arrive at corrected inclinations/paleolatitudes of I** = 57 degrees/lambda = 38 degrees N for the Silverquick and I** = 55 degrees/lambda = 36 degrees N for the Nanaimo sediments. Our corrected paleolatitudes indicate that the Canadian terranes were indeed located adjacent to the Baja Californian margin during the Late Cretaceous, thus supporting the Baja BC hypothesis. (c) 2005 Elsevier B.V. All rights reserved.

2004
Tauxe, L, Gans P, Mankinen EA.  2004.  Paleomagnetism and Ar-40/Ar-39 ages from volcanics extruded during the Matuyama and Brunhes Chrons near McMurdo Sound, Antarctica. Geochemistry Geophysics Geosystems. 5   10.1029/2003gc000656   AbstractWebsite

Maps of virtual geomagnetic poles derived from international geomagnetic reference field models show large lobes with significant departures from the spin axis. These lobes persist in field models for the last few millenia. The anomalous lobes are associated with observation sites at extreme southerly latitudes. To determine whether these features persist for millions of years, paleomagnetic vector data from the continent of Antarctica are essential. We present here new paleomagnetic vector data and Ar-40/Ar-39 ages from lava flows spanning the Brunhes and Matuyama Chrons from the vicinity of McMurdo Sound, Antarctica. Oriented paleomagnetic samples were collected from 50 lava flows by E. Mankinen and A. Cox in the 1965-1966 austral summer season. Preliminary data based largely on the natural remanent magnetization (NRM) directions were published by Mankinen and Cox [1988]. We have performed detailed paleomagnetic investigations of 37 sites with multiple fully oriented core samples to investigate the reliability of results from this unique sample collection. Of these, only one site fails to meet our acceptance criteria for directional data. Seven sites are reversely magnetized. The mean normal and reverse directions are antipodal. The combined mean direction has (D) over bar =12, (I) over bar=-86, alpha=4, kappa=37 and is indistinguishable from that expected from a GAD field. We obtained reproducible absolute paleointensity estimates from 15 lava flows with a mean dipole moment of 49 ZAm(2) and a standard deviation of 28 ZAm(2). Ar-40/Ar-39 age determinations were successfully carried out on samples from 18 of the flows. Our new isotopic ages and paleomagnetic polarities are consistent with the currently accepted geomagnetic reversal timescales.

2003
Schwehr, K, Tauxe L.  2003.  Characterization of soft-sediment deformation: Detection of cryptoslumps using magnetic methods. Geology. 31:203-206.   10.1130/0091-7613(2003)031<0203:cossdd>2.0.co;2   AbstractWebsite

Many workers have explored anisotropy of magnetic susceptibility (AMS) of sediments as an indicator of deformation. Several studies have used deflection of the eigen-vector associated with the minimum in susceptibility, V-3, as a criterion for deformation. We examine the AMS record of a well-exposed slump and find that although demonstrable deformation can occur without deflecting the V-3 directions, an oblate AMS fabric is transformed into a triaxial fabric during initial deformation. Transformation of the fabric from oblate to triaxial appears to be highly correlated with an increase in natural remanent magnetization scatter, whereas deflection of the V-3 axes is not. We suggest that subtle soft-sediment deformation can be detected by using AMS fabric.

2002
Bowles, J, Gee J, Hildebrand J, Tauxe L.  2002.  Archaeomagnetic intensity results from California and Ecuador: evaluation of regional data. Earth and Planetary Science Letters. 203:967-981.   10.1016/s0012-821x(02)00927-5   AbstractWebsite

We present new archaeointensity data for southeastern California (similar to33degreesN, similar to115degreesW, 50-1500 yr BP) and northwestern South America (Ecuador, 2.4degreesS, 80.7degreesW, 4000-5000 yr BP). These results represent the only data from California, as well as the oldest archaeointensity data now available in northwestern South America. In comparing our results to previously published data for the southwestern United States and northwestern South America, we note that significant scatter in the existing data makes comparisons and interpretations difficult. We undertake an analysis of the sources of data scatter (including age uncertainty, experimental errors, cooling rate differences, magnetic anisotropy, and field distortion) and evaluate the effects of scatter and error on the smoothed archaeointensity record. By making corrections where possible and eliminating questionable data, scatter is significantly reduced, especially in South America, but is far from eliminated. However, we believe the long-period fluctuations in intensity can be resolved, and differences between the Southwestern and South American records can be identified. The Southwest data are distinguished from the South American data by much higher virtual axial dipole moment values from similar to 0-600 yr BP and by a broad low between similar to 1000-1500 yr BP. Comparisons to global paleofield models reveal disagreements between the models and the archaeointensity data in these two regions, underscoring the need for additional intensity data to constrain the models in much of the world. (C) 2002 Elsevier Science B.V. All rights reserved.

Deino, AL, Tauxe L, Monaghan M, Hill A.  2002.  Ar-40/Ar-30 geochronology and paleomagnetic stratigraphy of the Lukeino and lower Chemeron Formations at Tabarin and Kapcheberek, Tugen Hills, Kenya. Journal of Human Evolution. 42:117-140.   10.1006/jhev.2001.0521   AbstractWebsite

Ar-40/Ar-39 single-crystal laser-fusion dating, K-Ar dating, and paleo-magnetic reversal stratigraphy have been used to determine the chronostratigraphy of the Kabarnet Trachyte, Lukeino Formation, Kaparaina Basalt Formation, and Chemeron Formation at the sites of Kapcheberek (BPRP#77) and Tabarin (BPRP#77) in the Tugen Hills, Kenya. The succession ranges in age from 6(.)56-3(.)8 Ma. The upper Lukeino Formation at Kapcherberek, including the fauna from the site BPRP#76, was deposited during chron C3r and can be constrained to the interval 5(.)88-5(.)72 Ma. The Chemeron Formation at Tabarin includes at the base an ignimbrite and associated basal air-fall tuff with a combined age of 5(.)31 +/- 0(.)03 Ma. Sedimentary and volcaniclastic rocks of the Chemeron Formation which unconformably overlie the ignimbrite record chrons C3n.2n through C2Ar. The combined Ar-40/Ar-39 and paleomagnetic data constrain the age of this sequence to 4(.)63-3(.)837 Ma. The age of the Tabarin mandible fragment (KNM-TH 13150) and associated fauna at site BPRP#77 in the Chemeron Formation is 4(.)48-4(.)41 Ma, marginally older than similar early hominids from Aramis, Ethiopia. Basin subsidence appears to be defining an overall accumulation rate of about 17 cm/ka over the 2(.)7 Ma represented at Tabarin and Kapcheberek, despite episodes of rapid accumulation and hiatuses. (C) 2002 Academic Press.

2001
Cronin, M, Tauxe L, Constable C, Selkin P, Pick T.  2001.  Noise in the quiet zone. Earth and Planetary Science Letters. 190:13-30.   10.1016/s0012-821x(01)00354-5   AbstractWebsite

We have carried out a detailed paleomagnetic investigation of two stratigraphically overlapping sections from the Scaglia Bianca Formation (similar to 85-89.5 Ma) in the Umbria-Marche area in central Italy. Sampling was conducted over 32 in and 7 in intervals at La Roccaccia and Furlo respectively. After AF cleaning the majority of specimens show the expected normal magnetic field orientation, however a number of specimens are directionally anomalous. Some of these deviant specimens are accompanied by apparent spikes or dips in normalized intensity. A detailed investigation of rock magnetics shows that most of these deviations are not a sign of excursionary geomagnetic field behavior, but rather correspond to specimens with distinct rock magnetic characteristics and are therefore rock magnetic 'noise'. Such specimens should not be interpreted as records of the geomagnetic field. Our experience suggests that detailed rock magnetic and magnetic fabric analysis should be done on all anomalous directions prior to interpreting them as geomagnetic field behavior. After elimination of rock magnetic noise in the Scaglia Bianca data sets, there is a high degree of agreement in direction and to a lesser extent relative intensity between correlative portions of the two sections. We therefore offer this data set as a robust record of geomagnetic field behavior during the 4.5 Myr interval represented by the La Roccaccia section. A statistical analysis of the relative intensity observations suggests that this period of the Cretaceous Normal Superchron is characterized by a normalized variability in paleointensity (standard deviation about 28% of the mean value) that is significantly lower than seen during the Oligocene over intervals in which reversals or tiny wiggles occur (typically about 50%). The directional stability results in virtual geomagnetic pole dispersion compatible with that found in volcanic rocks from around the same latitude and ranging in age from 80 to 110 Ma. (C) 2001 Elsevier Science B.V. All rights reserved.

2000
Katari, K, Tauxe L.  2000.  Effects of pH and salinity on the intensity of magnetization in redeposited sediments. Earth and Planetary Science Letters. 181:489-496.   10.1016/s0012-821x(00)00226-0   AbstractWebsite

The intensity of magnetization in redeposited sediments was measured as a function of salinity and pH of the sediment-water mixture. The intensity was relatively low at high salinity or low pH. Under these conditions, interparticle bonds are enhanced, which lead to the formation of larger flocs. Ferromagnetic minerals (magnetite in our sediment) are incorporated in the flocs consisting mainly of non-magnetic minerals, and orientation along an applied field is resisted by the drag proportional to the third power of the diameter of the floc. Higher intensity is recorded at lower salinity and higher pH, when inter-particle forces are weaker, and flee sizes are smaller. The increase of magnetization as a function of pH stops at a pH of about 5, which is the PZC of the edge of illite (the dominant nonmagnetic mineral in our sediment). Above this pH, both the edge and face of the illite grains are negative, and there is net repulsion, which retards flocculation. The interactions between clay particles therefore have a larger effect on the intensity of magnetization than interactions between magnetite and clay. This suggests that magnetite is always included in a clay-magnetite domain, and this domain is the smallest unit that is reoriented by a magnetic field. (C) 2000 Elsevier Science B.V. All rights reserved.

Katari, K, Tauxe L, King J.  2000.  A reassessment of post-depositional remanent magnetism: preliminary experiments with natural sediments. Earth and Planetary Science Letters. 183:147-160.   10.1016/s0012-821x(00)00255-7   AbstractWebsite

Realignment of magnetic grains below the sediment-water interface is thought to impart a post-depositional remanent magnetization (pDRM). However, there is little convincing evidence in the published literature that pDRM is the dominant mechanism by which sediments become magnetized. We report here preliminary results from two kinds of laboratory experiments designed to investigate whether post-depositional reorientation of magnetic particles is likely to occur in nature. In the first experiment, we monitored changes in the magnetization of natural sediments in response to changing laboratory fields. Our results are inconsistent with post-depositional reorientation of magnetic particles. In a second experiment, we put live worms in a multi-core tube with the original sediment-water interface intact. Remagnetization was only observed in samples taken from a mound of fecal pellets formed at the surface. These pellets had been suspended by a worm, and redeposited in the laboratory field. The other samples, which were not resuspended, but nonetheless bioturbated by the worms, showed no change in magnetization. Our preliminary results do not support the hypothesis that post-depositional reorientation occurs in natural, undisturbed sediments below the sediment-water interface. (C) 2000 Elsevier Science B.V. All rights reserved.

Juarez, MT, Tauxe L.  2000.  The intensity of the time-averaged geomagnetic field: the last 5 Myr. Earth and Planetary Science Letters. 175:169-180.   10.1016/s0012-821x(99)00306-4   AbstractWebsite

The existing database for paleointensity estimates of the ancient geomagnetic field contains more than 1500 data points collected through decades of effort. Despite the huge amount of work put into obtaining these data, there remains a strong bias in the age and global distribution of the data reward very young results from a few locations. Also, few of the data meet strict criteria for reliability and most are of unknown quality. In order to improve the age and spatial distribution of the paleointensity database, we have carried out paleointensity experiments on submarine basaltic glasses from a number of DSDP sites. Of particular interest are the sites that provide paleointensity data spanning the time period 0.3-5 Ma, a time of relatively few high quality published data points. Our new data are concordant with contemporaneous data from the published literature that meet minimum acceptance criteria, and the combined data set yields an average dipole moment of 5.49 +/- 2.36 x 10(22) Am-2. This average value is comparable to the average paleofield for the period 5-160 Ma (4.2 +/- 2.3 x 10(22) Am-2) [T. Juarez, L. Tauxe, J.S. Gee and T. Pick (1998) Nature 394, 878-881] and is substantially less than the value of approximately 8 x 10(22) Am-2 often quoted for the last 5 Myr (e.g. [McFadden and McElhinny (1982) J. Geomagn. Geoelectr. 34, 163-189; A.T. Goguitchaichvili, M. Prevot and P. Camps (1999) Earth Planet. Sci. Lett. 167, 15-34]). (C) 2000 Elsevier Science B.V. All rights reserved.

Selkin, PA, Gee JS, Tauxe L, Meurer WP, Newell AJ.  2000.  The effect of remanence anisotropy on paleointensity estimates: a case study from the Archean Stillwater Complex. Earth and Planetary Science Letters. 183:403-416.   10.1016/s0012-821x(00)00292-2   AbstractWebsite

Paleomagnetism of Archean rocks potentially provides information about the early development of the Earth and of the geodynamo. Precambrian layered intrusive rocks are good candidates for paleomagnetic studies: such complexes are commonly relatively unaltered and may contain some single-domain magnetite 'armored' by silicate mineral grains. However, layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy. Magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected. Here we examine the magnetic anisotropy of an anorthosite sample with a well-developed magmatic foliation. The effect of the sample's remanence fabric on paleointensity determinations is significant: paleointensities estimated by the method of Thellier and Thellier range from 17 to 55 muT for specimens magnetized in a field of 25 muT. We describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the Stillwater Complex (MT, USA) of similar to 32 muT (adjusted for the effects of slow cooling). (C) 2000 Elsevier Science B.V. All rights reserved.

1999
Kok, YS, Tauxe L.  1999.  Long-tau VRM and relative paleointensity estimates in sediments. Earth and Planetary Science Letters. 168:145-158.   10.1016/s0012-821x(99)00041-2   AbstractWebsite

Geomagnetic paleointensity measurements from sedimentary records can be severely affected by viscous remanent magnetization (VRM). We present a method for determining varying amounts of long-term VRM acquired during the present polarity interval, using the typically non-linear relationship between acquisition of artificial magnetization and demagnetization of NRM. The non-linear parts are to be avoided for paleointensity determinations, but here we focus on their use for indicators of long-relaxation time VRM. The method, which does not require determining paleointensity values, suggests correlations with paleoclimate curves and age-dependent growth of VRM. Furthermore, it appears that the long-tau VRM acquired during the Pleistocene is accompanied by short-tau effects detected in the laboratory environment. (C) 1999 Elsevier Science B.V. All rights reserved.

1998
Johnson, CL, Wijbrans JR, Constable CG, Gee J, Staudigel H, Tauxe L, Forjaz VH, Salgueiro M.  1998.  Ar-40/Ar-39 ages and paleomagnetism of Sao Miguel lavas, Azores. Earth and Planetary Science Letters. 160:637-649.   10.1016/s0012-821x(98)00117-4   AbstractWebsite

We present new Ar-40/Ar-39 ages and paleomagnetic data for Sao Miguel island, Azores. Paleomagnetic samples were obtained for 34 flows and one dike; successful mean paleomagnetic directions were obtained for 28 of these 35 sites. Ar-40/Ar-39 age determinations on 12 flows from the Nordeste complex were attempted successfully: ages obtained are between 0.78 Ma and 0.88 Ma, in contrast to published K-Ar ages of 1 Ma to 4 Ma. Our radiometric ages are consistent with the reverse polarity paleomagnetic field directions, and indicate that the entire exposed part of the Nordeste complex is of a late Matuyama age. The duration of volcanism across Sao Miguel is significantly less than previously believed, which has important implications for regional melt generation processes, and temporal sampling of the geomagnetic field. Observed stable isotope and trace element trends across the island can be explained, at least in part, by communication between different magma source regions at depth. The Ar-40/Ar-39 ages indicate that our normal polarity paleomagnetic data sample at least 0.1 Myr (0-0.1 Ma) and up to 0.78 Myr (0-0.78 Ma) of paleosecular variation and our reverse polarity data sample approximately 0.1 Myr (0.78-0.88 Ma) of paleosecular variation. Our results demonstrate that precise radiometric dating of numerous flows sampled is essential to accurate inferences of long-term geomagnetic field behavior. Negative inclination anomalies are observed for both the normal and reverse polarity time-averaged field. Within the data uncertainties, normal and reverse polarity field directions are antipodal, but the reverse polarity field shows a significant deviation from a geocentric axial dipole direction. (C) 1998 Elsevier Science B.V. All rights reserved.

1996
Constable, C, Tauxe L.  1996.  Towards absolute calibration of sedimentary paleointensity records. Earth and Planetary Science Letters. 143:269-274.   10.1016/0012-821x(96)00128-8   AbstractWebsite

Using relative paleointensity estimates derived from twelve globally distributed pelagic sediment cores, we assess whether they record a signal consistent with that expected from a dominant geocentric axial dipole, The cores span the Matuyama-Brunhes boundary and we normalize the observations by supposing that at the time the direction reverses the intensity low reflects only the non-axial-dipole contribution to the field. We further assume that this non-axial-dipole contribution to the field is invariant with geographic location. From absolute paleointensity compilations we estimate its size to be about 7.5 mu T; this supplies the calibration for the axial dipole signal away from the extreme low in intensity, The data predict the dipole field variation with latitude with similar accuracy to that observed in absolute paleointensity records, and show similar behavior when transformed to virtual axial dipole moments.

Kok, YS, Tauxe L.  1996.  Saw-toothed pattern of sedimentary paleointensity records explained by cumulative viscous remanence. Earth and Planetary Science Letters. 144:E9-E14.   10.1016/s0012-821x(96)00175-6   AbstractWebsite

The relative paleointensity of the earth's magnetic field from ODP Site 851 has been characterized by progressive decay towards polarity reversals, followed by sharp recovery of pre-reversal values [1]. We resampled the Gilbert-Gaup reversal boundary of this deep-sea core, and show that during demagnetization this 'saw-toothed' pattern disappears. Further, the recently published Cumulative Viscous Remanence model [2] using the herewith obtained paleointensity record and constraints from thermal treatment replicates the saw-tooth of [1], implying that it is of non-geomagnetic origin.

Tauxe, L, Herbert T, Shackleton NJ, Kok YS.  1996.  Astronomical calibration of the Matuyama-Brunhes boundary: Consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences. Earth and Planetary Science Letters. 140:133-146.   10.1016/0012-821x(96)00030-1   AbstractWebsite

We have compiled 19 records from marine carbonate cores in which the Matuyama-Brunhes boundary (MBB) has been reasonably well constrained within the astronomically forced stratigraphic framework using oxygen isotopes. By correlation of the delta(18)O data to a timescale based on astronomical forcing, we estimate astronomical ages for each of the MBB horizons. In all but one record the MBB occurs within Stage 19. Most magnetostratigraphic sections in Asian Loess place the MBB within a loess interval. Since loess deposition is presumed to be associated with glacial intervals, loess horizons should correspond to even-numbered oxygen isotope stages. A glacial age for the MBB is at odds with the results presented here, which firmly place the MBB within interglacial Stage 19. Inconsistency among the many loess sections and between the loess and the marine records suggests that the magnetic interpretation of loess sections may be more complicated than hitherto supposed. The mean of the Stage 19 age estimates for the MBB is 777.9 +/- 1.8 (N = 18). Inclusion of the single Stage 20 age results in a mean of 778.8 +/- 2.5 (N = 19). The astronomical age estimate of the MBB compares favorably with an (unweighted) mean of 778.2 +/- 3.5 (N = 10) from a compilation of Ar-40/Ar-39 results of transitional lava flows. Combining the two independent data sets yields a grand mean of 778.0 +/- 1.7 (N = 28). The new compilation shows virtually no trend in placement of the MBB within isotope Stage 19 as a function of sediment accumulation rate. We interpret this to mean that the average depth of remanence acquisition is within a few centimeters of the sediment-water interface. Separating the cores into two geographic regions (an Indo-Pacific-Caribbean [IPC] Group and an Atlantic Group) results in a significant difference in the position of the mid-point of the reversal with respect to the astronomical time scale. The data presented here suggest a difference of several thousand years between the two regions. This observation could be caused by systematic differences between the two regions in sedimentation rate within the interval of interest, systematic differences in remanence acquisition, or by genuine differences in the timing of the directional changes between the two regions.

Hartl, P, Tauxe L.  1996.  A precursor to the Matuyama/Brunhes transition-field instability as recorded in pelagic sediments. Earth and Planetary Science Letters. 138:121-135.   10.1016/0012-821x(95)00231-z   AbstractWebsite

The period some 20-25 kyr just prior to the most recent generally recognized geomagnetic field polarity transition, the Matuyama-to-Brunhes reversal, appears to be marked by significant geomagnetic variability, manifested as pronounced oscillations in intensity. We compare several previously published paleomagnetic records with new high resolution paleomagnetic data obtained from five pelagic marine sites: North Atlantic DSDP Hole 609B; equatorial Atlantic ODP Hole 665A; and western equatorial Pacific ODP Holes 803B, 804C, and 805B. Using standard rock magnetic normalization for all of the samples, as well as a Thellier/Thellier method on the sediments of Hole 804C, we consistently find a decrease in paleointensity (DIP of [1]) approximately 15 kyr prior to the Matuyama-to-Brunhes transition in the five new records, as well as in the previously published records. Despite sedimentation accumulation rates (SAR) that range from 11 cm/kyr to 1 cm/kyr, these sequences yield paleointensity curves that are broadly similar in form, even at the lowest SARs. The intensity of the pre-reversal tow (DIP1) appears to be of the same magnitude as that of the transition itself (DIP2 of [1]). In some of the records, a directional excursion to nearly full normal polarity accompanies DIP1 and remains after alternating field (AF) and/or thermal demagnetization, whereas in other records the directional changes vanish with demagnetization and appear to be caused by overprinting. A viscous remanent magnetization (VRM) contribution to NRM was identified in two of the records and, until removed by AF or thermal demagnetization, was found to blur the 'double-DIP' nature of the paleointensity profiles into an apparent single-DIP, and also resulted in an apparent, but erroneous, 'sawtooth'-like post-transitional sudden increase in paleointensity. After appropriate normalization, the magnitude of the post-transitional recovery was much reduced. The magnetic directions of three of the new records after 'cleaning' and adjusting the stable declinations to either 0 (normal) or 180 (reverse), map to VGP positions lying in the Pacific; the directional variations, however, are far less consistent than the intensity variations. The confirmed global existence of this DIP so closely preceding a major reversal invites questions about its relation to the reversal itself. The apparent normal character of this interval can also present problems for magnetostratigraphical interpretations based on coarse or incomplete sampling by mimicking the Brunhes/Matuyama reversal some 15 kyr earlier in the section than its true location.

1994
Tauxe, L, Watson GS.  1994.  The Fold Test - an Eigen Analysis Approach. Earth and Planetary Science Letters. 122:331-341.   10.1016/0012-821x(94)90006-x   AbstractWebsite

We combine eigen analysis and parameter estimation techniques for a newly constituted, more versatile fold test. The method is automatic, requiring no assumptions about the polarity or distribution of data, and gives confidence limits on the degree of unfolding required to produce the tightest grouping of data. We illustrate the method using several published data sets that show the tightest data groupings before, after and during correction for bedding tilt. The latter case is usually ascribed to acquisition of remanence during folding, but we show that this behavior can also arise from undetected multiple rotations. In our simulation, the beds undergo rotation about a vertical axis as well as a horizontal one, a case likely to occur in nature. These data, when rotated back to horizontal around what would be the observed strike, exhibit a peak in concentration at about 60% unfolding, very like the behavior of many published data sets. Thus, the origin of remanence in many such cases may not be syn-folding at all, but the behavior may purely be the result of an artifact of structural complications.

1993
Gallet, Y, Gee J, Tauxe L, Tarduno JA.  1993.  Paleomagnetic analyses of short normal polarity magnetic anomalies in the Matuyama Chron. Proceedings of the Ocean Drilling Program, Scientific Results. 130:547-559.   10.2973/odp.proc.sr.144.028.1995   Abstract

We document three short normal intervals in the natural remanent magnetization of sediments within the Matuyama Chron. These three anomalous zones of magnetization between the Jaramillo and Olduvai subchrons were identified from continuous measurements of archive halves from Hole 803 A using the pass-through 2G cryogenic magnetometer at Scripps. The U-channel samples were taken from the three intervals, analyzed using the pass-through system, and then cut into discrete 1 -cm-thick samples. Measurements on discrete samples confirmed the presence of the upper normal polarity zone. Based on sedimentation rate calculations, this zone is confidently correlated with the Cobb Mountain Subchron. For the two other anomalous zones, complete thermal demagnetization revealed a high-stability component (250°-575°C) of reversed polarity. The intensity of the low-stability normal polarity component, normalized by susceptibility, remains roughly constant throughout the entire interval sampled, whereas the intensity of the high-stability reversed component is much lower within the normal zone than outside. We interpret these two normal zones, then, as periods of low (reversed polarity) geomagnetic field intensity resulting in low magnetization of the sediments; the periods of these low magnetization reversed polarity zones are completely masked by the component acquired viscously in a normal polarity field.

1991
1990
Stokking, LB, Tauxe L.  1990.  Multicomponent Magnetization in Synthetic Hematite. Physics of the Earth and Planetary Interiors. 65:109-124.   10.1016/0031-9201(90)90080-h   AbstractWebsite

We have investigated the directional properties of chemical remanent magnetization (CRM) carried by hematite synthesized in two successive generations in two distinct magnetic fields. Previously, we showed that the magnetization of hematite synthesized in a single generation under constant magnetic field conditions parallels the field in which it grew; we now demonstrate that hematite precipitated in two magnetic fields carries a remanence that is far more complex. In the simplest of these two-field experiments, we precipitated hematite in one generation in the presence of a magnetic field (B1) and in a second generation in zero field. The synthetic material acquired a single component of remanence approximately parallel to B1. We then precipitated hematite in two generations, but under constant magnetic field conditions. The resulting remanence was also uni-vectorial and paralleled the applied field. Finally, we synthesized hematite in two generations using perpendicular orientations of the applied field for the two generations. The resulting behavior of magnetic remanence was complex and samples recorded a variety of directions: both parallel and antiparallel to B1 and B2, as well as intermediate between the two fields. Four categories of behavior describe all observations. We suggest that the various types of behavior reflect the complexity inherent in the process of remanence acquisition by crystals precipitating from solution. The behavior of remanence can be explained in terms of a competition between the effect of the ambient magnetic field, the demagnetizing fields generated by pre-existing particles and possibly also exchange effects between the second-generation particles and first-generation particles used as seed crystals. A model that accurately predicts the behavior of remanence in a particular multigenerational experiment is difficult to conceive at present because of the complexity of the interplay of competing factors on the magnetization of the second-generation particles.

1985
Tauxe, L, Monaghan M, Drake R, Curtis G, Staudigel H.  1985.  Paleomagnetism of Miocene East African Rift sediments and the calibration of the geomagnetic reversal time scale. Journal of Geophysical Research. 90:4639-4646., Washington, DC, United States (USA): American Geophysical Union, Washington, DC   10.1029/JB090iB06p04639   AbstractWebsite

Paleomagnetic stratigraphy and K-Ar age determinations are reported for the type section of the middle Miocene Ngorora Formation, found in the Kenya rift valley. The magnetostratigraphy is well correlated to the geomagnetic reversal time scale (GRTS) and spans from the lower part of Chron C5 (9) to Chron C5AB-r (14). K-Ar dates were determined for euhedral sanidines, handpicked from seven tuff horizons within the Ngorora Formation and the underlying Turn phonolite flow. These dates can therefore be tied directly to the GRTS. The eight dates fall into three discrete groups averaging 12.5 + or - 0.22 Ma (mean and standard deviation of results from four tuffs), 11.6 + or - 0.06 Ma (mean and standard deviation from three tuffs), and 10.16 + or - 0.38 (average of three analyses from one tuff). We interpret the age groups as resulting from three successive eruptive episodes, the stratigraphic positions of which are well constrained. In spite of episodic supply at the eruptive source, sediment accumulation is continuous at the resolution of the GRTS. This suggests that accumulation is controlled by basin subsidence rather than sediment supply. Sanidine dates support an age for the older boundary of marine magnetic anomaly 5 of about 10 Ma, as opposed to 11.12 Ma, suggested by the most recent results from Icelandic basaltic lava flows.