ArticlePDF Available

On the Possibility of Obtaining a High Resolution Relative Paleointensity Record of the Pringle Falls Excursion at the Type Locality of Pringle Falls, Oregon, USA

Authors:
Article

On the Possibility of Obtaining a High Resolution Relative Paleointensity Record of the Pringle Falls Excursion at the Type Locality of Pringle Falls, Oregon, USA

Natural Science, 2016, 8, 115-124
Published Online March 2016 in SciRes. http://www.scirp.org/journal/ns
http://dx.doi.org/10.4236/ns.2016.83015
How to cite this paper: Herrero-Bervera, E. (2016) On the Possibility of Obtaining a High Resolution Relative Paleointensity
Record of the Pringle Falls Excursion at the Type Locality of Pringle Falls, Oregon, USA. Natural Science, 8, 115-124.
http://dx.doi.org/10.4236/ns.2016.83015
On the Possibility of Obtaining a High
Resolution Relative Paleointensity Record
of the Pringle Falls Excursion at the
Type Locality of Pringle Falls, Oregon, USA
Emilio Herrero-Bervera
Paleomagnetics and Petrofabrics Laboratory, SOEST-Hawaii Institute of Geophysics and Planetology,
University of Hawaii at Manoa, Hawaii, USA
Received 15 November 2015; accepted 14 March 2016; published 17 March 2016
Copyright © 2016 by author and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/
Abstract
In order to further understand the full vector excursional details of the geomagnetic field, a pa-
leomagnetic and rock magnetic study of four sites has been conducted at the type locality of Prin-
gle Falls, Oregon where 827 samples were drilled and spaced along a distance of 5 km, for their
detailed directional and relative paleointensity studies. The profiles have registered a high-reso-
lution (>10 cm/kyr) paleomagnetic record of the excursion (ca. 211+/13 ka) as recorded by di-
atomaceous lacustrine sediments. Remanence as well as induced magnetization experiments to
investigate the reproducibility of the signal throughout the profiles have been conducted. In addi-
tion, low-field susceptibility vs. temperature analysis was performed indicating that the main
magnetic carrier is pure magnetite (Curie point 575˚C). The magnetic grain size also has indicated
Single Domain-Multi-Domain (SD-MD) magnetite. The demagnetization was done by alternating
field (a.f.) experiments, and the mean directions were determined by principal component ana-
lyses. In addition, induced magnetic tests were done, such as magnetic susceptibility (χ) analyses,
saturation IRM, anhysteretic remanent magnetization (ARM70) as well as the normalization of
J17.5 mT/ARM70 to attempt to obtain relative paleointensity records of these sediments in ques-
tion. The results of the induced rock magnetic tests such as the normalization studies indicate a
direct correlation between the decrease of the relative paleointensity variations (i.e. lows) with
respect to the directional changes. The detailed behavior of the paleosignal is highly consistent,
since they are rapidly deposited sediments providing a detailed representation of the paleofield.
The dissected VGP paths in 3 different phases are highly internally consistent and are defined by
clockwise and anticlockwise loops traveling from the high northern latitudes over eastern North
America and the North Atlantic to South America and then to high southern latitudes. They then
return to the high northern latitudes through the Pacific and over to Kamchatka. This VGP beha-
vior defines the geomagnetic signature of the Pringle Falls excursion as recorded at the type locality.
E. Herrero-Bervera
116
Keywords
Pringle Falls, Excursion, Lacustrine Sediments, Geomagnetic Signature
1. Introduction
The discovery of the Pringle Falls excursion took place in the late 1980s. At the beginning of the identification
of the excursion research, it was mistakenly identified as the Blake polarity episode [1] [2]. It was after the iden-
tification of the characteristic geomagnetic features recorded by the declination and inclination records and the
research work done on the chronostratigraphy, geochronology and tephrachronology that documented two sites
at Pringle Falls along the Deschutes River in Oregon (see Figure 1) that the excursion was officially described
and established as a geomagnetic feature [3].
Subsequent research work was performed to correlate the directional geomagnetic signal from additional pro-
files drilled (~837 samples) along the Deschutes River spaced along a distance of 5 km, for their detailed direc-
tional geomagnetic signature.
Thus far, the rock magnetic characterization as well as the entire directional analyses (i.e. declination and in-
clination) of the geomagnetic paleosignal of four widely spaced profiles has been completed and published re-
cently [4].
The aim of this paper is an attempt to study the rock magnetic parameters such as the magnetic susceptibility
(χ), the saturation isothermal remanent magnetization (SIRM) and the anhysteretic remanent magnetization
(ARM) in order to characterize the relative paleointensity of the sediments in question at the type section of
Pringle Falls, Oregon.
(a)
(b) (c)
Figure 1. Location of the type locality of Pringle Falls profiles sampled along the Deschutes River Pringle Falls, Oregon
USA (taken from Herrero-Bervera and Canon-Tapia, 2013).
E. Herrero-Bervera
117
2. Work up to Date at the Pringle Falls Type Sections
It is presented here the obtained high-resolution record of the Pringle Falls aborted reversalthat has been
dated by means of 40Ar/39Aranalys is yielding an age of 211 ± 13 ka [3] and correlated along a 5 km segment
in the Deschutes River area in Oregon. This paper shows a full vector description of the excursion by means of
directions [4] and relative paleointensity measurements that will be part of the global geomagnetic polarity time
scale. This record will be correlated to other stratigraphic markers such as 18Oxygen/16Oxygen and other biostra-
tigraphic proxies.
The directional results can be summarized as follows: The rock magnetic tests performed on the Pringle Falls
samples such as the remanent magnetization of the four profiles, show an excellent magnetostratigraphic corre-
lation of the main excursional features labeled as A, B and C present on the four records shown in Figure 2, and
have been published relatively recently [4]. The directional results have been converted to virtual geomagnetic
poles (VGPs) in order to compare the excursional characteristics of the profiles. Figure 3 shows the characteris-
tic geomagnetic signature of the excursion. The results of only one site are displayed as “snap shots” of the ab-
orted reversal paths as an initial/oldest and early phase corresponding to the geomagnetic feature “A” (see Fig-
ure 2), the subsequent intermediate middle phase “B” and the final and youngest phase “C”. The arrows indicate
the motion of the individual VGPs along the excursional paths showing the characteristic loops that define the
unique geomagnetic signature of the Pringle Falls excursion at the type section. In order to prove that the VGP
magnetic signature has been recorded by the four sites, Figure 4 shows the paths derived from the individual
profiles and the intrabasinal correlation of the signature. As a result of the VGP correlation paths one can con-
clude that the paths are highly internally correlateable and consistent, and show very distinct clockwise loops
traveling from high northern latitudes over the eastern part of the North American continent and the North At-
lantic to South America with a fast motion to high southern latitudes and a subsequent return to high northern
latitudes across the Pacific and over Kamchatka associated with the initial phase of the excursion, which cor-
responds to geomagnetic feature A. The other two geomagnetic features, such as B and C, corresponding to the
middle and late stages of the evolution of the excursional field, have their own looping, indicating a complex
non-dipolar behavior of the excursional field [4].
3. An Attempt to Recover a Relative Paleointensity Record from the Pringle
Falls Excursion at the Type Section
One of the most important reasons to stud the detailed behavior of polarity transitions and aborted reversals is to
determine the third component of the geomagnetic field vector, i.e. the paleointensity of the rapidly deposited
Pringle Falls lacustrine sediments. In order to reconstruct the variability the strength of the geomagnetic field,
one has to recur to the relative paleointensity (RPI) methodology [5]-[7] to obtain an estimate of the paleofield
from sedimentary sections, like the Pringle Falls lacustrine profiles. The relative paleointensity method has the
great benefit of the fact that potentially, the ultimate RPI records are relatively continuous and characterized by
a more or less complete dating of the sedimentary sequences. Unfortunately, one of the drawbacks of the RPI
method is that the exact strength of the local field intensity cannot be determined and only the relative fluctua-
tions of the paleofield over certain periods of time can be determined. Most of the recent RPI results have been
obtained from deep-sea sediments and from lake sediments particularly for the Holocene (i.e. 0 - 12,000 years
before the present). The study of the relative paleointensity of lake sediments has rendered a very good under-
standing of the paleofield from different localities all over the world [8]-[19]. Still, the RPI studies of excursions
of the geomagnetic field [20] recovered from lacustrine sediments are almost non-existent.
The type location at Pringle Falls offers the opportunity to recover the much needed RPI record. The rock
magnetic properties of the Pringle Falls sediments that have indicated a single phase magnetic mineralogy car-
ried by almost pure magnetite and very consistent magnetic grains sizes dominated by pseudo-single domain
(PSD) magnetite [4] and the well-defined magnetization component carried by PSD magnetite with variations of
less than a factor of ten in the magnetic concentration, satisfy the common standard criteria required for RPI
studies [5]-[7] [20] [21]. Therefore, the results obtained for this study have indicated a good suitability of the se-
diments in question for the RPI experiments.
The NRM of the discrete samples were measured using the ScT and the 2G760 cryogenic SRM instruments.
Susceptibility measurements of the samples were carried out with a Mini-Kappa bridge built by AGICO. An-
hysteretic remanent magnetization (ARM) was acquired in a peak alternating field of 70 mT and a 50 nT DC bias
E. Herrero-Bervera
118
Figure 2. Magnetostratigraphic correlation of the directional (i.e. declination, inclination and intensity of magnetization) be-
havior of four profiles recorded at the Pringle Falls site, Oregon. The red arrows show the characteristic inclination geomag-
netic features A, B and C of the Pringle Falls excursion (taken from Herrero-Bervera and Canon-Tapia, 2013).
E. Herrero-Bervera
119
Figure 3. Virtual Geomagnetic Poles (VGPs) of the Pringle Falls excursion showing the “geomagnetic signature” that cha-
racterize the excursion at Pringle Falls, Oregon (taken from Herrero-Bervera and Canon-Tapia, 2013).
Figure 4. Individual Virtual Geomagnetic Pole (VGPs) paths of the four profiles at the type locality of Pringle Falls (taken
from Herrero-Bervera and Canon-Tapia, 2013).
field, and saturation isothermal remanent magnetization (SIRM) was imparted to the samples using an SCT
pulse magnetizer in a 1.2 Teslas field. All NRM and induced magnetization experiments were conducted at the
E. Herrero-Bervera
120
Petrofabrics and Paleomagnetics Laboratory of the SOEST-HIGP at the University of Hawaii at Manoa.
Taking into consideration the results of the characteristic alternating field (AF)demagnetization experiments
of the NRM directions [4], the RPI was generated using the results of NRM, ARM and SIRM after AF demag-
netization was done at 17.5 mT (i.e. NRM17.5mT, ARM17.5mT, and SIRM17.5mT).
Natural Remanent Magnetization magnetic (NRM), susceptibility (χ), Anhysteretic Remanent Magnetization
(ARM) and Saturation Isothermal Remanent Magnetization (SIRM) experiments were carried out to attempt to
investigate the strength of the paleofield during the Pringle Falls excursion.
4. Relative Paleointensity Records
In order to test the idea that during the Pringle Falls excursion at the type section, the strength of the geomag-
netic field decreases during the “aborted reversal”, then we have plotted up the NRM17.5mT, susceptibility,
J17.5mT/ARM70, and SIRM1.2T of the original profile [2] against the inclination records of the four profiles in
question showing the characteristic geomagnetic features (i.e. A, B and C) (see Figure 5). In addition to that
comparison, show in Figure 6 the shows the results of the other three profiles.
5. Discussion
It has been discussed and concluded that the Pringle Falls excursion recorded globally in the 205 - 225 ka inter-
val [22] and has been recorded not only at the Pringle Falls type section but at other widely separated and far
removed localities [4] [23]-[25]. That makes the excursion a world-wide “aborted reversal” that has also been
correlated to stage 7β of ODPSite1062 [26].
However, very few of these records have firmly established the correlation between the directional geomag-
netic excursional features of Pringle Falls to the decrease of the intensity of the paleofield [3] [24]-[28]. Ourrock
magnetic experiments of both the remanence and the induced magnetization results have indicated a good cor-
relation of the directional features to the J17.5mT, magnetic susceptibility (χ), normalized J17.5mT/ARM70 as
Figure 5. Stratigraphic plot of Intensities (J), susceptibility (x), normalized intensity (at 17.5 mT) with respect to ARM
(J/ARM), Anhysteretic Remanent Magnetization (ARM) (a.f. at 70 mT in a DC field of 0.05 and Saturated Isothermal Re-
manent Magnetization (sIRM)). Notice the decreased normalized field is depicted by J17.5mT/ARM70 which is the best norma-
lized parameter for the Pringle Falls sediments (figures taken from Herrero-Bervera and Helsley, 1993 and Herrero-Bervera
and Canon-Tapia, 2013, respectively).
E. Herrero-Bervera
121
E. Herrero-Bervera
122
Figure 6. Diagrams showing the results of the relative Paleointensity (RPI)
experiments performed on Profiles 1 (first corner), Profile 2 (second corner)
and Profile 3 (third corner). The experiments performed were the demag-
netized intensity of magnetization of the samples (J), the Anhysteretic Re-
manent Magnetization (ARM), magnetic susceptibility and Saturation Iso-
thermal Remanent Magnetization (SIRM).
well as SIRM correlations with primarily the inclination geomagnetic features A, B and C, where there is a clear
decrease of these rock magnetic parameters in relation to the directional changes (see Figure 5). In addition,
Figure 6 shows the correlation between the NRM17.5mT and the other rock magnetic results. It is important to
point out that the four records show a very good agreement of the diminution of the presumably geomagnetic
field with respect to the demagnetized NRM records. The most salient and clear decrease of the relative pa-
leointensity with respect to the directional features are represented by Profiles 2 and 3 where one can see the
conspicuous concave down peaks of the three induced rock parameters to the NRM17.5mT (see Figure 6).
6. Conclusion
The conclusion of this work indicates that the there is a marked directional instability of the very fast deposited
lacustrine Pringle Falls sediments (i.e. >10 cm/k year) that characterizes the geomagnetic field during the so
called “excursions” or “aborted reversals”. In addition to the “anomalous” directional fluctuations one can ob-
serve that during the excursional behavior of the geomagnetic field, the intensity of the magnetic field decreases
substantially. This is the case of the Pringle Falls excursion records in this paper (see Figures 2-6). As reported
by [22], Polarity excursions are observed at time of low paleointensity when the strength of the axial dipole is
reduced by a factor of about 5, and reduced relative to the non-axialdipole (NAD) field. [29] have shown that the
critical Reynolds number (Rc) for the onset of core convection is very sensitive to the poloidal field, and the
E. Herrero-Bervera
123
strength of core convection varies wildly in response to changes in magnetic field strength particularly during
intensity minima”. Thus far, the results presented here indicate that the induced rock magnetic experiments prove
that the type locality lacustrine sediments that registered the Pringle Falls excursion are suitable recorders of the
instabilities of the paleofield during the “aborted reversal” of this study.
Acknowledgements
We are very grateful to Mr. James K. S. Lau for his laboratory assistance. Financial support to Emilio Herrero-
Bervera was provided by SOEST-HIGP and the National Science Foundation grants EAR-9909206, EAR-INT-
9906221, EAR-0207787, EAR-0213441, EAR-0510061, EAR-1215070. This is a SOEST contribution #9578,
HIGP contribution #2184.
References
[1] Herrero-Bervera, E., Helsley, C.E., Hammond, S.R. and Chitwood, L.A. (1989) A Possible Lacustrine Paleomagnetic
Record of the Blake Episode from Pringle Falls, Oregon, U.S.A. Physics of the Earth and Planetary Interiors, 56, 112-
123. http://dx.doi.org/10.1016/0031-9201(89)90041-1
[2] Herrero-Bervera, E. and Helsley, C.E. (1993) Global Paleomagnetic Correlation of the Blake Geomagnetic Polarity
Episode. In: Aissaoui, D.M., McNeill, D.F. and Hurley, N.F., Eds., Application of Paleomagnetism to Sedimentary Ge-
ology, SEPM Special Publications, 49, 71-82.
[3] Herrero-Bervera, E., Helsley, C.E., Sarna-Wojcicki, A.M., Lajoi, K.R., Meyer, C.E., McWilliams, M.O., Negrini, R.M.,
Turrin, B.D., Nolan, J.M. and Liddicoat, J.C. (1994) Age and Correlation of a Paleomagnetic Episode in the Western
United States by 40Ar/39Ar Dating Tephrochronology: The Jamaica, Blake, or a New Polarity Episode? Journal of
Geophysical Research, 99, 24091-24103. http://dx.doi.org/10.1029/94JB01546
[4] Herrero-Bervera, E. and Canon-Tapia, E. (2013) On the Directional Geomagnetic Signature of the Pringle Falls Excur-
sion Recorded at Pringle Falls, Oregon, USA. Geological Society, London, Special Publications Published Online.
[5] Levi, S. and Banerjee, S.K. (1976) On the Possibility of Obtaining Relative Paleointensities from Lake Sediments.
Earth and Planetary Science Letters, 29, 219-226. http://dx.doi.org/10.1016/0012-821X(76)90042-X
[6] King, J.W., Banerjee, S.K. and Marvin, J. (1983) A New Rock Magnetic Approach to Selecting Sediments for Geo-
magnetic Paleointensity Studies: Application to Paleointensity for the Last 4000 Years. Journal of Geophysical Re-
search, 88, 5911-5921. http://dx.doi.org/10.1029/JB088iB07p05911
[7] Tauxe, L. (1993) Sedimentary Records of Relative Paleointensities of the Geomagnetic Field: Theory and Practice. Re-
views of Geophysics, 31, 319-354. http://dx.doi.org/10.1029/93RG01771
[8] Creer, K.M., Tucholka, P. and Barton, C.E. (1983a) Paleomagnetism of Lake Sediments. In: Creer, K.M., et al., Eds.,
Geomagnetism of Baked Clays and Recent Sediments, Elsevier, Amsterdam, 172-197.
[9] Creer, K.M., Valencio, D.A., Sinito, A.M., Tucholka, P. and Vilas, J.F. (1983b) Geomagnetic Secular Variations 0 -
14000 Years BP as Recorded by Lake Sediments from Argentina. Geophysical Journal of the Royal Astronomical So-
ciety, 74, 199-221. http://dx.doi.org/10.1111/j.1365-246X.1983.tb01877.x
[10] Constable, C.G. and McElhinny, M.W. (1985) Holocene Geomagnetic Secular Variations Records from North-Eastern
Australian Lake Sediments. Geophysical Journal of the Royal Astronomical Society, 81, 103-120.
http://dx.doi.org/10.1111/j.1365-246X.1985.tb01353.x
[11] Gogorza, C.S.G., Irurzun, M.A., Sinito, A.M., Lisé-Pronovost, A., St-Onge, G., Haberzettl, T., Ohlendorf, C., Kastner,
S. and Zolitschka, B. (2012) High-Resolution Paleomagnetic Records from Laguna PotrokAike (Patagonia, Argentina)
for the Last 16,000 Years. Geochemistry, Geophysics, Geosystems, 13, Q12Z37.
http://dx.doi.org/10.1029/2011GC003900
[12] Lund, S.P. and Banerjee, S.K. (1985) Late Quaternary Field Secular Variation from Two Minnesota Lakes. Journal of
Geophysical Research, 90, 803-825. http://dx.doi.org/10.1029/JB090iB01p00803
[13] Verosub, K.L., Mehringer, P.J. and Waterstraat, P. (1986) Holocene Secular Variations in Western North America Pa-
laeomagnetic Record from Fish Lake, Harney County, Oregon. Journal of Geophysical Research, 91, 3609-3623.
http://dx.doi.org/10.1029/JB091iB03p03609
[14] Peng, L. and King, J.W. (1992) A Late Quaternary Geomagnetic Secular Variation Record from Lake Waiau, Hawaii,
and the Question of the Pacific Non-Dipole Low. Journal of Geophysical Research, 97, 4407-4424.
http://dx.doi.org/10.1029/91JB03074
[15] Stockhausen, H. (1998) Geomagnetic Palaeosecular Variation (0 - 13000 yr BP) as Recordedin Sediments from Three
Maar Lakes from the West Eifel (Germany). Geophysical Journal International, 135, 898-910.
E. Herrero-Bervera
124
http://dx.doi.org/10.1046/j.1365-246X.1998.00664.x
[16] Brandt, U., Nowaczyk, N.R., Ramrath, A., Brauer, A., Mingram, J., Wulf, S. and Negendank, J.F.W. (1999) Paleo-
magnetism of Holocene and Late Pleistocene Sediments from Lago di Mezzano and Lago Grance di Monticchio (Italy):
Initial Results. Quaternary Science Reviews, 18961-18976.
[17] Frank, U., Nowaczyk, N.R., Negendank, J.F.W. and Melles, M. (2002) A Paleomagnetic Record from Lake Lama,
Northern Central Siberia. Physics of the Earth and Planetary Interiors, 133, 3-20.
http://dx.doi.org/10.1016/S0031-9201(02)00088-2
[18] Ojala, A.E.K. and Saarinen, T. (2002) Palaeosecular Variation of the Earth’s Magnetic Field during the Last 10000
Years Based on the Annually Laminated Sediment of Lake Nautajärvi, Central Finland. Holocene, 12, 391-400.
http://dx.doi.org/10.1191/0959683602hl551rp
[19] Yang, X., Heller, F., Yang, J. and Su, Z. (2009) Paleosecular Variations Since 9000 yr BP as Recorded by Sediments
from Maar Lake Shuangchiling, Hainan, South China. Earth and Planetary Science Letters, 288, 1-9.
http://dx.doi.org/10.1016/j.epsl.2009.07.023
[20] Stoner, J.S. and St-Onge, G. (2007) Magnetic Stratigraphy in Paleoceanography: Reversals, Excursions, Paleointensity
and Secular Variation. In: Hillaire-Marcel, C. and de Vernal, A., Eds., Proxies in Late Cenozoic Paleoceanography.
Elsevier, Amsterdam, 99-138.
[21] Verosub, K.L., Herrero-Bervera, E. and Roberts, A.P. (1996) Relative Geomagnetic Paleointensity across the Jaramillo
Subchron and the Matuyama/Brunhes Boundary. Geophysical Research Letters, 23, 467-470.
http://dx.doi.org/10.1029/96GL00454
[22] Channell, J.E.T. (2006) Late Brunhes Polarity Excursions (Mono Lake, Laschamp, Iceland Basin ard, Pringle Falls)
Recorded at ODP Site 919 (Irminger Basin). Earth and Planetary Science Letters, 244, 378-393.
http://dx.doi.org/10.1016/j.epsl.2006.01.021
[23] McWilliams, M.O. (2001) Global Correlation of the 223 ka Pringle Falls Event. International Geology Review, 43,
191-195. http://dx.doi.org/10.1080/00206810109465007
[24] Singer, B.S., Jicha, B.R., Kirby, B.T., Geissman, J.W. and Herrero-Bervera, E. (2008) 40Ar/39Ardatinglinks Albu-
querque Volcanoes to the Pringle Falls Excursion and the Geomagnetic Instability Time Scale. Earth and Planetary
Science Letters, 267, 584-595. http://dx.doi.org/10.1016/j.epsl.2007.12.009
[25] Valet, J.P., Plenier, G. and Herrero-Bervera, E. (2008b) Geomagnetic Excursions Reflect an Aborted Polarity State.
Earth and Planetary Science Letters, 274, 472-478. http://dx.doi.org/10.1016/j.epsl.2008.07.056
[26] Lund, S., Stoner, J.S., Channell, E.T. and Acton, G. (2006) A Summary of Brunhes Paleomagnetic Field Variability
Recorded in Ocean Drilling Program Cores. Physics of the Earth and Planetary Interiors, 156, 194-204.
http://dx.doi.org/10.1016/j.pepi.2005.10.009
[27] Guyodo, Y. and Valet, J.P. (1999) Global Changes in Intensity of the Earth’s Magnetic Field during the Past 800 kyr.
Nature, 399, 249-252. http://dx.doi.org/10.1038/20420
[28] Valet, J.P., Meynadier, L. and Guyodo, Y. (2005) Geomagnetic Field Strength and Reversal Rate over the Past 2 Mil-
lion Years. Nature, 435, 802-805. http://dx.doi.org/10.1038/nature03674
[29] Zhang, K. and Gubbins, D. (2000) Is the Geodynamo Process Intrinsically Unstable? Geophysical Journal Internation-
al, 140, F1-F4. http://dx.doi.org/10.1046/j.1365-246x.2000.00024.x
... Thus far, the rock magnetic characterization as well as the entire directional analyses (i.e. declination and inclination) of the geomagnetic paleosignal of four widely spaced profiles has been completed and published recently [40] [67]. ...
... There is a published record of the Pringle Falls "aborted reversal" that has been dated by means of 40 Ar/ 39 Ar yielding an age of 211 ± 13 ka [57] and correlated along a 5 km segment in the Deschutes river in Oregon. A full vector description of the excursion by means of directions [40] Relative Paleointensity (RPI) measurements that will be part of the geomagnetic polarity time global scale [67] have been published as well. ...
Data
Component natural remanent magnetizations derived from u-channel and 1-qcm discrete samples from ODP Site 919 (Irminger Basin) indicate the existence of four intervals of negative inclinations in the upper Brunhes Chronozone. According to the age model based on planktic oxygen isotope data, these "excursional" intervals occur in sediments deposited during the following time intervals: 32-34 ka, 39-41 ka, 180-188 ka and 205-225 ka. These time intervals correspond to polarity excursions detected elsewhere, known as Mono Lake, Laschamp, Iceland Basin and Pringle Falls. The isotope-based age model is supported by the normalized remanence (paleointensity) record that can be correlated to other calibrated paleointensity records for the 0-500 ka interval, such as that from ODP Site 983. For the intervals associated with the Mono Lake and Laschamp excursions, virtual geomagnetic poles (VGPs) reach equatorial latitudes and mid-southerly latitudes, respectively. For intervals associated with the Iceland Basin and Pringle Falls excursions, repeated excursions of VGPs to high southerly latitudes indicate rapid directional swings rather than a single short-lived polarity reversal. The directional instability associated with polarity excursions is not often recorded, probably due to smoothing of the sedimentary record by the process of detrital remanence (DRM) acquisition.
Article
A palaeomagnetic study of the Lake Nautajarvi sediment sequence in central Finland demonstrates, that varved lake sediments can provide regionally applicable secular variations curves for Holocene stratigraphic correlation and age control. Based on x-ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the Lake Nautajarvi varve sequence, which covers nearly 10000 years with an estimated counting error of less than +/-1% and a mean sedimentation rate of 0.66 mm yr(-1). We reconstructed a record of the palaeomagnetic secular variation (PSV) of the Earth's magnetic field in this nearly 7 in long section of clastic-organic vanes. Mineral magnetic measurements indicated that pseudo-single-domain magnetite is the major carrier of the remanence. PSV shows many of the familiar features of declination and inclination that have previously been recorded in northern Europe, In addition, the Lake Nautajarvi record contains a continuous record of relative palaeointensity.
Article
Sediments have proved irresistible targets for attempts at determining the relative variations in the Earth's magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution. The assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited. Early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short, no dependence on magnetic field was expected. Nonetheless, a number of experiments showed that sedimentary magnetizations varied in accordance with the field, albeit not always in a simple, linear fashion. Experiments in which the sediments were stirred in the presence of a field (to simulate bioturbation) showed a reasonably linear relationship with the applied field, and these results spurred the hope that variations in the Earth's magnetic field might indeed be recoverable from appropriate sedimentary sequences. Examination of existing paleointensity data sets allows a few general conclusions to be drawn. It appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the Earth's magnetic field. The dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences. Moreover, when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences, there is considerable agreement among the various records. When viewed over timescales of hundreds to thousands of years, relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another, suggesting that they are dominated by nondipole field behavior. When viewed over timescales of a few tens of thousands to hundreds of thousands of years, however, the records show coherence over large distances (at least thousands of kilometers) and may reflect changes in the dipole field. On the basis of a sequence spanning the Brunhes and Matuyama chrons, the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years, but these oscillations are not clear in the record prior to about 300 ka; thus they are probably not an inherent feature in the geomagnetic field, and the correspondence of the period of oscillation to that of obliquity is probably coincidence.
Article
We studied the detailed characteristics of the Pringle Falls excursion from samples at the original site recovered from four profiles drilled along the Deschutes River, Oregon. We drilled 827 samples spaced along 5 km for their detailed directional study. The profiles registered a highresolution (>10 cm/ka) palaeomagnetic record of the excursion (c. 211±13 ka) recorded by diatomaceous lacustrine sediments. We conducted palaeomagnetic and rock magnetic studies to investigate the reproducibility of the signal throughout the profiles. We performed low-field susceptibility v. temperature analysis that indicated that the main magnetic carrier is pure magnetite (Curie point 575 °C). The magnetic grain size also indicated single domain-multi domain (SD- MD) magnetite. The demagnetization was performed by alternating field experiments and the mean directions were determined by principal component analyses. The detailed behaviour of the palaeosignal is highly consistent since they are rapidly deposited sediments providing a detailed representation of the palaeofield. The dissected virtual geomagnetic pole paths in three different phases are highly internally consistent and are defined by clockwise and anticlockwise loops travelling from high northern latitudes over eastern North America and the North Atlantic to South America and then to high southern latitudes; then they return to high northern latitudes through the Pacific and over to Kamchatka.
Article
A continuous paleomagnetic record for the last 13,000 years was obtained from the sediments of Lake Waiau, located near the summit of Mauna Kea Volcano on the island of Hawaii. The secular variation (SV) of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector. The hypothesis that there has been anomalously low geomagnetic SV in the central Pacific was tested using angular dispersion analysis. The inclination record has a mean value of 27° that is much lower than the 35° predicted by the geocentric axial dipole hypothesis. The spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100, 2000, 3300, and 7800 years. The approximately 8000- and 3500-year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation, respectively. The approximately 1100- and 2000-year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections. In addition, Bauer plots of the magnetic vector are dominated by clockwise motion. The angular dispersion calculated from lake sediments is 5.9° with respect to the mean virtual geomagnetic pole (VGP) and 9.1° with respect to the geographic pole. Both values are much lower than the 13.5° expected from paleosecular variation model G which separates the angular dispersion into components from the dipole and the quadruple families. Our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central Pacific. Furthermore, this geomagnetic behavior persists on time scales of 104 years. Regional anomalies in temperature, topography or electrical conductivity at the core-mantle boundary are inferred to cause the low SV.
Article
Detailed paleomagnetic records from the wet sediments of two Minnesota lakes are the basis for estimating the local secular variation of the earth's magnetic field during late Quaternary time. Results from Lake St. Croix cover the interval 0-9500 years B.P., and results from Kylen Lake cover the interval 4000-14,000 years B.P. Paleomagnetic data were recovered from two replicate cores in each lake by sampling the sediments at 3- to 10-cm intervals. Analysis of the potential errors in the results indicates that all cores were correctly oriented in the vertical plane but that some azimuthal offsets of individual core segments did occur. Various methods for correcting the occasional azimuthal offsets are described. The final paleomagnetic data sets from each lake show a high degree of internal consistency. These results also show close correspondence (1) between the two lakes, (2) with the known historic magnetic field variation, and (3) with paleomagnetic results from dated archeological material and lava flows from the western United States. Rock magnetic analysis of the lake sediments indicates that the natural remanent magnetization is the result of a physical remanence acquisition process (detrital remanent magnetization) active at or near the sediment/water interface. There is no evidence for a systematic inclination error in the results. Statistical analysis of vector time series determined from the paleomagnetic data indicates that both the field-vector and virtual geomagnetic pole (VGP) distributions are non-Fisherian and essentially axial-dipolar when averaged over 10,000 years. Spectral analysis of the scalar inclination and declination suggests that the field behavior is separable into a dominant low-frequency dipolelike waveform (period of ˜9500 years) and a higher-frequency band irregular waveform ("fundamental" period of ˜2400 years with multiples at 1200, 800, and 600 years) that may represent the nondipole field. This irregular waveform is interpreted as resulting from zonal drift of the nondipole field past Minnesota on the basis of waveform morphology and VGP circularity. Zonal drift of the nondipole field plus a low-frequency dipole variation can account for almost all of the observed paleomagnetic field variation.
Article
This chapter focuses on the magnetic stratigraphy in paleoceanography. Magnetic stratigraphy rests on the idea that the recorded magnetization of a rock reflects the behavior of the geomagnetic field. In the simplest case, the natural remanent magnetization (NRM) of sediment is aligned with the (geo)magnetic field and is a function of its intensity and direction at the time of deposition. In practice, many factors may work to modify the original geomagnetic input signal. Under favorable circumstances and with detailed diligence, some of these effects can be separated and others avoided so that an accurate paleomagnetic record is recovered. Paleomagnetism has been working to keep pace and a significant new understanding of geomagnetic field behavior during times of constant polarity has begun to emerge. Essentially, it has been found that high amplitude, high frequency variations in the Earth's magnetic field occur over large spatial scales even during times of constant polarity. New magnetostratigraphic opportunities over a range of temporal and spatial scales are emerging. The chapter also outlines the practical aspects of reconstructing the paleomagnetic record from marine sediments, and discusses some of the recent observations on the Quaternary geomagnetic record that are being made and their uses as a stratigraphic tool for paleoceanographic research.
Article
A palaeomagnetic study of the Lake Nautajärvi sediment sequence in central Finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for Holocene stratigraphic correlation and age control. Based on x-ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the Lake Nautajärvi varve sequence, which covers nearly 10000 years with an estimated counting error of less than ±1% and a mean sedimentation rate of 0.66 mm yr-1. We reconstructed a record of the palaeomagnetic secular variation (PSV) of the Earth's magnetic field in this nearly 7 m long section of clastic-organic varves. Mineral magnetic measurements indicated that pseudosingle-domain magnetite is the major carrier of the remanence. PSV shows many of the familiar features of declination and inclination that have previously been recorded in northern Europe. In addition, the Lake Nautajärvi record contains a continuous record of relative palaeointensity.
Article
The hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization (DRM/ARM) for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches. One approach is a detailed rock-magnetic examination of the implicit assump- tions of the DRM/ARM method and the construction of a selection process by which to identify sedi- ments that conform to requirements satisfying these assumptions. Sediments are 'uniform' with respect to DRM/ARM ratio if they contain magne- tite in the 1-15 m particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20-30 times the minimum concentration. The DRM/ARM ratios of these sediments should provide estimates of rela- tive geomagnetic paleointensity. Relative particle size variations in magnetite are detected with a plot of anhysteretic suscep- tibility (XAR M) versus low-field susceptibility (X) and the size range 1-15 m is approxi- mately identified by high-field hysteresis para- meters. A rock-magnetic evaluation of LeBoeuf Lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study. The second approach to evaluating the DRM/ARM ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data. A comparison be- tween the LeBoeuf Lake estimates and Thellier- Thellier results from the western United States supports the conclusion that suitable sediments can record geomagnetic paleointensity fluc- tuations.