Institut de Physique du Globe de Paris (IPGP)
1, rue Jussieu,
75238 Paris Cedex 05, France
tel : 33 - 1- 83-95-75-03
Geomagnetic secular variation
Geomagnetic reversals and excursions
Relative and absolute paleointensity
Magnetization acquisition processes
Paleoenvironment and diagenesis
I have been actively studying the geomagnetic field variations recorded by magnetization of lava flows and sediments with typical time constants from hundreds to millions years. Measurements of the total field vector allow us to address questions such as: what drives the fluctuations of the field refered as secular variation, what causes field reversals and what happens during the transition between the two polarity states, why does the field sometimes fails to reverse, what happens during field excursions, whether the mantle has a significant influence on some field instabilities etc.. Exploring the field behaviour in the past requires to assess the nature and the geomagnetic origin of the signals that are recorded by the magnetization of rocks. This can only be achieved by detailed knowledge of the processes involved in the acquisition of magnetization that are documented by rock magnetic experiments and analyzes.
I have also been interested in various other aspects linked to magnetism, such as studies related to the signature of climatic changes in rock magnetic parameters, in depositional processes, in mineralogical studies and in biomagnetism.
A few results
My initial interest went to geomagnetic reversals. After several years spent to decipher reversal records from sedimentary sequences, it became clear that the response of magnetization to the field was not appropriate to record the very rapid field changes prevailing during periods of very low field intensity and that sediments do not provide the appropriate resolution.
An impressive piece of work has been conducted with Emilio Herrero-Bervera after sampling huge piles of lava flows in the Waianeae sequence of Oahu, Hawaii. For the first time, we could deal with a succession of reversals from volcanic flows. We also obtained duplicate records of the same reversals from different locations. The results indicate complex field behaviour with precursors and rebounds, similarly to what would be observed with the secular variation of the present field in presence of a very weak or zero axial dipole field of the non dipole field. We have also shown that clustering of directions frequently reported in records were caused by periods of intense volcanic activity and not by a standstill in the reversal porcess.
These results have been integrated in a compilation of the most detailed records from volcanics from sequences of overlying lava flows with well defined reversed and normal polarities prior to the transition and several distinct transitional directions. Very few records meet these basic criteria, but they all show the same characteristics. There is no systematics in the apparent reversal geometry, all transitions being characterized by complex pole paths between the two polarities. It appears also that these detailed volcanic records do not show any preference of the pole for a specific longitude when switching between the two polarities.
However the most striking feature is a remarkable coherency when plotting all records in terms of angular changes form the axial dipole. It appears clearly that processes and time constants have remained unchanged for all reversals. The reversal process can be divided in three phases, a precuror, a rapid transit between the two polarities and/or a rebound. We can estimate the duration of the transition by comparison with paleosecular variation. The precursor and rebound correspond to secular variation of the non-axial dipole in presence of a very weak axial dipole Thes phases do not last longer than 2500 yrs while the the transit between north and south if of the order of 1ka only.
Problems encountered with sedimentary records have generated interest to further constrain the mechanisms involved in the magnetization of sediments using artifical redeposition in laboratory. The results obtained with carbonated sediments point out the linearity of magnetization with field strength which is a very good news for studies of relative paleointensity in sediments. In contrast, we have seen no linearity and no suitable orientation of magnetic grains observed for experiments conducted with clayish sediments. This points out the importance of using carbonated sediments for studies related to the geomagnetic field behaviour. Awe also reported that post-depositional reorientation of the magnetic grauns is extremely limited. Other diagenetic processes that remain to be documented would thus favour a time-averaging of the paleomagnetic records which affects the resolution of the signal in sediments.
Dynamics of reversals and duration of the 3 successive phases.
Geomagnetic excursions represent short episodes that last a few thousand years at most during which the field considerably exceeds its normal range of variability during a polarity state. The Laschamp event discovered in lava flows of Massif central (France) is the youngest and the most studied field excursion. Its geomagnetic origin has been controversial due to the existence of self-reversal processes. We have confirmed that reverse polarity flows are affected by self-reversals, but we found that this is also the case for normal flows. A direct consequence is that self-reversals cannot be taken as responsible for the reverse directions. We sampled a large collection of flows. New K-Ar dates by Gilles Gurin provided a coherent chronology of the successive polarities. The 37 ka old reverse directions of the Olby flow are consistent with the 41.9 kyr old normal polarity flows preceding the event. A younger flow with intermediate directions dated at 33.3 ka may be related to the Mono Lake event.
Surprisingly, no attention has been given to the fact that the Laschamp and Mono Lake events occurred during the period of Neandertal extinction (this is even clearer after recalibration of the 14C ages) which lasted for several thousand years. During this time interval the geomagnetic field strength was considerably reduced and shielding efficiency of the magnetosphere lowered, leaving energetic particles reach latitudes as low as 30Ħ. The enhanced flux of high-energy protons (linked to solar activity) into the atmosphere yielded significant ozone depletion down to latitudes of 40-45Ħ. A direct consequence was an increase of UV-B radiations at the surface by at least 15-20% in Europe with significant impacts for human populations. With Hlne Valladas we suggest that these conditions, maybe added to other factors, have contributed to the demise of Neanderthal population.
We have compiled the most detailed records of excursions that occurred during the Brunhes and Matuyama chrons. The virtual geomagnetic poles (VGPs) of at least one record of each event are able to reach the opposite polarity. It is impossible to reach the ratio of reversed to intermediate VGPs present in the paleomagnetic records if the excursions were not associated with a short period of reversed dipole field. Therefore, excursions should be regarded as two successive reversals bracketing an aborted polarity interval. We propose that the same underlying mechanisms prevail in both situations (excursions or reversals) and that below a certain strength, the field reaches an unstable position which preludes either the achievement of a reversal or its return to former polarity.
Relative and absolute paleointensity
Sediments provide continuous long-term records of the axial dipole intensity. Our first studies focused on 5 distinct mediterranean cores. The similarity of the results between all cores provided the first positive test for relative paleointensity in sediments and the coherence with the existing volcanic dataset further validated the concept. The demonstration has been completed with Laure Meynadier after comparing the results from mediterranean cores with 5 other cores from the Indian ocean for the past 140 ka. This very first check revealed the coherency of geomagnetic changes recorded at very distinct locations, and thus validated the approach. Subsequently, newly acquired records yielded the construction of Sint-200 with Yohan Guyodo from 15 worldwide distributed records of relative paleointensity. The overall agreement of Sint-200 with variations in 10Be production has been another significant step. Following the same track we produced a composite curve covering the entire Brunhes period (Sint-800).
The next challenge was to investigate the evolution of the field across reversals. With Laure Meynadier we had the chance of finding a carbonated sequence at site 851 during the ODP leg 138 with a very accurate time reference completed by an excellent stable and homogeneous magnetization. The records of relative paleointensity spanning the past 4 Ma revealed a slow decrease of the field prior to the reversals likely caused by diffusion and which is in sharp contrast with the intense and rapid recovery marking the end of the transition and the advection processes associated with the restoration of the dipole. Studies conducted on volcanic sequences in the Canary islands and Hawaii (see above) further confirmed the pattern of field intensity across recent reversals including the last one. Subsequently we produced a composite and global record for the past 2Ma (Sint-2000) which serves also as a constraint to the dynamo models.
Francois Ptrlis and Stphane Fauve have been working on the Van Karman sodium experiment, the first experimental dynamo that produced a field evolution with reversals. It is surprising that the field changes accompanying the reversals are quite similar to Sint-2000, particularly the asymmetrical pattern of field intensity and the overshoot occurring at the end of the recovery phase. These features are also predicted by Petrelis et al reversal model involving a coupling between the dipolar and the quadrupolar modes during reversals.
Evolution of the geomagnetic dipolar field intensity during the past 2Ma calibrated
with volcanic records
Success met for the recent million years incited us to scrutunize the other end of the field history in archean rocks. The results obtained with Mlina Macouin and Jean Besse on canadian dykes 1.1 to 2.4Ga old suggest a reduced field intensity with possible implications on formation of the inner core.
Using a simple dipole model calculated from the directional changes recorded at 5 different sites during the past 2 ka, we have shown that field changes derived from the archeomagnetic data at other multiple sites are of equivalent quality to those derived from complex inversion models with a spherical harmonic description of the field up to degree 5 and more. We thus consider that these models are not fully relevant in the present state of the databases and given the uneven geographical distribution of the sites.
The geocentric axial dipole (GAD) field describes most of the structure in the time-averaged geomagnetic field. However the paleomagnetic record displays small but persistent departures. Successive analyses of the new databases have revealed that departures from the GAD can be fitted by an axial quadrupole component amounting 3 to 5% of the axial dipole. Using the Sint-2000 composite curve and the most recent directional volcanic database for the past 4Ma we have shown that the deviations from the GAD are larger when the dipole field is smaller, suggesting that it keeps more or less the same strength.
The geodynamo shows evidence for long time scales that cannot be connected with fluid dynamical processes in the core. Slowly evolving processes like the modulation in reversal frequency are linked to the influence of the mantle. Thermal interaction and /or chemical exchange between core and mantle should be associated with heterogeneities which would modify the circulation in the core and hence be reflected by magnetic anomalies. The existence of long-term standing field anomalies is critical to test these concepts. In this perspective, the debate regarding the persistence of the Pacific anomaly reflected by a weak non dipole field is critical. The lava flows that we have studied in Hawaii do not indicate any significant anomaly except for the past 2ka, but this period may be too short for a complete time-averaged of the field changes.
Going further south with Agns Elmaleh we have measured marine cores from the Fiji basin. They are characterized by a large inclination anomaly in agreement with previous measurements in the same area. However, we have not detected any deviation in a large set of lava flows sampled in the Java island and thus conclude to the absence of a long-term persistent non zonal anomaly of the non-dipole field. Tthe large deviations in the Fiji area were likely caused by local tectonics.
Rock magnetism and magnetization signals
Because magnetization acquisition depends on complex processes in sediment we developed experiments aimed at describing the limits that they imposed on records of field variations. Redeposition experiments using a gelatin allowed us to measure the proportion of magnetic grains that are mechanically locked for different water contents. The magnetic moment normalized by concentration was then compared to the natural magnetization to define the concentration level at which the magnetization has been locked-in. With Simo Spassov we are have investigated different kinds of sediments (see above in the reversal section).
Much effort has been carried out at improving techniques for relative and absolute paleointensity using different approaches for normalization. Among those we have investigated the influence of rock magnetic parameters that are sensitive to climatic changes. We proposed to detect the residual climatic components using principal component analysis.
Studies of absolute paleointensity from lava flows are very tedious and poorly successful. Various techniques have been proposed during the past 20 years. We are convinced that the double heating technique of Thellier remains the unique approach. We conducted multiple studies of contemporaneous flows. They all revealed that samples with single domain grains of pure magnetite are the most suitable, if not the only ones, capable of providing accurate determinations of the paleofield intensity. Therefore, we consider that robust paleointensity experiments can only be conducted using samples with high unblocking temperatures of the natural magnetization.
We have carried out mineralogical analyses on volcanic rocks, especially on several lava flows that cooled down during the last reversal. Surprisingly, a few flows recorded the two polarities, which given their thickness would imply that the transition was as short as a few weeks. The most coherent interpretation is that baking by the overlying flow was accompanied by low-temperature oxidation of titanomagnetite to cation deficient magnetite and produced partial remagnetization. Similarities with rapid field changes reported in the Steens Mountain record suggest that these events should be interpreted with caution.
Magnetotactic bacteria are well known for their ability of mineralizing magnetite grains with potential interest for industry and medicine. A freshwater population of magnetotactic bacteria has been extracted from the Seine River (France). Transmission electron microscopy by Aude Isambert and Nicolas Menguy has revealed seventeen different morphotypes based on morphological criteria. X-ray energy dispersive spectroscopy and electron diffraction analyses have also shown cells containing Ba-rich and CaO inclusions. Two major modes of magnetite crystals have been identified. The population does not meet some of the criteria for biogenicity, which have been used so far for biomagnetites, particularly those concerning the  elongation axis.
Selection of significant scientific contributions:
- First record of two successive reversals (Nature 304, 1983; Nature 309, 1984)
- Sedimentary records of multiple reversals with recurrent characteristics (Nature 311, 1984)
- Persistance of secular variation during a reversal (Nature 322, 1986).
- Records of the last transition suggest the a non-dipole field during reversals (Earth Planet Sci. Lett. 87, 1988; Earth Planet Sci. Lett. 94, 1989).
- The poles lie 90Ħ away from the site longitude in sedimentary records of reversals (Nature 356 , 1992).
- Records of relative paleointensity from Mediterranean and the Indian ocean demonstrate the suitability of paleointensity records in sediments (Earth Planet Sci. Lett. 114, 1992).
- First record of field intensity for the past 4Ma - asymmetrical evolution (Nature 366, 1993).
- Effect of magnetic fabric on reversal records from sediments (Nature 374, 1995).
- First composite curve of field intensity changes during the past 200 ka (Earth Planet. Sci. Lett., 143, 1996 )
- First composite and reference curve of paleointensity for the past 800 ka (Nature 399, 1999).
- Absolute paleointensity across reversals in volcanics confirms asymmetry (J. Geophys. Res. 101, 1996).
- Time variations in geomagnetic intensity (Rev. Geophys, 41, 2003).
- Stable Mn siderite produces stable magnetite: implications for carbonate spherules in meteorites (J. Geophys. Res., 108, 2003)
- Geomagnetic field strength and reversal rate over the past 2Ma (Nature 435, 2005).
- Low Precambrian dipole recorded in Canadian dykes (G-cubed, 7, 2006).
- A selective procedure for experiments of absolute paleointensity (Geophys. Res. Lett. 37, 2010)
Link between the Laschamp event and Neandertal demise (Quatern. Sci. Rev. 29, 2010).
- Dynamics of reversals in three phases - transitions are shorter than 1ka (Nature 49, 2012)
Analyse bibliomtrique lĠadresse : http://scholar.google.fr/citations?user=QZlwr_cAAAAJ
1- Valet J.-P., Laj C., Paleomagnetic record of two successive miocene geomagnetic reversals in western Crete, Earth Planet. Sci. Lett., 54 , 53-53, 1981.
2- Valente J.-P., Laj C., Sorel D., Roy S. Valet J.-P., Paleomagnetic results from mio-Pliocene sedimentary series in Crete, Earth Planet. Sci. Lett., 57, 159-172, 1982.
3- Valet J.-P., Laj C., Langereis C.G.,Two different geomagnetic reversals with identical VGP paths recorded at the same site, Nature, 304, NĦ5924, 330-332, 1983.
4- Valet J.-P., Laj C., Reply to the comment by K. Hoffman, Nature, 309, NĦ5963,"Matters Arising" NĦ 5963, 90-91, 1984.
5- Valet J.-P., Laj C., Invariant and changing transitional field configurations in a sequence of geomagnetic reversals, Nature, 311, NĦ5986, 552-555, 1984.
6- Valet J.-P., Laj C., Tucholka P., Volcanic record of reversal, Nature, 316, Ç News and Views È, 217-218, 1985.
7- Valet J.-P., Laj C., Tucholka P., Reply to the comment by Gromme et al, Nature, 318, 487, 1985.
8- Sen S., Valet J.-P., Ioakim C., Magnetostratigraphy of the Neogene of Kastellios Hill in Crete, Paleogeogr. Paleoclimat. Paleoecol., 53, 321-334, 1986.
9- Valet J.-P., Laj C., Tucholka P., High resolution sedimentary record of a geomagnetic reversal, Nature, 322, NĦ6074, 27-32, 1986.
10- Valet J.-P. and the shipboard scientific party of leg 108, Paleoclimate studied in the east Atlantic, Geotimes, October, 21-25, 1986.
11- Sen S., Valet J.-P., Magnetostratigraphy of late Miocene continental deposits in Samos, Greece, Earth Planet. Sci. Lett., 80, 167-174, 1986.
12- Faugres J.-C, Mannivit H., Valet J.-P., L'enregistrement des palocirculations et des paloclimats dans les dpots nognes de l'Atlantique est subtropical et quatorial: apports du leg ODP 108, C.R. Acad. Sci. Paris, t 303, Srie II, NĦ17, 1986.
13- Valet J.P. with the shipboard scientific party of ODP leg 108 Paleoclimatic linkage between high and low latitudes, Nature, 322, Ç News and Views È 211-212, 1986.
14- Bloemendal J., Tauxe L., Valet J.-P., High-resolution whole-core magnetic susceptibility logs from leg 108, Proc.Ocean Drilling Program PtA 108,1005-1013 , 1988.
15- Valet J.-P., Tauxe L., Clark D., The Matuyama-Brunhes polarity transition recorded from lake Tecopa sediments (California), Earth Planet. Sci. Lett. 87, 463-472, 1988.
16- Valet J.-P., Laj C. Langereis C.G., Sequential geomagnetic reversals recorded in upper tortonian marine clays in western Crete (Greece), J. Geophys. Res. Vol 93, NĦB2, 1131-1151, 1988.
17- Tauxe L., Valet J.-P., Relative paleointensity of the Earth's magnetic field from marine sedimentary records: a global perspective, Phys. Earth Planet. Inter., 56, 59-68, 1989.
18-Valet J.-P., Tauxe L., Bloemendal J., The Matuyama-Brunhes geomagnetic reversal from two deep-sea cores of the east-equatorial Atlantic, Proceedings of the Ocean Drilling Program, Scientific Results Vol 108, 441-454 , 1989.
19- Tauxe L., Valet J.-P., Bloemendal J.,The magnetostratigraphy of leg 108 sediments, Proceedings of the Ocean Drilling Program, Scientific Results Vol 108, 429-440, 1989.
20- Valet J.-P., Tauxe L., Clement B.M., Equatorial and mid-latitudes records of the last geomagnetic reversal from the Atlantic Ocean, Earth Planet. Sci. Lett., 94,371-384,1989.
21- Bloemendal J., King J.W., Tauxe L., Valet J.-P., Rock magnetic stratigraphy of leg 108 sites 658, 659, 661 and 665 eastern equatorial Atlantic. Proceedings of the Ocean Drilling Program, Scientific Results Vol 108, 415-428, 1989.
22- Weaver P.P.E., Backman J., Baldauf J.-G., Bloemendal J., Mannivit H., Pokras E.M., Raymo M.E., Tauxe L., Valet J.-P., Chephow-Lasty A. Glafsson G., Biostratigraphic synthesis ODP leg 108 Tropical Atlantic, Proceedings of the Ocean Drilling Program, Scientific Results Vol 108, 455-462, 1989.
23- Tric E., Laj C., Jehanno C., Valet J.-P., Mazaud A., Kissel C., Iaccarino S.,A detailed record of the upper Olduvai polarity transition from high sedimentation rate marine deposits of the Po valley, Phys. Earth Planet. Inter., 65,319-336, 1991.
24- Valet J.-P., Les transitions de polarit du champ gomagntique, Rapport quadriennal XXme assemble de l'Union Godsique et Gophysique Internationale 125-140, 1991.
25- Tric E., Laj C., Valet J.-P., Tucholka P., Guichard F., The Blake geomagnetic event: transition geometry, dynamical characteristics and geomagnetic significance, Earth Planet. Sci. Lett., 102,1-13,1991.
26- Valet J.-P., Leg 138 Participants, Ancient ocean -Climate link, Nature , Vol 353, Ç News and Views È, 304-305,1992.
27- Valet J.-P., Courtillot V.,, Les inversions du champ magntique terrestre, La Recherche, 23, 1002-1013, 1992.
28- Valet J.-P. Leg 138 Participants, High-resolution studies of the eastern equatorial Pacific, Eos Transactions 73 , 257-262, 1992
29- Tric E., Valet J.-P., Tucholka P., Paterne M., Labeyrie L., Guichard F., Tauxe L. and Fontugne M, Paleointensity of the geomagnetic field during the last eighty thousand years, J. Geophys. Res., Vol.97, NoB6, 9337-9351, 1992
30- Valet J.P., Tucholka P., Courtillot V., Meynadier L., Paleomagnetic constraints on the geometry of the geomagnetic field during reversals, Nature , 356, 400-407, 1992
31- Quidelleur X., Valet J.-P., Thouveny N., Multicomponents of magnetization in paleomagnetic records of reversals from continental sediments in Bolivia, Earth Planet. Sci. Lett., 111, 23-39, 1992
32- Courtillot V., Valet J.-P., Hulot G., Le Moul J.-L.,The earth's magnetic field: a chaotic, randomly reversing geocentric axial dipole with superimposed white noise at the core mantle boundary, Eos transactions, 73, 337-342, 1992
33- Meynadier L., Valet J.-P., Weeks R., Shackleton N., Hagee V.L., Relative paleointensities of the geomagnetic field during the last fourteen hundred thousand years, Earth Planet. Sci. Lett., 114, 39-57, 1992
34- Meynadier L., Valet J.-P., Vincent E., Leg ODP 138: un tournant dans les analyses haute rsolution des sdiments ocaniques, Gochronique NĦ41, 18, 1992
35- Shackleton N.J., Hall M.A., Meynadier L., Pate D., Valet J.-P., High resolution stable isotope stratigraphy from bulk sediments, Paleoceanography, vol 8, No.2, 141-148, 1993
36- Nagy E., Valet J.-P., New advances for paleomagnetic studies of sediment cores using U-channels, Geophys. Res. Lett., vol 20, No 8, 671-674, 1993
37-Valet J.-P., Meynadier L., Geomagnetic field intensity and reversals during the last four million years. Nature, Vol 366, 234-238, 1993.
38- Valet J.-P., Meynadier L., Bassinot F., Garnier F., Relative paleointensity across the last geomagnetic reversal from sediments of the Atlantic, Indian and Pacific oceans. Geophys. Res. Lett. , Vol 21, NĦ6, 485-488, 1994.
39- Gallet Y., Valet J.-P., Magnetic stratigraphy in deep-sea sediments: from the superchron to the microchron, Oceanus Vol 36, NĦ4, 99-102, 1994.
40- Quidelleur X., Valet J.-P., Paleomagnetic records of excursions and reversals: possible biases caused by magnetization artefacts? Phys. Earth Planet. Inter., 82, 27-48, 1994.
41- Tric E., Valet J.-P., Gillot P.Y., Le Meur I., Absolute paleointensities between 60 and 160 kyrs B.P. from Mount Etna (Sicily), Phys. Earth Planet. Inter. 85, 113-119, 1994.
42- Quidelleur X., Valet J.-P., Courtillot V., Hulot G ., Long-term geometry of the geomagnetic field derived from an updated base on secular variation for the last 5 million years, Geophys. Res. Lett., Vol 21, NĦ15, 1639-1642, 1994.
43- Meynadier L., Valet, J.-P., Bassinot, F. Shackleton, N., Guyodo Y., Asymmetrical saw-tooth pattern of the geomagnetic field intensity from equatorial sediments in the Pacific and the Indian oceans, Earth Planet. Sci. Lett. , 126, 109-127, 1994.
44- Meynadier L. Valet, J.-P., Grousset, F., Magnetic properties and origin of late quaternary sediments in the Somali basin (Indian ocean), Paleoceanography, Vol. 10, N0.3, 459-472, 1995.
45- Quidelleur X. , Holt, J., Valet J.-P., Confounding influence of magnetic fabric on sedimentary records of a field reversal, Nature, Vol 374, 246-249, 1995.
46- Valet J.-P., Les inversions du champ magntique: de la peau de Zbre aux dents de scie, Geochronique, 1995.
47- Meynadier L, Valet J.-P., Shackleton N.J., Relative geomagnetic intensity during the last 4Ma from the equatorial Pacific, Proceedings of the Ocean Drilling Program, Scientific Results Vol 138, 779-795, 1995.
48- Quidelleur X., Valet, J.-P., LeGoff M., Bouldoire, X., Field dependence on magnetization of laboratory redeposited deep-sea sediments: first results, Earth Planet. Sci. Lett., 133 , 311-325, 1995.
49- Valet J.P, ODP Leg 154 scientific party, Ceara Rise sediments document ancient climate change, Eos Transactions 76, NĦ5, 41-42, 1995.
50- Courtillot V., Valet J.-P., Secular variation of the earthĠs magnetic field : from jerks to reversals, C.R. Acad.Sci., 320, IIa, 903-922, 1995.
51- Quidelleur, X., Valet J.-P., Geomagnetic changes across the last reversal recorded in lava flows from La Palma (Canaries islands), J. Geophys. Res., Vol 101, NĦB6 13755-13774, 1996.
52- Meynadier L. and Valet J.-P., Post-depositional realignment of magnetic grains and saw-toothed variations of relative paleointensity, Earth Planet. Sci.. Lett., 140, 123-132 , 1996.
53- Guyodo Y., Valet J.-P., Relative variations in geomagnetic intensity from sedimentary records: the past 200 thousand years, Earth Planet. Sci. Lett., 143, 23-36, 1996.
54- Valet J.-P., Brassart J. , Le Meur I., Soler V., Quidelleur X., Tric E., Absolute paleointensity and magnetomineralogical changes, J. Geophys. Res. , Vol101, NoB11, 25029-25044, 1996
55- Richter C., Valet J.-P., Solheid P. A., Rock magnetic properties of sediments from Ceara Rise and implications for the origin of their magnetic susceptibility, Proceedings of the Ocean Drilling Program, Scientific Results 154, 169-180, 1997
56- Solheid P., Banerjee S.K., Richter C., Valet J.-P., High resolution rock magnetic study of Ceara Rise sediments (Site 925), Proceedings of the Ocean Drilling Program, Scientific Results 154, 181-188, 1997.
57- Brassart J., Tric E., Valet J.-P., Herrero-Bervera E., Absolute paleointensity between 60 and 400 ka from the Kohala Mountain (Hawai), Earth Planet. Sci. Lett., Vol 148, 141-156, 1997.
58- Meynadier, L., Valet, J.-P., Guyodo, Y., Richter, C., Saw-toothed variations of relative paleointensity and cumulative viscous remanence: testing the records and the model? J. Geophys. Res., Vol. 103, B4, 7095-7105, 1998.
59- Valet, J.-P., Meynadier, L., A comparison of different techniques of relative paleointensity, Geophys. Res. Lett., Vol. 25, NĦ1, 89-92, 1998.
60- Valet, J.-P., Kidane, T., Soler, V., Brassart, J., Courtillot ,V., Meynadier, L., Remagnetization in lava flows recording pretransitional directions, J. Geophys. Res., Vol 103, NĦ B5, 9755-9775, 1998.
61- Rousseau, D.-D., Zller, L., Valet, J.-P., Late pleistocene climatic variations at Achenheim, France, Based on a magnetic susceptibility and TL chronology of loess, Quaternary Research 49, 255-263, 1998.
62- Valet, J.-P., Tric, E., Herrero-Bervera, E., Meynadier, L., Lockwood, J. ,P., Absolute paleointensity from hawaiian lavas younger than 35ka, Earth and Planet Sci. Lett., 161, 19-32, 1998.
63- Valet, J.-P., Gallet, Y., Paleomagnetism: ancient inclinations, Nature, ÇNews and ViewsÈ, Vol 396, 315-316, 1998.
64- Valet, J.-P. , Brassart, J., Quidelleur, X., Soler, V., Gillot, P.-Y., Hongre, L., Paleointensity variations across the last geomagnetic reversal at La Palma (Canary islands, Spain, J. Geophys. Res. Vol. 104 , No. B4 , p. 7577, 1999.
65- Guyodo, Y., Valet, J.-P., Global changes in geomagnetic intensity during the past 800 thousand years, Nature, Vol 399, 249-252, 1999
66- Carlut, J., Valet, J.-P., Quidelleur, X., Courtillot, V., Kidane, T., Gallet, Y., Gillot, P.Y., Paleointensity across the Runion event in Ethiopia, Earth Planet. Sci. Lett., 170, 17-34, 1999.
67- Herrero-Bervera, E., Valet, J.-P., Paleosecular variation during sequential geomagnetic reversals from Hawaii, Earth and Planet. Sci. Lett., 171, 139-148, 1999.
68- Valet, J.-P., Soler, V., Magnetic anomalies induced by lava flows and possible consequences for paleomagnetic records, Phys. Earth Planet. Inter., 115 , 109-118, 1999.
69- Richter, C., Hayashida, A., Guyodo, Y., Valet, J.-P., Verosub, K., Magnetic intensity loss and core diagenesis in long-core samples from the East Cortez Basin and the San Nicolas Basin (California Borderland), Earth, Planets and Science 51, 329-336, 1999.
70- Guyodo, Y., Richter, C., Valet, J.-P., Paleointensity record from pleistocene sediments off the California Margin, J. Geophys. Res.,Vol. 104, NĦB10, 22953-22965, 1999.
71- Guyodo Y., Valet, J.-P., Integration of volcanic and sedimentary paleointensity data, Constraints imposed by irregular eruption rates, Geophys. Res. Lett. Vol. 26 , No. 24 , p. 3669, 1999.
72- Valet, J.-P. and Herrero-Bervera, E., Paleointensity experiments using alternating field demagnetization, Earth and Planet. Sci. Lett. 177, 43-53, 2000.
73- Meynadier, L., Valet, J.-P., Reply to the comment on Ò Saw-toothed variations of relative paleointensity and cumulative viscous remanence : Testing the records and the modelÓ, J. Geophys. Res. Vol. 105 , No. B7 , p. 16,613, 2000.
74- Herrero-Bervera, E., Vinuela, J.-M., Valet, J.-P., Paleomagnetic study of lavas of the island of LanaĠi, Hawaii, J. Vol. Geoth. Res., 104, 21-31, 2000.
75- Dormy, E., Valet, J.-P., Courtillot, V., Observational constraints and numerical dynamos., Geochem. Geophys. Geosyst, Vol 1, October 18, 2000.
76- Valet, J.-P., Meynadier, L., Comment on Ç A relative paleointensity stack from Ontong-Java plateau sediments for the Matuyama È by Yvo S. Kok and L. Tauxe, J. Geophys. Res. Vol. 106 , No. B6 , p. 11,013, 2001.
77- Elmaleh, A., Valet J.-P., Herrero-Bervera, E., A map of the Pacific anomaly during the Brunhes chron, Earth Planet. Sci. Lett., 193 NĦ3-4, p. 315-332, 2001.
78- Kravchinsky, V.A., Konstantinov, K.M., Courtillot, V., Valet, J.-P., Savrasov, J.I., Cherniy, S.D., Mishenin, S.G., Parasotka, B.S., Paleomagnetism of east Siberian traps and kimberlites: two new poles and paleogeographic reconstructions at about 360 and 250 Ma, Geophys. J. Int., 148, 1-33, 2002.
79- Valet, J.-P., La Terre perd-elle son magntisme ? La Recherche, NĦ 351, 36-39, 2002.
80- Herrero-Bervera, E. , Valet J.-P., Paleomagnetic secular variation of the Honolulu volcanic series (33-700ka), OĠahu, Hawaii, Physics Earth Planet. Inter., 133, 83-97, 2002.
81- Valet, J.-P., Time variations in Geomagnetic Intensity, Reviews of Geophysics, 41, 1/ 1004, 2003.
82- Isambert, A., Valet, J.-P., Gloter, A., Guyot F., Stable Mn-magnetite derived from siderite by heating in air, J. Geophys. Res. Vol. 108, No. B6, 2283, 2003.
83- Valet, J.-P., Herrero-Bervera E., Characteristics of geomagnetic reversals inferred from detailed volcanic records, C.R. Gosciences, 335, 79-90, 2003.
84- Quidelleur, X., Carlut,J., Soler, V., Valet, J.-P., Gillot P.Y., The age and duration of the Matuyama-Brunhes transition from new K-Ar data from La Palma (Canary islands) and revisited 40Ar/39 Ar ages, Earth Planet. Sci. Lett. 208, 149-163, 2003.
85- Herrero-Bervera, E. , Valet J.-P., Persistent anomalous inclinations recorded in the Koolau volcanic series of the island of Oahu (Hawaii, USA) between 1.8 and 2.6 Ma, Earth Planet. Sci. Lett 6633, 1-14, 2003.
86- Macouin, M., Valet, J.-P., Besse, J., Buchan, K. , Ersnt, R., LeGoff, M, U.Schrer U., Low Paleointensities recorded in 1 to 2.4 Ga old Proterozoic dykes, Superior province, Canada, Earth Planet. Sci. Lett., 213, 79-95, 2003.
87- Glen, J., Valet, J.-P., Soler, V., Renne, P.R., Elmaleh, A., A Neogene geomagnetic polarity transition record from lavas of the Canary islands, Spain: episodic volcanism and/or metastable transitional fields ? Geophys. J. Int., Vol. 154, Issue 2, Page 426-440, 2003.
88- Elmaleh, A., Valet J.-P., Solihin, A., Quidelleur, X., Bouquerel, H., Tesson, T., Mulyadi, E., Wirakusumah A.D., Paleosecular variation in Java and Bawean Islands (Indonesia) during the Brunhes chron, Geophys. J. Int., Vol. 157, Issue 1, Page 441-454, 2004.
89- Macouin, M., Valet J.-P., Besse J., Long-term evolution of the geomagnetic dipole moment, Phys. Earth Planet. Inter., Vol 147, 2-3, 239-246, 2004.
90- Herrero-Bervera, E., Ubangoh, R., Aka, F.T., Valet, J.-P. Paleomagnetic and paleosecular variation study of the Mt Cameroun volcanics (0.0-0.25 Ma), Cameroun, West Africa, Phys. Earth Planet. Inter., Vol 147, 2-3, 171-182, 2004.
91- Herrero-Bervera, E., Valet, J.-P., Absolute paleointensity from the Waianae volcanics (Oahu, Hawaii) between the Gilbert-Gauss and the upper Mammoth reversals, Earth Planet. Sci. Lett., Vol 234, 279-296, 2005.
92- Bouquerel, H., Valet, J.-P., Le prote est-il quip pour le magntotactisme? C. R. Goscience., 337, 806-813, 2005.
93- Valet, J.-P., Meynadier L., Guyodo, Y., Geomagnetic field strength and reversal rate over the past 2 Million years, Nature, Vol 435, 802-805, 2005.
94- Letard, I. , Sainctavit, P., Menguy, N., Valet, J.P., Isambert, A., Dekkers, M., Gloter, A., Mineralogy of greigite, Physica Scripta, Vol. T115, 489-491, 2005.
95- Macouin, M., Valet, J.-P., Besse, J., Ernst R.E., Absolute Paleointensity at 1.27 Ga from the Mackenzie dyke swarm (Canada), G-cubed, Vol. 7, Q01H21, doi:10.1029/2005GC000960, 2006.
96- Isambert, A., T., De Resseguier, Gloter A., Reynard, B., Guyot, F. Valet, J.-P., Magnetite-like nanocrystals formed by laser-driven shocks in siderite, Earth Planet. Sci. Lett. 243, 820-827, 2006.
97- Carter-Stiglitz, B., Valet, J.-P., LeGoff, M., Constraints on the acquisition of remanent magnetization in fine grain sediments imposed by redeposition experiments, Earth Planet. Sci. Lett. 245, 427-437, 2006.
98- Guyodo, Y., Valet, J.-P., A comparison of relative paleointensity records of the Matuyama chron for the period 0.75-1.25Ma, Phys. Earth Planet. Inter., 156, 3-4, 205-212, 2006.
99- Valet, J.-P., Paleointensity, absolute, techniques, Encyclopedia of Geomagnetism and Paleomagnetism, D. Gubbins & E. Herrero-Bervera edts., 753-757, 2007
100- Isambert, A., Menguy., N,. Larquet, E., Guyot, F., Valet, J.-P., Morphological study of magnetites in a freshwater population of magnetotactic bacteria, Am. Mineral., Vol 92, 621-630, 2007.
101- Valet, J.-P., Herrero-Bervera, E., Geomagnetic reversals, archives, Encyclopedia of Geomagnetism and Paleomagnetism, D. Gubbins & E. Herrero-Bervera edts., 339-346, 2007.
102- Herrero-Bervera, E., Browne, E.J., Valet J.-P., Singern B.S, Jichan B., Cryptochron C2r.2r-1 recorded 2.51 Ma in the Koolau Volcano at Halawa, Oahu, Hawaii, US : palomagnetic and 40Ar/39Ar evidence, Earth Planet. Sci. Lett. 254, 3-4, 256-271, 2007.
103- Herrero-Bervera, E., Valet, J.-P., Holocene paleosecular variation from dated lava flows in Maui, Phys. Earth Planet. Int., 161 (3), 267-280, 2007.
104- Plenier, G., Valet, J.-P., Gurin, G., Lefvre, J.C., Carter-Stiglitz, B., Origin and age of the directions recorded during the Laschamp event in the Chane des Puys (France), Earth Planet. Sci. Lett., 259, 414-431, 2007.
105- Narteau, C., LeMoul, J.-L., Valet, J.-P., The oscillatory nature of the geomagnetic field during reversals, Earth Planet. Sci. Lett., Vol 262, 1-2, 66-76, 2007.
106- Valet, J.-P., Herrero-Bervera, E., LeMoul, J.L., Plenier, G., Secular variation of the geomagnetic dipole during the past 2 thousand years, Geochem. Geophys. Geosyst., 9, Q01008, doi:10.1029/2007GC001728, 2008.
107- Valet, J.-P., Plenier, G., Simulations of a time-varying non dipole field during geomagnetic reversals and excursions, Phys. Earth. Planet. Inter.,169, 178-193, 2008.
108- Valet, J.-P., Plenier, G., Herrero-Bervera, E., Geomagnetic excursions reflect an aborted polarity state, Earth and Planet. Sci. Lett. 274, 472-478, 2008.
109 – Ptrlis, F., Fauve, S., Dormy, E., Valet, J.P., Mechanism for magnetic field reversals, Phys. Rev. Lett ., 102,14, 144503, 2009.
110 - Herrero-Bervera, E.,Valet, J.P., Testing Determinations of Absolute Paleointensity from the 1955 and 1960 Hawaiian Flows, Earth Planet. Sci. Lett., http://dx.doi.org/10.1016/j.epsl.2009.08.035, 2009.
111 – Valet, J.P., Herrero-Bervera, E., Carlut, J., A selective procedure for absolute paleointensity in lava flows, Geophys. Res. Lett., 37, L16308, doi:10.1029/2010GL044100, 2010.
112 – Valet, J.P., Valladas, L., The Laschamp-Mono lake geomagnetic events and the extinction of Neanderthal : a causal link or a coincidence?, Quatern. Sci. Rev 29, 3887-3893, 2010.
113 - Spassov, S., Valet, J.P., Kondopoulou, D., Zananiri, I., Casas, L., Le Goff, M., Rock magnetic property and paleointensity determination on historical Santorini lava flows. Geochemistry Geophysics Geosystems, 11, Q07006, 2010.
114 - Valet, J.P., Herrero-Bervera, E., A few characteristic features of the geomagnetic field during reversals, The Earth's Magnetic Interior, IAGA Special Sopron Book Series, Springer, Germany, 138-151, 2011.
115 – Valet, J.P., Herrero-Bervera, E, Meynadier, L., Time-averaged and mean axial dipole field, The Earth's Magnetic Interior, IAGA Special Sopron Book Series, Springer, Germany, 131-137, 2011.
117 – Petrelis, F., Besse, J. , Valet, J.P., Plate Tectonics may control reversal frequency, Geophys. Res. Lett., 38, L19303, 2011.
118 – Blanco, D., Kravchinsky, V.A., Valet, J.P., Ali, A., Potter, D.K., Does the Permo-Triassic geomagnetic dipole low exist? Phys. Earth Planet. Inter. 204, 11-21, doi:10.1016/j.pepi.2012.06.005, 2012
119 – Moulin, M., Courtillot, V., Fluteau, F. , Valet, J.P., The van Zijl Jurassic geomagnetic reversal revisited, Geochem. Geophys. Geosyst., 13, doi:10.1029/2011GC0039101, 2012.
120 - Spassov, S., Valet, J.P., Detrital magnetization from redeposition experiments of natural sediments, Earth Planet. Sci. Lett., 351, 147-157,: doi 10.1016/j.epsl.2012.07.016, 2012
121 - Petrelis, F., Valet, J-P., Besse, J., When North heads South, Physics world, 25- 3, 51-55 , 2012
122 - Valet, J.P., Fournier, A., Courtillot, V., Herrero-Bervera, E., Dynamical similarity of geomagnetic field reversals, Nature Vol.490, 7418, 89-+94, doi: 10.1038/, 2012.
123 - Bouilloux, A., Valet, J.P., Bassinot, F., Joron, J.L., Blanc-Valleron, M.M., Moreno, E., Dewilde, F., Kars, M., Lagroix, F., Diagenetic modulation of the magnetic properties in sediments from the Northern Indian Ocean, Geochem. Geophys. Geosyst., 14, 9, 3779-3800, doi: 10.1002/ggge.20234, 2013.
124 - Bouilloux, A., Valet, J.P., Bassinot, F., Joron, J.L., Dewilde F., Blanc-Valleron,, M.M., Moreno, E., Influence of seawater exchanges across the Bab-el-Mandab Strait on sedimentation in the Southern Red Sea during the last 60 ka, Paleoceanography, in press.