Simo Spassov - Academia.edu (original) (raw)

Papers by Simo Spassov

We present a detailed investigation of the geomagnetic polarity transition that terminated the Ol... more We present a detailed investigation of the geomagnetic polarity transition that terminated the Olduvai subchron as recorded by loess/paleosol sediments at Lingtai in the central Chinese Loess Plateau (CLP). The polarity transition occurs within loess layer L25, where mineral magnetic parameters show considerable variations and sedimentation rate changes occur. The magnetic record obtained after thermal cleaning exhibits more than twenty

Geochemistry Geophysics Geosystems, 2010

low Curie temperature phase with a narrow grain size distribution. The results were characterized... more low Curie temperature phase with a narrow grain size distribution. The results were characterized by low dispersion and were found in good agreement with the historical field.

Physics and Chemistry of The Earth, 2008

Three pottery kilns from a large Hellenistic ceramic workshop at Katerini (Macedonia, Northern Gr... more Three pottery kilns from a large Hellenistic ceramic workshop at Katerini (Macedonia, Northern Greece) were studied archaeomagnetically. Palaeomagnetic investigation revealed a stable remanent magnetisation, well grouped with a mean direction of Dsite = 349.3, Isite = 57.6 (k = 1913.0; α95 = 2.8). A few samples exhibited anomalous results, this behaviour being related to sample locations in the archaeological feature, where the heating was probably not homogeneous. Archaeointensity determinations gave an averaged weighted result of Fsite = 85.8 ± 7.8 μT. Rock magnetic analyses proved the suitability of the sampled materials for archaeomagnetic studies and revealed the presence of (metal substituted) magnetite as the main remanence carrier. Anisotropy of magnetic susceptibility and, mainly, of the remanence magnetisation showed a comparatively high degree of anisotropy.Archaeomagnetic dating was performed using the three (inclination, declination and intensity) secular variation curves for Bulgaria, by applying a recently developed hierarchical Bayesian approach. The proposed age span corresponding to the most probable last usage of the kilns is from 505 BC to 287 BC, in good agreement with the archaeological estimation.

The reconstruction of paleosurfaces represents a unique tool to access the evolution of ancient c... more The reconstruction of paleosurfaces represents a unique tool to access the evolution of ancient continents. Paleosurfaces contribute to the study of global changes through paleoweathering features/profiles and record uplift and subsidence of the ancient continents driven by crustal geodynamics and plate tectonics. However, age constraints for basement paleosurfaces are often difficult to obtain since the geological record of ancient land surfaces is usually limited, fragmented by unconformities and scrambled by successive superimposed evolutions, leaving a patchwork of relict landforms and weathering products, discontinuous over time and space. The crystalline basement of European Paleozoic massifs, consisting of igneous and metamorphic rocks, often show Permo-Triassic overprints resulting in underestimated age determinations. These remagnetisations are ubiquitous [e.g. Edel & Schneider, 1995], affecting many emerged Paleozoic rocks in Europe. The rejuvenated age estimations are attributed to an alteration of the primary paleomagnetic signal and carried by secondary hematite [Ricordel et al., 2007; Preeden et al., 2009; Preeden, 2009]. Moreover, published paleomagnetic ages [Ricordel et al., 2007] showed a strong relationship between the remagnetization and the development of pinkish-red crystalline facies associated to the albitized underlying rocks of the Morvan Massif (France). Parcerisa et al. [2009] performed further field and petrographic analyses and proposed that the albitization was linked to the precipitation of secondary haematite. Since hematite forms under oxidising conditions one may deduce that the remagnetization occurring in the Paleozoic crystalline rocks formed during the exposure of these rocks at the Permo-Triassic (paleo)surface. The extent of the altered zone (~200 m in depth) points to a sodium enriched groundwater environment [Thiry et al., 2009]. Demonstrating that the albitized facies are of supergenic origin and bound to the Triassic paleosurface deeply renews the ideas about the evolution of basement areas. The recognition of the Triassic paleosurface on widespread basements in Europe will provide spatio-temporal benchmarks to constrain the ablation of these massifs since the Triassic. This will be a major contribution to the geodynamic modelling of continental evolution of Europe. To deepen our understanding of this paleoalteration phenomenon on a supra-regional scale and to obtain a reasonable distribution of paleomagnetic age determinations, we aim to acquire more tie points for this Permo-Triassic surface, which was preserved in the crystalline basement of Europe throughout the Mesozoic and Cenozoic epochs. We will present results from paleomagnetic investigations as well as magneto-mineralogic analyses of the profiles through albitized granite and porphyry from the Sudetes in SW-Poland and the Catalonian Mountains in NE-Spain, for which preliminary age estimations have been carried out. Further European Paleozoic sample sites are in process. Depending on the depth situation of the sampled facies compared to the weathering profile, the Triassic paleomagnetic ages show dispersion towards rather older ages at the top and younger ages at the bottom of the sequence. This seems to correlate with the results from magneto-mineralogical analyses which show a decreasing hematite concentration with depth. The oldest ages are carried by a single component, identified as single-domain secondary hematite inclusions in the secondary albite crystals. With increasing depth the samples are rather characterized by a two-component signal, still showing (younger) Triassic ages for both components. These were identified as secondary hematite and maghemite. The latter is most probably a product of either low-temperature magnetite oxidation or precipitates during the albitization of the primary rock. These processes are both linked to less oxidising conditions than at the top of the weathering profile. A systematic interpretation of the paleomagnetic ages and the identification of the magnetic carrier assemblage for all European sites will provide valuable insights into (a) the geodynamic evolution of the crystalline complexes, by estimation of erosion/stability rates and (b) an advanced mineralogical understanding of the specific conditions linked to this Triassic paleoweathering event. Edel & Schneider, 1995, Geophys. J. Int., 122, 858-876; Edel et al., 1997, C.R.AS. Paris, Earth Planet. Sci., 325, 479-486. Parcerisa D., Thiry M., Schmitt J.-M., 2009, Albitisation related to the Triassic unconformity in igneous rocks of the Morvan Massif (France)? Int. J. Earth Sci., doi: 10.1007/s00531-008-0405-1. Preeden, U., 2009, Remagnetization in sedimentary rocks of Estonian and shear and fault zone rocks of southern Finland, disertationes geologicae Universatis Tartuensis, Ph.D. thesis, Estonia, 26, 121, ISSN 1406-2658. Preeden U., Mertanen S., Elminen T., Plado J., 2009, Secondary magnetizations in shear and fault zones in southern Finland, Tectonophysics, 49/3-4, 203-213, doi.org/10.1016/j.tecto.2009.08.011. Ricordel C., Parcerisa D., Thiry M., Moreau M.-G., Gomez-Gras D., 2007, Triassic magnetic overprints related to albitization in granites from the Morvan massif (France), Palaeogeogr. Palaeoclimatol. Palaeoecol., 251:268-282. Thiry et al., Parcerisa, D., Ricordel-Prognon, C., Schmitt, J-M., 2009, Sodium storage in deep paleoweathering profiles beneath the Paleozoic-Triassic unconformity, EGU General Assembly 2009, Vienna, Austria.

Palaeogeography Palaeoclimatology Palaeoecology, 2008

A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possessi... more A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possession (Iles Crozet), has been investigated, based on a multi-proxy approach. The methods applied are macrobotanical (mosses, seeds and fruits) and diatom analyses, complemented by geochemical (Rock-Eval6) and rock magnetic measurements. The chronology of the core is based on 5 radiocarbon dates.

Quaternary Science Reviews, 2009

Botanical macrofossil analysis of a more than 9000 years old, radiocarbon dated peat sequence of ... more Botanical macrofossil analysis of a more than 9000 years old, radiocarbon dated peat sequence of a moss peat bank from South Georgia, shows a clear evolution in the vegetation. Seven ecological phases could be distinguished and they can be interpreted in terms of climate development during the Holocene. Until 2200 years ago, Warnstorfia fontinaliopsis was the dominant moss species pointing to a wet environment. Lower numbers of this species in association with the presence of drier species are assumed to indicate drier periods, such as occurring between ca 6000–5200 and 4400–3400 cal yr BP. The most prominent and definitive vegetation change took place around 2200 cal yr BP. A Polytrichum–Chorisodontium moss peat bank was formed, which is still growing there today. The forcing mechanism for this vegetation change is thought to be a temperature decrease, rather than a precipitation decrease. This conclusion is mainly based on the fact that, today, moss peat banks have their optimal occurrence range in the maritime Antarctic, a region were the mean annual temperature is ca 4 °C lower than on South Georgia. The remarkable change in the moss bank vegetation at 2200 cal yr BP raises the question whether this moment was only a short climatic deterioration, or a definitive change to a cooler and wetter climate after a Holocene climatic optimum period.

Physics and Chemistry of The Earth, 2008

Archaeological burnt materials and structures provide unique records of direction and intensity o... more Archaeological burnt materials and structures provide unique records of direction and intensity of the Earth’s magnetic field in the past, elements that can be absolutely determined applying the archaeomagnetic method. At present, such records within Europe are irregular in both space and time. Presented here is the archaeomagnetic investigation of three kilns that were discovered during a preventive excavation of an archaeological site considered of High Middle Age in Corroy-le-Grand (Belgium) and that are assumed to be related to iron working activities. Archaeological context dating points to kiln operation between the second half of the 10th century until the 12th century AD. As the site is not far from Paris, declination and inclination of the characteristic remanent magnetisation of the kilns were compared with the standard directional secular variation curve for France in order to propose archaeomagnetic dates for the cessation of kiln operation by using probability densities [Lanos, Ph., 2004. Bayesian inference of calibration curves, application to archaeomagnetism. In: Buck, C.E., Millard, A.R. (Eds.), Tools for Constructing Chronologies: Crossing Disciplinary Boundaries. Lecture Notes in Statistics. Springer Verlag, London, pp. 43–82; Lanos, Ph., Le Goff, M., Kovacheva, M., Schnepp, E., 2005. Hierarchical modelling of archaeomagnetic data and curve estimation by moving average technique. Geophysical Journal International 160 (2), 440–476]. This confirms the presumed archaeological age and resulted in more precise time constraints for the last kiln operation. Rock magnetic techniques, proposed by Spassov and Hus [Spassov, S., Hus, J., 2006. Estimating baking temperatures in a Roman pottery kiln by rock magnetic properties: implications of thermochemical alteration for archaeointensity determinations. Geophysical Journal International 167, 592–604], were applied to examine the suitability of the burnt materials from the kilns for archaeointensity determinations and to increase the success rate of the Thellier–Thellier double heating technique. An average value for the field intensity of 69.4 ± 2.5 μT was estimated from 10 specimens from a single kiln, which corresponds reasonably well with published data for Western Europe.

Physics and Chemistry of The Earth Part A-solid Earth and Geodesy, 2001

A refined pedostratigraphic scheme in the western Black sea region is proposed on the basis of pa... more A refined pedostratigraphic scheme in the western Black sea region is proposed on the basis of paleopedological reconstructions coupled with magnetic susceptibility, and other rock magnetic parameters, and Mössbauer spectroscopy. The new scheme matches well with oxygen isotope stages despite local variations in erosion/deposition, strong welding of paleosols and subtle discrepancies in the position of the Matuyama/Brunhes boundary. These limitations are reduced by optimizing resolution of magnetic cycles and paleosol identification. Two humid/warm maxima during the Quaternary are found in pedocomplex PK4 at about 0.5 Ma (corresponding to oxygen isotope stages 13 and 15), and in pedocomplex PK8 related to the Jaramillo subchron. Comparison with the oxygen isotope curve shows that the apparent major driving force of regional soil/loess cyclicity is the 100 ka eccentricity period.

Quaternary International, 2006

Loess/paleosol sequences in the western Black sea area at Roxolany (48 m thick) and Novaya Etuliy... more Loess/paleosol sequences in the western Black sea area at Roxolany (48 m thick) and Novaya Etuliya (30 m thick) were studied using paleo- and rock-magnetic methods in conjunction with micromorphology and Mössbauer investigations. Although seemingly complete, the sites show variability in the type and number of loess/paleosol cycles, and inconsistency of the Matuyama/Brunhes boundary (MBB) stratigraphic position. At Roxolany, nine pedocomplexes (PK) and several incipient paleosols, alternating with thick loesses, were observed with the MBB being located between PK6 and PK7. At Novaya Etuliya, 13 PKs occur upon terrace XII with Khapry fauna and with the MBB in the upper part of PK7 and the Jaramillo subchron within the lower part of PK8. The depth functions of rock magnetic properties, organic carbon content Corg, both for bulk samples and for clay extracts, along with micromorphology and Mössbauer spectra, allowed objective identification of individual soils within PKs, and maximizing the resolution of paleopedological reconstructions of global climatic stages. The Mössbauer studies demonstrate that paleosols are basically enriched in ferric montmorillonite. Oxidized magnetite, ultrafine iron hydroxides and hematite are intimately associated with clay minerals. In contrast, Fe-compounds in loess consist mainly of ferrous silicates. These data indicate that the paleosol magnetism is basically of bio-chemogenic origin and is related to pedogenic transformation of Fe-compounds in a changing environment, while loess magnetism is primarily detrital. Pedogenic magnetically “soft” and partly oxidized magnetite may also originate during or even after burial. This ensuing transformation of Fe minerals in paleosols seems to be crucial for the understanding of the timing of natural remanent magnetization (NRM) in subaerial sediments. Given that paleosols formed on the similar parent material (loess), their typological variability seems to depend on climate and/or chronology. Hence, the different paleosol types from Roxolany and Novaya Etuliya provide key information for intra- and inter-regional correlation of loess/soil sequences, and represent valid paleoclimatic proxies.

Geophysical Journal International, 2006

Absolute past geomagnetic field intensity determinations requiring laboratory heating are labouri... more Absolute past geomagnetic field intensity determinations requiring laboratory heating are labourious and the success rate is rather low, mostly because of induced thermochemical magnetic mineral alterations. Archaeomagnetic intensity determinations are mainly limited to displaced ceramics produced in kilns. In this study, the suitability of an in situ baked structure is investigated. Different magnetic properties of baked material taken from the combustion chamber wall and floor of a Roman pottery kiln, with variable colouring, are examined in dependence on the distance to the combustion chamber. The temperature distribution is re-constructed based on rock magnetic experiments after stepwise heating. The rock magnetic temperature estimates agree fairly well with a mathematical heat conduction model demonstrating the penetration of heat into the combustion chamber wall. The rock magnetic results show that blackish- and greyish-coloured kiln parts, that had been in close contact with the fuel, during ancient kiln operation, are not suitable for intensity determinations. Although sufficiently baked, they strongly alter during laboratory heating and new remanence-carrying minerals are formed. The brownish-coloured material at a distance 65–80 mm away from the combustion chamber seems to be most suitable as its magnetic properties remain nearly unchanged during laboratory heating. Rock magnetic and modelled temperature estimates for this material consistently indicate ancient baking temperatures of about 600°C. The model demonstrates that cooling takes longer in the inner parts of the combustion chamber wall. Retarded cooling affects the blocking temperatures and hence the strength of the thermoremanent magnetization. The variability of cooling rates should be taken into account when investigating archaeointensities of specimens cut from large samples, or of samples taken from different parts of a kiln.

Geophysical Journal International, 2004

A new method is presented for fast quantification of urban pollution sources in atmospheric parti... more A new method is presented for fast quantification of urban pollution sources in atmospheric particulate matter (PM). The remanent magnetization of PM samples collected in Switzerland at sites with different exposures to pollution sources is analysed. The coercivity distribution of each sample is calculated from detailed demagnetization curves of anhysteretic remanent magnetization (ARM) and is modelled using a linear combination of appropriate functions which represent the contribution of different sources of magnetic minerals to the total magnetization. Two magnetic components, C1 and C2, are identified in all samples. The low-coercivity component C1 predominates in less polluted sites, whereas the concentration of the higher-coercivity component C2 is large in urban areas. The same sites were monitored independently by Hüglin using detailed chemical analysis and a quantitative source attribution of the PM. His results are compared with the magnetic component analysis. The absolute and relative magnetic contributions of component C2 correlate very well with absolute and relative mass contributions of exhaust emissions, respectively. Traffic is the most important PM pollution source in Switzerland: it includes exhaust emissions and abrasion products released by vehicle brakes. Component C2 and traffic-related PM sources correlate well, which is encouraging for the implementation of non-destructive magnetic methods as an economic alternative to chemical analysis when mapping urban dust pollution.

Physics of The Earth and Planetary Interiors, 2003

A detailed rock magnetic investigation of loess/palaeosol samples from the section at Lingtai on ... more A detailed rock magnetic investigation of loess/palaeosol samples from the section at Lingtai on the central Chinese Loess Plateau (CLP) is presented. Thermal demagnetisation of isothermal remanent magnetisation (IRM) and Curie temperature measurements suggest the presence of magnetite, maghemite and hematite as remanence carrying components. Bulk and grain size fractionated samples have been analysed using coercivity spectra of remanence acquisition/demagnetisation curves, which identify four main remanence carriers in different grain size fractions of loesses and palaeosols. A linear source mixing model quantifies the contribution of the four components which have been experimentally derived as dominating endmembers in specific grain size fractions. Up to two thirds of the total IRM of the palaeosols are due to slightly oxidised pedogenic magnetite. Two detrital components dominate up to 90% of the IRM of the loess samples and are ascribed to maghemite of different oxidation degree. Detrital hematite is present in all samples and contributes up to 10% of the IRM. The iron content of the grain size fractions gives evidence that iron in pedogenically grown remanence carriers does not originate from the detrital iron oxides, but rather from iron-bearing clays and mafic silicates. The contribution of pedogenic magnetite to the bulk IRM increases with the increasing degree of pedogenesis, which depends in turn on climate change.

Physics and Chemistry of The Earth Part A-solid Earth and Geodesy, 2001

Two sections on the Chinese Loess Plateau (CLP) at Lingtai and Baoji have been investigated to ob... more Two sections on the Chinese Loess Plateau (CLP) at Lingtai and Baoji have been investigated to obtain detailed information about the exact stratigraphic position and the recording quality of the Matuyama/Brunhes geomagnetic polarity boundary (MBB). The continuously sampled MBB occurs in the glacial period loess layer L8 in both sections at a similar profile depth indicating comparable average sedimentation rates of about 8 cm/kyr. This stratigraphic position has been recognized in many previous Chinese loess studies and contrasts with observations in marine sediments where this polarity transition is found at the beginning of interglacial oxygen isotope stage 19. The directional patterns of the characteristic remanent magnetization (ChRM) of the two transitional loess records are inconsistent and even depend on the demagnetization technique used to isolate the ChRM. The MBB records also differ significantly from those obtained from the loess section at Weinan and at ODP site 792A near Japan. The VGP paths recorded in loess are not well defined, switch polarity several times and do not prefer specific longitudinal bands. It is suggested that the loess MBB transitional records do not reflect geomagnetic field variations directly, but are the result of a complicated magnetization lock-in mechanism. By comparison with the astronomically-tuned prediction, this process has been delayed in the loess sediment column by 1.5 to 2 m corresponding to about 25'000 yr after deposition.

Geophysical Journal International, 2003

In most marine sedimentary records, the Matuyama-Brunhes boundary (MBB) has been found in intergl... more In most marine sedimentary records, the Matuyama-Brunhes boundary (MBB) has been found in interglacial oxygen isotope stage 19. In the magnetostratigraphic records of most Chinese loess/palaeosol profiles the MBB is located in loess layer L8, which was deposited during a glacial period. The MBB at Lingtai (central Chinese Loess Plateau) also occurs in L8 and is characterized by multiple polarity flips. The natural remanent magnetization is mainly carried by two coexisting components. The higher coercivity (harder) component dominates in loess layers and is thought to be of detrital origin. The lower coercivity (softer) component prevails in palaeosols and was most probably formed in situ by (bio-)chemical processes. A lock-in model for the Lingtai MBB record has been developed by extending the lithologically controlled PDRM model of Bleil & von Dobeneck (1999). It assumes two lock-in zones. The NRM of the magnetically harder component is physically locked by consolidation shortly after loess deposition, whereas the softer component is formed at greater depth by pedogenesis and acquires a chemical remanent magnetization of younger age. At polarity boundaries, grains carrying reversed and normal directions may therefore occur together within a single horizon. The model uses ARM coercivity spectra to estimate the relative contributions of the two components. It is able to explain the observed rapid multiple polarity flips and low magnetization intensities as well as the stratigraphic shift of the Lingtai MBB with respect to the marine records.

We present a detailed investigation of the geomagnetic polarity transition that terminated the Ol... more We present a detailed investigation of the geomagnetic polarity transition that terminated the Olduvai subchron as recorded by loess/paleosol sediments at Lingtai in the central Chinese Loess Plateau (CLP). The polarity transition occurs within loess layer L25, where mineral magnetic parameters show considerable variations and sedimentation rate changes occur. The magnetic record obtained after thermal cleaning exhibits more than twenty

Geochemistry Geophysics Geosystems, 2010

low Curie temperature phase with a narrow grain size distribution. The results were characterized... more low Curie temperature phase with a narrow grain size distribution. The results were characterized by low dispersion and were found in good agreement with the historical field.

Physics and Chemistry of The Earth, 2008

Three pottery kilns from a large Hellenistic ceramic workshop at Katerini (Macedonia, Northern Gr... more Three pottery kilns from a large Hellenistic ceramic workshop at Katerini (Macedonia, Northern Greece) were studied archaeomagnetically. Palaeomagnetic investigation revealed a stable remanent magnetisation, well grouped with a mean direction of Dsite = 349.3, Isite = 57.6 (k = 1913.0; α95 = 2.8). A few samples exhibited anomalous results, this behaviour being related to sample locations in the archaeological feature, where the heating was probably not homogeneous. Archaeointensity determinations gave an averaged weighted result of Fsite = 85.8 ± 7.8 μT. Rock magnetic analyses proved the suitability of the sampled materials for archaeomagnetic studies and revealed the presence of (metal substituted) magnetite as the main remanence carrier. Anisotropy of magnetic susceptibility and, mainly, of the remanence magnetisation showed a comparatively high degree of anisotropy.Archaeomagnetic dating was performed using the three (inclination, declination and intensity) secular variation curves for Bulgaria, by applying a recently developed hierarchical Bayesian approach. The proposed age span corresponding to the most probable last usage of the kilns is from 505 BC to 287 BC, in good agreement with the archaeological estimation.

The reconstruction of paleosurfaces represents a unique tool to access the evolution of ancient c... more The reconstruction of paleosurfaces represents a unique tool to access the evolution of ancient continents. Paleosurfaces contribute to the study of global changes through paleoweathering features/profiles and record uplift and subsidence of the ancient continents driven by crustal geodynamics and plate tectonics. However, age constraints for basement paleosurfaces are often difficult to obtain since the geological record of ancient land surfaces is usually limited, fragmented by unconformities and scrambled by successive superimposed evolutions, leaving a patchwork of relict landforms and weathering products, discontinuous over time and space. The crystalline basement of European Paleozoic massifs, consisting of igneous and metamorphic rocks, often show Permo-Triassic overprints resulting in underestimated age determinations. These remagnetisations are ubiquitous [e.g. Edel & Schneider, 1995], affecting many emerged Paleozoic rocks in Europe. The rejuvenated age estimations are attributed to an alteration of the primary paleomagnetic signal and carried by secondary hematite [Ricordel et al., 2007; Preeden et al., 2009; Preeden, 2009]. Moreover, published paleomagnetic ages [Ricordel et al., 2007] showed a strong relationship between the remagnetization and the development of pinkish-red crystalline facies associated to the albitized underlying rocks of the Morvan Massif (France). Parcerisa et al. [2009] performed further field and petrographic analyses and proposed that the albitization was linked to the precipitation of secondary haematite. Since hematite forms under oxidising conditions one may deduce that the remagnetization occurring in the Paleozoic crystalline rocks formed during the exposure of these rocks at the Permo-Triassic (paleo)surface. The extent of the altered zone (~200 m in depth) points to a sodium enriched groundwater environment [Thiry et al., 2009]. Demonstrating that the albitized facies are of supergenic origin and bound to the Triassic paleosurface deeply renews the ideas about the evolution of basement areas. The recognition of the Triassic paleosurface on widespread basements in Europe will provide spatio-temporal benchmarks to constrain the ablation of these massifs since the Triassic. This will be a major contribution to the geodynamic modelling of continental evolution of Europe. To deepen our understanding of this paleoalteration phenomenon on a supra-regional scale and to obtain a reasonable distribution of paleomagnetic age determinations, we aim to acquire more tie points for this Permo-Triassic surface, which was preserved in the crystalline basement of Europe throughout the Mesozoic and Cenozoic epochs. We will present results from paleomagnetic investigations as well as magneto-mineralogic analyses of the profiles through albitized granite and porphyry from the Sudetes in SW-Poland and the Catalonian Mountains in NE-Spain, for which preliminary age estimations have been carried out. Further European Paleozoic sample sites are in process. Depending on the depth situation of the sampled facies compared to the weathering profile, the Triassic paleomagnetic ages show dispersion towards rather older ages at the top and younger ages at the bottom of the sequence. This seems to correlate with the results from magneto-mineralogical analyses which show a decreasing hematite concentration with depth. The oldest ages are carried by a single component, identified as single-domain secondary hematite inclusions in the secondary albite crystals. With increasing depth the samples are rather characterized by a two-component signal, still showing (younger) Triassic ages for both components. These were identified as secondary hematite and maghemite. The latter is most probably a product of either low-temperature magnetite oxidation or precipitates during the albitization of the primary rock. These processes are both linked to less oxidising conditions than at the top of the weathering profile. A systematic interpretation of the paleomagnetic ages and the identification of the magnetic carrier assemblage for all European sites will provide valuable insights into (a) the geodynamic evolution of the crystalline complexes, by estimation of erosion/stability rates and (b) an advanced mineralogical understanding of the specific conditions linked to this Triassic paleoweathering event. Edel & Schneider, 1995, Geophys. J. Int., 122, 858-876; Edel et al., 1997, C.R.AS. Paris, Earth Planet. Sci., 325, 479-486. Parcerisa D., Thiry M., Schmitt J.-M., 2009, Albitisation related to the Triassic unconformity in igneous rocks of the Morvan Massif (France)? Int. J. Earth Sci., doi: 10.1007/s00531-008-0405-1. Preeden, U., 2009, Remagnetization in sedimentary rocks of Estonian and shear and fault zone rocks of southern Finland, disertationes geologicae Universatis Tartuensis, Ph.D. thesis, Estonia, 26, 121, ISSN 1406-2658. Preeden U., Mertanen S., Elminen T., Plado J., 2009, Secondary magnetizations in shear and fault zones in southern Finland, Tectonophysics, 49/3-4, 203-213, doi.org/10.1016/j.tecto.2009.08.011. Ricordel C., Parcerisa D., Thiry M., Moreau M.-G., Gomez-Gras D., 2007, Triassic magnetic overprints related to albitization in granites from the Morvan massif (France), Palaeogeogr. Palaeoclimatol. Palaeoecol., 251:268-282. Thiry et al., Parcerisa, D., Ricordel-Prognon, C., Schmitt, J-M., 2009, Sodium storage in deep paleoweathering profiles beneath the Paleozoic-Triassic unconformity, EGU General Assembly 2009, Vienna, Austria.

Palaeogeography Palaeoclimatology Palaeoecology, 2008

A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possessi... more A 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possession (Iles Crozet), has been investigated, based on a multi-proxy approach. The methods applied are macrobotanical (mosses, seeds and fruits) and diatom analyses, complemented by geochemical (Rock-Eval6) and rock magnetic measurements. The chronology of the core is based on 5 radiocarbon dates.

Quaternary Science Reviews, 2009

Botanical macrofossil analysis of a more than 9000 years old, radiocarbon dated peat sequence of ... more Botanical macrofossil analysis of a more than 9000 years old, radiocarbon dated peat sequence of a moss peat bank from South Georgia, shows a clear evolution in the vegetation. Seven ecological phases could be distinguished and they can be interpreted in terms of climate development during the Holocene. Until 2200 years ago, Warnstorfia fontinaliopsis was the dominant moss species pointing to a wet environment. Lower numbers of this species in association with the presence of drier species are assumed to indicate drier periods, such as occurring between ca 6000–5200 and 4400–3400 cal yr BP. The most prominent and definitive vegetation change took place around 2200 cal yr BP. A Polytrichum–Chorisodontium moss peat bank was formed, which is still growing there today. The forcing mechanism for this vegetation change is thought to be a temperature decrease, rather than a precipitation decrease. This conclusion is mainly based on the fact that, today, moss peat banks have their optimal occurrence range in the maritime Antarctic, a region were the mean annual temperature is ca 4 °C lower than on South Georgia. The remarkable change in the moss bank vegetation at 2200 cal yr BP raises the question whether this moment was only a short climatic deterioration, or a definitive change to a cooler and wetter climate after a Holocene climatic optimum period.

Physics and Chemistry of The Earth, 2008

Archaeological burnt materials and structures provide unique records of direction and intensity o... more Archaeological burnt materials and structures provide unique records of direction and intensity of the Earth’s magnetic field in the past, elements that can be absolutely determined applying the archaeomagnetic method. At present, such records within Europe are irregular in both space and time. Presented here is the archaeomagnetic investigation of three kilns that were discovered during a preventive excavation of an archaeological site considered of High Middle Age in Corroy-le-Grand (Belgium) and that are assumed to be related to iron working activities. Archaeological context dating points to kiln operation between the second half of the 10th century until the 12th century AD. As the site is not far from Paris, declination and inclination of the characteristic remanent magnetisation of the kilns were compared with the standard directional secular variation curve for France in order to propose archaeomagnetic dates for the cessation of kiln operation by using probability densities [Lanos, Ph., 2004. Bayesian inference of calibration curves, application to archaeomagnetism. In: Buck, C.E., Millard, A.R. (Eds.), Tools for Constructing Chronologies: Crossing Disciplinary Boundaries. Lecture Notes in Statistics. Springer Verlag, London, pp. 43–82; Lanos, Ph., Le Goff, M., Kovacheva, M., Schnepp, E., 2005. Hierarchical modelling of archaeomagnetic data and curve estimation by moving average technique. Geophysical Journal International 160 (2), 440–476]. This confirms the presumed archaeological age and resulted in more precise time constraints for the last kiln operation. Rock magnetic techniques, proposed by Spassov and Hus [Spassov, S., Hus, J., 2006. Estimating baking temperatures in a Roman pottery kiln by rock magnetic properties: implications of thermochemical alteration for archaeointensity determinations. Geophysical Journal International 167, 592–604], were applied to examine the suitability of the burnt materials from the kilns for archaeointensity determinations and to increase the success rate of the Thellier–Thellier double heating technique. An average value for the field intensity of 69.4 ± 2.5 μT was estimated from 10 specimens from a single kiln, which corresponds reasonably well with published data for Western Europe.

Physics and Chemistry of The Earth Part A-solid Earth and Geodesy, 2001

A refined pedostratigraphic scheme in the western Black sea region is proposed on the basis of pa... more A refined pedostratigraphic scheme in the western Black sea region is proposed on the basis of paleopedological reconstructions coupled with magnetic susceptibility, and other rock magnetic parameters, and Mössbauer spectroscopy. The new scheme matches well with oxygen isotope stages despite local variations in erosion/deposition, strong welding of paleosols and subtle discrepancies in the position of the Matuyama/Brunhes boundary. These limitations are reduced by optimizing resolution of magnetic cycles and paleosol identification. Two humid/warm maxima during the Quaternary are found in pedocomplex PK4 at about 0.5 Ma (corresponding to oxygen isotope stages 13 and 15), and in pedocomplex PK8 related to the Jaramillo subchron. Comparison with the oxygen isotope curve shows that the apparent major driving force of regional soil/loess cyclicity is the 100 ka eccentricity period.

Quaternary International, 2006

Loess/paleosol sequences in the western Black sea area at Roxolany (48 m thick) and Novaya Etuliy... more Loess/paleosol sequences in the western Black sea area at Roxolany (48 m thick) and Novaya Etuliya (30 m thick) were studied using paleo- and rock-magnetic methods in conjunction with micromorphology and Mössbauer investigations. Although seemingly complete, the sites show variability in the type and number of loess/paleosol cycles, and inconsistency of the Matuyama/Brunhes boundary (MBB) stratigraphic position. At Roxolany, nine pedocomplexes (PK) and several incipient paleosols, alternating with thick loesses, were observed with the MBB being located between PK6 and PK7. At Novaya Etuliya, 13 PKs occur upon terrace XII with Khapry fauna and with the MBB in the upper part of PK7 and the Jaramillo subchron within the lower part of PK8. The depth functions of rock magnetic properties, organic carbon content Corg, both for bulk samples and for clay extracts, along with micromorphology and Mössbauer spectra, allowed objective identification of individual soils within PKs, and maximizing the resolution of paleopedological reconstructions of global climatic stages. The Mössbauer studies demonstrate that paleosols are basically enriched in ferric montmorillonite. Oxidized magnetite, ultrafine iron hydroxides and hematite are intimately associated with clay minerals. In contrast, Fe-compounds in loess consist mainly of ferrous silicates. These data indicate that the paleosol magnetism is basically of bio-chemogenic origin and is related to pedogenic transformation of Fe-compounds in a changing environment, while loess magnetism is primarily detrital. Pedogenic magnetically “soft” and partly oxidized magnetite may also originate during or even after burial. This ensuing transformation of Fe minerals in paleosols seems to be crucial for the understanding of the timing of natural remanent magnetization (NRM) in subaerial sediments. Given that paleosols formed on the similar parent material (loess), their typological variability seems to depend on climate and/or chronology. Hence, the different paleosol types from Roxolany and Novaya Etuliya provide key information for intra- and inter-regional correlation of loess/soil sequences, and represent valid paleoclimatic proxies.

Geophysical Journal International, 2006

Absolute past geomagnetic field intensity determinations requiring laboratory heating are labouri... more Absolute past geomagnetic field intensity determinations requiring laboratory heating are labourious and the success rate is rather low, mostly because of induced thermochemical magnetic mineral alterations. Archaeomagnetic intensity determinations are mainly limited to displaced ceramics produced in kilns. In this study, the suitability of an in situ baked structure is investigated. Different magnetic properties of baked material taken from the combustion chamber wall and floor of a Roman pottery kiln, with variable colouring, are examined in dependence on the distance to the combustion chamber. The temperature distribution is re-constructed based on rock magnetic experiments after stepwise heating. The rock magnetic temperature estimates agree fairly well with a mathematical heat conduction model demonstrating the penetration of heat into the combustion chamber wall. The rock magnetic results show that blackish- and greyish-coloured kiln parts, that had been in close contact with the fuel, during ancient kiln operation, are not suitable for intensity determinations. Although sufficiently baked, they strongly alter during laboratory heating and new remanence-carrying minerals are formed. The brownish-coloured material at a distance 65–80 mm away from the combustion chamber seems to be most suitable as its magnetic properties remain nearly unchanged during laboratory heating. Rock magnetic and modelled temperature estimates for this material consistently indicate ancient baking temperatures of about 600°C. The model demonstrates that cooling takes longer in the inner parts of the combustion chamber wall. Retarded cooling affects the blocking temperatures and hence the strength of the thermoremanent magnetization. The variability of cooling rates should be taken into account when investigating archaeointensities of specimens cut from large samples, or of samples taken from different parts of a kiln.

Geophysical Journal International, 2004

A new method is presented for fast quantification of urban pollution sources in atmospheric parti... more A new method is presented for fast quantification of urban pollution sources in atmospheric particulate matter (PM). The remanent magnetization of PM samples collected in Switzerland at sites with different exposures to pollution sources is analysed. The coercivity distribution of each sample is calculated from detailed demagnetization curves of anhysteretic remanent magnetization (ARM) and is modelled using a linear combination of appropriate functions which represent the contribution of different sources of magnetic minerals to the total magnetization. Two magnetic components, C1 and C2, are identified in all samples. The low-coercivity component C1 predominates in less polluted sites, whereas the concentration of the higher-coercivity component C2 is large in urban areas. The same sites were monitored independently by Hüglin using detailed chemical analysis and a quantitative source attribution of the PM. His results are compared with the magnetic component analysis. The absolute and relative magnetic contributions of component C2 correlate very well with absolute and relative mass contributions of exhaust emissions, respectively. Traffic is the most important PM pollution source in Switzerland: it includes exhaust emissions and abrasion products released by vehicle brakes. Component C2 and traffic-related PM sources correlate well, which is encouraging for the implementation of non-destructive magnetic methods as an economic alternative to chemical analysis when mapping urban dust pollution.

Physics of The Earth and Planetary Interiors, 2003

A detailed rock magnetic investigation of loess/palaeosol samples from the section at Lingtai on ... more A detailed rock magnetic investigation of loess/palaeosol samples from the section at Lingtai on the central Chinese Loess Plateau (CLP) is presented. Thermal demagnetisation of isothermal remanent magnetisation (IRM) and Curie temperature measurements suggest the presence of magnetite, maghemite and hematite as remanence carrying components. Bulk and grain size fractionated samples have been analysed using coercivity spectra of remanence acquisition/demagnetisation curves, which identify four main remanence carriers in different grain size fractions of loesses and palaeosols. A linear source mixing model quantifies the contribution of the four components which have been experimentally derived as dominating endmembers in specific grain size fractions. Up to two thirds of the total IRM of the palaeosols are due to slightly oxidised pedogenic magnetite. Two detrital components dominate up to 90% of the IRM of the loess samples and are ascribed to maghemite of different oxidation degree. Detrital hematite is present in all samples and contributes up to 10% of the IRM. The iron content of the grain size fractions gives evidence that iron in pedogenically grown remanence carriers does not originate from the detrital iron oxides, but rather from iron-bearing clays and mafic silicates. The contribution of pedogenic magnetite to the bulk IRM increases with the increasing degree of pedogenesis, which depends in turn on climate change.

Physics and Chemistry of The Earth Part A-solid Earth and Geodesy, 2001

Two sections on the Chinese Loess Plateau (CLP) at Lingtai and Baoji have been investigated to ob... more Two sections on the Chinese Loess Plateau (CLP) at Lingtai and Baoji have been investigated to obtain detailed information about the exact stratigraphic position and the recording quality of the Matuyama/Brunhes geomagnetic polarity boundary (MBB). The continuously sampled MBB occurs in the glacial period loess layer L8 in both sections at a similar profile depth indicating comparable average sedimentation rates of about 8 cm/kyr. This stratigraphic position has been recognized in many previous Chinese loess studies and contrasts with observations in marine sediments where this polarity transition is found at the beginning of interglacial oxygen isotope stage 19. The directional patterns of the characteristic remanent magnetization (ChRM) of the two transitional loess records are inconsistent and even depend on the demagnetization technique used to isolate the ChRM. The MBB records also differ significantly from those obtained from the loess section at Weinan and at ODP site 792A near Japan. The VGP paths recorded in loess are not well defined, switch polarity several times and do not prefer specific longitudinal bands. It is suggested that the loess MBB transitional records do not reflect geomagnetic field variations directly, but are the result of a complicated magnetization lock-in mechanism. By comparison with the astronomically-tuned prediction, this process has been delayed in the loess sediment column by 1.5 to 2 m corresponding to about 25'000 yr after deposition.

Geophysical Journal International, 2003

In most marine sedimentary records, the Matuyama-Brunhes boundary (MBB) has been found in intergl... more In most marine sedimentary records, the Matuyama-Brunhes boundary (MBB) has been found in interglacial oxygen isotope stage 19. In the magnetostratigraphic records of most Chinese loess/palaeosol profiles the MBB is located in loess layer L8, which was deposited during a glacial period. The MBB at Lingtai (central Chinese Loess Plateau) also occurs in L8 and is characterized by multiple polarity flips. The natural remanent magnetization is mainly carried by two coexisting components. The higher coercivity (harder) component dominates in loess layers and is thought to be of detrital origin. The lower coercivity (softer) component prevails in palaeosols and was most probably formed in situ by (bio-)chemical processes. A lock-in model for the Lingtai MBB record has been developed by extending the lithologically controlled PDRM model of Bleil & von Dobeneck (1999). It assumes two lock-in zones. The NRM of the magnetically harder component is physically locked by consolidation shortly after loess deposition, whereas the softer component is formed at greater depth by pedogenesis and acquires a chemical remanent magnetization of younger age. At polarity boundaries, grains carrying reversed and normal directions may therefore occur together within a single horizon. The model uses ARM coercivity spectra to estimate the relative contributions of the two components. It is able to explain the observed rapid multiple polarity flips and low magnetization intensities as well as the stratigraphic shift of the Lingtai MBB with respect to the marine records.