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Tim Rolph

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University of Liverpool

The University of Auckland

IOANNIS LIRITZIS

Northwestern Polytechnical University

Mediterranean Archaeology and Archaeometry (MAA)

University of the Aegean

East Tennessee State University

Bulgarian Academy of Sciences

Carolina Meza Rodríguez

Centro INAH Morelos

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Papers by Tim Rolph

Microwave archaeointensities from Peruvian ceramics

Geophysical Journal International, 1996

Accurate determination of the strength of the ancient geomagnetic field is limited by mineralogic... more Accurate determination of the strength of the ancient geomagnetic field is limited by mineralogical alteration that may occur when samples are heated to produce a thermoremanent magnetization (Thellier & Thellier 1959; Shaw 1974). By using direct microwave excitation of the magnetic grains we have been able to form a thermoremanent magnetization without significantly heating the bulk sample, thus avoiding thermal alteration (Walton et al. 1993). Incorporation of this new microwave heating technique with the conventional Thellier palaeointensity method has dramatically reduced the scatter of archaeointensity results from Peruvian ceramics and clearly defined how the field strength has varied in Peru over the past 2000 years. The new microwave technique will therefore enhance the feasibility of archaeointensity dating and provide accurate field strength data for geomagnetic modelling.

A detailed record of normal-reversed-polarity transition obtained from a thick loess sequence at Jiuzhoutai, near Lanzhou, China

Geophysical Journal International, Dec 1, 1996

A record of normal-reversed-polarity transition has been obtained from a 4 m thickness of loess e... more A record of normal-reversed-polarity transition has been obtained from a 4 m thickness of loess exposed at a section near Lanzhou, China. Magnetostratigraphic studies suggest it may represent a reversal bounding the onset of a reversed-polarity zone within the Jaramillo Normal Subchron. The natural remanent magnetization consists of two components: a low-coercivity (I 20 mT), low-unblocking-temperature (I 300 "C) component of viscous origin and a high-coercivity (> 20 mT), high-unblockingtemperature (25G700 "C) component carrying the characteristic remanence. Mineral magnetic analyses confirmed the presence of magnetite, its low-temperature oxidation products and haematite, each contributing to the remanence properties. Grain size and concentration showed limited variations and there was little evidence for the presence of the ultrafine magnetic phase commonly associated with palaeosol formation. Pedogenic processes appeared negligible and their effects unimportant, with detrital processes dominating the mineralogy and most probably the acquisition of the characteristic remanence. The reversal record was characterized by the decay and recovery of the geocentric axial dipole term with large directional swings occurring during periods of reduced relative palaeofield intensity. The virtual geomagnetic poles traced a complex path exhibiting no particular geographical confinement. Relative palaeofield intensity determinations were insensitive to the choice of normalization parameter and showed a distinctive asymmetry. Striking similarities were observed with the Matuyama-Jaramillo reversal record, obtained from the same section (Rolph 1993), and the Steens Mountain reversal record (PrCvot et al. 1985), lending further support for the existence of unusually high post-transitional field intensities

Paleoclimatic significance of magnetic properties on the Red Clay underlying the loess and paleosols in China

Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2003

The Red Clay unit of northern China is a widespread MiocenePliocene (7.22.5 Ma) aeolian deposit... more

Correlation of the magnetic susceptibility stratigraphy of Chinese loess and the marine oxygen isotope record: chronological and palaeoclimatic implications

Earth and Planetary Science Letters, Apr 1, 1995

The thick deposits of wind-blown silt of the Loess Plateau in central China constitute arguably t... more

Geomagnetic field variations as a dating tool: Application to Sicilian lavas

Journal of Archaeological Science, Mar 1, 1987

Over 40 historically dated Mt Etna lava flows have been carefully sampled for the purpose of pala... more Over 40 historically dated Mt Etna lava flows have been carefully sampled for the purpose of palaeomagnetic analysis. The natural remanent magnetization (NRM) of each lava flow contains a record of both the magnitude and direction of the Earth's magnetic field at the time of its eruption. Our analysis has thus enabled us to determine the change of the magnetic field in Sicily through historic times and to construct curves which show this secular variation of the field in both direction and magnitude. In this paper, the curves are used to reconsider the historical dates attributed to a number of Etna lavas, dates which had since been questioned by recent palaeomagnetic and geological studies. In a similar manner, these secular variation curves can be used as a powerful archaeological dating tool by comparison with the NRM of fired artifacts.

Origin of maghaemite in Chinese loess deposits: aeolian or pedogenic?

Physics of the Earth and Planetary Interiors, Apr 1, 1999

Maghaemite and magnetite, common ferrimagnetic minerals in surficial soils, have physical propert... more Maghaemite and magnetite, common ferrimagnetic minerals in surficial soils, have physical properties which are similar except for the thermal instability of the former. Utilising this exception, a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the Ž Luochuan section of the central Chinese Loess Plateau. This investigation has shown that although maghaemite thermally. Ž 2 y1. unstable component occurs in greater amounts in palaeosols M s 0.0187 Am kg " 1.1% than in loess units S Ž 2 y1. M s 0.0156 Am kg " 1.1% , in relative terms its contribution to the ferrimagnetic component of magnetisation is S Ž Ž. . Ž Ž. . higher in the loess units D M % s 32.2 " 2.0 than the soils D M % s 23.5 " 3.7. Such an observation suggests that S S much of the maghaemite component originates in the aeolian source area, with some addition of pedogenic maghaemite occurring in the palaeosols.

Quantitative estimates of palaeoprecipitation at Xifeng, in the Loess Plateau of China

Palaeogeography, Palaeoclimatology, Palaeoecology, Feb 1, 1995

Using lOBe, recent studies (Heller et aI., 1993; Beer et aI., 1993) have tried to reconstruct pal... more Using lOBe, recent studies (Heller et aI., 1993; Beer et aI., 1993) have tried to reconstruct palaeoclimatic records by separating the secondary (pedogenic) and primary (aeolian; detrital) contributions to the magnetic susceptibility of Chinese loess. Here we use a technique, which monitors the temperature dependence of magnetic remanence, to estimate the magnetisation and relative contribution of the superparamagnetic (SP), single-domain (SD) and multidomain (MD) ferrimagnetic components in the Xifeng loess section. On the assumption that the SP ferrimagnetic component is dominantly of pedogenic origin, the magnetisation of this component has also been determined for samples taken from the topmost palaeosol (SO), at six sites over the Loess Plateau, and directly correlated with present day precipitation at these sites. This correlation is then used to estimate quantitatively palaeoprecipitation for the topmost 16 m of the Xifeng section, which covers about the last 140,000 years. The data indicate a considerably reduced precipitation during the glacial, loess-forming periods and a significantly higher level of precipitation than today during the last interglacial period.

The Matuyama-Jaramillo R-N Transition Recorded in a Loess Section near Lanzhou, P. R. China

Journal of geomagnetism and geoelectricity, 1993

A palaeomagnetic and palaeointensity study of the Mauchline lavas, south-west Scotland

Physics of the Earth and Planetary Interiors, Mar 1, 1996

The Mauchline lavas of SW Scotland erupted close to the Carboniferous-Permian boundary and near t... more The Mauchline lavas of SW Scotland erupted close to the Carboniferous-Permian boundary and near the middle of the Permo-Carboniferous Reversed Superchron (PCRS). Rock magnetic studies have identified mixed magnetite-hematite assemblages; both minerals record reversed components of magnetisation. A fold test is not diagnostic but the mean remanence recovered in 23 stable samples at five sites (D/I = 192.5/-26.1 °, a95 = 14.3 °) accords with the regional field at the time of eruption and the pole position (346.8°E, 47.2°S) is coincident with late Carboniferous-Early Permian poles. A palaeointensity study of 15 samples employing the modified Thellier-Thellier method yields nine acceptable estimates of ancient field intensity with a mean value of 13.6 4-4.5/~T from four lava flows. The corresponding virtual dipole moment of 3.3 × 1022 Am 2 is approximately 40% of the present day value. This result supports recent studies from western Europe which suggest that the geomagnetic field strength was low during the PCRS but is in conflict with Russian data which suggest that the field strength was close to, or slightly higher than the present day value.

Permo-Carboniferous (Kiaman) palaeointensity results from the western Bohemian Massif, Germany

Geophysical Journal International, Jul 1, 1997

Thellier palaeointensity analyses were carried out on samples from three quartz porphyry intrusio... more Thellier palaeointensity analyses were carried out on samples from three quartz porphyry intrusions located within the western part of the Bohemian Massif close to the German-Czech Republic border. These intrusives have been dated at 28&275 Ma, which places them in the main part of the Permo-Carboniferous (Kiaman) Reversed Superchron (P-CRS). This age is consistent with the mean characteristic remanence direction calculated at D/Z = 204 "/-1 ", giving a VGP at 36"N, 341"E. Palaeointensity values range from 6.6 pT to 22.1 pT, with a mean value of 12.0+ 1.3 pT, which has a corresponding VDM value of (3.0 i 1.2) x loz2 A m2. This suggests that the geomagnetic field strength recorded by the quartz porphyries is only 37 per cent of the current value, supporting recent studies that report a field strength of between 25 and 40 per cent of the present-day value during the P-CRS.

Matuyama/Brunhes (M/B) Transition Recorded in Chinese Loess

Journal of geomagnetism and geoelectricity, 1993

Here we present a detailed record of the Matuyama/Brunhes (M/B) polarity transition recorded in a... more Here we present a detailed record of the Matuyama/Brunhes (M/B) polarity transition recorded in a loess section at Xifeng (36°N, 108°E), in the central part of the Chinese loess plateau. The transition zone, which occurs in loess unit L8, has a thickness of 3.8 m and was sampled in full. At this point in the section the loess accumulation rate has been estimated at 10 cm/ka, and with the size of sub-sample used provides a potential time resolution of 240 years. Magnetite has been identified as the main magnetic mineral with a small contribution from maghaemite or cation deficient magnetite. The remanence of all samples was investigated using thermal demagnetisation from room temperature up to 650°C. The results indicate a duration of 32,000 years for the decay and recovery of the main dipole intensity, and 20,000 years for the period of maj or directional change. During the transition the field intensity falls to an average of 30% of its value before and after the transition, although there are strong variations about this weak value which accompany a sequence of 4 reversed/normal/reversed fluctuations of the local field vector. These fluctuations immediately preceed the final reversed-normal transition, after which the field intensity recovers to its pre-transition value. Calculated VGP paths of most stages are continuous and confined to preferred longitude bands which include America, the Atlantic Ocean or Africa. Field behaviour during the transition period suggests that non-dipolar terms are dominant while the dipole field is weak, with the dipole decay and recovery associated with the increased influence of low order zonal terms of the geomagnetic field.

Archaeointensity Studies of Peruvian Pottery-from 1200 B.C. to 1800 A.D

Journal of geomagnetism and geoelectricity, 1993

Archaeointensities were determined by the Thellier method from about 60 ceramic samples from Peru... more Archaeointensities were determined by the Thellier method from about 60 ceramic samples from Peru, with ages ranging from 1200 B.C. to 1800 A.D. The stability of NRM was analyzed for each sample using stepwise thermal demagnetisation. Partial TRM (PTRM) checks were used to detect any chemical change due to the laboratory heating. Anisotropy of both magnetic susceptibility and TRM were measured but found to be very small. The mineral magnetic properties of the samples were investigated using several techniques, including Curie temperatures, susceptibility variations from low temperature (about-200°) to room temperature, and hysteresis measurements, and the results were used to estimate magnetic mineralogy and successfully select samples suitable for archaeointensity measurements. Finally a secular variation curve covering the past 3000 years was obtained for Peru.

Pedogenic destruction of ferrimagnetics in Alaskan loess deposits

Soil Research, 2001

The positive correlation between magnetic susceptibility and pedogenic degree or weathering inten... more The positive correlation between magnetic susceptibility and pedogenic degree or weathering intensity, observed in the loess-palaeosol sequences from China and central Europe, has been widely used by Quaternary scientists for palaeoclimatic studies. The in-situ pedogenic enhancement of ferrimagnetic content is normally believed to be the main reason for the increase of susceptibility in soil units. However, this pattern of high magnetic susceptibility in palaeosols, and lower values in loess, is not replicated in some loess deposits. Alaskan and Siberian loess deposits display a completely opposite susceptibility behaviour: high values in loess and low values in palaeosols. This inverse relationship has been explained by the idea that magnetic susceptibility is reflecting the magnitude of an aeolian ferrimagnetic component of consistent mineralogy, the grain size of which is related to average wind velocity. Our magnetic study of Alaskan samples in this paper suggests that there are...

Do ENSO and Coastal Development Enhance Coastal Burial of Terrestrial Carbon?

PLOS ONE, 2015

Carbon cycling on the east coast of Australia has the potential to be strongly affected by El Niñ... more Carbon cycling on the east coast of Australia has the potential to be strongly affected by El Niño-Southern Oscillation (ENSO) intensification and coastal development (industrialization and urbanization). We performed paleoreconstructions of estuarine sediments from a seagrass-dominated estuary on the east coast of Australia (Tuggerah Lake, New South Wales) to test the hypothesis that millennial-scale ENSO intensification and European settlement in Australia have increased the transfer of organic carbon from land into coastal waters. Our data show that carbon accumulation rates within coastal sediments increased significantly during periods of maximum millennial-scale ENSO intensity ("super-ENSO") and coastal development. We suggest that ENSO and coastal development destabilize and liberate terrestrial soil carbon, which, during rainfall events (e.g., La Niña), washes into estuaries and becomes trapped and buried by coastal vegetation (seagrass in this case). Indeed, periods of high carbon burial were generally characterized as having rapid sedimentation rates, higher content of fine-grained sediments, and increased content of wood and charcoal fragments. These results, though preliminary, suggest that coastal development and ENSO intensification-both of which are predicted to increase over the coming century-can enhance capture and burial of terrestrial carbon by coastal ecosystems. These findings have important relevance for current efforts to build an understanding of terrestrial-marine carbon connectivity into global carbon budgets.

Viscous remanent magnetization: a tool for orientation of drill cores

Geological Society, London, Special Publications, 1995

Abstract To interpret the directional physical properties of reservoirs it is necessary to obtain... more Abstract To interpret the directional physical properties of reservoirs it is necessary to obtain orientated specimens of well material. The standard technique in the petroleum industry has been the use of ‘down the hole’ tools, which leave a physical scribe on the core material during the drilling procedure. This method is expensive and is subject to a number of problems which can limit the accuracy of the results. A new orientation technique is presented in which a present day component of magnetization is isolated during the progressive thermal demagnetization of core material. This component is essentially a magnetic compass bearing for the core which can be used to rotate the core reference frame into the geographical system. Unlike the standard palaeomagnetic method it can be used both on undated core and core taken from complex tectonic areas.

The Strength of the Geomagnetic Field at the Cretaceous-Tertiary Boundary: Palaeointensity Results from the Deccan Traps(India)and the Disko Lavas(Greenland)

Journal of geomagnetism and geoelectricity, 1991

High field intensity results from recent and historic lavas

Physics of the Earth and Planetary Interiors, Mar 1, 1992

A total of 45 recent and historic lava flows of Mount Etna, Sicily, were sampled to investigate c... more A total of 45 recent and historic lava flows of Mount Etna, Sicily, were sampled to investigate changes in the strength and orientation of the geomagnetic field in the region. Of the flows sampled, 11 yielded one or more samples which provided anomalously high field intensity results. A rock magnetic study has shown that a high resistance to alternating field demagnetization and group 2 low-temperature susceptibility behaviour are the two factors common to these samples.

Holocene record of Tuggerah Lake estuary development on the Australian east coast: Sedimentary responses to sea-level fluctuations and climate variability

GeoResJ, 2015

We investigated the Holocene palaeo-environmental record of the Tuggerah Lake barrier estuary on ... more We investigated the Holocene palaeo-environmental record of the Tuggerah Lake barrier estuary on the south-east coast of Australia to determine the influence of local, regional and global environmental changes on estuary development. Using multi-proxy approaches, we identified significant down-core variation in sediment cores relating to sea-level rise and regional climate change. Following erosion of the antecedent land surface during the post-glacial marine transgression, sediment began to accumulate at the more seaward location at $8500 years before present, some 1500 years prior to barrier emplacement and $4000 years earlier than at the landward site. The delay in sediment accumulation at the landward site was a consequence of exposure to wave action prior to barrier emplacement, and due to high river flows of the mid-Holocene post-barrier emplacement. As a consequence of the mid-Holocene reduction in river flows, coupled with a moderate decline in sea-level, the lake experienced major changes in conditions at $4000 years before present. The entrance channel connecting the lake with the ocean became periodically constricted, producing cyclic alternation between intervals of fluvial-and marinedominated conditions. Overall, this study provides a detailed, multi-proxy investigation of the physical evolution of Tuggerah Lake with causative environmental processes that have influenced development of the estuary.

A high resolution late Holocene palaeo environmental record from the central Adriatic Sea

Quaternary Science Reviews, 2003

A multi-proxy study of a Holocene sediment core (RF 93-30) from the western flank of the central ... more A multi-proxy study of a Holocene sediment core (RF 93-30) from the western flank of the central Adriatic, in 77 m of water, reveals a sequence of changes in terrestrial vegetation, terrigenous sediment input and benthic fauna, as well as evidence for variations in sea surface temperature spanning most of the last 7000 yr. The chronology of sedimentation is based on several lines of evidence, including AMS 14 C dates of foraminifera extracted from the core, palaeomagnetic secular variation, pollen indicators and dated tephra. The temporal resolution increases towards the surface and, for some of the properties measured, is sub-decadal for the last few centuries. The main changes recorded in vegetation, sedimentation and benthic foraminiferal assemblages appear to be directly related to human activity in the sediment source area, which includes the Po valley and the eastern flanks of the central and northern Appenines. The most striking episodes of deforestation and expanding human impact begin around 3600 BP (Late Bronze Age) and 700 BP (Medieval) and each leads to an acceleration in mass sedimentation and an increase in the proportion of terrigenous material, reflecting the response of surface processes to widespread forest clearance and cultivation. Although human impact appears to be the proximal cause of these changes, climatic effects may also have been important. During these periods, signs of stress are detectable in the benthic foram morphotype assemblages. Between these two periods of increased terrigeneous sedimentation there is smaller peak in sedimentation rate around 2400BP which is not associated with evidence for deforestation, shifts in the balance between terrigenous and authigenic sedimentation, or changes in benthic foraminifera. The mineral magnetic record provides a sensitive indicator of changing sediment sources: during forested periods of reduced terrigenous input it is dominated by authigenic bacterial magnetite, whereas during periods of increased erosion, anti-ferromagetic minerals (haematite and/or goethite) become more important, as well as both paramagnetic minerals and super-paramagnetic magnetite. Analysis of the alkenone, U k 0 37 ; record provides an indication of possible changes in sea surface temperature during the period, but it is premature to place too much reliance on these inferred changes until the indirect effects of past changes in the depth of the halocline and in circulation have been more fully evaluated. The combination of methods used and the results obtained illustrate the potential value of such high resolution near-shore marine sedimentary sequences for recording wide-scale human impact, documenting the effects of this on marine sedimentation and fauna and, potentially, disentangling evidence for human activities from that for past changes in climate.

Seismic stratigraphy of Chinese loess

Quaternary Science Reviews, 1993

ABSTRACT

Microwave archaeointensities from Peruvian ceramics

Geophysical Journal International, 1996

Accurate determination of the strength of the ancient geomagnetic field is limited by mineralogic... more Accurate determination of the strength of the ancient geomagnetic field is limited by mineralogical alteration that may occur when samples are heated to produce a thermoremanent magnetization (Thellier & Thellier 1959; Shaw 1974). By using direct microwave excitation of the magnetic grains we have been able to form a thermoremanent magnetization without significantly heating the bulk sample, thus avoiding thermal alteration (Walton et al. 1993). Incorporation of this new microwave heating technique with the conventional Thellier palaeointensity method has dramatically reduced the scatter of archaeointensity results from Peruvian ceramics and clearly defined how the field strength has varied in Peru over the past 2000 years. The new microwave technique will therefore enhance the feasibility of archaeointensity dating and provide accurate field strength data for geomagnetic modelling.

A detailed record of normal-reversed-polarity transition obtained from a thick loess sequence at Jiuzhoutai, near Lanzhou, China

Geophysical Journal International, Dec 1, 1996

A record of normal-reversed-polarity transition has been obtained from a 4 m thickness of loess e... more A record of normal-reversed-polarity transition has been obtained from a 4 m thickness of loess exposed at a section near Lanzhou, China. Magnetostratigraphic studies suggest it may represent a reversal bounding the onset of a reversed-polarity zone within the Jaramillo Normal Subchron. The natural remanent magnetization consists of two components: a low-coercivity (I 20 mT), low-unblocking-temperature (I 300 "C) component of viscous origin and a high-coercivity (> 20 mT), high-unblockingtemperature (25G700 "C) component carrying the characteristic remanence. Mineral magnetic analyses confirmed the presence of magnetite, its low-temperature oxidation products and haematite, each contributing to the remanence properties. Grain size and concentration showed limited variations and there was little evidence for the presence of the ultrafine magnetic phase commonly associated with palaeosol formation. Pedogenic processes appeared negligible and their effects unimportant, with detrital processes dominating the mineralogy and most probably the acquisition of the characteristic remanence. The reversal record was characterized by the decay and recovery of the geocentric axial dipole term with large directional swings occurring during periods of reduced relative palaeofield intensity. The virtual geomagnetic poles traced a complex path exhibiting no particular geographical confinement. Relative palaeofield intensity determinations were insensitive to the choice of normalization parameter and showed a distinctive asymmetry. Striking similarities were observed with the Matuyama-Jaramillo reversal record, obtained from the same section (Rolph 1993), and the Steens Mountain reversal record (PrCvot et al. 1985), lending further support for the existence of unusually high post-transitional field intensities

Paleoclimatic significance of magnetic properties on the Red Clay underlying the loess and paleosols in China

Palaeogeography, Palaeoclimatology, Palaeoecology, Oct 1, 2003

The Red Clay unit of northern China is a widespread MiocenePliocene (7.22.5 Ma) aeolian deposit... more

Correlation of the magnetic susceptibility stratigraphy of Chinese loess and the marine oxygen isotope record: chronological and palaeoclimatic implications

Earth and Planetary Science Letters, Apr 1, 1995

The thick deposits of wind-blown silt of the Loess Plateau in central China constitute arguably t... more

Geomagnetic field variations as a dating tool: Application to Sicilian lavas

Journal of Archaeological Science, Mar 1, 1987

Over 40 historically dated Mt Etna lava flows have been carefully sampled for the purpose of pala... more Over 40 historically dated Mt Etna lava flows have been carefully sampled for the purpose of palaeomagnetic analysis. The natural remanent magnetization (NRM) of each lava flow contains a record of both the magnitude and direction of the Earth's magnetic field at the time of its eruption. Our analysis has thus enabled us to determine the change of the magnetic field in Sicily through historic times and to construct curves which show this secular variation of the field in both direction and magnitude. In this paper, the curves are used to reconsider the historical dates attributed to a number of Etna lavas, dates which had since been questioned by recent palaeomagnetic and geological studies. In a similar manner, these secular variation curves can be used as a powerful archaeological dating tool by comparison with the NRM of fired artifacts.

Origin of maghaemite in Chinese loess deposits: aeolian or pedogenic?

Physics of the Earth and Planetary Interiors, Apr 1, 1999

Maghaemite and magnetite, common ferrimagnetic minerals in surficial soils, have physical propert... more Maghaemite and magnetite, common ferrimagnetic minerals in surficial soils, have physical properties which are similar except for the thermal instability of the former. Utilising this exception, a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the Ž Luochuan section of the central Chinese Loess Plateau. This investigation has shown that although maghaemite thermally. Ž 2 y1. unstable component occurs in greater amounts in palaeosols M s 0.0187 Am kg " 1.1% than in loess units S Ž 2 y1. M s 0.0156 Am kg " 1.1% , in relative terms its contribution to the ferrimagnetic component of magnetisation is S Ž Ž. . Ž Ž. . higher in the loess units D M % s 32.2 " 2.0 than the soils D M % s 23.5 " 3.7. Such an observation suggests that S S much of the maghaemite component originates in the aeolian source area, with some addition of pedogenic maghaemite occurring in the palaeosols.

Quantitative estimates of palaeoprecipitation at Xifeng, in the Loess Plateau of China

Palaeogeography, Palaeoclimatology, Palaeoecology, Feb 1, 1995

Using lOBe, recent studies (Heller et aI., 1993; Beer et aI., 1993) have tried to reconstruct pal... more Using lOBe, recent studies (Heller et aI., 1993; Beer et aI., 1993) have tried to reconstruct palaeoclimatic records by separating the secondary (pedogenic) and primary (aeolian; detrital) contributions to the magnetic susceptibility of Chinese loess. Here we use a technique, which monitors the temperature dependence of magnetic remanence, to estimate the magnetisation and relative contribution of the superparamagnetic (SP), single-domain (SD) and multidomain (MD) ferrimagnetic components in the Xifeng loess section. On the assumption that the SP ferrimagnetic component is dominantly of pedogenic origin, the magnetisation of this component has also been determined for samples taken from the topmost palaeosol (SO), at six sites over the Loess Plateau, and directly correlated with present day precipitation at these sites. This correlation is then used to estimate quantitatively palaeoprecipitation for the topmost 16 m of the Xifeng section, which covers about the last 140,000 years. The data indicate a considerably reduced precipitation during the glacial, loess-forming periods and a significantly higher level of precipitation than today during the last interglacial period.

The Matuyama-Jaramillo R-N Transition Recorded in a Loess Section near Lanzhou, P. R. China

Journal of geomagnetism and geoelectricity, 1993

A palaeomagnetic and palaeointensity study of the Mauchline lavas, south-west Scotland

Physics of the Earth and Planetary Interiors, Mar 1, 1996

The Mauchline lavas of SW Scotland erupted close to the Carboniferous-Permian boundary and near t... more The Mauchline lavas of SW Scotland erupted close to the Carboniferous-Permian boundary and near the middle of the Permo-Carboniferous Reversed Superchron (PCRS). Rock magnetic studies have identified mixed magnetite-hematite assemblages; both minerals record reversed components of magnetisation. A fold test is not diagnostic but the mean remanence recovered in 23 stable samples at five sites (D/I = 192.5/-26.1 °, a95 = 14.3 °) accords with the regional field at the time of eruption and the pole position (346.8°E, 47.2°S) is coincident with late Carboniferous-Early Permian poles. A palaeointensity study of 15 samples employing the modified Thellier-Thellier method yields nine acceptable estimates of ancient field intensity with a mean value of 13.6 4-4.5/~T from four lava flows. The corresponding virtual dipole moment of 3.3 × 1022 Am 2 is approximately 40% of the present day value. This result supports recent studies from western Europe which suggest that the geomagnetic field strength was low during the PCRS but is in conflict with Russian data which suggest that the field strength was close to, or slightly higher than the present day value.

Permo-Carboniferous (Kiaman) palaeointensity results from the western Bohemian Massif, Germany

Geophysical Journal International, Jul 1, 1997

Thellier palaeointensity analyses were carried out on samples from three quartz porphyry intrusio... more Thellier palaeointensity analyses were carried out on samples from three quartz porphyry intrusions located within the western part of the Bohemian Massif close to the German-Czech Republic border. These intrusives have been dated at 28&275 Ma, which places them in the main part of the Permo-Carboniferous (Kiaman) Reversed Superchron (P-CRS). This age is consistent with the mean characteristic remanence direction calculated at D/Z = 204 "/-1 ", giving a VGP at 36"N, 341"E. Palaeointensity values range from 6.6 pT to 22.1 pT, with a mean value of 12.0+ 1.3 pT, which has a corresponding VDM value of (3.0 i 1.2) x loz2 A m2. This suggests that the geomagnetic field strength recorded by the quartz porphyries is only 37 per cent of the current value, supporting recent studies that report a field strength of between 25 and 40 per cent of the present-day value during the P-CRS.

Matuyama/Brunhes (M/B) Transition Recorded in Chinese Loess

Journal of geomagnetism and geoelectricity, 1993

Here we present a detailed record of the Matuyama/Brunhes (M/B) polarity transition recorded in a... more Here we present a detailed record of the Matuyama/Brunhes (M/B) polarity transition recorded in a loess section at Xifeng (36°N, 108°E), in the central part of the Chinese loess plateau. The transition zone, which occurs in loess unit L8, has a thickness of 3.8 m and was sampled in full. At this point in the section the loess accumulation rate has been estimated at 10 cm/ka, and with the size of sub-sample used provides a potential time resolution of 240 years. Magnetite has been identified as the main magnetic mineral with a small contribution from maghaemite or cation deficient magnetite. The remanence of all samples was investigated using thermal demagnetisation from room temperature up to 650°C. The results indicate a duration of 32,000 years for the decay and recovery of the main dipole intensity, and 20,000 years for the period of maj or directional change. During the transition the field intensity falls to an average of 30% of its value before and after the transition, although there are strong variations about this weak value which accompany a sequence of 4 reversed/normal/reversed fluctuations of the local field vector. These fluctuations immediately preceed the final reversed-normal transition, after which the field intensity recovers to its pre-transition value. Calculated VGP paths of most stages are continuous and confined to preferred longitude bands which include America, the Atlantic Ocean or Africa. Field behaviour during the transition period suggests that non-dipolar terms are dominant while the dipole field is weak, with the dipole decay and recovery associated with the increased influence of low order zonal terms of the geomagnetic field.

Archaeointensity Studies of Peruvian Pottery-from 1200 B.C. to 1800 A.D

Journal of geomagnetism and geoelectricity, 1993

Archaeointensities were determined by the Thellier method from about 60 ceramic samples from Peru... more Archaeointensities were determined by the Thellier method from about 60 ceramic samples from Peru, with ages ranging from 1200 B.C. to 1800 A.D. The stability of NRM was analyzed for each sample using stepwise thermal demagnetisation. Partial TRM (PTRM) checks were used to detect any chemical change due to the laboratory heating. Anisotropy of both magnetic susceptibility and TRM were measured but found to be very small. The mineral magnetic properties of the samples were investigated using several techniques, including Curie temperatures, susceptibility variations from low temperature (about-200°) to room temperature, and hysteresis measurements, and the results were used to estimate magnetic mineralogy and successfully select samples suitable for archaeointensity measurements. Finally a secular variation curve covering the past 3000 years was obtained for Peru.

Pedogenic destruction of ferrimagnetics in Alaskan loess deposits

Soil Research, 2001

The positive correlation between magnetic susceptibility and pedogenic degree or weathering inten... more The positive correlation between magnetic susceptibility and pedogenic degree or weathering intensity, observed in the loess-palaeosol sequences from China and central Europe, has been widely used by Quaternary scientists for palaeoclimatic studies. The in-situ pedogenic enhancement of ferrimagnetic content is normally believed to be the main reason for the increase of susceptibility in soil units. However, this pattern of high magnetic susceptibility in palaeosols, and lower values in loess, is not replicated in some loess deposits. Alaskan and Siberian loess deposits display a completely opposite susceptibility behaviour: high values in loess and low values in palaeosols. This inverse relationship has been explained by the idea that magnetic susceptibility is reflecting the magnitude of an aeolian ferrimagnetic component of consistent mineralogy, the grain size of which is related to average wind velocity. Our magnetic study of Alaskan samples in this paper suggests that there are...

Do ENSO and Coastal Development Enhance Coastal Burial of Terrestrial Carbon?

PLOS ONE, 2015

Carbon cycling on the east coast of Australia has the potential to be strongly affected by El Niñ... more Carbon cycling on the east coast of Australia has the potential to be strongly affected by El Niño-Southern Oscillation (ENSO) intensification and coastal development (industrialization and urbanization). We performed paleoreconstructions of estuarine sediments from a seagrass-dominated estuary on the east coast of Australia (Tuggerah Lake, New South Wales) to test the hypothesis that millennial-scale ENSO intensification and European settlement in Australia have increased the transfer of organic carbon from land into coastal waters. Our data show that carbon accumulation rates within coastal sediments increased significantly during periods of maximum millennial-scale ENSO intensity ("super-ENSO") and coastal development. We suggest that ENSO and coastal development destabilize and liberate terrestrial soil carbon, which, during rainfall events (e.g., La Niña), washes into estuaries and becomes trapped and buried by coastal vegetation (seagrass in this case). Indeed, periods of high carbon burial were generally characterized as having rapid sedimentation rates, higher content of fine-grained sediments, and increased content of wood and charcoal fragments. These results, though preliminary, suggest that coastal development and ENSO intensification-both of which are predicted to increase over the coming century-can enhance capture and burial of terrestrial carbon by coastal ecosystems. These findings have important relevance for current efforts to build an understanding of terrestrial-marine carbon connectivity into global carbon budgets.

Viscous remanent magnetization: a tool for orientation of drill cores

Geological Society, London, Special Publications, 1995

Abstract To interpret the directional physical properties of reservoirs it is necessary to obtain... more Abstract To interpret the directional physical properties of reservoirs it is necessary to obtain orientated specimens of well material. The standard technique in the petroleum industry has been the use of ‘down the hole’ tools, which leave a physical scribe on the core material during the drilling procedure. This method is expensive and is subject to a number of problems which can limit the accuracy of the results. A new orientation technique is presented in which a present day component of magnetization is isolated during the progressive thermal demagnetization of core material. This component is essentially a magnetic compass bearing for the core which can be used to rotate the core reference frame into the geographical system. Unlike the standard palaeomagnetic method it can be used both on undated core and core taken from complex tectonic areas.

The Strength of the Geomagnetic Field at the Cretaceous-Tertiary Boundary: Palaeointensity Results from the Deccan Traps(India)and the Disko Lavas(Greenland)

Journal of geomagnetism and geoelectricity, 1991

High field intensity results from recent and historic lavas

Physics of the Earth and Planetary Interiors, Mar 1, 1992

A total of 45 recent and historic lava flows of Mount Etna, Sicily, were sampled to investigate c... more A total of 45 recent and historic lava flows of Mount Etna, Sicily, were sampled to investigate changes in the strength and orientation of the geomagnetic field in the region. Of the flows sampled, 11 yielded one or more samples which provided anomalously high field intensity results. A rock magnetic study has shown that a high resistance to alternating field demagnetization and group 2 low-temperature susceptibility behaviour are the two factors common to these samples.

Holocene record of Tuggerah Lake estuary development on the Australian east coast: Sedimentary responses to sea-level fluctuations and climate variability

GeoResJ, 2015

We investigated the Holocene palaeo-environmental record of the Tuggerah Lake barrier estuary on ... more We investigated the Holocene palaeo-environmental record of the Tuggerah Lake barrier estuary on the south-east coast of Australia to determine the influence of local, regional and global environmental changes on estuary development. Using multi-proxy approaches, we identified significant down-core variation in sediment cores relating to sea-level rise and regional climate change. Following erosion of the antecedent land surface during the post-glacial marine transgression, sediment began to accumulate at the more seaward location at $8500 years before present, some 1500 years prior to barrier emplacement and $4000 years earlier than at the landward site. The delay in sediment accumulation at the landward site was a consequence of exposure to wave action prior to barrier emplacement, and due to high river flows of the mid-Holocene post-barrier emplacement. As a consequence of the mid-Holocene reduction in river flows, coupled with a moderate decline in sea-level, the lake experienced major changes in conditions at $4000 years before present. The entrance channel connecting the lake with the ocean became periodically constricted, producing cyclic alternation between intervals of fluvial-and marinedominated conditions. Overall, this study provides a detailed, multi-proxy investigation of the physical evolution of Tuggerah Lake with causative environmental processes that have influenced development of the estuary.

A high resolution late Holocene palaeo environmental record from the central Adriatic Sea

Quaternary Science Reviews, 2003

A multi-proxy study of a Holocene sediment core (RF 93-30) from the western flank of the central ... more A multi-proxy study of a Holocene sediment core (RF 93-30) from the western flank of the central Adriatic, in 77 m of water, reveals a sequence of changes in terrestrial vegetation, terrigenous sediment input and benthic fauna, as well as evidence for variations in sea surface temperature spanning most of the last 7000 yr. The chronology of sedimentation is based on several lines of evidence, including AMS 14 C dates of foraminifera extracted from the core, palaeomagnetic secular variation, pollen indicators and dated tephra. The temporal resolution increases towards the surface and, for some of the properties measured, is sub-decadal for the last few centuries. The main changes recorded in vegetation, sedimentation and benthic foraminiferal assemblages appear to be directly related to human activity in the sediment source area, which includes the Po valley and the eastern flanks of the central and northern Appenines. The most striking episodes of deforestation and expanding human impact begin around 3600 BP (Late Bronze Age) and 700 BP (Medieval) and each leads to an acceleration in mass sedimentation and an increase in the proportion of terrigenous material, reflecting the response of surface processes to widespread forest clearance and cultivation. Although human impact appears to be the proximal cause of these changes, climatic effects may also have been important. During these periods, signs of stress are detectable in the benthic foram morphotype assemblages. Between these two periods of increased terrigeneous sedimentation there is smaller peak in sedimentation rate around 2400BP which is not associated with evidence for deforestation, shifts in the balance between terrigenous and authigenic sedimentation, or changes in benthic foraminifera. The mineral magnetic record provides a sensitive indicator of changing sediment sources: during forested periods of reduced terrigenous input it is dominated by authigenic bacterial magnetite, whereas during periods of increased erosion, anti-ferromagetic minerals (haematite and/or goethite) become more important, as well as both paramagnetic minerals and super-paramagnetic magnetite. Analysis of the alkenone, U k 0 37 ; record provides an indication of possible changes in sea surface temperature during the period, but it is premature to place too much reliance on these inferred changes until the indirect effects of past changes in the depth of the halocline and in circulation have been more fully evaluated. The combination of methods used and the results obtained illustrate the potential value of such high resolution near-shore marine sedimentary sequences for recording wide-scale human impact, documenting the effects of this on marine sedimentation and fauna and, potentially, disentangling evidence for human activities from that for past changes in climate.

Seismic stratigraphy of Chinese loess

Quaternary Science Reviews, 1993

ABSTRACT