Luminescence and radiocarbon chronologies for the Xindian Culture site of Lamafeng in the Guanting Basin on the NE edge of the Tibetan Plateau

The archaeological Lajia and Lamafeng sites were situated in the Guanting Basin in the northeastern edge of the Tibetan Plateau, and were in the second terrace of the Yellow River. The Lamafeng site is only 1500 m away from Lajia site. The Lajia site belongs to typical Qijia culture (4100–3600 cal a BP). Many human skeletons were found in the Lajia site. These remains presented a state of unnatural deaths. They were all buried in-situ. The Lajia site recorded a prehistoric natural disaster, and the cause of which was probably a combination of earthquake and flooding due to the outburst of a lake that had been dammed by a landslide on the Yellow River. The Lajia site was abandoned by the prehistoric people after the disaster, but follow-up cultural relics were not found. Lamafeng site is a representative of Xindian Culture (3400–2600 cal a BP). The investigation of the Xindian Culture is intensive. However, the chronological data is still very limited, and no luminescence data has been reported so far. In the current study, both optically stimulated luminescence (OSL) (three samples) and accelerator mass spectrometry (AMS) (five charcoal samples) dating are applied to samples from Lamafeng archaeological site. The results showed that: (1) For the sample from the cultural layer, within error margins OSL and ¹⁴C ages are in good agreement. The ¹⁴C ages show that the cultural layer has an age range of ∼2400–2300 cal a BP. (2) The Lamafeng site was inhabited by the people of Xindian Culture, which indicated that the natural disaster occurred in the Qijia culture period did not completely destroy the prehistoric culture in the basin. (3) There was an enhanced extreme flood activity during Qijia and Xindian Culture periods, and the extreme flood period was ended at 2.6 ± 0.2 ka.     

Magnetisation of titanomagnetites from Bulgarian basalts

A number of basalt samples containing titanomagnetites, with varying degrees and modes of oxidation, have been collected from 13 sites in northern Bulgaria, the degree of oxidation being determined from Curie point and lattice parameter determination. The stability of natural remanent magnetization and artificially induced thermoremanences (TRM) has been studied in an attempt to determine whether the oxidized rocks carry a TRM inherited from their original, unoxidized state. From the samples studied, it appears that the intensity and direction of the original TRM's are retained, but that there is some loss in stability.     

ARM,TRM and magnetic interactions: Concentration dependence

ARM (anhysteretic remanence)/SIRM (saturation isothermal remanence) and TRM (thermoremanence)/SIRM were measured as a function of the concentration (volume fraction) of single-domain magnetite (3 × 10^?6 ? C ? 2 × 10^?2), ARM/SIRM increases with decreasing concentration, showing that there is magnetic interaction between fine particles. The role of magnetic interaction in TRM acquisition is also important at higher concentrations of magnetite (C ? 0.1%), where the value of TRM/SIRM increases with decreasing concentration. It is only for concentrations ofC ? 0.1% that the value of TRM/SIRM is fairly constant and interactions among magnetite grains seem to be ignored. The ratio TRM/ARM decreases from seven to almost unity as the concentration of magnetite decreases.     

The Afragola settlement near Vesuvius,Italy: The destruction and abandonment of a Bronze Age village revealed by archaeology,volcanology and rock-magnetism

Public works in progress in the Campanian plain north of Somma-Vesuvius recently encountered the remains of a prehistoric settlement close to the town of Afragola. Rescue excavations brought to light a Bronze Age village partially destroyed and buried by pyroclastic density currents (PDCs) of the Vesuvian Pomici di Avellino eruption (3.8 ¹⁴C ka BP) and subsequently sealed by alluvial deposits. Volcanological and rock-magnetic investigations supplemented the excavations.Careful comparison between volcanological and archaeological stratigraphies led to an understanding of the timing of the damage the buildings suffered when they were struck by a series of PDCs. The first engulfed the village, located some 14 km to the north of the inferred vent, and penetrated into the dwellings without causing major damage. The buildings were able to withstand the weak dynamic pressure of the currents and deviate their path, as shown by the magnetic fabric analyses. Some later collapsed under the load of the deposits piled up by successive currents. Stepwise demagnetization of the thermal remanent magnetization (TRM) carried by potsherds embedded in the deposits yields deposition temperatures in the order of 260–320 °C, fully consistent with those derived from pottery and lithic fragments from other distal and proximal sites. The fairly uniform temperature of the deposits is here ascribed to the lack of pervasive air entrainment into the currents. This, in turn, resulted from the lack of major topographical obstacles along the flat plain.The coupling of structural damage and sedimentological analyses indicates that the currents were not destructive in the Afragola area, but TRM data indicate they were still hot enough to cause death or severe injury to humans and animals. The successful escape of the entire population is apparent from the lack of human remains and from thousands of human footprints on the surface of the deposits left by the first PDCs. People were thus able to walk barefoot across the already emplaced deposits and escape the subsequent PDCs. The rapid cooling of the deposits was probably due to both their thinness and heat dissipation due to condensation of water vapour released in the mixture by magma–water interaction.     

Are ARM and TRM analogs? Thellier analysis of ARM and pseudo-Thellier analysis of TRM

We test the possibility of using the pseudo-Thellier method as a means of determining absolute paleointensity. Thellier analysis of anhysteretic remanent magnetization (ARM) and pseudo-Thellier analysis of thermoremanent magnetization (TRM) have been carried out on a large collection of sized synthetic magnetites and natural rocks. In all samples, the intensity of TRM is larger than that of ARM and the ratio R (=TRM/ARM) is strongly grain size dependent. The best-fit slope (b_TA) from pseudo-Thellier analysis of TRM shows a linear correlation with R. The ratio b_TA/R yielded approximately correct paleointensities, although uncertainties are larger than in typical Thellier-type determinations. For single-domain and multidomain magnetites, alternating field and thermal stabilities of ARM and TRM are fairly similar. However, for ∼0.24 μm magnetite, ARM is both much less intense and less resistant to thermal demagnetization than TRM, reflecting different domain states for the two remanences and resulting in severely non-linear Arai plots for Thellier analysis of ARM.     

Intensity of the geomagnetic field from recent Italian lavas using a new paleointensity method

A new method has been tested on Etna historic lavas for determining the geomagnetic field intensity (F) using the thermoremanent magnetization of volcanic rocks. The procedure involves a number of very short duration heatings above the Curie point, to produce successive laboratory TRM. Thus, it is possible to check the variations in the TRM-acquiring capacity of the samples with the time of heating (t). The curve J = f(t) is then extrapolated towards t = 0, leading to a virtual value of TRM without any laboratory heating, i.e., without the changes that currently occur when the lavas are heated to produce the TRM. Using such virtual values of TRM, satisfactory results of F had been derived from the majority of the samples studied. These results are consistent with Thellier's archeomagnetic data: they show a nearly constant intensity of the geomagnetic field during the last three centuries and, further back into the past, a significant increase of this.     

Influence of partial pressure of oxygen on thermoremanent magnetization of basalts

An electric furnace with oxygen-fugacity control was constructed. Oxygen partial pressure inside the furnace is controlled by flowing H₂ and CO₂ gas mixtures in different ratios. The system is set up inside a three-layer permalloy shield and a solenoid coil to produce an axial magnetic field. Oxygen fugacities are directly measured by an yttriadoped zirconia probe. The difference between the predicted and measured values of fugacities was small at 1,200°C, but a substantial discrepancy was observed at 780°C. Thermoremanent magnetization (TRM) was produced in various gas mixtures by heating the samples of recent basaltic lavas of Oshima (Japan) and Hawaii to 600 or 800°C for 1 h and cooling in a 0.4-Oe field. In general, the TRM is larger when produced in an oxidizing atmosphere and smaller in a reducing atmosphere. Alternating field demagnetization shows that the coercivity is also increased (decreased) when the TRM is acquired in oxidizing (reducing) conditions. However, these properties depend also on the previous heat treatments of the samples.     

Methane Production and Isotopic Fingerprinting in Ethanol Fuel Contaminated Sites

Biodegradation of organic compounds in groundwater can be a significant source of methane in contaminated sites. Methane might accumulate in indoor spaces posing a hazard. The increasing use of ethanol as a gasoline additive is a concern with respect to methane production since it is easily biodegraded and has a high oxygen demand, favoring the development of anaerobic conditions. This study evaluated the use of stable carbon isotopes to distinguish the methane origin between gasoline and ethanol biodegradation, and assessed the occurrence of methane in ethanol fuel contaminated sites. Two microcosm tests were performed under anaerobic conditions: one test using ethanol and the other using toluene as the sole carbon source. The isotopic tool was then applied to seven field sites known to be impacted by ethanol fuels. In the microcosm tests, it was verified that methane from ethanol (δ¹³C = −11.1‰) is more enriched in ¹³C, with δ¹³C values ranging from −20‰ to −30‰, while the methane from toluene (δ¹³C = −28.5‰) had a carbon isotopic signature of −55‰. The field samples had δ¹³C values varying over a wide range (−10‰ to −80‰), and the δ¹³C values allowed the methane source to be clearly identified in five of the seven ethanol/gasoline sites. In the other two sites, methane appears to have been produced from both sources. Both gasoline and ethanol were sources of methane in potentially hazardous concentrations and methane could be produced from organic acids originating from ethanol along the groundwater flow system even after all the ethanol has been completed biodegraded.     

Magnetic properties of the Olivenza meteorite—possible implications for its evolution and an early solar system magnetic field

The magnetic properties of samples of the Olivenza chondrite (LL5) obtained from four collections have been investigated. The natural remanent magnetization (NRM) consists of a very stable primary component, which is randomly scattered in direction on a scale of 1 mm³ or less within the samples, and a secondary magnetization widely varying in intensity, and probably also in direction. The origin of the secondary NRM is not clear, and may be of terrestrial origin. It is concluded that the NRM is carried by the ordered nickel-iron mineral, tetrataenite. The origin of the primary NRM could be a magnetic field associated with the solar nebula, out of which the metal grains condensed and acquired a thermo-remanent magnetization (TRM), or Olivenza could be a fine-grained breccia, the constituent fragments possessing randomly directed magnetization. The implications for the origin and evolution of Olivenza and its parent body if the former magnetizing process has occurred are discussed.     

Luminescence dating of a hearth from the archaeological site of Jiangxigou in the Qinghai Lake area of the northeastern Qinghai-Tibetan Plateau

Archeological research over the past several years has started to provide evidence relevant to understanding both the timing of and processes for human colonization of the high Qinghai-Tibetan Plateau. Much of this research has been in the Qinghai Lake area and the Qaidam Basin in the northeastern Qinghai-Tibetan Plateau. However, chronological data are still limited. Recently, a hearth was discovered in the Jiangxigou site in the south of the Qinghai Lake area, which was likely used by prehistoric hunters. The site is in the mouth of a canyon approximately 4.5 km from Qinghai Lake. Previous ages in this site are based on ¹⁴C dating only. The current study provides additional OSL dates for the hearth. The ages of four OSL samples bracketing the hearth range from 12.9 ± 0.9 to 14.4 ± 1.0 ka, but standard deviations overlap extensively and they likely represent the same age. The OSL ages show that by about 14.3 ± 1.0 ka prehistoric peoples were living in the Qinghai Lake area.     

Thermal history of the nakhlites by the40Ar-39Ar method

This paper reports the results of thermal-release argon analyses of neutron-irradiated samples of the two nakhlite meteorites, Lafayette and Nakhla. The initiation of retention of radiogenic⁴⁰Ar in Lafayette appears to have been a reasonably well-defined event which occurred (1.33 ± 0.03) × 10⁹ yr ago, as determined by the⁴⁰Ar-³⁹Ar method. Nakhla also appears to have been retaining argon no longer than 1.3 × 10⁹ yr, but its gas-retention age cannot be considered well-defined because its apparently most-retentive sites have nominal gas-retention ages shorter than those of the less-retentive sites which contain most of its potassium.     

Palaeomagnetic estimates of emplacement temperatures of pyroclastic deposits on Santorini,Greece

Thermal remanent magnetism provides a method of quantitatively determining the emplacement temperature of individual lithic clasts in a volcaniclastic rock. The technique is reviewed and applied to two types of Quaternary pyroclastic deposit on Santorini. Emplacement-temperature estimates for lithic clasts from two co-ignimbrite lithic breccias (Cape Riva and Middle Pumice eruptions) range from 250°C to 580°C, showing unambiguously that the breccias were emplaced hot. Good precision on temperature estimates (about ±20°C) were obtained from the Cape Riva breccias. Lithics in a Plinian airfall deposit from the Middle Pumice eruption give less precise results because the primary magnetisation has been partly overprinted by chemical (and/or viscous) remanence, and some clasts may have rotated during compaction of the deposit. Temperatures from proximal airfall are consistent with welding of the deposit within 1.5 km from vent. Temperature estimates for lithic clasts further from vent scatter, but a falloff of temperature away from vent can be recognised if an average emplacement temperature for the whole deposit is identified at each location. The study highlights some difficulties in interpreting quantitative temperature estimates for prehistoric pyroclastic deposits.     

A New Method for Determining Compound Specific Carbon Isotope of Chlorinated Solvents in Porewater

A new method for the extraction of chlorinated solvents (CSs) from porewater with dimethylacetamide (DMA) used as a solvent and the determination of δ¹³C by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) with solid-phase microextraction (SPME) are presented. This method was used for the determination of δ¹³C of chloroethenes and chloromethanes. The extraction of the CSs from porewater with DMA led to a minimal loss of mass of solvent and chlorinated compounds. The accuracy of the method was verified with the analysis of the pure injected compounds using elemental analyzer—isotope ratio mass spectrometry (EA-IRMS). It has been effectively applied in a study area in saturated soil samples of a pollutant source zone of perchloroethylene (PCE) and trichloroethylene (TCE). The limit of quantification of the new method was 0.034 μg/g for PCE and TCE for 10–20 g of soil sample. This new method allows for compound-specific isotope analysis of CSs in porewater, which can be beneficial in sites where the identification of contamination sources and the behavior of the contaminants are not clear.     

East Pacific Rise at latitude 21°N: isotopic composition and origin of the hydrothermal sulphur

The sulphur isotope composition of 16 pyrite and chalcopyrite samples from recent sulphide deposits (“Cyana”—project RITA) and active sulphide mineralisation (“Alvin”—project RISE) associated with hydrothermal sources at 380±30°C on the East Pacific Rise at latitude 21°N have been measured. The³⁴S/³²S ratios are relatively uniform and essentially identical for both sites: δ³⁴S=+1.4to3.0%. (CDT), mean +2.1‰. The sulphides were analysed after the majority of the very numerous micro-inclusions of anhydrite had been removed.Two independent physico-chemical analyses of the data demonstrate that about 90% of the sulphur was leached from the basaltic host rocks by the circulating seawater-hydrothermal fluids.     

The behaviour of ulvöspinel samples containing magnetized inclusions

Composite samples containing either magnetized iron or a ferrite magnet embedded in ulvöspinel have been cooled through the ulvöspinel Curie point. The observed changes in magnetic moment which occur are shown to be a result of TRM acquisition in the ulvöspinel rather than an effect of high permeability. Nevertheless by defining an effective permeability of about (1 + TRM/H), magnetostatic theory relevant to magnetized inclusions in a permeable medium can be applied to explain the main features observed in this system.     

Quantification of TCE Co‐Oxidation in Groundwater Using a 14C–Assay

Bacteria that degrade natural organic matter in groundwater contain oxygenase enzymes that can co‐oxidize trichloroethene (TCE). This degradation pathway is promising for large dilute plumes, but its evaluation is limited because the density of the bacteria with oxygenase enzymes has not been correlated to field scale rates of degradation. A ¹⁴C–TCE assay was developed to determine pseudo first‐order rate constants for the aerobic co‐oxidation of TCE in groundwater. The assay involved incubating ¹⁴C–TCE in samples of groundwater contained in 160 mL serum bottles, and monitoring the accumulation of radiolabel in degradation products. A first‐order rate constant for co‐oxidation was extracted from the rate of accumulation of ¹⁴C in products, accounting for volumetric changes in the serum bottles due to sampling and subsequent changes to the distribution of TCE between the aqueous and gaseous phases. Of the groundwater samples evaluated from 19 wells at five sites, eight samples at three sites had ¹⁴C product accumulation rates that exceeded the accumulation rate in filter‐sterilized groundwater controls. First‐order rate constants ranged from 2.65 to 0.0066 year^?1, which is equivalent to half‐lives of 0.26 to 105 years. Groundwater samples from a few of the wells in which co‐oxidation occurred had volatile organic contaminants in addition to TCE; their presence may have induced the oxygenase enzymes that are needed for TCE co‐oxidation. ¹⁴CO₂ represented ~37% to 97% of the ¹⁴C products that accumulated; the balance of the products was soluble and non‐volatile.     

The laboratory simulation of deuteric oxidation of titanomagnetites: effect on magnetic properties and stability of thermoremanence

Synthetic single crystals of titanomagnetite of nominal composition Fe_2.4Ti_0.6O₄ have been oxidized at 1275°C in controlled gas atmospheres, producing multiphase intergrowths to simulate the natural process of deuteric oxidation. The evolution of the intergrowths was monitored using the conventional techniques of petrology: optical and electron microscopy and X-ray and electron microprobe analyses. In addition, the measured magnetic properties — particularly the temperature-dependence of hysteresis properties — provided further information about the composition and concentrations of magnetic phases, and their domain state, as oxidation proceeded. The evolution of a trellis pattern of ilmenite lamellae, characteristic of the “exsolution” stages of deuteric oxidation, was observed in the oxidized crystals. The interlamellar spinel region consisted of two iron-enriched titanomagnetites, one thought to occur along the lamellar boundaries. The magnetic hardness of both phases was found to be greater than the original homogeneous multidomain titanomagnetite crystals, although neither phase achieved monodomain characteristics, and the stability of thermoremanence (TRM) remained quite low (median destructive fields (MDF) of the order of a few thousend A m^?1). The lamellae made little contribution to the total remanence. A sharp rise in magnetic hardness, observed during the post-exsolution stages of oxidation, was due to the presence of fine-grain monodomain magnetite, thought to be distributed within the haemoilmenite matrix, but probably not having been formed by lamellar subdivision. The crystals could now carry an intense and stable TRM with MDFs of many tens of thousands of A m^?1.     

A comparison of ARM and TRM in magnetite

Experiments comparing anhysteretic remanence (ARM) and thermoremanence (TRM) in samples containing natural and synthetic magnetite, whose mean particle sizes range from single domain to multidomain, show that ARM and TRM are very similar (but not identical) in their stabilities with respect to alternating field (AF) demagnetization, temperature cycles in zero field to below magnetite's isotropic temperature near 130°K, and stability with respect to spontaneous decay in zero field. Therefore, for magnetites, ARM can be used to model (with reasonable success) these stability properties of TRM. The field dependence of the acquisition of ARM and TRM shows that the low field susceptibility ratio, χ_ARM/χ_TRM, has a particle size dependence, increasing from 0.1 for certain submicron particles to 2.0 for large multidomain crystals. Even for samples whose remanence is predominantly carried by submicron particles χ_ARM/χ_TRM is highly variable, 0.11 ≤ χ_ARM/χ_TRM ≤ 0.50. Therefore, ARM paleointensity methods which do not take into account the large variability in and the particle size dependence of χ_ARM/χ_TRM are subject to order-of-magnitude uncertainties.     

The A.R.M. correction method of paleointensity determination

A new method has been developed for recovering paleointensities from igneous rocks which requires only a single heating to the Curie temperature, utilizing partial ARM acquisition measurements before and after the heating to carefully separate distortions of the coercivity spectrum, caused by the heating, from viscous components present in the natural remanence. In addition, the changes in the partial ARM curves may be used to correct to some extent for chemical alterations that occur during the heating. As a result, the method allows one to use a number of samples for paleointensities that would normally be rejected by the Thellier-Thellier method, especially those contaminated by strong viscous overprints. The key to this process is the high sensitivity to changes in the TRM and ARM acquisition spectrum (and hence the coercivity spectrum) of partial ARM acquisition curves, which may be obtained at room temperature.Paleointensity results from recent historic Hawaiian lava flows have demonstrated the reliability of the ARM correction method.     

The potential of historic rock avalanches and man-made structures as chlorine-36 production rate calibration sites

Samples from three medieval rock avalanches from the French (Le Claps, Mont Granier) and Austrian Alps (Dobratsch) and a man-made structure, i.e. the Stephansdom in Vienna, have been analysed for in-situ produced ³⁶Cl by accelerator mass spectrometry (AMS). All four sampling sites of independently known exposure duration turned out to be not appropriate as calibration sites for the determination of the ³⁶Cl-production rate from Ca. Indeed, the determination of short exposure ages for dating rock avalanches and man-made structures by ³⁶Cl is hindered dramatically by inheritance, especially for samples characterized by high ^natCl-concentrations. Generally, there are hints that the theoretical calculation of ³⁶Cl-production from epithermal and thermal neutron-capture on ³⁵Cl is highly underestimated in all existing models, thus, asking for particular precaution if working on high-Cl samples for any project. Hence, this work evidences that potential high inheritance, even for samples reasonably shielded before exhumation, has to be considered especially when dealing with recently exposed surfaces such as glacially polished rocks, alluvial terraces, fault scarps etc.