Future Dating Research Articles

Dating Icelandic glacial floods using a new viscous remanent magnetization protocol

Abstract A new protocol using the viscous remanent magnetization (VRM) of boulders to date cataclysmic geological events such as tsunamis, glacial floods, and landslides is presented and its performance is assessed against two jökulhlaups (glacial floods) of known age in Iceland. High-intensity jökulhlaups have the ability to break off large boulders from bedrock and emplace and rotate them. These rocks originally carried a remanent magnetization parallel to the geomagnetic field during their formation. After being rotated by the flood, they acquire a VRM parallel with Earth’s magnetic field. In continuous thermal demagnetization experiments the unblocking temperature of the VRM can be determined, and subsequent rock magnetic VRM acquisition experiments can be used to establish a relationship between the unblocking temperature and the acquisition time, from which the time since the flood can be determined. The protocol was tested on 44 boulders from 2 historical jökulhlaups in Iceland and found to yield good order-of-magnitude estimates: 72 yr (confidence limits 11–360 yr) versus known 155 yr at the Sólheimajökull jökulhlaup and 290 yr (confidence limits 80–2300 yr) versus known 288 yr for the Kotarjökull jökulhlaup. The method can therefore be a valuable tool for future dating of cataclysmic events.

Body mass-corrected molecular rate for bird mitochondrial DNA.

Mitochondrial DNA remains one of the most widely used molecular markers to reconstruct the phylogeny and phylogeography of closely related birds. It has been proposed that bird mitochondrial genomes evolve at a constant rate of ~0.01 substitution per site per million years, that is that they evolve according to a strict molecular clock. This molecular clock is often used in studies of bird mitochondrial phylogeny and molecular dating. However, rates of mitochondrial genome evolution vary among bird species and correlate with life history traits such as body mass and generation time. These correlations could cause systematic biases in molecular dating studies that assume a strict molecular clock. In this study, we overcome this issue by estimating corrected molecular rates for birds. Using complete or nearly complete mitochondrial genomes of 475 species, we show that there are strong relationships between body mass and substitution rates across birds. We use this information to build models that use bird species' body mass to estimate their substitution rates across a wide range of common mitochondrial markers. We demonstrate the use of these corrected molecular rates on two recently published data sets. In one case, we obtained molecular dates that are twice as old as the estimates obtained using the strict molecular clock. We hope that this method to estimate molecular rates will increase the accuracy of future molecular dating studies in birds.

Erosion and Errors: Testing the Use of Repeated LIDAR Analyses and Erosion Modelling for the Assessment and Prediction of Erosion of Archaeological Sites?

Slope soil erosion is one of the main threats to archaeological sites. Several methods were applied to establish the erosion rates at archaeological sites. Digital elevation models (DEMs) from three different dates were used. We compared the elevations from these three models to estimate erosion. We also applied the landscape evolution model LAPSUS with the available DEMs as basis. Spatial processing errors and effects of tillage and harvesting practices explain most of the DEM elevation differences between the recordings. Increased DEM resolution does not result in more precise or reliable erosion. The present technological level of landscape evolution modelling makes it possible to indicate areas most vulnerable to soil displacement by surface runoff erosion and tillage. Future research, using sediment and surface dating techniques such as deposit of radionuclides, heavy metals and OSL dating will provide a more accurate estimation of erosion rates and the subsequent impact on archaeological sites.

A new Eemian record of Antarctic tephra layers retrieved from the Talos Dome ice core (Northern Victoria Land)

Polar ice sheets are remarkable repositories of tephra layers. The Talos Dome ice core (72°49′S, 159°11′E), drilled at the edge of the East Antarctic Plateau, close to Late Quaternary volcanoes, offers considerable potential to extend the current tephra time-stratigraphic framework. A tephrochronological study was undertaken of the ice core sections related to the Last Interglacial and the transition to the subsequent glacial period. Thirteen macroscopically visible layers, interpreted to be related to primary deposition of fallout tephra, have been analysed for quantitative grain size and glass shard geochemistry. The layers, precisely framed within the climate (δ18O) record for the core, span in age from 111.6±1.9 to 123.3±2.2ka. Coarse particle size suggests origin from regional sources. Indeed, the vast majority of the samples display an alkaline affinity and trachytic composition that are both typical geochemical features of rifting Antarctic volcanism. Using subtle differences in the geochemical signatures and the comparison with data from previous studies, a few layers are attributed to known coeval Mt. Melbourne eruptions. Another sample subset is consistent with derivation from The Pleiades and Mt. Rittmann volcanoes. One peculiar trachytic glass population appears to be related to activity of the more distant Marie Byrd Land volcanoes. The newly detected tephras provide stratigraphic markers that could facilitate future synchronisation and dating of palaeoclimatic records. The Talos Dome tephra inventory also contributes significantly to the reconstruction of the Northern Victoria Land explosive volcanism, for which chronostratigraphic data for the Last Interglacial temporal segment are poor.

10Be ages reveal > 12 ka of gravitational movement in a major sackung of the Western Alps (France)

The Rognier sackung, which extends NE–SW for more than 9km, is a major gravitational morpho-structure located in the Western Alps. We used the 10Be cosmic ray exposure dating method on 23 samples to unravel its history and better understand its genetic mechanism. We found that the average slip rate on sackung faults varies from 0.3 to 3.2mmyr−1. Conjugate sackung faults are contemporaneous, in agreement with a model in which the whole mountain ridge is involved in the gravitational deformation (600m thick). Multiple samples on single faults suggest that the development of this sackung started before 12ka and that it is still active. We cannot exclude the possibility that the dissolution of the underlying Triassic evaporites participated in the sagging of Mt. Rognier. However, the age of this sackung and the presence of the Lauzière sackung on the other side of the Arcs valley support glacial erosion and debuttressing following the retreat of the valley glacier as the main causes of these large gravitational structures. The long and permanent activity of the Rognier sackung contrasts with that of the neighbouring Arcs sackung, which we previously dated using the same method and showed that it is a result of flexural toppling. Along with the proximity of the Rognier sackung to the Belledonne border active fault, its long history suggests that earthquake shaking contributed to maintain its activity. Additionally, two ages confirm that in the western Alps, rock glaciers formed mainly during the Younger Dryas. This study allowed the determination of the best sampling strategy for future CRE dating of these types of gravitational structures.

Precambrian mafic magmatism in south Indian granulite terrain

South Indian granulite terrain had witnessed significant part of Precambrian mafic igneous activity in the form of episodic mafic dyke intrusions of the Palaeoproterozoic period. Strike trends of these dykes are not uniform over the region and the dykes are generally fresh, massive, black dolerites except in the Bhavani shear zone bordering the southern fringes of Nilgiri massif. In Agali-Coimbatore area of our study in the western Bhavani shear zone, the dykes appear to be penecontemporaneous with shearing. Isotopic data place age of Agali-Coimbatore dyke intrusions at about 2.1 Ga. The age of these dykes is significant to constrain an early Palaeoproterozoic age for major shearing event in the Bhavani shear zone. Other dyke emplacement ages are placed at about 1.8 Ga and 1.65 Ga based on the Ar/Ar and K-Ar isotopic results of dykes in Dharmapuri and Tiruvannamalai areas. Older ages comparable to those of the Dharwar craton are not known and in this respect future isotopic dating is vital. Geochemically, these dykes are quartz/hypersthene normative subalkalic tholeiites. An attempt is made here to provide insights into the general petrogenetic history of the Precambrian dykes. Compositional trends are explained by the fractional crystallization of ferromagnesian phases and plagioclase control is conspicuous at the advanced stages of fractionation. Geochemical characteristics suggest that the dykes have tapped Fe-rich non-pyrolite mantle sources with LIL and LREE enrichment as in many continental basalts. The data suggest that role of crustal contamination is limited in petrogenesis; crustal signatures are noticed in the more mafic end members formed in early stage of evolution suggesting that contamination was temperature controlled with most primitive high temperature magmas being most vulnerable to the process. Nd-Sr isotopic data, at present restricted to Agali-Coimbatore dykes, suggest that Palaeoproterozoic magmas tapped subcontinental lithosphere that may have stabilized in the Archaean times at about 3 Ga during the major crustal building activity in the shield region. Further work coupled with isotopic and mineral chemistry will improve our knowledge on the petrological evolution of the dyke magmas and mafic magmatism in general.

Late Quaternary stratigraphy and luminescence geochronology of the northeastern Mojave Desert

The chronology of the Holocene and late Pleistocene deposits of the northeastern Mojave Desert have been largely obtained using radiocarbon ages. Our study refines and extends this framework using optically stimulated luminescence (OSL) to date deposits from Valjean Valley, Silurian Lake Playa, Red Pass, and California Valley. Of particular interest are eolian fine silts incorporated in ground-water discharge (GWD) deposits bracketed at 185–140 and 20–50 ka. Alluvial fan deposits proved amenable for OSL by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy. Lacustrine sand in spits and bars also yielded acceptable OSL ages. These OSL ages fill gaps in the geochronology of desert deposits, which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate. This study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the Mojave Desert, sediments from previously undated landforms can be more accurately placed within correct geologic map units.

Absolute chronology and stratigraphy of Lepenski Vir

Absolute chronology and stratigraphy of Lepenski Vir

The first independent chronology for Middle and Late Weichselian sediments from southern Sweden and the Island of Bornholm

Conventional Optically Stimulated Luminescence (OSL) dating using the equivalent dose distributions of 8 mm aliquots have been extended to key stratigraphical sites in southernmost Sweden and the island of Bornholm. The objective has been to bridge the lack of an independent chronology, which might catalyze a new understanding of the ice flow patterns related to the initiation of the Last Glacial Maximum, and the stratigraphical development during the deglaciation sequence. Sediments from proximal environments are usually 10-15 kyr older than expected from regional stratigraphical correlations and radiocarbon dates of mammoth tusks. We propose that OSL signals are inherited from reworked sediments that were sufficiently bleached prior to glacial or glaciofluvial transportation and deposition. Sediments from distal and beach environments seem to indicate proper depositional ages. Thus, the main Weichselian stadial was preceded by almost 20 kyr of ice free conditions, succeeded by an ice advance from south-southeast before northeasterly ice flow predominated. Major inconsistencies still exists for the final deglaciation. Two distinct environmental reconstructions of the uppermost diamict at two separate sites, both superimposed on a periglacial surface, predict either deposition during subaquatic conditions associated with drifting icebergs after 16 kyr or subglacial sedimentation associated with an ice advance in Öresund. It remains unsolved whether the periglacial surface at the two sites can be correlated or if they represent two different stratigraphical levels. In perspective, the introduction of OSL dates in Skåne has identified the periglacial marker horizon or horizons as targets for future intensive dating.

Trans-arctic-ocean tests of fine-silt luminescence sediment dating provide a basis for an additional geochronometer for this region

New geochronometers are needed for sediments of the Arctic Ocean spanning at least the last half million years, largely because oxygen-isotope stratigraphy is relatively ineffective in this ocean, and because other dating techniques require significant assumptions about sedimentation rates. Multi-aliquot luminescence sediment-dating procedures were applied to polymineral, fine-silt samples from 9 core-top and 37 deeper samples from 20 cores representing 19 sites across the Arctic Ocean. Most samples have independent age assignments and other known properties (e.g., % coarse fraction, % carbonate, U-Th isotopes). Thick-source alpha-particle counting indicates that for most regions the contribution of measured unsupported 230Th and 231Pa to calculated dose rates is <ca+5–11%. IR-PSL dating of polymineral fine-silt fractions from core-top and near-core-top samples indicates that three sites (mainly from the western Arctic Ocean) have long-bleach inherited ages of only 3–7 kyr, suggesting potential for accurate PSL and TL dating without an inherited correction when older interglacial samples are selected. Samples from a giant gravity core from the western region (Northwind Ridge) yield acceptable long-bleach TL and IR-PSL ages up to 100 kyr. A sample from the eastern region (near Gakkel Ridge) gives a long-bleach age of ca 60 kyr, agreeing with an independent age assignment. Several samples in the 10–40 kyr 14C range from other sites produce large long-bleach age overestimates, indicating the variable effects of ice-rafting and other depositional and bottom-current-reworking (re-suspension) processes during glacial stages. Short-bleach dating tests provide IR-PSL age estimates for core tops that appear to penetrate the ‘reworking veil’ of inherited ages, and not only suggest a procedure to greatly reduce long-bleach inherited ages but also have implications for the 14C reservoir correction. This study identifies the most promising regions for future luminescence dating, and suggests that for several regions of the Arctic Ocean, interglacial-stage (foram-‘rich’) sediments from ridge tops are preferred for the fine-grain luminescence dating methods.

Alpha-recoil track densities in mica and radiometric age determination

Recoiling daughters of α -decaying U and Th impurities in mica and other minerals produce localised lattice damage: alpha-recoil tracks. The age of a sample can be calculated from the number of tracks per unit volume ( N ART ) . To this end, the mica is etched and the etch pits at the sites of recoil-tracks are counted under the optical microscope. Because the measured track densities increase with etching time, N ART is calculated from the fitted regression line. A number of problems inherent in this approach are overcome by the etch–anneal–etch and the mirror-image methods. The track densities determined with these methods are independent of etching time. Although both methods need improvement, they hold the potential of a precise determination of N ART from a single measurement in future recoil-track dating.

Chronology, Culture, and Climate: A Radiometric Re-evaluation of Late Prehistoric Occupations at Cape Denbigh, Alaska

This paper presents new data about the chronological placement of two archaeological sites at Cape Denbigh, Norton Sound, Alaska and others along the Kobuk River, Alaska. Direct radiometric dates on arrowpoints and harpoon heads indicate that selected type specimens are not always reliable temporal indicators for late prehistoric sequences in northwest Alaska and Arctic Canada. In the future new fieldwork and direct dating of artifacts and associated sediments will be necessary in order to refine culture-history sequences, evaluate the utility of artifact types as chronological indicators, and to examine the relationship between past culture change and environmental change in coastal Alaska.

Plio–Pleistocene diatom biostratigraphy from ODP Leg 177, Atlantic sector of the Southern Ocean

Seven sites were drilled during Ocean Drilling Program Leg 177 in the Atlantic sector of the Southern Ocean (SO) on a transect over the Antarctic Circumpolar Current from the Subantarctic to the Antarctic Zone. At four sites sediments were recovered with a Pliocene/Pleistocene sediment package of up to 580 m allowing the refinement of previous diatom zonation concepts. Samples were analyzed on stratigraphic distribution and abundance of diatom species. A refined diatom biozonation tied to the geomagnetic polarity record is proposed. For the middle and late Pleistocene two zonations applicable to the northern and southern area of the SO were constructed, considering different latitudinal distributions of biostratigraphic diatom marker species. The southern zonation for the Pleistocene relies on the occurrence of species of the genus Rouxia, R. leventerae and R. constricta n. sp. as well as on a revised last occurrence datum (LOD) of Actinocyclus ingens (0.38 Ma, late marine isotope stage (MIS) 11). The use of these new stratigraphic marker species refines the temporal resolution for biostratigraphic age assignment to up to 0.1 Myr. In particular the LOD of R. leventerae as an indicator for the MIS 6/5 boundary (Termination II) will improve future dating of carbonate-free Antarctic sediments. These new data were obtained from sediments of Sites 1093 and 1094 (Antarctic Zone). The northern zonation for the middle and late Pleistocene time interval is based on the Pleistocene abundance pattern of Hemidiscus karstenii which was already proposed by previous investigations (e.g. Gersonde and Bárcena, 1998). One new species ( R. constricta) and two new combinations ( Fragilariopsis clementia, Fragilariopsis reinholdii) are proposed in this study.

Luminescence chronology of loess‐paleosol sequences from Canterbury, South Island, New Zealand

The extensive Quaternary loess‐paleosol deposits of South Island, New Zealand, represent one of the major proxy records of paleoclimatic changes in the Southern Hemisphere. We attempted to produce the first numeric chronology of these subaerial sequences in the Canterbury region by using thermoluminescence and infrared‐stimulated luminescence dating methods. We examined five exposures: a 6 m thick section at Cust, north of Christchurch; two thicker (c. 14 m) sequences on Banks Peninsula (Barrys Bay and Onawe sites); farther south, a c. 12 m sequence in Timaru; and a c. 7 m sequence on the coast at the Normanby site near Timaru. Our results are largely based on single experiments per sample, and therefore provide imprecise ages for several of the older samples. The most satisfactory results are those from the youngest site (Cust), for which three samples were dated. Here, phases of maximum loess deposition are dated at 73 ± 13 ka (basal loess‐paleosol unit L3), 41 ± 5 ka (basal L2), and 27 ± 3 ka (basal LI). At Barrys Bay an age of 70 ± 15 ka was obtained in the basal LI, and at Timaru two separate samples in the base of LI also yielded ages of c. 70 ka, thus correlating the entire Cust loess sequence with the LI loess unit at these two other study sites. Only at Barrys Bay were ages (c. 130–250 ka) in stratigraphic order obtained for older samples (units L2 and deeper). At the other sites, some samples in the sub‐L1 units gave age reversals, and some (including the oldest sample at Barrys Bay) yielded poor precision (e.g., 20%). Units L2 at Timaru and Barrys Bay may correlate to all or part of MIS 6; however, the poor precision and some age reversals in other units at these sites and at Normanby and Onawe preclude any unambiguous correlations between sites or to the MIS time‐scale. Nevertheless, in the absence of any prior numeric ages, these first results serve as a basis for more precise future dating of these units. Although these reconnaissance dating results illustrate some of the problems for luminescence dating of such sequences in South Island, they do provide a beginning for a more accurate correlation of terrestrial and terrestrial‐marine sedimentary sequences in this part of the Southern Hemisphere.

Radiocarbon and thermoluminescence dating of the pottery from the early Neolithic site of Gasya (Russian Far East): initial results

Both the AMS radiocarbon technique and TL dating have been used to study the age of organic-tempered pottery from Gasya, one of the earliest Neolithic sites in the Russian Far East. The results obtained are consistent with the previous set of radiocarbon dates from the site, that were obtained for charcoal, and show that the hypothesis that the earliest pottery from the Amur River basin dates to before 10,000 BP (calendar years) is valid. The organic-tempered pottery from the Russian Far East therefore looks promising for future dating by the AMS radiocarbon and TL methods.

Identifying sedimentation patterns in Lake Baikal using whole core and surface scanning magnetic suceptibility

Forty seven ca. 1 m sediment cores were collected from Lake Baikal during a summer cruise in 1996 and analysed for whole-core susceptibility. Fifteen of these cores were further analysed using a new prototype surface scanning sensor on board the ship R.V. Vereshchagin. The main purpose of this paper is to show that the measurement of Lake Baikal short cores using two susceptibility sensors gives valuable field data and can be used as a tool for identifying undisturbed sediment sequences. Four coring transects were sampled to identify sedimentation patterns reaching from the shelves and sub-basins of the near lake shore and across mainly the northern basin of Lake Baikal (water depth ca. 1500 m). Also in the sub-basins and in the southern basin other groups of cores were taken. One of the main sediment features of interest is that of turbidite sedimentation. Whole core magnetic susceptibility traces are used to identify turbidite ‘fingerprints’ and correlate them between cores along the transects. The results from the two magnetic susceptibility sensors the whole-core sensor and the new prototype surface scanning sensor, both giving volume Kappa values, are compared and are found to be significantly correlated given the difference in resolution. The whole-core sensor gives a smoothed equivalent to a ‘moving average’ curve of magnetic susceptibility while the surface scanner can give fine resolution (ca. 2 mm) results picking out fine peaks with Kappa values of between 150 to 650. The results show that most turbidite sedimentation can be clearly identified; they give a specific magnetic susceptibility ‘fingerprint’ with larger Kappa values (up to 120) at the base of the turbidite corresponding with the settling of coarser sandy sediments and a steady and gradual decline in values to about 15 at the top of the turbidite where the fines settle incorporating the normal diatomaceous sedimentation. The main control on the magnetic susceptibility of the turbidite sediments is the concentration of ferrimagnetic minerals in different particle size fractions. The turbidites can be correlated between many of the cores collected along the transects but it must be noted that these correlations are partly speculative and will be confirmed with future dating, diatom analysis and geochemistry. Other very fine peaks of less than 5 mm in width identified using the surface scanning sensor may indicate concentrations of ferrimagnetic minerals, namely greigite, formed during the reduction phase.

Thermoluminescence (TL) and ESR study of γ-irradiated SO 2 frost for future dating in outer planets

Thermoluminescence (TL) and electron spin resonance (ESR) of SO 2 frost were studied for future TL and ESR dating of materials from the outer planets. The solid SO 2 gamma-ray-irradiated at 77 K shows five TL peaks at about 110, 125, 140, 150 and 180 K. TL curves were simulated to obtain the activation energy E and the frequency factor v 0. The thermal annealing of the ESR spectrum indicates that SO 3 −, O 3 − and S 4 ∗ may be related to TL peaks at 125, 140 and 180 K, respectively.

Future ESR and optical dating of outer planet ICY materials

The possibility of future TL and ESR dating of icy materials in the outer planet world in our solar system is discussed. considering radiation effects by solar wind protons and cosmic rays as well as the long lifetime of radical species at extremely low ambient temperatures. A lightweight portable ESR and a gas combustion heating type TL using a photodetector are described for the in-situ observation, i.e. for the use on a landing craft with a -further suggestion to develop remote TL and OSL using laser beams. Both TL and ESR studies of ice (solid H 2O doped with H 2SO 3 were made to estimate the lifetimes of SO 3 − at the ambient temperature for comets from the Arrhenius plot of lifetimes. Molecular orbital calculation and g-factors of SO 3 − were made with MOPAC software. It is suggested that both ESR and optical dating of icy materials are useful for future dating in planetary science.

Preliminary study for future ESR dating of solid SO 2

Paramagnetic properties of irradiated solid SO 2 have been studied for future ESR dating of icy materials on Io, the satellite of Jupiter. Radical species in solid SO 2 formed by irradiation with γ-rays were measured with ESR at various temperatures to obtain the isothermal decay data, which gave their lifetimes at the ambient temperature on Io by the extrapolation in the Arrhenius plot. ESR parameters and speculative models for observed signals are presented.

A reappraisal of neutron dosimetry and uranium-238 λ f values in fission-track dating

Use of the fission-track age equation necessities evaluation of the neutron fluence and of λ f . The reproducibility of neutron fluence measurement is discussed and the results of a five-year study of irradiations in the Herald Reactor (Aldermaston, England) are presented. The conclusion is reached that absolute neutron dosimetry is exceedingly difficult, creating doubt about those values of λ f derived using an irradiation technique. The common practice of determining a calibration ratio (π/λ f ), where π is the thermal-neutron fluence, by reference to age standards, and then splitting that ratio into its component parts, is criticized and the case is presented for a formalized approach evaluating the unknown age of samples by reference either to age standards included in every irradiation, or to a standard glass calibrated against age standards. Criteria for the selection of mineral age standards are outlined. A recommended procedure is given for future fission-track dating.