Kobo 1 and L'Abri aux Vaches (Mali,West Africa): Two case studies for the optical dating of bioturbated sediments

The purpose of the study was to provide further chronological data for the microlithic assemblages in the region of the Dogon Country (Mali). In two sites, Kobo 1 and L'Abri aux Vaches, the absence of any characteristic material could not help in concluding whether the microliths were of Pleistocene or Holocene age. Radiocarbon dating failed because the analysed charcoals appeared to have been introduced following recent bioturbation. These were visible in the archaeological sections and therefore, an attempt at dating with single-grain optically stimulated luminescence was made. After discussing the appropriate way of applying the Finite Mixture Model, we are able to conclude that the sediments containing the microliths from L'Abri aux Vaches were deposited during the beginning and the middle of the Holocene period (13.5 ± 1.0 and 5.9 ± 0.4 ka). For Kobo 1, the analysis reveals extensive bioturbation, precluding the obtaining of any reliable result.     

Luminescence dating of baked earth and sediments from the Qujialing archaeological site,China

The Qujialing site is a representative Neolithic archaeological site in the middle reaches of the Yangtze River, China. Absence of suitable material for radiocarbon dating in this region makes the timing of the similar sites difficult. Here we applied optically stimulated luminescence (OSL–SAR) and thermoluminescence (TL–SAR) techniques to date the archaeological and natural deposits from the Qujialing site with known age, testing the techniques on samples at archaeological sites in this region. The results showed that the luminescence properties of quartz from sediment and baked earth samples are very similar. The quartz OSL ages obtained for a sediment sample and a baked earth sample from the cultural layer are 5.4 ± 0.3 and 5.1 ± 0.3 ka, respectively. The quartz TL age of the baked earth sample is 5.6 ± 0.5 ka. These dates are consistent with the calibrated radiocarbon ages (4.9 ± 0.1 and 5.1 ± 0.1 ka cal BP (±1σ)) of the two charcoal samples from the cultural layer at a nearby locality, and are also in agreement with the age of Qujialing culture period. The results indicate that the OSL dating techniques can be applied to date similar archaeological sites in the middle reaches of the Yangtze River, China.     

Luminescence dating of ephemeral stream deposits around the Palaeolithic site of Ifri n'Ammar (Morocco)

The prehistoric site of Ifri n'Ammar is situated in northeastern Morocco, in the northern prolongation of the Middle Atlas Mountains. It is a key location in unravelling the history of anatomically modern humans (AMH) in northern Africa as it reveals Middle and Late Palaeolithic occupation phases since ∼170 ka. Whilst the archaeological sequence within the rock shelter has been well studied, the timing of landscape dynamics around Ifri n'Ammar is still poorly understood. This study therefore aims to establish a detailed chronology of the Wadi Selloum profile at the apron of the shelter, based on optically stimulated luminescence (OSL) dating of ephemeral stream deposits. Coarse-grain quartz was used for single-grain and multiple-grain dating procedures to investigate the luminescence properties of these deposits and to get more accurate age information concerning the phases of human occupation. Continuous wave OSL (CW-OSL) revealed a dominant fast component for all quartz samples. The dose distribution of the uppermost samples showed overdispersion values >25% and significant positive skewness. We identified partial bleaching as the main source of scatter in the equivalent dose (D_e) distribution. The lowermost sample appeared to be close to signal saturation. The shapes of the dose response curve varied widely between aliquots and coarse quartz grains exhibited therefore very different dose saturation behaviours among aliquots. With fully saturated dose response curves (DRCs), meaningful D₀ values were assumed for D_e estimation.The eight OSL samples yielded stratigraphically consistent ages ranging from 1.3 ± 0.2 ka to 76 ± 5 ka, thus reaching the Middle Palaeolithic period. Moreover, a pottery shard dated to 7.4 ± 0.6 ka (Early Neolithic period) by thermoluminescence (TL), perfectly matched the Holocene OSL samples extracted at the same depth of the profile. In summary, our results point to fluvial aggradation during OIS 5.1, the late glacial period, and the Holocene.     

14C age anomalies in modern land snails shell carbonate from Southern Italy

Radiocarbon dating based on geomorphological, archaeological and biological data is widely used in geomorphological studies to reconstruct sequences of climatic variations and coastal evolution during the Holocene. The coastal area of Southern Italy is characterized by aeolian dune belts shaped during the Holocene that crop out along the present shoreline. Archaeological data and previous radiocarbon results suggest three aeolian morphogenetic phases. The first phase corresponds to the end of the rapid post-glacial transgression (7.0–6.0 ka BP); the second to the aeolian sand deposition during the “Greek–Roman” period (2.5–1.9 ka BP); and the most recent phase occurred in the period from the Middle Ages to the present time. The reconstruction of the sequence of the morphogenetic phases was mainly based on radiocarbon analyses carried out on both terrestrial gastropods and marine bivalves. The reliability of the radiocarbon analyses on terrestrial gastropod shells has been questioned by several Authors and a closer understanding of the carbon uptake mechanism in this kind of organisms is needed.A systematic study was carried out by performing Accelerator Mass Spectrometry (AMS) ¹⁴C dating on the shells of terrestrial gastropods sampled alive in different geomorphological settings along the Adriatic and Ionian coasts of Southern Italy. The results show significant anomalies in the radiocarbon content and in the carbon stable isotopic ratio. This can be due to the ingestion of ¹⁴C-depleted calcium carbonate in the diet of these organisms. We also calculated the carbon fraction from air X_a (between 16% and 48%), plants X_v (between 36% and 73%) and limestone X_c (between 3% and 23%) giving insight to the origin of the age anomalies.     

Holocene moist period recorded by the chronostratigraphy of a lake sedimentary sequence from Lake Tangra Yumco on the south Tibetan Plateau

Palaeolimnological studies together with geomorphological investigations of exposed lacustrine sections on the Tibetan Plateau provided valuable palaeoclimate records. Radiocarbon dating is the most commonly used method for establishing chronologies of lake sediments. However, ¹⁴C dating of such sediments could be problematic due to the lack of organic matter or a reservoir effect, which commonly appears in radiocarbon ages of lacustrine sediments from the Tibetan Plateau. OSL dating is an alternative for dating the lake sediments and also provides the opportunity to independently test radiocarbon chronologies. The current study tries to compare OSL and ¹⁴C dating results in order to evaluate the reservoir effect of ¹⁴C dating, and then based on quartz OSL dating and stratigraphic analysis, to construct the chronostratigraphy of a lacustrine sedimentary sequence (TYC section), an offshore profile from Tangra Yumco lake on the southern Tibetan Plateau. Results suggest that: (1) it is possible to obtain robust OSL age estimates for these lake sediments and the OSL ages of the three samples range from ca. 7.6 ka to ca. 2.3 ka; (2) The discrepancy between the OSL and ¹⁴C ages is ca. 4–5 ka, which possibly results from the age overestimate of ¹⁴C dating due to a reservoir effect in the studied lake; (3) the chronostratigraphy of TYC section and sedimentological environmental analysis show a large lake with a lake level distinctively above the present during ca. 7.6–2.7 ka indicating a wet mid-Holocene in the study area.     

Optical dating of clastic deposits generated by an extreme marine coastal flood: The 1755 tsunami deposits in the Algarve (Portugal)

Identification of past tsunamis is important for risk assessment and management of coastal areas. Obtaining accurate and precise ages of sediments originating from such extreme marine coastal floods is crucial for a reliable estimation of the recurrence interval of these often devastating events. We present here the results of quartz optical dating and ¹⁴C dating of two sites (Boca do Rio and Martinhal) on the Algarve coast (southern Portugal). These sites contain deposits of the great tsunami of November 1, 1755. The sections were described using sedimentological techniques; at both sites tsunami-laid sands and gravels were identified, intercalated between estuarine muds. Quartz luminescence ages from these sedimentary successions were derived using standard SAR-OSL dating using multi-grain sub-samples. A multiple sampling strategy was employed with several samples taken from the AD 1755 tsunami deposit and from the sediments bracketing the tsunami layer. Our SAR-OSL protocol was shown to be appropriate using dose recovery measurements (measured/given dose ratio of 1.004 ± 0.007, n = 165). The several OSL ages from the 1755 tsunamigenic deposits are internally reproducible but yield age overestimates of between 20 and 125% (60–310 years respectively); this is in agreement with values reported in the literature for similar deposits. The age overestimation of the tsunami-laid sands is presumably due to the rapid erosion and deposition of older sediments, with insufficient light exposure for complete bleaching during the tsunami event itself. The absence of significant bleaching during the tsunami is also suggested by the shape of the dose distributions based on sub-samples made up of only about 100 grains. Analysis of the distributions with the minimum-age model seems to yield the expected age for two of the three distributions. It is important to note that age offsets of a few tens of years to a few hundred years rapidly become insignificant when dating older (>1 to few ka) tsunami layers.     

Optical luminescence dating of a loess section containing a critical tephra marker horizon,SW North Island of New Zealand

A new IRSL dataset is presented for the age and setting of a critical Late Glacial Maximum tephra isochron marker. The rhyolitic tephra, known as the Kawakawa Tephra, occurs as a 14 cm thick layer within a 5.9 m thick loess section overlying alluvial gravels in the Rangitikei River valley, SW North Island of New Zealand. Ages range from 21 at the base to 5 ka near the top of the loess and bracket an age of 17.0 ± 2.2 for the tephra. The new IRSL ages are in agreement with published and unpublished luminescence ages from other localities of loess, sand and ash above and below the tephra and of the tephra itself, that indicate an age of ca. 19 ka for the Kawakawa Tephra. This age is considerably younger than the generally accepted ¹⁴C 27.1 ka cal yrs BP age of the Kawakawa Tephra and highlights an unresolved discrepancy between the two dating systems.     

Evaluating Quaternary dating methods: Radiocarbon,U-series,luminescence, and amino acid racemization dates of a late Pleistocene emu egg

A whole emu egg, with infilling sediment believed to be coeval with egg laying and burial, was found in late Pleistocene lunette sediments near Lake Eyre, central Australia. The stratigraphic context and initial amino acid racemization (AAR) results suggested an age between 25 ka and 35 ka, ideal for a multiple cross-dating comparison. The sediment infilling the egg provided material for luminescence dating that minimized problems of association. Age estimations from AAR, ¹⁴C and U series methods were obtained from the eggshell and optically stimulated luminescence (OSL) of the infilling sediment. All methods agreed within their respective dating uncertainties confirming the utility of all four methods. They indicate an age for the emu egg of 31.24 ± 0.34 ka.     

Developments in optically stimulated luminescence age control for geoarchaeological sediments and hearths in western New South Wales,Australia

Research conducted by the Western New South Wales Archaeology Program (WNSWAP) provides the opportunity to assess the reliability of optically stimulated luminescence (OSL) dating of late Pleistocene and Holocene fluvial sediments and burnt stone samples from arid zone geoarchaeological contexts. A large number of radiocarbon age determinations of charcoal preserved in heat retainer hearths provides independent chronological control at these contexts. We describe a rapid OSL methodology for dating burnt hearth stones to complement previously applied radiocarbon methods, which we have tested using 37 samples from hearths with radiocarbon determinations. We propose a geoarchaeological model in which these hearths were constructed by people whose activity took place on an archaeological surface, formed by the earlier deposition of fluvial sediments. Here we demonstrate the veracity of this model by dating sediments lying stratigraphically below the hearths, and use the radiocarbon age control and chronological consistency to assess the accuracy and reliability of both small aliquot and single grain single aliquot regenerative-dose (SAR) OSL dating. While small aliquot age estimates are in most cases in agreement with independent control, the single grain determinations using a finite mixture model (FMM) appear to provide improved chronological resolution. Using single grains, we note some problems in the application of the FMM and in the dating of young samples in the range of 1–100 years. As many samples may have resided close to the surface since deposition, we have developed a mathematical function to describe gamma and cosmic dose rate contributions at burial depths down to 40 cm. These OSL age estimates allow us to reject the model of intensification of human activity as responsible for the observed pattern of archaeological radiocarbon determinations in this part of the Australian arid zone.     

Optical dating and lithic microwaste—Archaeological applications

Lithic microwaste (<1 mm in maximum dimensions) is produced during lithic tools and rock engraving manufacture. For tools or rocks containing quartz, small particles persist as microwaste initially on the ground surface but later at least some particles are incorporated into sedimentary deposits associated with the occupation site. If microwaste is distinguished from naturally occurring sediments, then optical dating of microwaste or its surrounding sediment would provide a mechanism for establishing a terminus-ante-et-post-quem for archaeological deposits. Identification of microwaste is undertaken by comparing the shape of microwaste particles with those from surface sediments, taking particular note of angularity and irregular shapes; and by analysing quartz grain surface morphologies. On the basis of surface features identified on experimental microwaste, particles identified as microwaste are separated from the sedimentary grains. Scanning electron microscopy and light microscopy are used to determine surface differences between pedogenic grains and anthropogenic material from archaeological deposits. Single-grain OSL dating technique is then employed for age determinations for particles identified as microwaste. It has been noted in previous research that microwaste particles may lie within or close to the age boundaries of the surrounding sediments but not necessarily where larger lithic material is found. Microwaste is incorporated into sediment and is not subjected to the same degree of movement as larger lithic waste and stone tools within the deposit. The advantage of dating microwaste directly by OSL is that it removes ambiguity about archaeological association. Archaeological events can be dated directly and correlated with sediment ages from surrounding environments, regardless of post-depositional processes. Sand grains surrounding artefacts are dated, usually leaving open the question of the association of the artefact to the sedimentary level, as the artefact may have been displaced from its original depositional level.     

Optical dating of the upper 22 m of cored sediments from Daihai Lake,northern China

Daihai Lake is one of the largest lakes in the mid-latitude of northern China. Previous environmental change investigations using the sediments from the lake have been mainly focused on the last 13 ka. In 2006, we drilled an 80-m borehole on the southwest coast of the lake. Here we report the results of initial optical dating of the upper 22-m sediments from the core. Most of the samples allow separation of the 4–11 μm fine-grained and 45–63 μm medium-grained quartz, both of which were used for equivalent dose (D_e) determination. Dose recovery test experiments with the single-aliquot regeneration-dose (SAR) protocol indicate that a preheat at 240 °C for 10 s combined with a cut-heat of 240 °C is suitable for these samples. The D_e values show marked discrepancy between the two grain size fractions with the fine-grained quartz yielding up to over 50% higher D_e values than the medium ones for some samples. We consider the OSL ages for the samples from upper ～10 m to be overestimated. The main cause of the overestimation is attributed to the incomplete bleaching of the sediment grains at deposition. The OSL ages for the lower part of the sequence are considered to be reasonable age estimates which provide useful temporal constrains on the deposition of the sediments for the period of 20–40 ka.     

Quartz OSL dating of archaeological sites in Xiao Qaidam Lake of the NE Qinghai–Tibetan Plateau and its implications for palaeoenvironmental changes

In the past decades, archaeologists have found evidences for prehistorical human activity in the Qinghai–Tibetan Plateau (QTP). In 1982, some Paleolithic stone tools were found in a section from a terrace of the Xiao Qaidam Lake in the Qaidam Basin, NE of the QTP. The age of this Paleolithic site has remained unknown by far. Some believed that the age of human inhabitation in this Paleolithic site was about 30 ka. In this study, quartz optically stimulated luminescence was used to date 10 samples collected from four sections in the Xiao Qaidam Lake, using the single-aliquot regeneration-dose protocol. The two samples from section XCDH2, which is from a lake terrace about ～7–8 m above the present lake level and in which the top gravel layer contains stone tools, were not well-bleached before deposition. Their ages (>101 and >159 ka) determined by SAR should be considered minimums. OSL dating results of six samples from two sections (XCDH1 and XCDH3) of an adjacent lake terrace, which is ～12 m above the present lake level, suggest two possibilities for the age of the tool-bearing gravel layer: (1) younger than ～3 ka if the lake terrace of XCDH2 is younger than the terrace represented by XCDH1 and XCDH3; or (2) between ～3 and 11 ka if these two terraces are part of the deposit of the same time period. In either case, the age of the archaeological layer should be much younger than the previously proposed ～30 ka. As the climate in the early Holocene after 11 ka was increasingly warm and the Xiao Qaidam Lake area could be suitable for human inhabitation then, we deduce that the age range of ～3–11 ka is more likely the time frame for this archaeological site. The age of 3.1 ± 0.3 ka for the surface of terrace XCDH1/XCDH3 suggests a significant lake level decrease after this time and a corresponding arid event at ～3 ka; the lake level did not reach this level again after that time. Section XCDH4 is more than 40 m above the present lake level, and two samples gave ages of 37 ± 4 and 51 ± 4 ka. These two dates and the dates from the other sections demonstrate that two lake levels higher than present existed for Xiao Qaidam Lake, one at ～12 m and dated ～3–11 ka and the another at >40 m and dated ～37–51 ka.     

High resolution OSL dating back to MIS 5e in the central Sea of Okhotsk

Marine sediments contain important archives of past ocean and climate changes, but at high latitudes the absence of carbonate has prevented the construction of accurate chronological models. We have begun a study to (1) determine the accuracy of luminescence ages in deep-sea marine sediments, e.g. by comparison with marine oxygen isotope stratigraphy where possible, (2) describe changes in sedimentation rate through time, and (3) test whether it is possible to date back to marine isotope stage 5e (MIS 5e). We show here that optical dating of fine grains of quartz from the central Sea of Okhotsk is able to provide an accurate and precise chronology for the reconstruction of the palaeoceanic and palaeoclimatic environment at our site. The upper 6.5 m of the 18.42 m long core MR0604-PC07A is believed, based on its magnetic susceptibility and the oxygen isotope (δ¹⁸O) records to contain the last ～150 ka. Forty OSL samples were taken from this upper part of the core. The single-aliquot regenerative-dose (SAR) procedure is used for equivalent dose (D_e) determination. The luminescence characteristics of fine-grained quartz (4–11 μm) extracted from the core are described. The OSL signal is dominated by the fast component and a dose recovery test shows that we can accurately measure a known dose given in the laboratory prior to any heat treatment. Dose rates were determined using high-resolution gamma spectrometry, and vary between 0.4 and 1.6 Gy/ka. The OSL ages from this section lie between ～140 ka and ～15 ka and are in very good agreement with the δ¹⁸O stratigraphy up to MIS 5e. A clear change in sedimentation rate is identified: between ～139 and 110 ka, the sedimentation rate was ～0.09 m/ka, but then from ～110 to 15 ka, the sedimentation rate decreases to a constant value of ～0.04 m/ka. Our data confirm that OSL dating using widely distributed fine-grain quartz has great potential for dating deep-sea sediments. Because luminescence methods use clastic materials, they do not depend on the presence of biogenic carbonate. As a result it is now likely that we can establish a chronology in regions of the ocean that were previously undatable.     

Comparison of OSL ages from young dune sediments with a high-resolution independent age model

In order to test the accuracy of quartz optically stimulated luminescence (OSL) dating for young dune sediments (<100 a), a series of aerial images of a migrating sand dune is used to cross validate OSL ages. The investigated dune is situated on the northern part of the island of Sylt (southern North Sea). Based on aerial images and a map from 1925 to 2009 and the internal architecture of the dune obtained by ground-penetrating radar (GPR), an independent age model has been developed to attribute sedimentary-architectural elements of the dune to time. The annual rate of dune migration is calculated to be around 4.1 m/a. Along a 245 m transect oriented parallel to the direction of dune movement, 13 samples for OSL dating were collected at equidistant locations. Sand-sized quartz (150–250 μm) was used for determining the equivalent dose (D_e) applying a single-aliquot regenerative-dose (SAR) protocol. Results show that the oldest OSL age from the investigated recent dune appeared to be 110 ± 10 a, whereas the modern analogue was dated to 34 ± 3 a. In comparison with the aerial images, the OSL ages show a systematic overestimation of 10–40 a for six out of seven younger samples, which are expected to be younger than ∼60 a. This offset is negligible for older samples, but a substantial error in these younger ages. The overestimation is originated from a combination of small thermal transfer of 4–12 mGy during preheat and incomplete bleaching in medium OSL component causing a residual dose of about 15 mGy. The contribution of the incompletely bleached medium component cannot be removed totally by an early background subtraction approach. Despite the observed offset for youngest samples, this study corroborates the suitability of the OSL technique to date young dune sediments (<100 a).     

Re-evaluation of the chronology of the palaeolithic site at Jeongokri,Korea, using OSL and TT-OSL signals from quartz

Seven samples were collected from sediments at the Palaeolithic site of Jeongokri, Korea, known for the first discovery of Acheulian-like handaxes in East Asia. Optically stimulated luminescence (OSL) ages obtained from chemically purified quartz from the upper five samples are in stratigraphic order, but the ages of the lower samples are not. The OSL signal of the oldest samples occurs well above the saturation level of the exponential part of the dose response curve; however, the OSL signal has an additional component that grows linearly at high doses, making it possible to calculate a D_e value and thus an age. However the reliability of calculating D_e using this linear component is not clear. In contrast, the thermally transferred OSL (TT-OSL) signal grows linearly with dose up to at least 1600 Gy, thus permitting its use for dating. The TT-OSL ages are in agreement with those from the OSL for the four uppermost samples, but give older ages for the lower three samples. Ages obtained using TT-OSL are in stratigraphic order and indicate that the oldest artefacts have an age of ～195 ka.     

Optically stimulated luminescence dating of fluvioglacial (sandur) sediments from north-eastern Germany

This study presents first results of a project which aims to develop an absolute chronology of the Weichselian ice marginal positions in north-eastern Germany using Optically Stimulated Luminescence (OSL) dating. Owing to the special geomorphological and stratigraphical setting, many of the sampling sites were situated close to the former ice margin. At some sections the sediments showed an incomplete resetting of the OSL signal. For this study the representative sandur sediment section from the Beelitz outwash cone was chosen to elaborate a strategy to reliably detect insufficient bleaching and to choose an appropriate age model for the calculation of the true burial dose of each sample. The age determined for the formation of the Beelitz outwash cone is 34.1 ± 3.0 ka. Although this age might still be a maximum age, this study shows that by applying the proposed methodological strategy, plausible ages can be derived from insufficiently bleached, ice proximal sandur sediments.     

OSL dating of sediments from the Gobi Desert,Southern Mongolia

The present study focuses on the chronological relationship between alternating dune sand and silty water-lain sediments in the central part of the Khongoryn Els dune field in the Gobi Desert, Southern Mongolia. The 23 m high section evolved from the construction of a natural dam by west–east moving sand dunes and fluvial inundation by a river system from the mountain ranges in the south. To resolve the chronology of events, optically stimulated luminescence (OSL) dating was applied and from sedimentological and geochemical analysis the depositional processes could be characterised. Quartz OSL dating of these sediments is hindered by feldspar contamination. Thus, dating of coarse-grain K-feldspars is applied to provide a more reliable chronostratigraphy. As this fraction might be influenced by signal loss over geological time scales, the extent of fading is measured and corrected for. The resulting ages fit well in a supraregional reconstruction of Central Asian palaeoclimate. The data imply that the basal aeolian sediments were deposited 27 ka ago, while the major part of the profile was accumulated in a rather short period of time around ～15 ka. The temporal differentiation implies that the stratification of aeolian and fluvial sediments is not caused by long term climatic variations. It rather represents arid conditions with episodical fluvial activity. Samples between 20 and 15 m depth could not be taken, but it is assumed that this part of the section represents an extremely arid time period with an intensive remobilisation of sand around LGM. A dune overlying the section was deposited during the Late Holocene and represents the ongoing aridity in this region.     

Evidence for glaciation in the Northern Hemisphere back to 44 Ma from ice-rafted debris in the Greenland Sea

The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for glacial onset may be significantly older. We report the presence of ice-rafted debris (IRD) in ～ 44 to 30 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Early Oligocene. Detailed sedimentological evidence indicates that glaciers extended to sea level in the region, allowing icebergs to be produced. IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet.     

Paleomagnetic dating of Phanerozoic kimberlites in Siberia

Diamond bearing kimberlite pipes are exposed across the north-central part of the Siberian platform. Three main time intervals are considered to be the age of emplacement: the Devonian–Early Carboniferous, Triassic, and Cretaceous. However, isotopic age data from of the pipes are scattered and provide a very broad age interval for the magmatic activity. New paleomagnetic poles from four kimberlite pipes (Eastern Udachnaya, Western Udachnaya, International and Obnazhennaya) are obtained to estimate their paleomagnetic age. The mean primary magnetization directions for the pipes are as follows: D = 4.3°, I = − 44.5° (k = 29.4, α₉₅ = 7.4°, N = 14); D = 340.5°, I = − 65.6° (k = 12.9, α₉₅ = 19.4°, N = 6); D = 291.1°, I = − 78.1° (k = 27.5, α₉₅ = 14.9°, N = 5); and D = 306.7°, I = − 82.6° (k = 38.4, α₉₅ = 5.8°, N = 17), respectively. On the basis of a comparison with the Siberian apparent polar wander path (APWP) we estimate the age of kimberlite magmatism, assuming primary magnetizations in these rocks. The paleomagnetic ages are as follows: 428 ± 13 Ma for Eastern Udachnaya; 251 ± 30 Ma for International pipe; and 168 ± 11 Ma for Obnazhennaya pipe. The Western Udachnaya pipe was remagnetized and no clear paleomagnetic age could be determined. The ages of magmatic activity span the Early Silurian to Middle Late Jurassic. Early Silurian magmatism could be associated with the formation of the Viluy rift. Middle to Late Jurassic magmatic activity is most likely related to subduction related to the accretion of surrounding terranes to Siberia.     

OSL chronology of Lynch's Crater,the longest terrestrial record in NE-Australia

Lynch's Crater on the Atherton Tablelands in NE-Australia formed about 230,000 years ago during an explosive eruption, creating a maar more than 80 m deep. Since the eruption, the maar has been filled with lake sediments that are topped by peat material. A 64 m long core was recovered and an OSL dating project was undertaken to extend the chronology beyond 16 m depth, which according to ¹⁴C age control represents ～60 ka. The predominantly organic lake sediments contained abundant fine quartz of aeolian origin, and the Single Aliquot Regenerative Method (SAR) provided satisfactory equivalent dose (D_E) estimates. However, the determination of the dose rate proved both critical and difficult. Extremely low radionuclide contents led to cosmic radiation being the dominant dose rate contribution for most samples. The OSL chronology presented in this paper thus relies on modelling the changing cover by sediments and lake water over the burial time.