Sedimentary Context Research Articles

Diagenetic analysis of tetrapod from the Upper Triassic, Puesto Viejo Group, Argentina

The Puesto Viejo Group crops out in the San Rafael Block, southwest Mendoza, Argentina. This group is an important unit for the knowledge theTriassic faunas. It is composed of basal Quebrada de los Fósiles Formation (QF) overlying by the Río Seco de la Quebrada Formation (RSQ). In this study, we report tetrapod remains from the RSQ Formation that includes, until now, exclusively therapsids. Non-mammalian therapsids predominated in terrestrial ecosystems during the Late Paleozoic and Early Mesozoic. Although cynodonts and dicynodonts have been studied from several perspectives, the relation between taxa and sedimentary context has been scarcely documented. This study is aimed to elucidate the diagenesis of tetrapods from the Puesto Viejo Group and its relation to depositional environment. Diagenetic features of therapsid bones from the RSQ Formation were analyzed through thin sections to interpret the degree of taphonomic alteration. Diagenetic processes inferred include substitution; fracturing; brittle deformation and different permineralization events. Combined analyses through scanning electron microscopy; energy-dispersive X-ray spectrometry (SEM-EDX); X-ray diffractometry (XRD) and petrographic studies reveals the substitution of hydroxyapatite by francolite. The presence of fluorine in some samples suggests a link between the elemental composition and depositional environments: floodplain and crevasse splay. Permineralization stages include infilling of vascular canals, trabeculae and fractures with iron oxides and iron carbonate minerals during the burial history. This contribution represents a relevant approach to elucidate the relation between diagenesis on tetrapods and their paleoenvironments, as exemplified in this case study from the Puesto Viejo Group during the Upper Triassic.

Indicators and Methods to Understand Past Environments from ExoMars Rover Drills.

Great advances are expected during the analysis of drilled material acquired from 2m depth by ExoMars rover, supported by the comparison to local context, and the joint use of different instruments. Textural information might be less detailed relatively to what is usually obtained at outcrops during classical geological field work on the Earth, partly because of the lack of optical imaging of the borehole wall and also because the collected samples are crushed. However sub-mm scale layering and some other sedimentary features might be identified in the borehole wall observations, or in the collected sample prior to crushing, and also at nearby outcrops. The candidate landing sites provide different targets and focus for research: Oxia Planum requires analysis of phyllosilicates and OH content, at Mawrth Vallis the layering of various phyllosilicates and the role of shallow-subsurface leaching should be emphasized. At Aram Dorsum the particle size and fluvial sedimentary features will be interesting. Hydrated perchlorates and sulphates are ideal targets possibly at every landing sites because of OH retention, especially if they are mixed with smectites, thus could point to even ancient wet periods. Extensive use of information from the infrared wall scanning will be complemented for geological context by orbital and rover imaging of nearby outcrops. Information from the context is especially useful to infer the possible action of past H2O. Separation of the ice and liquid water effects will be supported by cation abundance and sedimentary context. Shape of grains also helps here, and composition of transported grains points to the weathering potential of the environment in general. The work on Mars during the drilling and sample analysis will provide brand new experience and knowledge for future missions.

A new Upper Cretaceous titanosaur nesting site from La Rioja (NW Argentina), with implications for titanosaur nesting strategies

AbstractCretaceous titanosaur nesting sites are currently known only from Europe, Asia and South America. In the latter, only the Auca Mahuevo and Sanagasta nesting sites have been confidently assigned to this clade of sauropod dinosaurs. Here we report the discovery of the first eggs and egg clutches found at Tama, a new Upper Cretaceous fossiliferous locality in the Los Llanos Formation, Sierra de Los Llanos (La Rioja, NW Argentina). At least five egg clutches, several partially preserved, isolated eggs and many eggshell fragments were discovered in a single outcrop of a sandstone horizon which represents a cumulative palaeosol profile. Although the mechanical and digital preparation of eggs did not reveal any embryonic remains in ovo, the morphology of the eggs and eggshells closely matches that of titanosaur eggs and eggshells found worldwide. The morphology and spatial grouping of the titanosaur eggs from Tama, along with geological observations support a burrow‐nesting strategy for these dinosaurs. Although the Sanagasta and Tama eggs were found in the same stratigraphical unit and share several morphological characters, they clearly differ in shell thickness and egg size. This, coupled with the interpretation of different sedimentary contexts for these nesting sites, strongly suggests that at least two different titanosaur species nested in La Rioja during the Late Cretaceous, using different nesting strategies. The occurrence of this new titanosaur nesting site in a semiarid palaeoenvironment represents an interesting case study for the reproductive biology of the titanosaur dinosaurs, particularly their labile nesting behaviour.

Polished walls as indirect evidence of both the use of caves and stone enclosures as livestock folds and dung management strategies: Ethnological and archaeological examples

The polish generated by sheep and goats in the walls of caves and stone-made enclosures is a clear indicator about their use as a livestock folds. The study of the polish distribution and intensity, together with the data revealed by the sedimentary context, or even if it is absent, allows to understand the kind of management carried out with the animal dung. In this way it is possible to identify if the dung has been merely dismissed, if it has been periodically extracted for the field manuring, and also if it has been intensively exploited by the completely emptying of the caves.

Multiple water isotope proxy reconstruction of extremely low last glacial temperatures in Eastern Beringia (Western Arctic)

Precipitation isotopes are commonly used for paleothermometry in high latitude regions. Here we present multiple water isotope proxies from the same sedimentary context – perennially frozen loess deposits in the Klondike Goldfields in central Yukon, Canada, representing parts of Marine Isotope Stages (MIS) 4, 3 and 2 – allowing us to uniquely corroborate fractionations and temperature conversions during these Late Pleistocene cold stages. We include new and existing proxy data from: relict wedge ice, a direct archive for snowmelt; relict pore ice, an archive for bulk soil water integrating year-round precipitation; and hydrated volcanic glass shards and fossil plant waxes, which are also thought to integrate year-round precipitation but are subject to large fractionations. In some cases, our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean, new transfer functions calibrated specifically for northern North America (δDprecip = 3.1‰·°C−1 × T – 155‰; and δ18Oprecip = 0.41‰·°C−1 × T – 20.2‰), and novel insights on the apparent net fractionation correction for Eastern Beringian steppe-tundra plant waxes (εwax/precip = −59 ± 10‰). The snowmelt origin of wedge ice ensures a relatively constrained winter-spring seasonality of contributing precipitation, as supported by the consistency between water isotope measurements from Late Holocene wedge ice and modern winter-spring precipitation. Wedge ice dating to the transitional MIS 3/2 is isotopically depleted relative to modern spring-winter precipitation by an amount that indicates a temperature depression of ∼14 ± 5 °C below modern. The soil water origin of pore ice, and other proxies integrating year-round precipitation from soil water, allows for a more variable precipitation seasonality. The isotopic composition of modern pore ice is consistent with mean annual precipitation. However, the isotopic composition of pore ice during MIS 3/2 converges on wedge ice values, signalling an increase in the ratio of cold-to-warm-season precipitation integrated by pore ice during glacial times, possibly due to drier summers as supported by the fossil record and climate model simulations. In the study region, water isotope proxies integrating year-round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality, as detected here, and thus are best interpreted as upper bound estimates. Based on these proxies, we estimate that annual temperatures during MIS 4, 3/2 and 2 were depressed below the modern climate to a maximum of ∼18 °C, 16 °C and 21 °C ± 4–5 °C, respectively. Our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate, and may be particularly important for studies of the major climate transformations over glacial-interglacial timescales.

Evidences of fossil landslides from the Lower Pleistocene on the northwestern margin of the Mesima basin (southern Calabria, Italy)

The present work aims to study the Pleistocene landslides located on the eastern side of the Vibo Valentia hill (southern Calabria, Italy). The Vibo Valentia hill, situated on the Tyrrhenian side of the Calabria-Peloritani Arc, is constituted by basement rocks made up of granulitic gneiss crossed by a network of marine sediment veins. Recent excavations for a new road have made possible seeing some indication of old landslide morphologies. The landslides are fully integrated into the existing topography and little indications of the former landslide morphologies remain. The principal evidences of the landslide morphologies are represented by presence of breccias and heterometric conglomerates made up of gneiss embedded in a fossiliferous carbonatic matrix. Furthermore, failure surfaces are marked by a thin calcareous micritic layer enriched in pelagic foraminifera. The fossil assemblage allowed to date the landslides at the Lower Pleistocene and classify them as fossil landslides. The geomorphologic and sedimentary context suggested that the Vibo Valentia hill was a coastal cliff developed in an active fault zone during the Lower Pleistocene and characterized by a rapid uplift. This geological context created favorable conditions for the trigger of landslides along the cliff made up of gneissic rocks.

Spatio-temporal variation in the preservation of ancient faunal remains

Palaeodemographic studies of animals using frequency distributions of radiocarbon dates are increasingly used in studies of Quaternary extinction but are complicated by taphonomic bias, or the loss of material through time. Current taphonomic models are based on the temporal frequency distributions of sediments, but bone is potentially lost at greater rates because not all sedimentary contexts preserve bone. We test the hypotheses that (i) the loss of bone over time is greater than that of sediment and (ii) this rate of loss varies geographically at large scales. We compiled radiocarbon dates on Pleistocene-aged bone from eastern Beringia (EB), the contiguous United States (CUSA) and South America (SA), from which we developed models of taphonomic loss. We find that bone is lost at greater rates than terrestrial sediment in general, but only for CUSA and SA. Bone in EB is lost at approximately the same rate as terrestrial sediments, which demonstrates the excellent preservation environments of arctic regions, presumably due to preservative effects of permafrost. These differences between bone and sediment preservation as well as between arctic and non-arctic regions should be taken into account by any research addressing past faunal population dynamics based on temporal frequency distributions.

Assessing long-term habitability at an eastern Sahara oasis: ESR dating of molluscs and herbivore teeth at Dakhleh Oasis, Egypt

In the northeastern Sahara, electron spin resonance (ESR) dating of when animals lived documents their habitability in Dakhleh Oasis, Egypt. A Middle Pleistocene paleolake(s) covered >1700 km2. At eastern Locality Dak348, 10 m thick, remnant lacustrine marls yielded Pleistocene fauna, rare artefacts, and plant casts. No obvious unconformity exists within these deposits. From upper horizons, a hartebeest tooth ESR dated at 195 ± 11 ka, correlates with Marine Isotope Stage (MIS) 7, while molluscs from a stratigraphically higher horizon averaged 89 ± 10 ka, correlating with MIS 5a/b. At western Locality Dak006, upslope deflation has left a temporally mixed surficial lag. Numerous lagged tooth fragments, independently dated by ESR, correlate with MIS 5 through 17. Fragments from a slope sand unit correlate with MIS stages 3 through 6. One bovid tooth associated with Younger Middle Stone Age artefacts in the base of the sand dated at 84 ± 7 ka (MIS 5a/b). Molluscs from Romano-Byzantine backdirt at a breached artesian vent dated to 8–15 ± 1 ka, suggesting that ponds formed during MIS 1 and 2. Even without well defined sedimentary contexts, ESR frequency data indicate that the oasis was habitable for herbivores during at least twelve stages in the Mid-Late Quaternary, and, therefore, likely also for humans.

Analysing the proximal gamma radiometry in contrasting Mediterranean landscapes: Towards a regional prediction of clay content

The analysis of γ-radiometric data from proximal soil sensing measurements can be used to predict key soil properties for environmental and agricultural issues. These predictions require prior calibrations that use a large sampling of field data that could be significantly reduced if regional predictions can be established. However, such predictions may be challenging for Mediterranean regions because of the highly contrasted soils and specific geopedological characteristics (sedimentary rocks, low weathering, etc.). Our study focuses on the regional prediction of a key soil property (clay content), within highly contrasting geopedological groups (GPG) from the Languedoc region. The aims of the research were (i) to understand the relationship between γ-radiometric data and the clay content within the different complex GPGs and (ii) to predict the clay content from γ radiometry with a regional calibration based on the GPG as an auxiliary variable. A proximal soil survey using the γ radiometer, called “The Mole”, was conducted in 8 areas of the Languedoc region. The plots were selected over different GPGs that are representative of the soil diversity and materials according to their weathering intensity and igneous components. In total, 242 sites were sampled based on a random grid cell for soil laboratory measurements. The soil texture and stoniness were analysed, and the particle size fractions were separated for mineral identification via X-ray diffraction. The activity of 232Th [1 to 71bq/kg] and 40K [40 to 771bq/kg] exhibits the largest range between the different GPGs, which spans the range of values measured in previous European studies. The relationship between the clay content and 232Th is significant at a regional level [R2=0.60; RMSE=42g/kg]. The residuals are significantly distributed according to the different GPGs. A new linear model based on the 232Th activity and the GPGs improves the prediction of the clay content [R2=0.72; RMSE=35g/kg]. Our study showed that ground γ radiometry can be used to predict the clay content within a complex Mediterranean sedimentary context. The 232Th radionuclide is the best predictor. The disturbance of the relationship between the 232Th and the clay content corresponds to the fine earth mineralogy type and the proportion of igneous pebbles.

F-content variation in mammoth ivory from Aurignacian contexts: Preservation, alteration, and implications for ivory-procurement strategies

This article presents the results of two series of micro-PIXE/PIGE analysis on mammoth ivory samples from four Aurignacian sites in France (Abri Castanet, Grotte d'Isturitz) and Germany (Hohle Fels, Vogelherd). Specifically, we report variation in ivory preservation as indicated by fluorine (F) content and ratios of MgO/CaO from Aurignacian horizons known to contain ivory industries. Though all samples derive from respectively homogenous sedimentary contexts, results show very different pattern of F-content variation among sites. F uptake in ivory is a more complex process than that observed for bone, and the structural/morphological reasons for this are explained. High-resolution data on the archaeological context of the samples from Abri Castanet also allows for examination of the effects of horizontal and vertical distribution on F-content and the sorting of F-content data by sedimentary unit. A definitive model for fluorine uptake during ivory diagenesis will require further investigation, but a close examination of the current data provides novel insight into processes of taphonomy and diagenesis in this exceptional and highly valued raw material, as well as further evidence to support regionally distinct strategies of ivory procurement in the Early Aurignacian. In combination with additional lines of faunal and archaeological evidence, it is demonstrated that ivory procurement in the Swabian Jura focused on fresh local sources of ivory, while procurement strategies in Northern Aquitaine focused on ivory collection from natural deposits of varying age.

Ediacaran sedimentology and paleoecology of Newfoundland reconsidered

Ediacaran fossils of Mistaken Point and other localities in Newfoundland have been reconstructed as denizens of a deep, dark ocean, based on a turbidite interpretation of their sedimentary context. Objections to this view include geochemical indications of fresh water and volcanological and sedimentological evidence that they lived in soils of coastal plains and tidal flats. Two distinct assemblages of these fossils are recognized: a low-diversity Aspidella–Heimalora community on sulfidic grey paleosols (Sulfaquent) and a high diversity Fractofusus–Charniodiscus community on red ferruginous paleosols (Fluvent and Udept). These two assemblages and their paleosols were comparable in habitat with Phanerozoic intertidal salt marsh and coastal woodlands, respectively. Paleosol chemical composition is also evidence that Ediacaran communities of Newfoundland lived in humid, cool temperate paleoclimates, unlike arid paleoclimates of the classical Ediacaran biota of South Australia.

Extended residence times for foraminifera in a marine-influenced terrestrial archaeological deposit and implications for palaeoenvironmental reconstruction

Accelerator Mass Spectrometry (AMS) radiocarbon dating and taphonomic grading was undertaken on foraminifera preserved in the archaeological shell matrix site of Thundiy, Bentinck Island, southern Gulf of Carpentaria, Australia. Foraminifera were assigned to one of six taphonomic grades ranging from pristine to severely abraded. AMS dating demonstrates a weak relationship between preservation status and age. Foraminifera ages are inconsistent with multiple ages on marine shell from the same deposit implying significant sediment transport system residence ages (the time between death of the organism and final deposition) for foraminifera in the deposit. Results demonstrate that foraminifera cannot be assumed to be contemporary with other components of the sedimentary context in which they occur, indicating that caution is required in interpreting chronologies and palaeoenvironmental records based on foraminifera recovered from highly dynamic depositional settings. Findings point to the potential of foraminifera AMS dating of coastal archaeological deposits to contribute to evaluations of site integrity and chrono-stratigraphic analyses.

Bone diagenesis at the Florisbad spring site, Free State Province (South Africa): Implications for the taphonomy of the Middle and Late Pleistocene faunal assemblages

The Middle to Late Pleistocene spring site of Florisbad, South Africa, is the name site of the Florisian Land Mammal Age (LMA), and it has produced a large collection of fossil bones from different sedimentary contexts. The largest of these faunal assemblages derives from vertically intrusive dormant spring vents and is taphonomically distinct from specimens associated with a Middle Stone Age occupational horizon. The Florisbad faunal assemblages include several extinct and extant animal species, mainly grazing ungulates that represent a highly productive open grassland environment. The Florisian LMA was characterized by substantially wetter conditions compared to the Holocene. Geological evidence at Florisbad and the characteristic occurrence of water-dependent species, such as lechwe, waterbuck, hippopotamus and a variety of water birds, reflect the presence of a vast intermittent paleolake forming during the wet phases of the Middle and Late Pleistocene. During dry phases, the area of spring activity was not inundated and provided a suitable habitat for both humans and animals. Bones collected from different sedimentary contexts exhibit a number of post-depositional alterations that reflect specific diagenetic processes, which led to fossilization. Two contrasting hypotheses regarding these processes, based on morphological studies of bones and groundwater chemistry, were proposed in the past. The first identified spring water as a major fossilization agent, whereas the second saw it as a medium conducive to bone dissolution. Using Fourier Transform infrared spectrometry (FTIR) and micro-spectrometry (μFTIR), we determined the mineralogical composition of these bones. We show here that specimens from inactive paleo-spring vents are characterized by the formation of carbonate fluorapatite on the outer surface of cortical bone, and locally exhibit authigenic calcite crystals, as opposed to bones collected from non-spring contexts at the site. The nucleation of carbonate fluorapatite is linked to the high fluoride content of the alkaline spring water, thus confirming its key role in the fossilization process of bones recovered from paleo-spring vents. Therefore, our results support the first of the two hypotheses advanced in the past.

The sedimentary record of the 1960 tsunami in two coastal lakes on Isla de Chiloé, south central Chile

This study describes sediments deposited by the tsunami following the 1960 Great Chilean Earthquake (MW 9.5) in two coastal lakes, Lakes Cucao and Huelde, on the west coast of Isla de Chiloé, south central Chile (42.6°S). Sub-bottom profiles and side scan sonar mosaics illustrate the sedimentary context of transects of gravity cores. The stratigraphy of both lakes features gyttja sedimentation, interrupted by the abrupt emplacement of a sandy layer with mud rip-up clasts and a mud cap. This sandy layer reflects a sudden change in sedimentary environment, most probably caused by a high-energy inundation. Radionuclide analyses (137Cs and 210Pb) date the inundation deposit to shortly before the mid 1960s. The only known event that matches the sedimentological and chronological criteria is the AD 1960 tsunami. Using grain size analysis and comparisons with samples from modern environments, we demonstrate that the proximal (seaward) part of the deposit consists of a mixture of sand derived from subaerial sources and reworked gyttja lake sediment. In the distal (landward) part of Lake Cucao, the sand component is lost and the deposit consists entirely of remobilised lake sediments. The repetition of tsunami deposit sequences in Lake Huelde suggests a minimum of three inundating waves. Sub-bottom profiles and side scan sonar mosaics reveal tsunami inundation over the barrier and more prominently through the outlet river channel. The dominant role of the river channel as a pathway for sediment transport is also described in core samples by tsunami deposits that fine away from the channel mouth. The identification and description of the deposit left by a known tsunami provide important insights into tsunami sedimentation in coastal lakes and have the potential to help in the search for paleotsunami evidence.

A new Cenomanian vertebrate tracksite at Tamajón (Guadalajara, Spain): Palaeoichnology and palaeoenvironmental implications

A new Upper Cretaceous vertebrate tracksite has been discovered at Tamajón (Iberian Ranges, Guadalajara, Spain). The track level is a relatively smooth and slightly undulating sandy ferruginous crust, corresponding to an erosive surface at the base of a small meandering channel. It is incised into the underlying planar cross-bedded sandstones of coastal bars located at the middle-upper part of the Utrillas Formation (middle-upper Cenomanian). The site shows an extraordinary concentration of vertebrate tracks, among which numerous sets of two to five isolated digit impressions (“swim tracks”) and, at least, two trackways referred to crocodyliforms, and a single tridactyl footprint probably produced by a theropod dinosaur can be recognized. There are also several long traces (epichnial grooves) revealing sharp direction changes (up to 90°) which seem to be fish fin traces (Undichna unisulca), although crocodyliforms (tail marks) and/or fish invertebrates cannot be rejected as possible tracemakers. Some crocodyliform tracks reveal a thin raised rim, due to the displacement of the sediment by the pressure produced by the feet. Several impressions are moderately deformed by small sediment slides, only preserving their deepest part (claw marks). This is clearly indicative of a soft substrate with a high degree of plasticity and water content at the time of the track registration. Nevertheless, the sediment was hard enough to preserve manus and pes print morphologies and also possible crocodyliform tail and/or fish fin traces. Small rhizoliths can also be recognized and may belong to herbaceous wetland vegetation. The morphology of the palaeochannel, the sedimentary context and the track preservation seem to indicate that the tracks were impressed in a shallow channel located near the coast, under wet conditions and in different moments of time. This discovery represents the first occurrence of vertebrate ichnites in the Utrillas Formation, a stratigraphic unit where osteological and ichnological remains are relatively scarce, and it confirms that some crocodyliforms lived in near coast channels during the deposition of this unit.

Leftover prey remains: a new taphonomic mode from the Late Miocene Cerro Azul Formation of Central Argentina

The Cerro Azul Formation (La Pampa Province, Argentina) comprises a rich vertebrate fauna of small mammals dominated by notoungulates and rodents. The fauna pertains to the Late Miocene specifically to the Huayquerian Stage/Age. Taphonomic analysis of micro-mammals from Estancia Re locality evidenced that the faunal assemblage was accumulated by the activity of a predator. This assemblage was compared with others from the Cerro Azul Formation in Telen and Caleufu localities (La Pampa Province), previously interpreted as products of predator activities. These microfossil accumulations differ from assemblages attributed to pellets and faeces produced by modern predators (nocturnal and diurnal bird raptors and carnivore mammals). However, due to their anatomical representation, degree of bone breakage and presence of tooth marks, they are interpreted as accumulations of uneaten prey remains discarded by the predator. The predator involved could not be determined with certainty, although the presence of tooth marks in some skeletal remains and the presence of coprolites in Telen and Caleufu suggest that it could be a carnivore mammal. Similarities in the accumulation mechanism, patterns of preservation and sedimentary contexts in the three assemblages support the recognition of a new taphonomic mode, termed ‘leftover prey remains’.

An ecogeomorphic model of tidal channel initiation and elaboration in progressive marsh accretional contexts

The formation and evolution of tidal networks have been described through various theories which mostly assume that tidal network development results from erosional processes, therefore emphasizing the chief role of external forcing triggering channel net erosion such as tidal currents. In contrast, in the present contribution we explore the influence of sediment supply in governing tidal channel initiation and further elaboration using an ecogeomorphic modeling framework. This deliberate choice of environmental conditions allows for the investigation of tidal network growth and development in different sedimentary contexts and provides evidences for the occurrence of both erosional and depositional channel-forming processes. Results show that these two mechanisms in reality coexist but act at different time scales: channel initiation stems from erosional processes, while channel elaboration mostly results from depositional processes. Furthermore, analyses suggest that tidal network ontogeny is accelerated as the marsh accretional activity increases, revealing the high magnitude and prevalence of the depositional processes in governing the morphodynamic evolution of the tidal network. On a second stage, we analyze the role of different initial topographic configurations in driving the development of tidal networks. Results point out an increase in network complexity over highly perturbed initial topographic surfaces, highlighting the legacy of initial conditions on channel morphological properties. Lastly, the consideration that landscape evolution depends significantly on the parameterization of the vegetation biomass distribution suggests that the claim to use uncalibrated models for vegetation dynamics is still questionable when studying real cases.

Potential of establishing a ‘global standardised growth curve’ (gSGC) for optical dating of quartz from sediments

We report investigations of the optically stimulated luminescence (OSL) signals of sedimentary quartz from different regions of Asia, Africa, Europe and North America using a single-aliquot regenerative-dose (SAR) procedure. We show that variations in the shape of dose response curves (DRCs), or growth curves, of the test dose sensitivity-corrected OSL signals among single aliquots composed of multiple grains can be greatly reduced by normalising the DRCs using one of the regenerative dose OSL signals. We refer to this regenerative-dose normalisation procedure as ‘re-normalisation’. We find a common re-normalised DRC extends to doses of ∼250 Gy for samples that differ significantly in terms of geological provenance, sedimentary context and depositional age. This feature permits the development of a ‘global standardised growth curve’ (gSGC) for OSL signals from single aliquots of quartz. The equivalent dose (De) of an aliquot can be estimated from the natural signal, one regenerative dose signal and their corresponding test dose signals. For the variety of samples investigated, we find that De estimates obtained from the gSGC are consistent with those obtained using full SAR procedures for doses of up to ∼250 Gy. Use of the gSGC for single aliquots would greatly reduce the time required to estimate the De values of older samples and for a large number of aliquots.

New evidence for the presence of Changbaishan Millennium eruption ash in the Longgang volcanic field, Northeast China

The Changbaishan Millennium eruption (~AD 940s) produced a widely distributed tephra layer around northeast Asia. This tephra layer serves as a marker bed in Greenland ice cores and in marine, lake, archeological and tsunami sediments in Japan and the surrounding region. However, little attention has been paid to the widespread sediments west of Changbaishan volcano. Here we present new stratigraphic, geochemical, varve chronology, and 14C geochronological data from the varved sediments in Lake Sihailongwan, Longgang volcanic field, Northeast China, extending the westerly margin of this eruption. The distinctive geochemical characteristic of volcanic glass (ranging from trachyte to rhyolite), similar to those of proximal and distal tephra, confirmed the occurrence of Changbaishan Millennium eruption ash in the lake, illustrating the westward dispersal fan of the ash deposits. The position of the peak concentration of glass shards of this tephra was dated to 953±37 AD by varve chronology, and the radiocarbon samples immediately above this tephra gave a date of 940–1020 AD, overlapping the most recent ages for this eruption. The occurrence of Changbaishan Millennium eruption ash in this lake enables a direct and precise synchronization with other high-resolution archives in Northeast Asia, such as maar lakes and peat and marine sediments, thus providing an isochronous marker for a range of sedimentary contexts.

Construction of a ‘global standardised growth curve’ (gSGC) for infrared stimulated luminescence dating of K-feldspar

We investigated the infrared stimulated luminescence (IRSL) and post-infrared IRSL (pIRIR) signals emitted by K-feldspars from sedimentary samples from Asia, Europe and Africa using a single-aliquot multiple elevated temperature (MET) stimulation procedure. For separate aliquots of the same sample, we show that variation among the dose response curves (DRCs), or growth curves, constructed from the regenerative dose signal (Lx), the test dose signal (Tx, an indicator of luminescence sensitivity) and the sensitivity-corrected signal (Lx/Tx) can be largely eliminated by normalising the DRCs using one of the regenerative dose signals; we call this procedure ‘regenerative-dose normalisation’ or re-normalisation. Furthermore, for the MET-pIRIR signals measured at 250 °C, we find that different samples have re-normalised DRCs that follow the same growth function, despite the samples differing significantly in terms of their geological provenance, sedimentary context, equivalent dose (De) and luminescence sensitivity. This common feature offers the potential to establish a ‘global standardised growth curve’ (gSGC) for different samples of K-feldspar, and thereby enable De values to be estimated for a large number of single aliquots by projecting the re-normalised natural signals on to the gSGC. For the 18 samples investigated in this study, we find that De estimates obtained from the gSGC are consistent with those obtained using full single-aliquot regenerative dose (SAR) procedures for doses of up to ∼1600Gy. The establishment of a gSGC would greatly reduce the time required to date older samples using K-feldspar, as regenerative doses of several hundreds to a few thousands of Gy are typically delivered to each aliquot in each SAR cycle.