Radiocarbon and luminescence dating of the Wulanmulun site in Ordos,and its implication for the chronology of Paleolithic sites in China

After the Salawusu and Shuidonggou sites, the Wulanmulun site found in 2011 is another important Paleolithic site in Ordos, China, due to its numerous stone artifacts and animal fossils. Here, we carry out a combined luminescence and radiocarbon dating of the site. The luminescence dating was done on coarse-grained quartz from 24 sediment samples using a single-aliquot regenerative-dose (SAR) protocol. The radiocarbon dating was performed on ten charcoal samples and one bone sample using acid-base-acid (ABA) and acid–base-wet oxidation-stepped combustion (ABOx-SC) pretreatments. The results showed that: (i) although some samples show relative large (>20%) overdispersion in De distribution (small aliquots), the quartz grains are considered to be sufficiently bleached before burial; (ii) the quartz OSL ages of ∼4–65 ka obtained for the samples are generally stratigraphically consistent and reliable; (iii) the radiocarbon ages obtained using the ABA pretreatment procedure are much younger than the corresponding OSL ages, and the radiocarbon ages obtained using the ABOx-SC method are beyond or close to the laboratory background. The radiocarbon ages obtained using the ABA treatment were considered to be underestimated. This implication is that caution must be taken for dating Chinese Paleolithic (>25 ka) using the ABA pretreatment procedure on carbon samples. Finally, the cultural layers from the Wulanmulun site are deduced to be between 50 and 65 ka.     

Testing the ABOx-SC method: Dating known-age charcoals associated with the Campanian Ignimbrite

Over the past decade several studies have shown the improvements to radiocarbon chronologies that arise when Acid Base Oxidation-Stepped Combustion (ABOx-SC, Bird et al., 1999) pretreatment methods are applied to the dating of charcoal thought to be >30 ka BP. However, few studies have examined whether the use of ABOx-SC produces dates that are not only older, but accurate on known-age charcoal samples that could not be decontaminated using the routine Acid–Base–Acid (ABA) pretreatment protocol. In this study we date 9 charcoal fragments found below the Campanian Ignimbrite (CI) tephra layer, dated by ⁴⁰Ar/³⁹Ar to 39,230 ± 45 years (De Vivo et al., 2001, Rolandi et al., 2003), from three Palaeolithic sites. When treated with the ABOx-SC pretreatment protocol, the radiocarbon dates provide an accurate terminus post quem for the CI. In contrast, the ABA protocol consistently underestimates the age of the tephra. These results serve as a warning against the use of consistency as an indicator for reliability, demonstrate that the routine ABA method is not sufficient to decontaminate charcoal samples from sites of Palaeolithic age, and show that ABOx-SC produces not only older, but accurate age estimates.     

Hydropyrolysis as a new tool for radiocarbon pre-treatment and the quantification of black carbon

The first results concerning the potential of hydrogen pyrolysis (hypy) as a new tool for the quantification and isolation of Black Carbon (BC) for radiocarbon analysis are reported. BC is a highly stable form of carbon, produced during pyrolysis of biomass to materials such as charcoal. Isolation and quantification of this component is therefore of great interest in radiocarbon measurement, particularly for more ancient samples, where contamination issues become more critical. Hypy has been demonstrated to reliably separate labile and refractory carbonaceous sample components for engineering and geological applications, but its potential in ¹⁴C geochronological investigation has previously been unexplored. Here, we test the hypy technique using a selection of soil standard samples and ancient charcoals from deposits of geological and archaeological significance. The results show that hypy can effectively and reproducibly isolate different carbon fractions within a variety of sample types and thus has the potential to provide a rapid and robust pre-treatment technique for radiocarbon analysis. Hypy has the additional advantage that the non-BC fraction removed from a sample can be quantitatively collected for subsequent further analysis. The technique represents a promising new approach not only for ensuring reliable decontamination of pyrogenic carbon samples prior to radiocarbon dating, but also for BC quantification in a variety of environmental matrices.     

A radiocarbon chronology for Sanamere Lagoon,Cape York Peninsula,using multiple organic fractions

The selection and pre-treatment of reliable organic fractions for radiocarbon age determination is fundamental to the development of accurate chronologies. Sampling from tropical lakes is particularly challenging given the adverse preservation conditions and diagenesis in these environments. Our research is the first to examine and quantify the differences between radiocarbon ages from different carbon fractions and pretreatment protocols from tropical lake sediments. Six different organic fractions (bulk organics, pollen concentrate, cellulose, stable polycyclic aromatic carbon (SPAC), macrocharcoal >250 μm and microcharcoal >63 μm) were compared at six different depths along a 1.72 m long core extracted from Sanamere Lagoon, Cape York Peninsula, northern Australia. Acid-base-acid (ABA), modified ABA (30% hydrogen peroxide + ABA), 2chlorOx (a novel cellulose pre-treatment method) and hydrogen pyrolysis (hypy) were used to pre-treat the organic fractions. The oldest date is ∼31,300 calibrated years before present (cal yr BP) and the youngest is ∼2800 cal yr BP, spanning ∼28,500 years. The smallest offset between the minimum and the maximum age for different fractions and across pretreatment methods at a given depth was found to be 832 years (between SPAC and pollen) and the largest ∼16,750 years (between pollen concentrate and SPAC). The SPAC fractions pre-treated with hypy yielded older ages compared to all other fractions in most cases, while bulk organics yielded consistently younger ages. The magnitude and consistency of the offsets and the physical and chemical properties of the tested organic fractions suggest that SPAC is the most reliable fraction to date in tropical lake sediments and that hypy successfully removes exogenous carbon contamination.     

Use of heavy liquid density separation to remove pyrite from sediment samples for radiocarbon dating

Sample preparation protocols for concentrating organic material from sediments for radiocarbon dating often include a large number of steps and the use of hazardous chemicals. Thus, these protocols are often problematic for pollen-poor sediments as material can get lost or may become degraded. Pyrite in samples for radiocarbon dating hinders an effective graphitisation process and thus needs to be removed during sample preparation. Standard protocols require the use of nitric acid, a strong oxidant that corrodes organic material. Therefore, the use of nitric acid needs to be avoided when preparing pollen-poor but pyrite-rich sediments.We present a method that minimises the sample preparation steps by replacing acid treatment with heavy liquid separation. Using non-toxic LST at a density of 2.0 g cm⁻³ is shown to be effective for separating the organic fraction from sulphides, silicates and carbonates. We applied this method to pyrite-rich and pollen-poor sediments from Western Australia that had previously been problematic to date. The successful AMS radiocarbon dating of all samples pre-treated with LST demonstrates the effectiveness of this method.     

Testing less-conventional methods to date a late-pleistocene to Holocene eruption: Radiocarbon dating of paleosols and 36Cl exposure ages at Pelado volcano,Sierra Chichinautzin,Central Mexico

Despite their significance for estimating hazards and forecasting future activity, dating young volcanic deposits and landforms (<50,000 yrs old) remains a challenge due to the limitations inherent to the different isotopic chronometers used. The Trans-Mexican Volcanic Belt is one of the most active and populated continental arcs worldwide, yet its temporal pattern of activity is poorly constrained. Such deficiency is particularly problematic for the Sierra Chichinautzin Volcanic Field (SCVF) that is located at the doorstep of Mexico City and Cuernavaca and is hence a major source of risk for these cities. Existing ages for this area derive mostly from either radiocarbon on charcoal, which is rare and may be contaminated, or ⁴⁰Ar/³⁹Ar on rock matrix, which is poorly precise for this time period and rock type. Here, we focus on the Pelado monogenetic volcano, which is located in the central part of the SCVF and erupted both explosively and effusively, producing a large lava shield and a widespread tephra blanket. This unique eruptive event was previously dated at ∼12 calibrated (cal) kyrs BP, using radiocarbon dating on charcoal from deposits related to the eruption. To test alternative dating approaches and confirm the age of this significant eruption, we applied two less conventional techniques, radiocarbon dating of bulk paleosol samples collected below the complete tephra sequence at nine sites around the shield, and in-situ ³⁶Cl exposure dating of two samples of an aphyric lava from the base of the shield. Radiocarbon paleosol ages span a continuous time interval from 13.2 to 20.2 cal kyrs BP (2σ), except for one anomalously young sample. This wide age spread, along with the low organic contents of the paleosols, may be due to erosive conditions, related to the sloping topography of the sampling sites and the cool and relatively dry climate of the Younger Dryas (11.7–12.9 ka), during which the Pelado eruption probably occurred. The two ³⁶Cl-dated lava samples have consistent ages at 1σ analytical errors of 15.5 ± 1.4 ka and 13.2 ± 1.2 ka, respectively, yielding an average age of 14.3 ± 1.6 ka for this lava flow. The high full uncertainty in ³⁶Cl ages (24%) is due to high rock Cl content. We conclude that paleosol radiocarbon dating is useful if numerous samples are analyzed and climatic and relief conditions at the time of the eruption and at the sites of tephra deposition are considered. The ³⁶Cl dating technique is an alternative method to date volcanic eruptions, as it gave consistent results, but in the specific case of Pelado volcano, the high Cl content in the analyzed rocks increases the age uncertainties.     

Comparison between luminescence and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia

Dust depositions are critical archives for understanding interior aridification and westerly climatic changes in Central Asia. Accurate and reliable dating of loess is very important for interpreting and correlating environmental records. There remains a disparity between luminescence ages and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia. In this study, we establish a closely spaced quartz optically stimulated luminescence (OSL) chronology for the 20.5-m-thick Nilka loess section in the Ili Basin. Based on OSL ages, two intervals of higher mass accumulation rate occurred at 49–43 ka and 24–14 ka. We further compare these OSL ages with 23 accelerator mass spectrometry (AMS) ¹⁴C ages of bulk organic matter. The results indicate that the OSL and radiocarbon ages agree well for ages younger than ca. 25 ¹⁴C cal ka BP. However, beyond 30 cal ka BP, there is no consistent increase in AMS ¹⁴C age with depth, while the OSL ages continue to increase. These differences confirm the observation that the AMS ¹⁴C ages obtained using conventional acid–base–acid (ABA) pretreatment are severely underestimated in other terrestrial deposits in Central Asia, which could be due to 2–4% modern carbon contamination. However, OSL dating is applicable for constructing an accurate chronology beyond 30 cal ka BP. We suggest caution when interpreting paleoenvironmental changes based on radiocarbon ages older than 25 cal ka BP.     

Low temperature (LT) combustion of sediments does not necessarily provide accurate radiocarbon ages for site chronology

Radiocarbon dating of soils and sediments is notoriously problematic for the purposes of dating a specific event due to their heterogeneous mix of multiple organic fractions, each of which may have a different radiocarbon age. Numerous studies have failed to agree on which sedimentary fraction or radiocarbon pre-treatment method, if any, provides the closest agreement between the age of a sedimentary fraction and that of associated plant macrofossils or charcoal. We tested the stepped-combustion method of McGeehin et al. (2001), as well as standard radiocarbon humin and humic extraction techniques, using samples from a chronologically well-constrained perennially-frozen site at Quartz Creek, Yukon Territory, Canada. The ages in closest agreement with associated radiocarbon-dated plant macrofossils and with the overlying Dawson tephra were given by the humic and humin fractions, but even these were still older than the macrofossil ages by up to 4195 ± 260 radiocarbon years. The low temperature (LT) humin method recommended by McGeehin et al. (2001) yielded ages older than the macrofossils by up to nearly 4425 ± 240 radiocarbon years. These fractions, while still providing information on the mobility and potential residence times of carbon in soils and sediments, should not be relied upon to provide consistently accurate site chronologies.     

U-series,ESR and 14C studies of the fossil remains from the Mousterian levels of Zafarraya Cave (Spain): A revised chronology of Neandertal presence

Zafarraya Cave is considered a reference site for the last presence of Homo neanderthalensis presence in the south of the Iberian Peninsula. In this paper, accelerator mass spectrometry (AMS) radiocarbon dates were carried out on charcoals and faunal remains, U–Th dating using either alpha spectrometry or Thermal-Ionization Mass Spectrometry (TIMS) and ESR dating were performed on faunal remains. These analyses were carried out on samples from the Mousterian levels of the site (archaeostratigraphic units UC, UD, UE, UF, UG). The ¹⁴C AMS dates of charcoal samples (n = 11) were scattered and displayed no coherence with the stratigraphy suggesting possible alteration. The delicate charcoal and faunal samples underwent the gentle RR, ZR (ABA) or AG (ABA) pretreatment procedures at ORAU. The RR protocol is currently considered too gentle and the results are considered with caution. Four ZR charcoal pretreatments failed due to the fact that the charcoal samples were altered. Only two charcoals samples subjected to the ZR pretreatment yielded a reliable % C (>60%) (OxA-9001 and OxA-9002, 40,294–42,761 and 38,763–40,604 cal BP). Their ages are consistent with the stratigraphy and are considered to provide the best age estimate for the level bearing the Z2 Neandertal mandible (Unit UE). For the dentine and the bone samples, the ¹⁴C AMS were less dispersed. ¹⁴C analyses failed for four bone samples due to insufficient collagen content. Moreover, the %C is very low for two samples, suggesting alteration of the fossil remains at Zafarraya. Only two other samples with enough %C (>30%) were retained: OxA-8024 and OxA-8999 (Unit UE). The respective ¹⁴C ages range from ∼34 to 39 ka cal BP. The U/Th (TIMS) analyses of enamel samples displayed an extremely low uranium content (< ∼ 0.02–0.04 ppm). Moreover, the U/Th age range of faunal remains is large, thus providing no conclusive results. ESR dating was chosen for this exercise as, in combination with U-series, it can be used to assess U-uptake in open systems. The combined ESR and U/Th (TIMS) age estimates on tooth enamel yielded US-ESR ages between 33 (+3/−4) ka to 43 ± 3 ka (MIS3) for two Equus teeth and one Capra tooth in unit UE, overlapping with the oldest charcoal and bone ¹⁴C dates. The age of the Zafarraya fossil remains was derived from the US-ESR time range of 30–46 ka (MIS 3). We consider this age range to be more representative of the Neandertal occupations at the site than the hitherto widely cited uncalibrated ¹⁴C age of around 30 ka.     

Radiocarbon redating of contaminated samples from a tropical volcano: the Mansion ‘Series’ of St Kitts,West Indies

Heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits, in addition to easy contamination of this wood by root systems and soluble humic material. Because the physical nature of the charcoal varies, some samples are more prone to contamination. Two independent studies of the same volcano, Mt Liamuiga on St Kitts in the Lesser Antilles, sometimes using samples from the same carbonized tree, yielded a systematic difference in radiocarbon ages. An exchange of samples and a re-investigation of three physically distinct types of charcoal yielded the following results. Rare, hard, dense charcoal, lacking contamination, which had yielded a spurious age of 2860 years bp, was redated at 1845±58 years bp. Common soft, friable charcoal with good cellular structure proved to be susceptible to contamination. A field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre-treatment was used, indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets. A previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the Mansion Series contradicted ages older than 41000 years bp from common friable charcoal in the lower Mansion Series. The soft powdery charcoal was re-investigated using a sample collected a few centimeters from the original, although field decontamination of this sample was not possible, more extensive laboratory treatment yielded an age of ca. 43000 years bp, again proving that routine laboratory pretreatments are inadequate. A revised geochronology for the Mansion Series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits.     

泥炭样品不同有机组分的~(14)C测年的初步研究

分别用ＮａＣｌＯ、ＮａＯＨ溶液、Ｎａ４Ｐ２Ｏ７和ＮａＯＨ混合溶液和有机溶剂对采自延庆盆地大王庄两个泥炭样品进行前处理，每个样品获得１０个不同有机组分，对这些有机组分的１４Ｃ年龄测定值进行对比。以探讨泥炭等样品不同有机组分１４Ｃ测年的可靠性     

Identifying a reliable target fraction for radiocarbon dating sedimentary records from lakes

Lake basins that experience rapid rates of deposition act as high-resolution environmental archives because they produce sedimentary records that have centennial or even decadal resolution. However, identifying target fractions for radiocarbon dating of lake sediments remains problematic because reworked organic material from fluvial catchments can produce anomalously old radiocarbon ages. This study determines the extent to which reworked material from catchment soils impacts radiocarbon dates on pollen and other organic concentrates by comparing radiocarbon dates produced by these techniques against a chronostratigraphic marker in cores from Lake Mapourika, New Zealand. Pollen preferentially preserved and reworked from catchment soils was identified using soil palynology. A technique was then developed to remove reworked pollen types from pollen concentrates extracted from lake sediment. Identification and removal of reworked pollen from pollen concentrates produced ages that were consistently closer to the age of the chronostratigraphic horizon than other organic concentrates. However, these dates were still between 736 and 366 calendar years older than expected. The only organic fractions that reliably reproduced the age of the chronostratigraphic horizon were terrestrial leaf macrofossils, although terrestrial leaf macrofossils isolated from megaturbidite deposits, which are formed by high-energy depositional events, also provided anomalously old ages. The results indicate that leaf material extracted from hemipelagite, which accumulates gradually, is likely to be the only organic fraction to produce reliable chronology in lakes where a component of sedimentation is driven by the fluvial system. The results also demonstrate the importance of conducting a detailed investigation of physical sedimentology before selecting material for radiocarbon dating lake sediments.     

Charcoal chronology of the Amazon forest: A record of biodiversity preserved by ancient fires

The Amazon region holds a wide variety of ethnic groups and microclimates, enabling different interactions between humans and environment. To better understand the evolution of this region, ancient remains need to be analysed by all possible means. In this context, the study of natural and/or anthropogenic fires through the analysis of carbonized remains can give information on past climate, species diversity, and human intervention in forests and landscapes. In the present work, we undertook an anthracological analysis along with the ¹⁴C dating of charcoal fragments using accelerator mass spectrometry (AMS). Charcoal samples from forest soils collected from seven different locations in the Amazon Basin were taxonomically classified and dated. Out of the 16 groups of charcoal fragments identified, five contained more than one taxonomic type, with the Fabaceae, Combretaceae and Sapotaceae families having the highest frequencies. ¹⁴C charcoal dates span ∼6000 years (from 6876 to 365 yr BP) among different families, with the most significant variation observed for two fragments from the same sampling location (spanning 4000 ¹⁴C yr). Some sample sets resulted in up to five different families. These findings demonstrate the importance of the association between anthracological identification and radiocarbon dating in the reconstruction of paleo-forest composition and fire history.     

Age determination for a Neolithic site in northeastern Qinghai-Tibetan Plateau using a combined luminescence and radiocarbon dating

The archaeological Shaliuheqiaodong site, located at the junction between the estuary of Shaliu River and the northeast bedrock terrace of Qinghai Lake, is one of the earliest Neolithic Age sites in the Qinghai-Tibetan Plateau (QTP), which is critical for understanding patterns of prehistoric human inhabitation in the high plateau extreme environments. There are only two published radiocarbon ages by far for chronological control. Recently, a new section (Gangcha section) was found, with abundant charcoals and fish bones well-preserved in the matrix of aeolian sediments, providing a good opportunity for a combined study of luminescence and radiocarbon dating. In the current study, we obtained three luminescence ages on aeolian sediment, six radiocarbon ages (three on charcoals and three on fish bones). Our results showed that the luminescence ages (average of 3.2 ± 0.2 ka) are in agreement with charcoal radiocarbon ages (3165–3273 cal a BP) where applicable, and that the lake reservoir effect age of radiocarbon dating was approximately 0.3–0.7 cal ka BP and an average of 0.4 cal ka BP at ∼3.2 cal ka BP (age difference between that of charcoals and fish bones). The prehistoric residence in Qinghai Lake area seemed to be sequenced from 15 ka BP to 3.1 ka BP, based on our data and previously published data altogether. The obvious baked vestiges on the bones of fish and animals, as well as a number of artifacts, indicate that naked carps had become a food resource for prehistoric people at least since 3.2 cal ka BP.     

海原断裂带刺儿沟古地震剖面炭屑~(14)C年龄及其意义

在青藏高原东北缘海原断裂带刺儿沟古地震剖面上不仅保存了地震活动的崩积楔遗迹,还发现多层炭屑以及与人类活动有关的铁渣、陶片等遗物,文中运用14C测年法和经红外释光照射后的绿光释光测年法(Post-IR OSL)分别对剖面上的炭屑、烘烤黏土、沉积物等样品进行年龄测定和比对,获得了各炭屑层和人类活动遗迹的年代。测定的人类活动遗迹年代与海原周缘历史记载的强震发生时间序列比对结果表明,刺儿沟人类活动遗迹的形成可能与历史地震无关,过去以炭屑年代作为地层年代来限定古地震发生的时代,建立的古地震事件时序的结果可能不正确,上述工作为进一步研究海原断裂带的强震复发规律和海原地区考古提供了重要的基础资料     

Dating alluvial deposits with optically stimulated luminescence, AMS C and cosmogenic techniques, western Transverse Ranges, California, USA

In an effort to better understand chronology of alluvial episodes in Cuyama Valley in the western Transverse Ranges of California, USA, we employed optically stimulated luminescence, radiocarbon and cosmogenic radionuclide surface exposure dating methods. Twenty-one optical dates ranging from 0.01 to 27 ka were obtained from exposures of late-Holocene axial-fluvial deposits, Pleistocene–Holocene alluvial-fan deposits, and axial-fluvial sands interbedded within a late Pleistocene alluvial fan. These were cross-checked with 37 AMS radiocarbon dates from charcoal and wood from within a and five ¹⁰Be surface exposure dates from boulders on alluvial-fan surfaces. The OSL results show generally good stratigraphic consistency, logical comparison with the radiocarbon and cosmogenic data, and appear to be the best method for accurate dating within deposits of this nature because suitable material is fairly easy to find in these environments. The radiocarbon data contained numerous “detrital ages”, but well-bedded lenses of apparently in situ or minimally transported charcoal provide reliable age estimates for the associated alluvium. Radiocarbon dating of detrital charcoal in the older alluvial fan deposits was problematic. Our cosmogenic surface-exposure dating was consistent stratigraphically and with our other data, but we were unable to determine its accuracy due to the limited number of samples and the possibility of inherited radionuclides and post-depositional erosion. In light of our results, we suggest that OSL dating using the latest analytical techniques combined with rigorous methods for estimation of paleodase is reliable and of increasing utility in otherwise difficult-to-date coarse alluvial environments in the southwestern United States and elsewhere.     

Exploring the dating of “dirty” speleothems and cave sinters using radiocarbon dating of preserved organic matter

Speleothems and other carbonate deposits such as tufa containing high proportions of detrital material can be difficult to chemically date due to detrital thorium levels causing a high level of error in conventional U-Th disequilibrium dating. Here we investigate the use of an alternative technique centring on radiocarbon dating of organic matter preserved within the detrital fraction. Non-acid soluble humic, particulate and detritally absorbed organic matter was recovered from eight samples from a flowstone sinter formed within a roman aqueduct at Trento in Italy with a maximum age of 100 CE (1850 cal yr BP), and two repeat samples from a dripstone formed within the 20th Century on a wire fence at Lilly-Pilly Cave, Buchan Caves Reserve in Victoria, Australia. In the aqueduct samples the median calibrated ¹⁴C ages ranged from 2232 to 2889 cal yr BP, with 95.4% probability age range in the youngest and oldest samples of 2153–2337 and 2342–3449 cal yr BP respectively. The median age of the more modern dripstone was 336 cal yr BP, with a 95.4% probability age range of 148–486 cal yr BP. These results provide very approximate ball-park estimates of the age of the sample, but are consistently too old when compared to the known maximum ages of formation. It is hypothesised that this offset is due to a combination of the nature of the organic carbon transported from the source organic matter pools, and reworking of both modern and old organic carbon by in situ microbial communities.     

Characterization of organic matter in marine sediments to estimate age offset of bulk radiocarbon dating

Radiocarbon dating of Arctic marine sediment is often challenging due to the low availability of calcareous fossils. Consequently, bulk organic matter dating has at times been used to establish sediment core chronologies. Yet, radiocarbon dates based on bulk organic matter often appear to deviate vastly from dates based on fossils, mainly caused by input of allochthounous carbon, including terrigenous organic matter. In this study, we aim to examine the link between the composition of the bulk organic matter and the age offsets between the bulk radiocarbon dates and those obtained from calcareous foraminiferal tests. All samples are taken from the marine sediment core AMD14-204C from offshore Upernavik (eastern Baffin Bay). The radiocarbon dates for bulk organic matter are on average ∼3000 years older than the radiocarbon dates based on foraminifera, but with changing age offsets throughout the record. To investigate the cause of this age offset and its variations over time, we applied core scanning, X-ray Fluorescence analysis, stable isotopes, organic pyrolysis and microscopic organic petrology to examine the distribution and characterization of the organic matter. The results show that the older organic matter includes clastic input of reworked sedimentary rocks potentially originating from West Greenland and/or the Canadian Arctic Archipelago. Changes in the input of contemporary marine algal produced organic matter versus both terrigenous input and reworked ancient organic matter appear to control the age offsets between the bulk and foraminifera dates. A low Hydrogen Index and low δ¹³C_org values together with a high Oxygen Index, indicative of high influence of terrigenous organic matter, seem to correspond to samples with the largest age offsets; 1000–2000 years greater than in other samples. To examine the cause of the variations in the age offsets, a new quantification of the autochthonous organic matter as a fraction of the TOC was calculated. This shows that samples with the largest age offsets contained the lowest fraction (as low as ∼12%) of autochthonous organic matter in the TOC.     

Advances and limitations in establishing a contiguous high-resolution atmospheric radiocarbon record derived from subfossil kauri tree rings for the interval 60–27 cal kyr BP

Radiocarbon dating is the most widely applied and reliable dating technique for providing chronological control during Marine Isotope Stage 3 (MIS3; ∼60–27 cal kyr BP). Past variations in the atmospheric concentration of radiocarbon mean a calibration curve is required. IntCal20 and SHCal20 calibration curves covering MIS3 are presently largely based on non-atmospheric records which, in combination with larger radiocarbon (¹⁴C) dating uncertainties, results in significant smoothing and reduced resolution in calibration curve structure. Floating tree ring radiocarbon chronologies that are wiggle-matched to other palaeo records (particularly to Hulu Cave speleothems) have the potential to provide detailed structure to the MIS3 portion of extant calibration curves. New Zealand subfossil kauri (Agathis australis) trees are long-lived and are useful for constructing temporally-floating MIS3 atmospheric radiocarbon datasets. This paper presents extant and emerging data from several important Northland subfossil kauri locations (Omaha, Babylon Coast, Bream Bay, Kai Iwi Lakes, Mangawhai). We show the span of seven floating MIS3 kauri sequences (individual trees and chronologies) from which sequential radiocarbon series covering a total of 7556 years is now in development (representing 23% of the period 60–27 cal kyr BP). We also report radiocarbon dates for an additional 34 ancient kauri from MIS3 that can provide additional coverage. After these floating subfossil wood sequences have been produced, close to 40% of MIS3 (12,420 years) will be covered by contiguous subfossil kauri radiocarbon measurements. Based on our findings, we discuss the prospects and limitations for obtaining a highly resolved and precise atmospheric radiocarbon calibration curve comprehensively covering MIS3 using subfossil kauri.     

Age modelling of late Quaternary marine sequences in the Adriatic: Towards improved precision and accuracy using volcanic event stratigraphy

The first part of this paper presents a review of the problems that constrain the reliability of radiocarbon-based age models with particular focus on those used to underpin marine records. The reasons why radiocarbon data-sets need to be much more comprehensive than has been the norm hitherto, and why age models should be based on calibrated data only, are outlined. The complexity of the probability structure of calibrated radiocarbon data and the advantages of a Bayesian statistical approach for constructing calibrated age models are illustrated. The second part of the paper tests the potential for reducing the uncertainties that constrain radiocarbon-based age models using tephrostratigraphy. Fine (distal) ash layers of Holocene age preserved in Adriatic prodelta sediments are analysed geochemically and compared to tephras preserved in the Lago Grande di Monticchio site in southern Italy. The Monticchio tephras have been dated both by radiocarbon and varve chronology. The importance of basing such comparisons on standardised geochemical and robust statistical procedures is stressed. In this instance, both the Adriatic and Monticchio geochemical measurements are based on wavelength dispersive spectrometry, while discriminant function analysis is employed for statistical comparisons. Using this approach, the ages of some of the Adriatic marine ash layers could be estimated in Monticchio varve years, circumventing some of the uncertainty of radiocarbon-based age models introduced by marine reservoir effects. Fine (distal) ash layers are more widespread and better preserved in Mediterranean marine sequences than realised hitherto and may offer much wider potential for refining the dating and correlation of Mediterranean marine sequences as well as marine-land correlations.