Sedimentary and crystalline rock formations are currently being intensely investigated in several countries as potential host rocks for deep geological repositories for radioactive wastes. An important aspect of investigations is to characterise and understand the movement and compositions of water in these rocks—both mobile groundwater in aquifers and faults/fractures, and immobile porewater in the matrix of intact rock. Non-reactive solutes, primarily Cl and Br, water isotope ratios, and dissolved helium are ‘natural tracers’ of diffusive transport and exchange between groundwater and porewater. Recent developments of techniques for extracting and analysing porewaters from carefully preserved drill cores are summarised in this paper. It identifies practical challenges and suggests best practice strategies based on experience gained by various national research and repository programs in crystalline and sedimentary rocks.

A recently completed deep drilling campaign, comprising 9 deep boreholes penetrating the Mesozoic sedimentary sequence of northern Switzerland, yielded >6 km of drillcore. One of the main objectives was to characterise the low-permeability sequence with the lower Jurassic Opalinus Clay in its centre, motivated by the site selection for a deep geological repository for radioactive waste. In this context, the chemical and isotopic composition of the porewater, as well as the mineralogical and petrophysical properties of the rocks, were among the main study targets. In this paper, the main objective was the characterisation of the lithologically diverse Jurassic rock sequence with focus on mineralogy, porosity and pore-space architecture. Given the large amount of data, a well constrained relationship between clay content (relating to fine-grained sheet-silicate minerals) and porosity could be established. Porosity increases with clay content along a concave curve, but in detail minor formation-specific differences of the positions relative to the best-fit curve were identified. These are attributed to the highly variable deposition rates that resulted in different times available for early diagenesis to alter the rock fabric by mineral dissolution and cementation, thereby affecting the compaction behaviour. Pore-size distributions were obtained from N-2 ad-/desorption isotherms. A distinct peak at a radius of 3 nm can be clearly correlated with clay minerals, whereas limestones are dominated by pore sizes in the range of 40-100 nm, and marls show intermediate distributions. A conceptual framework is proposed distinguishing a nanometric porosity that is proportional to the clay content and a contribution of larger pores that are related to the geometric incompatibility between platy clay minerals and isometric calcite or quartz. The contribution of these larger pore is thought to explain the curvature of the clay content-porosity relationship and the more limited compaction of the clay in pressure shadows adjacent to the larger grains. A number of outliers towards high porosity at a given clay content were identified in oolites (most strongly in Fe-rich oolites), sandstones and a unit containing coral-reef material. All these units have in common the presence of competent calcite or quartz grains at the time of deposition, leading to grain-supported fabrics and therefore to a more limited compaction in the interstitial pore space.

Helium concentrations and He-3/He-4 ratios were measured on porewater extracted from the low-permeability rock matrix and groundwater in bounding aquifers in Northern Switzerland. The samples were collected from six deep boreholes, which were drilled across the Tertiary Molasse and the underlying Mesozoic sediments at three different study areas within the context of Nagra's deep drilling programme for the underground disposal of radioactive waste. Porewater helium data obtained from each borehole at high spatial resolution describe continuous profiles over multiple aquifer-aquitard intervals across the Jurassic to Triassic sediment sequence. Given the lateral distribution of the investigated areas (similar to 20 km apart) and having two boreholes in each area (a few km apart), this allows to investigate both vertical and lateral changes of He in the porewater and groundwater system at high resolution and over large scales. In the about 300-400 m thick Dogger-Lias aquitard sequence including the Opalinus Clay, porewater He concentrations are nearly identical and have very similar He-3/He-4 signatures in all boreholes. This suggests a common history in the development of these systems despite the boreholes being located in three study areas with different hydrogeological setting and tectonic history since their last burial and diagenesis. Proximal to the groundwaters, He profiles show that the porewater system is controlled by diffusive redistribution of in-situ produced He from high concentrations in the aquitards towards lower concentrations in the bounding groundwaters. At some locations, the influence of evaporitic strata with very low diffusivity acting as transport barriers becomes obvious. Close to the aquitards, differences between the profile shapes of helium and other conservative tracers such as delta H-2 in the different boreholes and areas indicate different boundary conditions for the different tracers over the more recent geological past, as well as, for some boreholes, the potential contribution of helium from the groundwater to the porewater in the nearby low-permeability rock matrix. In one study area, cross-formation transport of helium could be identified close to a deep reaching tectonic structure related to the Hegau-Lake Constance fault system. This basement derived gas is subsequently laterally distributed via groundwater in the different aquifers and influences the porewater of the adjacent aquitard formations, as evidenced by the helium concentrations and He-3/He-4 ratios in the groundwater and porewater in the two boreholes of this siting area.

Bentonite is a common backfill material used in Engineered Barrier Systems (EBS) for radioactive waste disposal. Its thermal, hydraulic, and chemical properties have been extensively studied. However, empirical evidence on the interactions with the free gas phase present in its pore space under conditions close to those prevailing in deep geological repositories (i.e., exposure to multiple gas species at temperature and humidity conditions close to those of freshly backfilled EBS) is scarce. This limits the prediction/assessment of the evolution of the gas composition in EBS. Here we present the outcome of laboratory experiments targeting such gas-bentonite interactions using two different types of bentonite (Italian bentonite; Wyoming bentonite) being exposed to atmospheric air in sealed stainless-steel vessels. The results indicate that gas sorption on bentonite can occur at repository-like conditions and is likely to play a significant role in the overall gas dynamics in the backfill of EBS. Drying of both bentonites was shown to partly re-activate their CO2 sorption capacity during a subsequent re-hydration phase. Furthermore, the grinding of Wyoming bentonite resulted in the generation of new pyrite surfaces that significantly enhanced O2 removal from the free gas phase by oxidation. Our initial investigations call for more systematic and extensive series of laboratory experiments in order to quantitatively constrain the different processes involved in gas-bentonite interactions.

Optically stimulated luminescence (OSL) dating of single grains is often required to determine an accurate age for partially-bleached sediment by identifying those grains with OSL signals that were well bleached prior to burial. However, single-grain De distributions are typically characterised by greater amounts of scatter in comparison to multiple grains. Here we investigate the scatter in single-grain De distributions of quartz from 56 proglacial samples associated with the retreat of the last British-Irish Ice Sheet. Our findings provide the first empirical dataset showing that beta-dose heterogeneity can impact the extrinsic scatter in single-grain De distributions, in addition to partial bleaching in nature. The additional scatter in single-grain De distributions caused by beta-dose heterogeneity suggests that it is inappropriate to apply a fixed threshold to determine between well-bleached and partially-bleached De distributions, but the skewness of the De distributions could alternatively be used. Autoradiography and QEMSCAN analyses show that there was a negative relationship between the relative standard deviation (RSD) of the beta-dose heterogeneity and the beta dose-rate. This relationship offers the opportunity to infer the RSD of the beta-dose heterogeneity for each sample using just the beta dose-rate, instead of acquiring empirical data for every sample. For this large suite of sedimentary samples, we observe a minimum OD of 20% arising from the effects of beta-dose heterogeneity (Fig. 3e), which should be added (in quadrature) to the intrinsic OD to determine σb for the minimum age model (MAM) to calculate accurate OSL ages and prevent underestimation of the burial age.

Helium concentrations and 3He/4He isotope ratios of porewater, groundwater and rock were measured on samples collected from a Jurassic sediment sequence at the Mont Terri underground rock laboratory (Northern Switzerland). Porewater He data of rock samples collected from borehole BDB-1 at high spatial resolution across a karstic limestone unit (Passwang Formation) into the underlying claystone sequence (Opalinus Clay, Staffelegg Formation) describe a continuous profile from the water-conducting zone in the limestone into the clay-rich rocks of low permeability. Concentrations of 4He, 3He and their parent nuclides in the rock allow calculating in-situ production and accumulation terms. Since the time of sedimentation, 90%–97% of the in-situ produced 4He has been released to the porewater. Today only 2.5% of the maximum possible accumulated 4He is still retained in the porewater while the major part of in-situ produced 4He was removed from the system presumably by porewater–groundwater exchange. The porewater 4He concentrations show a diffusion profile from the aquitard towards the aquifer, reflecting a) a transient state between 4He in-situ production and porewater–groundwater exchange, b) a transient state from previously higher 4He concentrations in the porewater, and c) a spatially variable boundary in the karstic limestone unit. Evolutionary models of porewater 4He concentration profiles in combination with constraints from independent chemical and isotopic tracers allow deciphering a complex palaeo-hydrogeological history of the system over about the last 30 ka. A local excursion from the general profile towards higher 4He concentrations and 3He/4He ratio in a limestone layer in the Opalinus Clay cannot be further constrained in time based on the present sample frequency, but appears to represent a hydrogeological signal.

The Jurassic clay-rich aquitard sequence underlying the Swiss Molasse Basin is locally penetrated by unusually frequent veins consisting of calcite +/- celestite, in particular in the Schlattingen-1 and Oftringen drill cores. The veins are linked to extensional brittle structures, with shear senses ranging between dip-slip and strike-slip. Deformation triggered transient and localised events of fluid flow within the aquitard followed by sealing of the structures by the vein minerals. Vein calcite was dated by LA-ICP-MS analysis using the U/Pb method. While this was a demanding undertaking, given the low U and high common Pb contents of calcite, 9 significant ages could be obtained. Two groups of ages can be distinguished, namely 31-39 and 11-18 Ma. Both age groups are consistent with the known regional tectonic evolution. The older age group corresponds to the main phase of rifting in the Upper Rhine Graben, a major crustal discontinuity, whose effects were not limited to the graben proper but affected large parts of the Molasse Basin. The younger age group is linked to crustal tilting and related extensional deformation. Isotopic compositions of O and C in vein calcite from the Schlattingen-1 core show substantial variability but do not discriminate between veins of the two age groups. In contrast, Sr-87/Sr-86 ratios in veins show different signatures. The depth trend of Sr-87/Sr-86 ratios in veins fits well with that in pore water obtained by rock squeezing. The two data sets define a trend of values increasing with depth, connecting the current values in the embedding Malm and Keuper aquifer waters. This trend is best explained as a near-steady-state diffusion profile. While advective mixing of waters originating from the embedding aquifers to produce the veins, implying structures that cross cut the whole low-permeability sequence, cannot be discarded on the basis of existing data, it is considered more likely that the veins have local fluid sources. These are mixtures of local pore water with a possible contribution of water from the nearest aquifer, implying maximum vertical advection distances in the order of 50-100 m.

The present study focuses on the geochemical characterisation of porewater solutes in the Opalinus Clay at the Mont Terri URL. The investigations were carried out within the Mont Terri Project DB-A Experiment (Deep inclined borehole across the Opalinus Clay) conducted by an international consortium. At the Mont Terri URL, borehole BDB-1 is the first borehole that crosscuts the Opalinus Clay in its entire thickness. Borehole BDB-1 cuts across the Jurassic sediment sequence of low-permeability rock, from the Hauptrogenstein, across the Passwang Formation (Fm) and the Opalinus Clay, and into the rocks of the Staffelegg Formation (Fm). This allowed, for the first time, collection of porewater samples at a high spatial frequency. Furthermore, all samples experienced the same history in drilling, sampling and laboratory treatment. This facilitates identification of artefacts induced by indirect porewater characterisation techniques and allows improved interpretation of the data in terms of porewater evolution as a function of space and time. In addition, groundwater could be collected from a water-conducting zone in the Passwang Fm at 58.6m BHL, but was not encountered in the lithologies in the footwall of the Opalinus Clay. The different natural tracers in the porewater (Cl–, δ37Cl, Br–, δ18O, δ2H, He, 3He/4He, Ar) all describe well-defined concentration profiles from the Staffelegg Fm across the Opalinus Clay into the Passwang Fm. The concentration profiles of all tracers indicate diffusion as the dominant solute transport process across the Opalinus Clay. These findings are in accordance with previous work conducted at the Mont Terri URL (Pearson et al., 2003; Mazurek et al., 2009, 2011). In the rocks of the Passwang Fm, the tracer concentrations display more complex profiles that are, at least, partly due to the poor knowledge about anion-accessible porosity in the low clay-content rocks. Chemical compounds and noble gas concentrations indicate local minima at locations closer to the Opalinus Clay than the present-day water-conducting zone. These local minima are also observed in isotope and ion-ion ratios, independent of any porosity value, and are interpreted to have acted at some time in the past as boundary conditions for the solute exchange between the Opalinus Clay and the Passwang Fm. Quantification of the 4He concentration profile suggest that these old boundaries may have been active until a few tens to a hundred thousand of years ago. Ion-ion ratios in aqueous extract solutions reveal similarly well-defined profiles across the Opalinus Clay into the Passwang Fm. Ratios of Br/Cl and SO4/Cl are below and above, respectively, those of modern seawater. Consistent with all natural porewater tracers, these ratios are best explained by long-term exchange between porewater in the Opalinus Clay with porewater or groundwater in the Triassic evaporite sequences underlying the Opalinus Clay. This contrasts previous interpretations, which assumed residual seawater as the main origin of solutes in porewater of the Opalinus Clay (e.g. Pearson and Waber, 2001; Pearson et al., 2003; Mazurek and de Haller, 2017). It is, however, not in conflict with the most recent history of tracer profile evolution over the last few millions of years (e.g. Mazurek et al., 2009, 2011). The present data, combined with geochemical modelling, indicate that the SO42– concentrations obtained by aqueous extraction are compatible with the geochemical properties of the Opalinus Clay rocks (such as the cation exchange properties and mineral equilibria) when compared to SO42– concentrations obtained by high-pressure squeezing and water accumulated over long time periods from boreholes, where potential for oxidation exists prior to analysis. It is concluded, that the SO42– concentration obtained from aqueous extraction serves as a suitable proxy for the in-situ porewater SO42– concentration. For future modelling of the porewater composition of the Opalinus Clay at Mont Terri, it is recommended to use the SO4/Cl ratio obtained in cautiously prepared aqueous extract solutions instead of the seawater SO4/Cl ratio or fixation of the SO42– concentration by mineral solubility controls.

Reliable age dating of coastal sedimentary landforms is crucial for inferring storm frequencies and magnitudes from geological archives. However, in highly energetic coastal settings, radiocarbon dating is often biased by reworking and/or poorly constrained marine reservoir effects. Due to this, most cyclone-driven sediment archives from the semiarid coast of NW Australia – a region frequently affected by tropical cyclones but with a historical record limited to ∼150 a, and therefore strongly in need of long-term data inferred from geological evidence – are affected by chronological inaccuracies. Optically stimulated luminescence dating (OSL) may overcome these shortcomings by dating the transport of sediment directly. In turn it may be related to other challenges when applied to cyclone deposits from semiarid environments. The cyclone-induced washover fans at Point Lefroy, NW Australia, are composed of a heterogeneous mixture of coral fragments, shell hash and siliciclastic sand. This makes them particularly prone to high dose scatter resulting from a combination of partial bleaching, sediment mixing and dose-rate heterogeneity. The washover fans are further characterised by a discontinuous nature of cyclone deposition, as indicated by erosional features and macroscopic brunification horizons. By using a combination of quartz single grain dating, autoradiography, alpha counting and gamma spectrometry, sediment mixing and dose rate heterogeneity are identified as the main sources of dose scatter. The resulting chronology allows us to discriminate at least four well constrained phases of washover fan activity at ∼180, ∼360, ∼870, and ∼1300 a ago. Older but less well constrained activity phases occurred ∼1950, ∼2300, and ∼2830 a ago. While these phases of increased cyclone activity correlate with depositional units separated by potential palaeosols, OSL ages, quasi-continuous portable OSL reader measurements and gamma spectrometry measured with increased sampling resolution point to deposition of distinct washover units within a very short period of time. However, unambiguous discrimination between deposition of individual units by single events and deposition by several cyclones within periods of only a few decades is currently not possible.

The development of a combined experimental-modelling approach has enabled to constrain the porewater chemistry of different low-permeability clay formations (Boom Clay, Callovo-Oxfordian Fm., Opalinus Clay) foreseen as host rocks for nuclear waste repositories. A variety of methods are available to directly sample porewater or to derive information on the solute concentrations. These include analysis from seepage waters in boreholes, aqueous extractions, high-pressure squeezing, and advective displacement from core samples. Geochemical equilibrium modelling is used for data integration and calculation of internally consistent reference water compositions. The paper provides an overview of current achievements in experimental developments, modelling approaches and open questions.

Dissolved noble gases in matrix porewaters of low-permeable crystalline rocks are useful tracers for investigating porewater migration and interactions between porewater and groundwater. Samples from the 1160m deep OL-KR56 borehole, drilled at the Olkiluoto site (southwestern Finland), have been analysed for concentrations and isotope signatures of helium in porewater, groundwater and in the rock matrix. These are the first 3He/4He ratios combined with 4He concentrations in porewaters and rocks from the Fennoscandian Shield. High 4He porewater concentrations suggest long porewater residence times, while concentration differences of one order of magnitude between porewater and groundwater indicate a transient state between these reservoirs. Concentrations of 4He in porewater show small variations with depth, which are mimicked in the concentrations of conservative chemical tracers as well as in 4He concentrations of groundwaters from various regional boreholes. 3He/4He ratios in porewaters are higher than in the rock matrix, requiring either fractionation during redistribution of He between these reservoirs or the addition of an isotopically light component.

The geochemistry of an argillaceous rock sequence from a deep borehole in NE-Switzerland was investigated. The focus was to constrain the porewater chemistry in low permeability Jurassic rocks comprising the Liassic, the Opalinus Clay formation, the ‘Brown Dogger’ unit and the Effingen Member (Malm). A multi-method approach including mineralogical analysis, aqueous and Ni-ethylenediamine extraction, squeezing tests and pCO2 measurements as well as geochemical modelling was applied for this purpose. A consistent dataset was obtained with regard to the main solutes in the porewaters. A fairly constant anion-accessible porosity of ~50% of the total porosity was deduced for all analysed samples which displayed variable clay-mineral contents. Sulphate concentrations were shown to be constrained by a sulphate-bearing phase, presumably by celestite or a Sr–Ba sulphate. Application of a simple equilibrium model, including cation exchange reactions, calcite and celestite equilibrium showed good agreement with squeezing data, indicating the suitability of the modelling approach to simulate porewater chemistry in the studied argillaceous rocks. The modelling highlighted the importance of correct determination of the exchangeable cation population. The analysis corroborates that squeezing of the studied rocks is a viable and efficient way to sample porewater.

It is important to evaluate the porewater chemistry of argillaceous host rocks for safety assessment because it affects radionuclide migration. The nanometric pore-space architecture and the resulting very low hydraulic conductivity, however, make the sampling and characterisation of porewater chemistry a difficult task. Thus, in order to understand and reduce uncertainties induced by sampling and experimental disturbances, a multi-method strategy is generally required. Here a combined experimental and modelling approach is presented for the analysis of the porewater chemistry in a rock sequence comprising Opalinus Clay and so-called confining 'Brown Dogger' and Staffelegg Fm. (Liassic). The data was obtained from analyses on drillcores of a deep borehole at Schlattingen (NE Switzerland). The studied rock sequence can be roughly divided into four units: The top unit (∼25 m thick) corresponds to the lower part of the Effingen Member (Malm) and is made up of silty to sandy calcareous marls. The underlying unit (∼77 m thick), termed 'Brown Dogger', exhibits rather variable lithology. It consists predominantly of clayrocks and marls with variable contents of calcite and quartz. The third unit is the ∼120 m thick Opalinus Clay, which is characterized by fairly homogeneous silty to fine sandy clayrocks. The lowest unit (Staffelegg Fm., ∼53 m thick) is also rather rich in clay minerals and consists of a variable sequence of marls, clayrocks and few limestone beds. Only the three lower units were considered for porewater chemistry modelling. Experimental: Rock core samples representative for the overall lithology of the corresponding stratigraphic unit were taken about every 5 m, sealed on-site according to a standardized protocol to protect them from oxidation and evaporation, stored cool and sent to the laboratory for subsequent analyses. Mineralogical compositions, water contents and density measurements were obtained for 30 samples. From water contents and grain density, water-loss porosity was derived. Aqueous leachates were prepared at a solid/liquid (S/L) ratio of 1, with contact times of 48 h. Cation exchange properties were studied using the Ni eythylenediamine method at S/L = 1. All procedures, except for milling, were carried out under N 2 atmosphere in a glovebox. Squeezing tests were conducted on 12 selected clay-rich samples. Porewaters were extracted at 200 to 500 MPa, but only data from the lowest squeezing pressure of 200 MPa are reported here. Porewater was also extracted with the advective displacement technique from a core sample of the 'Brown Dogger' unit. CO 2 partial pressure measurements were carried out on well-preserved cores in gas cells. Model setup: The aim of the modelling was to simulate porewater compositions using primarily chloride data from leachates and exchangeable cation data and to compare these with the data from squeezing and advective displacement. Leachate chloride data was recalculated to in-situ porosity by considering water contents and a uniform anion-accessible porosity of 0.5. The latter was based on the comparison of leachate and squeezing data (Wersin et al. 2012). Furthermore, pCO 2 as obtained from pCO 2 measurements was considered as input. The applied thermodynamic model was based on the studies of Pearson et al. (2011) and Gaucher et al. (2009). A base case and several variant cases were defined, all of which assumed equilibrium with calcite, omnipresent in the rock sequence. Further, sulphate equilibrium with respect to celestite or a CaSO 4 phase was considered. The uncertainty in pCO 2 was addressed by variation in pCO 2 in a specific model case.

Characterization of dissolved CO2 and alkane gas in clayrocks may help assessing the confinement properties of geological barriers considered as potential host rocks for a deep geological disposal as well as for caprocks of gas storages.A monitoring of alkanes with CO2, combined with carbon isotopes was performed on core samples coming from Underground ResearchLaboratories (Bure, Mont Terri, Tournemire) and the Schlattingen borehole in France and Switzerland. Compositionof hydrocarbon gas and δ13Cof methane strongly suggest a dominant thermogenic origin of methane which ismixed with a bacterial origin for the Toarcian shales, Pliensbachien and Callovian-Oxfordian clayrocks. Results also evidence the contrasted behavior of CO2, which is controlled by chemical equilibrium between pore water and carbonate mineralogy, compared to the alkanes which are present in the porosity as a stock of dissolved gases which can be depleted during degassing experiments.

The Quaternary Vakinankaratra volcanic field in the central Madagascar highlands consists of scoria cones, lava flows, tuff rings, and maars. These volcanic landforms are the result of processes triggered by intracontinental rifting and overlie Precambrian basement or Neogene volcanic rocks. Infrared-stimulated luminescence (IRSL) dating was applied to 13 samples taken from phreatomagmatic eruption deposits in the Antsirabe–Betafo region with the aim of constraining the chronology of the volcanic activity. Establishing such a chronology is important for evaluating volcanic hazards in this densely populated area. Stratigraphic correlations of eruption deposits and IRSL ages suggest at least five phreatomagmatic eruption events in Late Pleistocene times. In the Lake Andraikiba region, two such eruption layers can be clearly distinguished. The older one yields ages between 109 ± 15 and 90 ± 11 ka and is possibly related to an eruption at the Amboniloha volcanic complex to the north. The younger one gives ages between 58 ± 4 and 47 ± 7 ka and is clearly related to the phreatomagmatic eruption that formed Lake Andraikiba. IRSL ages of a similar eruption deposit directly overlying basement laterite in the vicinity of the Fizinana and Ampasamihaiky volcanic complexes yield coherent ages of 68 ± 7 and 65 ± 8 ka. These ages provide the upper age limit for the subsequently developed Iavoko, Antsifotra, and Fizinana scoria cones and their associated lava flows. Two phreatomagmatic deposits, identified near Lake Tritrivakely, yield the youngest IRSL ages in the region, with respective ages of 32 ± 3 and 19 ± 2 ka. The reported K-feldspar IRSL ages are the first recorded numerical ages of phreatomagmatic eruption deposits in Madagascar, and our results confirm the huge potential of this dating approach for reconstructing the volcanic activity of Late Pleistocene to Holocene volcanic provinces.

A combination of two autoradiography methods was applied to investigate the radionuclide distribution patterns in a range of different silices. We obtained greyscale images (β-radiation) and α-track patterns for qualitative assessment, and used a statistical approach to quantify the degree of uniformity of the radiation fields. It was found that almost all samples are poor in potassium, thorium and uranium, and that locally high concentrations are present only in dark-coloured veins and inclusions. Statistical analyses reveal evidence of radionuclide clustering in more than half of the 21 specimens. Concerning thermoluminescence dating of burnt lithics, such gradients should be taken into account to improve precision and accuracy in cases where the external radiation is not strongly dominating for the sample under consideration.

Diepkloof Rock Shelter offers an exceptional opportunity to study the onset and evolution of both Still Bay (SB) and Howiesons Poort (HP) techno-complexes. However, previous age estimates based on luminescence dating of burnt quartzites (Tribolo et al., 2009) and of sediments (Jacobs et al., 2008) were not in agreement. Here, we present new luminescence ages for 17 rock samples (equivalent dose estimated with a SAR-ITL protocol instead of classical MAAD-TL) as well as for 5 sediment samples (equivalent dose estimated with SAR-single grain OSL protocol) and an update of the 22 previous age estimates for burnt lithics (modified calibration and beta dose estimates). While a good agreement between the rock and sediment ages is obtained, these estimates are still significantly older than those reported by Jacobs et al. (2008). After our own analyses of the sediment from Diepkloof, it is suspected that these authors did not correctly chose the parameters for the equivalent dose determination, leading to an underestimate of the equivalent doses, and thus of the ages.From bottom to top, the mean ages are 100 +/- 10 ka for stratigraphic unit (SU) Noel and 107 +/- 11 ka for SU Mark (uncharacterized Lower MSA), 100 +/- 10 ka for SU Lynn-Leo (Pre-SB type Lynn), 109 +/- 10 ka for SUs Kim-Larry (SB), 105 +/- 10 ka for SUs Kerry-Kate and 109 +/- 10 ka for SU Jess (Early HP), 89 +/- 8 ka for SU Jude (MSA type Jack), 77 +/- 8 ka for SU John, 85 +/- 9 ka for SU Fox, 83 +/- 8 ka for SU Fred and 65 +/- 8 ka for SU OB5 (Intermediate HP), 52 +/- 5 ka for SUs OB2-4 (Late HP).This chronology, together with the technological analyses, greatly modifies the current chrono-cultural model regarding the SB and the HP and has important archaeological implications. Indeed, SB and HP no longer appear as short-lived techno-complexes with synchronous appearances for each and restricted to Oxygen Isotopic Stage (OIS) 4 across South Africa, as suggested by Jacobs et al. (2008, 2012). Rather, the sequence of Diepkloof supports a long chronology model with an early appearance of both SB and HP in the first half of OIS 5 and a long duration of the HP into OIS 3. These new dates imply that different technological traditions coexisted during OIS 5 and 4 in southern Africa and that SB and HP can no longer be considered as horizon markers. (C) 2012 Elsevier Ltd. All rights reserved.

The chloride and sulfate concentration profiles in a 260 m thick clay-rich Mesozoic sediment sequence have been analyzed by various methods. Chloride data generally indicate a good consistency between different methods if anion exclusion is accounted for in leaching tests. For sulfate, however, there is an apparent inconsistency between leaching data and those obtained from the other methods, which points to the dissolution of a sulfur-bearing mineral. Traces of diagenetic gypsum seem to be a likely source, but other sulfur minerals cannot be ruled out.

Thermoluminescence (TL) is routinely used to date heated lithic artefacts which mostly consist of silex (a mixture of amorphous opal and microcrystalline chalcedony). Analytical investigations of bulk samples confirmed that these materials contain considerable concentrations of radioactive elements, generating an internal dose rate contribution. Common dosimetric models assume the latter to be homogeneous throughout the sample. If this assumption would prove invalid, this will result in systematic errors in the calculated age, especially in the course of so called 'hot spots' of alpha-emitters (and associated local changes in a-sensitivity) and the dose response characteristics of alpha-radiation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of 22 silex samples are presented here, quantifying element concentrations at several tens analytical spots per sample. Along with radioactive elements (K, Rb, U, Th), another 21 major, minor and trace elements were measured in order to allow characterization of the impurities present in most of the samples. The dataset provides a detailed picture of the spatial distribution of radionuclides and hence of the uniformity of the internal alpha- and beta-dose rate. It is shown that the silex itself mostly contains low amounts of K (<0.1 wt.%), U (<1.0 mu g g(-1)) and Th (<0.4 mu g g(-1)), and dosimetrically negligible Rb concentrations. Systematically higher concentrations are obtained by ICP-MS measurements of the bulk samples. This matches with the finding that impurities (veins, inclusions) often yield significantly elevated radionuclide concentrations, up to two orders of magnitude higher than the silex values. These veins and inclusions, for example Ca or Mg carbonates and Fe-Mn-oxy-hydroxides, lead to steep gradients mainly in the internal alpha-radiation field. Alternative approaches are required to account for the non-uniform internal dose rate and improve the reliability of TL dates of problematic samples. (c) 2012 Elsevier B.V. All rights reserved.