Journal articles on the topic 'Dating method for rock surface exposures'

Abstract. In the last decades surface exposure dating using cosmogenic nuclides has emerged as a powerful tool in Quaternary geochronology and landscape evolution studies. Cosmogenic nuclides are produced in rocks and sediment due to reactions induced by cosmic rays. Landforms ranging in age from a few hundred years to tens of millions of years can be dated (depending on rock or landform weathering rates) by measuring nuclide concentrations. In this paper the history and theory of surface exposure dating are reviewed followed by an extensive outline of the fields of application of the method. Sampling strategies as well as information on individual nuclides are discussed in detail. The power of cosmogenic nuclide methods lies in the number of nuclides available (the radionuclides 10Be, 14C, 26Al, and 36Cl and the stable noble gases 3He and 21Ne), which allows almost every mineral and hence almost every lithology to be analyzed. As a result focus can shift to the geomorphic questions. It is important that obtained exposure ages are carefully scrutinized in the framework of detailed field studies, including local terrace or moraine stratigraphy and regional morphostratigraphic relationships; as well as in light of independent age constraints.

Schmidt-hammer rebound values ( R-values) enable relative-age dating of landforms, with R-values relating to degree of weathering and therefore length of exposure. This method – recently termed as Schmidt-hammer exposure-age dating (SHD) – was applied to date five rock glaciers (size range, 0.01–0.12 km2) and one recent rockfall deposit at the study area Schöderkogel-Eisenhut, in the Schladminger Tauern Range (14°03′E, 47°15′N), Austria. The rock glaciers consist of gneiss or high metamorphic series of mica-schist that are comparable in their R-values. Four of them are relict (permafrost absent) and one is intact (containing patches of permafrost). On each of the five rock glaciers, SHD was carried out at 4–6 sites (50 measurements per site) along a longitudinal transect from the frontal ridge to the root zone. Results at all five rock glaciers are generally consistent with each other sharing statistically significant R-values along transects. The range between the highest and the lowest mean R-value at each of the five rock glaciers is 9.9–5.2. Using rock glacier length and surface velocity data from nearby sites, the rock glacier development must have lasted for several thousand years. Furthermore, by using SHD results from rock glaciers of known age from other sites in the region with comparable geology, approximate surface ages of 6.7–11.4 ka were estimated. This indicates long formation periods for all five rock glaciers. Our results suggest that many of the 1300 relict rock glaciers in central and eastern Austria were formed over a long period during the Lateglacial and Holocene period.

AbstractThe 36Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the 36Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms 36Cl (g Ca)−1 yr−1 and are 228±18 atoms 36Cl (g K)−1 yr−1, respectively. The calculated ground-level secondary neutron production rate in air, Pf(0), inferred from thermal neutron absorption by 35Cl is 762±28 neutrons (g air)−1 yr−1 for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is ∼40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated 36Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated 14C ages, thereby supporting the validity of our 36Cl production rates integrated over the last ∼15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators.

AbstractDaylight radiation resets luminescence ‘clock’ to zero on rock surfaces, but transmission depends on the transparency of the rock. On burial, surfaces are no longer exposed to daylight and accumulation of trapped electrons takes place till the excavation. This reduction of luminescence as a function of depth fulfils the prerequisite criterion of daylight bleaching. Thus rock artefacts and monuments follow similar bleaching rationale as those for sediments. In limestone and marble, daylight can reach depths of 0.5–1 mm and up to 16 mm respectively, while for other igneous rocks e.g. quartz in granites, partial bleaching occurs up to 5mm depth under several hours of daylight exposures and almost complete beaching is achieved in the first 1 mm within about 1 min daylight exposure. The ‘quartz technique’ for limestone monuments containing traces of quartz enables their dating with Optically Stimulated Luminescence (OSL) techniques. The surface luminescence (thermoluminescence, TL or OSL) dating has been developed and further refined on various aspects of equivalent dose determination, complex radiation geometry, incomplete bleaching etc. A historical review of the development including important applications, along with some methodological aspects are discussed.

Lichenometry—a method developed by geologists for dating Holocene moraines and other landforms—has many potential applications in archaeology. Maximum-diameter lichenometry can suggest ages for features that were initially lichen-free, such as the moai of Easter Island, and rock surfaces exposed by toolstone quarrying. Size-frequency analysis can provide dates for structures built of lichen-covered rocks, such as game-drive walls and blinds, meat caches, and tent rings. Both methods require local calibration curves, best constructed by measuring lichens on substrata of known exposure age. Most lichenometric studies have involved yellow members of the crustose genus Rhizocarpon, which grow slowly and can live for as long as 10,000 years. Lichenometry has been particularly successful on siliceous rock types in arctic, subarctic, and alpine-tundra environments. The effects of wildfire and of competition from foliose lichens make the technique less well suited for forested terrain. Few data are available for tropical or desert environments or for calcareous substrata. The reliability of a lichenometric date will depend on the quality of the calibration curve, the size of the sample, the nature and postoccupational history of the substratum, and the ability of the archaeologist to recognize potential disturbance factors. An ecological perspective is essential. Known archaeological applications and problems are discussed.

Abstract. Cosmogenic exposure dating provides a method for estimating the ages of glacial moraines deposited in the last ~105 years. Cosmic rays break atoms in surface rocks at predictable rates. Thus, the ages of moraines are directly related to the concentrations of cosmic ray-produced nuclides in rocks on the moraine surfaces, under ideal circumstances. However, many geomorphic processes may interfere with cosmogenic exposure dating. Because of these processes, boulders sometimes arrive at the moraines with preexisting concentrations of cosmogenic nuclides, or else the boulders are partly shielded from cosmic rays following deposition. Many methods for estimating moraine ages from cosmogenic exposure dates exist in the literature, but we cannot assess the appropriateness of these methods without knowing the parent distribution from which the dates were drawn on each moraine. Here, we make two contributions. First, we describe numerical models of two geomorphic processes, moraine degradation and inheritance, and their effects on cosmogenic exposure dating. Second, we assess the robustness of various simple methods for estimating the ages of moraines from collections of cosmogenic exposure dates. Our models estimate the probability distributions of cosmogenic exposure dates that we would obtain from moraine boulders with specified geomorphic histories, using Monte Carlo methods. We expand on pioneering modeling efforts to address this problem by placing these models into a common framework. We also evaluate the sensitivity of the models to changes in their input parameters. The sensitivity tests show that moraine degradation consistently produces left-skewed distributions of exposure dates; that is, the distributions have long tails toward the young end of the distribution. In contrast, inheritance produces right-skewed distributions that have long tails toward the old side of the distribution. Given representative distributions from these two models, we can determine which methods of estimating moraine ages are most successful in recovering the correct age for test cases where this value is known. The mean is a poor estimator of moraine age for data sets drawn from skewed parent distributions, and excluding outliers before calculating the mean does not improve this mismatch. The extreme estimators (youngest date and oldest date) perform well under specific circumstances, but fail in other cases. We suggest a simple estimator that uses the skewnesses of individual data sets to determine whether the youngest date, mean, or oldest date will provide the best estimate of moraine age. Although this method is perhaps the most globally robust of the estimators we tested, it sometimes fails spectacularly. The failure of simple methods to provide accurate estimates of moraine age points toward a need for more sophisticated statistical treatments. We present improved methods for estimating moraine ages in a companion paper.

The production of radioisotopes at the Earth's surface by cosmic-ray effects has been discussed for many years. Only in the past few years, with the higher sensitivity provided by accelerator mass spectrometry (AMS) in detecting 10Be, 26A1 and 36Cl, have the radioisotopes produced in this way been measured. We report here our measurements of cosmogenic 14C in terrestrial rocks at high altitude, and comparisons to other exposure-dating methods.

AbstractLuminescence dating provides a direct age estimate of the time of last exposure of quartz or feldspar minerals to light or heat and has been successfully applied to deposits, rock surfaces, and fired materials in a number of archaeological and geological settings. Sampling strategies are diverse and can be customized depending on local circumstances, although all sediment samples need to include a light-safe sample and material for dose-rate determination. The accuracy and precision of luminescence dating results are directly related to the type and quality of the material sampled and sample collection methods in the field. Selection of target material for dating should include considerations of adequacy of resetting of the luminescence signal (optical and thermal bleaching), the ability to characterize the radioactive environment surrounding the sample (dose rate), and the lack of evidence for post-depositional mixing (bioturbation in soils and sediment). Sample strategies for collection of samples from sedimentary settings and fired materials are discussed. This paper should be used as a guide for luminescence sampling and is meant to provide essential background information on how to properly collect samples and on the types of materials suitable for luminescence dating.

Ossimo-Pat megalithic sanctuary (Valle Camonica, BS, Italy) is one of the most relevant archaeological findings of the southern alpine region, for the variety of its structures and the quality of its engraved monoliths. Its unique state of preservation gives the opportunity to apply the luminescence dating of the rock surface method. Here, we investigate the use of optically stimulated luminescence (OSL) for dating five cobbles from the site and compare cobble-surface derived ages to quartz OSL ages from sediments and to archaeological evidences. The obtained ages confirm the archaeological studies and open the way to a new hypothesis.

Dorn (1983) has proposed that changes in rock varnish chemistry can be used to date varnished artifacts. Specifically, he suggests that the varnish cation ratio, (K + Ca)/Ti, decreases as the age of the varnished surface increases. Although the method is generating significant archaeological interest, many of its underlying assumptions remain undemonstrated. This paper examines one premise of the method, that the varnishing process is regular. Data obtained from varnish distributional studies challenge this assumption and, when compared with the chemical data obtained from the same archaeological site, suggest that the cation-ratio dating technique may not be able to provide accurate dates for most varnished artifacts.

The surficial geology of the tectonically stable Bahamian archipelago preserves one of the most complete records of middle to late Quaternary sea-level-highstand cycles in the world. However, with the exception of deposits from marine isotope substage (MIS) 5e, fossil corals for radiometric dating of this rich stratigraphic sequence are rare. This study utilizes the previously published, independent lithostratigraphic framework as a testing ground for amino acid racemization in whole-rock limestone samples. At least six limestone–soil couplets provide a relative age sequence of events that encompass as many interglacial–glacial cycles. D-Alloisoleucine/L-isoleucine data fall into six clusters, or “aminozones.” On the basis of independent dating and the inferred correlation with global MIS, the ages of several aminozones are known, while the ages of others are calculated from calibrated amino acid geochronology. This study demonstrates the utility of the whole-rock aminostratigraphy method for dating and correlating widespread emergent marine deposits, constitutes the first regional geochronological framework for the Bahamas, and highlights major sea-level events over the past half million years.

Abstract There are many examples of buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating is a potential method which can be applied to dating such surfaces; as part of a research project which aims to develop such an approach, the degree of resetting of OSL signals in grains and slices from five different cobbles/boulders collected from a modern beach is investigated. All the rock surfaces are presumed to have been exposed to daylight for a prolonged period of time (weeks to years). Feldspar was identified as the preferred dosimeter because quartz extracts were insensitive. Dose recovery tests using solar simulator and IR diodes on both K-feldspar grains and solid slices taken from the inner parts of the rocks are discussed. Preheat plateau results using surface grains and slices show that significant thermal transfer in naturally bleached samples can be avoided by keeping preheat temperatures low. Equivalent doses from surface K-feldspar grains were highly scattered and much larger than expected (0.02 Gy to >100 Gy), while solid surface slices gave more reproducible small doses (mean = 0.17±0.02 Gy, n = 32). Neither crushing nor partial bleaching were found to be responsible for the large scattered doses from grains, nor did the inevitable contribution from Na-feldspar to the signal from solid slices explain the improved reproducibility in the slices. By modelling the increase of luminescence signal with distance into the rock surface, attenuation factors were derived for two samples. These indicate that, for instance, bleaching at a depth of 2 mm into these samples occurs at about ∼28% of the rate at the surface. We conclude that it should be possible to derive meaningful burial doses of >1 Gy from such cobbles; younger samples would probably require a correction for incomplete bleaching.

For the Altai Mountains’ region, especially the arid southeastern part of the Russian Altai, the data on glacier fluctuations in the Pleistocene and Holocene are still inconsistent. The study area was the Kargy River’s valley (2288–2387 m a.s.l.), a location that is not currently affected by glaciation and the glacial history of which is poorly studied. Field observations and geomorphological mapping were used to reveal the configuration of Pleistocene moraines. The relative dating method was applied to define the degree of weathering as an indicator of age. Three moraine groups of different ages (presumably MIS 6, MIS 4, and MIS 2) were identified based on a detailed investigation of their morphological features and the use of relative dating approaches. The latter were primarily based on weathering patterns. Data on the rock mineralogy, porosity, and specificity of biological colonization as an agent of weathering were obtained for the moraine debris. The studied moraines were composed of fine-grained schist, in which the specific surface area and fractality (self-similarity) were more developed in the older moraine. The growth of biota (crustose lichen and micromycetes) colonizing the rock surface led to rock disintegration and the accumulation of autochthonous fragments on the rock surface. Despite the fact that the initial stage(s) of moraine weathering affected by biota was fixed, the correlation trends of biota activity and moraine ages were not determined.

AbstractUsing samples from a prehistoric quarry site in the Mojave Desert, we tested and compared the two principal methods of rock-varnish cation-ratio dating, analysis of rock-varnish scrapings (R. I. Dorn, 1983, Quaternary Research 20, 49-73 and 1989, Physical Geography 13, 559-596) and analysis of rock varnish in situ (C. D. Harrington and J. W. Whitney, 1987, Geology 15, 967-970). Because we found no consistent relationship between the varnish cation ratio (K + Ca)/Ti, and the relative age of the varnish, neither method could be used to "cation-ratio date" the underlying chert artifacts. Moreover, in situ analyses yielded systematically higher cation ratios and lower Ti abundances than bulk analyses of scraped varnish or microprobe analyses of varnish in cross section. Our results, when considered along with other recently published evidence, indicate that these two methods of varnish chemical analysis and cation-ratio dating may not be comparable, nor consistently reliable, chronometers.

Abstract. As the accuracy and sensitivity of remote-sensing satellites improve, there is an increasing demand for more accurate and updated base datasets for surveying and monitoring. However, differentiating rock outcrop from snow and ice is a particular problem in Antarctica, where extensive cloud cover and widespread shaded regions lead to classification errors. The existing rock outcrop dataset has significant georeferencing issues as well as overestimation and generalisation of rock exposure areas. The most commonly used method for automated rock and snow differentiation, the normalised difference snow index (NDSI), has difficulty differentiating rock and snow in Antarctica due to misclassification of shaded pixels and is not able to differentiate illuminated rock from clouds. This study presents a new method for identifying rock exposures using Landsat 8 data. This is the first automated methodology for snow and rock differentiation that excludes areas of snow (both illuminated and shaded), clouds and liquid water whilst identifying both sunlit and shaded rock, achieving higher and more consistent accuracies than alternative data and methods such as the NDSI. The new methodology has been applied to the whole Antarctic continent (north of 82°40′ S) using Landsat 8 data to produce a new rock outcrop dataset for Antarctica. The new data (merged with existing data where Landsat 8 tiles are unavailable; most extensively south of 82°40′ S) reveal that exposed rock forms 0.18 % (21 745 km2) of the total land area of Antarctica: half of previous estimates.

AbstractPrestahnúkur is a 570m high rhyolite glaciovolcanic edifice in Iceland’s Western Rift Zone with a volume of 0.6 km3. Uniform whole rock, mineral and glass compositions suggest that Prestahnúkur was constructed during the eruption of one magma batch. Ar-Ar dating gives an age of 89± 24 ka, which implies eruption during the transition (Oxygen Isotope substages 5d to 5a) between the Eemian interglacial and the Weichselian glacial period. Prestahnu´kur is unique among published accounts of rhyolite tuyas because a base of magmatically-fragmented tephra appears to be absent. Instead, basal exposures consist of glassy lava lobes and coarse hyaloclastite, above which are single and multiple lava sheets with matrix-supported basal breccias and hyaloclastite upper carapaces. Steepening ramp structures at sheet termini are interpreted as ice-contact features. Interactions between erupting magma and water/ice have affected all lithologies. A preliminary model for the construction of Prestahnúkur involves an effusive subglacial eruption between 2–19 years duration which never became emergent, into an ice sheet over 700m thick. If 700m of ice had built up during this interglacial–glacial transition, this would corroborate models arguing for the swift accumulation of land-based ice in rapid response to global cooling.

Abstract. Biological rock crusts (BRCs) are ubiquitous features of rock surfaces in drylands composed of slow-growing microbial assemblages. BRC presence is often correlated with rock weathering, soiling effect or mitigating geomorphic processes. However, their development rate is still unknown. In this work, we characterised and dated BRCs in an arid environment, under natural conditions, by integrating archaeological, microbiological and geological methods. To this end, we sampled rocks from a well-documented Byzantine archaeological site and the surrounding area located in the central Negev, Israel. The archaeological site, which is dated to the fourth to seventh centuries CE, was constructed from two lithologies, limestone and chalk. BRC started developing on the rocks after being carved, and its age should match that of the site. Using stable carbon and oxygen isotope ratios, we confirmed the biogenic nature of the crusts. The BRC samples showed mild differences in the microbial community assemblages between the site and its surroundings, irrespective of lithology, confirming the dominance of aeolian inoculation sources. All BRCs were dominated by Actinobacteria, Cyanobacteria and Proteobacteria. We further measured the BRC thickness on 1700-year-old building stone blocks and determined it to be 0.1–0.6 mm thick. Therefore, a BRC growth rate was estimated, for the first time, to be 0.06–0.35 mm kyr−1. Our dating method was then validated on a similar archaeological site located ca. 20 km away, giving comparable values. We propose that BRC growth rates could be used as an affordable yet robust dating tool in archaeological sites in arid environments.

AbstractPresent study provides a review of the latest results on fluvial and aeolian landscape evolution in Hungary achieved by our team during the last 20 years.– The Hungarian river terrace system and its chronology was described with special emphasise on the novel threshold concept. A revised terrace system was created by the compilation of novel terrace chronology and MIS data. Evolution of river terraces was not only governed by climatic factors but tectonic ones too. Incision rate of the Danube, and uplift rate of the Transdanubian Range (TR) was around 0.1-0.3 mm/a in the marginal zones of the TR (mostly based on the published U-series data) and was above 1 mm/a in its axial zone (based on 3He exposure age dating of strath terraces).– According to a detailed geomorphological investigation of the different channel-planform morphologies in the Middle Tisza region and Sajó-Hernád alluvial fan, six phases of river pattern change and four incision periods were detected during the last 20,000 years.– Wind polished rock surfaces dated by in situ produced cosmogenic 10Be suggest that deflation was active in Hungary as early as 1.5 Ma ago. According to these exposure age data, Pleistocene denudation rate of the study area (Balaton Highland) was 40-80 m/Ma.– In sand covered areas the alternations of wind-blown layers and buried fossil soils provide information about climate and environment changes. In this study, periods of sand movement were mostly determined by optically stimulated luminescence (OSL) dating methods and five aeolian sand accumulation periods were recognised during the last 25 000 years.– A new loess stratigraphical view was elaborated using the most recent dating methods (luminescence, AAR). The lower part of Mende Upper (MF1-2) pedokomplex is suggested to represent the last interglacial period (MIS 5e). During the last interglacial/glacial period (MIS 5 - MIS 2) several soil-forming periods existed but the preservation of these paleosoils is variable depending on their paleogeomorphological position.

The contrast in the emissivity spectra of phosphorite and associated carbonate rock can be used as a guide to delineate phosphorite within dolomite. The thermal emissivity spectrum of phosphorite is characterized by a strong doublet emissivity feature with their absorption minima at 9 µm and 9.5 µm; whereas, host rock dolomite has relatively subdued emissivity minima at ~9 µm. Using the contrast in the emissivity spectra of phosphorite and dolomite, data obtained by the thermal bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor were processed to delineate phosphorite within dolomite. A decorrelation stretched ASTER radiance composite could not enhance phosphorite rich zones within the dolomite host rock. However, a decorrelation stretched image composite of selected emissivity bands derived using the emissivity normalization method was suitable to enhance large surface exposures of phosphorite. We have found that the depth of the emissivity minima of phosphorite gradually has increased from dolomite to high-grade phosphorite, while low-grade phosphate has an intermediate emissivity value and the emissivity feature can be studied using three thermal bands of ASTER. In this context, we also propose a relative band depth (RBD) image using selected emissivity bands (bands 11, 12, and 13) to delineate phosphorite from the host rock. We also propose that the RBD image can be used as a proxy to estimate the relative grades of phosphorites, provided the surface exposures of phosphorite are large enough to subdue the role of intrapixel spectral mixing, which can also influence the depth of the diagnostic feature along with the grade. We have validated the phosphorite pixels of the RBD image in the field by carrying out colorimetric analysis to confirm the presence of phosphorite. The result of the study indicates the utility of the proposed relative band depth image derived using ASTER TIR bands for delineating Proterozoic carbonate-hosted phosphorite.

Dating earthquake geological effects associated with historical earthquakes gives us relevant information for estimating the seismic acceleration value experienced in the ground. Historical manuscripts describing earthquakes and its effects help to assign a seismic intensity about the ground motion. In this context, lichenometry represents a good semi-quantitative method for dating exposed rock surfaces related to earthquake phenomena. In this work, we have carried out a lichenometry analysis for dating a large rockfall located 700 km from the epicentre of the Great Lisbon Earthquake, which occurred in 1755 CE and which was probably triggered by the surface shaking, according to the historical transcripts. A rock mobilization of about 2300 m 3 was caused by the earthquake, the largest historical earthquake affecting Western Europe (estimated magnitude of M 8.5, and close to 100,000 fatalities). The macroseismic intensity of the geological and environmental effects ESI07 estimated ranges between VI and VII, in contrast to the attributed European Macroseismic scale EMS98 of V from other studies. The EMS98 estimation was derived from a contemporaneous document of 1756 CE, describing the earthquake effects in buildings and environmental effects throughout the entire Kingdom of Spain. Aspicilia radiosa was used as the lichen species for dating purposes, and the annual growth-curve was estimated as 0.25 mm/yr as a linear growth rate. The resulting age for 19 analyzed blocks was 1733 CE, for the oldest lichen measured on the block side related to the broken-face. The error was estimated in 33 years based upon the comparison between the observed thalli and the calculated values from the linear fitting. The delayed time for lichen colonization was not estimated. Other error sources as lichen mortality, coalescence of thallus could ex- plain the deviation between the resulting lichen age and the earthquake occurrence.

This paper presents the first estimates for the life expectancy of the very surface of bedrock desert landforms, such as bornhardts, cliff faces, fault scarp, inselbergs, ridge crests, and slickrock. The correlative dating method of varnish microlaminations yields minimum ages for the timing of the last spalling event caused by the physical weathering process of dirt cracking. Minimum percentage of a bedrock surface spalled per thousand years is a metric that can be estimated using multiple varnish lamination ages. Understanding rates of surface spalling provides a quantitative measure of Gilbert’s (1877: 105) weathering-limited ‘rate of disintegration’, because this metric directly links to the rock disintegration process of dirt cracking. Rates of percent surface spalled then translate into estimates of how long it takes for the very surface of a desert bedrock landform to die. For a variety of example landforms in the southwestern USA, the maximum time required to completely resurface a desert bedrock landform by spalling from dirt cracking ranges from 89 to 600 ka.

Telescope Array (TA) has completed analysis of nearly nine years of data measuring the atmospheric depth of air shower maximum (Xmax) utilizing the TA surface detector array and the Black Rock Mesa and Long Ridge fluorescence detector stations. By using both the surface array and the fluorescence detector, the geometry and arrival time of air showers can be measured very precisely providing good resolution in determining Xmax. Xmax is directly related to the air shower primary particle mass and is therefore important for understanding the composition of ultra high energy cosmic rays (UHECRs). UHECR composition will help answer questions such as the distance and location of their sources. We discuss the experimental apparatus, analysis method, and Xmax data collected. We compare the energy dependent distributions of the observed data to detailed Monte Carlo simulations of four chemical species, then test which individual species are not compatible with the data through an analysis of the shapes of the distributions. We also discuss the present state of composition analysis and interpretation between the Auger and TA experiments. These are the two largest UHECR observatories in the world with large exposures and should shed light on UHECR composition.

Abstract. A multi-method investigation into Lauzière granite, located in the external Belledonne massif of the French Alps, reveals unusually hot hydrothermal conditions in vertical open fractures (Alpine-type clefts). The host-rock granite shows sub-vertical mylonitic microstructures and partial retrogression at temperatures of < 400 ∘C during Alpine tectonometamorphism. Novel zircon fission-track (ZFT) data in the granite give ages at 16.3 ± 1.9 and 14.3 ± 1.6 Ma, confirming that Alpine metamorphism was high enough to reset the pre-Alpine cooling ages and that the Lauzière granite had already cooled below 240–280 ∘C and was exhumed to < 10 km at that time. Novel microthermometric data and chemical compositions of fluid inclusions obtained on millimetric monazite and on quartz crystals from the same cleft indicate early precipitation of monazite from a hot fluid at T > 410 ∘C, followed by a main stage of quartz growth at 300–320 ∘C and 1.5–2.2 kbar. Previous Th-Pb dating of cleft monazite at 12.4 ± 0.1 Ma clearly indicates that this hot fluid infiltration took place significantly later than the peak of the Alpine metamorphism. Advective heating due to the hot fluid flow caused resetting of fission tracks in zircon in the cleft hanging wall, with a ZFT age at 10.3 ± 1.0 Ma. The results attest to the highly dynamic fluid pathways, allowing the circulation of deep mid-crustal fluids, 150–250 ∘C hotter than the host rock, which affect the thermal regime only at the wall rock of the Alpine-type cleft. Such advective heating may impact the ZFT data and represent a pitfall for exhumation rate reconstructions in areas affected by hydrothermal fluid flow.

The Longquanzhan deposit is one of the largest gold deposits in the Yi-Shu fault zone (central section of the Tan-Lu fault zone) in Shandong Province, China. It is an altered-rock type gold deposit in which ore bodies mainly occur at the contact zone between the overlying Cretaceous rocks and the underlying Neoarchean gneissic monzogranite. Shi et al. reported that this deposit formed at 96 ± 2 Ma using pyrite Rb–Sr dating method and represents a new gold mineralization event in the Shandong Province in 2014. In this paper, we present new He–Ar–S isotopic compositions to further decipher the sources of fluids responsible for the Longquanzhan gold mineralization. The results show that the δ34S values of pyrites vary between 0.9‰ and 4.4‰ with an average of 2.3‰. Inclusion-trapped fluids in ore sulfides have 3He/4He and 40Ar/36Ar ratios of 0.14–0.78 Ra and 482–1811, respectively. These isotopic data indicate that the ore fluids are derived from a magmatic source, which is dominated by crustal components with minor mantle contribution. Air-saturated water may be also involved in the hydrothermal system during the magmatic fluids ascending or at the shallow deposit site. We suggest that the crust-mantle mixing signature of the Longquanzhan gold deposit is genetically related to the Late Cretaceous lithospheric thinning along the Tan-Lu fault zone, which triggers constantly uplifting of the asthenosphere surface and persistent ascending of the isotherm plane to form the gold mineralization-related crustal level magma sources. This genetic model can be applied, to some extent, to explain the ore genesis of other deposits near or within the Tan-Lu fault belt.

AbstractThe Department of the Environment and the Welsh Office jointly sponsored a South Wales Desk Study into the feasibility of producing thematic maps of the Mining subsidence risk for planners. A method was to be developed and tested for a 25 km2 Pilot Area centred on Ebbw Vale.The study was started by collecting geological and mining data for the Pilot Area and compiling this information on a map. It was then intended to prepare the mining subsidence map from this map by back analysing subsidence incidents to determine the hazardous areas. This simple approach could not be followed for two reasons. First, the record of mining was incomplete and it was therefore necessary to define ‘worked’ seams and areas from the total historical record and not only from the surviving mine plans. Secondly, insufficient subsidence incidents were discovered in the Pilot Area to carry out meaningful back analysis.The study was extended to collect all readily available records of subsidence incidents throughout the Coalfield. A total of 388 were traced, mainly dating from 1960. About threequarters were collapses through superficial materials and were either close to the outcrop or above mine entries, the remaining 25% propagated to the ground surface through rock. The upper limit of migration was typically 8 times the extracted height where the dip was shallow, incrasing to as much as 18 times for steep dips. Selected grout contracts and opencast mining sites were also examined to gain information on the present condition of old workings and to study the ‘reputations’ of the various seams for voids.The results of the coalfield study were applied to the Pilot Area to produce a 1:10 000 scale Development Advice Map, ‘Mining Subsidence for use by developers and planners’. The map is zoned to show areas where specialist advice is necessary to support a planning application and it also shows all mine entries traced by the desk study. The method of production is general for the South Wales Coalfield and further maps could be prepared, using the Coalfield Study, quickly and cheaply.

Abstract. Before operational use or for decision making, models must be validated, and the degree of trust in model outputs should be quantified. Often, model validation is performed at single locations due to the lack of spatially-distributed data. Since the analysis of parametric model uncertainties can be performed independently of observations, it is a suitable method to test the influence of environmental variability on model evaluation. In this study, the sensitivities and uncertainty of a physically-based mountain permafrost model are quantified within an artificial topography consisting of different elevations and exposures combined with six ground types characterized by their hydraulic properties. The analyses performed for all combinations of topographic factors and ground types allowed to quantify the variability of model sensitivity and uncertainty within mountain regions. We found that modeled snow duration considerably influences the mean annual ground temperature (MAGT). The melt-out day of snow (MD) is determined by processes determining snow accumulation and melting. Parameters such as the temperature and precipitation lapse rate and the snow correction factor have therefore a great impact on modeled MAGT. Ground albedo changes MAGT from 0.5 to 4°C in dependence of the elevation, the aspect and the ground type. South-exposed inclined locations are more sensitive to changes in ground albedo than north-exposed slopes since they receive more solar radiation. The sensitivity to ground albedo increases with decreasing elevation due to shorter snow cover. Snow albedo and other parameters determining the amount of reflected solar radiation are important, changing MAGT at different depths by more than 1°C. Parameters influencing the turbulent fluxes as the roughness length or the dew temperature are more sensitive at low elevation sites due to higher air temperatures and decreased solar radiation. Modeling the individual terms of the energy balance correctly is hence crucial in any physically-based permafrost model, and a separate evaluation of the energy fluxes could substantially improve the results of permafrost models. The sensitivity in the hydraulic properties change considerably for different ground types: rock or clay for instance are not sensitive while gravel or peat, accurate measurements of the hydraulic properties could significantly improve modeled ground temperatures. Further, the discretization of ground, snow and time have an impact on modeled MAGT that cannot be neglected (more than 1°C for several discretization parameters). We show that the temporal resolution should be at least one hour to ensure errors less than 0.2°C in modeled MAGT, and the uppermost ground layer should at most be 20 mm thick. Within the topographic setting, the total parametric output uncertainties expressed as the standard deviation of the Monte Carlo model simulations range from 0.1 to 0.5°C for clay, silt and rock, and from 0.1 to 0.8°C for peat, sand and gravel. These uncertainties are comparable to the variability of ground surface temperatures measured within 10 m × 10 m grids in Switzerland. The increased uncertainties for sand, peat and gravel is largely due to the high hydraulic conductivity.

Abstract. This study explores influences on flood frequency distributions in Irish rivers. A Generalised Extreme Value (GEV) type I distribution is recommended in Ireland for estimating flood quantiles in a single site flood frequency analysis. This paper presents the findings of an investigation that identified the GEV statistical distributions that best fit the annual maximum (AM) data series extracted from 172 gauging stations of 126 rivers in Ireland. Analysis of these data was undertaken to explore hydraulic and hydro-geological factors that influence flood frequency distributions. A hierarchical approach of increasing statistical power that used probability plots, moment and L-moment diagrams, the Hosking goodness of fit algorithm and a modified Anderson-Darling (A-D) statistical test was followed to determine whether a type I, type II or type III distribution was valid. Results of the Hosking et al. method indicated that of the 143 stations with flow records exceeding 25 yr, data for 95 (67%) was best represented by GEV type I distributions and a further 9 (6%) and 39 (27%) stations followed type II and type III distributions respectively. Type I, type II and type III distributions were determined for 83 (58%), 16 (11%) and 34 (24%) stations respectively using the modified A-D method (data from 10 stations was not represented by GEV family distributions). The influence of karst terrain on these flood frequency distributions was assessed by incorporating results on an Arc-GIS platform showing karst features and using Monte Carlo simulations to assess the significance of the number and clustering of the observed distributions. Floodplain effects were identified by using two-sample t-tests to identify statistical correlations between the distributions and catchment properties that are indicative of strong floodplain activity. The data reveals that type I distributions are spatially well represented throughout the country. While also well represented throughout the country, the majority of type III distributions appear in areas where attenuation influences from floodplains are likely. The majority of type II distributions appear in a single cluster in a region in the west of the country that is underlain by karst but importantly, is characterised by shallow of glacial drift with frequent exposures of rock outcrops. The presence of karst in river catchments would be expected to provide additional subsurface storage and in this regard, type III distributions might be expected. The prevalence of type II distributions in this area reflects the finite nature of this storage. For prolonged periods of rainfall, rising groundwater levels will fill karst voids, remove subsurface storage and contribute to recharge related sinkhole flooding. Situations where rainfall intensities exceed karst percolation rates also produce high levels of surface runoff (discharge related flooding) that can promote type II distributions in nearby river catchments. Results therefore indicate that in some instances, assuming type I distributions is incorrect and may result in erroneous estimates of flood quantiles at these locations. Where actual data follows a type II distribution, flood quantiles may be underestimated by in excess of 35% and for type III distributions, overestimates by over 25% can occur.

The Q-slope method for rock slope engineering provides an empirical means of assessing the stability of excavated rock slopes in the field. It enables rock engineers and engineering geologists to make potential adjustments to slope angles as rock mass conditions become apparent during the construction of reinforcement-free road or railway cuttings and in open cast mines. Q-slope was developed by supplementing the Q-system which has been extensively used for characterizing rock exposures, drill core and underground mines and tunnels under construction for over 40 years. The Q׳ parameters (RQD, Jn ,Jr and Ja) have remained unchanged in Q-slope, although a new method for applying Jr /Ja ratios to both sides of a potential wedge is used, with relative orientation weightings for each side. The term Jw has been replaced with the more comprehensive term Jwice , which takes into account long-term exposure to various climatic and environmental conditions such as intense erosive rainfall and ice-wedging effects. SRF categories have been developed for slope surface conditions, stress-strength ratios and major discontinuities such as faults, weakness zones or joint swarms. Through case studies across Europe, Australia, Asia, and Central America, a simple relationship between Q-slope and long-term stable slope angles was established. The Q-slope method is designed such that it suggests stable, maintenance-free, bench face slope angles of, for instance, 40–45°, 60–65° and 80–85° with respective Q-slope values of approximately 0.1, 1.0 and 10. Q-slope has also been found to be compatible with P-wave velocity and acoustic and optical televiewer data obtained from borehole and surface-based geophysical surveys to determine appropriate rock slope angles.

Isótopos cosmogênicos são formados na atmosfera, na superfície e nos primeiros metros da crosta terrestre através da colisão de partículas sub-atômicas com núcleos de elementos químicos ali existentes. Entre um largo espectro de isótopos gerados 10Be e 26Al produzidos no interior do mineral quartzo podem ser utilizados para calcular o soterramento de sedimentos e superfícies geológicas previamente expostos aos raios cósmicos. Três diferentes abordagens podem ser evocadas na obtenção de idades: (i) o soterramento simples para quando há um soterramento completo das amostras (> 10m); (ii) idades máximas e mínimas quando as amostras não se encontram a uma profundidade suficiente para interromper a produção pós-soterramento destes isótopos e (iii) o método da isócrona derivado de uma solução gráfica onde múltiplas amostras de uma mesma camada são utilizadas para obtenção de uma idade. Além das idades em si o emprego destes isótopos carrega outro importante resultado em estudos geomorfológicos, quer seja a taxa de erosão pré-soterramento. O método possui um alcance compreendido entre 100 mil e 4-5 milhões de anos antes do presente e uma resolução nunca inferior a 60 mil anos. A literatura registra a obtenção de idades em sedimentos de caverna, terraços fluviais, dunas, solos, entre outros, e soma resultados no campo da determinação de taxas de incisão fluvial, no balizamento geocronológico da evolução do modelado, na investigação da dinâmica de solos, bem como em investigações paleoclimáticas e arqueológicas.Palavras-chave: Isótopos cosmogênicos; Datação de soterramento; Sedimentos Abstract: BURIAL DATING WITH COSMOGENIC ISOTOPES 10BE AND 26AL: METHODOLOGICAL SYNTHESIS AND A BRIEF REVIEW OF APPLICATIONS IN GEOSCIENCES. Comogenic isotopes are formed in Earth’s atmosphere, surface and very shallow crust as a result of the collision of sub-atomic particles (cosmic ray) with nuclei in the atmosphere and rock. The cosmogenic isotopes 10Be and 26Al generated inside quartz grains may be used in burial dating of sediments or geological surfaces previously exposed to cosmic rays. Three different approaches can be used for age determinations: (i) simple burial dating when samples are totally buried from cosmic rays; (ii) minimum and maximum ages when samples did not get deep enough to avoid post burial production and (iii) an isochron method derived from a graphical solution where multiple samples from a single layer are used to obtain a single burial age. Burial dating also brings to light another important geomorphic result: the pre-burial erosion rate. The method can be applied in samples buried in a range of 100 thousand to 4-5 million years ago, with a resolution limited to about 60 thousand years. The literature records burial ages from cave sediments, fluvial terraces, dunes, soil related materials, and others, allowing researchers to constrain river incision rates, landscape evolution, soil dynamics and paleoclimate and archeological issues as well.Keywords: Cosmogenic isotopes; Burial dating, Sediments.

IntroductionThe perception of the archive as the warehouse of tradition is inflected with the notion that what it stores is also removed from the everyday, at once ancient but also irrelevant, standing still outside time. Yet, if the past is of any relevance, the archive cannot maintain a rigid fixity that does not intersect with the present. In the work of the Atlas Group, the fabrication of “archival material” reflects what Hal Foster has termed an “archival impulse” that is constructed of multiple temporalities. The Atlas Group archive interrogates forms that are at once still, excavated from life, while still being in the present. In the process, the reductive singularity of the archive as an immobile monument is opened up to the complexity of a radical stillness through which the past enters the present in a moment of recognition. What is still, and what is still there, intersect in the productivity of a stillness that cuts through an undifferentiated continuity. This juncture echoes the Benjaminian flash which heralds the arrival of past in the presentTo articulate the past historically does not mean to recognize it ‘the way it really was’ (Ranke). It means to seize hold of a memory as it flashes up at a moment of danger. (Benjamin, Theses)Klee’s Angelus Novus stands still between past and future as a momentary suspension of motion brings history and prophecy into the present. For “the historian of the dialectic at a standstill”, Walter Benjamin, historical materialism was not simply a means of accessing the past in the present, but of awakening the potential of the future (Tiedemann 944-945). This, Rolf Tiedemann suggests, was the revolution of historical perception that Benjamin wanted to bring about in his unfinished Arcades Project (941). By carrying the principle of montage into history, Benjamin indicates an intention “to discover in the analysis of the small individual moment the crystal of the total event” (Benjamin Arcades 461). This principle had already been alluded to in his “Theses on the Philosophy of History” where he had written that a historical materialist cannot do without a present in which time stands still, and later, that it is in the arrest of thought that what has been and what will be “crystallizes into a monad” (Benjamin “Theses” 262-263).Everywhere in Benjamin’s writings on history, there is something of the irreducibility of the phrase “standing still”. Standing still: still as an active, ongoing form of survival and endurance, still as an absence of movement. The duality of stillness is amplified as semantic clarity vacillates between one possibility and another: to endure and to be motionless. Is it possible to reduce “standing still” to a singularity? Benjamin’s counsel to take hold of memory at the “moment of danger” might be an indication of this complexity. The “moment of danger” emerges as the flash of the past in the present, but also the instant at which the past could recede into the inertia of eternity, at once a plea against the reduction of the moment into a “dead time” and recognition of the productivity of stillness.Something of that “flash” surfaces in Gilles Deleuze’s reading of Michel Foucault: “a first light opens up things and brings forth visibilities as flashes and shimmerings, which are the ‘second light’” (Deleuze 50). The first flash makes “visibilities visible” and determines what can be seen in a given historical period, while the second makes “statements articulable” and defines what can be said (Deleuze 50). These visibilities and statements, however, are distributed into the stratum and constitute knowledge as “stratified, archivized, and endowed with a relatively rigid segmentarity” (Deleuze 61). Strata are historically determined, what they constitute of perceptions and discursive formations varies across time and results in the presence of thresholds between the stratum that come to behave as distinct layers subject to splits and changes in direction (Deleuze 44). Despite these temporal variations that account for differences across thresholds, the strata appear as fixed entities, they mimic rock formations shaped over thousands of years of sedimentation (Deleuze and Guattari 45). Reading Deleuze on Foucault in conjunction with his earlier collaborative work with Felix Guattari brings forth distant shadows of another “stratification”. A Thousand Plateaus is notably less interested in discursive formations and more concerned with “striation”, the organisation and arrangement of space by the diagrams of power. Striated space is state space. It is offset by moving in the opposite direction, effectively turning striated space into smooth space (Deleuze and Guattari 524).Whether on striation or stratification, Deleuze’s work exhibits more than a cautionary distrust of processes of classification, regulation, and organization. Despite the flash that brings visibilities and statements into being, stratification, as much as striation, remains a technique of knowledge shaped by the strategies of power. It is interesting however, that Deleuze sees something as indeterminate as a flash, creating structures that are as determined as stratum. Yet perhaps this is a deceptive conjecture since while the strata appear relatively rigid they are also “extremely mobile” (Deleuze and Guattari 553). Foucault had already given an indication that what the archaeological method uncovers is not necessarily suspended, but rather that it suspends the notion of an absolute continuity (Archaeology 169). He suggests that “history is that which transforms documents into monuments” (7). The task of archaeology, it would seem, is to recover documents from monuments by demonstrating rather than reversing the process of sedimentation and without necessarily relying on a motionless past. While there is a relative, albeit interstratically tentative, stillness in the strata, absolute destratification proceeds towards deterritorialisation through incessant movement (Deleuze and Guattari 62-63).If A Thousand Plateaus is any indication, the imperative for the creative thinker today seems to be stirring in this direction: movement, motion, animation. Whatever forms of resistance are to be envisioned, it is motion, rather than stillness, that emerges as a radical form of action (Deleuze and Guattari 561). The question raised by these theoretical interventions is not so much whether such processes are indeed valuable forms of opposition, but rather, whether movement is always the only means, or the most effective means, of resistance? To imagine resistance as “staying in place” seems antithetical to nomadic thinking but is it not possible to imagine moments when the nomad resists not by travelling, but by dwelling? What of all those living a life of forced nomadism, or dying nomadic deaths, those for whom movement is merely displacement and loss? In Metamorphoses Rosi Braidotti reflects upon forced displacement and loss, yet her emphasis nonetheless remains on “figurations”, mappings of identity through time and space, mappings of movement (2-3). Braidotti certainly does not neglect the victims of motion, those who are forced to move, yet she remains committed to nomadism as a form of becoming. Braidotti’s notion of “figurations” finds a deeply poignant expression in Joseph Pugliese’s textual maps of some of these technically “nomadic” bodies and their movement from the North African littoral into the waters of the Mediterranean where they eventually surface on southern European shores as corpses (Pugliese 15). While Braidotti recognizes the tragedy of these involuntary nomads, it is in Pugliese’s work that this tragedy is starkly exposed and given concrete form in the figures of Europe’s refugees. This is movement as death, something akin to what Paul Virilio calls inertia, the product of excessive speed, the uncanny notion of running to stand still (Virilio 16).This tension between motion and stillness surfaces again in Laura Marks’ essay “Asphalt Nomadism.” Despite wanting to embrace the desert as a smooth space Marks retorts that “smooth space seems always to be elsewhere” (Marks 126). She notes the stability of the acacia trees and thorny shrubs in the desert and the way that nomadic people are constantly beset with invitations from the “civilising forces of religion and the soporific of a daily wage” (Marks 126). Emphatically she concludes that “the desert is never really ‘smooth’, for that is death” (Marks 126). On this deviation from Deleuze and Guattari’s notion of the desert as smooth space she concludes: “we who inherit their thinking need to stay on the ground: both in thought, moving close to the surface of concepts, and literally, remaining alert to signs of life in the sand and the scrub of the desert” (Marks 126). In Marks’ appeal for groundedness the tension between motion and stillness is maintained rather than being resolved through recourse to smoothness or in favour of perpetual movement. The sedentary and still structures that pervade the desert remain: the desert could not exist without them. In turn we might ask whether even the most rigorous abstraction can convince us that the ground between radical nomadism and perpetual displacement does not also need to be rethought. Perhaps this complexity is starkest when we begin to think about war, not only the potentiality of the war-machine to destabilize the state (Deleuze and Guattari 391), but war as the deterritorialisation of bodies, lives and livelihoods. Is the war of nomadism against the state not somehow akin to war as the violence that produces nomadic bodies through forced displacement? One of the questions that strikes me about the work of the Atlas Group, “an imaginary non-profit research foundation established in Beirut to research and document the contemporary history of Lebanon” (Raad 68) through the production and exhibition of “archival” material, is whether their propensity towards still forms in the creation of documentary evidence cannot be directly attributed to war as perpetual movement and territorial flexibility, as the flattening of structure and the creation of “smooth space” (Deleuze and Guattari 389). One need only think of the reigns of terror that begin with destratification – abolishing libraries, destroying documents, burning books. On the work of the Atlas Group, Andre Lepecki offers a very thorough introduction:The Atlas Group is an ongoing visual and performative archival project initiated by Walid Raad …whose main topic and driving force are the multiple and disparate events that history and habit have clustered into one singularity named “The Lebanese Civil Wars of 1975-1991”. (Lepecki 61).While the “inventedness” of the Atlas Group’s archive, its “post-event” status as manufactured evidence, raises a myriad of questions about how to document the trauma of war, its insistence on an “archival” existence, rather than say a purely artistic one, also challenges the presumption that the process of becoming, indeed of producing or even creating, is necessarily akin to movement or animation by insisting on the materiality of producing “documents” as opposed to the abstraction of producing “art”. The Atlas Group archive does not contribute directly to the transformation of visibilities into statements so much as statements into visibilities. Indeed, the “archival impulse” that seems to be present here works against the constitution of discursive formations precisely by making visible those aspects of culture which continue to circulate discursively while not necessarily existing. In other words, if one reads the sedimentary process of stratification as forming knowledge by allowing the relationships between “words” and “things” to settle or to solidify into historical strata, then the Atlas Group project seems to tap into the stillness of these stratified forms in order to reverse the signification of “things” and “words”. Hal Foster’s diagnosis of an “archival impulse” is located in a moment where, as he says, “almost anything goes and almost nothing sticks” in reference to the current obliviousness of contemporary artistic practices to political culture (Foster 2-3). Foster’s observation endows this paper with more than just an appropriate title since what Foster seems to identify are the limitations of the current obsession with speed. What one senses in the Atlas Group’s “archival impulse” and Foster’s detection of an “archival impulse” at play in contemporary cultural practices is a war against the war on form, a war against erasure through speed, and an inclination to dwell once more in the dusty matter of the past, rather than to pass through it. Yet the archive, in the view of nomadology, might simply be what Benjamin Hutchens terms “the dead-letter office of lived memory” (38). Indeed Hutchens’s critical review of the archive is both timely and relevant pointing out that “the preservation of cultural memories eradicated from culture itself” simply establishes the authority of the archive by erasing “the incessant historical violence” through which the archive establishes itself (Hutchens 38). In working his critique through Derrida’s Archive Fever, Hutchens revisits the concealed etymology of the word “archive” which “names at once the commencement and the commandment” (Derrida 1). Derrida’s suggestion that the concept of the archive shelters both the memory of this dual meaning while also sheltering itself from remembering that it shelters such a memory (Derrida 2) leads Hutchens to assert that “the archival ‘act’ opens history to the archive, but it closes politics to its own archivization” (Hutchens 44). The danger that “memory cultures”, archives among them, pose to memory itself has also been explored elsewhere by Andreas Huyssen. Although Huyssen does not necessary hold memory up as something to be protected from memory cultures, he is critical of the excessive saturation of contemporary societies with both (Huyssen 3). Huyssen refers to this as the “hypertrophy of memory” following Nietzsche’s “hypertrophy of history” (Huyssen 2-3). Although Hutchens and Huyssen differ radically in direction, they seem to concur nonetheless that what could be diagnosed as an “archival impulse” in contemporary societies might describe only the stagnation and stiltedness of the remainders of lived experience.To return once more to Foster’s notion of an “archival impulse” in contemporary art practices, rather than the reinstitution of the archive as the warehouse of tradition, what seems to be at stake is not necessarily the agglutination of forms, but the interrogation of formations (Foster 3). One could say that this is the archive interrogated through the eyes of art, art interrogated through the eyes of the archive. Perhaps this is precisely what the Atlas Group does by insisting on manufacturing documents in the form of documentary evidence. “Missing Lebanese Wars”, an Atlas Group project produced in 1998, takes as its point of departure the hypothesisthat the Lebanese civil war is not a self-evident episode, an inert fact of nature. The war is not constituted by unified and coherent objects situated in the world; on the contrary, the Lebanese civil war is constituted by and through various actions, situations, people, and accounts. (Raad 17-18)The project consists of a series of plates made up of pages taken from the notebook of a certain Dr Fadl Fakhouri, “the foremost historian of the civil war in Lebanon” until his death in 1993 (Raad 17). The story goes that Dr Fakhouri belonged to a gathering of “major historians” who were also “avid gamblers” that met at the race track every Sunday – the Marxists and the Islamists bet on the first seven races, while the Maronite nationalists and the socialists bet on the last eight (Raad 17). It was alleged that the historians would bribe the race photographer to take only one shot as the winning horse reached the post. Each historian would bet on exactly “how many fractions of a second before or after the horse crossed the line – the photographer would expose his frame” (Raad 17). The pages from Dr Fakhouri’s notebook are comprised of these precise exposures of film as the winning horse crossed the line – stills, as well as measurements of the distance between the horse and the finish line amid various other calculations, the bets that the historians wagered, and short descriptions of the winning historians given by Dr Fakhouri. The notebook pages, with photographs in the form of newspaper clippings, calculations and descriptions of the winning historians in English, are reproduced one per plate. In producing these documents as archival evidence, the Atlas Group is able to manufacture the “unified and coherent objects” that do not constitute the war as things that are at once irrelevant, incongruous and non-sensical. In other words, presenting material that is, while clearly fictitious, reflective of individual “actions, situations, people, and accounts” as archival material, the Atlas Group opens up discourses about the sanctity of historical evidence to interrogation by producing documentary evidence for circulating cultural discourses.While giving an ironic shape to this singular and complete picture of the war that continues to pervade popular cultural discourses in Lebanon through the media with politicians still calling for a “unified history”, the Atlas Group simultaneously constitute these historical materials as the work of a single person, Dr Fakhouri. Yet it seems that our trustworthy archivist also chooses not to write about the race, but about the winning historian – echoing the refusal to conceive of the war as a self-evident fact (to talk about the race as a race) and to see it rather as an interplay of individuals, actions and narratives (to view the race through the description of the winning historian). Indeed Dr Fakhouri’s descriptions of the winning historians are almost comical for their affinity with descriptions of Lebanon’s various past and present political leaders. A potent shadow, and a legend that has grown into an officially sanctioned cult (Plate 1).Avuncular rather than domineering, he was adept at the well-timed humorous aside to cut tension. (Plate 3).He is 71. But for 6 years he was in prison and for 10 years he was under house arrest and in exile, so those 16 years should be deducted – then he’s 55 (Plate 5). (Raad 20-29)Through these descriptions of the historians, Lebanon’s “missing” wars begin to play themselves out between one race and the next. While all we have are supposed “facts” with neither narrative, movement, nor anything else that could connect one fact to another that is not arbitrary, we are also in the midst of an archive that is as random as these “facts.” This is the archive of the “missing” wars, wars that are not documented and victims that are not known, wars that are “missing” for no good reason.What is different about this archive may not be the way in which order is manufactured and produced, but rather the background against which it is set. In his introduction to The Order of Things Michel Foucault makes reference to “a certain Chinese encyclopaedia” in a passage by Borges whereanimals are divided into: (a) belonging to the Emperor, (b) embalmed, (c) tame, (d) suckling pigs, (e) sirens, (f) fabulous, (g) stray dogs, (h) included in the present classification, (i) frenzied, (j) innumerable… (xvi)“The uneasiness that makes us laugh when we read Borges”, writes Foucault, is the sense of loss of a “common” name and place (Order, xx). Whereas in Eusethenes, (“I am no longer hungry. Until the morrow, safe from my saliva all the following shall be: Aspics, Acalephs, Acanathocephalates […]”) the randomness of the enumerated species is ordered by their non-location in Eusthenes’ mouth (Foucault, Order xvii), in Borges there is no means through which the enumerated species can belong in a common place except in language (Foucault, Order, xviii). In the same way, the work of the Atlas Group is filtered through the processes of archival classification without belonging to the archives of any real war. There is no common ground against which they can be read except the purported stillness of the archive itself, its ability to put things in place and to keep them there.If the Atlas Group’s archives of Lebanon’s wars are indeed to work against the fluidity of war and its ability to enter and reshape all spaces, then the archival impulse they evoke must be one in which the processes of sedimentation that create archival documents are worked through a radical stillness, tapping into the suspended motion of the singular moment – its stillness, in order to uncover stillness as presence, survival, endurance, to be there still. Indeed, if archives turn “documents into monuments” (Enwezor 23), then the “theatre of statements” that Foucault unearths (Deleuze 47) are not those recovered in the work of the Atlas Group since is not monuments, but documents, that the Atlas Group archive uncovers.It is true that Benjamin urges us to seize hold of memory at the moment of danger, but he does not instruct us as to what to do with it once we have it, yet, what if we were to read this statement in conjunction with another, “for every image of the past that is not recognized by the present as one of its own concerns threatens to disappear irretrievably” (Benjamin, “Theses” 255). By turning monuments into documents it is possible that the Atlas Group reconfigure the formations that make up the archive, indeed any archive, by recognizing images of the past as being still in the present. Not still as a past tense, motionless, but still as enduring, remaining. In the work of the Atlas Group the archival impulse is closely aligned to a radical stillness, letting the dust of things settle after its incitation by the madness of war, putting things in place that insist on having a place in language. Against such a background Benjamin’s “moment of danger” is more than the instant of sedimentation, it is the productivity of a radical stillness in which the past opens onto the present, it is this moment that makes possible a radical reconfiguration of the archival impulse.ReferencesBenjamin, Walter. The Arcades Project. Trans. Howard Eiland and Kevin McLaughlin. Cambridge, Mass.: Belknap Press of Harvard U Press, 2002.———. “Theses on the Philosophy of History.” Illuminations. Ed. Hannah Arendt. New York: Schocken Books, 2007.Braidotti, Rosi. Metamorphoses: Towards a Materialist Theory of Becoming. Cambridge: Polity, 2002.Deleuze, Gilles. Foucault. Trans. Seán Hand. New York: Continuum, 1999.Deleuze, Gilles, and Felix Guattari. A Thousand Plateaus. 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