Weathering Rinds: Archives of Paleoenvironments on Mount Kenya, East Africa

Weathering-rind thicknesses on pebble-and cobble-size sediment have been used for the past half-century, at least, as an age indicator of postdepositional time following a geologic event. In mountainous terrain, rind thickness is taken as a measurement of weathering over time frames of 0.5 m.yr.; variable thicknesses are used to discriminate relative ages of glacial deposits. The effects of chemical and physical weathering that together produce rinds are only rarely considered, and most research objectives have centered on lichen alteration of clast surfaces. Recent microscopic analyses of weathering rinds on volcanic clasts of similar to 70.0-ka to similar to 2.0-m.yr. age produced new data on weathering products as well as unexpected incorporated biotic materials undergoing diagenesis. The question as to how much physical/mineral/chemical/ biotic paleoenvironmental data might be archived in rinds is discussed. The character and classification of organic materials undergoing diagenesis are also discussed.

Later Pleistocene evolution of the Exe valley: A chronstratigraphic model of terrace formation and its implications for Palaeolithic archaeology

This paper presents the ?rst systematic chronostratigraphic study of the river terraces of the Exe catchment in South West England and a new conceptual model for terrace formation in unglaciated basins with applicability to terrace staircase sequences elsewhere. The Exe catchment lay beyond the maximum extent of Pleistocene ice sheets and the drainage pattern evolved from the Tertiary to the Middle Pleistocene, by which time the major valley systems were in place and downcutting began to create a staircase of strath terraces. The higher terraces (8-6) typically exhibit altitudinal overlap or appear to be draped over the landscape, whilst the middle terraces show greater altitudinal separation and the lowest terraces are of a cut and ?ll form. The terrace deposits investigated in this study were deposited in cold phases of the glacial-interglacial Milankovitch climatic cycles with the lowest four being deposited in the Devensian Marine Isotope Stages (MIS) 4-2. A new cascade process-response model is proposed of basin terrace evolution in the Exe valley, which emphasises the role of lateral erosion in the creation of strath terraces and the reworking of inherited resistant lithological components down through the staircase. The resultant emergent valley topography and the reworking of artefacts along with gravel clasts, have important implications for the dating of hominin presence and the local landscapes they inhabited. Whilst the terrace chronology suggested here is still not as detailed as that for the Thames or the Solent System it does indicate a Middle Palaeolithic hominin presence in the region, probably prior to the late Wolstonian Complex or MIS 6. This supports existing data from cave sites in South West England.

Distal Deposition of Tephra from the Eyjafjallajökull 2010 Summit Eruption

The 2010 Eyjafjallajökull lasted 39 days and had 4 different phases, of which the first and third (14–18 April and 5–6 May) were most intense. Most of this period was dominated by winds with a northerly component that carried tephra toward Europe, where it was deposited in a number of locations and was sampled by rain gauges or buckets, surface swabs, sticky-tape samples and air filtering. In the UK, tephra was collected from each of the Phases 1–3 with a combined range of latitudes spanning the length of the country. The modal grain size of tephra in the rain gauge samples was 25 um, but the largest grains were 100 um in diameter and highly vesicular. The mass loading was equivalent to 8–218 shards cm2, which is comparable to tephra layers from much larger past eruptions. Falling tephra was collected on sticky tape in the English Midlands on 19, 20 and 21st April (Phase 2), and was dominated by aggregate clasts (mean diameter 85 um, component grains <10 um). SEM-EDS spectra for aggregate grains contained an extra peak for sulphur, when compared to control samples from the volcano, indicating that they were cemented by sulphur-rich minerals e.g. gypsum (CaSO4⋅H2O). Air quality monitoring stations did not record fluctuations in hourly PM10 concentrations outside the normal range of variability during the eruption, but there was a small increase in 24-hour running mean concentration from 21–24 April (Phase 2). Deposition of tephra from Phase 2 in the UK indicates that transport of tephra from Iceland is possible even for small eruption plumes given suitable wind conditions. The presence of relatively coarse grains adds uncertainty to concentration estimates from air quality sensors, which are most sensitive to grain sizes <10 um. Elsewhere, tephra was collected from roofs and vehicles in the Faroe Islands (mean grain size 40 um, but 100 um common), from rainwater in Bergen in Norway (23–91 um) and in air filters in Budapest, Hungary (2–6 um). A map is presented summarizing these and other recently published examples of distal tephra deposition from the Eyjafjallajökull eruption. It demonstrates that most tephra deposited on mainland Europe was produced in the highly explosive Phase 1 and was carried there in 2–3 days.

Presence of cave bears in western Austria before the onset of the Last Glacial Maximum: new radiocarbon dates and palaeoclimatic considerations

Tischoferhohle and Pendling-Barenhohle near Kufstein, Tyrol, are among the only locations where remains of cave bear, Ursus spelaeus-group, were found in the western part of Austria. One sample from each site was radiocarbon-dated four decades ago to ca. 28 C-14 ka BP. Here we report that attempts to date additional samples from Pendling-Barenhohle have failed due to the lack of collagen, casting doubts on the validity of the original measurement. We also unsuccessfully tried to date flowstone clasts embedded in the bone-bearing sediment to provide maximum constraints on the age of this sediment. Ten cave bear bones from Tischoferhohle showing good collagen preservation were radiocarbon-dated to 31.1-39.9 C-14 ka BP, again pointing towards an age underestimation by the original radiocarbon-dated sample from this site. These new dates from Tischoferhohle are therefore currently the only reliable cave bear dates in western Austria and constrain the interval of cave occupation to 44.3-33.5 cal ka BP. We re-calibrate and re-evaluate dates of alpine cave bear samples in the context of available palaeoclimate information from the greater alpine region covering the transition into the Last Glacial Maximum, eventually leading to the demise of this megafauna.

Characterizing Aquifer Heterogeneity Using Bacterial and Bacteriophage Tracers

Gravel aquifers act as important potable water sources in central western Europe yet they are subject to numerous contamination pressures. Compositional and textural heterogeneity makes protection zone delineation around groundwater supplies in these units challenging; artificial tracer testing aids characterization. This paper reappraises previous tracer test results in light of new geological and microbiological data. Comparative passive gradient testing, using a fluorescent solute (Uranine), virus (H40/1 bacteriophage), and comparably sized bacterial tracers Escherichia coli and Pseudomonas putida, was used to investigate a calcareous gravel aquifer’s ability to remove microbiological contaminants at a test site near Munich, Germany. Test results revealed E. coli relative recoveries could exceed those of H40/1 at monitoring wells 10 m and 20 m from an injection well by almost four times; P. putida recoveries varied by a factor of up to three between wells. Application of filtration theory suggested greater attenuation of H40/1 relative to similarly charged E. coli occurred due to differences in microorganism size, while estimated collision efficiencies appeared comparable. By contrast, more positively charged P. putida experienced greater attenuation at one monitoring point, while lower attenuation rates at the second location indicated the influence of geochemical heterogeneity. Test findings proved consistent with observations from nearby fresh outcrops that suggested thin open framework gravel beds dominated mass transport in the aquifer, while discrete intervals containing stained clasts reflect localized geochemical heterogeneity. Study results highlight the utility of reconciling outcrop observations with artificial tracer test responses, using microbiological tracers with well-defined properties, to characterize aquifer heterogeneity.

A stacked Late Quaternary fluvio-periglacial sequence from the Axe valley, southern England with implications for landscape evolution and Palaeolithic archaeology

The current model of mid-latitude late Quaternary terrace sequences, is that they are uplift-driven but climatically controlled terrace staircases, relating to both regional-scale crustal and tectonic factors, and palaeohydrological variations forced by quasi-cyclic climatic conditions in the 100 K world (post Mid Pleistocene Transition). This model appears to hold for the majority of the river valleys draining into the English Channel which exhibit 8–15 terrace levels over approximately 60–100 m of altitudinal elevation. However, one valley, the Axe, has only one major morphological terrace and has long-been regarded as anomalous. This paper uses both conventional and novel stratigraphical methods (digital granulometry and terrestrial laser scanning) to show that this terrace is a stacked sedimentary sequence of 20–30 m thickness with a quasi-continuous (i.e. with hiatuses) pulsed, record of fluvial and periglacial sedimentation over at least the last 300–400 K yrs as determined principally by OSL dating of the upper two thirds of the sequence. Since uplift has been regional, there is no evidence of anomalous neotectonics, and climatic history must be comparable to the adjacent catchments (both of which have staircase sequences) a catchment-specific mechanism is required. The Axe is the only valley in North West Europe incised entirely into the near-horizontally bedded chert (crypto-crystalline quartz) and sand-rich Lower Cretaceous rocks creating a buried valley. Mapping of the valley slopes has identified many large landslide scars associated with past and present springs. It is proposed that these are thaw-slump scars and represent large hill-slope failures caused by Vauclausian water pressures and hydraulic fracturing of the chert during rapid permafrost melting. A simple 1D model of this thermokarstic process is used to explore this mechanism, and it is proposed that the resultant anomalously high input of chert and sand into the valley during terminations caused pulsed aggradation until the last termination. It is also proposed that interglacial and interstadial incision may have been prevented by the over-sized and interlocking nature of the sub-angular chert clasts until the Lateglacial when confinement of the river overcame this immobility threshold. One result of this hydrogeologically mediated valley evolution was to provide a sequence of proximal Palaeolithic archaeology over two MIS cycles. This study demonstrates that uplift tectonics and climate alone do not fully determine Quaternary valley evolution and that lithological and hydrogeological conditions are a fundamental cause of variation in terrestrial Quaternary records and landform evolution.

Towards a budget approach to Pleistocene terraces: preliminary studies using the River Exe in South West England, UK

This paper presents a first approach to using a sediment budget methodology for paired terrace staircase sediments in SW England. Although a budget approach has become firmly established in Holocene fluvial studies, it has not been used in Pleistocene sequences due to the problems of temporal resolution, catchment changes and downstream loss from the system. However, this paper uses a budget approach in a paired non-glaciated basin, primarily as a method of interrogating the terrace record concerning the degree of reworking and new sediment input required to produce the reconstructed terrace sequences. In order to apply a budget approach a number of assumptions have to be made and these are justified in the paper. The results suggest that the Exe system can most parsimoniously be explained principally by the reworking of a Middle Pleistocene floodplain system with relatively little input of new resistant clasts required and a cascade-type model in geomorphological terms. Whilst this maybe partially a result of the specific geology of the catchment, it is likely to be representative of many Pleistocene terrace systems in NW Europe due to their litho-tectonic similarities. This cascade-type model of terrace formation has archaeological implications and sets the context for the Palaeolithic terrace record in the UK. Future work will involve the testing of this and similar budget models using a combination of landscape modelling and chronometric dating. ?? 2009 The Geologists' Association.

Biomineralization of Weathered Rock Rinds:Examples from the Lower Afroalpine Zone on Mount Kenya

Rock rinds have been used for half a century to date glacial deposits and recently inroads have been developed to use nuclides to provide absolute ages of weathering rinds in pebble clasts. Although maximum and minimum rind thicknesses have helped to elucidate time since deposition and allowed stratigraphic division of deposits at glacial rank, little has been done to investigate the wealth of mineral degradation, growth of alteration products and biomineralization that occur in these weathered crusts. In some cases the mass of microbe-mineral intergrowth is nearly present on a 50%/50% basis, with the biotic mass intergrown with mineral matter to such an extent that it probably controls pH and redox phenomena that act as accelerators in the weathering process. Assuming weathering time spans of 2 × 10⁶ years or more for a complete cycle, eventual clast decomposition is the end product. Here we present evidence of microbe-clast intergrowth from selected sites of Pleistocene age (~70 ka to 2.0 Ma) in the lower Afroalpine of Mt. Kenya and hypothesize about its role in rock decomposition and fossilization of biotic end-members. © 2013 Copyright Taylor and Francis Group, LLC.