The stratigraphical signature of the Anthropocene in England and its wider context

The Anthropocene deposits of England, here regarded as those formed after ～1950 CE, are now extensive, take various forms, and may be characterized and recognized by a number of stratigraphic signals, such as artificial radionuclides, pesticide residues, microplastics, enhanced fly ash levels, concrete fragments and a novel variety of ‘technofossils’ and neobiotic species. They include the uppermost parts of both ‘natural’ deposits such as the sediment layers formed in lakes and estuaries, and more directly human-made or human-influenced ones such as landfill deposits and the ‘artificial ground’ beneath urban areas and around major constructions. ‘Negative deposits’ include the worked areas of quarries and regions such as the English Fenland, where thick peat deposits have ablated to leave a strongly modified underlying landscape, and extend beneath into the subterranean realm as mine workings, metro systems and boreholes. The production of these is still rapidly increasing and evolving in character, while the early signs of global change, such as warming, sea level rise, and modifications to biotic assemblages, are beginning to further modify the emerging geology of this new phase of Earth history.     

Surface Geophysical Methods used to Verify the Karst Geological Structure in the Built-up Area: A Case Study of Specific Engineering-Geological Conditions

This article presents a research study of complex limestone karst engineering-geological conditions in the municipality Valaská near Banská Bystrica in Slovakia. The aim of the study is to demonstrate the impossibility of spatial identification of cave spaces using surface geophysical methods due to the specific engineering-geological conditions of a thick surface layer of anthropogenic fill containing highly heterogeneous anthropogenic material. Its maximum thickness is 3 m. Another specificific condition of the study area is its location in the built-up area, due to which the applicability of geophysical methods was limited. The article contains methodological recommendations to be used in analogous geological conditions with karst structures topped with anthropogenic fill, which complicates the identification of cave spaces. The recommended solution herein is the identification of the cave system using underground mapping of the karst and its projection onto the surface for which surface geophysical methods have been combined.     

Small-strain behaviour of unsaturated silty clay: experiments and model interpretation

Acta Geotechnica - The experimental data dealing with the so-called small strain stiffness of soils are indispensable in developing and calibrating advanced numerical models. A literature review...     

Combined three-dimensional electric and seismic tomography study on the Åknes rockslide in western Norway

We present a combined 3-D geoelectric and seismic tomography study conducted on the large Åknes rockslide in western Norway. Movements on the slope are strongly influenced by water infiltration, such that the hydrogeological regime is considered as a critical factor affecting the slope stability. The aim of our combined geophysical study was to identify and visualize the main shallow tension fractures and to determine their effect on hydraulic processes by comparing the geophysical results with information from borehole logging and tracer tests. To resolve the complex subsurface conditions of the highly fractured rock mass, a three-dimensional set-up was chosen for our seismic survey. To map the water distribution within the rock mass, a pattern of nine intersecting 2-D geoelectric profiles covered the complete unstable slope. Six of them that crossed the seismic survey area were considered as a single data set in a 3-D inversion. For both methods, smoothing-constraint inversion algorithms were used, and the forward calculations and parameterizations were based on unstructured triangular meshes. A pair of parallel shallow low-velocity anomalies (< 1400 m/s) observed in the final seismic tomogram was immediately underlain by two anomalies with resistivities <13 kΩm in the resistivity tomogram. In combination with borehole logging results, the low-velocity and resistivity anomalies could be associated with the drained and water-filled part of the tension fractures, respectively. There were indications from impeller flowmeter measurements and tracer tests that such tension fractures intersected several other water-filled fractures and were responsible for distinct changes of the main groundwater flow paths.     

Spatial patterns of groundwater‐lake exchange – implications for acid neutralization processes in an acid mine lake

Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m^‐2 d^‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m^‐2 d^‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g^‐1 d^‐1) compared to alternating sites (<220 nmol g^‐1 d^‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.     

Impact of soil and water conservation measures on catchment hydrological response—a case in north Ethiopia

Impact studies of catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200‐ha catchment in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post‐harvest grazing, and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1·6% in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff curve number (CN) for various land uses and land management techniques. The pre‐implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26·5 mm (RC = 8%), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002–2003 (ΔT/WS = 3·4) and 2006 (ΔT/WS >11·1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81% which has had a positive influence on the catchment water balance. Copyright © 2010 John Wiley & Sons, Ltd.     

Formation of intracratonic basins by lithospheric shortening and phase changes: a case study from the ultra‐deep East Barents Sea basin

The origin of large subsidence in intracratonic basins is still under debate. We propose a new and self‐consistent model for the formation of those basins, where lithospheric shortening/buckling triggers metamorphism and densification of crustal mafic heterogeneities. We use a forward thermo‐mechanical finite element technique to evaluate this mechanism for the typical example of the East Barents Sea basin (EBB) where a very large and compensated subsidence, accommodating an up to 20‐km‐thick sediment succession, is observed. The lower crust in the dynamic model is modelled with petrologic‐consistent densities for a wet mafic gabbroic composition that depend on pressure and temperature taking into account dehydration at high PT conditions. The model successfully explains the main characteristics of the EBB, notably the large anomalous and fast subsidence during the Late Permian–Early Triassic, its present‐day geometry and the absence of a significant gravity anomaly.     

Palaeo-environmental and dietary analysis of intestinal contents of a mammoth calf (Yamal Peninsula,northwest Siberia)

Intestinal samples from the one-month-old Siberian mammoth calf ‘Lyuba’ were studied using light microscopy and ancient DNA to reconstruct its palaeo-environment and diet. The palynological record indicates a ‘mammoth steppe’. At least some pollen of arboreal taxa was reworked, and thus the presence of trees on the landscape is uncertain. In addition to visual comparison of 11 microfossil spectra, a PCA analysis contributed to diet reconstruction. This yielded two clusters: one of samples from the small intestine and the other of large-intestine samples, indicating compositional differences in food remains along the intestinal tract, possibly reflecting different episodes of ingestion. Based on observed morphological damage we conclude that the cyperaceous plant remains and some remains of dwarf willows were originally eaten by a mature mammoth, most likely Lyuba’s mother. The mammoth calf probably unintentionally swallowed well-preserved mosses and mineral particles while eating fecal material deposited on a soil surface covered with mosses. Coprophagy may have been a common habit for mammoths, and we therefore propose that fecal material should not be used to infer season of death of mammoths. DNA sequences of trnL and rbcL genes amplified from ancient DNA extracted from intestinal samples confirmed and supplemented plant identifications based on microfossils and macro-remains. Results from different extraction methods and barcoding markers complemented each other and show the value of longer protocols in addition to fast and commercially available extraction kits.