Calibration of decomposition of serine to alanine in Bithynia opercula as a quantitative dating technique for Middle and Late Pleistocene sites in Britain

The concentration ratio of the amino acids alanine and serine in calcite opercula of freshwater gastropods of genus Bithynia has been assessed as an age proxy for British Middle and Late Pleistocene sites. Due to decomposition of peptide-bound serine within intra-crystalline protein molecules, alanine/serine ratios increase with sample age, enabling resolution of the marine oxygen-isotope stage of almost all sites and substage resolution for some sites. However, slight overlaps are evident in alanine/serine ratios between some sites from late in one temperate stage and early in the next; this effect results from the low decomposition rates during cold stages, combined with an evident slight dependence of decomposition rates on site conditions. The technique, which can be extended to the Early Pleistocene without technical refinements, is amenable to quantitative calibration using a first-order rate equation, making it feasible in future to present results as numerical ages, subject to an assumed temperature history. Most Pleistocene sites investigated are shown using this technique to have the same ages as previously deduced using biostratigraphy. However, the serine–alanine ages obtained preclude glaciation of southeast England during MIS 16 or of central England during MIS 10.     

Channel Representation in Physically Based Models Coupling Groundwater and Surface Water: Pitfalls and How to Avoid Them

Recent models that couple three‐dimensional subsurface flow with two‐dimensional overland flow are valuable tools for quantifying complex groundwater/stream interactions and for evaluating their influence on watershed processes. For the modeler who is used to defining streams as a boundary condition, the representation of channels in integrated models raises a number of conceptual and technical issues. These models are far more sensitive to channel topography than conventional groundwater models. On all spatial scales, both the topography of a channel and its connection with the floodplain are important. For example, the geometry of river banks influences bank storage and overbank flooding; the slope of the river is a primary control on the behavior of a catchment; and at the finer scale bedform characteristics affect hyporheic exchange. Accurate data on streambed topography, however, are seldom available, and the spatial resolution of digital elevation models is typically too coarse in river environments, resulting in unrealistic or undulating streambeds. Modelers therefore perform some kind of manual yet often cumbersome correction to the available topography. In this context, the paper identifies some common pitfalls, and provides guidance to overcome these. Both aspects of topographic representation and mesh discretization are addressed. Additionally, two tutorials are provided to illustrate: (1) the interpolation of channel cross‐sectional data and (2) the refinement of a mesh along a stream in areas of high topographic variability.     

Forecast of Natural Aquifer Discharge Using a Data‐Driven,Statistical Approach

In the Western United States, demand for water is often out of balance with limited water supplies. This has led to extensive water rights conflict and litigation. A tool that can reliably forecast natural aquifer discharge months ahead of peak water demand could help water practitioners and managers by providing advanced knowledge of potential water‐right mitigation requirements. The timing and magnitude of natural aquifer discharge from the Eastern Snake Plain Aquifer (ESPA) in southern Idaho is accurately forecast 4 months ahead of the peak water demand, which occurs annually in July. An ARIMA time‐series model with exogenous predictors (ARIMAX model) was used to develop the forecast. The ARIMAX model fit to a set of training data was assessed using Akaike's information criterion to select the optimal model that forecasts aquifer discharge, given the previous year's discharge and values of the predictor variables. Model performance was assessed by application of the model to a validation subset of data. The Nash‐Sutcliffe efficiency for model predictions made on the validation set was 0.57. The predictor variables used in our forecast represent the major recharge and discharge components of the ESPA water budget, including variables that reflect overall water supply and important aspects of water administration and management. Coefficients of variation on the regression coefficients for streamflow and irrigation diversions were all much less than 0.5, indicating that these variables are strong predictors. The model with the highest AIC weight included streamflow, two irrigation diversion variables, and storage.     

A skeleton design theory for spatial data infrastructure

In this paper, we look into the theory of designing geoservice systems, i.e., SDI networks and their constituent SDI nodes. As the field of SDI is strongly about bridging between geoservice systems, interoperability and harmonisation, it is not surprising that standardisation efforts are of crucial importance in it. These efforts have historically addressed abstract and concrete content models for data and metadata exchange, as well as abstract and concrete behavioural models for computational processes. The list of standards that are in use in the SDI field continues to expand, and reaches out to neighbouring fields such as sensor nets. We argue that given these trends, the resulting levels of standardisation in actual systems, and the complexity of geoservice systems in general, it appears only natural to look into the possibility to define a standardised design theory for SDI and its nodes, which addresses the function base and the communication base. Specifically, we provide an overview of those components that need to be designed, and what are their relationships. We do so in an abstract way, focussing on the concern of information content in this paper, and only hinting at an appropriate theory of realisation based on our skeleton theory.     

Late Cenozoic surface uplift,basaltic volcanism,and incision by the River Tigris around Diyarbakır,SE Turkey

We document the staircase of terraces of the River Tigris in the Diyarbakır area of SE Turkey, in the northern Arabian Platform, and improve control on the ages of these terrace deposits by dating of overlying basalt flows using the unspiked K–Ar technique. These fluvial terraces are formed of polymict gravel, including clasts derived from the Anatolian metamorphic terrane farther north as well as of local basalt. At least 9 Tigris terraces have been recognised so far, the highest of which, ∼200 m above present river level, marks the local transition from stacked deposition to fluvial incision, the timing of which is bounded between the mid Late Miocene and the Middle Pliocene. Our K–Ar dating indicates a hiatus in fluvial incision in the late Early Pleistocene, as basalts dated to 1.22 ± 0.02 and 1.07 ± 0.03 Ma overlie Tigris gravels at very similar levels, ∼60–70 m above the present river. The lower terraces record the subsequent entrenchment of the modern Tigris valley following an increase in incision rates in the early Middle Pleistocene, evident from the disposition of younger basalt, dated to 0.43 ± 0.02 Ma, capping fluvial gravel only ∼21–22 m above the present river level. Numerical modelling can account for the observed uplift history, as the response to coupling between surface processes and induced flow in the lower crust, with the mobile lower-crust thin (∼5–7 km thick), consistent with the known presence of a thick layer of mafic underplating at the base of the crust beneath the Arabian Platform. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Regional isostatic response to Messinian Salinity Crisis events

The salinity crisis of the Mediterranean during Messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years, resulting in the deposition of kilometer thick evaporitic sequences. A large and rapid drawdown of the Mediterranean water level caused erosion and deposition of non-marine sediments in a large ‘Lago Mare’ basin. Both the surface loading by the Lower Messinian evaporites, and the removal of the water load resulted in isostatic/flexural rebound that significantly affected river canyons and topographic slopes. We use flexure models to quantitatively predict possible signatures of these events, and verify these expectations at well-studied margins. The highly irregular shape of the reconstructed basin calls for a three-dimensional model. Near basin margins, plate-bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the Mediterranean. We focus on one specific sea level scenario for the Messinian Salinity Crisis, where most of the evaporite load was deposited during a sea level highstand, followed by a rapid desiccation. Evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins. Differential uplift may lead to significant slope angle changes and thus gravity flows. The relative scarcity of Lower Evaporite sequences along the margins may be a result of these phenomena. Normal faulting of Lower Evaporite and older sediments and rocks is expected on the margins. Desiccation enhances erosion of the freshly exposed continental shelf and slope. Subsidence and riverbed sedimentation occurs on the continental margins, and significant uplift towards the basin center. Reverse faulting is predicted at the margins. Finally, regional isostatic uplift following Zanclean flooding is predicted to destabilize margin slope deposits, and to cause marginal uplift, river down-cutting, and normal faulting.     

Fault seal prediction of seismic-scale normal faults in porous sandstone: A case study from the eastern Gulf of Suez rift,Egypt

A study of normal faults in the Nubian Sandstone Sequence, from the eastern Gulf of Suez rift, has been conducted to investigate the relationship between the microstructure and petrophysical properties of cataclasites developed along seismic-scale faults (slip-surface cataclasites) and smaller displacement faults (deformation bands) found in their damage zones. The results help to quantify the uncertainty associated with predicting the fluid flow behaviour of seismic-scale faults by analysing small faults recovered from core, a common procedure in the petroleum industry. The microstructure of the cataclasites was analysed as well as their single-phase permeability and threshold pressure. Faulting occurred at a maximum burial depth of ∼1.2 km. The permeability of deformation band and slip-surface cataclasites varies over ∼1.5 orders of magnitude for a given fault. Our results suggest that the lowest measured deformation band permeabilities provide a good estimate for the arithmetic-mean permeability of the major slip-surface cataclasites. This is because the cataclastic permeability reduction is mostly established early in the deformation history. Stress at the time of faulting rather than final strain appears to be the critical factor determining fault rock permeability. For viable predictions it is important that the slip-surface cataclasites and deformation bands originate from the same host. On the other hand, a higher uncertainty is associated with threshold pressure predictions, as the arithmetic-mean slip-surface cataclasite threshold pressure exceeds the highest measured deformation band threshold pressure by at least a factor of 4.     

Stratigraphic expression of the lateral propagation and growth of isolated fault-related uplifts

The lateral propagation of faults and folds is known to be an important process during the development of mountain belts, but little is known about the manner in which along‐strike fault–fold growth is expressed in pre‐ and syntectonic (growth) strata. We use a coupled tectonic and stratigraphic model to investigate the along‐strike stratigraphic expression of fault‐related folds/uplifts that grow in both the transport and strike directions. We consider faults that propagate following a quadratic (nonself‐similar evolution) or linear (self‐similar evolution) scaling law, using different slip distributions per episode of fault propagation, under general background sedimentation. We find that the long‐strike geometry of pre‐ and syntectonic strata and the geometry of growth axial surfaces reflect the mode of fault propagation. The geometry of strata observed in the model is similar to that observed in natural contractional structures when: (1) the evolution of the fault is nonself‐similar, or (2) the fault grows as a result of thrust faulting events with similar displacements along strike that are terminated abruptly at the fault tips.     

Formation of syngenetic and early diagenetic iron minerals in the late Archean Mt. McRae Shale, Hamersley Basin, Australia: New insights on the patterns, controls and paleoenvironmental implications of authigenic mineral formation

A section through the late Archean Mt. McRae Shale comprising, in ascending order, a lower shale interval (LSI), a banded iron formation (BIF), an upper shale (USI) and a carbonate (C1) has been analyzed for total Fe and Al contents and authigenic Fe present as carbonate, oxide, sulfide and silicate phases. The authigenic mineralogy is controlled by the episodic addition of Fe from hydrothermal activity and removal of Fe by sulfide, relative to rates of clastic sedimentation. The LSI and BIF have mean Fe_T/Al values of 2 and 5, respectively, that record iron enrichment from hydrothermal sources. Iron was precipitated primarily as siderite accompanied by Fe-rich chlorite from anoxic bottom waters rich in dissolved Fe. Pyrite formation was probably limited by the availability of sulfate, which was present at low concentrations and became rapidly depleted. The USI has generally lower Fe_T/Al values (0.6-1.3), similar to those found in Paleozoic shales, with the exception of one interval where enrichment may reflect either a weak hydrothermal source or the operation of an iron shuttle. This interval contains authigenic Fe predominantly as pyrite, where high values for DOP (>0.8) indicate the existence of a water column that became rich in dissolved sulfide (euxinic) when sulfate concentrations increased due to a transient or secular increase in ocean/atmosphere oxygenation. High concentrations of dissolved sulfide maintained low concentrations of dissolved Fe, which allowed only minor amounts of Fe to be precipitated as carbonates and silicates. The USI also has elevated concentrations of organic matter that most probably reflect increased productivity and likely limited euxinia to midportions of the water column on the basin margin. The carbonate C1 represents a basinal chemistry where sulfide has been removed and Fe_T/Al values are ∼1 indicating that hydrothermal activity again produced dissolved Fe-rich bottom waters. Detailed iron speciation of the Mt. McRae Shale can be used to recognize spatial and temporal variations in iron and sulfur inputs to the late Archean Hamersley Basin, just prior to the Paleoproterozoic rise in atmospheric oxygenation, and our refined methods have relevance to all Fe-rich deposits.     

Development of secondary porosity in the Fairholme carbonate complex (southwest Alberta, Canada)

Because of their economic importance as hydrocarbon reservoirs, the Upper Devonian dolomitized carbonate reefs in southwest Alberta have been the subject of several studies. Still, there is no consensus on the process of matrix dolomitization and furthermore, the process of vug development is not often addressed. The studied outcrops show features of an early diagenetic matrix-selective dolomitization by a Late Devonian seawater-derived fluid. Seepage reflux dolomitization combined with latent reflux is proposed, which best explains most chemical characteristics. The cements in the vugs are precipitated from warm saline, ⁸⁷Sr-enriched fluids and testify to thermogenic sulphate reduction based on the presence of sulphur, CO₂ and H₂S in inclusions, relatively high homogenization temperatures and depleted δ¹³C values, which sets constraints on the timing of vug formation. Secondary porosity may be created by the mixing of formation water with a tectonically and topographically driven fluid and by the dissolution of anhydrite nodules.