bluuebunny/crossref_metadata_2025 huggingface dataset:
Igneous sills record far-field and near-field stress interactions during volcano construction: Isle of Mull, Scotland
Authors: Stephens Tara , Walker Richard , Healy David , Bubeck Alodie , England Richard , McCaffrey Ken
Published: July 2018

Sill emplacement is typically associated with horizontally mechanically layered host rocks in a near-hydrostatic far-field stress state, where contrasting mechanical properties across the layers promote transitions from dykes, or inclined sheets, to sills. We used detailed field observations from the Loch Scridain Sill Complex (Isle of Mull, UK), and mechanical models to show that layering is not always the dominant control on sill emplacement. The studied sills have consistently shallow dips (1◦–25◦) and cut vertically bedded and foliated metamorphic basement rocks, and horizontally bedded cover sedimentary rocks and lavas. Horizontal and shallowly-dipping fractures in the host rock were intruded with vertical opening in all cases, whilst steeply-dipping discontinuities within the sequence (i.e. vertical fractures and foliation in the basement, and vertical polygonal joints in the lavas) were not intruded during sill emplacement. Mechanical models of slip tendency, dilation tendency, and fracture susceptibility for local and overall sill geometry data, support a radial horizontal compression during sill emplacement. Our models show that dykes and sills across Mull were emplaced during NW–SE horizontal shortening, related to a far-field tectonic stress state. The dykes generally accommodated phases of NE–SW horizontal tectonic extension, whereas the sills record the superposition of the far-field stress with a near-field stress state, imposed by emplacement of the Mull Central Volcano. We show that through detailed geometric characterisation coupled with mechanical modelling, sills may be used as an indication of fluctuations in the paleostress state.
Resolving the era of river-forming climates on Mars using stratigraphic logs of river-deposit dimensions
Authors: Kite Edwin , Howard Alan , Lucas Antoine , Lewis Kevin
Published: July 2018

River deposits are one of the main lines of evidence that tell us that Mars once had a climate different from today, and so changes in river deposits with time tell us something about how Mars climate changed with time. In this study, we focus in on one sedimentary basin – AeolisDorsa – which contains an exceptionally high number of exceptionally well-preserved river deposits that appear to have formed over an interval of >0.5 Myr. We use changes in the river deposits’ scale with stratigraphic elevation as a proxy for changes in river paleodischarge. Meander wavelengths tighten upwards and channel widths narrow upwards, and there is some evidence for a return to wide large-wavelength channels higher in the stratigraphy. Meander wavelength and channel width covary with stratigraphic elevation. The factor of 1.5-2 variations in paleochannel dimensions with stratigraphic elevation correspond to ~2.6-fold variability in bank-forming discharge (using standard wavelength-discharge scalings and width-discharge scalings). Taken together with evidence from a marker bed for discharge variability at ~10m stratigraphic distances, the variation in the scale of river deposits indicates that bank-forming discharge varied at both 10m stratigraphic (10^2 – 10^6 yr) and ~100 m stratigraphic (10^3 – 10^9 yr) scales. Because these variations are correlated across the basin, they record a change in basin-scale forcing, rather than smaller-scale internal feedbacks. Changing sediment input leading to achange in characteristic slopes and/or drainage area could be responsible, and another possibility is changing climate (±50 W/m2 in peak energy available for snow/ice melt).
Sedimentology and reservoir properties of tabular and erosive offshore transition deposits in wave-dominated, shallow-marine strata: Book Cliffs, USA
Authors: Eide Christian , Howell John , Buckley Simon
Published: July 2018

Facies models for wave-dominated shorelines include an "offshore transition zone" between shelfal mudstones and nearshore shoreface sandstones. Offshore transition zone deposits are commonly tabular sandstone beds interbedded with continuous mudstone beds. However, observations from the Blackhawk Formation show that the offshore transition zone locally consists of erosive-based sandstone beds with “pinch-and-swell” geometries containing steep-walled gutter-casts, in areas larger than 6 x 2 km along strike and dip. This increases the amount of sand-on-sand-contacts, and leads to improved vertical permeability. Predicting the distribution of erosive offshore transition within the subsurface is therefore desirable.In this study, offshore transition zone deposits have been studied using virtual outcrops. Tabular offshore transition zone deposits have continuous sandstone and mudstone beds much longer than 500 m, and erosive offshore transition zone deposits have discontinuous shales on average 60 m long. Reservoir modelling shows a 10-3 times increase in vertical permeability in erosive compared to tabular offshore transition deposits, the magnitude decreasing with increasing fraction of shale.Erosive offshore transition deposits occur near distributary channels, subaqueous channels and abrupt bathymetric breaks. A regional study shows that erosive offshore transition zone deposits are mainly developed where parasequences prograde into deeper water offshore the platform break of the preceding parasequence, are commonly associated with basinal turbidites, and may be related to erosion by bypassing turbidity currents.
Asthenosphere flow modulated by megathrust earthquake cycles
Authors: Barbot Sylvain
Published: July 2018

Subduction megathrusts develop the largest earthquakes, often close to large population centers. Understanding the dynamics of deformation at subduction zones is therefore important to better assess seismic hazards. Here, I develop consistent earthquake cycle simulations that incorporate localized and distributed deformation based on laboratory-derived constitutive laws by combining boundary and volume elements to represent the mechanical coupling between megathrust slip and solid-state flow in the oceanic asthenosphere and in the mantle wedge. The model is simplified, in two dimensions, but may help the interpretation of geodetic data. Megathrust earthquakes and slow-slip events modulate the strain-rate in the upper mantle, leading to large variations of effective viscosity in space and time and a complex pattern of surface deformation. While fault slip and flow in the mantle wedge generate surface displacements in the same, i.e., seaward, direction, the viscoelastic relaxation in the oceanic asthenosphere generates transient surface deformation in the opposite, i.e., landward, direction above the rupture area of the mainshock. Aseismic deformation above the seismogenic zone may be challenging to record, but it may reveal important constraints about the rheology of the subducting plate.
Distal turbidites reveal a common distribution for large (>0.1 km3) submarine landslide recurrence
Authors: Clare Michael , Talling Peter , Hunt James , Challenor Peter , Malgesini Giusseppe
Published: July 2018

Submarine landslides can be far larger than those on land, and are one of the most important processes for moving sediment across our planet. Landslides that are fast enough to disintegrate can generate potentially very hazardous tsunamis, and produce long run-out turbidity currents that break strategically important cable networks. It is important to understand their frequency and triggers. We document the distribution of recurrence intervals for large landslide-triggered turbidity currents (>0.1 km3) in three basin-plains. A common distribution of recurrence intervals is observed, despite variable ages and disparate locations, suggesting similar underlying controls on slide triggers and frequency. This common distribution closely approximates a temporally-random Poisson distribution, such that the probability of a large disintegrating slide occurring along the basin margin is independent of the time since the last slide. This distribution suggests that non-random processes such as sea level are not a dominant control on frequency of these slides. Recurrence intervals of major (>M 7.3) earthquakes have an approximately Poissonian distribution, suggesting they could be implicated as triggers. However, not all major earthquakes appear to generate widespread turbidites, and other as yet unknown triggers or sequential combinations of processes could produce the same distribution. This is the first study to show that large slide-triggered turbidites have a common frequency distribution in distal basin plains, and that this distribution is temporally random. This result has important implications for assessing hazards from landslide-tsunamis and seafloor cable breaks, and the long-term tempo of global sediment fluxes.
Development of cutoff-related knickpoints during early evolution of submarine channels
Authors: Sylvester Zoltan , Covault Jacob
Published: July 2018

Submarine channels are often thought of as having relatively simple geometries, with significant along-channel morphologic and stratigraphic continuity. Using high-resolution seismic reflection data from offshore Angola and a kinematic model of channel evolution, we present evidence that channels on the seafloor can develop slope variability as a result of meander cutoff events. When cutoffs develop, the shortened flow paths produce locally steep gradients, thus initiating knickpoints. Waves of knickpoint retreat and the related channel incision explain the occurrence of terraces and associated remnant channel deposits above the youngest channel thalweg. The simple processes of meander cutoff followed by knickpoint retreat are intrinsic to submarine channels and result in significant morphologic variability, erosion, and stratigraphic complexity, without any external forcing. These insights highlight the early evolution of submarine channels, a phase with a record that is commonly fragmented or completely absent as a result of subsequent erosion, and allow a better understanding of the autogenic controls on deep-marine stratigraphy.
Identifying causes of ground-penetrating radar reflections using time-domain reflectometry and sedimentological analyses
Authors: van Dam Remke , Schlager Wolfgang
Published: July 2018

Ground-penetrating radar (GPR) is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves. However, little is known about the exact cause of GPR reflections because few studies have coupled wave theory to petrophysical data. In this study, a 100- and 200-MHz GPR survey was conducted on aeolian deposits in a quarry. Time-domain reflectometry (TDR) was used to obtain detailed information on the product of relative permittivity and relative magnetic permeability, which mainly controls the GPR contrast parameter in the subsurface. Combining TDR data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and the product of relative permittivity and relative magnetic permeability. Synthetic radar traces, constructed using the TDR logs and sedimentological data from the lacquer peels, were compared with the actual GPR sections. Numerous peaks in the product of relative permittivity and relative magnetic permeability, which are superimposed on a baseline value of 4 for dry sand, are caused by potential GPR reflectors. These increases in the product of relative permittivity and relative magnetic permeability coincide with the presence of either organic material, having a higher water content and relative permittivity than the surrounding sediment, or iron oxide bands, enhancing relative magnetic permeability and causing water to stagnate on top of them. Sedimentary structures, as reflected in textural change, only result in possible GPR reflections when the volumetric water content exceeds 0.055. The synthetic radar traces provide an improved insight into the behaviour of radar waves and show that GPR results may be ambiguous because of multiples and interference.
Turbulence, displacement, death and worms: a day in the life of a fluvial Carboniferous bivalve
Authors: Kane Ian
Published: July 2018

In the Pennsylvanian Rough Rock Flags and Rough Rock of northern England, trace fossils attributed to the non-marine bivalve Carbonicola are found. Carbonicola, recorded by Lockeia and associated trace fossils, lived a semi-infaunal lifestyle and thus were influenced by both the sediment in which they were hosted, and the currents which supplied their nutrients and oxygen. A number of palaeocurrent indictors are commonly associated with Lockeia and are confirmed by this study: (a) downstream inclination of vertical burrows; (b) palaeoflow-parallel orientation of long axes. Additional palaeocurrent indicators include: (c) steeper scouring and higher sediment surface on the upstream side; (d) diffuse lamination downstream of the trace, or, more widespread downstream erosion. These semi-infaunal bivalves were partly exposed to the prevailing flow and acted as bed defects, disturbing flow over an otherwise relatively smooth surface; flow separation and acceleration enhanced flow turbulence around the bivalve leading to erosion and the development of a variably developed fan shaped zone of scour immediately downstream. Disturbance and destabilisation of sediment in this way may affect bivalves immediately downstream, plausibly explaining the relatively regular spacing pattern of individual Lockeia, or clusters of Lockeia, exposed on bedding planes and revealed by nearest neighbour analyses. Bivalves that did not survive high energy flow events were either trapped within the sediment, or transported downstream and deposited in lower-energy environments within the otherwise high-energy deposits of the Rough Rock. These are often associated with Planolites and Cochlichnus, trace fossils of scavenging worms which radiate around the imprints of dead bivalves. This assemblage of trace fossil s indicates that areas suitable for bivalve colonisation occurred in upstream areas.
Geological applications of digital terrain analysis
Authors: Grohmann Carlos
Published: July 2018

Editorial to the IJGIS Special Issue on "Geological applications of digital terrain analysis". In this volume, the modern advances in the field of geological terrain analysis are presented, while emphasis is given to the quantitative analysis of modern datasets.
Depth constraints on azimuthal anisotropy in the Great Basin from Rayleigh-wave phase velocity maps
Authors: Beghein Caroline , Snoke J. , Fouch Matthew
Published: July 2018

We present fundamental-mode Rayleigh-wave azimuthally anisotropic phase velocity maps obtained for the Great Basin region at periods between 16 s and 102 s. These maps offer the first depth constraints on the origin of the semi-circular shear-wave splitting pattern observed in central Nevada, around a weak azimuthal anisotropy zone. A variety of explanations have been proposed to explain this signal, including an upwelling, toroidal mantle flow around a slab, lithospheric drip, and a megadetachment, but no consensus has been reached. Our phase velocity study helps constrain the three-dimensional anisotropic structure of the upper mantle in this region and contributes to a better understanding of the deformation mechanisms taking place beneath the western United States. The dispersion measurements were made using data from the USArray Transportable Array. At periods of 16 s and 18 s, which mostly sample the crust, we find a region of low anisotropy in central Nevada coinciding with locally reduced phase velocities, and surrounded by a semi-circular pattern of fast seismic directions. Away from central Nevada the fast directions are ∼ N–S in the eastern Great Basin, NW–SE in the Walker Lane region, and they transition from E–W to N–S in the northwestern Great Basin. Our short-period phase velocity maps, combined with recent crustal receiver function results, are consistent with the presence of a semi-circular anisotropy signal in the lithosphere in the vicinity of a locally thick crust. At longer periods (28–102 s), which sample the uppermost mantle, isotropic phase velocities are significantly reduced across the study region, and fast directions are more uniform with an ∼ E–W fast axis. The transition in phase velocities and anisotropy can be attributed to the lithosphere–asthenosphere boundary at depths of ∼ 60 km. We interpret the fast seismic directions observed at longer periods in terms of present-day asthenospheric flow-driven deformation, possibly related to a combination of Juan de Fuca slab rollback and eastward-driven mantle flow from the Pacific asthenosphere. Our results also provide context to regional SKS splitting observations. We find that our short-period phase velocity anisotropy can only explain ∼ 30% of the SKS splitting times, despite similar patterns in fast directions. This implies that the origin of the regional shear-wave splitting signal is complex and must also have a significant sublithospheric component.
SRTM-based morphotectonic analysis of the Poços de Caldas Alkaline Massif, southeastern Brazil
Authors: Grohmann Carlos
Published: July 2018

An evaluation of SRTM 03” data applicability in geomorphology and morphotectonics analysis is proposed, considering the morphometric parameters slope, aspect, surface roughness and isobase surface. The study area, in southeastern Brazil, comprises the Poços de Caldas Alkaline Massif, a 33km-diameter Late Cretaceous collapsed volcanic caldera. Morphometric indices evaluated showed the correlation of landscape within the massif with NE-SW and NW-SE structures, as well as landforms related with recent tectonic influence. DEM-derived drainage presented satisfactory results when compared to a 1:50 000 topographic map.SRTM 03” proved to be a good resource for geomorphological analysis, up to the semi-detail scale.
How do we understand and visualize uncertainty?
Authors: Sambridge Malcolm , Beghein Caroline , Simons Frederik , Snieder Roel
Published: July 2018

Geophysicists are often concerned with reconstructing subsurface properties using observations collected at or near the surface. For example, in seismic migration, we attempt to reconstruct subsurface geometry from surface seismic recordings, and in potential field inversion, observations are used to map electrical conductivity or density variations in geologic layers. The procedure of inferring information from indirect observations is called an inverse problem by mathematicians, and such problems are common in many areas of the physical sciences. The inverse problem of inferring the subsurface using surface observations has a corresponding forward problem, which consists of determining the data that would be recorded for a given subsurface configuration. In the seismic case, forward modeling involves a method for calculating a synthetic seismogram, for gravity data it consists of a computer code to compute gravity fields from an assumed subsurface density model. Note that forward modeling often involves assumptions about the appropriate physical relationship between unknowns (at depth) and observations on the surface, and all attempts to solve the problem at hand are limited by the accuracy of those assumptions. In the broadest sense then, exploration geophysicists have been engaged in inversion since the dawn of the profession and indeed algorithms often applied in processing centers can all be viewed as procedures to invert geophysical data.
Time-dependent compaction as a mechanism for regular stick-slips
Authors: van den Ende Martijn , Niemeijer André
Published: July 2018

Owing to their destructive potential, earthquakes receive considerable attention from laboratory studies. In friction experiments, stick-slips are studied as the laboratory equivalent of natural earthquakes, and numerous attempts have been made to simulate stick-slips numerically using the Discrete Element Method (DEM). However, while laboratory stick-slips commonly exhibit regular stress drops and recurrence times, stick-slips generated in DEM simulations are highly irregular. This discrepancy highlights a gap in our understanding of stick-slip mechanics, which propagates into our understanding of earthquakes. In this work, we show that regular stick-slips emerge in DEM when time-dependent compaction by pressure solution is considered. We further show that the stress drop and recurrence time of stick-slips is directly controlled by the kinetics of pressure solution. Since compaction is known to operate in faults, this mechanism for frictional instabilities directly relates to natural seismicity.
Seismic Interpretation of Sill-Complexes in Sedimentary Basins: The ‘Sub-Sill Imaging Problem’
Authors: Eide Christian , Schofield Nick , Lecomte Isabelle , Buckley Simon , Howell John
Published: July 2018

Application of 3D-seismic reflection-data to igneous systems in sedimentary basins has led to a revolution in the understanding of mafic sill-complexes. However, there is considerable uncertainty on how geometries and architecture of sill complexes within the subsurface relates those imaged in seismic reflection-data. To provide constraints on how sill complexes in seismic data should be interpreted, we present synthetic seismograms generated from a seismic-scale (22x0.25 km) outcrop in East Greenland constrained by abundant field-data.This study highlights how overlying igneous rocks adversely affect imaging of underlying intrusions and rocks by decreasing seismic amplitude, frequency and making steeply dipping features near-impossible to image. Furthermore, seismic modelling shows that because of the high impedance contrast between siliciclastic host rock and dolerites, thin (< 5m) intrusions should in principle be imaged at relatively high amplitudes. This is contrary to many published ‘rules of thumb’ for seismic detectability of sill intrusions. However, actual seismic data combined with well-data shows significant amounts of un-imaged sill intrusions, and this is likely due to limited resolution, overburden complexity, poor velocity-models, and interference between closely spaced sill-splays. Significant improvements could be made by better predicting occurrence and geometry of sill intrusions and including these in velocity models.
Is the Earth Lazy? A review of work minimization in fault evolution
Authors: Cooke Michele , Madden Elizabeth
Published: July 2018

The principle of work minimization has been used in various forms to account for the development of active fault systems within a wide range of tectonic settings. We review the successes, challenges and implications learned from previous applications of work minimization. Examination of the energy budget provides insight into the competing influences of different processes within fault systems at a variety of scales. We present each work budget component with considerations for numerical implementation. Additionally, we demonstrate numerical implementation by solving for the energy budgets and finding the most efficient propagation paths of a joint and several faults. Consideration of the energy budget captures growth patterns that are consistent with both laboratory observations and theoretical predictions using the energy release rate, G. Unlike using G, work minimization is not limited to collinear growth. In comparison with predictions using Coulomb failure planes, work minimization eliminates uncertainty in predicting fault propagation by (1) evaluating the trade-off between tensile and shear failure ahead of the fault and (2) avoiding the ambiguity introduced by the two potential Coulomb failure planes. Application of work minimization to faulting demonstrates the effectiveness of this approach in predicting both the orientation and timing of fault propagation.
Numerical solution of a non-linear conservation law applicable to the interior dynamics of partially molten planets
Authors: Bower Dan , Sanan Patrick , Wolf Aaron
Published: July 2018

The energy balance of a partially molten rocky planet can be expressed as a non-linear diffusion equation using mixing length theory to quantify heat transport by both convection and mixing of the melt and solid phases. Crucially, in this formulation the effective or eddy diffusivity depends on the entropy gradient, dS/dr, as well as entropy itself. First we present a simplified model with semianalytical solutions that highlights the large dynamic range of dS/dr---around 12 orders of magnitude---for physically-relevant parameters. It also elucidates the thermal structure of a magma ocean during the earliest stage of crystal formation. This motivates the development of a simple yet stable numerical scheme able to capture the large dynamic range of dS/dr and hence provide a flexible and robust method for time-integrating the energy equation.Using insight gained from the simplified model, we consider a full model, which includes energy fluxes associated with convection, mixing, gravitational separation, and conduction that all depend on the thermophysical properties of the melt and solid phases. This model is discretised and evolved by applying the finite volume method (FVM), allowing for extended precision calculations and using dS/dr as the solution variable. The FVM is well-suited to this problem since it is naturally energy conserving, flexible, and intuitive to incorporate arbitrary non-linear fluxes that rely on lookup data. Special attention is given to the numerically challenging scenario in which crystals first form in the centre of a magma ocean.The computational framework we devise is immediately applicable to modelling high melt fraction phenomena in Earth and planetary science research. Furthermore, it provides a template for solving similar non-linear diffusion equations that arise in other science and engineering disciplines, particularly for non-linear functional forms of the diffusion coefficient.
Fine-Scale SAR Soil Moisture Estimation in the Subarctic Tundra
Authors: Zwieback Simon , Berg Aaron
Published: July 2018

In the subarctic tundra, soil moisture information can benefit permafrost monitoring and ecological studies, but fine-scale remote sensing approaches are lacking. We explore the suitability of C-band SAR, paying attention to two challenges soil moisture retrieval faces. First, the microtopography and the heterogeneous organic soils impart unique microwave scattering properties, even in absence of noteworthy shrub cover. Empirically, we find the polarimetric response is highly random (entropies > 0.7). The randomness precludes the application of purely polarimetric approaches to soil moisture estimation, as it causes a tailor-made decomposition to break down. For comparison, the L-band scattering response is much more surface-like (entropies of 0.1-0.2), also in terms of its angular characteristics. The second challenge concerns the large spatial but small temporal variability of soil moisture. Accordingly, the Radarsat-2 C-band backscatter has a limited dynamic range (approx. 2 dB). However, contrary to polarimetric indicators, it shows a clear soil moisture signal. To account for the small dynamic range while retaining a 100 m spatial resolution, we embed an empirical time-series model in a Bayesian framework. This framework adaptively pools information from neighboring grid cells, thus increasing the precision. The retrieved soil moisture index achieves correlations of 0.3-0.5 with in-situ network data and, upon calibration, RMSEs of < 0.04 m3m-3. As this approach is applicable to Sentinel-1 data, it can potentially provide frequent soil moisture estimates across large regions. In the long term, L-band data hold greater promise for operational retrievals.
Metrology and Traceability of U-Pb Isotope Dilution Geochronology (EARTHTIME Tracer Calibration Part I)
Authors: Condon Daniel , Schoene Blair , McLean Noah , Bowring Samuel , Parrish Randall
Published: July 2018

Mixed 235U–233U–205Pb(–202Pb) tracers for U–Pb isotope-dilution isotope ratio mass spectrometry have been prepared under the auspices of the EARTHTIME Initiative. The methods and results for the preparation and calibration of the U/Pb ratio and isotopic abundances are given, and the various sources of uncertainty are discussed and quantified. The accuracy of the EARTHTIME U–Pb tracer isotopic composition can be traced back to SI units via a series of assay and isotopic composition reference materials combined with the experiments described herein. The parameters used in calculating U/Pb ratios (and inferentially U–Pb dates) have correlated uncertainties that result in a total uncertainty contribution to 206Pb/238U dates of ± < 0.03% (95% confidence). For suitable terrestrial materials such as zircon, when other sources of uncertainty have been minimised (e.g., open-system behaviour, 238U/235U variation, intermediate daughter product disequilibrium, common Pb, etc.) the U–Pb tracer calibration uncertainty is a limiting factor in the accuracy of U–Pb geochronology – but less so than the uncertainty in the 238U and 235U decay constants (±0.11 and 0.14% 2σ). The calibration approach of the mixed EARTHTIME 235U–233U–205Pb(–202Pb) tracers, in addition to updated values for reference materials (e.g., mixed gravimetric reference solutions), and parameters (e.g., Pb reference material assay), can be applied to other laboratory-specific U–Pb tracers and will facilitate the generation of accurate and directly inter-comparable U–Pb data.
Monoclinal flexure of an orogenic plateau margin during subduction, south Turkey
Authors: Fernández-Blanco David , Bertotti Giovanni , Aksu Ali , Hall Jeremy
Published: July 2018

Geologic evidence across orogenic plateau margins enables the discrimination of the relative contributions of orogenic, epeirogenic and/or climatic processes that lead to growth and maintenance of those plateaus and their margins. Here, we discuss the mode of formation of the southern margin of the Central Anatolian Plateau (SCAP) and evaluate its time of formation using fieldwork in the onshore and seismic reflection data in the offshore. In the onshore, uplifted Miocene rocks in a dip-slope topography show monocline flexure over >100 km, km-scale asymmetric folds verging south, and outcrop-scale syn-sedimentary reverse faults. On the Turkish shelf, vertical faults transect the basal latest Messinian of a ~10 km fold where on-structure syntectonic wedges and synsedimentary unconformities indicate pre-Pliocene uplift and erosion, followed by Pliocene and younger deformation. Collectively, Miocene rocks delineate a flexural monocline at plateau margin scale that is expressed along our on-offshore sections as a kink-band fold with a steep flank ~20–25 km long. In these reconstructed sections, we estimate a relative vertical displacement of ~3.8 km at rates of ~0.5 mm/y, and horizontal shortening values <1 %. We use this evidence together with our observations of shortening at outcrop, basin, plateau-margin and forearc-system scales to infer that the SCAP forms as a monoclinal flexure to accommodate deep-seated thickening and shortening since >5 Ma, and to contextualize the plateau margin as the forearc high of the Cyprus subduction system.
Using filtered and semi-continuous high rate GPS for monitoring deformations
Authors: Ragheb Ahmed , Edwards Stuart , Clarke Peter
Published: July 2018

Multipath is a major sidereally-repeating error affecting precise GPS positioning and deformation monitoring. Because satellite-receiver geometry repeats almost exactly every sidereal day, filtering can reduce multipath in near-static situations. Here, we investigate how sidereal filtering can be used in a switched multi-antenna array system providing semi-continuous GPS data, which may be adopted in order to reduce hardware costs. Depending on the receiver’s set-up, the optimum session switching interval is 119 seconds or a multiple thereof. This provides sufficient reliable epochs using a short switching interval, and is synchronized with the appropriate geometry repeat interval for sidereal filter application. The semi-continuous sidereally-filtered GPS technique is efficient in detecting horizontal and vertical displacements, surpassing 5 mm and 8 mm precision respectively per epoch in near-static environments with moderately high multipath. This provides the capability of monitoring deformations occurring at periods greater than double the switching interval, although it can also be used for monitoring rapid structural deformations despite data gaps which may affect temporal resolution. Consequently, this combined method presents an efficient, cost-effective and precise GPS technique.
Exogenic forcing and autogenic processes on continental divide location and mobility -- preprint
Authors: Moodie Andrew
Published: July 2018

The position and mobility of drainage divides is an expression of exogenic landscape forcing and autogenic channel network processes integrated across a range of scales. At the large scale, represented by major rivers and continental drainage divides, the organization of drainage patterns and divide migration reflects the long-wavelength gradients of the topography, which are exogenically influenced by tectonics, isostasy, and/or dynamic topography. This analysis utilizes long-wavelength topography synthesized by a low-pass filter, which provides a novel framework for predicting the direction of divide movement as well as an estimate of the ultimate divide location, that is complementary to recent studies that have focused on the χ channel metric. The Gibraltar Arc active plate boundary and Appalachian stable plate interior, two tectonically diverse settings with ongoing drainage system reorganization, are chosen to explore the length scales of exogenic forcings that influence continental drainage divide location and migration. The major watersheds draining both the active and decay-phase orogens studied here are organized by topographic gradients that are expressed in long-wavelength low-pass filtered topography (λ ≥ 100 km). In contrast, the river network and divide location is insensitive to topographic gradients measured over filtered wavelengths < 100 km that are set by local crustal structures and rock type. The lag time between exogenic forcing and geomorphic response and feedbacks cause divide migration to be unsteady, and occur through pulses of drainage capture and drainage network reorganization that are recorded in sedimentological, geomorphic, or denudation data.
High Resolution, Millennial-Scale Patterns of Bed Compensation on a Sand-Rich Intraslope Submarine Fan, Western Niger Delta Slope
Authors: Jobe Zane , Sylvester Zoltan , Howes Nick , Pirmez Carlos , Parker Andrew , Cantelli Alessandro , Smith Ru , Wolinsky Matthew , O'Byrne Ciaran , Slowey Niall
Published: July 2018

Near-seafloor core and seismic-reflection data from the western Niger Delta continental slope document the facies, architecture, and evolution of submarine channel and intraslope submarine fan deposits. The submarine channel enters an 8 km long x 8 km wide intraslope basin, where more than 100 m of deposits form an intraslope submarine fan. Lobe deposits in the intraslope submarine fan show no significant downslope trend in sand presence or grain size, indicating that flows were bypassing sediment through the basin. This unique dataset indicates that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by traditional lobe facies models, and that thickness patterns in intraslope submarine fans do not necessarily correlate with sand presence and/or quality.Core and radiocarbon age data indicate that sand beds progressively stack southward during the late Pleistocene, resulting in the compensation of at least two lobe elements. The youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location and age of these two compensating lobe elements. A third compensation event would have shifted sand deposition back to the northern part of the fan, but sediment supply was interrupted by rapid sea level rise during Meltwater Pulse 1-A at ca. 14 ka, resulting in abandonment of the depositional system.
Unravelling intrusion-induced forced fold kinematics and ground deformation using 3D seismic reflection data
Authors: Reeves Jennifer , Magee Craig , Jackson Christopher
Published: July 2018

Sills emplaced at shallow-levels are commonly accommodated by overburden uplift, producing forced folds. We examine ancient forced folds developed above saucer-shaped sills using 3D seismic reflection data from the Canterbury Basin, offshore SE New Zealand. Seismic-stratigraphic relationships indicate sill emplacement occurred incrementally over ~31 Myr between the Oligocene (~35–32 Ma) and Early Pliocene (~5–4 Ma). Two folds display flat-topped geometries and amplitudes that decrease upwards, conforming to expected models of forced fold growth. Conversely, two folds display amplitudes that locally increase upwards, coincident with a transition from flat-topped to dome-shaped morphologies and an across-fold thickening of strata. We suggest these discrepancies between observed and expected forced fold geometry reflect uplift and subsidence cycles driven by sill inflation and deflation. Unravelling these forced fold kinematic histories shows complex intrusion geometries can produce relatively simple ground deformation patterns, with magma transgression corresponds to localisation of uplift.
Plants and Drought in a Changing Climate
Authors: Swann Abigail
Published: July 2018

Purpose of review: Climate is changing in response to rising concentrations of atmospheric CO2 and it is commonly asserted that this will cause droughts to become more frequent and severe. However, different metrics of drought give diverging estimates of future impacts. I present a summary of the significant yet underappreciated influence that plant stomatal and growth responses to CO2 have on drought, and highlight new insights into the impacts of drought on plants in a warmer world. Recent findings: Plants influence the water availability on land, and thus reduce the duration and intensity of droughts under higher CO2 conditions. Plants are concurrently more vulnerable to mortality when droughts occur under hotter conditions.Summary: The frequency and severity of drought in the future depends on the response of plants to a changing climate—ignoring plant responses leads to over-prediction of drought. Nonetheless, the impact of current frequencies of drought on plants could lead to higher mortality rates in the future as plants must withstand drought stress simultaneously with hotter temperatures.
Influence of cell size on volume calculation using digital terrain models: A case of coastal dune fields
Authors: Grohmann Carlos
Published: July 2018

In this work, we analyze how variation in cell size influences the volume calculated from Digital Terrain Models (DTMs) derived from a LiDAR (Light Detection and Ranging) survey in two coastal Late Holocene dune fields in southern Brazil. Cell size varied from 1 to 100 m. The RMSE (Root Mean Square Error) of the resampled DTMs from the original LiDAR (with 0.5 m resolution) increases linearly with cell size, while the R-squared decreases following a second-order trend. The volume does not show simple linear or exponential behavior, but fluctuates with positive and negative deviations from the original DTM. This fluctuation can be explained by a random factor in the position of the cell with regard to landforms and a relationship between cell and landform size, wherein a small change in cell size can lead to an under- or overestimation of volume. ASTER GDEM (Global Digital Elevation Model) and X-SAR SRTM (Shuttle Radar Topography Mission) 1 arcsec Digital Elevation Models (DEMs) were not considered viable volume sources due to large deviations from the reference data, either as a consequence of noise in the SRTM X-SAR data or lack of bias elevation correction to a common reference base in the GDEM processing chain. Volumes from a 3-arcsec SIR-C SRTM deviated around +- 5% from the reference data and are considered suitable input for numerical simulations of Quaternary dune field evolution models because these values should be within the expected range of sediment volume changes over hundreds to millions of years.
Impacts of land-use and land-cover change on stream hydrochemistry in the Cerrado and Amazon biomes
Authors: Nóbrega Rodolfo , Guzha Alphonce , Lamparter Gabriele , Amorim Ricardo , Couto Eduardo , Hughes Harold , Jungkunst Hermann , Gerold Gerhard
Published: July 2018

Studies on the impacts of land-use and land-cover change on stream hydrochemistry in active deforestation zones of the Amazon agricultural frontier are limited and have often used low-temporal-resolution datasets. Moreover, these impacts are not concurrently assessed in well-established agricultural areas and new deforestations hotspots. We aimed to identify these impacts using an experimental setup to collect high-temporal-resolution hydrological and hydrochemical data in two pairs of low-order streams in catchments under contrasting land use and land cover (native vegetation vs. pasture) in the Amazon and Cerrado biomes. Our results indicate that the conversion of natural landscapes to pastures increases carbon and nutrient fluxes via streamflow in both biomes. These changes were the greatest in total inorganic carbon in the Amazon and in potassium in the Cerrado, representing a 5.0- and 5.5-fold increase in the fluxes of each biome, respectively. We found that stormflow, which is often neglected in studies on stream hydrochemistry in the tropics, plays a substantial role in the carbon and nutrient fluxes, especially in the Amazon biome, as its contributions to hydrochemical fluxes are mostly greater than the volumetric contribution to the total streamflow. These findings demonstrate that assessments of the impacts of deforestation in the Amazon and Cerrado biomes should also take into account rapid hydrological pathways; however, this can only be achieved through collection of high-temporal-resolution data.
In-depth examination of spatio-temporal figures in open reproducible research (Preprint)
Authors: Konkol Markus , Kray Christian
Published: July 2018

Figures such as maps and time series are essential means to visualize spatio-temporalresults in scientific papers. Being able to recompute them using the underlying sourcecode and data is thus a core aspect in reproducible research. However, many scientistssee the preparation of code and data for publication as an additional burdenwithout immediate benefits. In this work, we investigate advantages and new capabilitiesof reproducible research papers. Our key contributions are (i) the extensionof a geoscientist’s workflow while examining papers including reproducible figuressuch as maps and (ii) the prototypical implementation of the workflow as a webapplication. The workflow is based on current practices of geoscientists and encapsulatesbenefits of reproducible figures. It is informed by ideas and needs identifiedby geoscientists in a survey, interviews, and a focus group. Based on their statements,we first extend the traditional workflow steps Discovery and Inspection byadditional capabilities and propose two new steps: Manipulation of the content ofa spatio-temporal figure and Substitution of the underlying code and data. The extendedworkflow and its implementation might facilitate in-depth examination andreusability of geoscientific results.
Ocean tide loading and relative GNSS in the British Isles
Authors: Clarke Peter , Penna Nigel
Published: July 2018

Ocean tide loading (OTL) affects all parts of the British Isles to varying degree, causing peak-to-peak vertical displacements of up to 13 cm in South-West England over semi-diurnal and diurnal timescales. Lateral displacements are typically around one-third of the magnitude of vertical displacements at a point, so are also considerable for carrier phase GNSS surveying. Using a recent numerical ocean tide model, we predict that widespread residual displacements up to ~1 cm remain in kinematic or short-occupation static relative GNSS positions computed with respect to the nearest continuously operating reference station. Even if OTL is not modelled explicitly, these errors will be mitigated by network GNSS to an extent dependent on the number and location of reference stations used, and the adjustment or error interpolation scheme adopted in the processing. For a selection of error interpolation algorithms, we predict that throughout most inland regions of Great Britain and Ireland, network processing reduces the residual OTL error to within the expected kinematic GNSS system noise. However, pockets of OTL error exceeding 1 cm may remain, especially in coastal locations and in South-West Ireland, South Wales, South-West England, and the islands off the west coast of Scotland. Residual OTL error at semi-diurnal periods dominates that at diurnal periods. We derive a simple heuristic for estimating the magnitude of this error from a sample of observations at a locality, valid within a short window of the spring/neap tidal cycle, and show how the residual error may, if necessary, be mitigated by a suitable averaging scheme.
Moisture balance over the Iberian Peninsula according to a regional climate model: The impact of 3DVAR data assimilation.
Authors: González-Rojí Santos , Saenz Jon , Ibarra-Berastegi Gabriel , de Argandoña Javier
Published: July 2018

An analysis of the atmospheric branch of the hydrological cycle by means of a 15 km resolution numerical integration performed using WRF nested in ERA Interim is presented. Two WRF experiments covering the period 2010-2014 were prepared. The first one (N) was configured as in standard numerical downscaling experiments. The second one (D), with the same parameterizations, included a step of 3DVAR data assimilation every six hours. Apart from comparing our results with ERA Interim data, several observational datasets were used to validate the precipitable water (radiosondes and MODIS data), precipitation (EOBS, ECA\&D, TRMM and GPCP) or evaporation (GLEAM). The verification results showed that the D experiment systematically performs better than N and in many instances, too, better than the forcing reanalysis. According to the results, the leading terms of the water balance are the tendency of the precipitable water, the divergence of moisture flux, evaporation and precipitation. No spatial patterns were recognizable for the annual accumulated evaporation, but the effect of the Atlantic fronts was detected in the precipitation patterns. The transboundary moisture fluxes through the contour of the Iberian Peninsula behave differently depending on the season during 2010-2014. During winter, they show a net moisture import through the boundaries. During spring, summer or autumn moisture is exported specially through the Mediterranean coast, and only during midday this feature is reversed due to sea breezes.