bluuebunny/crossref_metadata_2025 huggingface dataset:
The INTAV intercomparison of electron-beam microanalysis of glass by tephrochronology laboratories, results and recommendation
Authors: Kuehn Stephen , Froese Duane , Shane Phil
Published: July 2018

The INternational focus group on Tephrochronology And Volcanism (INTAV) of the International Union for Quaternary Research (INQUA) has conducted an intercomparison of tephrochronology laboratories with electron-beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries. This assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community. The intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation. Participating laboratories were each supplied with a mount containing three samples for analysis: (1) rhyolitic Lipari obsidian ID3506, (2) phonolitic Sheep Track tephra from Mt. Edziza, British Columbia, Canada, and (3) basaltic Laki 1783 A.D. tephra. A fourth sample, rhyolitic Old Crow tephra, was also distributed.Most laboratories submitted extensive details of their analytical procedures in addition to their analytical results. Most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration. Approximately two-thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance. Despite substantial variety in procedures and calibration standards, most mean concentrations compare favorably between laboratories and with other data. Typically, four or fewer data contributions had means for a given element on a given sample that differed by more than ±2 standard deviations from the overall means. Obtaining accurate Na2O concentrations for the phonolitic tephra proved to be a challenge for many laboratories. Only one-half of the data sets had means within ±1 standard deviation of the ∼8.2 wt% Na2O value obtained by other methods. One mean is higher and 14 are lower. Three of the data set means fall below 7 wt% Na2O. Most submissions had relative precision better than 1–5% for the major elements. For low-abundance elements, the precision varied substantially with relative standard deviations as small as 10% and as large as 110%. Because of the strong response to this project, the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories. Finally, recommendations are provided for improving accuracy, precision, and reporting of electron-beam microanalytical data from glasses.
Revisiting the crustal structure and kinematics of the Central Andes at 33.5°S : implications for the mechanics of Andean mountain-building
Authors: Riesner Magali , Lacassin Robin , Simoes Martine , Carrizo Daniel , Armijo Rolando
Published: July 2018

The Andean belt is the only present-day active case example of a subduction-type orogeny. However, an existing controversy opposes classical views of Andean growth as an east-verging retro-wedge, against a recently proposed bi-vergent model involving a primary west-vergent crustal-scale thrust synthetic to the subduction. We examine these diverging views by quantitatively re-evaluating the orogen structural geometry and kinematics at the latitude of 33.5°S. We first provide a 3D-geological map and build an updated section of the east-vergent Aconcagua fold-and-thrust belt (Aconcagua-FTB), which appears as a critical structural unit in this controversy. We combine these data with geological constraints on nearby structures to derive a complete and larger scale section of the Principal Cordillera within the forearc region. We restore our section and integrate published chronological constraints to build an evolutionary model showing the evolving shortening of this forearc part of the Andes. The proposed kinematics implies uplift of the Frontal Cordillera basement since ~20-25 Ma, supported by westward thrusting over a crustal ramp that transfers shortening further west across the Principal Cordillera. The Aconcagua-FTB is evidenced as a secondary east-verging roof thrust atop the large-scale basement antiform culmination of the Frontal Cordillera. We estimate a shortening of ~27-42 km across the Principal Cordillera, of which only ~30% is absorbed by the Aconcagua-FTB. Finally, we combine these findings with published geological data on the structure of the eastern back-arc Andean mountain front, and build a crustal-scale cross-section of the entire Andes at 33.5° S. We estimate a total orogenic shortening of ~31-55km, mainly absorbed by crustal west-vergent structures synthetic to the subduction. Our results provide quantitative key geological inferences to revisit this subduction-type orogeny and compare it to collisional alpine-type orogenic belts.
Lake Baikal isotope records of Holocene Central Asian precipitation
Authors: Swann George , Mackay Anson , Vologina Elena , Jones Matthew , Panizzo Virginia , Leng Melanie , Sloane Hilary , Snelling Andrea , Sturm Michael
Published: July 2018

Climate models currently provide conflicting predictions of future climate change across Central Asia. With concern over the potential for a change in water availability to impact communities and ecosystems across the region, an understanding of historical trends in precipitation is required to aid model development and assess the vulnerability of the region to future changes in the hydroclimate. Here we present a record from Lake Baikal, located in the southern Siberian region of central Asia close to the Mongolian border, which demonstrates a relationship between the oxygen isotope composition of diatom silica (δ18Odiatom) and precipitation to the region over the 20th and 21st Century. From this, we suggest that annual rates of precipitation in recent times are at their lowest for the past 10,000 years and identify significant long-term variations in precipitation throughout the early to late Holocene interval. Based on comparisons to other regional records, these trends are suggested to reflect conditions across the wider Central Asian region around Lake Baikal and highlight the potential for further changes in precipitation with future climate change.
The role of glacier retreat for Swiss hydropower production
Authors: Schaefli Bettina , Manso Pedro , Fischer Mauro , Huss Matthias , Farinotti Daniel
Published: July 2018

High elevation or high latitude hydropower production (HP) strongly relies on water resources that are influenced by glacier melt and are thus highly sensitive to climate warming. Despite of the wide-spread glacier retreat since the development of HP infrastructure in the 20th century, little quantitative information is available about the role of glacier mass loss for HP. We provide the first regional quantification for the share of Alpine hydropower production that directly relies on the waters released by glacier mass loss, i.e. on depletion of long-term ice storage that cannot be replenished by precipitation in the coming decades. Based on the case of Switzerland (which produces over 50% of its electricity from hydropower), we show that since 1980, 3.0% to 4.0% (1.0 to 1.4 TWh yr-1) of the country-scale hydropower production was directly provided by the net glacier mass loss and that this share is likely to reduce substantially by 2040-2060. For the period 2070-2090, a production reduction of about 1.0 TWh yr-1 is anticipated. The highlighted regional differences, both in terms of HP share from glacier mass loss and in terms of timing of production decline, emphasize the need for similar analyses in other Alpine or high latitude regions.
The relationships between regional Quaternary uplift, deformation across active normal faults and historical seismicity in the upper plate of subduction zones: The Capo D’Orlando Fault, NE Sicily.
Authors: Meschis Marco , Roberts Gerald , Robertson Jenni , Briant Rebecca
Published: July 2018

In order to investigate deformation within the upper plate of the Calabrian subduction zone we have mapped and modelled a sequence of Late Quaternary palaeoshorelines tectonically‐deformed by the Capo D’Orlando normal fault, NE Sicily, which forms part of the actively deforming Calabrian Arc. In addition to the 1908 Messina Strait earthquake (Mw 7.1), this region has experienced damaging earthquakes, possibly on the Capo D’Orlando Fault, however, it is not considered by some to be a potential seismogenic source. Uplifted Quaternary palaeoshorelines are preserved on the hangingwall of the Capo D’Orlando Fault, indicating that hangingwall subsidence is counteracted by regional uplift, likely because of deformation associated with subduction/collision. We attempt to constrain the relationship between regional uplift, crustal extensional processes and historical seismicity, and we quantify both the normal and regional deformation signals. We report uplift variations along the strike of the fault and use a synchronous correlation technique to assign ages to palaeoshorelines, facilitating calculation of uplift rates and the fault throw‐rate. Uplift rates in the hangingwall increase from 0.4 mm/yr in the centre of the fault to 0.89 mm/yr beyond its SW fault tip, suggesting 0.5 mm/yr of fault related subsidence, which implies a throw‐rate of 0.63 ± 0.02 mm/yr, and significant seismic hazard. Overall, we emphasise that upper plate extension and related vertical motions complicate the process of deriving information on the subduction/collision process, such as coupling and slip distribution on the subduction interface, parameters that are commonly inferred for other subduction zones without considering upper plate deformation.
Data quality of collocated portable broadband seismometers using direct burial and vault emplacement
Authors: Aderhold Kasey , Anderson Katherine , Reusch Angela , Pfeifer Mary , Aster Richard , Parker Tim
Published: July 2018

Temporary broadband sensor deployments have traditionally been predominantly emplaced using shallow vaults that require more materials, personnel, and time than direct burial. However, new developments in seismometer and seismograph technology are increasingly facilitating systems that can be directly buried in earth or snow without vault enclosures. We analyze data from two identical shallow vaults installed adjacent to two identical direct burial sites in soft flood plain alluvial and shallow water table conditions near Socorro, New Mexico. Data recorded from these four sensors over eight months in 2012 were assessed to determine if the emplacement type had a significant and systematic effect on data quality.
Work optimization predicts accretionary faulting: An integration of physical and numerical experiments
Authors: McBeck Jessica , Cooke Michele , Herbert Justin , Maillot Bertrand , Souloumiac Pauline
Published: July 2018

We employ work optimization to predict the geometry of frontal thrusts at two stages of an evolving physical accretion experiment. Faults that produce the largest gains in efficiency, or change in external work per new fault area, ΔWext/ΔA, are considered most likely to develop. The predicted thrust geometry matches within 1 mm of the observed position and within a few degrees of the observed fault dip, for both the first forethrust and backthrust when the observed forethrust is active. The positions of the second backthrust and forethrust that produce >90% of the maximum ΔWext/ΔA also overlap the observed thrusts. The work optimal fault dips are within a few degrees of the faults dips that maximize the average Coulomb stress. Slip gradients along the detachment produce local elevated shear stresses and high strain energy density regions that promote thrust initiation near the detachment. The mechanical efficiency (Wext) of the system decreases at each of the two simulated stages of faulting and resembles the evolution of experimental force. The higher ΔWext/ΔA due to the development of the first pair relative to the second pair indicates that the development of new thrusts may lead to diminishing efficiency gains as the wedge evolves. The numerical estimates of work consumed by fault propagation overlap the range calculated from experimental force data, and crustal faults. The integration of numerical and physical experiments provides a powerful approach that demonstrates the utility of work optimization to predict the development of faults.
Rupture Process during the Mw 8.1 2017 Chiapas Mexico Earthquake: Shallow Intraplate Normal Faulting by Slab Bending
Authors: Okuwaki Ryo , Yagi Yuji
Published: July 2018

A seismic source model for the Mw 8.1 2017 Chiapas, Mexico, earthquake was constructed by kinematic waveform inversion using globally observed teleseismic waveforms, suggesting that the earthquake was a normal-faulting event on a steeply dipping plane, with the major slip concentrated around a relatively shallow depth of 28 km. The modeled rupture evolution showed unilateral, down-dip propagation northwestward from the hypocenter, and the down-dip width of the main rupture was restricted to less than 30 km below the slab interface, suggesting that the down-dip extensional stresses due to the slab bending were the primary cause of the earthquake. The rupture front abruptly decelerated at the northwestern end of the main rupture where it intersected the subducting Tehuantepec Fracture Zone, suggesting that the fracture zone may have inhibited further rupture propagation.
Reactivation of intrabasement structures during rifting - A case study from offshore southern Norway
Authors: Phillips Thomas , Jackson Christopher , Bell Rebecca , Duffy Oliver , Fossen Haakon
Published: July 2018

Pre-existing structures within crystalline basement may exert a significant influence over the evolution of rifts. However, the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood. Using borehole-constrained 2D and 3D seismic reflection data from offshore southern Norway we identify and constrain the three-dimensional geometry of a series of enigmatic intrabasement reflections. Through 1D waveform modelling and 3D mapping of these reflection packages, we correlate them to the onshore Caledonian thrust belt and Devonian shear zones. Based on the seismic-stratigraphic architecture of the post-basement succession, we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events. Reactivation preferentially occurs along relatively thick (c. 1 km), relatively steeply dipping (c. 30°) structures, with three main styles of interactions observed between them and overlying faults: i) faults exploiting intrabasement weaknesses represented by intra-shear zone mylonites; ii) faults that initiate within the hangingwall of the shear zones, inheriting their orientation and merging with said structure at depth; or iii) faults that initiate independently from and cross-cut intrabasement structures. We demonstrate that large-scale discrete shear zones act as a long-lived structural template for fault initiation during multiple phases of rifting.
Rapid Adjustment of Submarine Channel Architecture to Changes in Sediment Supply
Authors: Jobe Zane , Sylvester Zoltan , Parker Andrew , Howes Nick , Slowey Niall , Pirmez Carlos
Published: July 2018

Changes in sediment supply and caliber during the last ~130 ka have resulted in a complex architectural evolution of the Y channel system on the western Niger Delta slope. This evolution consists of four phases, each with documented or inferred changes in sediment supply. Phase 1 flows created wide (1,000 m), low-sinuosity (1.1) channel forms with lateral migration and little to no aggradation. During Phase 2, the Y channel system began to aggrade, creating more narrow (300 m) and sinuous (1.4) channel forms with many meander cutoffs. This system was abandoned at ~ 130 ka, perhaps related to rapid relative sea-level rise during MIS (Marine Isotope Stage) 5. Phase 3 flows were mud-rich and deposited sediment on the outer bends of the channel form, resulting in the narrowing (to 250 m), straightening (to a sinuosity of 1.22), and aggradation of the Y channel system. Renewed influx of sand into the Y channel system occurred with Phase 4 at ~ 50 ka, during MIS 3 sea-level fall. The onset of Phase 4 is marked by the initiation of the Y′ tributary channel, which re-established sand deposition in the Y channel system. Flows entering the Y channel from the Y′ channel were underfit, resulting in inner levee deposition that is most prevalent on outer banks, acting to further straighten (1.21) and narrow (to 200 m wide) the Y channel. The inner levees accumulated quickly as the flows sought equilibrium, with deposition rates > 200 cm/ky. Marked by the presence of the last sand bed, abandonment occurred at ~19 ka in the Y channel and ~15 ka in the Y′ channel and is likely related to progressive abandonment due to shelf-edge delta avulsion and/or progressive sea level rise associated with Melt Water Pulse 1-A. The muddy, 5-meter-thick Holocene layer has thickness variations that mimic those seen in the sandy part of Phase 4, suggesting that dilute, muddy flows continue to affect the modern Y channel system. This unique dataset allows us to unequivocally link changes in submarine channel architecture to variations in sediment supply and caliber. Changes in the updip sediment routing system (i.e. the channel “plumbing”) are shown to have profound implications for submarine channel architecture and reservoir connectivity.
Delayed Recognition of Geomorphology Papers in The Geological Society of America Bulletin
Authors: Goldstein Evan
Published: July 2018

The Geological Society of America Bulletin was an early home for quantitative geomorphology research. Though geomorphology papers are not uniformly the highest cited papers in the Bulletin, many show ‘delayed recognition’ —they garner only few citations directly after publication, before suddenly being widely and numerously cited (sometimes decades after publication). I focus here on 1) algorithmically detecting cases of delayed recognition in geomorphology literature from the Bulletin and 2) providing insight into why delayed recognition occurred for these papers.
Determining geophysical responses from burials in graveyards and cemeteries
Authors: Dick Henry , Pringle Jamie , Wisniewski Kristopher , Goodwin Jon , van der Putten Rob , Evans Gethin , Francis James , Cassella John , Hansen Jamie
Published: July 2018

Graveyards and cemeteries around the world are increasingly designated as full. There is therefore a requirement to identify vacant spaces for new burials or to identify existing ones to exhume and then re-inter if necessary. Geophysical methods offer a potentially non-invasive target detection solution; however, there has been limited research to identify optimal geophysical detection methods against burial age. This study has collected multi-frequency (225 MHz – 900 MHz) ground penetrating radar, electrical resistivity and magnetic susceptibility surface data over known graves with different burial ages and soil types in three UK church graveyards. Results indicate that progressively older burials are more difficult to detect but this decrease is not linear and is site specific. Medium-high frequency GPR and magnetic susceptibility was optimal in clay-rich soils, medium-high frequency GPR and electrical resistivity in sandy soils and electrical resistivity and low frequency GPR in coarse sand and pebbly soils respectively. A multi-geophysical technique approach should be utilised by survey practitioners where grave locations are not known to maximise target detection success. Grave soil and grave cuts are important grave position indicators. Grave headstones were not always located where burials were located. This study demonstrates the value of these techniques in grave detection and could potentially date burials from their geophysical responses.
Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions
Authors: Lichtman Ian , Baas Jaco , Amoudry Laurent , Thorne Peter , Malarkey Jonathan , Hope Julie , Peakall Jeffrey , Paterson David , Bass Sarah , Cooke Richard
Published: July 2018

Many coastal and estuarine environments are dominated by mixtures of non-cohesive sand and cohesive mud. The migration rate of bedforms, such as ripples and dunes, in these environments is important in determining bed material transport rates to inform and assess numerical models of sediment transport and geomorphology. However, these models tend to ignore parameters describing the physical and biological cohesion (resulting from clay and extracellular polymeric substances, EPS) in natural mixed sediment, largely because of a scarcity of relevant laboratory and field data. To address this gap in knowledge, data were collected on intertidal flats over a spring-neap cycle to determine the bed material transport rates of bedforms in biologically-active mixed sand-mud. Bed cohesive composition changed from below 2 volume % up to 5.4 volume % cohesive clay, as the tide progressed from spring towards neap. The amount of EPS in the bed sediment was found to vary linearly with the clay content. Using multiple linear regression, the transport rate was found to depend on the Shields stress parameter and the bed cohesive clay content. The transport rates decreased with increasing cohesive clay and EPS content, when these contents were below 2.8 vol% and 0.05 weight%, respectively. Above these limits, bedform migration and bed material transport was not detectable by the instruments in the study area. These limits are consistent with recently conducted sand-clay and sand-EPS laboratory experiments on bedform development. This work has important implications for the circumstances under which existing sand-only bedform migration transport formulae may be applied in a mixed sand-clay environment, particularly as 2.8 vol% cohesive clay is well within the commonly adopted definition of ‘clean sand’.
Fluctuation Analysis of Redox Potential to Distinguish Microbial Fe(II) Oxidation
Authors: Enright Allison , Ferris Grant
Published: July 2018

We developed a novel method for distinguishing abiotic and biological iron oxidation in liquid media using oxidation-reduction (redox) potential time series data. The instrument and processing algorithm were tested by immersing the tip of a Pt electrode with an Ag-AgCl reference electrode, into an active iron-oxidizing biofilm in a groundwater discharge zone, as well as in two abiotic systems: a killed sample and a chemical control from the same site. We used detrended fluctuation analysis to characterize average root-mean-square fluctuation behaviour, which was distinct in the live system. The calculated α value scaling exponents determined by detrended fluctuation analysis were significantly different at p < 0.001. This indicates that time series of electrode response data may be used to distinguish live and abiotic chemical reaction pathways. Due to the simplicity, portability, and small size, it may be suitable for characterization of extraterrestrial environments where water has been observed, such as Mars and Europa.
Iterative Strategies for Aftershock Classification in Automatic Seismic Processing Pipelines
Authors: Gibbons Steven , Kværna Tormod , Harris David , Dodge Douglas
Published: July 2018

Aftershock sequences following very large earthquakes present enormous challenges to near‐real‐time generation of seismic bulletins. The increase in analyst resources needed to relocate an inflated number of events is compounded by failures of phase‐association algorithms and a significant deterioration in the quality of underlying, fully automatic event bulletins. Current processing pipelines were designed a generation ago, and, due to computational limitations of the time, are usually limited to single passes over the raw data. With current processing capability, multiple passes over the data are feasible. Processing the raw data at each station currently generates parametric data streams that are then scanned by a phase‐association algorithm to form event hypotheses. We consider the scenario in which a large earthquake has occurred and propose to define a region of likely aftershock activity in which events are detected and accurately located, using a separate specially targeted semiautomatic process. This effort may focus on so‐called pattern detectors, but here we demonstrate a more general grid‐search algorithm that may cover wider source regions without requiring waveform similarity. Given many well‐located aftershocks within our source region, we may remove all associated phases from the original detection lists prior to a new iteration of the phase‐association algorithm. We provide a proof‐of‐concept example for the 2015 Gorkha sequence, Nepal, recorded on seismic arrays of the International Monitoring System. Even with very conservative conditions for defining event hypotheses within the aftershock source region, we can automatically remove about half of the original detections that could have been generated by Nepal earthquakes and reduce the likelihood of false associations and spurious event hypotheses. Further reductions in the number of detections in the parametric data streams are likely, using correlation and subspace detectors and/or empirical matched field processing.
Bacterial Fe(II)-oxidation Distinguished by Long-Range Correlation in Redox Potential
Authors: Enright Allison , Ferris Grant
Published: July 2018

The kinetics of bacterial Fe(II) oxidation was investigated 297m underground at the Äspö Hard Rock Laboratory (near Oskarshamn, Sweden) under steady state groundwater flow conditions in a flow-through cell containing well-developed flocculent mats of bacteriogenic iron oxides (BIOS). Pseudo first-order rate constants of 0.004 min^-1 and 0.009 min^-1 were obtained for chemical and bacterial Fe(II) oxidation, respectively, based on the 104 min retention time of groundwater in the flow cell, inlet Fe(II) concentration of 21.0± 0.5μm, outlet Fe(II) concentration of 8.5 ± 0.7 μm, as well as constant pH = 7.42 ± 0.01, dissolved O2 concentration of 0.11 ± 0.01mg/L, and groundwater temperature of 12.4± 0.1°C. Redox potential was lower at the BIOS-free inlet (-135.4± 1.16mV) compared to inside BIOS within the flow cell (-112.6± 1.91mV), consistent with the Nernst relationship and oxidation of Fe(II) to Fe(III). Further evaluation of the redox potential time series data using detrended fluctuation analysis (DFA) revealed power law scaling in the amplitude of fluctuations over increasing intervals of time with significantly different (p<0.01) DFA α scaling exponents of 1.89 ± 0.03 for BIOS and 1.67 ± 0.06 at the inlet. These α values not only signal the presence of long-range correlation in the redox potential time series measurements but also distinguish between the slower rate of chemical Fe(II) oxidation at the inlet and faster rate accelerated by FeOB in BIOS.
The influence of community recommendations on metadata completeness
Authors: Gordon Sean , Habermann Ted
Published: July 2018

Many communities use standard, structured documentation that is machine-readable, i.e. metadata, to make discovery, access, use, and understanding of scientific datasets possible. Organizations and communities have also developed recommendations for metadata content that is required or suggested for their data developers and users. These recommendations are typically specific to metadata representations (dialects) used by the community. By considering the conceptual content of the recommendations, quantitative analysis and comparison of the completeness of multiple metadata dialects becomes possible. This is a study of completeness of EML and CSDGM metadata records from DataONE in terms of the LTER recommendation for Completeness. The goal of the study is to quantitatively measure completeness of metadata records and to determine if metadata developed by LTER is more complete with respect to the recommendation than other collections in EML and in CSDGM. We conclude that the LTER records are broadly more complete than the other EML collections, but similar in completeness to the CSDGM collections.
Improvements to Seismic Monitoring of the European Arctic Using Three-Component Array Processing at SPITS
Authors: Gibbons Steven , Schweitzer Johannes , Ringdal Frode , Kværna Tormod , Mykkeltveit Svein , Paulsen Berit
Published: July 2018

The detectability of low magnitude seismic events in the European Arctic is determined primarily by the small-aperture International Monitoring System arrays ARCES and SPITS. In August 2004, the SPITS array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 Hz. Most important, however, for the detection and location of small-magnitude seismic events was the deployment of three-component instruments at six of the nine sites. Detection and correct classification of secondary phases are of paramount importance for events observed by only a small number of stations at regional distances; and, in the absence of the strong Lg phases typically observed for continental propagation paths, multiple three-component stations were deemed necessary to exploit the higher S-phase amplitudes anticipated on the horizontal sensors. We demonstrate improved signal-to-noise ratios (SNRs) for S phases on horizontal beams for several events close to Novaya Zemlya. Horizontal component f-k analysis improves direction estimates and phase classification for low-SNR signals. We demonstrate secondary phases that are misidentified by vertical-only f-k analysis but which are correctly classified by three-component array processing. A significant problem with array processing at SPITS is the overlap in slowness space of regional P and S phases. Phase identification is improved greatly by comparing the coherence between vertical traces with the coherence between horizontal traces. Considerations in the routine array processing of SPITS data are reviewed, including the need for elevation corrections in slowness estimation and the need to take into account azimuth-dependent variation of apparent velocity estimates for regional phases.
Facies and Architectural Asymmetry in a Conglomerate-Rich Submarine Channel Fill, Cerro Toro Formation, Sierra Del Toro, Magallanes Basin, Chile
Authors: Jobe Zane , Bernhardt Anne , Lowe Donald
Published: July 2018

Cross-sectional asymmetry is characteristic of sinuous channels, in both fluvial and submarine settings. Less well documented are the facies distributions of asymmetric channels, particularly in submarine settings. Exposures of the axial channel-belt in the Magallanes retro-arc foreland basin on Sierra del Toro represent the fill of a 3.5 km wide, 300 m thick channel complex, here termed the “Wildcat,” that displays an asymmetric cross section and facies distribution. Measured sections and mapping demonstrate that facies proportion, degree of amalgamation, and margin architecture vary laterally from east to west across the Wildcat channel complex. The eastern side is characterized by thick-bedded, amalgamated sandstone and clast- and matrix-supported conglomerate that onlap a steep, simple margin adjacent to sandy overbank deposits. The western side contains thin-bedded, sandy and muddy strata that onlap a shallow composite margin adjacent to mud-rich out-of-channel strata.The observed asymmetry is likely due to centrifugal flow forces and was caused by a low-sinuosity right-hand meander bend of the Cerro Toro axial channel-belt. The facies and architecture of the opposing margins indicate that the eastern and western sides constitute the outer and inner bends of the Wildcat channel complex, respectively. The modest cross-sectional asymmetry of the Wildcat complex is likely a product of the low channel-belt sinuosity. The absence of lateral accretion surfaces and deposits suggests that the channel did not migrate during filling. Flows depositing the uppermost channel fill were only weakly confined, resulting in flow divergence and overbank deposition.A depositional model that incorporates the asymmetric facies distributions and the contrasting outer-bend and inner-bend architecture of the Wildcat channel complex is also presented. Similar facies distributions exist in other low-sinuosity submarine channels, and even more extreme facies and cross-sectional asymmetry probably characterize more highly sinuous channels. Data on facies distributions presented here represents a useful resource for constraining numerical and experimental models of the evolution of sinuous submarine channels as well as reservoir models of sinuous submarine channels.
Multiple Palaeoproterozoic carbon burial episodes and excursions
Authors: Martin Adam , Condon Daniel , Prave Anthony , Lepland Aivo , Fallick Anthony , Romashkin A , Medvedev P , Rychanchik D
Published: July 2018

Organic-rich rocks (averaging 2–5% total organic carbon) and positive carbonate-carbon isotope excursions (‰δC13>+5‰ and locally much higher, i.e. the Lomagundi-Jatuli Event) are hallmark features of Palaeoproterozoic successions and are assumed to archive a global event of unique environmental conditions following the c. 2.3 Ga Great Oxidation Event. Here we combine new and published geochronology that shows that the main Palaeoproterozoic carbon burial episodes (CBEs) preserved in Russia, Gabon and Australia were temporally discrete depositional events between c. 2.10 and 1.85 Ga. In northwest Russia we can also show that timing of the termination of the Lomagundi-Jatuli Event may have differed by up to 50 Ma between localities, and that Ni mineralisation occurred at c. 1920 Ma. Further, CBEs have traits in common with Mesozoic Oceanic Anoxic Events (OAEs); both are exceptionally organic-rich relative to encasing strata, associated with contemporaneous igneous activity and marked by organic carbon isotope profiles that exhibit a stepped decrease followed by a stabilisation period and recovery. Although CBE strata are thicker and of greater duration than OAEs (100 s of metres versus metres, ∼106 years versus ∼105 years), their shared characteristics hint at a commonality of cause(s) and feedbacks. This suggests that CBEs represent processes that can be either basin-specific or global in nature and a combination of circumstances that are not unique to the Palaeoproterozoic. Our findings urge circumspection and re-consideration of models that assume CBEs are a Deep Time singularity.
Geochemistry and origin of the Neoproterozoic Natkusiak Flood Basalts and related Franklin Sills, Victoria Island, Arctic Canada
Authors: Beard Charles , Scoates James , Weis Dominique , Bedard Jean , Dell'Oro Trent
Published: July 2018

The Natkusiak continental flood basalts and Franklin sills of Victoria Island preserve an exceptional record of the ca. 716–723 Ma Franklin large igneous province and are synchronous with major climatic variations and breakup of the supercontinent Rodinia. The Natkusiak Formation basalts record an early phase of discontinuous rubbly flows (<100 m, low-Ti Type 1 magmas) overlain by a thicker series of extensive tholeiitic sheet flows (~1100 m, high-Ti Type 2 magmas). Coeval intrusions hosted by underlying Shaler Supergroup sedimentary rocks are differentiated low-Ti Type 1 Franklin sills and doleritic high-Ti Type 2 sills, both of which show correlations in isotope plots with the northernmost basalts on Victoria Island. Whole-rock Pb-Sr-Nd-Hf isotopic compositions from 66 samples indicate that the earliest magmas (Type 1) had similar primary melt compositions (Fo90 olivine) to oceanic island basalts and incorporated up to 10% granitoid basement (initial eNd = –0.8 to –7, Nb/La = 0.42 to 0.67), a relatively weak continental signature compared to many other continental flood basalt provinces. Type 2 doleritic sills and the northern sheet flow basalts incorporated up to 5% granitoid (initial eNd = +0.9 to +5.5), consistent with a waning continental influence during maturation of the magmatic system. Radiogenic isotope ratios are not correlated with indices of fractional crystallisation, which indicates that the continental material was either dispersed within the melt source, or that magmas were heterogeneously contaminated prior to differentiation. In the southwestern part of Victoria Island, Type 1 basalts show negligible continental influence (Nb/La = 0.81 to 0.94) and have unusually high initial eNd ratios (+4.4 to +11.8) that are decoupled from initial eHf (+0.8 to +11.1). These radiogenic eNd compositions persist throughout the southern volcanic stratigraphy and indicate involvement of a component with high time-integrated Sm/Nd that lacked correspondingly high Lu/Hf. We suggest that the source region for the southwestern Natkusiak basalts and related sills included isotopically matured oceanic crust, which was recycled through the asthenospheric mantle into a laterally heterogeneous plume. The distinct trace element signatures of the southern and northern sources became attenuated with the onset of voluminous melting (corresponding to emplacement of the Type 2 doleritic sills and sheet flow basalts) and may reflect contributions from hydrous eclogitic material emplaced into the lithospheric mantle during the ca. 1.9 Ga Wopmay Orogeny. As both the northern and southern volcanic rocks exhibit contrasting isotopic signatures throughout the preserved stratigraphy, the magma plumbing system must have limited lateral mixing and homogenisation, which allowed for the expression of distinct mantle source signatures in the high-level sills and basaltic lavas.
Growing forced bars determine non-ideal estuary planform
Authors: Leuven Jasper , Braat Lisanne , van Dijk Wout , de Haas Tjalling , van Onselen Erik , Ruessink Gerben , Kleinhans Maarten
Published: July 2018

The planform of estuaries is often described with an ideal shape, which exponentiallyconverges in landward direction. We show how growing topographically forced nonmigratory (i.e., anchored) bars determine the large-scale estuary planform, which explains the deviations observed in the planform of natural estuaries filled with bars compared to the ideal planform. Experiments were conducted in a 20-m long, 3-m-wide tilting flume, the Metronome. From a narrow, converging channel a self-formedestuary developed characterized by multiple channels, braided bars, a meandering ebb channel, and an ebb delta. Bars hardly migrated due to the alternating current, but the bar width increased with increasing estuary width. At locations where the estuary width was narrow, major channel confluences were present, while the zones between the confluences were characterized by a higher braiding index, periodicallymigrating channels, and a relatively large estuary width. At the seaward boundary, confluences were forced in place by the presence of the ebb tidal delta. Between confluences, bars were topographically forced to be nonmigratory. Diversion of flow around forced midchannel bars caused bank erosion. This resulted in a planform shape with a quasiperiodic widening and narrowing at the scale of forced bars. Observations in natural systems show that major confluence locations can also be caused by inherited geology and human engineering, but otherwise the estuary outline is similarly affected by tidal bars. These observations provide a framework for understanding the evolution of tidal bar patterns and the planform shape of the estuary, which has wide implications for navigation, dredging, and ecology.
Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography
Authors: Papaleo Elvira , Cornwell David , Rawlinson Nick
Published: July 2018

We present high resolution S‐wave teleseismic tomography images of the western segment of the North Anatolian Fault (NAFZ) in Turkey using teleseismic data recorded during the deployment period of the DANA array. The array comprised 66 stations with a nominal station spacing of 7 km, thus permitting a horizontal and vertical resolution of approximately 15 km. We use the current S‐wave results with previously published P‐wave teleseismic tomography to produce maps of relative VP/VS anomalies, which we use to highlight the difference in overall composition of the three terranes separated by the northern (NNAF) and southern (SNAF) branches of the NAFZ. Our results show a narrow S‐wave low velocity anomaly beneath the northern branch of the NAFZ extending from the upper crust, where it has a width of ∼10 km, to the lower crust, where it widens to ∼30 km. This low velocity zone most likely extends into the upper mantle, where we constrain its width to be ≤50 km and interpret it as indicative of localised shear beneath the NNAF; this structure is similar to what has been observed for the NAFZ west of 32°and therefore we propose that the structure of the NNAF is similar to that of the NAFZ in the east. The SNAF does not show a very strong signature in our images and we conclude that it is most likely rooted in the crust, possibly accommodating deformation related to rotation of the Armutlu/Almacik Blocks situated between the two NAFZ branches.
Local and Remote Influences on the Heat Content of the Labrador Sea: an Adjoint Sensitivity Study
Authors: Jones Daniel , Forget Gael , Sinha Bablu , Josey Simon , Boland Emma , Meijers Andrew , Shuckburgh Emily
Published: July 2018

The Labrador Sea is one of the few regions on the planet where the interior ocean can exchange heat directly with the atmosphere via strong, localized, wintertime convection, with possible implications for the state of North Atlantic climate and global surface warming. Using an observationally-constrained ocean adjoint model, we find that annual mean Labrador Sea heat content is sensitive to temperature/salinity changes (1) along potential source water pathways (e.g. the subpolar gyre, the North Atlantic Current, the Gulf Stream) and (2) along the West African and European shelves, which are not significant source water regions for the Labrador Sea. The West African coastal/shelf adjustment mechanism, which may be excited by changes in along-shelf wind stress, involves pressure anomalies that propagate along a coastal waveguide towards Greenland, changing the across-shelf pressure gradient in the North Atlantic and altering heat convergence in the Labrador Sea. We also find that non-local (in space and time) heat fluxes (e.g. in the Irminger Sea, the seas south of Iceland) can have a strong impact on Labrador Sea heat content. Understanding and predicting the state of the Labrador Sea and its potential impacts on North Atlantic climate and global surface warming will require monitoring of oceanic and atmospheric properties at remote sites in the Irminger Sea, the subpolar gyre, and along the West African and European shelf/coast system, among others.
Dating the termination of the Palaeoproterozoic Lomagundi-Jatuli carbon isotopic event in the North Transfennoscandian Greenstone Belt
Authors: Martin Adam , Condon Daniel , Prave Anthony , Melezhik Victor , Lepland Aivo , Fallick Anthony
Published: July 2018

Existing radio-isotopic age constraints indicate that the global Palaeoproterozoic Lomagundi-Jatuli large, positive carbonate carbon isotopic excursion, with δ13C values >+5‰, occurred between 2.2 and 2.06 Ga. In the North Transfennoscandian Greenstone Belt of the Kola Peninsula, NW Russia, northern Norway and Finland, the Lomagundi-Jatuli Event is recorded in the carbonate rocks of the Umba and Kuetsjärvi Sedimentary Formations in the Imandra-Varzuga and Pechenga greenstone belts. In both areas, thick mafic volcanic units (Umba and Kuetsjärvi Volcanic Formations) overlie the carbon isotopic excursion-bearing sedimentary units. Overlying and younger sedimentary units contain carbonate rocks with δ13C values typically ranging between c. −1 and +3‰, signalling the termination of the Lomagundi-Jatuli excursion.Two new U–Pb ID-TIMS (isotope-dilution thermal ionisation mass spectrometry) zircon dates constrain this termination in both successions. The lower unit of the Il’mozero Sedimentary Formation is a cross- and parallel-bedded volcaniclastic greywacke derived largely from erosion of the underlying Umba Volcanic Formation. It has yielded detrital zircons with 207Pb/206Pb dates as young as 2055.5 ± 2.3 Ma, which is a maximum age for deposition and is inferred to date part of the underlying Umba volcanics. In Pechenga, the Kolosjoki Sedimentary Formation was intersected by a drill hole obtained by the ICDP (International Continental Scientific Drilling Program)-supported FAR-DEEP (Fennoscandian Arctic Russia-Drilling Early Earth Project) drilling programme. Zircons from a mafic fine tuff in this drill core have yielded a 207Pb/206Pb age of 2056.6 ± 0.8 Ma. This age is interpreted as an eruption age contemporaneous with sedimentation. The new age determinations overlap each other within uncertainty, and is within error of previously published detrital zircon ages of 2058 ± 2 Ma from the Kolosjoki Sedimentary Formation and 2049 ± 28 Ma from the Kuetsjärvi Volcanic Formation. Combined, these indicate that the Lomagundi-Jatuli excursion terminated across Fennoscandia by 2056.6 ± 0.8 Ma and may correlate with similar termination ages in Fennoscandia and the Transvaal, South Africa.
Unsupervised clustering of Southern Ocean Argo float temperature profiles
Authors: Jones Daniel , Holt Harry , Meijers Andrew , Shuckburgh Emily
Published: July 2018

The Southern Ocean has complex spatial variability, characterized by sharp fronts, steeply tilted isopycnals, and deep seasonal mixed layers. Methods of defining Southern Ocean spatial structures traditionally rely on somewhat ad-hoc combinations of physical, chemical, and dynamic properties. As a step towards an alternative approach for describing spatial variability in temperature, here we apply an unsupervised classification technique (that is, Gaussian mixture modelling or GMM) to Southern Ocean Argo float temperature profiles. GMM, without using any latitude or longitude information, automatically identifies several spatially coherent circumpolar classes influenced by the Antarctic Circumpolar Current. In addition, GMM identifies classes that bear the imprint of mode/intermediate water formation and export, large-scale gyre circulation, and the Agulhas Current, among others. Because GMM is robust, standardized, and automated, it can potentially be used to identify structures (such as fronts) in both observational and model datasets, possibly making it a useful complement to existing classification techniques.