Short-lived Events Research Articles

Sedimentology and depositional environments of the Ordovician Umm Sahm Sandstone Formation in southern Jordan

The Ordovician Umm Sahm Sandstone Formation of Jordan comprises approximately 200-m-thick succession of fluvial quartzarenites with subordinate claystone and siltstone lithologies of shallow marine conditions. The Umm Sahm Formation is characterized by its dark brown color, frequent jointing, and steep scarps. The Umm Sahm Formation is bounded by the marine claystones of Hiswah Formation at the top and the fluvial sandstones of the Disi Formation at the bottom. The Umm Sahm Formation is composed of two main facies: fluvial facies and tidal facies. The fluvial facies constitutes about 93% of the total thickness. The lower few meters of the succession passes upward from the Disi Sandstone Formation into similar massive white sandstone facies exhibiting similar white color, fine- to coarse-grained sandstone, with round-shaped pebbles. Trough and planar cross-bedding show a northwest unidirectional palaeocurrent trend. Light brown colored quartzarenites similar to those of the Cambrian Umm Ishrin Sandstone Formation are most common in the upper part of the succession. The tidal facies occupies three intervals in the middle part of the succession. It is composed of laminated and thin-bedded sandstones, siltstones, and claystones. They are rippled and varicolored with abundant trace fossils (Cruziana, Harlania, ruzophycus). The presence of hummocky cross stratification indicates the earliest short-lived tempestite conditions during the Paleozoic erathem of Jordan. The first appearance of Graptolites in the Ordovician rocks of Jordan was recorded during this study in the tidal facies of the Umm Sahm Formation. The vertical arrangement of both fluvial and tidal facies indicates three successive short-lived transgressions and regressions. These marine incursions indicate the successive shoreline advances of the Tethys Ocean, which was located northward, and inundated the southern braid plain. The three short-lived transgressive events took place, and the Tethys marine margin was displaced southward, giving rise to deposition of tidal facies in an open coast tidal flat. Following the transgressive events, renewed progradation and strandline retreat took place, fed by large amounts of siliciclastics derived from the continent and transported by braided streams across the intertidal zone.

Predicting in shock: on the impact of negative, extreme, rare, and short lived events on judgmental forecasts

The occurrence of unexpected events that are extreme in magnitude, rare in frequency, and short-lived in duration poses distinctive challenges to decision makers and planners. In this paper we examine the impact of negative versions of these events, which we term “shocks”, on the judgmental forecasts of subjects experiencing them. A behavioral experiment asking participants to forecast monthly time series in the presence of temporary but extreme decreases in those series is used. Average changes to annual prediction intervals and 1-month ahead forecasts were much smaller than the magnitude of the shock and occurred in proportion to the size of the shock. Changes to prediction intervals were more persistent for moderate than large shocks, and larger for shocks occurring a second time. Our results provide supporting evidence for the view that decision makers underweight rare and extreme events rather than overweight them, consistent with a discounting or forgetting effect. The behavioral findings are relevant to operations researchers involved in expert judgment elicitation and in supporting decision making.

Street floods in Metro Manila and possible solutions

Urban floods from thunderstorms cause severe problems in Metro Manila due to road traffic. Using Light Detection and Ranging (LiDAR)-derived topography, flood simulations and anecdotal reports, the root of surface flood problems in Metro Manila is identified. Majority of flood-prone areas are along the intersection of creeks and streets located in topographic lows. When creeks overflow or when rapidly accumulated street flood does not drain fast enough to the nearest stream channel, the intersecting road also gets flooded. Possible solutions include the elevation of roads or construction of well-designed drainage structures leading to the creeks. Proposed solutions to the flood problem of Metro Manila may avoid paralyzing traffic problems due to short-lived rain events, which according to Japan International Cooperation Agency (JICA) cost the Philippine economy 2.4billionpesos/day.

The coastal ridge sequence at Rio Grande do Sul: A new geoarchive for past climate events of the Atlantic coast of southern Brazil since the mid Holocene

Abstract We present here the first geochronometric analysis of a large succession of coastal ridges that developed south of Rio Grande do Sul inlet, aided by OSL dating of samples taken in this succession that amounts c. 306 coastal ridges. This succession allows defining epochs of enhanced coastal drift or fluvial transport to the river mouth. Additionally, changes in the preservation of ridges also suggest the additional effect of transverse winds that create blow outs, while changes in the ridge packages planview onlap suggest possible changes in the dominant longshore drift. Four OSL samples located strategically allow defining the age of five main stages of this succession. The first stage comprises 2 substages. The first substage shows ridges #1 to #36 onlapping the boundary coastal scarp northwardly, while the second (ridges #37 to #84) shows an inversion of ridge shape wedging out southwards until coast returns to be quasi parallel to the initial coastal scarp estimated to be c. 6 ka. We estimate this first stage to comprise enhanced coastal drift due to higher and sandier ridges, ending at c. 4.1 ka. The second stage (ridges #85 to #124) ridges is marked by a slight unconformity, and indicates a period of enhanced fluvial progradation and less coastal drift suggesting milder winds up to 3.6 ka. The third stage (ridges #125 to #204) initiates with erosion of ridges near the delta front, being higher and sandier ridges, suggesting enhanced coastal drift due to windier conditions, being the windiest time bracketed between 3.3 and 2.35 ka. The fourth stage (ridges #205 to c. #270) shows again, as second stage, a tendency of wedging out southwards, suggesting enhanced fluvial progradation, estimated between 2.34 and 1.7 ka. The fifth stage is defined by a complete change of coastal plain progradation, due to the rapid recycling of beach ridges into a complex of blow outs and arcuate sand dunes. Ridges are sparsely recognized in cases they developed during short lived events of enhanced longshore drift, with an outstanding group (ridges #288 to #290) that we correlate to a 1.1–0.9 ka cooling event. Future studies, improving the chronostratigraphy of the beach ridges succession at Rio Grande and comparing it with the Parana river delta ridges, will help understanding the complex environmental history of South America, that include a reversal of the longshore drift, given the fact they are among the most complete upper Holocene geoarchives available.

Masculinity and Power in Irish Nationalism, 1884–1938 by Aidan Beatty

Reviewed by: Masculinity and Power in Irish Nationalism, 1884–1938 by Aidan Beatty Peter B. Strickland Masculinity and Power in Irish Nationalism, 1884–1938, by Aidan Beatty, pp. 266. New York: Palgrave MacMillan, 2016. $100. Timed to coincide with the Paris Olympics, the revival of the Tailteann Games in 1924 was intended as a public display of the strength and vitality of a newly independent Ireland. The Olympic-style competitions were open to all men of Irish descent, with athletes traveling to Ireland from the settler colonies of the British Empire, as well as from Britain itself. Organizers hoped that hosting the games every four years would exhibit Ireland's physical prowess and enthusiastic nationalism. Diminishing budgets hampered the games over the next decade, and because the competitions were largely associated with, and promoted by, the Free State government, the project did not survive the rise of Fianna Fáil. One [End Page 144] could easily dismiss the attempted revival of the Tailteann Games as a shortlived minor event in the history of Irish sport. In Masculinity and Power in Irish Nationalism, 1884–1938, however, Aidan Beatty persuasively examines the event within a much larger context; he repositions the games as a piece of a longer history of the conflation of Irish "national sovereignty and masculine strength." Gender analysis remains a rare commodity in political histories of Ireland; rarer still are studies that employ masculinity as a category for historical analysis. Masculinity and Power in Irish Nationalism corrects this oversight by placing masculine concerns at the center of the nationalist movement. Beatty demonstrates that, regardless of changes in state power and the varying dominance of political parties, the common denominator of Irish nationalism was the importance it placed on establishing and reinforcing Irish masculinity. Asserting the centrality of masculinity to Irish nationalism allows Beatty to place the revolutionary years into a wider framework, and in doing so, to undermine the very notion of a singular, watershed "Irish Revolution" by connecting the ideas and experiences of Irish nationalists across generations. To accomplish the goal of minimizing the "Irish Revolution," Beatty approaches his subject thematically. He begins with the revolutionary years (1916–1923) in chapter two, and asserts that questions of masculinity were central to each of the dramatic moments of those years. The next three chapters turn to the period before 1916, and the final two chapters shift the discussion to the years after the civil war. In examining such themes as space, land, or the body, each of these chapters uses the histories of organizations and political parties to provide topical focus. This deprioritizing of the revolutionary years allows Masculinity and Power in Irish Nationalism to connect the muscular vision of Irish nationalism promoted by the GAA in the 1880s (chapter 3), with Fianna Fáil's economic policies toward privately owned farms in the 1930's (chapter 6). This longue durée approach aligns Beatty's interpretation of Irish nationalism with the wider field of postcolonial studies, which seeks to demonstrate the long legacy of the colonial experience. This already ambitious work also seeks to escape the exceptionalism of what Beatty calls the "Irish Sonderweg" by comparing the connections between Irish nationalism and masculinity to similar intersections in other European and postcolonial contexts. In this case, Beatty takes the Zionist movement as his comparative example. Considering both the Irish and the European Jews as "quasi-colonial" peoples, he argues that comparing the two provides a "Zionist mirror" that can reveal many of the intricacies in the relationship between Irish nationalism and masculinity. This is an intriguing interpretive tack, but unfortunately, this comparative turn rarely adds to the study beyond confirming the unsurprising conclusion that ideas and practices in Ireland had analogs in the Zionist experience. In its role as "mirror," the Zionist story itself is not subject [End Page 145] to the same close examination as the Irish story. Beatty's consideration of moments when Zionism, or Jewishness, and Irish nationalism actually intersected result in more effective comparisons. A fine example of this is the third chapter's discussion of a 1924 political cartoon titled "Jew Regard for the Law," which appeared in Guth na Gharda ("The Policeman's...

Repeated enrichment of trace metals and organic carbon on an Eocene high-energy shelf caused by anoxia and reworking

Abstract Petroleum source rocks are strongly enriched in organic carbon (OC), and their trace metal (TM) contents often reach low-grade ore levels. The mechanisms leading to these coenrichments are important for understanding how extreme environmental conditions support the formation of natural resources. We therefore studied organic-rich Eocene marls and limestones (oil shale) from the central Jordan Amzaq-Hazra subbasin, part of a Cretaceous–Paleogene shelf system along the southern Neo-Tethys margin. Geochemical analyses on two cores show highly dynamic depositional conditions, consistent with sedimentological and micropaleontological observations. Maximum and average contents, respectively, in OC (∼26 and ∼10 wt%), sulfur (∼7 and ∼2.4 wt%), phosphorus (∼10 and ∼2 wt%), molybdenum (>400 and ∼130 ppm), chromium (>500 and ∼350 ppm), vanadium (>1600 and ∼550 ppm) and zinc (>3800 and ∼900 ppm) are exceptional, in particular without any indication of hydrothermal or epigenetic processes. We propose a combination of two processes: physical reworking of OC- and metal-rich material from locally exposed Cretaceous–Paleogene sediments (as supported by reworked nannofossils), and high marine productivity fueled by chemical remobilization of nutrients and metals on land that sustained anoxic-sulfidic conditions. Burial of high-quality organic matter (hydrogen index 600–700 mgHC/gOC) was related to strongly reducing conditions, punctuated by only short-lived oxygenation events, and to excess H2S, promoting organic matter sulfurization. These processes likely caused the OC and TM coenrichments in a high-energy shallow-marine setting that contradicts common models for black shale formation, but may explain similar geochemical patterns in other black shales.

MOSAIC: A Modular Single-Molecule Analysis Interface for Decoding Multistate Nanopore Data.

Biological and solid-state nanometer-scale pores are the basis for numerous emerging analytical technologies for use in precision medicine. We developed Modular Single-Molecule Analysis Interface (MOSAIC), an open source analysis software that improves the accuracy and throughput of nanopore-based measurements. Two key algorithms are implemented: ADEPT, which uses a physical model of the nanopore system to characterize short-lived events that do not reach their steady-state current, and CUSUM+, a version of the cumulative sum statistical method optimized for longer events that do. We show that ADEPT detects previously unreported conductance states that occur as double-stranded DNA translocates through a 2.4 nm solid-state nanopore and reveals new interactions between short single-stranded DNA and the vestibule of a biological pore. These findings demonstrate the utility of MOSAIC and the ADEPT algorithm, and offer a new tool that can improve the analysis of nanopore-based measurements.

U-Pb LA-ICP-MS dating of apatite in mafic rocks: Evidence for a major magmatic event at the Devonian-Carboniferous boundary in the Armorican Massif (France)

Apatite is a ubiquitous accessory mineral found in most magmatic rocks and is often the only U-bearing mineral available to date mafic rocks because primary zircon and/or baddeleyite are not present. In this paper, U-Pb LA-ICP-MS dating of apatite was applied to seven different dike and sill samples of dolerite from the Variscan belt of Brittany (Armorican Massif, western France). These dolerites, which are characterized by a within-plate tholeiite geochemical signature, are organized in several dense swarms across the belt. Their geochemical compositions are homogeneous although they intrude a large geographical area subdivided into several domains each characterized by different tectonic-metamorphic settings. Their emplacement ages were so far poorly constrained due to the difficulty to date these mafic rocks using either the 40Ar/39Ar or the U-Pb methods on classical minerals like mica, plagioclase, or zircon. Although the closure temperature of apatite is lower than the emplacement temperature of the magma, physical models show that the time needed to solidify and cool these mafic dikes and sills below the apatite closure temperature is basically of the order of 100 years or less. Consequently, the U-Pb dates obtained on apatite can be interpreted as the emplacement ages for these mafic intrusions. Our results demonstrate that, in all cases, the apatite grains do carry enough radiogenic Pb to be dated by in situ U-Pb analyses and yield a 207Pb-corrected mean age of 363.4 ± 5.8 Ma. These results reveal the existence of a major and short-lived magmatic event in the Variscan belt of Brittany during the Devonian-Carboniferous transition, a feature further highlighted by field evidence. Beyond the geological implications of these results, U-Pb LA-ICP-MS dating of apatite appears to represent an ideal tool to date small size mafic intrusions.

Proterozoic–Mesozoic history of the Central Asian orogenic belt in the Tajik and southwestern Kyrgyz Tian Shan: U-Pb,40Ar/39Ar, and fission-track geochronology and geochemistry of granitoids

Multimethod geochronology (U-Pb zircon; 40 Ar/ 39 Ar hornblende, biotite, feldspar; apatite fission track) on granitoids, gneisses, and Cenozoic intramontane basin clastics of the Gissar-Alai ranges, South Tian Shan collisional belt, west of the Talas-Fergana fault, elucidates a history of Neoproterozoic magmatism, late Paleozoic magmatism and metamorphism, and Mesozoic−Cenozoic thermal reactivation. Zircon-core and grain-interior U-Pb ages of ca. 2.7−2.4, 2.2−1.7, 1.1−0.85, and 0.85−0.74 Ga tie the early evolution of the Gissar-Alai ranges to that of the Tarim craton. At least part of the Gissar range crystalline basement—the Garm massif—shows U-Pb zircon crystallization ages of ca. 661‒552 Ma (median ca. 609 Ma), again suggesting a Tarim craton connection. Tarim collided with the Middle Tian Shan block at ca. 310‒305 Ma, completing the protracted formation of the South Tian Shan collisional belt. The massive Gissar range granitoids intruded later (ca. 305‒270 Ma), contemporaneous with peak Barrovian-type metamorphism in the Garm massif rocks. Major- and trace-element compositions suggest that the Gissar granitoid melts have continental arc affinity. Zircon e Hf and whole-rock e Nd values of −2.1 to −6.9 and −2.7 to −7.2, respectively. and Hf-isotope crustal model and Nd-isotope depleted mantle model ages of ca. 1.0‒1.2 and ca. 1.1‒2.2 Ga, respectively, suggest significant input of Precambrian crust in the Gissar granitoid and Garm orthogneiss melts, consistent with the U-Pb ages of inherited and detrital zircons. The distinct ca. 661‒552 Ma Garm gneiss crystallization ages and the ca. 1.0−2.2 Ga model ages (and the lack of 2.4−3.4 Ga model ages) tie the Garm gneisses and the reworked crust of the Gissar range to the northern rim—the Kuqa and Kolar sections—of the Tarim craton, suggesting a united Karakum-Tarim craton. Although about contemporaneous with widespread postcollisional magmatism in the entire Tian Shan, the large volume and short duration of the Gissar range magmatism, including crustal thickening and prograde metamorphism during Tarim craton‒Middle Tian Shan block collision, and formation and closure of an oceanic back-arc basin (the Gissar basin), indicate its origin in a distinct setting. Combined, this likely resulted in midcrustal melting and upper-crustal batholith emplacement. Mafic dikes and pipes intruded at ca. 256−238 Ma (median ca. 241 Ma); the source region of the parental melts was within the asthenospheric mantle. The simplest interpretation for these basanites is that they were part of the Tarim flood basalt province; this would extend this province westward from the Tarim craton into the southwestern Tian Shan and imply that the relatively short-lived flood basalt event (ca. 290‒270 Ma) was followed by much less voluminous but longer-lasting hotspot magmatism. The 40 Ar/ 39 Ar and detrital apatite fission-track dates outline post−Gissar-Alai range granitoid emplacement cooling, Cimmerian collision events at the southern margin of Asia, Late Cretaceous crustal extension and local magmatism, and early Cenozoic shortening and burial in the far field of the India-Asia collision.

Scramjet to ramjet transition in a dual-mode combustor with fin-guided injection

A dual-mode scramjet combustor featuring a fin-guided hydrogen injector and a cavity flame holder was operated in a transitional regime characterized by frequent combustion mode hopping and large flame front movements. In this regime, which occurred at equivalence ratios between 0.19 and 0.24, the combustor operated in scramjet mode initially, but transitioned into ramjet mode with time. The experiments were performed using a direct-connect vitiated-air facility which generated a high-enthalpy Mach 1.9 flow at the isolator inlet. High-speed schlieren visualizations, OH* chemiluminescence, and wall pressure measurements were used to study the alternating combustion behavior that occurs throughout the scramjet to ramjet mode transition. The results showed that the transition process was characterized by a series of flame oscillations driven by mode hopping cycles, consisting of transient thermal choking, flame flashback, cavity flame holding and detachment. These mode oscillations were initially sporadic and short-lived events of upstream-downstream flame propagation, but as the transition advanced and the presence of the flame in the cavity increased, they transformed into longer and more stable cycles. The characteristic duration of the entire transition process was determined to range between 0.42–0.61s using a statistical analysis based on image processing of the schlieren visualizations. Increasing the overall equivalence ratio decreased the transition duration, but had no significant effect on the dynamics of this process. The results suggest that thermal choking due to wall heating downstream of the cavity drives the scramjet to ramjet mode hopping, while flame quenching and blow-off at the cavity caused by its initially cold walls reinitializes scramjet operation.

Parallel 4-Dimensional Cellular Automaton Track Finder for the CBM Experiment

The CBM experiment (FAIR/GSI, Darmstadt, Germany) will focus on the measurement of rare probes at interaction rates up to 10 MHz with data flow of up to 1 TB/s. It requires a novel read-out and data-acquisition concept with self-triggered electronics and free-streaming data. In this case resolving different collisions is not a trivial task and event building must be performed in software online. That requires full online event reconstruction and selection not only in space, but also in time, so-called 4D event building and selection. This is a task of the First-Level Event Selection (FLES).The FLES reconstruction and selection package consists of several modules: track finding, track fitting, short-lived particles finding, event building and event selection. The Cellular Automaton (CA) track finder algorithm was adapted towards time-slice-based reconstruction and included into the CBMROOT framework. In this article, we describe the modification done to the algorithm, as well as the performance of the developed time-based approach.

An Insurance Perspective on U.S. Electric Grid Disruption Costs

Large yet infrequent disruptions of electrical power can impact tens of millions of people in a single event, triggering significant economic damages, portions of which are insured. Small and frequent events are also significant in the aggregate. This article explores the role that insurance claims data can play in better defining the broader economic impacts of grid disruptions in the U.S. context. We developed four case studies, using previously unpublished data for specific actual grid disruptions. The cases include the 1977 New York City blackout, the 2003 Northeast blackout, multi-year national annual lightning-related electrical damage and multi-year national line-disturbance events. Insured losses represent between 3 and 64 per cent of total loss costs across the case studies. The household sector emerges as a larger locus of costs than indicated in previous studies, and short-lived events emerge as important sources of loss costs.

Relative sea-level data from southwest Scotland constrain meltwater-driven sea-level jumps prior to the 8.2 kyr BP event

The most significant climate cooling of the Holocene is centred on 8.2 kyr BP (the ‘8.2 event’). Its cause is widely attributed to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) associated with the sudden drainage of Laurentide proglacial Lakes Agassiz and Ojibway, but model simulations have difficulty reproducing the event with a single-pulse scenario of freshwater input. Several lines of evidence point to multiple episodes of freshwater release from the decaying Laurentide Ice Sheet (LIS) between ∼8900 and ∼8200 cal yr BP, yet the precise number, timing and magnitude of these events – critical constraints for AMOC simulations – are far from resolved. Here we present a high-resolution relative sea level (RSL) record for the period 8800 to 7800 cal yr BP developed from estuarine and salt-marsh deposits in SW Scotland. We find that RSL rose abruptly in three steps by 0.35 m, 0.7 m and 0.4 m (mean) at 8760–8640, 8595–8465, 8323–8218 cal yr BP respectively. The timing of these RSL steps correlate closely with short-lived events expressed in North Atlantic proxy climate and oceanographic records, providing evidence of at least three distinct episodes of enhanced meltwater discharge from the decaying LIS prior to the 8.2 event. Our observations can be used to test the fidelity of both climate and ice-sheet models in simulating abrupt change during the early Holocene.

Möwe Bay Dykes, Northwestern Namibia: Geochemical and geochronological evidence for different mantle source regions during the Cretaceous opening of the South Atlantic

Dyke emplacement in the course of Paraná-Etendeka volcanism in northwestern Namibia has been considered as a short-lived event related to a specific magma source at approximately 135–130Ma. New geochemical, whole rock Sr-Nd-Pb isotope data and 40Ar/39Ar ages reveal that at least three geochemically and isotopically different tholeiitic dyke generations, with intrusion ages of 135.2±0.7, 124.1±0.8Ma and 113.0±0.5Ma, can be distinguished in the Möwe Bay area, Skeleton Coast of northwestern Namibia. Distinct mantle source components were identified in the petrogenesis of the various dyke generations. Magma composition of the two older dyke suites, both of which were emplaced in a tectonic setting dominated by E-W extension, evolved from a within-plate to an enriched mid-ocean ridge basalt type. Contamination by continental crust and/or lithospheric mantel is suggested by a high 238U/204Pb-value (=μ2) of 9.97, which is typical of the Kalahari Craton. The third dyke generation, which intruded in a tectonic regime dominated by SE-NW extension, corresponds to high-Ti ocean island-type basalt with unradiogenic isotopic compositions derived from a mantle source with a μ2-value of 9.35.The formation of the older dykes is attributed to the presence of a thermal anomaly in the upper sublithospheric mantle. This anomaly was most likely caused by the peripheral part of a mantle plume that impinged at the base of the lithosphere and caused erosion of the subcontinental mantle lithosphere and melting above the plume head. The initial break-up of SW Gondwana and the formation of early oceanic crust were most likely due to passive rather than active rifting. Continued plume upwelling facilitated by progressive thinning of SW-Gondwana crust led to the formation of the younger, c. 113Ma old dykes, which are chemically and isotopically identical to coeval rocks from the northeastern portion of the Walvis Ridge and thus are interpreted as onshore expressions of the Tristan-Gough plume head at that time. The difference in the dominant extension directions of the older and the younger dyke generations can be explained by rotation induced by the Aptian/Albian opening of the Equatorial Central Atlantic, accompanied by a substantial increase in the South Atlantic spreading rate.

Assessing mid-latitude dynamics in extreme event attribution systems

Atmospheric modes of variability relevant for extreme temperature and precipitation events are evaluated in models currently being used for extreme event attribution. A 100 member initial condition ensemble of the global circulation model HadAM3P is compared with both the multi-model ensemble from the Coupled Model Inter-comparison Project, Phase 5 (CMIP5) and the CMIP5 atmosphere-only counterparts (AMIP5). The use of HadAM3P allows for huge ensembles to be computed relatively fast, thereby providing unique insights into the dynamics of extremes. The analysis focuses on mid Northern Latitudes (primarily Europe) during winter, and is compared with ERA-Interim reanalysis. The tri-modal Atlantic eddy-driven jet distribution is remarkably well captured in HadAM3P, but not so in the CMIP5 or AMIP5 multi-model mean, although individual models fare better. The well known underestimation of blocking in the Atlantic region is apparent in CMIP5 and AMIP5, and also, to a lesser extent, in HadAM3P. Pacific blocking features are well produced in all modeling initiatives. Blocking duration is biased towards models reproducing too many short-lived events in all three modelling systems. Associated storm tracks are too zonal over the Atlantic in the CMIP5 and AMIP5 ensembles, but better simulated in HadAM3P with the exception of being too weak over Western Europe. In all cases, the CMIP5 and AMIP5 performances were almost identical, suggesting that the biases in atmospheric modes considered here are not strongly coupled to SSTs, and perhaps other model characteristics such as resolution are more important. For event attribution studies, it is recommended that rather than taking statistics over the entire CMIP5 or AMIP5 available models, only models capable of producing the relevant dynamical phenomena be employed.

Elucidating the magmatic history of the Austurhorn silicic intrusive complex (southeast Iceland) using zircon elemental and isotopic geochemistry and geochronology

The Austurhorn intrusive complex (AIC) in southeast Iceland comprises large bodies of granophyre and gabbro, and a mafic–silicic composite zone (MSCZ) that exemplifies magmatic interactions common in Icelandic silicic systems. Despite being one of Iceland’s best-studied intrusions, few studies have included detailed analyses of zircon, a mineral widely recognized as a valuable tracer of the history and evolution of its parental magma(s). In this study, we employ high spatial resolution zircon elemental and isotopic geochemistry and U–Pb geochronology as tools for elucidating the complex construction and magmatic evolution of Austurhorn’s MSCZ. The trace element compositions of AIC zircon crystals form a broad but coherent array that partly overlaps with the geochemical signature for zircons from Icelandic silicic volcanic rocks. Typical of Icelandic zircons, Hf concentrations are relatively low (<10,000 ppm) and Ti concentrations range from 5 to 40 ppm (Ti-in-zircon model temperatures = 761–981 °C). Zircon δ18O values vary from +2.2 to +4.8 ‰, consistent with magmatic zircons from other Icelandic silicic rocks, and preserve evidence for recycling of hydrothermally altered crust as a significant contribution to the generation of silicic magmas within the AIC. Zircon e Hf values generally range from +11 to +15. This range overlaps with that of Icelandic basalts from off-rift settings as well as the least depleted rift basalts, suggesting that the AIC developed within a transitional rift environment. In situ zircon U–Pb ages yield a weighted mean of 6.52 ± 0.03 Ma for the entire complex, but span a range of ~320 kyr, from 6.35 ± 0.08 to 6.67 ± 0.06 Ma (2σ SE). Gabbros and the most silicic units make up the older part of this range, while granophyres and intermediate units make up the younger part of the complex, consistent with field relationships. We interpret the ~320 kyr range in zircon ages to represent the approximate timescale of magmatic construction of the MSCZ. These U–Pb data suggest that the complex was constructed by multiple short-lived magmatic intrusion events occurring closely spaced in time, allowing periodic re-melting and rejuvenation of mush-like material and a prolonged lifetime for the complex.

Short-lived reheating events in the Sommartuva shear zone hosted in cold crust: Ar-diffusion modelling constraints for the exhumation of eclogites in Flakstadøy, Lofoten Islands, Norway

The exhumation of the Norwegian Lofoten eclogites, formed during the continental collision of Laurentia and Baltica, is mainly due to the reactivation of shear zones during the collapse of the Caledonian orogen. The current cooling history [temperature–time (T–t) paths] for the exhumation of these rocks as determined by 40Ar/39Ar dating and geothermometry involves a protracted period of slow cooling (c. −1.7°CMa−1) from high T. The Sommartuva shear zone, hosted in a Palaeoproterozoic anorthosite, contains retrogressed eclogite and amphibolite-facies lenses and served as an open system for Ar with 40Ar-rich and 40Ar-poor hot fluid infiltration. Ca-rich amphiboles from amphibolites contain excess Ar and are mantled by phlogopites that yield Ar-diffusion loss profiles with plateau ages of 413–400Ma associated with an extensional event in Lofoten. Locally, the zone was intruded in its late-stage history (c. 333Ma) by a granitoid rock crystallizing annite and muscovite, previously inferred to be injected synchronously with amphibolite-facies metamorphism. An alternative cooling path related to the exhumation of the eclogites was determined by a combination of i) 40Ar/39Ar ages in minerals that grew during different thermal events, ii) thermal modelling of the Ar systematics in these minerals and iii) exploration of the thermal effects caused by the superposition of each event on pre-existing mineral phases. The best-fit T–t path as constrained by the Ar data reveals that, in order to preserve Ar (radiogenic and excess) within the minerals, the ambient T must have been relatively low (≤300°C) over 80Ma (413–333Ma). Likewise, the associated intrusion of the granitoid and the hot fluid that percolated the shear zone and crystallized the phlogopites were likely to have been short-lived (c. 100–25ka) and at relatively moderate T (500°C). In contrast to previous thermal models where the thermal events are represented as simple inflexions in a T–t curve, our cold-crust model incorporates short-lived thermal disturbances (including estimates of the magnitude of their maximum temperature and duration) superimposed on protracted periods of slow cooling from high T. A new proposed T–t path obtained for the exhumation of this terrane indicates that the eclogites resided for 80Ma (413–333Ma) at relatively cool ambient temperatures (c. 300°C), highlighting the enormous potential of coupling geochronological data from multiple isotopic systems with thermal modelling to identify and constrain the duration of short-lived events.

Discovery, Geology, and Origin of the Fruta del Norte Epithermal Gold-Silver Deposit, Southeastern Ecuador

Fruta del Norte is a completely concealed and extraordinarily well preserved epithermal gold-silver deposit located in the remote Cordillera del Condor mountain ranges of southeastern Ecuador. Currently defined resources in a single, steep, relatively small body, displaying exceptional grade continuity, contain 9.81 million ounces (Moz) of gold and 15.0 Moz of silver, with an indicated resource grade of 9.59 g/t Au and 12.9 g/t Ag. The deposit was discovered in early 2006 during a greenfields program conducted by Aurelian Resources, a Canadian junior explorer. Discovery resulted from systematic drill testing of a conceptual geologic model, which predicted that auriferous veins would be present in andesitic volcanic rocks inferred to underlie a steep silicified rib cutting a fluvial conglomerate sequence. The rib is highly anomalous in arsenic, antimony, and mercury but contains low-order gold values. The second drill test—the discovery hole—intersected >230 m of ore-grade gold-silver mineralization beneath ~200 m of the barren conglomerate cover. The host andesitic volcanic rocks, crosscutting feldspar porphyry, and associated phreatic breccias are assigned to the Piuntza unit of the Santiago Formation, which, along with the Zamora batholith and a series of porphyry copper stocks, was generated in a continental margin magmatic arc during the Middle to Late Jurassic. The deposit is located near the northeastern extremity of the ~10-km-long, Suarez pull-apart basin where it is linked to the steep West and Central faults, part of the regionally extensive Las Penas strike-slip fault zone. The pull-apart basin was progressively filled by fluviatile conglomerate, dacitic ignimbrite flows, finer grained siliciclastic sedimentary rocks, and, finally, andesite flows, all assigned to the Chapiza Formation. The Fruta del Norte deposit consists of a 1.3-km-long and up to >300-m-wide vein-stockwork associated with quartz-illite-pyrite alteration. The deposit comprises two principal vein types, one in the south dominated by quartz, manganoan carbonates, and abundant base metal sulfides and the other in the north dominated by manganese- and base metal-poor quartz and calcite. Adularia is a minor main-stage gangue mineral in each. Both types are abruptly transitional upward and westward to a third ore type marked by intense silicification and chalcedony veining, with disseminated and veinlet marcasite (±pyrite). The uppermost part of this silicic zone is sulfide deficient, probably the result of a short-lived supergene oxidation event prior to initial conglomerate deposition. The deposit is notable for the widespread occurrence of fine to coarse visible gold, which gives rise to bonanza grades and is closely associated with quartz, chalcedony, carbonate, and sulfide gangue. The sulfide-free, silicic zone is overlain by an extensive silica sinter horizon, which may either directly overlie the Piuntza volcanic rocks and/or occur as interbeds in the basal 20 m of the conglomerate, which are invariably silicified and marcasite bearing. Otherwise, the conglomerate above the orebody lacks silicification, with one critical exception: the steeply inclined zone that is exposed as the silicified rib that led to discovery. The sinter horizon, containing localized mud-pool deposits and hydrothermal eruption breccias, is in unusual proximity to the underlying gold-silver orebody. The northern and southern parts of the Fruta del Norte deposit possess characteristics that are usually considered typical of low and intermediate sulfidation epithermal deposits, respectively; they may have required two discrete mineralizing fluids, both of which are suspected to have ascended via the West and Central faults. The upward change to the silicified zone is attributed to cooling of the ascendant fluid on approach to the paleosurface sinter. Progressive burial of the deposit beneath the Suarez basin fill may have contributed to the suppression and eventual extinction of the epithermal system, with gold mineralization of the conglomerate being inhibited by rheologic and chemical factors. Formation of the Fruta del Norte deposit and complete filling of the Suarez basin took place in >3 to 6 m.y. during the Late Jurassic ( 157–154 Ma).

Releasing the sequence stratigraphy paradigm. Overview and perspectives

Sequence stratigraphy arose as a paradigm in stratigraphy after the integration of the descriptive seismic method, introduced by Exxon researchers in the 1970s, with genetic concepts linking seismic attributes to sedimentary dynamics. Since then, the sequence stratigraphy model underwent significant modification owing to the increasing scenarios of application, each with its own practical requirements. This led to the fragmentation of the original model into a plethora of sub-methods and the flourishing of redundant notions and terminology. Reviewers striving to preserve the unity and fitness of sequence stratigraphy systematically weakened the central assumption by which it stood as a novelty and a paradigm: the relevance of relative sea-level cycles in shaping strata ‘sequentially’. In contrast to this attitude, the value of a model explicitly relying on the upholding control of sea-level is herein reconsidered, based on the marine record of Quaternary, climate-driven, sea-level cycles. Traditionally conceived as exceptionally short-lived and extraordinary events in the history of the Earth, these cycles are documented worldwide on modern continental margins, providing convincing evidence of how sea-level fluctuations actually shape sequences.

Trace metal anomalies in bleached Porites coral at Meiji Reef, tropical South China Sea

Coral bleaching has generally been recognized as the main reason for tropical coral reef degradation, but there are few long-term records of coral bleaching events. In this study, trace metals including chromium (Cr), copper (Cu), molybdenum (Mo), manganese (Mn), lead (Pb), tin (Sn), titanium (Ti), vanadium (V), and yttrium (Y), were analyzed in two Porites corals collected from Meiji Reef in the tropical South China Sea (SCS) to assess differences in trace metal concentrations in bleached compared with unbleached coral growth bands. Ti, V, Cr, and Mo generally showed irregular fluctuations in both corals. Bleached layers contained high concentrations of Mn, Cu, Sn, and Pb. Unbleached layers showed moderately high concentrations of Mn and Cu only. The different distribution of trace metals in Porites may be attributable to different selectivity on the basis of vital utility or toxicity. Ti, V, Cr, and Mo are discriminated against by both coral polyps and zooxanthellae, but Mn, Cu, Sn, and Pb are accumulated by zooxanthellae and only Mn and Cu are accumulated by polyps as essential elements. The marked increase in Cu, Mn, Pb, and Sn are associated with bleaching processes, including mucus secretion, tissue retraction, and zooxanthellae expulsion and occlusion. Variation in these trace elements within the coral skeleton can be used as potential tracers of short-lived bleaching events.