High-energy Events Research Articles

Exceptional middle latitude electron precipitation detected by balloon observations: implications for atmospheric composition

Abstract. Energetic particle precipitation leads to ionization in the Earth's atmosphere, initiating the formation of active chemical species which destroy ozone and have the potential to impact atmospheric composition and dynamics down to the troposphere. We report on one exceptionally strong high-energy electron precipitation event detected by balloon measurements in geomagnetic midlatitudes on 14 December 2009, with ionization rates locally comparable to strong solar proton events. This electron precipitation was possibly caused by wave–particle interactions in the slot region between the inner and outer radiation belts, connected with still poorly understood natural phenomena in the magnetosphere. Satellite observations of odd nitrogen and nitric acid are consistent with widespread electron precipitation into magnetic midlatitudes. Simulations with a 3D chemistry–climate model indicate the almost complete destruction of ozone in the upper mesosphere over the region where high-energy electron precipitation occurred. Such an extraordinary type of energetic particle precipitation can have major implications for the atmosphere, and their frequency and strength should be carefully studied.

Investigation of Overburden Movement and Ground Stress Behaviour in Multiseam Mining

Abstract In multiple-seam mining, severe deformation of roadways and coal bursts caused by overlying coal pillars can occur in the lower seams. Overburden movement and ground pressure behaviour when mining thick seam below the strong roof and upper four extracted coal seams were investigated in the Tongxin coal mine, China. The numerical model indicated that the abutment stress in the lower seam is affected by overlying coal pillars as suggested by the bubble and the cantilever beam models. The microseismic monitoring indicated that high-energy seismic events caused by large overburden movement under the overlying pillars were the source of the dynamic loads. The influence of upper pillar on lower longwall mining conditions can be broken down into three cases: (a) under no pillar area, no excessive deformation or dynamic failure was observed in the tailgate with medium static loads and low dynamic loads; (b) under single pillars or two overlapping pillars, severe deformation occurred in the tailgate with low to medium static loads and medium dynamic loads; and (c) under the three to four overlapping pillars, extreme deformation was observed with the high static loads and high dynamic loads. These findings can provide guidance for the roadway layout in the multiple-seam operations.

Microbially induced sedimentary structures (MISS) generated by episodic storm surges in a temperate coast

This study recognizes the creation of primary sedimentary structures in a modern environment that reports valuable insights into the role of microbiota in sculpting sedimentary structures, and it may explain many previously confusing sedimentary structures in the rock record. The research considered the frequent flooding events on a coastal sedimentary flat colonized by microbial mats and the effect produced by severe storm surge events. Large-scale microbially induced sedimentary structures (MISS) were created; thus, the interaction between meteorologic, oceanographic, and geomorphologic conditions necessary to form them was analysed. The study was developed in Paso Seco, Argentina (40°38′31” S - 62°12′54” W), a sedimentary flat behind a sand spit, coated by thick microbial mats recurrently affected by storm events. Water level measurements were recorded continuously for five years (measurement interval 10 min). The seawater inundations were related to synoptic weather maps and oceanographic parameters (wave height, period, and tides) to analyse the cause of storm surges. Two situations of severe storms were studied in 2018 and 2019. The inundation of the study area occurs when a cold front in association with a low-pressure centre in the Atlantic Ocean, moving in an SW-NE direction, produces strong SW winds higher than 45 km h−1 and wave height higher than 2 m. Strong winds and storm duration (two or three days) in co-occurrence with spring tides create an extreme erosional event that affects the sedimentary microbial flat. In sum, the interaction between storm surge, high tide, wave setups and wave heights in Paso Seco produces coastal hinterland flooding that creates meter-sized MISS such as roll-ups, erosional pockets, and remnants mats structures. The impact of storm surges on the coast is common and catastrophic in modern times but is challenging to identify in the sedimentary record. Therefore, the microbial structures presented here could help interpret high-energy events occurrence, favourable to assessing past environmental conditions.

Multi-proxy approach to identify the origin of high energy coastal deposits from Laem Son National Park, Andaman Sea of Thailand

Understanding the frequency of high energy storm and tsunami events is crucial for apprehending the vulnerability of coastal communities. Identifying and dating sedimentary evidence deposited by such high energy events can assist in the planning and installation of suitable protection measurements. The Andaman Sea coast of Thailand is particularly vulnerable to such events as illustrated by the 2004 Indian Ocean Tsunami. Here, three shore-perpendicular transects and ten sediment cores along a beach ridge in the northern part of Lam Son National Park, Ranong Province, Andaman Sea coast are investigated with respect to high energy deposits. A multi-proxy analysis was conducted including stratigraphical correlations between cores, detailed description of physical characteristics, sedimentary structure, grain size, organic matter and carbonate content as well as identification of the remains of marine organisms. Optically stimulated luminescence (OSL) dating was applied for determining the age of the sediments on this beach ridge plain. The stratigraphy and sediment characteristics, in particular composition, of the sands in the study area clearly allow us to distinguish between high energy deposits and normal beach sediments. Two high energy deposits were identified and attributed to result from the 2004 Indian Ocean Tsunami as well as a past storm, which, based on OSL dating occurred more than 340 ± 20 years ago.

Study on Matching Between Environmental Warning Information and Spacecraft Anomalies

The accuracy of space environmental warning information is the basic support for the response mitigation to impact. There are multiple environmental events before and after the solar eruption of the X9.3 megaflare, which has caused many satellite anomalies. In this case, the matching between the warning information and the occurrence levels of four space environmental events was investigated using the analysis methods of statistical analysis and decision tree. The results show that there is a significant correlation between high-energy electron storm events and high-Earth-orbit satellite anomalies, and the accuracy could achieve 67%. Other kinds of space environmental events are weakly related to satellite anomalies. The decision tree evaluation method has advantages in the comprehensive statistical analysis of long-term anomalies data and can effectively reduce the bias introduced by individual cases of solar events. The tree model using multi-environment parameters will be an effective way to reduce false positive rates, which can provide diagnostic methods for medium- and long-term space environment risks in orbit spacecraft in the future.

Drilling predation on spatangoid echinoids from the Miocene of Sardinia: a taphonomic and paleoecological perspective

AbstractPredation is of great importance in understanding the diversification of spatangoid echinoids as well as their preservation in the fossil record. Herein, the spatangoid-dominated Miocene carbonate succession of Punta Foghe (Montiferru area, central-western Sardinia, Italy) is studied with the aim of reconstructing paleoenvironmental conditions and investigating abiotic and biotic factors, including predation, that influence the paleoecology and preservation potential of spatangoid echinoids.The echinoid fauna is dominated by the spatangoid Agassizia and, to a lesser extent, the clypeasteroid Clypeaster. The fauna also includes both regular (undetermined diadematoids and camarodonts) and irregular (Plagiobrissus, Echinocyamus, and Koehleraster) forms. Echinoids and associated fossil content, along with taphonomic and sedimentological signatures, indicate an inner sublittoral environment with moderate energy conditions affected by high-energy events. Agassizia remains, which consist mainly of complete and well-preserved tests, commonly bear subcircular drill holes that are interpreted as the result of cassid gastropod predation and investigated with respect to size selectivity and stereotypy of attack sites. Potential biases related to drilling predation and biostratinomy on the preservation potential of spatangoid tests are discussed.Agassizia lacks any morphological adaptation to minimize high predation risk, including defensive spines and the ability to burrow deeply into the sediment. An antipredator behavior possibly relied on a gregarious life-history strategy, reducing the frequency of attacks on specific individuals by cassid predators.

Testing Lorentz Violation with IceCube Neutrinos

Lorentz violation (LV) induced by Quantum Gravity has been tested at much lower energies than the Planck scale with more and more observational evidence. In recent studies, the time of flight difference between the TeV neutrino and MeV photon from Gamma Ray Bursts (GRBs) have been used to constrain the LV energy scale, based on the energy-dependent speed variation. Here, we performed a correlation study between the updated 7.5 year high-energy starting events (HESE), neutrino alert events detected by IceCube, and a full sample of more than 7000 GRBs, and we found six GRB-neutrino candidates, including four alerts and two track events. We obtained the first order energy scale of quantum gravity, namely EQG=8−5+15×1017GeV, which was consistent with other authors‘ work. We suggest that neutrinos and anti-neutrinos can be identified, respectively, due to the delay or advance of the observed time. For future point source search study of neutrinos, the arrival time difference of different particles may have to be taken into account.

Damage analysis of a SiCf/SiC ceramic matrix composite under stepwise fatigue loading with acoustic emission

Continuous fiber-reinforced ceramic matrix composites (CMCs) exhibit different damage mechanisms at multiple scales under cyclic loading. In this paper, the tension-tension fatigue behavior of a plain woven SiCf/SiC CMC was investigated, and damage accumulation and evolution process were studied in detail via acoustic emission (AE) method. With the increase of cycles, the material exhibits obvious hysteresis behavior affected by interfacial slip and wear mechanisms. Most of the fibers with radial fracture characteristic have relatively high strength, showing excellent toughening property. In the stepwise cyclic loading process, the Kaiser effect of AE determines the initiation of AE activities at each initial loading moment, which shows obvious nonlinear damage accumulation behavior of the material. High-energy events are related to significant matrix cracking and fiber fracture, and the evolution process of material damage initiation and propagation is monitored in real time.

Microtextures on quartz grains from the Gulf of Mexico and the Mexican Pacific coastal sediments: Implications for sedimentary processes and depositional environment

Microtexture analyes on quartz from coastal sediments of the Gulf of Mexico and the Mexican Pacific Coast reveal 35 and 30 types of microtextures, respectively, which were grouped into mechanical, mechanical/chemical and chemical categories based on their mode of origin. Microtextures of chemical origin are rarer in the El Carrizal than in the Manzanillo beach sediments of the Mexican Pacific Coast. Microtextures of mechanical origin like straight and curved scratches, pits, broken edges, and V-shaped marks indicate high energy, fluvial to marine depositional environments. The scarcity to absence of chemical features suggest that the energy level was higher at the Mexican Pacific coast than on the Gulf of Mexico coast. V-shaped marks are common in the Gulf of Mexico sediments, whereas they are abundant in the quartz grains from the Mexican Pacific coast. Increased frequency and density of V-shaped marks are produced by exceedingly high wave velocity during storm events or tsunamis. Abundance of V-shaped marks with fresh surfaces of quartz grains from the Mexican Pacific coast indicate an extremely high-energy impact event. Many quartz grains from the El Carrizal beach of the Mexican Pacific coast have abundant closely spaced V-shaped marks with fewer fresh surfaces. Such high frequency of V-shaped marks is mainly linked to grain-to-grain collision, typically associated with high-energy sub-aqueous conditions with a large volume of sedimentary particles in the water column that are produced during a tsunami or storm events. In contrast, many quartz grains from the Gulf of Mexico have large fresh surfaces with moderate percentages of V-shaped marks that might have been produced by high-energy waves with low sediment concentrations during storm events.

Boulder displacements along rocky coasts: A new deterministic and theoretical approach to improve incipient motion formulas

Several impacts of high-energy marine events – tsunamis and storms – which have occurred along the Mediterranean coasts, have determined boulder displacements in different ways, spanning from sliding and overturning to saltation. The dynamics of these transport modes to the incipient motion of boulders, strictly connected to the pre-setting scenarios, has been extensively studied considering the boulder size and the hydrodynamic parameters of high-energy marine events, such as the wave flow velocity. Notwithstanding this, known hydrodynamic relationships provide some unrealistic flow values concerning the real wave flow velocity registered along the Mediterranean coasts. In this work, a new deterministic and theoretical approach has been developed to assess the minimum flow velocities required to move coastal boulders. The proposed approach is based on the introduction of modified parameters, which consider the real dimensional features of the boulders assessed by means of modern geophysical survey techniques, into the incipient motion formulas. To accurately define these parameters, we created a database composed of boulders located along the coasts of Apulia and Sicily (Italy) that were surveyed in previous studies through photogrammetric and Terrestrial Laser Scanner techniques. Results highlighted that the incipient motion formulas, revised with the new proposed parameters, provided minimum flow velocity values for boulder transport initiation, which were significantly lower compared to those calculated using the previous approach. Thus, the proposed modifications are a step forward towards defining the dynamics of boulder displacement.

End-to-end jet classification of boosted top quarks with the CMS open data

We describe a novel application of the end-to-end deep learning technique to the task of discriminating top quark-initiated jets from those originating from the hadronization of a light quark or a gluon. The end-to-end deep learning technique combines deep learning algorithms and low-level detector representation of the high-energy collision event. In this study, we use low-level detector information from the simulated CMS Open Data samples to construct the top jet classifiers. To optimize classifier performance we progressively add low-level information from the CMS tracking detector, including pixel detector reconstructed hits and impact parameters, and demonstrate the value of additional tracking information even when no new spatial structures are added. Relying only on calorimeter energy deposits and reconstructed pixel detector hits, the end-to-end classifier achieves an AUC score of 0.975$\pm$0.002 for the task of classifying boosted top quark jets. After adding derived track quantities, the classifier AUC score increases to 0.9824$\pm$0.0013, serving as the first performance benchmark for these CMS Open Data samples. We additionally provide a timing performance comparison of different processor unit architectures for training the network.

Variability in High Wave Energy Events Around the Southern African Coast

AbstractThe wave energy flux along the southern African coastline often reaches extreme levels, seriously impacting coastal communities, infrastructure, as well as near‐coast and offshore marine operations. Understanding the drivers behind past high wave energy events and their frequency is key to forecasting future events. Using in‐situ wave buoy data recorded by the Council for Scientific and Industrial Research (CSIR), the ERA5 and CACWR global wave model products are evaluated. The better‐performing ERA5 product is used to assess long‐term variability and trends around the coastline between 1979 and 2020. There are significant increasing trends in offshore flux for all seasons, with spring having the strongest coastal trends. Substantial interannual variability exists in wave energy flux and direction. Possible drivers, the Southern Annular Mode (SAM), El Niño Southern Oscillation (ENSO), and the semi‐annual oscillation (SAO), were assessed to find that SAM appears to show the strongest relationship overall. Negative (positive) SAM is associated with above (below) average and westerly (easterly) anomalies in both flux and direction. ENSO directly impacts the summer wave climate while the SAO indirectly impacts the wave energy flux over spring and winter. During many seasons, more than one climate mode is active. It is found the strongest significant near‐coast positive westerly anomalies occurred under negative SAM and negative SAO, with more intense offshore anomalies under El Niño, whereas the strongest significant negative east‐northeasterly anomalies occurred under a combination of La Niña with positive SAM and SAO phases.

Impact of Radiation Quality on Microdosimetry and Chromosome Aberrations for High-Energy (>250 MeV/n) Ions

Studying energy deposition by space radiation at the cellular scale provides insights on health risks to astronauts. Using the Monte Carlo track structure code RITRACKS, and the chromosome aberrations code RITCARD, we performed a modeling study of single-ion energy deposition spectra and chromosome aberrations for high-energy (>250 MeV/n) ion beams with linear energy transfer (LET) varying from 0.22 to 149.2 keV/µm. The calculations were performed using cells irradiated directly by mono-energetic ion beams, and by poly-energetic beams after particle transport in a digital mouse model, representing the radiation exposure of a cell in a tissue. To discriminate events from ion tracks directly traversing the nucleus, to events from δ-electrons emitted by distant ion tracks, we categorized ion contributions to microdosimetry or chromosome aberrations into direct and indirect contributions, respectively. The ions were either ions of the mono-energetic beam or secondary ions created in the digital mouse due to interaction of the beam with tissues. For microdosimetry, the indirect contribution is largely independent of the beam LET and minimally impacted by the beam interactions in mice. In contrast, the direct contribution is strongly dependent on the beam LET and shows increased probabilities of having low and high-energy deposition events when considering beam transport. Regarding chromosome aberrations, the indirect contribution induces a small number of simple exchanges, and a negligible number of complex exchanges. The direct contribution is responsible for most simple and complex exchanges. The complex exchanges are significantly increased for some low-LET ion beams when considering beam transport.

Dynamics, Evolution, and Facies Preservation of a Microtidal Chenier Plain, Joal-Fadiouth (Senegal, West Africa)

Youm, C.I.; Morales, J.A.; Doumbouya, M.F.; Garcia-Villalba, E.; Sow, I.S., and Sow, E., 2023. Dynamics, evolution, and facies preservation of a microtidal chenier plain, Joal-Fadiouth (Senegal, West Africa). Journal of Coastal Research, 39(2), 257–265. Charlotte (North Carolina), ISSN 0749-0208. Cheniers are coarse sediment ridges formed above finer sediments deposited on a tidal flat, the origin and development of which have traditionally been attributed to storm waves. Joal-Fadiouth is a microtidal system located on the southern coast of Senegal (West Africa). This system presents a succession of sandy and shelly ridges displaying a facies architecture consistent with a chenier plain facies model. This study combines aerial orthophotographs and sediment cores to interpret the sedimentary dynamics and facies of the chenier plain under analysis. The genesis of the last active chenier is related to the arrival of sand from the frontal ebb-tidal delta. Breaching processes occurred in the ebb delta, inducing the abandonment of the frontal lobe by the ebb-tidal currents. Fair-weather waves rework the sand from the frontal lobe, causing a migration of the sand in a manner similar to the formation of a typical nearshore swash bar. In Joal-Fadiouth, these bars soar and migrate over a tidal flat through the action of normal waves during spring high tides. Relict cheniers present shelly gravel sediments coarser than those observed in active cheniers. Thus, the final stage of stabilization of cheniers was attributed to the action of more energetic storm waves. The cheniers that accumulate during the action of ordinary and continuous processes tend not to persist, and only the coarsest cheniers formed during high-energy events finally remain in the sedimentary record. In addition to discussing the preservation of active coastal forms, this work is of regional interest, given that so far there has been only one work on cheniers in West Africa since 1989.

Solar activity and space weather

After providing an overview of solar activity as measured by the sunspot number (SSN) and space weather events during solar cycles (SCs) 21-24, we focus on the weak solar activity in SC 24. The weak solar activity reduces the number of energetic eruptions from the Sun and hence the number of space weather events. The speeds of coronal mass ejections (CMEs), interplanetary (IP) shocks, and the background solar wind all declined in SC 24. One of the main heliospheric consequences of weak solar activity is the reduced total (magnetic + gas) pressure, magnetic field strength, and Alfvén speed. There are three groups of phenomena that decline to different degrees in SC 24 relative to the corresponding ones in SC 23: (i) those that decline more than SSN does, (ii) those that decline like SSN, and (iii) those that decline less than SSN does. The decrease in the number of severe space weather events such as high-energy solar energetic particle (SEP) events and intense geomagnetic storms is deeper than the decline in SSN. The reduction in the number of severe space weather events can be explained by the backreaction of the weak heliosphere on CMEs. CMEs expand anomalously and hence their magnetic content is diluted resulting in weaker geomagnetic storms. The reduction in the number of intense geomagnetic storms caused by corotating interaction regions is also drastic. The diminished heliospheric magnetic field in SC 24 reduces the efficiency of particle acceleration, resulting in fewer high-energy SEP events. The numbers of IP type II radio bursts, IP socks, and high-intensity energetic storm particle events closely follow the number of fast and wide CMEs (and approximately SSN) because all these phenomena are closely related to CME-driven shocks. The number of halo CMEs in SC 24 declines less than SSN does, mainly due to the weak heliospheric state. Phenomena such as IP CMEs and magnetic clouds related to frontside halos also do not decline significantly. The mild space weather is likely to continue in SC 25, whose strength has been predicted to be not too different from that of SC 24.

Cosmogenic gamma-ray and neutrino fluxes from blazars associated with IceCube events

Context.Blazars constitute the vast majority of extragalacticγ-ray sources. They can also contribute a sizable fraction of the diffuse astrophysical neutrinos detected by IceCube. In the past few years, the real-time alert system of IceCube has led to the multiwavelength follow-up of very high-energy neutrino events of plausible astrophysical origin. Spatial and temporal coincidences of a number of these neutrino events withγ-ray blazars provide a unique opportunity to decipher cosmic-ray interactions in the relativistic jets.Aims.The aim of this work is to test if theγ-ray blazars associated with the IceCube neutrino events are also sources of ultra-high-energy cosmic rays (UHECRs;E > 1018eV).Methods.Assuming that blazars accelerate UHECRs, we calculate the “guaranteed” contribution to the line-of-sight cosmogenicγ-ray and neutrino fluxes from four blazars associated with IceCube neutrino events. We compare these fluxes with the sensitivities of the upcomingγ-ray imaging telescopes, such as the CTA, and with the planned neutrino detectors, such as IceCube-Gen2.Results.We find that detection of the cosmogenic neutrino fluxes from the blazars TXS 0506+056, PKS 1502+106, and GB6 J1040+0617 would require UHECR luminosity ≳10 times the inferred neutrino luminosity from the associated IceCube events, with the maximum UHECR proton energyEp, max ≈ 1020eV. Cosmogenicγ-ray emission from blazars TXS 0506+056, 3HSP J095507.9 +355101, and GB6 J1040+0617 can be detected by the CTA if the UHECR luminosity is ≳10 times the neutrino luminosity inferred from the associated IceCube events and forEp, max ≳ 1019eV.Conclusions.Detection of cosmogenic neutrino and/orγ-ray flux(es) from blazars associated with IceCube neutrinos may lead to the first direct signature(s) of UHECR sources. Given their relatively low redshifts and hence total energetics, TXS 0506+056 and 3HSP J095507.9+355101 should be the prime targets for upcoming large neutrino andγ-ray telescopes.

Unraveling the record of a tropical continental Cretaceous-Paleogene boundary in northern Colombia, South America

The Cretaceous-Paleogene (K-Pg) boundary event, triggered by the Chicxulub asteroid impact in Mexico ∼66 Myr ago, is recognized as one of the major environmental crises in Earth's history. Its effects on the evolution of tropical vegetation were drastic, giving rise to the closed-canopy tropical rainforest. Despite of its importance, the actual K-Pg boundary event layer has not yet been identified in terrestrial sections within tropical latitudes. Here, we study a sediment core (Diablito-1) from northern Colombia and described its lithofacies, palynostratigraphic content, magnetic susceptibility and geochemical composition, including the concentration of key elements linked to a meteoritic contribution such as iridium. We found an 8.2 cm-thick (0.27 inches) interval with gravel-size calcareous intraclasts, broken skeletal fragments and siliceous spherules that were transported during a short-duration high-energy event into the coastal plain. Very fine-to medium-grained spherules, concentrated in several layers of the flow structure, could be interpreted as derived from the K-Pg impact event. This thin intraclastic packstone interval lies within the extinction level of the palynomorph Echimonocolpites franciscoi, an important biostratigraphic event associated with the K-Pg boundary in Colombia. In addition, this layer is associated with both a small iridium anomaly and high concentration of several other major and trace elements that are occurring above a low Magnetic Susceptibility (MS) interval and within the initial phase of a high MS interval. These lines of evidence support the position of the K-Pg event layer within the thin interval that includes the spherules in the Diablito-1 core.

Geophysical Characterization of Mining-Induced Complex Geological Deformations in a Deep Coalmine

Abstract In this paper, a new way of characterizing the mining-driven complex geological deformations is presented by utilizing a continuous real-time microseismic (MS) data acquired through passive seismological monitoring. The data was processed, and the source parameters were computed encompassing over 60,000 MS events. The correlation between MS events and regional stratigraphy reveals that the Upper and Middle Xishanyao Formations substantially contributed to induced seismicity. Most of the high-energy events (>3000 J) are located between 1200 and 1400 m in the coal seams and above, indicative of formation of the macrofracture in the roof rock layers perturbing the limits required for the equilibrium state of roof structure. Taking advantage of the recorded events, a large number of induced fractures are mapped and interpreted associated lineaments and their deformation mechanism is discussed. The correlation of mapped fractures and lineaments with MS energy showed an extremely erratic and complicated pattern revealing the different levels of accumulated stress. Based on the orientation and geometry, regional lineaments were classified into two broad systems that provided guidance for determining the propagation directions of the deformation. Based on the in-depth analysis of fractures and lineaments, a new fault is identified with length>700 m and various splays oriented in different directions serving as a new tool in rock engineering. An upsurged shear stress and decreased normal stress along the fault may lead to enhanced induced seismicity. Furthermore, a total of 5 vulnerable zones are identified as an example offering insights for worldwide geohazard assessments.

INSIGHTS FROM FOSSIL FISH TAPHONOMY INTO THE DEPOSITIONAL ENVIRONMENT OF THE LOWER MILWAUKEE FORMATION (BERTHELET MEMBER, LATEST MIDDLE DEVONIAN)

ABSTRACT The fossiliferous, argillaceous dolostone of the latest Middle Devonian (Givetian) Milwaukee Formation contains abundant disarticulated fish skeletal elements. This study refines depositional environment reconstruction of the Milwaukee Formation through taphonomic analysis of this fish assemblage. Robust skeletal elements of placoderm grinding teeth, fin spines, and armored plating dominate the assemblage. Specimens display variation in taphonomic attributes including color, luster, corrasion (chemical corrosion and/or physical abrasion), presence of pyrite and phosphate permineralization, and epibionts. Rare occurrences of teeth belonging to osteichthyan fish are also taphonomically variable. Associated invertebrates are diverse and include abundant cephalopod internal molds and pyritized brachiopods often randomly oriented in shell hashes. In sum, these observations suggest deposition on a marine shelf between normal and storm wave base. During low-energy background periods, fish plates exposed on the seafloor would undergo initial disarticulation, epibiont attachment, and color- and luster-altering corrasion and phosphatization. Buried skeletal elements were ‘protected' from epibiont attachment and corrasion, but occasional low oxygen conditions in the substrate led to early diagenetic pyrite permineralization. Periodic high-energy storm events were responsible for complete disarticulation as well as reworking and reexposure of buried skeletal elements (and burial of others), resulting in a time-averaged assemblage with a wide range of taphonomic attributes. Robust placoderm skeletal elements were best suited to survive fossilization in this setting and therefore the placoderm-dominated fossil assemblage appears to be an artifact of taphonomic processes and energy of the depositional environment.

Fluences of solar energetic particles for last three GLE events: Comparison of different reconstruction methods

Fluxes of solar energetic particles (SEPs), produced and accelerated in and in the vicinity of the Sun, are an important part of cosmic ray induced terrestrial effects such as ionizing radiation on the Earth’s orbit, which affects the exposure to radiation in space as well as the atmospheric ionization. Calculation of these effects requires the knowledge of the integral fluences of SEPs. High-energy solar particles are subject of special interest since they can significantly contribute to the total radiation dose and/or ionization. The main instrument to study the high-energy SEP events is a network of ground-based neutron monitors (NMs), used over the years to register a specific class of SEP, which is called ground-level enhancement (GLE) events. Up today, we possess records from 72 GLE events. Reconstruction of SEP integral and differential fluxes for GLE events using NM data is not an easy task, requires a careful and precise calculation of particle transport in the magnetosphere, atmosphere, and detector itself. In this work, we compare two methods of fluence reconstruction, “fast” and “full”, for the last three registered GLE events and additionally verify one of them using PAMELA experimental data.