Composition and origin of holotype Al‐Cu‐Zn minerals in relation to quasicrystals in the Khatyrka meteorite

We investigated the khatyrkite–cupalite holotype sample, 1.2 × 0.5 mm across. It consists of khatyrkite (Cu,Zn)Al₂, cupalite (Cu,Zn)Al, and interstitial material with approximate composition (Zn,Cu)Al₃. All mineral phases of the holotype sample contain Zn and lack Fe that distinguishes them from khatyrkite and cupalite in the Khatyrka meteorite particles (Bindi et al. 2009 , 2011 , 2012 , 2015 ; MacPherson et al. 2013 ; Hollister et al. 2014 ). Neither highly fractionated natural systems nor geo‐ or cosmochemical processes capable of forming the holotype sample are known so far. The bulk chemistry and thermal history of khatyrkite–cupalite assemblage in the holotype sample hint for its possible industrial origin. Likewise, the aluminides in the Khatyrka meteorite particles may also be derived from industrial materials and mixed with extraterrestrial matter during gold prospecting in the Listvenitovy Stream valley.     

Water retention effects on elastic properties of Opalinus shale

Shales play an important role in many engineering applications such as nuclear waste, CO₂ storage and oil or gas production. Shales are often utilized as an impermeable seal or an unconventional reservoir. For both situations, shales are often studied using seismic waves. Elastic properties of shales strongly depend on their hydration, which can lead to substantial structural changes. Thus, in order to explore shaly formations with seismic methods, it is necessary to understand the dependency of shale elastic properties on variations in hydration. In this work, we investigate structural changes in Opalinus shale at different hydration states using laboratory measurements and X-ray micro-computed tomography. We show that the shale swells with hydration and shrinks with drying with no visible damage. The pore space of the shale deforms, exhibiting a reduction in the total porosity with drying and an increase in the total porosity with hydration. We study the elastic properties of the shale at different hydration states using ultrasonic velocities measurements. The elastic moduli of the shale show substantial changes with variations in hydration, which cannot be explained with a single driving mechanism. We suggest that changes of the elastic moduli with variations in hydration are driven by multiple competing factors: (1) variations in total porosity, (2) substitution of pore-filling fluid, (3) change in stiffness of contacts between clay particles and (4) chemical hardening/softening of clay particles. We qualitatively and quantitatively analyse and discuss the influence of each of these factors on the elastic moduli. We conclude that depending on the microstructure and composition of a particular shale, some of the factors dominate over the others, resulting in different dependencies of the elastic moduli on hydration.     

The impact of surface‐wave attenuation on 3‐D seismic survey design

Three‐dimensional seismic survey design should provide an acquisition geometry that enables imaging and amplitude‐versus‐offset applications of target reflectors with sufficient data quality under given economical and operational constraints. However, in land or shallow‐water environments, surface waves are often dominant in the seismic data. The effectiveness of surface‐wave separation or attenuation significantly affects the quality of the final result. Therefore, the need for surface‐wave attenuation imposes additional constraints on the acquisition geometry. Recently, we have proposed a method for surface‐wave attenuation that can better deal with aliased seismic data than classic methods such as slowness/velocity‐based filtering. Here, we investigate how surface‐wave attenuation affects the selection of survey parameters and the resulting data quality. To quantify the latter, we introduce a measure that represents the estimated signal‐to‐noise ratio between the desired subsurface signal and the surface waves that are deemed to be noise. In a case study, we applied surface‐wave attenuation and signal‐to‐noise ratio estimation to several data sets with different survey parameters. The spatial sampling intervals of the basic subset are the survey parameters that affect the performance of surface‐wave attenuation methods the most. Finer spatial sampling will reduce aliasing and make surface‐wave attenuation easier, resulting in better data quality until no further improvement is obtained. We observed this behaviour as a main trend that levels off at increasingly denser sampling. With our method, this trend curve lies at a considerably higher signal‐to‐noise ratio than with a classic filtering method. This means that we can obtain a much better data quality for given survey effort or the same data quality as with a conventional method at a lower cost.     

Modeling of climate tendencies in Arctic seas based on atmospheric forcing EOF decomposition

Ocean Dynamics - The article analyzes the results of the EOF decomposition of climatic data and assesses the role of its components in the formation of climatic ice tendencies of recent decades....     

The sources and seasonal fluxes of particulate organic carbon in the Yellow River

The Yellow River transports a large amount of sediment and particulate organic carbon (POC), which is thought to mainly derive from erosion of the Chinese Loess Plateau (CLP). However, the compositions, sources and erosional fluxes of POC in the Yellow River remain poorly constrained. Here we combined measurements of mineralogy, total organic carbon content (OC_total), stable organic carbon isotopes (δ¹³C_org), radiocarbon (¹⁴C) activity of organic matter in bulk suspended sediments collected seasonally from the upper and middle Yellow River, to quantify the compositions and fluxes of the POC and to assess its sources (biospheric and petrogenic POC, i.e. POC_bio and POC_petro, respectively). The results showed that the POC loading of sediments was controlled by mineralogy, grain size and specific surface area of loess particles. The F_mod of POC (0.71 to 0.31) can be explained by mixing of POC_petro with modern and aged POC_bio. A binary mixing model based on the hyperbolic relationship of the F_mod and OC_total revealed a wide range of ages of POC_bio from 1300 to 11100 ¹⁴C years. Relative to the upstream station, the annual POC_bio and POC_petro fluxes in the Yellow River are more than doubled after it flows crossing the CLP within 35% drainage area gain, resulting in POC_bio and POC_petro yields of the CLP at 3.50 ± 0.59 and 0.48 ± 0.49 tC/km²/yr, respectively. POC flux seasonal variation revealed that monsoon rainfall exerts a first-order control on the export of both POC_bio and POC_petro from the CLP to the Yellow River, resulting in more than 90% of the annual POC exported during the monsoon season. Around one third of annual POC erosional flux was transported during a storm event period, highlighting the important role of extreme events in POC export in this large river. © 2020 John Wiley & Sons, Ltd.     

Anatomy and facies distribution of terminal lobes in ephemeral fluvial successions: Jurassic Tordillo Formation,Neuquén Basin,Argentina

In terminal fluvial-fan systems, characteristic proximal to distal variations in sedimentary architectures are recognized to arise from progressive downstream loss of water discharge related to both infiltration and evaporation. This work aims to elucidate downstream trends in facies and architecture across the medial and distal zones of terminal-fan systems, which record transitions from deposits of channel elements to lobe-like and sheet-like elements. This is achieved via a detailed characterization of ancient ephemeral fluvial deposits of the well-exposed Kimmeridgian Tordillo Formation (Neuquén Basin, Argentina). The fine sand-prone and silt-prone succession associated with the medial to distal sectors of the system has been studied to understand relationships between depositional processes and resulting architectures. Facies and architectural-element analyses, and quantification of resulting sedimentological data at multiple scales, have been undertaken to characterize sedimentary facies, facies transitions, bed types, architectural elements and larger-scale architectural styles. Eight bed types with distinct internal facies transitions are defined and interpreted in terms of different types of flood events. Channelized and non-channelized architectural elements are defined based on their constituent bed types and their external geometry. The most common elements are terminal lobes, which are composite bodies within which largely unconfined sandy deposits are stacked in a compensational manner; a hierarchical arrangement of internal components is recognized. Proximal feeder-channel avulsion events likely controlled the evolution of terminal-lobe elements and their spatiotemporal shifts. Stratigraphic relations between architectural elements record system-wide trends, whereby a proximal sector dominated by channel elements passes downstream via a gradational transition to a medial sector dominated by sandy terminal-lobe elements, which in turn passes further downstream to a distal sector dominated by silty terminal lobe-margin and fringing deposits. This work enhances current understanding of the stratigraphic record of terminal fluvial systems at multiple scales, and provides insight that can be applied to predict the facies and architectural complexity of terminal fluvial successions.     

Genetic aspects of the petroleum resource potential of marine sedimentary basins

The historical-genetic method developed at the Institute of Oceanology of the Russian Academy of Sciences for the assessment of the petroleum resource potential is discussed with consideration of its main tasks and the successive procedures in its application. Such studies are crowned by a compilation of separate maps demonstrating scales of oil and gas generation and maps of hydrocarbon genesis zoning of basins with outlining centers of oil and gas generation and defining different-phase hydrocarbon-generation zones. The method was tested in over twenty continental-marginal and intracontinental basins studied to a different extent. The sedimentary basins of the Atlantic continental margin off Africa and the Caspian and Black seas were used as objects for applying the historical-genetic method for assessing their petroleum resource potential.     

Pilot assessment of depth related distribution of macrofauna in surf zone along Dutch coast and its implications for coastal management

Surf zones are highly dynamic, physically stressful parts of sandy beach ecosystems. The high wave energy of surf zones has in the past severely hampered ecological surveys of these systems. Here we used a novel technique to collect fauna from this environment along the Dutch coast. A large vehicle in the form a tripod that drives along the sandy seafloor and supports a sampling platform 11 m above the water line can collect both infaunal (grabs) samples and pull beam trawls for epibenthos. The distribution and diversity of macrofauna were studied at different depths in the surf zone along the Dutch coast. Species diversity and abundance increased with increasing depth of the water column. This increase was especially noticeable on the seaward side of the outer breaker bar. Within the surf zone, in the trough between the two breaker bars, there were spots of high diversity and abundance of macrobenthic infauna. Moreover, the area is also important for epibenthic and fish species, like the commercially important flatfish sole. Spatial patterns of species richness and abundance across an onshore-offshore gradient from the beach to seawards of the breakers suggest the presence of faunal zonation in this environment. The high abundance recorded in troughs was primarily caused by patches of juvenile Sand mason Lanice conchilega. The management implications of these results are that we suggest to protect the surf zone, including the trough between the two breaker bars, as a potential area of high diversity and abundance and to reconsider the objectives of the EU-Habitat Directive and the Water Framework Directive for the coastal area.     

Influence of seasonal forcing on habitat use by bottlenose dolphinsTursiops truncatus in the Northern Adriatic Sea

Bottlenose dolphins are the only cetaceans regularly observed in the northern Adriatic Sea, but they survive at low densities and are exposed to significant threats. This study investigates some of the factors that influence habitat use by the animals in a largely homogeneous environment by combining dolphin data with hydrological and physiographical variables sampled from oceanographic ships. Surveys were conducted year-round between 2003 and 2006, totalling 3,397 km of effort. Habitat modelling based on a binary stepwise logistic regression analysis predicted between 81% and 93% of the cells where animals were present. Seven environmental covariates were important predictors: oxygen saturation, water temperature, density anomaly, gradient of density anomaly, turbidity, distance from the nearest coast and bottom depth. The model selected consistent predictors in spring and summer. However, the relationship (inverse or direct) between each predictor and dolphin presence varied among seasons, and different predictors were selected in fall. This suggests that dolphin distribution changed depending on seasonal forcing. As the study area is relatively uniform in terms of bottom topography, habitat use by the animals seems to depend on complex interactions among hydrological variables, caused primarily by seasonal change and likely to determine shifts in prey distribution.