Silty Sediments Research Articles

The effect of particle breakage on the dilatancy and shear behavior of marine calcareous and siliceous deposits

A large part of ocean surface is covered by calcareous deposits. The Low stiffness and weak particles of calcareous soils deposited by marine organisms showed significant particle breakage under applied loads, which resulted in different behavior compared to terrigenous soils. A series of compression drained triaxial tests were carried out to evaluate the monotonic shear behavior of crushable and non-crushable soils. Three different soils, including Firoozkuh siliceous sand (as a non-crushable soil) and Hormuz and Bushehr calcareous sands (as crushable soils) which were different in mineralogy compositions were obtained from northern and southern Iran. The specimens were prepared in different relative densities (i.e., loose, medium and dense conditions) and consolidated under confining pressures ranging from 100 to 600 kPa. The monotonic shear and dilatancy behaviors of the soils have been presented in detail and the effect of particle breakage has been discussed. The results showed that particle breakage has a significant effect on the mobilized friction and dilatancy angles of marine crushable soils. There is a linear relationship between the amount of particle breakage occurring during a triaxial test and breakage angle. In addition, the mineralogical difference influences the breakage properties of calcareous deposits.

The effect of ceramic YSZ powder morphology on coating performance for industrial TBCs

The increasing turbine inlet temperatures in modern gas turbines have raised concerns about the corrosion of ceramic thermal barrier coatings (TBCs) caused by molten silicate deposits, commonly referred to as “CMAS” due to their main constituents (CaO-MgO-Al2O3-SiO2). The objective of this study was to investigate the combined influence of powder morphology and chemical composition on the CMAS resistance and thermal cycling resistance of ceramic monolayer and bi-layer coatings created through Atmospheric Plasma Spraying (APS). Three powder morphologies were examined: porous Agglomerated and Sintered (A&S) granules, Hollow Spherical (HOSP) powders, and dense, irregular Fused and Crushed (F&C) particles. Monolayer 7-8YSZ coatings with both porous and dense vertically cracked (DVC) microstructures, and bi-layer coatings consisting of a bottom layer of porous standard 7-8YSZ and a top layer composed of a porous high‑yttrium ZrO2–55 wt% Y2O3 were obtained using all three powder types (A&S, HOSP, or F&C). Furthermore, the bi-layer systems were deposited with different ratios between the individual layer thicknesses and/or different total thickness. FEG-SEM, EDX, and micro-Raman analyses, were conducted to assess the coatings' performance. Nanoindentation high-speed mapping and pillar splitting test were performed to evaluate the mechanical behaviour. The study on 8YSZ monolayers shows that coatings from a F&C feedstock exhibit higher density, reducing the CMAS penetration. However, these coatings demonstrate poorer thermal cycling performance due to increased stiffness and thermal stresses. Coatings from HOSP and A&S powders allow CMAS penetration but offer stress relief pathways, enhancing the coating's ability to withstand thermal stresses. Bi-layer coatings with a 55YSZ top coat show superior CMAS resistance compared to 7-8YSZ monolayer coatings, with limited penetration causing top coat peeling. The thickness ratio between the layers also affects thermal cycling resistance, where a thinner 55YSZ layer extends the TBC lifetime.

PHTALATES IN SEDIMENTS OF BAIKAL REGION LAKES

Phthalates are one of the most common pollutants, the concentrations of which in the environment in the near future, according to scientists, will only grow. High concentrations of these substances pose a serious threat to water bodies, especially for lake ecosystems, which are characterized by slow water exchange and accumulate pollutants faster, thereby reflecting anthropogenic load and environmental changes. The paper presents for the first time the results of determining the phthalate content in the bottom sediments of lakes Arangatui, Bormashovoe, Dukhovoe, Kotokel, Shchuchye. The total content of 6 phthalates varied from 51 to 2222 mkg/kg of dry weight, while the highest concentrations were noted for central stations. The distribution profile of phthalates in the bottom sediments of lakes is basically quite similar – DBP (average content of 213 mkg/kg) and DEHP (189 mkg/kg) prevailed. It is noted that the accumulation of the studied substances occurs mainly in silty sediments, which is indicated by medium and high positive correlations between phthalates, granulometric composition, the content of organic carbon and heavy metals. The high levels of individual phthalates in the sediments of the studied lakes indicate the need to study in detail the sources and distribution mechanisms in the system of “water-bottom sediments”.

Sedimentology and stratigraphy of the Jordan River Dureijat archeological site reveal subtle late Pleistocene water-level changes at Lake Hula, Jordan Valley, Israel

AbstractSedimentary records of environmental conditions retrieved from archeological sites provide valuable insight into the milieux of ancient humans and context to understand societal and cultural changes. At Jordan River Dureijat, an open-air site in Israel’s Hula Valley documenting the entire Epipaleolithic period as well as the Early Neolithic, sediments exposed on the walls of the excavation pit reveal a sequence of lacustrine deposits accumulated continuously between c. 21.1 and 11.3 cal ka BP near the southeast margin of Paleolake Hula. Through sediment-grain-size, geochemical, and paleontological analyses, we describe the nature of the Paleolake Hula from the Last Glacial Maximum (LGM) to the start of the Holocene. Until c. 17.2 cal ka BP, Paleolake Hula existed as a relatively large and well-buffered waterbody. A rapid and substantial drawdown of the lake occurred at 17.2 cal ka BP, followed by more frequent changes in the position of the shoreline in a smaller and shallower lake, resulting in the deposition of alternating near-shore and deeper lacustrine facies. Since the LGM, seven beds of structureless, silty sediments preserve archeological artifacts belonging to three Epipaleolithic cultures as well as the Early Neolithic pre-pottery Neolithic A culture. These sediments were deposited during phases of low lake level during which times humans waded into the shallow part of the lake, leaving behind stone and bone tools such as bladelets, lunates and burins, fishing hooks, line weights and net sinkers. Using radiocarbon-dated charcoal and a Bayesian statistical model, we produced a chronostratigraphic model for the archeological site, which enables the comparison of proxy paleoclimate records produced from this site’s sediments with regional archives as well as with global trends and changes in the Northern Hemisphere climate. Periods of low lake stands are correlated with the end of the LGM, Heinrich Event 1, and the beginning of the Younger Dryas Stadial. High water stands occurred contemporaneously with the peak of the LGM and during the Bølling–Allerød interstadial. This new water-level record from Lake Hula confirms that lake-level changes here broadly paralleled those of the Dead Sea and Sea of Galilee during the late Pleistocene, highlighting the importance of northern water sources to the overall water balance of the lakes along the Dead Sea Transform.

Main Ordovician–Silurian events in the South Ural and event stratigraphy regional tasks

The main regional abiotic events of the Ordovician and Silurian of the Southern Urals are manifested in the restructuring of sedimentation in the paleobasin. Eustatic fluctuations and tectonic motions primarily cause changes in the lithological composition of strata. Geochemical events influence the isotopic composition of elements.
 Biotic events affect biodiversity in micro- and macrofauna complexes. The largest of the five Phanerozoic extinctions was the global extinction event at the Ordovician–Silurian boundary (LOME). The Ordovician biotic diversification event (GOBE) is divided into three phases. The Darrivillian level of manifestation of this event is noted in the Southern Urals.
 The location of the global biotic events GOBE, LOME, and the geochemical event HICE in the sections of the Southern Urals is substantiated. Based on the analysis of the connection between biotic and abiotic events in the Ordovician-Silurian deposits of the Southern Urals, the significant role of conodonts, graptolites, chitinosoans and their correlation potential were revealed. Insufficient knowledge of the sections makes it possible to correlate regional events with certain assumptions.
 In order to carry out global event correlations, in addition to the comprehensive biostratigraphic characteristics of the Ordovician and Silurian deposits of the Southern Urals, geochemical studies of a number of sections are necessary. The most promising sections for identifying event levels are the sections of the western slope of the Zilair synclinorium: Nabiullino, Maksyutovo, Gremyachiy, Kaga-V.Avzyan, Sermenevo.

Seismogenic Structures in Sediments of Different Lithological Composition and their Position in Mesozoic–Cenozoic Sections of the Northern Caucasus

A comparative analysis of the morphological features of rock horizons affected by paleoearthquakes showed that seismites from lithologically different deposits differ significantly. Powerful earthquakes determine not only the destruction of the sedimentary structure of near-surface deposits and their chaotic mixing, but also actively affect the underlying layers to a depth of several tens of meters; since the degree of diagenetic lithification of rocks in different horizons varies with depth, the nature of their seismogenic changes also changes. It was found that major seismic events were associated with the time intervals of tectonic and paleogeographic restructuring of sedimentation basins, which consisted in the intensification of the process of bowing of the reservoir bed, changes in the material composition of sediments accumulated in the paleobasin. A special type of seismites was formed during the impact of earthquakes on siliceous deposits, in which the processes of diagenetic redistribution of authigenic mineral matter, which passed through the gel stage during diagenesis, actively proceeded.

“Hypoxic” Silurian oceans suggest early animals thrived in a low-O2 world

Atmospheric oxygen (O2) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O2. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. Our results indicate that anoxic to severely hypoxic bottom waters dominated during deposition of the Silurian sediments cored in the Sommerodde-1 well (Bornholm, Denmark), and regional comparison suggests that these conditions persisted across the Baltoscandian foreland basin. Indeed, even during times of relative oxygenation, ichnological observations indicate that conditions were, at most, very weakly oxic. The results suggest that dissolved O2 was generally scarce in the bottom waters of the extensive Silurian seaway between Baltica and Avalonia, even between Paleozoic “Anoxic Events”. In light of delayed oxygenation of the atmosphere–hydrosphere system, it may be time to consider that early animals were adapted to “hypoxia” and thrived through ∼100 million years of low-O2 conditions after the Cambrian.

Propagation of ship noise in shallow water over a high shear-speed seabed

Assessing the acoustic impact of shipping close to the coast and within ports and harbours requires an understanding of the propagation of underwater sound in these environments. In the Australian context, this often means propagation over seabeds with shear speeds approaching the in-water sound speed, a situation that results in very different propagation conditions to the low shear speed sediments more commonly encountered in other parts of the world. Acoustic propagation modelling approaches were explored using a dataset of continuous underwater recordings featuring a mix of shipping, industrial, and recreational activities, acquired from 23 Jul to 16 Sep 2022 in Cockburn Sound, off the west coast of Australia. Cockburn Sound is a sheltered marine embayment with a relatively uniform water depth of 17–20 m in the 5 km × 11 km central portion of the basin, with a thin, variable thickness (0.5 m–5 m) layer of silty sediments overlying a calcarenite basement. The results of modelling the calcarenite basement as an equivalent fluid were compared to those obtained by modelling it as an elastic solid, and with measurements. Subsequent implications of the choice of geoacoustic model will be discussed

Provenance and depositional environment of Middle Miocene silicic volcaniclastic deposits from Mt. Medvednica (North Croatian Basin, Carpathian-Pannonian Region)

Extensive and protracted volcanism in the Carpathian-Pannonian Region climaxed during the Early to Middle Miocene with series of major ignimbrite-forming eruptions with their products dispersed across the Alpine-Mediterranean Region. The spatial and temporal dispersion of these volcanic horizons make them potentially important stratigraphic markers throughout the region, allowing better understanding of temporal and spatial changes in depositional environments and paleoclimate. Several of these Middle Miocene volcaniclastic layers are preserved in stratigraphically and environmentally variable sedimentary facies on Mt. Medvednica, located in the North Croatian Basin. In order to decipher the age, depositional environment and provenance of two volcaniclastic horizons intercalated within Central Paratethys marine sediments on Mt. Medvednica, we applied an integrated approach of volcanological, geochronological, and paleontological analyses. New high-precision zircon geochronology and volcanic glass geochemistry data allow to distinguish two primary rhyolitic volcaniclastic horizons derived from distinct eruptions, “Plaz“, and the “Bidrovec“, dated at 14.937 ± 0.012 Ma and 14.835 ± 0.012 Ma. Distinguished mineralogical and geochemical data enabled the correlation of the older (“Plaz”) horizon on Mt. Medvednica with the Demjén eruption, one of the six major Early–Middle Miocene ignimbrite-forming eruptions of the Carpathian-Pannonian Region. However, a correlation of the younger (“Bidrovec“) horizon and assignment to a specific eruption could not be established due to a lack of compositional data from coeval eruption products throughout the region. The newly gathered data establishes both “Plaz” and “Bidrovec” pyroclastic deposits as valuable marker horizons for regional reconstructions, and enable a better understanding of the eruption chronology and tephrostratigraphy of the Carpathian-Pannonian Region.

The effect of natural organic matter (NOM) on the distribution and resources of mobile phosphorus in the bottom sediments of small retention reservoirs

The purpose of the work detailed here was to determine the impact of the distribution of natural organic matter and grain size on the resources and distribution of mobile phosphorus in the bottom sediments of small reservoirs located in catchments subject to different levels of anthropopressure. The research objects were five small reservoirs located in southeast Poland. In small retention reservoirs, it is the anthropogenic impact of the catchment and its geological structure, and to a lesser extent sediment granulation, that determine the distribution of phosphorus fractions (especially in inorganic compounds) and the share of total P they account for. In general, a higher level of contamination of sediments with organic matter (OSION increase) is shown to be associated with a higher content of the organic fraction of phosphorus and easily decomposable organic matter. Within small retention reservoirs under significant anthropogenic influence from the catchment, sandy sediments compared with silty sediments were significantly less loaded with potentially mobile phosphorus as well as with organic forms of phosphorus and (sometimes) nitrogen. The occurrence of humic-metal-phosphate complexes is determined by there being sufficient organic matter, especially humic fractions. Fractions of inorganic phosphorus compounds and organic matter have the terrigenous source of these pollutants in common. The organic sediment index can serve as an adjunctive indicator with which to assess the potential ability of the sediments in small retention reservoirs to internal supply of the water column in nutrients.

Non-invasive investigations of closed landfills: An example in a karstic area

The monitoring of existing landfills is a pending environmental issue for the years to come. This monitoring is particularly challenging in the more and more common case of closed landfills, where direct investigation is difficult or impossible, calling for non-invasive methods, which in turn are stretched to maximizing their imaging capabilities in front of difficult logistical constraints, requiring novel and well-conceived scientific approaches. In this study we present a non-invasive approach designed and calibrated to identify the state of the subsoil underlying a closed urban waste landfill. In the presented case, two main questions had to be addressed: (a) whether large karstic cavities are present under the landfill, and (b) if any leachate leakage is present. A 3D Electrical Resistivity Tomography (ERT) configuration was used to solve the problem. The survey design has made use of forward model simulations, in order to verify whether the proposed approach was capable of imaging the possible large karstic cavities. This preliminary study showed the importance of choosing a suitable measurement protocol to recover the true position of the cavities. The analysis of the real field data did not show any anomaly compatible with the presence of large cavities, and thus, in comparison with the previous simulations, led to the conclusion that such cavities are not present. However, the results showed the presence of an electrically conductive anomaly, potentially be linked to leachate release. Direct investigations (drilling and sampling) confirmed the presence of fresh water in a silty sediment environment, both contributing towards the observed larger electrical conductivity, larger than the surrounding drier limestone bedrock. The presented general approach proved to be a valuable, generalizable, tool towards for the characterization and monitoring of closed landfills.

Early to Middle Jurassic sedimentation within the northern Sichuan Basin in response to exhumation of the South Qinling orogenic belt, central China

The northern Sichuan Basin of central China is an important region for investigating the continent-continent convergence that resulted from the closure of the Palaeo-Tethys Ocean. The Early-Middle Jurassic sediments of this basin record the palaeogeography, palaeoenvironments and tectonic evolution of the southern Qinling orogenic belt, especially the Dabashan thrust belt. Detailed sedimentological investigations, coupled with provenance analyses using zircon UPb geochronology, demonstrate that during Early Jurassic times, conglomerate megafan facies extended across the northern Sichuan Basin into the Micangshan area deformed by South Dabashan thrusting and reached even as far as the Mianlue suture belt. These megafan deposits were mainly reworked from the Silurian sediments of the North Dabashan thrust belt (also called the South Qinling orogenic belt), north of the Mianlue suture. These conglomerates record the initial thrust-driven uplift and exhumation of the Qinling orogenic belt that rapidly followed the diachronous closure of the Mianlue oceanic basin. Moreover, our results show that the detrital materials of meandering stream, lacustrine and braided river delta facies that accumulated in the Middle Jurassic mainly originated from the southern Qinling orogenic belt, Mianlue suture zone and northern South China block, suggesting the southward progradation of the Dabashan fold-thrust belt onto the northern Yangtze block and the southward migration of the basin centre. These findings support a model in which the Early to Middle Jurassic evolution of the northern Sichuan Basin may have been triggered by East Asian convergence.

The Rheic riddle: ocean closed, but no orogen

Abstract Although the Rheic Ocean was the widest to be closed during the assembly of Pangaea, its suture zone is dominated by a younger (Rhenohercynian) Wilson Cycle. The present paper briefly summarizes the Rhenohercynian and reviews the relicts of the Rheic. The absence of a Rheic orogen is mainly due to bipolar subduction of the Rheic Ocean, which created two magmatic arcs and largely destroyed the passive margin prisms, thus depriving the collision zone of building material. Also, displacement of Variscan zones in England, France and Germany along a curvature of the dextral Bristol/Bray/Bohemia shear zone has effected their anticlockwise rotation. Younger, ENE-trending reverse faults have truncated the NE-trending structural boundaries and excised pre-Devonian, Rheic-related rocks west of the River Rhine, while the northern Rheic Arc and Cambrian–Silurian deposits of the Rheic Ocean have been preserved further east. Opening of the Rhenohercynian successor ocean to the Rheic put a brake on plate convergence and hindered formation of a large collisional belt. Scarce relicts of the southern Rheic Arc and rocks with Silurian deformation exist in the (largely eroded) upper plate of the Rhenohercynian collisional belt, mostly in the form of clasts and detrital zircons in Upper Devonian/lower Carboniferous flysch and in tectonic mélange at the base of the allochthon.

Three Generations of the Basins of the Early Turkestan Ocean: Ediacaran–Silurian of the Southern and Middle Tien Shan

The results of U–Pb dating of detrital zircon from volcanoterrigenous Ediacaran–Silurian deposits, mainly from grauwacke turbidites, after accretion of which the “Caledonian” basement of the Paleozoic structure was formed in Kyzylkum and in the ridges of the Southwestern Tien Shan, including Northern Fergana, allowed us to clarify the age correlation and show the dynamics of the formation of this complex. It consists of deposits associated with the opening, filling and subsequent convergent development of three generations of oceanic basins, including the emergence and destruction of island arcs. The earliest of these basins was formed at the active volcanic margin of the eastern Rodinia/Gondwana, which included the Karakum-Tajik massif. Sandy turbidites (Besapan, etc.), whose age is not younger than the beginning of the Cambrian, were deposited here on top of siliceous (Taskazgan) Ediacaran sediments. The second generation is represented by Ordovician basins, in which radiolarian flints of the Lower Ordovician form the bathyal part of the sediments, and the main filling is turbidites of the middle Ordovician–Ruddan. The newly opened Silurian oceanic basins and their margins were filled with sediments of the third Caledonian generation, mainly graptolite aleuropelites and turbidites, starting from the end of the Llandovery. Incomplete preservation of the Ediacaran–Silurian sedimentary series is due to their partial absorption (tectonic erosion) during further subduction and collision, mainly already in the Carboniferous.

Interactions of hafnia/hafnon composites with molten silicate deposits

Interactions of hafnia/hafnon composites with molten silicate deposits

Nanoquartz in Late Cretaceous Deposits in the Lower Berezovskaya Subformation

The Lower Berezovskaya subformation in the Upper Cretaceous is a complex reservoir with unconventional reservoir rocks located in the north of Western Siberia. The clay–siliceous deposits in the Lower Berezovskaya subformation are represented by various types of silicites that have unique petrophysical and mineralogical characteristics that cause significant difficulties in the development of associated productive layers. The aim of the research is to study their mineral composition, the parameters of the void space structure, and the conditions of formation, as well as to determine the sources of silica and perform a detailed study on the structure of nanoquartz. To study the mineral composition, the structure of the void space, and the genesis, special methodological techniques were applied, and a comprehensive analysis of the results using a wide range of laboratory studies, including optical micro- and stereoscopy, scanning electron microscopy, X-ray diffraction analysis, and microtomography, was performed. Silicites in the Lower Berezovskaya subformation are caused by the complex structure of the void space, which includes a wide range of genetic types of voids ranging from micron and submicron dimensions to fractions of a millimeter (voids confined to the burrowing organisms, intraform voids, interform voids, lenticular voids, cellular voids, and voids confined to microstylolite seams). The most widespread type of void is the interaggregate (lenticular and cellular) void, which is formed by clay (montmorillonite) scales, on the surface of which numerous α-quartz nanocrystals ranging in size from 0.05 to 0.5 microns are noted. The content of such quartz reaches up to 80% of the total volume of the rock in individual samples. The source of siliceous material for nanoquartz crystals was most likely volcanic processes, since the revealed mineral paragenesis of montmorillonite, cristobalite, and zeolites indicates the active transformation of ash material that entered the basin from volcanic formations.

Influence of subducted carbonate on the composition of basalts in the Paleo-Asian Ocean domain

The fate of subducted carbonate of the Paleo-Asian Ocean and its control on the compositional variability of Cenozoic basalts to the west of the Daxing'anling–Taihang Gravity Lineament remain uncertain. Here we report major- and trace-element contents and Zn–Sr–Nd isotopic data for Cenozoic basalts from eastern Mongolia. The studied basalt samples from eastern Mongolia are classified as nephelinite, basanite, alkaline basalt, and tholeiite. They have different Zn–Sr–Nd isotopic compositions (δ66Zn = 0.38‰ ± 0.02‰ to 0.50‰ ± 0.04‰, 87Sr/86Sr = 0.704239–0.705175, εNd = 4.72–5.67) but display trace-element signatures of sedimentary marine carbonate, reflecting mantle heterogeneity and marine carbonate imprint. Compared with the high-Si tholeiites, which were erupted over thinner lithosphere, the nephelinites–basanites–alkaline basalts erupted over thicker lithosphere have higher δ66Zn values, La/Yb, Sm/Yb, and Nb/Y ratios, and Nb contents, indicating that these low-Si basalts were the product of lower-degree melting of carbonated mantle under higher pressure. By combining our data with available data for Cenozoic basalts from central Inner Mongolia, we suggest that the compositions of the nephelinite–basanite–alkaline-basalt–tholeiite suite show systematic spatial variation with respect to the northward subduction zone of the Paleo-Asian Ocean. The tholeiites, which have lower δ66Zn values, SiO2 contents, and Sm/Yb ratios, are dominant near the subduction zone, whereas the basanites and alkaline basalts, which have higher δ66Zn values, Sm/Yb ratios, and SiO2 contents, are dominant in the region far from the subduction zone. On the basis of a mixing model for Sr–Nd–Zn isotopic compositions, we suggest that the mantle source of the basanites and alkaline basalts incorporated a higher proportion of marine carbonate, whereas the tholeiite mantle source incorporated a higher proportion of siliceous sediments. We deduce that with increasing depth of slab subduction, more sedimentary carbonates and lesser siliceous sediments were released from the subducted slab.

Deciphering the parent-daughter relationship between Ediacaran high-silica ignimbrites and their complementary silicic cumulates: Insights from zircon trace element composition

The Ediacaran Campo Alegre-Corupá Basin (CACB) comprises a rare and excellent exposure of caldera-forming pyroclastic rocks and their cogenetic underlaying plutons. The CACB experienced at least two major episodes of bimodal volcanic activity. The Basin Stage (∼605–590 Ma), characterized by transitional OIB-like basaltic lava flows with minor trachydacites and rhyolites, interbedded with surge-like, silicic pyroclastic deposits, and the Caldera Stage (∼583–577 Ma), marked by at least one cycle of silicic alkaline, caldera-forming eruption, dominated by rhyolitic to trachytic ignimbrites and lava flows/domes with subordinate IAB-like basalts. During the Caldera Stage, granitoid plutons were emplaced at shallow crustal levels (∼5–8 km deep), correlating with the depth of the magma chamber responsible for the contemporaneous large silicic eruption(s). Previous studies have suggested a genetic connection between the post-collisional volcanic and plutonic rocks based on their similar ages, composition, and Sr-Nd-Hf isotopic signatures. In this study, we analyze zircon trace elements from the volcanic rocks of both stages in the CACB to constrain their evolutive compositional patterns, redox conditions, and Ti-in-zircon saturation temperatures. We compare our results with zircon compositions of the cogenetic granitoids, focusing on the Corupá Pluton, which likely supplied the magma for the caldera-forming eruption(s). By examining whole-rock and zircon chemical compositions, we establish a petrogenetic link between the volcanic rocks and their potential remnant magma reservoir. Our findings indicate that the silicic volcanic rocks from the Caldera Stage represent highly evolved compositions extracted from a crystal mush that solidified as a syenitic intrusion. During the evolution of the volcanic-plutonic system, zircon crystals tracked compositional changes associated with the extraction of residual silicic liquids from crystal mushes and the formation of intermediate-silicic cumulates. Unique variations in zircon compositions of volcanic and plutonic rocks, such as Eu/Eu*, Zr/Hf, and Th/U ratios support such a connection and suggest crystal-melt segregation processes at relatively low crystallinities (< 30 vol%). Additionally, our trace element data supports the occurrence of intense hydrothermal-induced recrystallization of zircon within the caldera structure, as suggested by the morphologic aspects of crystals previously analyzed for UPb and LuHf isotopes.

Mineralogy and petrography of Silurian deposits at the Western Mugodzhar Mountains

Mineralogy and petrography of Silurian deposits at the Western Mugodzhar Mountains

Experimental Investigation on Deformation and Permeability of Clayey–Silty Sediment during Hydrate Dissociation by Depressurization

The sediments in the South China sea are mainly composed of clayey silt, characterized by weak cementation, low strength, and poor permeability. These characteristics lead to slow gas and water transport and low gas production efficiency in the production process, which is not conducive to reservoir stability. Therefore, this paper studied the influence of different factors on the displacement and permeability of hydrate-bearing sediments by using remolded cores from the South China Sea. It was found that, when the depressurization method was used for hydrate decomposition, the displacement change in sediments could be divided into three stages: depressurization stage, decomposition stage, and creep stage. During the decompression stage, sediment deformation was rapid and displacement was small. During the decomposition process of hydrates, sediment deformation was slow and displacement was maximum. The creep stage had the slowest deformation and the smallest displacement. The displacement increased with the increase in initial porosity, hydrate saturation, effective pressure, and depressurization amplitude. The permeability of the sediments was lower than that of the original sediments after hydrate decomposition. This permeability damage increased with the increase in the sediment porosity, hydrate saturation, depressurization range and effective pressure. Furthermore, the displacement of sediments was positively correlated with the permeability damage.