Typical Crust Research Articles

Crustal Structure, Deformational History, and Tectonic Origin of the Bahamas Carbonate Platform

AbstractThe 2–10‐km‐thick, mainly carbonate cap of the 14,000 km2 Bahamas carbonate platform (BCP) has impeded imaging of its underlying crustal structure. The deeper structure of the BCP records both its Mesozoic rift and hotspot history and its later deformation related to its Paleogene collision with the Great Arc of the Caribbean (GAC). We use regional gravity data to model the crustal structure, type, and deformational processes of the BCP by: (a) integrating publicly available seismic data; (b) inverting the Moho along 2D regional gravity transects across the collisional zone; (c) modeling flexural uplift of a forebulge that reflects the attempted subduction of the BCP beneath the GAC; and (d) using downhole temperatures and radiogenic heat production in 1D basin models to differentiate crustal types related to the Mesozoic rift history. We interpret three crustal domains underlying the BCP: (a) 27–12‐km‐thick, rifted, and thinned continental crust of the northern Bahamas between the Blake Plateau and Exuma Sound; (b) 24–12‐km‐thick, volcanically‐thickened oceanic crust related to the Triassic‐Jurassic Bahamas hotspot in the central Bahamas southeast of Long Island; and (c) 20–12‐km‐thick, thickened oceanic crust north of Hispaniola. We propose that these crustal types reflect northwest‐southeastward, Triassic‐Jurassic rifting of the Bahamas region during the breakup of Pangea and accompanying magmatic activity related to the Triassic‐Jurassic Bahamas hotspot and early oceanic spreading. Growth of the BCP during the Cretaceous in this area was followed by Late Cretaceous‐Paleogene subduction‐related flexure and terminal Paleogene collision between the GAC and the BCP.

Simplified Vulnerability Assessment of Historical Churches in Banat Seismic Region, Romania

ABSTRACT Romania, a mid-eastern European country, has a moderate seismicity and a large stock of historical buildings and churches. One of the most important seismic areas of the country is the Banat area, which ranks as the second most seismic area in Romania, with shallow earthquakes of crustal type. Many Orthodox and Catholic churches can be found in the area, the majority of them having a central nave. The churches are built in masonry, with vaults and wooden frameworks, and they present valuable architectural-artistic details, including paintings made by recognized painters. Various forms of structural damage appeared to the historical churches after past earthquakes, depending on the architectural configuration. This paper illustrates a study made on six historic churches in the Banat region, to investigate seismic vulnerability with simplified methods. The study highlights the most vulnerable points of the historic religious structures and the importance of investigating in a quick and simplified way the seismic behavior of such important buildings for the local community. Moreover, the main novelty of the paper is the highlighting of the importance of the sustainability aspect in the process of heritage preservation, as simplified assessment procedures are essential for more resilient risk reduction policies.

Anatomical features of ecological importance and taxonomic value revealed by scanning electron microscopy and light microscopy in Camonea umbellata (L.) A.R. Simões & Staples (Convolvulaceae).

This article describes detailed and novel data on the anatomy and histochemistry of leaves, stems, and roots of Camonea umbellata (L.) A.R.Simões & Staples in different environments for the identification of characters with taxonomical value and of ecological importance, with provision of light and scanning electron microscopy images. To analyze the characters, we collected samples of the vegetative organs of three individuals in each of three populations, which were in a grazing area, an urban environment, and a biological reserve. The main diagnostic anatomical markers for the identification of C. umbellata include amphistomatic leaves, tetracytic and brachyparatetracytic stomata, peltate trichomes, long simple trichomes, epidermis with striated cuticle ornamentation, mesophyll with acute borders, presence of druses, secretory channels, angular collenchyma, fibrous pericycle in the stem, intraxylary phloem in the vegetative organs, oil bodies throughout the midrib, petiole, stem and root, and epicuticular waxes of the crust and coiled rodlet types. Since the characters above did not show variation in the environments evaluated, we consider these characters taxonomically useful for the identification of C. umbellata. RESEARCH HIGHLIGHTS: The anatomy of the aerial vegetative organs of Camonnea umbellata retains common Convolvulaceae characters. The sinuosity of the epidermal cell walls and the density of trichomes in the epidermis of the petiole were visually variable characters among the analyzed individuals. Amphistomatic leaves, tetracytic and brachyparatetracytic stomata, peltate trichomes, epidermis with striated cuticle ornamentation, dorsiventral mesophyll with border acute, presence of druses, secretory structures, angular collenchyma, fibrous pericycle in the stem, intraxillary phloem, presence of oil bodies in all organs, and epicuticular waxes of the crust type and coiled rods were considered important anatomical markers for the recognition and correct identification of Camonea umbellata.

Early Jurassic and Late Cretaceous plagiogranites in Nain–Baft ophiolitic mélange zone in Iran: remnants of rift–drift and SSZ evolution of a Neotethyan seaway

We have investigated the geology, geochemistry and geochronology of various plagiogranite intrusions that are spatially associated with ophiolitic subunits in a mélange terrain exposed within the Nain–Baft fault zone along the western boundary of the Central–East Iranian Microcontinent (CEIM). One group of plagiogranites is intrusive into foliated amphibolites, whereas the plagiogranites of the other group are intrusive into gabbros, dyke swarms and pillow lavas that are tectonically juxtaposed. U–Pb zircon dating of the first group of plagiogranites has revealed near-concordant crystallization ages of 176.94 ± 0.71, 179.84 ± 0.92 and 190.40 ± 2.1 Ma, indicating the early Jurassic timing of their emplacement. U–Pb zircon dating of the second group of plagiogranites has revealed a weighted average age of 92.34 ± 0.38 Ma, indicating that they were emplaced in the early Late Cretaceous. The Early Jurassic plagiogranites are low-K, sub-alkaline rocks with negative Eu anomalies, low Ti and high La and Ce contents. They display elevated ratios of large ion lithophile elements to high field strength elements. They were part of a magmatic system that facilitated the earliest rift–drift stages of a Neotethyan seaway development, and their magmas were produced by fractional crystallization of a mafic melt associated with asthenospheric upwelling beneath a rift system. The Late Cretaceous plagiogranites are low-K, sub-alkaline rocks with negative Eu anomalies, high Y and low Ta contents. They show light REE depletion relative to flat heavy REE patterns, and high Ba/Th ratios. Magmas of these plagiogranites were the products of partial melting of amphibolites in the subducting oceanic lithosphere in the same Neotethyan seaway. Thus, we posit that plagiogranite rocks in suture zones can be excellent trackers of geochemical, geochronological and magmatic evolution of various types of oceanic crust through rift–drift, seafloor spreading and subduction initiation stages within the same ocean basins in the past. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

The contribution of Rob Westaway to the study of fluvial archives

Robert Westaway was a structural and hard-rock geologist who turned his attention to the study of Late Cenozoic fluvial archives, believing that the preservation of staircases of river terraces, particularly representing the Middle and Late Pleistocene, could only be explained in terms of crustal activity in response to surface processes, the latter affected by climatic change. His entry into this research area coincided with the realisation that such terrace sequences required surface or crustal uplift to have taken place over the time interval represented. Workers were unable to explain the observed amounts of uplift in terms of erosional isostasy, a process that could potentially have explained such one-way crustal movement. Westaway envisaged a mechanism by which mobile lower crust migrated to beneath uplifting areas, maintaining and reinforcing their uplift. The mechanism requires complex mathematics to explain it, as well as lending itself to mathematical modelling of the process, based on varying crustal properties and changes in the rates of surface processes in response to climatic fluctuation. Essentially the lower-crustal effect can be envisaged as a positive-feedback enhancement of erosional isostasy.It became apparent that Westaway's theories could explain geomorphological and sedimentary fluvial archives that were otherwise difficult to elucidate. Mantle-based erosional isostasy could not explain terrace staircases, for example. Many of these occur in regions that are tectonically inactive, and so cannot be attributed to neotectonic activity. A game-changer in terms of persuading the wider community came from the recognition of crustally ultrastable regions in which progressive long-timescale uplift has not occurred: Archaean cratons. Westaway's envisaged lower-crustal flow would not be expected in such regions, which have cold, brittle and immobile crust to its full depth. Ancient fluvial deposits are found close to modern valley-floor levels in such areas. Regions of younger Precambrian crust (Proterozoic) showing intermediate situations were subsequently identified. Other dilemmas could be resolved, such as the ‘back-tilting’ of the early-Middle Pleistocene Bytham River in the English Midlands, caused by its drainage crossing crustal blocks with different properties that have accordingly experienced differential uplift. Although glacio-isostasy, mostly seen in the effects of rebound since the Last Glacial Maximum (LGM), is largely accommodated in the mantle, and thus is reversed as a response to glacial loading and unloading, in areas of suitable crustal type there is evidently a small lower-crustal component that is less readily reversible.Westaway's important contribution has yet to be fully integrated into received wisdom in geomorphological and Quaternary circles, although much of it is now widely accepted and more will be explored and published in due course.

Whole community shotgun metagenomes of two biological soil crust types from the Mojave Desert.

We present six whole community shotgun metagenomic sequencing data sets of two types of biological soil crusts sampled at the ecotone of the Mojave Desert and Colorado Desert in California. These data will help us understand the diversity and function of biocrust microbial communities, which are essential for desert ecosystems.

Preparation of Crust Type Dust Suppression Gel Based on Plant Extraction Technology for Ginkgo biloba Leaves: Characterization, Properties, and Function Mechanism

The coal industry plays an essential role in China’s economic development, and issues such as occupational health and environmental pollution caused by coal dust have attracted a great deal of attention. In accordance with the principles of environmental protection and waste management, this study used carboxymethyl ginkgo cellulose (CL) extracted and modified from Ginkgo biloba leaves as a matrix, and a graft copolymerized with sodium 3-allyloxy-1-hydroxy-1-propanesulfonate (AHPS) and N-isopropylacrylamide (NIPAM) monomers to prepare low-cost, environmentally friendly, and high-performance coal dust suppression (C-A-N). By optimizing fitting experimental data through three factors and two response surface analyses, the optimal dust suppression efficiency ratio was determined to be 4:8:5, and its swelling and water retention properties were analyzed. The microstructure, chemical reaction process, combustion performance and crusting property of the dust suppression gel were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), cone calorimetry, and consolidation layer strength tests. Relevant experiments show that the dust suppression gel prepared in this study has the characteristics of a strong wettability and minor impacts on the calorific value of coal, as well as green and environmental protection. When the wind speed is 10 m/s, the dust suppression effect reaches 93%, and the hardness of the solidified layer reaches 39.6 KPa. This study analyzed the migration and combination of functional groups in the interaction system using molecular dynamics simulation software. The microscopic effect and mechanism between dust suppression gel and coal are revealed from a molecular point of view. The feasibility and accuracy of the molecular dynamics simulation were verified by the consistency between simulation results and experimental data. Therefore, combining the utilization of waste resources with dust suppression can have important economic and social benefits.

Investigation into a deep-rooted crustal framework deduced from potential field data in Cretaceous and Tertiary strata, Sokoto Basin NW, Nigeria

The Paleocene sediments from the Sokoto Group, which comprises of the Gamba, Dange, and Kalambaina formations, were covered by Maastrichtian sediments from the Rima Group, which includes the Wurno, Dukamaje, and Taloka formations. High-resolution aeromagnetic and satellite gravity measurements were used to study these sediments. The aforementioned strata correspond to the Cretaceous and Tertiary strata in this research area and are situated in the south-eastern part of the Iullemmeden Basin. Our aim is to determine and explain the horizontal variation in density and magnetization using the whole regional satellite gravity and aeromagnetic data. The deeper magnetic and density sources were scanned using a two-dimensional (2D) radially averaged power spectrum analysis to produce the NE to SW and E to W trending models for the Moho, lower, and upper lithosphere under the study area. The results were further assessed using upward continuation, derivative analysis, and two-dimensional gravity and magnetic modeling. Numerous important structural trends (i.e., NE-SW, E-W & ENE-WSW), have been identified as a result of the vertical gradients for the potential field data. Spectral analysis and Euler deconvolution can be used to calculate the depths to the lower and upper mantle crust boundaries as well as the depth to Moho. The findings of a qualitative analysis point to an intrusion of the Gundumi and Illo Formations that has a northeast orientation as the primary cause of the significant gravitational and magnetic interaction. The differences in the deep-seated crustal structures and mineralized anomalous bodies with depth were visible on anomaly maps with an upward continuation of 5 km, 7 km, 20 km, and 30 km. Quantitatively, the 2D regional models along the selected profiles (L1, L2, L4, L6 and L7) display a typical lithostratigraphic succession of the Gundumi and Illo Formation (Continental Intercalaire, CI) type of crust, which is subdivided into the lower and upper mantle crust as well as the Moho. The sediment thickness by surface depth ranges from ∼4.06 km and ∼23.31 km. The Moho interface, lower and upper mantle crusts, and magnetic crust are all located at depths of around ∼10.23 km. The distance between the local models of the foundation rocks to the north and south of the Sokoto Group was approximately ∼6 to ∼8 km and ∼4.5 km, respectively.

Metatranscriptomes of two biological soil crust types from the Mojave desert in response to wetting.

We present eight metatranscriptomic datasets of light algal and cyanolichen biological soil crusts from the Mojave Desert in response to wetting. These data will help us understand gene expression patterns in desert biocrust microbial communities after they have been reactivated by the addition of water.

A false paradigm? Do biocrust types necessarily reflect ‘successional stages’?

AbstractThe term ‘succession’ was first proposed to describe the gradual development of plants from an initial stage such as a bare ground to a well‐developed plant community, which at its peak, may reach a climax (primary succession). Accordingly, the earlier and fast growing stage (such as an annual plant community) may grant stability, organic matter and nutrients to the latter, high‐biomass and slow‐growing stages, such as trees. Commonly, reference to the different successional stages is also made once intact and disturbed communities (such as due to mechanical disturbance, tillage, fire, etc.) are compared (secondary succession). The concept was borrowed by many ecologists to describe variable biocrust types. Cyanobacterial or algal biocrust is regarded as an initial stage before turning to a later, more mature biocrust, whether composed of lichens or mosses. The underlain assumptions are that (a) the cyanobacteria provide essential stability and (b) nutrients that are required for the development of the later stages; (c) the initial biocrusts improve the water regime for the later successional stages; (d) cyanobacteria promote the lichen symbiosis; (e) due to substantial differences in the recovery time, a linear succession is inevitable, commonly from cyanobacterial/alga to lichen and lastly to moss; and (f) the cyanobacterial/algal biocrust is a temporary stage, just before being outcompeted by a later stage. It is argued hereafter that the above‐mentioned assumptions are not necessarily correct. As with higher plants, unless a direct comparison between disturbed and intact crusts justifies a reference to successional stages, different types of biocrusts commonly reflect the abiotic conditions at their site, and as such, unless the abiotic conditions change, they reflect stable communities of variable crust types. This paradigm shift may have important implications regarding inoculation efforts and directions and may explain the low success thus far obtained following inoculation experiments once performed with the more developed biocrusts, lichens and mosses.

The Earth’s Crust Structure of the Persian Gulf According the Results of Deep Seismic Sounding

The article presents the results of seismic work performed by the DSS method in the Persian Gulf. Bottom analog type seismographs and seismic airgun sources were used in the works. The bottom seismographs were placed and the shooting was carried out according to three regional profiles with a length from 100 to 250 km. The main result of these studies was to obtain velocity-depth model of the sedimentary cover and the Earth’s crust up to Moxo boundary, which was revealed at a depth of about 43 km in the water area. Given that the thickness of the upper crust is only 4–5 km, and the speed characteristics of the remaining layers, the crust type can be attributed to the subcontinental Archean type. This situation (complete absence or drowning of the upper layer of the Earth’s crust) is typical for the waters closest to the Persian Gulf: the Black Sea, the Caspian Sea, the Mediterranean and the Red Seas. A structure was found in the Earth’s crust of the studied area, which may be a brachianticline having an isometric dome-shaped shape, which corresponds to the folding of the platform type in the areas of salt-dome tectonics. No faults have been found in the Earth’s crust of the Persian Gulf water area adjacent to the Bushehr Peninsula.

New insights into the crustal architecture and tectonic evolution of the Eastern Gulf of Mexico

AbstractThe Gulf of Mexico is an intraplate oceanic basin where rifting commenced in the Late Triassic, leading to drifting and ensuing oceanic accretion by Middle‐Late Jurassic, which ceased by the Early Cretaceous. Its tectonic evolution encompasses multiple rifting phases dominated by orthogonal extension, variable magmatism and salt deposition. This complex tectonic history is recorded within the rifted margins of the Gulf of Mexico, including along the eastern part of the basin, where considerable uncertainty remains regarding the tectonic evolution and resulting crustal configuration. This study presents new insights into the crustal types and an updated tectonic framework for the Florida margin. An integrated analysis of seismic and potential field data allows us to characterize the nature of the crust, which shows wide zones of hyperextended continental crust, seaward dipping reflection (SDR) packages, exhumed mantle and magmatic crust. Our results propose elements that could improve the plate model of the Gulf of Mexico, by accounting for the polyphase nature of rifting, the counter‐clockwise rotation of the Yucatan block and the observed increase in magmatic supply.

Continent‐Ocean Transition or Boundary? Crowd‐Sourced Seismic Interpretations of the East‐India Passive Margin

AbstractOn the edge of our continents, oceanic crust meets continental crust. At passive margins, those where there is no active tectonics, subduction or transform faulting, these crustal types are connected as sharp continent‐ocean boundaries (COB) or as diffuse continent‐ocean transition (COT) zones. Passive margins are hard to explore and consequently relatively little is known about their morphology or the geological processes of their formation. Here we elicit and analyze seismic image interpretations of the passive margin offshore East India conducted by 17 groups of geoscientists to better understand the differences, or lack therein, of COB or COT interpretations of the margin. The group interpretations provide a wide range of margin models, five of which are abrupt COB based and 11 which are diffuse COT based. However, interpretations within the COB set vary in the placement of the boundary line between continental and oceanic crust, the boundary placement lying within the range of interpreted COT zones, with the average COB location falling in the center of the interpreted COT zones. These crowd‐sourced results are then compared with 10 published interpretations across the margin, which show COB and COT zones falling in the same area. These findings raise questions as to the real differences in COB and COT models and the geological processes involved in their formation. Considering this, we discuss the implications for passive margin models and the use of Wisdom of Crowds‐type approaches in reflecting on both the range of interpretation‐based models and in the value of determining “average” model approaches.

The heterogeneous crustal architecture of the Falkland Plateau Basin

AbstractContinental break‐up can be oftentimes associated with intracontinental wrenching that can lead to the generation of transform margins and transform marginal plateaus. The wrenching phase can be accompanied by complicated processes, which result in heterogeneous structural and crustal architectures. This makes understanding the evolution of such tectonic settings challenging. The Falkland Plateau is an example of a transform marginal plateau where regional wrenching accompanied the incipient stages of Gondwanan continental break‐up to result in a mosaic of crustal types underlying its largest basin: the Falkland Plateau Basin (FPB). The uncertainties in crustal boundaries have led to several models for the evolution of the plateau, which hinder the development of a reliable plate reconstruction of Southern Gondwana. We integrate seismic reflection, gravity and magnetic data to propose an updated crustal architecture of the FPB. The results show that extended continental crust underlies the basin in the west and north. The eastern and central parts consist of a juxtaposition of intruded and underplated continental crust which transitions southwards to a thick oceanic domain. The basin is crosscut by three main NE–SW trending shear zones which facilitated the development of the contrasting crustal and structural domains interpreted across the plateau. This integrated reassessment of the FPB provides new insights into the tectonic evolution of the plateau, the deformation associated with wrenching and transform margin formation and our understanding of the tectono‐stratigraphic evolution of such areas.

Contribution to the Ostracoda (crustacea) Fauna of the karstic region of Texas with the description of a new species

Iron oxide deposits in the form of crusts are examined in the field and in the laboratory with scanning electron microscopy. Samples came from two caves developed in different geological settings but assumed by previous studies to be of hydrothermal-hypogene origin. The relation of iron oxide crusts to cave wall and ceiling morphology created by the cave’s primary dissolution (speleogenesis), as well as to the formation of other speleothems, is investigated. Scanning electron microscope (SEM) elemental analysis showed a high iron content (20–78 % by weight) consistent with iron oxide minerals such as goethite, hematite, magnetite, etc. Three distinct types of iron oxide crusts were identified from the four samples that were analyzed: (1) high iron content crusts with some porosity formed on the host rock surface and discontinuities, (2) high iron content (but lower than type 1) crusts, including limestone clasts and pores originating from dissolved clasts, and (3) high iron content, significantly-porous crusts that are formed by a network of filaments that indicate microbial activity. The formation of these deposits in relation to other speleothems and to dissolution events is discussed.

Runoff and soil loss in biocrusts and physical crusts from the Tabernas Desert (southeast Spain) according to rainfall intensity.

Biological soil crusts (biocrusts) influence hydrological and erosive processes in drylands, and their effects increase with hypothetic successional development. Runoff and raindrops, both dependent on rain intensity, are among the main causes of erosion in these areas. However, little is known about the existence of soil loss nonlinearity in relation to rain intensity and crust types; this nonlinearity could control biocrust succession and dynamics. The assumption of biocrust types as successional stages, which allow space-for-time sampling, makes it advisable to include all the successional stages when exploring possible nonlinearity. We considered seven types of crusts, three physical and four biological. We created four rainfall intensity levels in controlled laboratory conditions: 18, 60, 120, and 240 mm/h. In all but the last, we conducted the experiments at two levels of antecedent soil moisture. Generalized Lineal Models enabled us to test for differences. These analyses confirmed previous knowledge regarding the significant effect of rainfall intensity, crust type and antecedent soil moisture and their interactions on runoff and soil loss, despite the small sample size of the sample units. For example, runoff, and particularly soil loss, decreased along succession. Moreover, some results were novel: the runoff coefficient increased only up to 120 mm/h of rain intensity. A decoupling between runoff and soil loss occurred at high intensities. Soil loss increased as rainfall intensity increased only up to 60 mm/h, and then it decreased, mainly due to physical crusts, because of the formation of a water sheet on the surface due to the incoming rainwater exceeding the drainage capacity. Although soil loss was greater in the incipient cyanobacteria than in the most developed lichen biocrust (Lepraria community), the protection provided by any biocrust against soil loss was great compared to the physical crust, and almost as strong at all rain intensities. Soil loss increased with antecedent soil moisture only in physical crusts. Biocrusts resisted the rain splash even at a rainfall intensity of 240 mm/h.

Crustal control on the petrogenesis of adakite-like rocks

Adakite-like rocks have attracted extensive interest as they record magmatic processes and mantle-crustal material recycling, and because they are associated with major porphyry Cu deposits. However, their petrogenesis is still under debate. In this study, we compiled ca. 7000 sets of whole-rock geochemical and Nd isotopic data of Phanerozoic adakite-like rocks worldwide from published literature, with the aim to characterize geochemically adakite-like rocks from subduction, collision, and post-collision settings. Statistical analysis highlights the different lanthanides + Y patterns from various types of juvenile and mature crust. Modelling of the statistically-processed data suggest that pure fractionation of amphibole and/or garnet cannot account for the lanthanides + Y patterns of adakite-like rocks, whereas partial melting of mafic protoliths is a possible mechanism. This study supports a adakite-like magma generation model by partial melting of the eclogitic lower crust. The melt was then mixed with depleted mantle-derived basaltic melt, and subsequently fractionated. Compared with the adakite-like magma formation from the juvenile crust, that from the mature crust is featured by higher degree of partial melting, greater depths and higher water content. Additionally, secular peaks of La/Yb value (which reflects the depth of magma source) of adakite-like rocks worldwide suggest that the period of magmatic activity in deep-level magma reservoirs could be used as the indicator of either the final stages of the Phanerozoic orogenesis, or craton activation by subduction.

Biocrust carbon exchange varies with crust type and time on Chihuahuan Desert gypsum soils.

In dryland systems, biological soil crusts (biocrusts) can occupy large areas of plant interspaces, where they fix carbon following rain. Although distinct biocrust types contain different dominant photoautotrophs, few studies to date have documented carbon exchange over time from various biocrust types. This is especially true for gypsum soils. Our objective was to assess the carbon exchange of biocrust types established at the world's largest gypsum dune field at White Sands National Park. We sampled five different biocrust types from a sand sheet location in three different years and seasons (summer 2020, fall 2021, and winter 2022) for carbon exchange measurements in controlled lab conditions. Biocrusts were rehydrated to full saturation and light incubated for 30 min, 2, 6, 12, 24, and 36 h. Samples were then subject to a 12-point light regime with a LI-6400XT photosynthesis system to determine carbon exchange. Biocrust carbon exchange values differed by biocrust type, by incubation time since wetting, and by date of field sampling. Lichens and mosses had higher gross and net carbon fixation rates than dark and light cyanobacterial crusts. High respiration rates were found after 0.5 h and 2 h incubation times as communities recovered from desiccation, leveling off after 6 h incubation. Net carbon fixation of all types increased with longer incubation time, primarily as a result of decreasing respiration, which suggests rapid recovery of biocrust photosynthesis across types. However, net carbon fixation rates varied from year to year, likely as a product of time since the last rain event and environmental conditions preceding collection, with moss crusts being most sensitive to environmental stress at our study sites. Given the complexity of patterns discovered in our study, it is especially important to consider a multitude of factors when comparing biocrust carbon exchange rates across studies. Understanding the dynamics of biocrust carbon fixation in distinct crust types will enable greater precision of carbon cycling models and improved forecasting of impacts of global climate change on dryland carbon cycling and ecosystem functioning.

Changes of bacterial community structure,monosaccharide composition and CO2 exchange along the successional stages ofbiological soil crusts.

Biological soil crusts (BSCs) are a dominantecological landscape of drylands, which have asignificant impact on global biogeochemical flux. However, it is unclear how bacterial community and physiological characteristics vary along the BSCssuccessional stages. In this study, bacterial community composition, physiological characteristics, and monosaccharide composition of extracellular polysaccharides (EPSs)were compared among different successional stages. Our findings demonstrated that besidesthe dominant bacterial species, the bacterial communities also showed considerable differences between these two stages. Cyanobacteria were keystone taxain the early stage, while heterotrophic bacteria (Proteobacteria, Actinobacteria and Acidobacteria) were keystone taxa in the later stages. According to the results ofCO2 exchange, cyanobacterial crusts accumulated net carbon faster than moss crusts, whilemoss crusts had a significantly higher respiration rate. The monosaccharide analysis indicated that the EPSs components also varied depending on BSCs' successional stages. Specifically, the contents of rhamnose and arabinose were higher in thecyanobacterial cruststhan other types of crusts, while the contents of fucose, xylose, mannose and glucose were the highest in cyanobacterial-lichen crusts, andgalactose contentwas highest inthe moss crusts. Altogether, our results stress the heterogeneous variation of BSCs along with succession, andthis work offered a fresh viewpoint for a deeper comprehension of the interactions between the monosaccharide components of EPS and the networks of bacterial communities in BSCs.

Stability of neutron stars with dark matter core using three crustal types and the impact on mass–radius relations

We investigate the effects of dark matter (DM) on the nuclear equation of state (EoS) and neutron star structure, in the relativistic mean field theory, both in the absence and presence of a crust. The σ−ω model is modified by adding a WIMP-DM component, which interacts with nucleonic matter through the Higgs portal. This model agrees well with previous studies which utilized either a more complicated nuclear model or higher-order terms of the Higgs potential, in that DM softens the EoS, resulting in stars with lower maximum masses. However, instabilities corresponding to negative pressure values in the low-energy density regime of the DM-admixed EoS are present, and this effect becomes more prominent as we increase the DM Fermi momentum. We resolve this by confining DM in the star’s core. The regions of instability were replaced by three types of crust: first by the Friedman-Pandharipande-Skyrme (FPS), Skyrme-Lyon (SLy) and BSk19 EoS from the Brussels-Montreal Group, which can be represented by analytical approximations. For a fixed value of the DM Fermi momentum pFDM, the DM-admixed neutron star does not have significant changes in its mass with the addition of the crusts. However, the entire mass–radius relation of the neutron star is significantly affected, with an observed increase in the radius of the star corresponding to the mass. The effect of DM is to reduce the mass of the star, while the crust does not affect the radius significantly, as the value of the pFDM increases.