We present previously unknown stacked bowl-shaped bioherms reaching a size of 45 cm in diameter and 40 cm in height from weakly solidified peloidal sand from the upper Sarmatian of the Paratethys ...Sea. The bioherms were mostly embedded in sediment, and the "growth stages" reflect a reaction on sediment accretion and sinking into the soft sediment. The bioherms are spirorbid-microclot-acicular cement boundstones with densely packed Janua tubes surrounded by microclots and acicular cement solidifying the bioherm. The surrounding sediment is a thrombolite made of peloids and polylobate particles (mesoclots) which are solidified synsedimentarily by micrite cement and dog-tooth cement in a later stage. The shape of the bioherms reflects a series of growth stages with an initial stage ("start-up stage") followed by a more massive "keep-up stage" which grades into a structure with a collar-like outer rim and a central protrusion and finally by a termination of growth ("give-up stage"). The setting was a shallow subtidal environment with normal marine or elevated saline, probably oligotrophic, conditions with an elevated alkalinity. The stacked bowl-shaped microbialites are a unique feature that has so far been undescribed. Modern and Neogene microbialite occurrences are not direct analogues to the described structures, but the marine examples, like in The Bahamas, Shark Bay and the Persian Gulf, offer insight into their microbial composition and environmental parameters.
This numerical study delves into the dynamic interaction between reservoir heterogeneity and its impact on the dual objectives of geothermal energy extraction and COsub.2 sequestration. Employing ...finite element models, this research scrutinizes the effects of variable porosity, permeability, and capillary entry pressures on fluid dynamics and thermal processes within geothermal systems. Key findings reveal that these heterogeneities significantly dictate fluid behavior and heat distribution, influencing the operational efficiency and environmental sustainability of geothermal–COsub.2 storage operations. By integrating the nonlinear, temperature-dependent properties of fluids, simulations provide in-depth insights into the coupled fluid–thermal interactions that govern system performance. The outcomes offer a refined understanding of the complex interdependencies within heterogeneous reservoirs, underpinning the optimization of design and operational methodologies for co-optimized geothermal energy and COsub.2 storage solutions. Ultimately, this research contributes to the advancement of sustainable energy technologies, highlighting further investigative pathways to bolster the efficiency and longevity of two-phase water–COsub.2 geothermal systems.
Diatoms are among the most common epibionts and have been recorded on the surfaces of various living substrates, either plants or animals. However, studies on them are still scarce in view of the ...many substrata available. In this study, epibiotic diatoms living on Callinectes bellicosus were identified for the first time from a subtropical coastal lagoon in Northwest Mexico. We tested the null hypothesis that the diatom flora living on the carapaces of C. bellicosus would not be similar to that recorded for mangrove sediments, its typical habitat. The epibiotic diatoms were brushed off from the carapaces of two specimens, acid-cleaned, mounted in synthetic resin, and identified based on frustule morphology. This way, 106 taxa from 46 genera were recorded, including 25 singletons, and 6 new records for the Mexican northwest region. The best-represented genera were Nitzschia (10 taxa), Mastogloia (9), Diploneis (8), Navicula (7), Amphora (5), Cocconeis (5), Tryblionella (4), and Gyrosigma (4). Species composition included 93% of local taxa, thus refuting the proposed hypothesis and supporting the alternate one. Although the estimated species richness was lower than that in sediments, it deems the green crab carapace a favorable substrate for the growth of benthic diatoms.
This study used gravity data and 2D seismic data to determine subsurface structures, including fault systems and the depth of the basement. The analysis of gravity data has been conducted using a ...low-pass filter, total horizontal gradient (THG), and source parameter imaging (SPI) techniques. In addition, a 2D seismic line and a well data were used in the study. The results indicate that the trough was influenced by many fault trends, including NW-SE, NNW-SSE, and NS. These fault patterns are suggestive of post-rift and syn-rift events that took place within the Sirt Basin. Based on the findings of the source parameter imaging (SPI), the depth of the basement at the depocenter exhibits a range of 5000 m to 5900 m. However, this range is not well captured by 2D seismic datasets. The depocenter is characterised by a significant accumulation of sediment, spanning from the Cambro-Ordovician to Oligocene periods, which provides evidence of the basin's filling and the evolutionary processes of Abu Tumayam. Keywords: Low-Pass Gravity 2D Seismic Well data Depocenter
Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re ...concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)Osub.4 sup.−) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReOsub.4 with magnetite (Fesub.3Osub.4), siderite (FeCOsub.3), vivianite (Fesub.3(POsub.4)sub.2•8Hsub.2O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)Osub.6 octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReOsub.4 sup.− in sedimentary environments requires further investigation.
The effects of desert dust upon climate and ecosystems depend strongly on its particle size and size-resolved mineralogical composition. However, there is very limited quantitative knowledge on the ...particle size and composition of the parent sediments along with their variability within dust-source regions, particularly in dust emission hotspots. The lower Drâa Valley, an inland drainage basin and dust hotspot region located in the Moroccan Sahara, was chosen for a comprehensive analysis of sediment particle size and mineralogy. Different sediment type samples (n= 42) were collected, including paleo-sediments, paved surfaces, crusts, and dunes, and analysed for particle-size distribution (minimally and fully dispersed samples) and mineralogy. Furthermore, Fe sequential wet extraction was carried out to characterise the modes of occurrence of Fe, including Fe in Fe (oxyhydr)oxides, mainly from goethite and hematite, which are key to dust radiative effects; the poorly crystalline pool of Fe (readily exchangeable ionic Fe and Fe in nano-Fe oxides), relevant to dust impacts upon ocean biogeochemistry; and structural Fe. Results yield a conceptual model where both particle size and mineralogy are segregated by transport and deposition of sediments during runoff of water across the basin and by the precipitation of salts, which causes a sedimentary fractionation. The proportion of coarser particles enriched in quartz is higher in the highlands, while that of finer particles rich in clay, carbonates, and Fe oxides is higher in the lowland dust emission hotspots. There, when water ponds and evaporates, secondary carbonates and salts precipitate, and the clays are enriched in readily exchangeable ionic Fe, due to sorption of dissolved Fe by illite. The results differ from currently available mineralogical atlases and highlight the need for observationally constrained global high-resolution mineralogical data for mineral-speciated dust modelling. The dataset obtained represents an important resource for future evaluation of surface mineralogy retrievals from spaceborne spectroscopy.
