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.
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.
Remains of Rhynchotalona latens (Sarmaja-Korjonen, Hakojärvi et Korhola 2000) were found in the bottom sediments of several glaciogenic lakes in northwestern Russia. Subfossil remains of the species ...were noted both in the bottom sediments of the Late Pleistocene and Mid-Holocene. We discovered a rare species, R. latens, in the bottom sediments of Lake Medvedevskoye (Karelian Isthmus). This species prefers shallow oligo-mesotrophic lakes with organic sediments and has attracted the interest of scientists around the world as it is considered a glacial relict and has recently been found in surface sediments and as a living population in Finland and Russia.
Sedimentary bulk organic matter and various molecular organic components exhibit strong CO.sub.2 -dependent carbon isotope fractionation relative to dissolved inorganic carbon sources. This ...fractionation (ε.sub.p) has been employed as a proxy for paleo-pCO.sub.2 . Yet, culture experiments indicate that CO.sub.2 -dependent ε.sub.p is highly specific at genus and even species level, potentially hampering the use of bulk organic matter and non-species-specific organic compounds. In recent years, significant progress has been made towards a CO.sub.2 proxy using controlled growth experiments with dinoflagellate species, also showing highly species-specific ε.sub.p values. These values were, however, based on motile specimens, and it remains unknown whether these relations also hold for the organic-walled resting cysts (dinocysts) produced by these dinoflagellate species in their natural environment. We here analyze dinocysts isolated from core tops from the Atlantic Ocean and Mediterranean Sea, representing several species (Spiniferites elongatus, S. (cf.) ramosus, S. mirabilis, Operculodinium centrocarpum sensu Wall and Dale (1966) (hereafter referred to as O. centrocarpum) and Impagidinium aculeatum) using laser ablation-nano-combustion-gas-chromatography-isotope ratio mass spectrometry (LA/nC/GC-IRMS). We find that the dinocysts produced in the natural environment are all appreciably more .sup.13 C-depleted compared to the cultured motile dinoflagellate cells, implying higher overall ε.sub.p values, and, moreover, exhibit large isotope variability. Where several species could be analyzed from a single location, we often record significant differences in isotopic variance and offsets in mean delta.sup.13 C values between species, highlighting the importance of single-species carbon isotope analyses. The most geographically expanded dataset, based on O. centrocarpum, shows that ε.sub.p correlates significantly with various environmental parameters. Importantly, O. centrocarpum shows a CO.sub.2 -dependent ε.sub.p above ⼠240 µatm pCO.sub.2 . Similar to other marine autotrophs, relative insensitivity at low pCO.sub.2 is in line with active carbon-concentrating mechanisms at low pCO.sub.2, although we here cannot fully exclude that we partly underestimated ε.sub.p sensitivity at low pCO.sub.2 values due to the relatively sparse sampling in that range. Finally, we use the relation between ε.sub.p and pCO.sub.2 in O. centrocarpum to propose a first pCO.sub.2 proxy based on a single dinocyst species.
The sedimentary history of two stromatoporoid accumulations - an allobiostrome and a parabiostrome-are studied in the shallow water carbonates of the Middle to Upper Devonian Kowala Formation in the ...Olowianka Quarry, Holy Cross Mountains, central Poland. Sedimentological and facies observations are accompanied by morphometrical and taphonomical analyses of redeposited stromatoporoid skeletons. Stromatoporoid features, including shape profile, latilaminae arrangement, surface character, dimensions, and preservation state, are interpreted in terms of their original growth habitats and susceptibility to exhumation and transport. Sedimentary features of the studied beds are interpreted with regards to the high-energy processes that lead to their deposition. In the allobiostrome, the original stromatoporoid habitat was located below storm wave base, in a calm setting characterised by a low and stable depositional rate and clear bottom waters. The large scale onshore redeposition of stromatoporoid skeletons from such a setting was only possible due to an extraordinary event causing erosion at considerable depths: a tsunami is the most probable explanation. The sedimentary and textural features of the allobiostromal accumulation, such as clast supported textures and lack of vertical sorting, point to a single act of deposition and high flow velocities, in agreement with the tsunami interpretation. In contrast, the parabiostromal stromatoporoid accumulation does not exhibit any features that would require a non-tempestitic explanation, the default and most probable interpretation of high energy facies interbedding shallow water lagoonal sediments. This comparison has shown that studies of variously developed stromatoporoid beds, and particularly the analysis of morphometric features of stromatoporoid skeletons, can provide a unique opportunity to identify palaeotsunamites, which commonly remain undetected in the sedimentary record, leading to underestimates of their abundance.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
