The chemical weathering indices of the sediments can serve as tools for estimating the intensity of weathering in the sediment source rock area and its changes in response to the dynamic interplay of ...climate, tectonics, and bioevolution. The siliciclastic terrigenous component, comprising sediment particles formed during weathering, carries information regarding weathering. Nevertheless, the presence of volcanic material with silicate composition in the sedimentary record can introduce bias to the weathering estimate by incorporating pyroclastic material that has not undergone weathering but is susceptible to diagenetic alteration. Therefore, a comprehensive understanding of the nature and significance of the volcanic component in sediments is imperative for accurately interpreting weathering derived from sedimentary successions. Our study focuses on investigating the presence of the volcanic component and its influence on weathering indices calculation in the Upper Ordovician sedimentary succession of the Baltic Basin. The results from geochemical massbalance mixing modelling reveal that volcanic material is not confined solely to discrete altered volcanic ash beds (bentonites), and a substantial amount of volcanic material is dispersed or re-deposited into the host rock. Within the interval containing discrete bentonite beds, the volcanic component in the carbonate host rock sections ranges from 50% to 90%, and significantly impacts the terrigenous fraction weathering index calculations. This underscores the necessity of considering the nature and significance of the volcanic component when interpreting geochemical-mineralogical signals.
•Volcanic component impacts weathering index calculations.•Higher volcanic component exhibits significant variability in chemical index values.•In active margin settings, weathering intensity interpretation should be done with care.
The ~2.22-2.06 Ga Lomagundi Event was the longest positive carbon isotope excursion in Earth's history and is commonly interpreted to reflect perturbations in continental weathering and the ...phosphorous cycle. Previous models have focused on mechanisms of increasing phosphorous solubilization during weathering without focusing on transport to the oceans and its dispersion in seawater. Building from new experimental results, here we report kaolinite readily absorbs phosphorous under acidic freshwater conditions, but quantitatively releases phosphorous under seawater conditions where it becomes bioavailable to phytoplankton. The strong likelihood of high weathering intensities and associated high kaolinite content in post-Great-Oxidation-Event paleosols suggests there would have been enhanced phosphorus shuttling from the continents into marine environments. A kaolinite phosphorous shuttle introduces the potential for nonlinearity in the fluxes of phosphorous to the oceans with increases in chemical weathering intensity.
Cold seep environments are characterized by methane-rich fluid migration and discharge at the seafloor. These environments are also intimately linked to microbial communities, which oxidize methane ...anaerobically, increase alkalinity and promote authigenic carbonate precipitation. We have analyzed a suite of methane-derived authigenic carbonate (MDAC) crusts from the North and Barents Sea using stable and clumped isotopes (δ13C, δ18O, δ44Ca, and Δ47) to characterize the sources of fluids as well as the environment of carbonate authigenesis. We additionally assess the potential of MDACs as a Δ47-based paleotemperature archive.
The MDACs occur as three main textural-mineralogic types: micritic Mg-calcite cements, micritic aragonite cements and cavity filling aragonite cements. We find that micritic Mg-calcite cements have low δ13CVPDB values (−30 to −47‰), high δ44CaSW values (−0.4 to −0.8‰), and Δ47-temperatures (0–6 °C) consistent with shallow sub-seafloor precipitation in isotopic equilibrium. Micritic aragonite cements and cavity filling aragonite cements both have a wider range in δ13CVPDB values (−18 to −58‰), lower δ44CaSW values (−0.8 to −1.6‰) and a larger range in Δ47-based apparent temperatures (–2 – 25 °C) with samples displaying equilibrium and disequilibrium clumped isotope values.
The range in apparent temperatures as well as δ44CaSW values seen in the aragonite MDACs suggest two kinetic processes: a kinetic isotope effect (KIE) due to the incomplete equilibration of carbon and oxygen isotopes among DIC species from the different sources of DIC (i.e., seawater, methane-sourced DIC and DIC residual to CO2 degassing or diffusion) and a KIE due to a fast, irreversible precipitation affecting the cations, particularly Ca, bound to carbonate mineral. Our results improve the understanding of kinetic effects on clumped isotope temperatures in MDACs and demonstrate how the multi-isotopic approach combined with textural-mineralogic criteria can be used to identify MDACs for accurate paleotemperature reconstructions.
Growing concerns on global industrial greenhouse gas emissions have boosted research for developing alternative, less CO2 intensive binders for partial to complete replacement of ordinary Portland ...cement (OPC) clinker. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically not considered as viable cementitious materials for blending with or substituting the OPC. We studied the physical, chemical-mineralogical characteristics of the mechanically activated Ca-rich CFBC fly ash pastes and mortars with high volume OPC substitution rates to find potential alternatives for OPC in building materials and composites. Our findings indicate that compressive strength of pastes and mortars made with partial to complete replacement of the mechanically activated CFBC ash to OPC is comparable to OPC concrete, showing compared to OPC pastes reduction in compressive strength only by <10% at 50% and <20% at 75% replacement rates. Our results show that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative CSA-cement type binder.
Fast pyrolysis of the oil shale type kerogenous fuels is a novel way to produce shale oil with different properties depending on the process conditions. Until now, little has been known about the ...fast pyrolysis process of Estonian oil shale. This study focused on the fast pyrolysis process, the evaporation of gases and the properties of the solid residues produced during Estonian oil shale fast pyrolysis. The end-temperatures of the process were varied from 303 to 825 °C, thereby producing semicokes where the organic matter had different decomposition grades and the carbonate minerals exhibited different degrees of degradation. SEM, ATR-FT-IR and XRD analysis were performed to describe the differences between the produced materials. HHR-TGA-MS analysis revealed that the evaporation of H
2
S can be decreased by lowering the pyrolysis temperature below 490 °C. ATR-FT-IR analysis showed that structural changes in the methyl- or methylene groups of the organic matter occurred mainly in the temperature range of 385–439 °C.
Sedimentary phosphorites are important carriers of Rare Earth Elements and Yttrium (REE + Y). Primary biogenic and sedimentary apatite contain very low amounts of REE + Y and enrichment of these ...elements occurs during diagenesis. Although the influence of post-depositional processes on REE + Y concentrations in sedimentary phosphorites is well established, the processes controlling the degree of enrichment are poorly constrained. In this study, we examine the REE + Y composition of Early Paleozoic shelly phosphorites of the Baltica paleocontinent, using ICP-MS and LA-ICP-MS. Phosphate containing phases in these deposits are (i) phosphatic brachiopod shells, (ii) phosphatic clasts and (iii) phosphatic grain coatings. Measured REE + Y concentrations range from 162.7 to 2415.3 mg/kg. The distribution of REE + Y in phosphatic shells and clasts is heterogeneous, with the highest concentrations found in the outer margins. In the phosphatic shells, remnants of skeletal apatite contain higher REE + Y concentrations than authigenic apatite in baculate laminae. In addition, our results show significant locality-based variability, with up to 14 times differences in REE + Y concentrations from localities situated only a few tens of km apart. Based on (i) the heterogeneous distribution of REE + Y in apatite, (ii) LaN/YbN and LaN/SmN ratios pointing to diagenetic REE + Y uptake from sediment pore-fluids, as well as (iii) variable pyrite content, the geographic variations of REE + Y in sedimentary phosphorites of the Baltica paleocontinent are most parsimoniously explained by differences in local redox conditions during early diagenesis.
Integrated petrography, mineralogy, geochronology and geochemistry of cold seep carbonate crusts and free gas from the Alvheim channel elucidate diagenetic carbonate precipitation and related seepage ...histories in the central North Sea. Free gas isotope characteristics coupled with carbonate δ13C values as low as −66‰ VPDB, indicate a predominantly microbial methane source with minor thermogenic contribution. We estimate that ~70% of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane. The early stage of crust growth is represented by microcrystalline aragonite and Mg-calcite (10 to 40% mol MgCO3) cementing seafloor sediments consisting of clays, quartz, feldspar, and minor detrital low Mg-calcite and dolomite. Typical association of aragonite cement with coarse-grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor. Middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction. The later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts. In contrast to early generation cements, late generation cavity infills have rare earth elements and Y patterns with small negative Ce anomalies similar to seawater, consistent with carbonate precipitation in a more open, seawater dominated system. Aragonite U–Th ages indicate carbonate precipitation between 6.09 and 3.46kyr BP in the northern part of the channel, whereas in the southern part precipitation occurred between 1.94 and 0.81kyr BP reflecting regional changes in fluid conduit position.
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•Approximately 70% of carbon in carbonates is derived from microbial methane carbon.•Distinct REY patterns differ with carbonate phases rather than mineralogy.•U–Th ages constrain two distinct seepage events between 6.1 and 0.8ka BP.•Late generation aragonites correspond to carbonate hosted methanotrophy.
The Alum Shale Formation, a widespread metal-rich black shale in Baltoscandia, was deposited during the Cambrian–Ordovician transition. Given that it straddles a period of alternating ...extinction/recovery events following the Cambrian Explosion and prior to the Great Ordovician Biodiversification Event, the Alum Shale in Scandinavia has been extensively studied to assess the effect of oceanic redox variations on these biotic events. However, there is an on-going debate about the depositional environment and the prevailing redox state. An Early Ordovician (Tremadocian) equivalent of the Scandinavian Alum Shale, locally known as graptolite argillite, can be found in Estonia and NW Russia, in the easternmost extension of the ‘Alum Shale Sea’. In this contribution, we studied the redox-sensitive metal distribution and accumulation mechanisms in graptolite argillite successions in NW Estonia. Our aim was to provide better constraints on redox and depositional environments in the Baltic Palaeobasin. Our findings reveal that despite a consistent mineral and major elemental composition, V, Mo, Re and U contents vary systematically within the stratigraphy of the up to 7-m-thick black shale unit, with element contents reaching up to hyper-enrichment at the base (Mo > 200 mg/kg, U > 100 mg/kg and V > 1000 mg/kg) followed by a declining trend towards the upper part of the succession. This implies that temporal changes in redox conditions or sedimentation rates controlled trace element accumulation in the graptolite argillite. Although the redox-sensitive trace elements are hyper-enriched (particularly Mo), which has previously been interpreted to reflect euxinic depositional conditions, the V/Al vs. U/Al and V/Al vs. Mo/Al ratios indicate a non-euxinic anoxic depositional environment within a perennial oxygen minimum zone for the graptolite argillite. Further evidence of an unrestricted, relatively open marine depositional environment possibly influenced by upwelling is suggested by Cd/Mo and Co × Mn relationships. These results are supported by UEF and MoEF ratios that follow a seawater enrichment trend. The observed redox-sensitive element contents could be explained via diffusion-controlled uptake owing to the low sedimentation rates of the graptolite argillite (3–5 mm/kyr). These results highlight considerable redox variability within the Baltic Palaeobasin underscoring the need for a careful and critical reassessment of global redox interpretations based on Alum Shale data and emphasise the importance of using multiple independent redox and depositional environment proxies to determine palaeoredox conditions.
•Despite uniform mineral and major element, V, Mo, Re and U contents vary systematically within the Tremadocian shale.•Multiple redox-sensitive element proxies were applied to reconstruct the palaeo-environment duringshale deposition.•We suggest an unrestricted, relatively open marine depositional environment, possibly influenced by upwelling.•High redox-sensitive element contents are attributed to diffusion-controlled uptake owing to low sedimentation rates.
Rare Earth Elements and Yttrium (REE+Y) distribution in authigenic phases are frequently used as proxies for reconstructing past seawater conditions. Sedimentary apatite precipitates near the ...sediment-water interface and is therefore capable of recording the REE+Y composition of the overlying water column. While the overprinting of primary REE+Y signal during late stage diagenesis is a widely known phenomenon, less is known about early diagenetic effects. In this study, we investigate the REE+Y distribution in Recent sedimentary apatites found on the Namibian shelf using in situ mapping by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The Namibian phosphorite deposits consist of reworked and redeposited pelletal apatitic grains, ranging from Miocene to Pleistocene in age, and pristine concretionary apatitic grains that formed during Pleistocene to Recent. The results of this study show that the REE+Y signatures of pelletal and concretionary apatitic grains are different with both types showing intragranular variability and differences between grain centers and rims. The REE+Y are concentrated in the external part of the apatitic grains, forming a 10–20 μm wide “enrichment zone”. While the central parts of apatitic grains are low in REE+Y (∑REE+Y < 450 mg/kg), the external layers can reach ∑REE+Y concentrations as high as 4100 mg/kg. REE+Y patterns from the center of Recent concretionary apatitic grains are similar to the REE+Y distribution of modern seawater. Enriched rims of Recent concretionary apatitic grains as well as pelletal grains have lost the characteristic modern seawater features: negative Ce-anomaly and high Y/Ho ratio. The REE+Y patterns of these enrichment zones indicate REE+Y scavenging from suboxic-sulfidic pore water after burial or during precipitation at the fluctuating redoxcline. It is evident that REE+Y patterns in bulk digests of authigenic apatite cannot be relied on to record paleoseawater characteristics. Micro-scale REE+Y analyses of apatitic grains can, however, reveal aspects of their diagenetic histories.
•Spatially resolved LA-ICP-MS measurements of sedimentary apatites reveal intragranular variability of REE+Y•Primary nucleation of sedimentary apatite occurs in equilibrium with oxic seawater•Majority of REE+Y are incorporated into the apatite during early diagenesis•Uptake of REE+Y from suboxic-sulfidic pore-water leads to the formation of a 10-20 μm wide "enrichment zone"
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