Volcanic Ash Deposits Research Articles

Insight into the 2021 Semeru volcano eruption from rapid monitoring of its pyroclastic deposits using Google Earth Engine and multi-sensor data

The objective of this study is to map the pyroclastic deposits resulting from the Semeru eruption in 2021 and to analyse the process of pyroclastic deposit formation, including the tephra and lithification phases, using multi-sensor data. The distribution of pyroclastic deposits was mapped using machine learning algorithms, Sentinel 2 and Sentinel 1 imagery on Google Earth Engine. Data acquisition in the Semeru volcano area was conducted both prior to and following the 2021 eruption. Additionally, field investigations were conducted to analyse the distribution of pyroclastic deposits, including the characteristics of individual layers, the lithification process of pyroclastic layers, and their relationship with the characteristics of the eruption. The results demonstrate that pyroclastic deposits in the proximal facies are composed of lithic, lapilli tuff, lava and tuff. The mapping results also indicate the presence of volcanic ash deposits in the central facies or summit area of Semeru, exhibiting distinctive characteristics associated with volcanic ash. The 2021 eruption has also resulted in rapid changes to river morphometry, as evidenced by notable shifts in a significant decrease in pixel values for NDVI (−0.0781-0.0625), a significant increase in pixel frequency of EVI (1800–6000), and MNDWI (1700–3000), respectively. The change of pyroclastic fall into consolidated tephra occurred from December 2021 to May 2023, where in May 2023 volcanic ash had changed into tuff and lapilli had changed into lapilli tuff. Furthermore, data from Sentinel-1 indicated that pyroclastic flows could be identified using both vertical and horizontal polarization. It can therefore be concluded that the 2021 eruption of Semeru exhibited distinctive characteristics of pyroclastic deposits, where some of the characteristics of the pyroclastic distribution can be monitored rapidly with Google Earth Engine. Therefore, the use of Google Earth Engine with integration of radar and optical data can be recommended to mapping pyroclastic deposits rapidly.

Productive conservation at the landslide prone area under the threat of rapid land cover changes

Abstract Landslides often occur in the study area as a continuation of the erosion process on very thick soil from a series of volcanic ash deposition during the Tertiary and Quaternary periods. Rapid land cover changes from agricultural land into settlement increase runoff significantly causing accelerated soil erosion. Soil conservation approaches using parameters to reduce surface runoff and soil loss are less acceptable in agricultural society. Soil conservation methods aimed at reducing runoff and soil loss are not widely embraced in agricultural communities, efforts in soil conservation must be economically beneficial. Vegetative-based erosion control is the most suitable option for the agricultural communities. However, there needs to be improvements in terms of plant arrangement that is adapted to the spatial arrangement of slopes and is focused on zones along rills and gullies. Selection of tree species planted for erosion control that have the value of increasing economic income is the key to the success of planned soil and water conservation efforts.

Distribution and modes of occurrence of Nb in subbituminous coal: A case study from the Jungar Coalfield, Ordos Basin, China

Niobium has been considered to be enriched in high-Al-Ga in north China coal and coal-hosted Nb(Ta)-Zr(Hf)-REY-Ga polymetallic deposits in the southwestern region of China. However, modes of occurrence and influencing factors of Nb in Al-Ga-rich coal in North China are rarely reported. This study investigated the distribution characteristics of Nb in the No.6 high-Al-Ga coal of the Jungar Coalfield in North China. The in-situ Nb concentration of selected minerals, including kaolinite, Ti-oxides, boehmite, and zircon, is further quantitatively characterized based on multiscale in-situ elemental analyses, including SEM-EDS and LA-ICP-MS spot and mapping analyses. The results showed that Nb is rich in the tonstein and mudstone partings among bulk samples and is highly concentrated in Ti-oxides, followed by zircon among the minerals. A certain amount of Nb is associated with kaolinite and boehmite with different modes of occurrence: vermicular kaolinite (65.94 ppm) > clastic kaolinite (25.43 ppm) > altered K-bearing kaolinite (18.11 ppm) > cryptocrystalline kaolinite (17.03 ppm) > clastic boehmite (9.08 ppm) > cryptocrystalline boehmite (7.97 ppm). The Nb-Nb/Ta and Zr/Hf-Nb/Ta ratios suggest that the primary source of Nb in the No.6 coal is the altered felsic volcanic ash and bauxite deposit. The high-Fe concentration in Ti-bearing minerals indicates that anatase may originate from the alteration of ilmenite with a process of Fe depletion and Nb enrichment. The enrichment of Nb in coal is attributed to the substitution of Nb for Ti in isomorphism in all Ti-oxides, high-Ti, and Ti-bearing minerals.

Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites.

Knowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system. Previously unknown anatomy includes a soft-tissue labrum attached to the hypostome, a slit-like mouth, and distinctive cephalic feeding appendages. Our findings resolve controversy over whether the trilobite hypostome is the labrum or incorporates it and establish crown-group euarthropod homologies in trilobites. This occurrence of moldic fossils with 3D soft parts highlights volcanic ash deposits in marine settings as an underexplored source for exceptionally preserved organisms.

Effects on local atmospheric environment of volcanic ash from Sakurajima volcano, inferred from atmospheric deposition of Potassium-40 at Kagoshima City, Japan

In this study, we statistically demonstrated that an anomalous high of 40K fallout in the atmospheric fallout in Kagoshima City is caused by heavy ashfall associated with eruptions of Sakurajima volcano. Sakurajima is one of the most active volcanoes in Japan, and its repeated explosive eruptions cause large amounts of ash to fall on Kagoshima City. The fallout of crust-derived natural radionuclides, 40K, 212Pb, and 214Bi, from the atmosphere in Kagoshima City showed a significant correlation with the number of eruptions of Sakurajima volcano and the amount of ashfall in Kagoshima City. In contrast, no significant correlation was found between 40K and 7Be fallout. The 40K fallout indicates that almost all of the atmospheric fallout in Kagoshima City is composed of volcanic ash particles. The contribution from mineral and sea salt particles other than volcanic ash is minimal. The mass balance of the observed 40K fallout, ashfall, and atmospheric fallout yield indicates that there is a significant amount of volcanic ash deposition that is not accounted for as ashfall. In most cases, the ash deposition observed as ashfall is only 30–70 wt% of the total deposition collected as atmospheric fallout samples, and the remaining portion is fine-grained and behaves as suspended volcanic ash particles, which significantly impact the atmospheric environment.

Climate, wildfire, and volcanic ash drivers of ecosystem change in high mountain forests, British Columbia, Canada

Northwest North America has unique high elevation Picea–Abies forests and parkland classified in British Columbia as the Engelmann Spruce–Subalpine–fir (ESSF) Biogeoclimatic zone. These ecosystems occur on a topographically and climatically complex landscape, juxtaposed with diverse vegetation types including alpine tundra, inland rain forest, dry conifer forest, and grasslands. Spatio-temporal ecosystem disturbance is varied, driven by factors such as climate variation, wildfire, volcanic eruptions, and insect herbivory. A pollen and charcoal record derived from a lake sediment core from the ESSF reveals a unique late-glacial to modern vegetation history progressing from alpine steppe through dry open conifer forest to moist spruce–fir ecosystems, the latter arising only 4600 years ago, late by comparison to other ESSF sites in the region. Repeated disturbance in the mid Holocene by wildfire coupled with volcanic ash deposition and increased climatic variation resulted in recurring Pinus contorta-dominated seral forest stands before cooling and moistening in the late Holocene led to stable Picea–Abies forest. With rapid climate change, changing disturbance regimes, and timber harvest, the management of dry ESSF forests needs to consider that this forest-type could transform into parkland or open seral pine stands, with a high frequency disturbance regime.

Deep seafloor hydrothermal vent communities buried by volcanic ash from the 2022 Hunga eruption

Mass mortality of marine animals due to volcanic ash deposition is present in the fossil record but has rarely been documented in real time. Here, using remotely-operated vehicle video footage and analysis of ash collected at the seafloor, we describe the devastating effect of the record-breaking 2022 Hunga submarine volcanic eruption on endangered and vulnerable snail and mussel species that previously thrived at nearby deep-sea hydrothermal vents. In contrast to grazing, scavenging, filter-feeding, and predatory vent taxa, we observed mass mortality, likely due to smothering during burial by thick ash deposits, of the foundation species, which rely on symbiotic chemosynthetic bacteria for the bulk of their nutrition. This is important for our broad understanding of the natural disturbance of marine ecosystems by volcanic eruptions and for predicting the effects of anthropogenic disturbance, like deep-sea mining, on these unique seafloor habitats.

Organic matter enrichment in basin periphery: A case study of Wufeng-Longmaxi shale, Marcellus shale, and Ohio shale

Our study investigates organic matter (OM) enrichment at the peripheries of marine basins, contrasting with prior research focused on central regions. We analyze three shale formations at three distinct deposition sites: the Marcellus (M) shale near an orogenic belt, and the Wufeng-Longmaxi (WL) shale, the Ohio (O) shale adjacent to a forebulge uplift. By examining factors such as redox conditions, clastic input, paleoproductivity, sedimentary facies and geological activities, we identify that the OM enrichment in shale (M shale) near the orogen resulted from significant inputs of river detritus and semi-deep shelf environment. Additionally, local enrichment is primarily influenced by volcanic ash sedimentation. The shale (O shale) at the distal end of the forebulge shows high OM concentration due to its stable deep-water shelf environment. Local enrichment in this area is caused by sediment re-sedimentation and glaciation. Similarly, the shale (WL shale) at the proximal end also exhibits a high OM concentration due to its stable deep-water shelf environment. In this case, volcanic ash deposition and transgression are responsible for the local enrichment. Our findings reveal how paleogeography and geological activities impact OM enrichment in basin peripheries, while also offering insights into evaluating shale gas reservoirs.

Digital mapping of soil organic carbon in volcanic soils after prolonged eruption Mt. Sinabung, Karo Regency, North Sumatra, Indonesia

Mount Sinabung (at Karo Regency, North Sumatra) has been considered as an active volcano since 2010, and after three years of inactivity, the volcano’s activity resumed in 2013. The deposition of volcanic ash buried everything on the soil surface with various thicknesses. Volcanic ash is a valuable inorganic material and consists mostly of primary minerals. But with time, these materials can initiate carbon storage through the revegetation process. This study investigates carbon storage and sequestration in volcanic soils affected by the intermittent eruptions of Mt. Sinabung. A total of 34 soil samples were collected from areas of 3 to 7 km from the eruptive vent. The samples were analyzed to determine labile-C, very labile-C, total-C, Organic-C, non-crystalline-C, and metal complex-C fractions. Regression kriging (RK) was applied to spatially predict the carbon distribution. The results showed that the highest labile-C was 1.65% found in the Southeast slope and the lowest, 1.20%, in the Southern slope. The highest value of very labile-C was in the Southeast (1.20%), and the lowest was in the Northern (0.46%). The highest (11.66%) and lowest values (8.84%) of total C were in the Northeast and South slopes, respectively. The highest Organic-C value was detected 7.42% in the Northeast volcanic soils, and the lowest, 5.74%, is in the South slopes soil. The lowest non-crystalline- C was found in the soils of Northeast slope (0.60%), and the highest was in the Southeast (0.82%) soil. While the highest metal complex-C value was 0.88% in the Southeast, and the lowest is 0.36% in the soil of South slope. These data show that the highest carbon storage is parallel with the direction of the ash distribution, which tends to the Southeast side of Mt. Sinabung. The results of this study demonstrated that volcanic regions have a strong resilience capacity to bounce back after devastating natural hazards. Volcanic deposits interact with atmospheric water to initiate vegetation regrowth and create a carbon pool within their particles.

Effect of the incorporation of ashes from the Calbuco volcano on the porous function of an andosol

Soils derived from volcanic ashes represent >60% of the arable land in Chile. Permanent volcanic activity makes seeking solutions for the management of volcanic material deposited after an eruption essential. The aim of this research was to evaluate how incorporating ashes from the eruption of the Calbuco Volcano affected the structure of a volcanic soil in southern Chile. Undisturbed soil samples were collected in 2022, under three field conditions: soils from which the ashes were entirely removed after the eruption (c), soils in which the ashes were incorporated (c/i) and soils on which the ashes remained on the surface (s/i). The pore-size distribution and the air conductivity were determined based on the water retention curve (WRC), the coefficient of linear extensibility (COLE), the pore shrinkage index (PSI) and the air permeability (Ka). Under c/i field conditions, an increase in total porosity (TP) of 5.57 and 3.48% was found when compared to the control and s/i field conditions, respectively. The highest volume of plant available water capacity (PAWC) was observed in the s/i field conditions, which increased by 65% compared to the other soil conditions. The incorporation of ash into the first 20 cm of depth did not guarantee an increase in usable water for plants; nonetheless, changes in structure did generate a redistribution in the pore size. Therefore, it is essential to evaluate how volcanic ash deposits and their incorporation affect soil physical properties under field conditions.

Hydrothermal Plume Fallout, Mass Wasting, and Volcanic Eruptions Contribute to Sediments at Loki's Castle Vent Field, Mohns Ridge

AbstractSediments surrounding hydrothermal vents are important transition spaces between hydrothermal and pelagic environments. These sediments accumulate through diverse processes that include water column plume fallout, volcanic ash deposition, and mass wasting of hydrothermal chimneys and mounds superimposed upon background sedimentation which may originate from pelagic, terrestrial, and volcanic sources. In addition to being a sink for elements discharged from hydrothermal vents, elements may also be scavenged from seawater onto oxidized hydrothermal material. Preservation of these hydrothermal sediments may occur depending on the extent of oxidative and/or reductive dissolution processes after burial. Sediments remaining adjacent to active venting may also be hydrothermally altered after emplacement. To better understand these processes, here we evaluate sediment push cores collected from the Loki's Castle vent field at the intersection of the slow‐ultraslow spreading Mohns and Knipovich mid‐ocean ridges. All samples were collected within ∼225 m of current high‐temperature (299–316°C) “black smoker” fluid discharge. These sediment cores are highly heterogeneous and lack stratigraphic correlation, even for samples taken within meters of each other. Most sediment cores are dominated by either pelagic sediments or mass wasted hydrothermal material, with hydrothermal plume fallout contributing a low proportion of material, and only a single volcanic ash layer occurring in one of the 13 cores. Dominant hydrothermal minerals found include talc, goethite, pyrite, pyrrhotite, and sphalerite. We find that even after several thousand years, most mass wasted hydrothermal material remains minimally altered, with sedimentation rates indistinguishable from background rates within several hundred meters of the hydrothermal vent source.

Evidence of Ice‐Rich Layered Deposits in the Medusae Fossae Formation of Mars

AbstractSubsurface reflectors in radar sounder data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express spacecraft indicate significant dielectric contrasts between layers in the Martian Medusae Fossae Formation (MFF). Large density changes that create dielectric contrasts are less likely in deposits of volcanic ash, eolian sediments, and dust, and compaction models show that homogeneous fine‐grained material cannot readily account for the inferred density and dielectric constant where the deposits are more than a kilometer thick. The presence of subsurface reflectors is consistent with a multi‐layer structure of an ice‐poor cap above an ice‐rich unit analogous to the Martian Polar Layered Deposits. The volume of an ice‐rich component across the entire MFF below a 300–600 m dry cover corresponds to a global equivalent layer of water of ∼1.5 to ∼2.7 m or ∼30%–50% of the total estimated in the North Polar cap.

Detrital U[sbnd]Pb zircon geochronology, zircon Lu[sbnd]Hf and Sr[sbnd]Nd isotopic signatures of the Lopingian volcanic-ash-derived Nb-Zr-REY-Ga mineralized horizons from eastern Yunnan, SW China

The Lopingian altered volcanic-ash horizons in southwest China have attracted significant attention due to highly-elevated concentrations of critical element Nb-Zr-REY-Ga. Despite extensive investigation, the provenance of these distinctive horizons remains controversial. Are they a product of air-born volcaniclastic, erosional source sedimentation, or a complex mixture of multiple sources?This investigation performs a diverse array of mineralogical and isotopic geochemical analyses to investigate the provenance of these horizons and critical-element mineralization time. The results showed that the concordant ages of detrital zircons 207Pb/206Pb-206Pb/238U from five representative mineralized samples are 253.84 ± 2.60 Ma, 252.49 ± 2.39 Ma, 253.47 ± 2.99 Ma, 257.44 ± 2.01 Ma, and 243.94 ± 2.32 Ma, respectively. Importantly, this dating does not correspond to the stratigraphic position of the studied deposits. Instead, this data set indicates that the low-temperature hydrothermal alteration of the primary Nb-Zr-REY-Ga mineralized layers occurred in Late Permian-Middle Triassic times (260–240 Ma) immediately after volcanic ash deposition at 257–260 Ma. The Sr-Nd-Lu-Hf isotopic compositions, diagrams of both the Al2O3/TiO2 vs. Eu/Eu* and Zr/TiO2 vs. Nb/Y, and the trace element patterns of the zircons (Nb/Hf vs. Th/U, Hf/Th vs. Th/Nb) indicate that the mineralized horizons were derived from both ELIP alkaline rocks and arc-related intermediate-felsic magmatic rocks from the Paleo-Tethys realm. Furthermore, varying amounts of older (∼350 Ma and older) zircon grains defined by the dominant Late Permian-Middle Triassic zircons indicate that there was also some erosional-source input from the uplands surrounding the basin at the time of deposition.

Godzilla mineral dust and La Soufrière volcanic ash fallout immediately stimulate marine microbial phosphate uptake

During the “Godzilla” dust storm of June 2020, unusually high fluxes of mineral dust traveled across the Atlantic from the Sahara Desert, reaching the Caribbean Basin, Gulf Coast, and southeastern United States. Additionally, an eruption of the La Soufrière volcano on St. Vincent in April 2021 generated substantial ashfall in the southeastern Caribbean. While many studies have analyzed mineral dust’s ability to relieve nutrient limitation of phosphorus (P) in the P-stressed North Atlantic, less is known about the impact of extreme events and other natural aerosols on fluxes of P into seawater and from seawater into marine microbial cells. We quantified P and iron (Fe) content in mineral dust from the Godzilla dust storm and volcanic ash from the La Soufrière eruption collected at Ragged Point, Barbados. We also performed seawater incubations to assess the marine microbial response to aerosol deposition. Using environmentally-relevant concentrations of atmospheric particles for within the ocean’s mixed layer allowed us to draw realistic conclusions about how these deposition events impacted P cycling in situ. Volcanic ash has lower P content than mineral dust, and P in volcanic ash is far less soluble (~1%) than assumed in current atmospheric deposition models. Adding mineral dust and the volcanic ash leachate in concentrations representing different deposition scenarios increased soluble reactive phosphorus (SRP) concentrations in coastal seawater by ~7-32 nM. Phosphate uptake rate was stimulated in coastal seawater after either mineral dust or volcanic ash deposition at aerosol concentrations relevant to the Godzilla dust event, with ash eliciting the fastest uptake rate. Furthermore, high concentrations of both the mineral dust and volcanic ash led to slightly elevated alkaline phosphatase activity (APA) compared to the relevant controls, indicating higher potential for use of dissolved organic phosphorus (DOP) as a P source. Quantifying these aerosols’ impacts on P cycling is a significant step towards achieving a better understanding of their potential roles in relieving nutrient limitation and fueling the biological carbon pump.

Geological factors for the enrichment of critical elements within the Lopingian (Late Permian) coal-bearing strata in western Guizhou, Southwestern China: Constrained with whole-rock and zircon geochemistry

A number of volcanic ash-bearing layers deposited in the Upper Permian coal-bearing strata on the southwestern margin of the Yangtze Craton are well preserved, and some layers show the enrichment of critical elements such as an assemblage of Zr(Hf)–Nb(Ta)–Ga–REE (REE, rare earth elements). Based on previous work, we studied the source of the Upper Permian volcanic ash-bearing layers widely distributed in western to northwestern Guizhou and the geological factors for the enrichment of critical elements. This article provides a detailed analysis of the mineralogical and geochemical characteristics of the Upper Permian volcanic ash-bearing layers. The mineralogy of the samples is dominated by clay minerals, quartz, anatase, plagioclase, and pyrite, with a few containing K-feldspar, calcite, dolomite, and siderite. The clay minerals are mainly composed of mixed-layer illite/smectite (I/S) and kaolinite. The whole rock geochemistry (Al2O3/TiO2, Nb/Ta vs. Zr/Hf, Nb/Al2O3 vs. Zr/Al2O3, and Th/Al2O3 vs. Zr/Al2O3) and zircon trace elements (Th/Nb vs. Hf/Th, Nb/Yb vs. U/Yb, Ta vs. Nb, and Yb/Sm vs. Y) were used to help determine the source. The results indicate that the sources of the samples include Emeishan high-Ti basalt, intraplate volcanic ash from the Emeishan large igneous province (ELIP), and arc volcanic ash. The critical elements (Zr[Hf]–Nb[Ta]–REE) are mainly derived from the syndepositional intraplate volcanic ash erupted from the ELIP. The results of zircon trace elements and Hf isotope ratios suggest that the magma from the ELIP has gradually evolved from the mantle to the crust, and became more enriched in critical elements such as Nb and Ta. The intraplate volcanic ash from ELIP is the main supplier of critical elements and plays a crucial role in their enrichment through the Late Permian in southwestern China. The paleoenvironment controlled the deposition of volcanic ashes, and most of the critical element enrichment layers developed in weak hydrodynamic environments. The paleogeography and acid rain influenced the migration of critical elements such as Nb, Ta, REE, and Y in some layers. The enrichment of critical elements is also controlled by the regularity and intensity of intraplate volcanic activity.

Allophanes in the weathered volcanic ash deposits distributed in southern Kyushu, Japan and their ion adsorption characteristics

Allophanes in the weathered volcanic ash deposits distributed in southern Kyushu, Japan and their ion adsorption characteristics

Production and preservation of organic carbon in sub-seafloor tephra layers

The deposition of volcanic ash into the ocean initiates a range of chemical and biological reactions. During diagenesis, these reactions may enhance the preservation of organic carbon (OC) in marine sediments, which ultimately promotes CO2 sequestration from the ocean-atmosphere system. However, this interpretation is reliant on a small number of studies that make a link between tephra and OC burial. Here, we compare organic and inorganic geochemical data from tephra-bearing marine sediments from three sites that differ widely in their location, age, and composition. We show that OC is buried in, and proximal to, tephra layers, in proportions higher than would be expected via simple admixture of surrounding sediment. Our data indicate that this OC is preserved primarily through interactions with reactive iron phases, which act to physically protect the carbon from oxidation. Analysis of the composition of the OC associated with reactive iron indicates it is isotopically (consistently more negative δ13C than sediment) and chemically (comprised of compounds not found in the sediment) distinct from OC in the background sediments. We interpret this signal as indicating a microbial source of OC, with autochthonous OC production resulting from autotrophic microbial exploitation of nutrients supplied from tephra. This finding has implications for our understanding of carbon cycling on Earth, and possibly for the emergence of life in terrestrial and perhaps even extra-terrestrial environments.

Heterogeneities in the Cohesion of the Deposits of the 2021 Tajogaite Eruption of La Palma (Canary Islands, Spain)

The present study analyzes the electrical and thermodynamic properties of the volcanic ash deposits from the recent eruption that started on 19 September 2021 in the Cumbre Vieja area on the island of La Palma. This work compares the analysis of the zeta potential and the surface free energy components of representative samples of unaltered tephra deposits with samples affected by the fumarolic activity near the emission zone, where sulfurous vapors were present. The results show that fumarolic activity modifies both the zeta potential and the surface free energy components of volcanic ash, decreasing its surface electrical charge and conferring less hydrophilicity on the deposit. Based on this, the interaction energies between ash particles in an aqueous medium have been calculated, in order to analyze the cohesion of the deposit and, where appropriate, its rheological properties, ending with the analysis of the effect produced by different chemical species on the surface charge and free energy of the ashes, and their influence on the cohesion of the deposit. The results confirm an attractive interaction energy between the ash particles and therefore greater stability to the deposit affected by fumarolic activity.

Continental Thermal Structure and Carbonate Storage of Subducted Sedimentary Origin Control on Different Increases in Atmospheric CO2 in Late Ediacaran and Jurassic

AbstractCarbon release during continental rifting is thought to regulate atmospheric CO2 levels. Supercontinent dispersal‐induced extensional tectonics is similar during the Late Ediacaran and Jurassic, while they exhibit different increases in atmospheric CO2 concentration. The underlying mechanism of distinct CO2 emissions remains to be understood. Here, we conduct petrological‐thermomechanical modeling to show that metamorphic decarbonation and melting of carbonates that are derived from subducted sediments are ubiquitous during continental extension. We find that the hotter lithosphere and deeper storage of these carbonates cause more significant amounts of rift‐related CO2 release through volcanoes and faults. They may cause ∼12%–77% larger decarbonation efficiency, providing an efficient driving mechanism for a ∼31% larger increase in atmospheric CO2 levels during the Late Ediacaran than throughout the Jurassic. The rapid eruption and deposition of recycled carbonatite volcanic ash may contribute to the production of Late Ediacaran marine carbonates with the largest negative δ13C (−12‰).

Volcanic ash content of Permian lucagou shale in the Jimsar sag, Junggar Basin: Evidence from comprehensive analysis of mercury (Hg), major elements, strontium isotope, and thin section

Volcanic ash deposits are commonly associated with shale oil enrichment worldwide, and their composition potentially playing a significant role in the origin of organic-rich shale and shale oil exploration potential. Volcanic activity occurred frequently during the depositional period of the Permian Lucaogou Formation in the Jimsar Sag, Junggar Basin. Microscopic examination shows the development of volcanic ash in the strata, but alteration of volcanic ash may affect the volcanic ash content recovered by the microscopic identification method. Through analyzing 49 rock samples, semi-quantitative restoration of volcanic ash content was conducted combined using Hg, major elements, strontium isotopes and thin section analysis. The restored volcanic ash content, measured via Hg and elemental methods, represents the stratigraphic unit's weight percentage, while the microscopic identification method denotes the stratigraphic unit's volume percentage. Although they are different ratios, they exhibit good correlation. Research suggests that volcanic ash is commonly present in the Lucaogou Formation of the Jimsar Sag. The volcanic ash content varies greatly, from 11% to 96%, mainly within the 10%–40% range. Only a few samples exhibited volcanic ash content exceeding 60%. The nutrients brought by the volcanic ash promoted organic productivity. This, in turn, increased the organic matter content in the water column and facilitated the formation of a reducing environment. The abundance and type of organic matter are crucial factors in determining the potential for shale oil. Thus, volcanic ash influences the enrichment of organic matter and the shale oil potential of the Lucaogou Formation.