Pyroclastic Research Articles

Volcanic tuff as a World Heritage Georesource, a Case Study of Tokaj Wine Region UNESCO Cultural Landscape

Volcanic tephra and pyroclastic rocks are common georesources worldwide. Volcanic eruptions produce these materials, and the freshly deposited volcaniclastic sediments undergo variable diagenesis and possible hydrothermal alteration. The rhyolitic pyroclastic rocks of the Carpathian Basin were formed as a result of major silicic volcanism during the Miocene and are exposed in several volcanic regions. The use of these stones depends on their physical properties, such as hardness, colour, and transportability, especially in masonry and ornamental design. The study site, the Tokaj Wine Region (TWR) Historic Cultural Landscape is a UNESCO site located in NE Hungary, which was inscribed on the World Heritage List in 2002. The silicic pyroclastic rocks, here we also referred to them as rhyolite tuffs, are significant geological resources in the UNESCO cultural heritage designation. The pyroclastic formations cover an area of about 100 km2 and were deposited by three major explosive eruptions (13.1–11.5 Ma). The local varieties are defined by primary volcanological features and secondary (diagenetic, hydrothermal) effects. The stone was extracted from more than 40 open pit quarries dating from the Middle Ages. The wine cellars and dry-built terrace walls are important cultural features of the volcanic tuff use. The geoconservation value of the rhyolite tuff is well illustrated by the exposed special geological features, which represent important sites of volcanic formations. However, only one site has been declared a nature conservation area. Several historic quarries are currently abandoned, and there are many problems due to the lack of their restoration. The most common problems are the instability of quarry walls, illegal dumping, pollution, and dense vegetation covering the geological values. The volcanic tuff has a great potential as a georesource (quarries, cellars, and terrace walls) adding value to World Heritage Site, but special efforts are needed to demonstrate its potential for geoconservation, geotourism, and geo-education.

Unravelling 6000 years of interplay among environmental changes, anthropogenic activities, and Vesuvius eruptions in the upper Sarno Plain (Campania, Italy)

Abstract Pollen analysis was carried out on the infilling succession of the Fossa San Vito sinkhole, at the NE foothills of the Sarno Plain (Italy). Four 14C dates and six tephra layers constrain the pollen sequence between ca. 6000 and 500 cal yr BP. A forested environment, with a few signs of human activities, characterizes the pre-protohistoric period (ca. 6000–2750 yr BP). Stability of the arboreal pollen grains to non-arboreal pollen grains (AP/NAP) curve is due to climate-related opposite oscillations of deciduous and evergreen forest. In this period, the pyroclastic products from Neapolitan volcanoes that reached the upper Sarno Plain seem to have affected neither vegetation nor human activities. In the archaic and classic periods (ca. 2750–1500 yr BP), intensive deforestation and increase in anthropogenic indicators indicate the occurrence of grazing and crop activities managed by the main urban centers located in the plain: Pompeii, Stabiae, and Nuceria. After the Pompeii eruption in CE 79, a rapid re-afforestation and decline in all anthropogenic indicators testify to the temporary abandonment of the area, linked to the disastrous demise of the main economic centers. The upper plain was repopulated and exploited in the Late Ancient and Middle Ages (ca. 1700–500 yr BP), as indicated by the increase in all crop and grazing indicators.

Early Paleogene alkaline magmatism in the Subandean Ranges of Jujuy Province

The Zapla Range (Jujuy province) represents the southern edge of the central Andean Subandean Ranges in Argentina. In the northernmost area of the Zapla Range, basaltic rocks are interbedded in the Mealla Formation. These volcanic units form part of the post-rift magmatism of the Salta rift basin, which mainly focused on the Lomas de Olmedo sub-basin to the east. In this paper, six of these basaltic occurrences are characterized on the basis of new geological, petrographic and geochemical data, in order to explore their emplacement, petrogenesis and possible tectonic setting during rift evolution. Peperites in the upper contact of sills evidence the interaction between basalts and unconsolidated or poorly consolidated wet sediments. This implies that there was concomitance between sedimentation and subsurface magma emplacement, suggesting a Paleocene age for the magmatic event according to zircon U-Pb data available for Mealla Formation rocks. Other basaltic units show hipocrystalline textures and lack peperites at the top, which points to their extrusive nature. Additionally, some of these lava flows are spatially associated with pyroclastic deposits that reveal the occurrence of explosive hydrovolcanic eruptions. The study rocks are classified as alkaline basalts and basanites with high Mg# and Ni- and Cr-rich compositions, close to primitive magmas. They show affinity with continental intraplate settings. The analyses of Ba/Nb, Nb/La, (La/Yb)N, (La/Sm)N, (Gd/Yb)N and (Dy/Yb)N ratios, as well as normalized trace and rare earth element patterns, suggests a genesis by low degrees of partial melting of a residual garnet-bearing mantle source. Therefore, basalts from this part of the Subandean Ranges evidence a magmatic episode probably linked to an extensional reactivation stage of the Salta Group rift system in the Lomas de Olmedo depocenter during the Paleocene (∼60 Ma).

The tectonostratigraphic evolution of a Miocene half-graben, Kerio Valley Basin, East African Rift of Kenya: analysis of a 3 km thick volcano-sedimentary succession

The Kerio Valley Basin is a classic half-graben within the Eastern Branch of the East African Rift System, though to date its tectonostratigraphic evolution has only been interpreted through an incomplete stratigraphic record exposed along structural highs. This study examines a 3 km thick, volcano-sedimentary succession recorded within a hydrocarbon exploration well, Cheptuket-1, located within the hanging wall of the Kerio Valley Basin. A suite of silicic extrusive volcanic and volcaniclastic rocks are also recorded, calibrated by a dense collection of thin-sections from 84 side-wall cores. These volcanic rocks include phonolite lava flows. Through documentation of the well stratigraphy and integrating newly acquired 40 Ar/ 39 Ar age dates from outcrop, we detail a substantially revised, simpler tectonostratigraphic evolution of this basin. Cheptuket-1 penetrated a Middle Miocene to recent stratigraphic succession, bottoming in metamorphic basement, likely through a fault plane. Several phases of lake development are elucidated, including both pre- and syn-mechanical rifting, with the latter phase containing beds exhibiting high organic matter content. This study ultimately represents a rare insight into a near complete rift-basin hanging-wall succession, as well as detailing a workflow for characterising mixed volcanic and sedimentary successions.

Variable preservation of the 1991 Hudson tephra in small lakes and on land

Volcanic ash (tephra) preserved in terrestrial environments and lake sediments contains information about volcanic processes and can be used to infer eruptive parameters and frequency of past eruptions, contributing to the understanding of volcanic hazards. However, tephra deposits can undergo transformation from their initial fallout sedimentation to being preserved as a tephra layer in the sedimentary record. The process is likely to be different in lakes and in terrestrial (soil) sequences. Here we compare the thickness, mass loading and grain size of tephra layers from the 1991 eruption of Cerro Hudson, Chile, from small lakes and adjacent terrestrial settings to measurements of the tephra made shortly after the eruption. We analysed samples from 35 cores in total from six small lakes (<0.25 km2), located 76 and 109 km from the volcano in two contrasting climatic areas (cool and humid northern site, and warm and dry southern site), and made 73 measurements of tephra thickness and 11 measurements of grain size in adjacent terrestrial areas. The major element geochemistry of our samples confirmed they were from the 1991 Hudson eruption. We found that some of the measured characteristics of the preserved tephra layers were comparable to those recorded in 1991 shortly after initial deposition, but that there was considerable variability within and between locations. This variability was not predictable and lake sediments did not preserve a notably more accurate record of the fallout than terrestrial sites. However, in aggregate the characteristics of the preserved tephra was similar to those recorded at the time of deposition, suggesting that, for palaeotephra research, a sampling strategy involving a wide range of environments is more robust than one that relies on a single sedimentary record or a single type of sedimentary environment.

New bulk rock and age data on the changes in magma evolution during the Miocene, Galatean volcanic area, central Anatolia, Turkey: A review

The Galatean Volcanic Province (GVP) lies within the Sakarya tectonic belt in the northwest of central Anatolia, Turkey, south of the North Anatolian Fault, cropping out over 12,000 km2. It consists of Early Miocene intermediate to acid lavas, pyroclastic rocks, volcaniclastic deposits, and Late Miocene OIB-like basalts. Our study is based on new bulk geochemistry, SrNd isotopes, and 40Ar/39Ar dating of the volcanic rocks from the south-western part of GVP, but integrates all the available previous data to understand how magmas evolved in the post-collisional geodynamic condition in the GVP. The initial eruptions were rhyolitic, as domes or pyroclastic deposits (Group 1) and basaltic lavas (Group 2) during the Early Miocene. Group 2 is also represented by large volumes of basaltic-andesitic, trachyandesite-dacite/trachydacite lava flows, small intrusions, and pyroclastic deposits as generated between 21 and 14 Ma. Relatively low 87Sr/86Sr ratios (0.705–0.706) of the early rhyolites (Group 1), similar to all the rocks from Group (2), suggest the generation of hybrid melts with variable contributions of mantle-derived and crustal material. The volcanic activity ends with OIB-like basalts (11–7 Ma) showing the lowest 87Sr/86Sr (∼0.703) suggesting an asthenospheric origin.The geodynamic model, based on post-Cyprian slab rollback, results in long-term (22–13 Ma) post-collisional delamination/drip processes that support magmatism. This magmatism is generated in the lithospheric mantle, with the formation of basaltic melts and acid hybrid melts showing variable contributions of mantle-derived and crustal materials in a complex trans-crustal magma plumbing system. Complex mixing of various intra-crustal magmas and fractional crystallization processes generated a huge volume of volcanic rocks. The Late Miocene small-volume OIB basalts were asthenospheric melts that during the late stage recorded localized decompression melting processes.

The characteristics of volcanic lithofacies and volcanic reservoirs in the Permian Jiamuhe Formation, Southern Zhongguai Rise, Junggar Basin, NW China

The southern Zhongguai Rise has gained wide attentions due to its commercial hydrocarbon discoveries from volcanic deposits in Jinlong Oilfield. The integrated analysis of geological and geophysical data assist in determination and depiction of volcanic lithology and volcanic facie, characterization of volcanic reservoirs as well as discussion of constrains on volcanic lithology/lithofacies. The conclusions suggest that two types of volcanic lithology, including volcaniclastic rocks and silicic moltenlava, can be identified based on cores. In addition, two types of volcanic lithofacies can be delineated according to cores and wireline responses. The explosive facies are mainly developed in early depositional period while the effusive facies are developed through depositional period. Furthermore, the reservoir space predominantly consists of pores and fractures according to thin sections. The physical property varies from time to time. That is, porosity distribution varies slightly. In contrast, permeability distribution varies significantly. The volcanic reservoirs can be generally attributed to high-porosity and low-permeability reservoirs no matter in volcaniclastic rocks or silicic molten lava. The volcanic lithofacies, facies distribution, diagenism and paleogeomorphology exserts controls on physical property and reservoir performance of volcanic reservoirs together.

Insight into the 2021 Semeru Volcano Eruption from Rapid Monitoring of Its Pyroclastic Deposits using Google Earth Engine and Multi-Sensor Data

Insight into the 2021 Semeru Volcano Eruption from Rapid Monitoring of Its Pyroclastic Deposits using Google Earth Engine and Multi-Sensor Data

The pre-Campi Flegrei caldera (>40 ka) explosive volcanic record in the Neapolitan Volcanic Area: New insights from a scientific drilling north of Naples, southern Italy

The oldest volcanism documented in near-vent sections around the Campi Flegrei (CF, southern Italy) caldera does not exceed ~78 ka, even though the mid- to ultra-distal tephrostratigraphic record would suggest that activity in this area started well before that. Reconstructing the activity preceding the large caldera-forming Campanian Ignimbrite (CI) eruption of ~40 ka, via surface geological surveys in proximal areas, is challenging because of the poor accessibility and paucity of sections recording the older chronostratigraphic interval. In order to fill the gap in knowledge of the activity preceding the CI eruption, a 113.2 m deep scientific drillhole was emplaced in the Ponti Rossi area, in the northern part of the city of Naples. The Ponti Rossi area was selected as representative of the stratigraphic setting prior to the CF caldera formation because it is close, although external, to any proposed caldera rim or downthrown area. The cored succession, consisting of pyroclastic deposits separated by paleosols, reworked humified deposits or subaerial erosional surfaces, has been logged and sampled for sedimentological, mineralogical, and geochronological analyses. Thirty-one Pyroclastic Units (PU) were identified. Based on the structural/textural features of the recovered sediments, the first relevant result is the possible absence of the CI, while the deposits of the ~15 ka Neapolitan Yellow Tuff eruption, the second largest caldera-forming event of CF, represent the shallowest sediments. 40Ar/39Ar age determinations on alkali feldspars, extracted from juvenile fragments collected at 45.8–45.9 (PU-29) and 99.5–99.6 (PU-1) metres of depth, yielded ages of 59.03 ± 0.50 ka and 110.00 ± 0.35 ka, respectively. The age obtained for the deepest cored unit, having sedimentological characteristics compatible with proximal deposition, represents the oldest age obtained for a pyroclastic deposit in the sequences near the CF caldera boundaries and extends by 30 ky the explosive history of this area. Furthermore, based on 40Ar/39Ar age constraints, at least 29 eruptions, spanning the ~59–110 ka interval, can be added to the volcanic history of the Neapolitan Volcanic Area. These eruptions can be largely attributed to the CF area, prior to the CI caldera formation, and testify to hitherto unknown, intense explosive activity.

Phosphorus dynamics in volcanic soils of Weizhou Island, China: implications for environmental and agricultural applications

The dynamics of phosphorus are intricately governed by geological and ecological processes. Examining phosphorus dynamics in volcanic islands can enhance our comprehension of its behavior within such unique geological systems. However, research on phosphorus dynamics in volcanic islands remains limited. We investigated the phosphorus content of volcaniclastic rocks and basalt soils from Weizhou Island, China, to understand the influencing factors on phosphorus dynamics. The results indicate that in the volcaniclastic profile, phosphorus concentrates at 20–40 cm (17 mg/kg), decreases at 40–60 cm (11.9 mg/kg), and increases at 80–200 cm up to 46.4 mg/kg proximate to the bedrock, for the basalt profile, phosphorus content increases from the surface (80.2 mg/kg) towards the bedrock (83.9 mg/kg). The differences in phosphorus distribution between volcaniclastic rocks and basalts reflect the influence of parent material, rock weathering degree, carbonate content, topographic elevation, sea level changes, and geological activities. A strong positive correlation (R = 0.96907) between total and available phosphorus has been observed, suggesting that total phosphorus content effectively predicts available phosphorus content. Volcaniclastic rocks in wharves and high-elevation areas show low total phosphorus, while forest land with dense vegetation and neutral to alkaline soil supports higher total phosphorus due to enhanced bioavailability for plant absorption and utilization. Overall, the basalt soil of the volcanic island Weizhou Island demonstrates superior long-term fertility compared to the volcaniclastic soil. Despite its low total phosphorus content, it mainly exists in a highly bioavailable form, facilitating plant absorption, which is crucial for enhancing agricultural yields and ecosystem restoration on volcanic islands.

Mildly explosive eruptions at Martian low-shield volcanoes

AbstractOngoing acquisition of Martian surface imagery constantly provides new opportunities to reveal previously undiscovered small-scale volcanic landforms, yielding critical insights into volcanic processes, and challenging existing inferences. Here, using the most recent, high-resolution topographical data, we mapped the accumulation of pyroclastic deposits occurring along the margins of several volcanic vents. They share morphological similarities with terrestrial volcanic deposits attributed to low-intensity lava fountaining occurring during mild explosive activity. Our identified, explosive volcanic deposits are associated with late Amazonian volcanic activity in Tharsis. The identification of these very recent (<100 Ma) deposits across the entire Tharsis volcanic province needs reconciling with our current view of the evolution of explosive volcanism on Mars. We contend that these small volume landforms, produced by mildly explosive volcanic activity, need to be considered in models surrounding planet-scale magmatic evolution and atmospheric volatile budgets.

First U-Pb (CA-ID-TIMS) Dating of the Uppermost Permian Coal Interval in the Minusinsk Coal Basin (Siberia, Russia) Using Zircon Grains from Volcanic Ashfalls

This study presents the first U-Pb (CA-ID-TIMS) radioisotopic dating of zircon grains extracted from tonsteins within the uppermost Permian coal interval of the Minusinsk Coal Basin (Siberia, Russia). Petrographic, structural, and mineralogical analyses confirm the volcanic ash origin of the tonsteins. The parent pyroclastic materials are identified as rhyolite–pantellerite for tonstein I-22 and dacite–rhyodacite for tonstein I-12. Morphological analysis of zircon crystals, along with cathodoluminescence and melt inclusion studies, confirms their volcanic origin and crystallisation temperatures of 700–900 °C. New radioisotopic dates of 261.4 ± 0.7 Ma and 261.3 ± 0.4 Ma clarify the age of the Izykh Formation, enabling its direct correlation with the Capitanian Stage of the International Chronostratigraphic Chart. The results emphasise the possible discontinuity of the coal-bearing succession of Siberian palaeocontinent and highlight the potential for further stratigraphic refinement through continued radioisotopic dating of tonsteins.

КАЛЬДЕРА КРАШЕНИННИКОВА (ВОСТОЧНАЯ КАМЧАТКА): ВОЗРАСТ И МАГНИТУДА ИЗВЕРЖЕНИЯ

New data on the composition of the pyroclastic deposits of the Krasheninnikov caldera allowed us to correlate it to the previously studied tephra horizon Geys30, which until recently was erroneously attributed to an eruption within the Geysernaya caldera. Pyroclastic flow deposits from the eruption that led to the formation of the Krasheninnikov caldera were found on the southern shore of Kronotsky Lake, and its distal tephra was found in the sediments of the Central Kamchatka Depression (CKD) at a distance of up to 200 km from the source (from Milkovo to Kliuchi villages). The age of this tephra was previously estimated at ~30 ka, which now allows us to accept this estimate for the Krasheninnikov caldera. The identification of the tephra of the caldera-forming eruption in distal sections allows a minimum estimate of the erupted pyroclastic volume of ~13 km3 and the eruption magnitude of 6.1.

40Ar/39Ar geochronologic and paleoenvironmental constraints to glacial termination III and MIS 7e, 7c, and 7a sea level fluctuations on the Tyrrhenian Sea coast of Italy

We provide detailed sedimentological, paleontological, and tephrochronological data on a complex sedimentary succession cropping out in the Tyrrhenian coastal area of central Italy, which was deposited in response to sea-level rise during MIS 7, coeval with the Latera phase of activity in the Vulsini Volcanic District. Diffuse intercalations of primary volcanic layers erupted during this phase and their geochronologic and chemostratigraphical characterization based on 40Ar/39Ar dating and EMP analyses, allowed for the identification of three stacked aggradational successions separated by erosive phases and their correlation with the Oxygen isotope record and phases in the relative sea-level curve. The ages of the tephra layers strictly frame the sedimentation in the interval of 253–206 ka, providing independent dating to glacial Termination III and to the three sea-level oscillations during MIS 7e, 7c, and 7a.Moreover, micro- and macrofaunal-based analyses provide information on the paleoenvironments and bathymetry during the highstands, which complement the geomorphological analysis reconstructing the inner edges of the corresponding marine terraces, allowing us to assess precise maximum sea level reached during MIS 7e and MIS 7a.The results of this multidisciplinary study enable us to establish in great detail the chronology, dynamics, relative amplitude, and effects of the sea-level fluctuations in the Tyrrhenian Sea during the whole MIS 7, providing independent, precise geochronological constraints for this period.

The Petrogenesis and Geological Implications of the Sanggeda Gabbros, Southern Tibet: Insights from the Amphibole Crystal Population

Amphibole is an important mineral during the differentiation of arc magmas but rarely as a phenocryst in arc lavas or eruptive pyroclastic rocks. The Sanggeda complex, intruded into the ophiolite of the Indus–Yarlung Zangbo Suture Zone (IYZSZ), Zedong, southern Tibet, mainly consists of amphibole-rich, fine-grained, and porphyritic gabbros. The complex provides an opportunity to study the differentiation of arc magmas through amphibole crystals. Four distinct amphibole crystal populations can be recognized according to petrographic observations, EMPA, and LA–ICP–MS analysis. The first ones (Type 1) are fined-grained and euhedral, are crystallized during ascent, and are the product of the shallow emplacement of host magma. The second ones (Type 2) are euhedral, with slight negative Eu and Sr anomalies, and crystallize from an evolved magma that previously experienced plagioclase fractionation. Type 3 amphiboles have similar morphological characteristics to Type 2 but are without Eu and Sr anomalies. Type 4 crystals are shown as pseudomorphs, formed by the reaction–replacement between the clinopyroxene and melt. Type 1 crystals are autocrysts. Other amphiboles within host magma, whether presented as phenocrysts or cumulate nodules, are antecrysts. Based on the amphibole crystal population developed in the complex, in this study, a trans-crustal magma plumbing system is proposed, containing at least three magma reservoirs located at different crust depths: the shallow emplaced crust (~4.8 km), the mid-crust (~12.9 km), and the lower crust (~21.8–24.9 km). Early amphibole crystallization is an effective process to generate silicic residual melts. Gravity could help in that sense. Precursor amphibole and clinopyroxene can efficiently delaminate back into the mantle and promote the generation of silicic continental crust.

Pre-Choiyoi volcanism at Cordillera del Viento, southwestern margin of Gondwana (∼37° S): Geological characterisation, geochronology and regional implications

This contribution provides a comprehensive description and classification of fifteen lithofacies within the Carboniferous rocks attributed to the Arroyo del Torreón Formation and Sofía Dacite in order to understand the eruptive dynamics and the evolution of volcanism associated with the onset of the Gondwanan Orogenic Cycle at the Cordillera del Viento (Argentina). The outcrops of Carboniferous volcanic and volcaniclastic rocks linked to this cycle are restricted to the Cordilllera del Viento range. In consequence, they offer a valuable opportunity to research the volcanic arc products of the pre-Choiyoi magmatism.The Arroyo del Torreón Formation lithofacies interpretation and its distribution indicate that the volcanism commenced with local andesitic lava flows followed by a volcano-sedimentary sequence formed by multiple pumice-rich quasi-steady concentrated pyroclastic density currents alternating with episodes of epiclastic sedimentation. The latter are covered ignimbrites developed by boiling over eruptions. Crystal-rich tuffs overlie the ignimbrites and represent a transition to a plinian eruption. This eruption style continued, developing concentrated pyroclastic density currents with highly unsteadiness conditions and scarce fall-out deposits. Conversely, the Sofía Dacite, represent a notable shift in the volcanism style, characterized by dacitic to rhyolitic lava flows with minor pyroclastic beds. Zircon dating of a pumice-rich lapilli-tuff from the Arroyo del Torreón Formation yielded a minimum age of 327.77 ± 1.79 Ma that was interpreted as the maximum depositional age for this unit. Similarly, zircons from a porphyritic dacite representing the Sofía Dacite provided a Concordia age of 329.11 ± 1.31 Ma that was interpreted as the crystallisation age of this rock.Consequently, we propose a new stratigraphic division of the Arroyo del Torreón Formation into two members. The Cerro San Pedro Member will comprise the pyroclastic rocks at the base of the sequence, while the Sofía Member will include the upper lava-dominated portion of the unit. In this sense, the whole lithostratigraphic unit represents a distinctive Carboniferous basin associated with arc-related volcanism representative from the pre-Choiyoi magmatism.

Genesis of Devonian volcanic-associated Lahn-Dill-type iron ores – part II: trace element fractionation evidences diffuse fluid venting

The iron (Fe)-oxide deposits of the Lahn-Dill-type are composed of haematite-quartz and rare siderite-haematite ores. These ores formed as marine chemical sediments on top of volcaniclastic rocks near the Middle to Late Devonian boundary (∼ 380 Ma). As such, their trace element fractionation patterns provide key information on venting style, ocean chemistry, particle-solution interaction, and depositional environment at the time of ore formation. This study combines WDXRF and ICP-MS/OES whole-rock geochemistry with complementary in-situ LA-ICP-MS analysis, and TEM element mapping of ore samples from the Fortuna Mine (Rhenish Massif, Germany). In-situ measurments were conducted on quartz-haematite, haematite, and siderite-haematite microdomains. Bulk major element contents of the ores indicate (volcani)clastic contamination and post-depositional hydrothermal alteration. Microdomain trace element distributions reveal four different trace element signatures, which are related to: (1) syngenetic apatite formation due to sorption of P and REY from seawater; (2) Fe-(oxyhydr)oxide-specific trace element scavenging and fractionation within the seawater column; (3) diagenetic Fe(III) reduction and trace element mobilisation in pore water; and (4) simultaneous deposition of (volcani)clastic material and Fe-(oxyhydr)oxides. These results show that Lahn-Dill-type iron ore formation resulted from mixing of a low-temperature vent fluid with ambient seawater at high seawater to vent fluid ratios. This likely was related to an environment in which diffuse venting dominated over focused venting, and in which quick Fe-particle precipitation led to formation of haematite-quartz ores. Local diagenetic Fe(III) reduction resulted in post-depositional siderite-haematite ore formation during which trace elements were partially remobilised in pore water.

Diatoms of soils and pyroclastic deposits from South Kamchatka volcanoes

Twenty-four species of diatoms belonging to 14 genera, 12 families and 5 orders were identified from soils and pyroclastic deposits of the Gorely, Mutnovsky, Avachinsky, Koryaksky and Vilyuchinsky volcanoes (Kamchatka Peninsula, Russia). Two species of these (Nupela tenuicephala, Pinnularia bullacostae) are new to the flora of the Kamchatka Peninsula, three ones (Eunotia palatina, Neidium bergii, Stauroneis borrichii) to the Russian Far East, and another three (Psammothidium lacustre, Humidophila sceppacuerciae, Gomphonema reichardtii) to the flora of Russia. Three revealed taxa (Navicula sp., Chamaepinnularia sp., and Pinnularia sp.) are probably new to science, as their morphological and morphometric characteristics differ from those of previously described species.

Discovery and environmental implications of Santorini tephras (Cape Riva and Minoan) in sediments of Lake Yayla (West Anatolia)

Throughout the long eruption history of the Santorini volcano, the Cape Riva/Y-2 and Minoan/Z-2 eruptions had a profound impact on the environment. The Minoan eruptions also had a significant impact on society. These two tephras, as well as the Y-2 tephra individually, have been recorded for the first time in a lacustrine area in western Anatolia. This study examines the geochemical properties of Y-2 (23 cm) and Z-2 tephra layers (19 cm; 14 cm pure and 5 cm mixed) from 18 m sediment cores in Lake Yayla (Denizli-Buldan). Additionally, high-resolution µXRF, fossil pollen, charcoal, and dating analyses were conducted on the cores to determine the chronologies and environmental effects of the tephra layers. Fossil pollen findings show consistent forest and steppe/grassland vegetation before and after the Z-2 tephra, with the forest impact lasting for 240 years after the eruption. Increased aquatic vegetation and changes in specific taxa (e.g. Pinus sp. and Amaranthaceae increased, while Quercus deciduous, Olea europaea, and cereals decreased) were observed following the Minoan eruption. Charcoal analysis indicates heightened fire activity post-Minoan eruption, while XRF data reveal no associated climatic change. At the same time, no correlation has been identified between the Cape Riva eruption and ecological changes (climate, vegetation, and fire activity). Contribution to dating the tephra was provided by radiocarbon dating from the lowest part of the tephra layer (17,684 ± 63 years BP). This study sheds light on the extensive impacts of the Y-2 and Z-2 tephra eruptions, focusing on their dating, geochemistry, environmental effects, tephra transport directions, and thicknesses. It demonstrates the presence of a significant geological event for the settlements in the Büyük Menderes Valley.

New Discovery of Natural Zeolite-Rich Tuff on the Northern Margin of the Los Frailes Caldera: A Study to Determine Its Performance as a Supplementary Cementitious Material.

The release of Neogene volcanism in the southeastern part of the Iberian Peninsula produced a series of volcanic structures in the form of stratovolcanoes and calderas; however, other materials also accumulated such as large amounts of pyroclastic materials such as cinerites, ashes, and lapilli, which were later altered to form deposits of zeolites and bentonites. This work has focused on an area located on the northern flank of the San José-Los Escullos zeolite deposit, the only one of its kind with industrial capacity in Spain. The main objective of this research is to characterize the zeolite (SZ) of this new area from the mineral, chemical, and technical points of view and establish its possible use as a natural pozzolan. In the first stage, a study of the mineralogical and chemical composition of the selected samples was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and thermogravimetric analysis (TGA); in the second stage, chemical-qualitative and pozzolanicity technical tests were carried out at 8 and 15 days. In addition, a chemical analysis was performed using XRF on the specimens of mortars made with a standardized mixture of Portland cement (PC: 75%) and natural zeolite (SZ: 25%) at the ages of 7, 28, and 90 days. The results of the mineralogical analyses indicated that the samples are made up mainly of mordenite and subordinately by smectite, plagioclase, quartz, halloysite, illite, and muscovite. Qualitative chemical assays indicated a high percentage of reactive silica and reactive CaO and also negligible contents of insoluble residues. The results of the pozzolanicity test indicate that all the samples analyzed behave like natural pozzolans of good quality, increasing their pozzolanic reactivity from 8 to 15 days of testing. Chemical analyses of PC/SZ composite mortar specimens showed how a significant part of SiO2 and Al2O3 are released by zeolite while it absorbs a large part of the SO3 contained in the cement. The results presented in this research could be of great practical and scientific importance as they indicate the continuation of zeolitic mineralization beyond the limits of the San José-Los Escullos deposit, which would result in an increase in geological reserves and the extension of the useful life of the deposit, which is of vital importance to the local mining industry.