Pyroclastic Research Articles

Indications of volcanic style of the Silurian Nová Ves Volcano (Hemrovy Rocks)

Studied locality of Hemrovy Rocks belongs to Nová Ves Volcanic Center, one of the Silurian volcanic centers of Prague Basin of Teplá-Barrandien area (lower Wenlock – lower Ludlow age). The aim of this work is to describe details of the volcanic rock structures and to contribute to the interpretation of the Silurian volcanic style. The macroscopic and microscopic structures of basaltic rocks in and close to the abandoned Kační Quarry in the southern part of Prague and at the adjacent locality – ridge of Hemrovy Rocks were studied. At these sites, volcaniclastics dominate over solid volcanic rocks and sediments. The volcanic rocks are represented by basalts, which form thin lava flows overlying both the volcaniclastics and sedimentary rocks. Massive fine-grained basalts pass to pillow lava facies, autobreccia or hyaloclastite breccia in-situ. These brecciated structures evolve into peperites or to unconsolidated volcaniclastic rocks of a previous eruption. Coarse-grained volcaniclastics with oversized subrounded to angular clasts of vesiculated lava or sediments within glassy matrix, sporadically with sediment admixture, are unsorted and thick-bedded. They were probably formed by gravity-driven mass flow. Basalt in the Kační Quarry probably represents a synvolcanic intrusion, as documented by its hyaloclastite rim and presence of clusters of resedimented volcaniclastics in the adjacent fine-grained sediments. Matrix of the volcaniclastics is mostly unsorted, formed mostly by quenched fragments of altered palagonitized and chloritized basaltic glass, locally scoriaceous, and fragments of chilled basaltic lava. Originally highly porous volcaniclastics, resp. hyaloclastites were secondarily cemented by calcite and silica. Secondary chlorite, calcite and silica also fill vesicles and cavities in fragments of glass and lava clasts. Dense vesicularity of lava fragments in volcaniclastics indicates an effective explosive interaction of lava with water. It is probable that much of the wet volcaniclastic material repeatedly slumped back down into the volcano’s crater to be re-ejected by subsequent phreato-magmatic explosions. Hydroclastic fragmentation was iniciated by repeated subaquatic eruptions in shallow subphotic marine zone. Unsorted crinoidal packstones mostly with trilobites, trepostomate bryozoan and volcaniclastic matrix were deposited in the vicinity of the Nová Ves Volcanic Center.

The >250-kyr Lake Chala record: A tephrostratotype correlating archaeological, palaeoenvironmental and volcanic sequences across eastern Africa

Regional tephrostratigraphic frameworks connect palaeoclimate, archaeological and volcanological records preserved in soils or lake sediments via shared volcanic ash (tephra) layers. In eastern Africa, tracing of tephra isochrons between geoarchaeological sequences is an established chronostratigraphic approach. However, to date, few long tephra records exist from sites with continuous depositional sequences, such as lake sediments, which offer the potential to connect local and discontinuous sequences at the regional scale. Long lake sediment sequences may also capture more complete eruptive histories of understudied volcanic centres. Here, we present and date the tephrostratigraphic record of a >250,000-year (>250-kyr) continuous sediment sequence extracted from Lake Chala, a crater lake on the Kenya-Tanzania border near Mt Kilimanjaro. Single-grain glass major and minor element analyses of visible and six cryptotephra layers reveal compositions ranging from mafic foidites and basanites to more evolved tephri-phonolites, phonolites, trachytes and a single rhyolite. Of these, nine are correlated to scoria cone eruptions of neighbouring Mt Kilimanjaro or the Chyulu volcanic field ∼60 km to the north; seven are correlated to phonolitic eruptions of Mt Meru, ∼100 km to the west; and four to voluminous trachytic eruptions of Central Kenyan Rift (CKR) volcanoes located ∼350 km to the north. The only rhyolitic tephra layer, a cryptotephra, correlates to the 73.7-ka BP (before present, taken as 1950 CE) Younger Toba Tuff (YTT) from Sumatra. Two of the CKR tephra layers provide direct ties with terrestrial sequences relevant to Middle Stone Age archaeology of the eastern Lake Victoria basin in Kenya. Absolute age estimates obtained by direct 40Ar/39Ar dating of 10 tephra layers are combined with six 210Pb and 162 14C dates covering the last 25-kyr and the well-constrained known age of the YTT to build a first absolute chronology for the full Lake Chala sediment sequence. The uninterrupted >250-kyr Lake Chala sedimentary archive represents a unique tephrostratotype sequence for eastern Africa, optimising the chronological value of tephra correlations in regional palaeoenvironmental, archaeological and volcanological research. Further study of cryptotephra in the Lake Chala sequence and additional geochemical characterisation and dating of ancient volcanic eruptions from nearby and further afield may eventually produce a regionally connected and detailed tephrostratigraphic framework for eastern equatorial Africa.

Marinoan glaciation in the Indian subcontinent - Anatomy and global implications

Detailed sedimentological analysis of the Pokaran Boulder Bed, representing the most basal unit of the Neoproterozoic-Lower Cambrian Marwar Supergroup, clearly indicates its glacial origin. The glacial sediments are interpreted as an ice-contact submarine fan deposit. Based on the detrital and inherited zircon population of the Marwar Supergroup sediments and interlayered pyroclastic deposits, a Marinoan cryochron of the Cryogenian Period is envisaged for the Pokaran Boulder Bed. The well-preserved Ediacaran elements in the post-glacial sedimentary succession also support a Cryogenian to Early Cambrian age of the Marwar Supergroup. The glacial deposition at the base of the Marwar Supergroup strengthens the regional correlation between the studied sediments with the Lesser Himalayan Blaini-Krol-Tal sediments and the Haqf Supergroup of Oman. The available zircon ages and paleomagnetic data of the Malani Igneous suite, along with the Marinoan glacial deposits, detrital zircon ages, and Ediacaran fossil elements of the Marwar Supergroup add significant information to the Neoproterozoic Earth history.

Multi‐channel seismic reflection study of tectonic–sedimentary features and subduction initiation in the middle Kyushu–Palau Ridge and adjacent basins

AbstractThe Kyushu–Palau Ridge and adjacent basins are ideal locations for investigating the formation and evolution of marginal seas and initiation of plate subduction. In this study, the tectonic–sedimentary features and crustal structure of the Kyushu–Palau Ridge and adjacent basins were investigated using newly obtained deep seismic reflection and borehole data. The initial mechanism of subduction in the West Philippine Sea and its tectonic evolution are discussed. Two sets of sedimentary strata with different provenances occur in the eastern Philippine Basin. The thickness of the lower strata is variable, and most of the sediment was sourced from island arc volcanism on the Kyushu–Palau Ridge. These strata thicken towards the Kyushu–Palau Ridge, and volcaniclastic rock aprons are developed near the foot of the Kyushu–Palau Ridge. The upper strata have a relatively uniform thickness and comprise fine‐grained, deep‐water marine sediments. The crustal thickness of the West Philippine and Parece Vela Basins is 6–7 km, which is similar to the global average thickness of oceanic crust. The Moho beneath the West Philippine Basin has a broad and undulating form that mimics the thickness of the oceanic crust beneath the sediments. The depth to the Moho decreases towards the Central Basin Spreading Center. The Moho beneath the Parece Vela Basin is planar, which is in contrast to the undulating nature of the oceanic crust base in this area. The West Philippine Basin may have been located at the northern margin of Australia in the Southern Hemisphere during the Mesozoic. It developed gradually in a continental margin arc as a result of Palaeogene inter‐arc and oceanic extension and contains fragments of continental crust. Seismic profiles and drillhole data in the West Philippine Basin reveal that compression occurred during the Eocene. Subduction along the paleo‐Izu–Bonin–Mariana arc may have been caused by the far‐field effects of the India–Asia collision. Subduction was accompanied by lateral propagation and a compressive stress field until the break‐up of the island arc at ca. 30 Ma.

Sequence Stratigraphic Analysis of the Volcanic Rock–Evaporite–Clastic Rock Symbiotic Zone in the Fourth Member of the Shahejie Formation in the South of Laizhou Bay

Laizhou Bay Sag is a typical continental rift lake basin, which is affected by strike–slip activity, salt rock activity, volcanic activity, and paleoclimate change in the Tanlu fault zone, where three major lithologies—volcanic rock, clastic rock, and evaporite—mainly develop. In order to determine the sequence correspondence between the different lithologies in the study area based on drilling, logging data, and seismic data, it is determined that the fourth member of the Shahejie Formation in the southern Laizhou Bay mainly develops three types of sequences: clastic rock type sequences, salt lake type sequences, and volcanic rock/clastic rock type sequences. Two second-order sequence boundaries (SBs3L, SBs4L) and one third-order sequence boundary (SBs4U) were identified, and the principle of three divisions of system tracts (LST, TST, HST) and sedimentary processes in different types of sequences were determined by analyzing the stacking patterns of different sequences. Compared with the previous research results, this study provides a more detailed analysis of the sequence boundary definition of different blocks and different lithologic strata, and it improves the previous general sequence stratigraphic division method. Based on the study of distinct types of sequences, a unified stratigraphic framework is established in the whole zone, and the stratum thickness distribution of the fourth member of Shahejie Formation is smaller in the southwest and larger in the northeast. The study area is generally filled with pyroclastic rocks–evaporite–clastic rocks, changing from fan delta–saline lake filling to braided river delta–freshwater lake–fan delta filling from bottom to top. A sequence stratigraphic model for the comparison of steep slope–gentle slope differences is established to provide guidance for future oil and gas field exploration and development.

Palaeoenvironmental changes in the Late Triassic lacustrine facies of the Ordos Basin of Northwest China were driven by multistage volcanic activity: Implications for the understanding the Carnian Pluvial Event

The Carnian Pluvial Event (CPE) induced an intense carbon-cycle disturbance and biological crisis at a global scale. The eruption of the Wrangellia Large Igneous Province (W-LIP) is considered a possible triggering mechanism; however, this cannot fully explain the significant differences in environmental perturbations across different regions. In this paper, we present detailed records of petrography, mercury geochemistry, carbon and sulfur isotopes, trace elements, and provenance data for the Triassic lacustrine facies of the Ordos Basin in the North China Plate, which provide insights into the important effects of volcanic activities, other than the W-LIP, on palaeoenvironment during the CPE interval. Massive emissions of SO2, CO2, and pyroclastic deposits resulting from these volcanic activities triggered four humid episodes, each characterized by lake-level rise, negative δ13Corg excursion, a transition from mudstones to organic-rich shales facies, as well as algal bloom within a time span of 180 kyrs. The establishment of an age framework in the Ordos Basin enables comparative analyses of environmental evolution during the Carnian age across the North China Plate, the western Tethys domain, and the South China Plate. During the period of global climate perturbation driven by the W-LIP eruption, we conclude that short-term localized volcanic activities may have further induced high frequentcy environmental perturbations, which influenced biological shifts and increase organic carbon burial. These short-term volcanic activities with different occurrence times and frequencies complicate local-scale palaeoenvironmental evolutions, which may be an important reason contributing to significant differences in environmental perturbations during the CPE interval across different regions of the globe.

New evidence of the Green Tuff deposits and post-caldera, recent explosive volcanic activity at Pantelleria volcano (Sicily Channel, Italy) recorded in near-vent marine areas

The record of the explosive activity of Pantelleria volcano is well documented by several distal tephra collected in various areas in and around the Mediterranean, while few tephrochronological studies exist on proximal marine areas. In this paper, we investigate three selected coring sites from the northern shoulder of the Pantelleria graben, about 15–30 km from the island, in near-vent position with respect to that volcanic source. Our multiproxy analyses revealed nine tephra layers, totally composed of juvenile materials, mostly ash and pumice fragments, as well as a coarse-grained tephra deposit at the bottom of one of the cores. The major element composition of glass shards indicates a very homogeneous geochemical composition for the tephra layers, suggesting their primary origin. Using litho-stratigraphic and paleoenvironmental proxies, we associated the tephra layers to the latest (<∼13.7 ka) explosive activity of Pantelleria. The coarse-grained deposit, instead, due to its distinctive composition is considered to represent the near-vent, marine equivalent of the distal Y-6 tephra layer, related to the ∼45 ka old co-ignimbrite fallout deposit of the Green Tuff event. The geochemical characterization of such deposit, mostly rhyolitic and partly trachytic, appears to enlarge the bimodal composition recorded in other distal tephra (Y-6) reported in the literature, highlighting the potential of near-vent record in providing additional information on the eruptive history.

Mineralogical properties of pyroclastic materials from Mount Merapi, Indonesia

Mount Merapi, located in Indonesia, is known as one of the most active volcanoes globally, often resulting in volcanic eruptions that produce pyroclastic materials. These materials from Mount Merapi’s eruptions have the potential to influence soil fertility in areas affected by the volcanic activities. This study aims to analyze the mineralogical properties of pyroclastic materials from Mount Merapi. The methodology involves collecting pyroclastic material samples from the 2010 eruption of Mount Merapi, followed by analysis using various mineralogical techniques such as polarized microscopy, X-ray diffraction, petrographic analysis, and wet chemical analysis. The findings offer detailed insights into the mineral composition, types of clay minerals, overall elemental presence, and the rock types forming these minerals in the pyroclastic materials. Variations in mineral composition are observed in the pyroclastic materials from Mount Merapi. Predominant minerals, including the plagioclase, pyroxene, and hornblende groups, are distinctly identified. These minerals’ presence suggests their susceptibility to weathering, categorized as easily weatherable minerals. This tendency for weathering is shown by the presence of elements like Na, Ca, and Mg in these minerals, which are crucial macro-nutrients for plant growth.

Potential Nutrient Carriers of Easily Weathered Minerals from Pyroclastic Materials of Mount Merapi, Yogyakarta

The eruption of Mount Merapi has had a negative impact on the community; however, on the other hand, it also has positive aspects that cannot be ignored. One of the major benefits associated with the eruption of this mountain is its ability to fertilize and restore the quality of the surrounding soil. This process of soil restoration involves the use of volcanic materials resulting from the eruption, specifically known as rejuvination or soil rejuvenation. In the concept of soil rejuvenation, pyroclastic materials play an important role due to their nutrient-rich content. These pyroclastic materials consist of various types of rocks and minerals, which have great potential to make a positive contribution in providing nutrients needed by plants. Based on the results of X-Ray diffraction analysis, the pyroclastic material from Mount Merapi is dominated by the mineral Albite, accounting for 81.3%. This mineral has the property of being easily weathered and susceptible to weathering agents. Volcanic materials from Mount Merapi can be utilized as agrominerals, this concept involves using volcanic material as a source of nutrients for plants since it contains both macro and micro nutrients required by plants.

Arc volcanism initiated on the eastern margin of Eurasia during the Early Cretaceous: Geochemistry of the Takanokura volcanic rocks in the Abukuma Mountains, Northeast Japan

AbstractThe Early Cretaceous Takanokura Formation in the eastern part of the Abukuma Mountains consists of a lower felsic ignimbrite and upper intermediate lavas and volcaniclastic rocks, representing the initial arc‐type in northeast Japan. In this study, I analyzed the major and trace element contents and Sr‐Nd‐Pb isotopic ratios of these eruptive products; then, I discussed their magma genesis based on their geochemical properties. Although igneous rocks of the same period in other localities of northeast Japan are characterized by the occurrence of adakites, these volcanism are composed of non‐adakitic high‐ to medium‐K andesite to rhyolite that are rich in large‐ion lithophile elements and poor in high‐field‐strength elements and have low Sr/Y values and flat heavy rare earth element patterns. Furthermore, these rocks have high radiogenic Pb isotopic ratios. The rhyolite and dacite have been thought to derive from crustal melting, whereas the andesite formed by the mixing of crustal felsic melts and mafic magmas generated by melting of the lithospheric mantle. Although previous studies attributed the formation of the Early Cretaceous adakites to the hot subduction of a mid‐ocean ridge, recent global plate motion reconstructions reject this model. To generate magma from a cold slab and lithospheric mantle that does not spontaneously melt, the mantle wedge under northeast Japan must have experienced heating. During this period, the volcanic province along the eastern margin of Eurasia expanded rapidly toward the trench, forming grabens. Therefore, I concluded that the advance of the hot asthenosphere into the forearc region that led to this expansion, which caused the retreat of the subduction boundary of the paleo‐Pacific plate to retreat and ultimately converted northeast Japan from an accretionary complex into a volcanically active region.

SO2 emissions from the Timanfaya eruption (1730–36 CE), Lanzarote, Canary Islands

The 1730–36 CE eruption of Lanzarote (Canary Islands) is the third largest basaltic fissure eruption known to have occurred in the last 1000 years, after the Icelandic events of Laki (1783–84 CE) and Eldgja (939 CE). Approximately 5.2 km3 (1.1 × 1012 kg) of alkalic basalt (sensu lato) lava and pyroclastic rocks were emplaced on land, with a further unknown amount entering the sea, The activity occurred in five eruptive phases from vents situated along a 15-km long, E-W trending fissure. Each phase began with Strombolian fire fountain activity, building large spatter and scoria cones, accompanied and followed by effusive ‘a'ā and pāhoehoe lava flow emplacement. Phases I and II were the most explosive and occurred between 1st September 1730 and June 1731. Samples of scoria and lava surfaces were collected from all phases and the major elements, S, Cl and F contents of matrix glasses and glass inclusions in olivine (the dominant phenocryst phase) were analysed by electron microprobe. Water contents of selected glasses were measured on polished wafers by Fourier Transform Infrared spectroscopy. Glass compositions mimic the range of published whole rock compositions, with Phase I being predominantly basanitic and later phases alkali basalt. Whole rock variations in incompatible trace element ratios are mimicked by ratios involving TiO2, K2O and P2O5 in glass. Matrix and glass inclusion analyses in a given sample are similar, indicating that the inclusions formed synchronously with eruption and that most phenocryst crystallization occurred during earlier evolution of the magmas. Matrix glasses in scoria and surface lava samples have 80–300 ppm S and 260–750 ppm H2O, whereas glass inclusions in olivine have 420–2650 ppm S and 0.1 to 0.5 wt% H2O. Glass inclusions with low sulfur contents were trapped during degassing-induced crystallization as the magma approached the surface. The inclusions with the highest sulfur contents, at given P2O5/TiO2 ratio, are inferred to represent un-degassed melt, and their S content and S/K2O ratios correlate very strongly with incompatible element concentrations and P2O5/TiO2 ratios. The original S contents of 131 matrix glasses were calculated from their P2O5/TiO2 ratios and compared to their measured degassed S contents. The mass of S released per unit mass of magma ranged from about 0.25% in Phase I Episode 1to 0.17% in later phases, with propagated uncertainties of about 2 to 5%. About 40 Mt. of SO2 was released overall, with ca. 25 Mt. being released during the first 5 months of the eruption (Phase I). Estimates of average magma discharge rates imply that plumes remained in the troposphere, with the possible exception of those associated with extreme peak discharge rates during Phase I Episode 1 which may have just reached the upper troposphere – lower stratosphere. Lower eruption rates during the later phases would have confined SO2 emissions to the troposphere. Although acid and sulfate peaks dated to 1730 and 1731 have been reported from some Greenland ice cores, the evidence for stratospheric impact, such as cooling at the Earth's surface and increased stratospheric turbidity, is minimal.

Physical and mechanical characteristics of pyroclastic soil for the construction of embankments

In the framework of wider research activity on the physical and mechanical behaviour of volcanic soils, this paper reports the results of some laboratory tests on this type of geomaterial. The background of this research is the need for a construction company to possibly use pyroclastic material excavated along a tunnel profile to build railway embankments included in the design of a new High-Speed Train Line near the city of Naples, Italy. However, according to the standards of the National Italian Railways Company, pyroclastic soils cannot be employed as construction materials unless they are supported by a specific testing program demonstrating their good performance. The pyroclastic soil, which is widespread in the project area, is the product of Mt. Vesuvius volcanic activity. It is a coarse-graded soil that includes a significant percentage of non-plastic fines. They should be placed under compact conditions. The experimental campaign was aimed at identifying some physical characteristics that can synthesize the homogeneity of the pyroclastic deposit in terms of shearing resistance. The preliminary results obtained in terms of grading curves, modified Proctor compaction curves, and stress-strain curves from conventional drained triaxial tests are presented and discussed in this paper. The latter were executed on fully saturated specimens after compacting the soil at the optimum water content and on the dry and wet sides of the Proctor curve. The overall initial outcomes of the experimental campaign indicated that this material has acceptable characteristics and is suitable for the construction of railway embankments.

New radiocarbon age constraints on the eruption history of the Quill volcano, St. Eustatius, Dutch Caribbean

Abstract The late Pleistocene to Holocene subaerial pyroclastic deposits of the Quill stratovolcano on the Caribbean island of St Eustatius form seven stratigraphic divisions. New radiocarbon ages of charcoal are presented for the second, third and seventh divisions in order to better constrain the Quill’s eruption history. Three samples from the same layer of Division 2 at two localities on the northeast coast yield ages of 18,020 ± 40 (1σ), 18,310 ± 45 and 18,490 ± 45 14C yr BP (∼19,800–20,600 yr cal BC). These are considerably younger (∼4400 yr) than a previously published result for this division. A single sample of Division 3 gave an age of 8090 14C yr BP (∼7100 yr cal BC) and overlaps with previously published 14C ages for this division. A charred root in the pyroclastic unit deposited by the last eruption of the Quill (Division 7) gave an age of 919 14C yr BP (∼1100–1200 yr cal AD). This result is ∼600 years younger than a previously published age, and its origin is attributed to human activity. The timing of the last eruption of the Quill therefore remains poorly constrained but is older than 600 AD. Terrestrial gastropods found in paleosols and organic material found in small streams that developed in Division 3 indicate that Division 4 must be younger than 6100 ± 500 yr cal BC. The oxygen and carbon isotope composition of the terrestrial gastropods derived from Division 3 paleosols indicates that the C4 and CAM-type vegetation was dominant and that the climate subsequently changed to wetter conditions. The minimum eruption frequency for the Quill volcano is one eruption every ∼1400 years during the past 22,000 years. This eruption frequency of the Quill volcano is of the same order of magnitude as other recent northern Lesser Antilles volcanoes, Soufrière Hills (Montserrat, ∼5000 years) and Mt Liamuiga (St. Kitts, ∼2500 years).

Middle Miocene volcanic flare up preceding and synchronous with the Langhian/Serravallian sea‐level decline in the North Pannonian Basin: Insights from 40Ar/39Ar dating, geo‐seismic analysis and 3D visualization of the subterranean Kráľová stratovolcano

AbstractThe Pannonian Basin System originated from the collision of the African and European tectonic plates, followed by the Miocene extensional collapse that led to the development of a back‐arc basins. Accurate dating is essential to comprehend the tectono‐volcanic evolution of the region, particularly in the under‐studied Danube Basin. Single‐grain 40Ar/39Ar dating has revealed that volcanic activity in the Danube Basin commenced around 14.1 million years ago, aligning with previous biostratigraphic and radioisotope data from nearby volcanic fields. The initial Middle Miocene pyroclastic deposits were generated by intermediate high K calc‐alkaline magmas, contributing significantly to the deposition of thick layers of fine vitric tuffs. The timing and chemistry of the volcanism are consistent with the Badenian rift phase in the Middle Miocene within the Carpathian–Pannonian region, suggesting an intraplate back‐arc volcanic environment. Three‐dimensional imaging has exposed the buried Kráľová stratovolcano, revealing its impressive scale with a thickness between 2620 and 5000 m and a base diameter of 18–30 km. Such dimensions place it among the ranks of the world's largest stratovolcanoes, indicating its substantial impact on the evolution of the Carpathian–Pannonian area. The complex formation history of the stratovolcano points to multiple phases of growth. Furthermore, the basin controlling Mojmírovce‐Rába fault's intersection with the stratovolcano implies that fault activity was subsequent to the volcanic activity, being younger than 14.1 million years. Regional age data consistently indicates that volcanic activity in the Danube Basin reached its zenith just prior to and during the lower/upper Badenian sea‐level fall (Langhian/Serravallian). K‐metasomatism is unique to the stratovolcanic structures and is not observed in the wider regional setting. This study supports the notion of an intricate, interconnected subterranean intrusive system within the stratovolcano, underscoring the complex interplay between geological structures and volcanic processes.

Sandstone Provenance of Walanae Formation as a Parent Rock in Bulukumpa area, Bulukumba Regency, South Sulawesi

The Walanae Formation has a wide distribution in the southern arm of Sulawesi, this rock formation was deposited during the formation of the basin due to the Walanae strike-slip fault. The Walanae Formation in the study area comprises sedimentary rocks and pyroclastic rocks, which give different soil characteristics. This study aims to determine the types of sandstones, rocks of origin, and provenance of sandstones in the study area by using spot sampling at representative stations and petrographic analysis. The sandstones of the study area are divided into two groups based on Folk (1974), namely arkose lithic and feldspathic litharenite. Based on the type of quartz, rock fragments, and associated minerals, the origin of the sandstones in the study area are plutonic igneous rocks, volcanic rocks, sedimentary rocks, and metamorphic rocks. The results show that the types of provenance sandstones in the study area are magmatic arc and recycled orogenic.

Vegetation reconstruction of the Agro Pontino and Fondi basin (central Italy) before and after the Bronze Age eruption of Somma-Vesuvius (c. 1900 BCE)

In the research project The Avellino Event: Cultural and Demographic Effects of the Great Bronze Age Eruption of Mount Vesuvius, the recording of local and regional changes in the vegetation of the landscapes of the Agro Pontino and the Fondi basin (southern Lazio, Italy) before and after the Bronze Age eruption of Somma-Vesuvius (c. 1900 BCE) was central to answer the project’s central question, which revolved around the nature of the distal effects of this high-magnitude eruption on the conditions of living for the Bronze Age human population inhabiting these landscapes. If adverse effects of the ash fall in these areas were minor, the Agro Pontino and the Fondi basin, located about 125 km north of the Vesuvius, could well have been the refuge area people might have fled to in their attempts to escape the pyroclastic flows that eventually would bury parts of Campania around the Vesuvius below a thick layer of tephra. If adverse effects of the ash fall were major, the situation might, likewise, have led to changes in vegetation but could have resulted in a decline in human and animal presence due to toxicity, for instance. In both scenarios, either population growth due to in-migration or population decline due to environmental impact, we expected to see changes in the vegetation record in the period during which the Avellino Event occurred. To test our hypotheses, we performed archaeobotanical research, using pollen and macro-remains, on stratified soil sequences from test pits in the Agro Pontino and the Fondi basin containing the Avellino tephra layers, thereby guaranteeing sound chronological control. (The research revealed the presence of other known distal tephras as well.) Contrary to our expectations, the research did not provide proof of any significant changes in the vegetation around the date of the Avellino Event, nor did it provide any strong signs of human impact on these landscapes in the longer term before and after the distal ash fall, thereby indicating low population levels during the final part of the Early Bronze Age (EBA) and the initial phase of the Middle Bronze Age. Although this finding about human impact is an important outcome, it is not the only finding. The archaeobotanical research provided the project with high-resolution information on the vegetation and environmental conditions in the Agro Pontino and the Fondi basin for the duration of the Bronze Age. This, in combination with the physical-geographical data collected during the project, added significantly to our ability to perform detailed palaeogeographical reconstruction of the Agro Pontino and the Fondi basin. In addition, it increased our understanding of how the landscape had been settled during the Bronze Age (Sevink et al. 2022; Attema et al. in press). A final spin-off consisted of possible new information on the 4.2 ka climatic event that impacted Italy during later prehistory, as reflected in the pollen diagrams presented.

The Middle to Late Holocene in the Agro Pontino and the Fondi basin (Lazio, Italy): A palaeogeographical overview

The Agro Pontino, a vast plain located south of Rome (southern Lazio, Italy), has served as a valuable resource for central Italian palaeogeographical, vegetational and archaeological studies for decades. This paper reviews the regional development of the Agro Pontino and adjacent Fondi basin from the Würmian (Marine Isotope Stages 2–5d) until the end of the protohistoric, with an emphasis on the period around the Early Bronze Age (EBA) date of the Avellino eruption. Following postglacial relative sea level rise, a dissected Pleistocene landscape drowned and was filled with lagoonal, fluvial, alluvial, lacustrine and marsh deposits. In the Agro Pontino, two lakes emerged divided by an alluvial fan. The unique regionally preserved stack of Middle to Late Holocene sediments, including multiple macroscopically visible tephra layers within a depositional environment, allowed for a detailed regional palaeogeographical, tephrochronological and vegetational reconstruction. This study presents the latest palaeogeographical findings from the Agro Pontino and the Fondi basin for the Middle Holocene and the EBA, for which tephra identification and dating forms the solid basis. It contributes to the reconstruction of the Pontine plain and the Fondi basin during this period and furthers our palaeoenvironmental knowledge of the conditions for human subsistence in this region during the later phase of the EBA, around the time of the Avellino eruption (c. 1900 calBC).

Evidence of the weakly stratified crystalline magma feeding an explosive Plinian eruption: A case study of the Holocene ‘Malalak Tephra’ deposit Tandikat volcano, West Sumatra, Indonesia

The Malalak Tephra (MT) in West Sumatra, Indonesia, is a thick (up to 5 m within 5 km distance around the vent) pumice fall deposit that consists of one initial ash layer (F-0) and five main lapilli layers (F-1 and F-2 are referred to as the early stage, and F-3, F-4, and F-5 as the late stage). White pumice (microlite-free) and grey pumice (microlite-bearing) occur as the main juvenile phase in the lapilli fall layers, with a tendency of increasing grey pumice content from the early to the late stage (3–4 and 6–12 vol%, respectively). Both pumice types shared identical petrographic and chemical (glass, plagioclase, and amphibole compositions) features, suggesting a similar magmatic origin. However, a slight increase in phenocrysts content (from 30–45 to 33–58 %), modal pyroxene (from 3 to 11 vol%), and anorthite contents (from An70 to An74) was observed from the early toward the late-stage products. Such evidence, coupled with the fact that the white pumice was relatively colder, more hydrous, and shallower than the grey pumice (based on plagioclase and amphibole geothermobarometers) suggests the occurrence of a weakly stratified crystalline magma reservoir. The ‘less silicic’ magma (as the source of grey pumice) experienced extensive microlite crystallization during magma ascent because undercooling can effectively occur under lower viscosity conditions (lower SiO2), forming microlite-bearing juvenile. Whereas the ‘more silicic’ magma did not experience such an extensive syn-eruptive crystallization due to the relatively higher viscosity condition. Finally, the glass compositions of the Malalak pumice were found to be similar to the V-5 deep-marine tephra layer on the west side of Sumatra, suggesting an approximate volume and eruption age of 7.5–16.1 km3 and 4,860 ± 60 cal. BP, respectively.

Study of Eruption Mechanism Pyroclastic Deposit of Banten Tuff (Qpvb) in Pancanegara and its surrounding Using Grainsize Distribution and Componentry Analysis

Banten Tuff (Qpvb) is pyroclastic deposit that is very significant in western Java Island. The importance of this deposit is caused by spreading and covering most of Banten region. In the middle of Banten Tuff, there is a caldera that has rectangular shape and the large area 13.7 km x 6.5 km. The research in this area has not studied yet that explain the characteristics of pyroclastics deposit in detail, therefore it’s hard to tell how the eruption process and mechanism that happened based on the deposit. This study become solution of a puzzle about process, mechanism, history, and episode of eruption. The research methods are using qualitative and quantitative analysis such as grain-size distribution and componentry. The study has succeed obtaining more than ten outcrops that described in detail. Description of outcrops resulted tephra-stratigraphy correlation in four facies unit. These four facies categorized into three eruption phases. Eruption phases are arranged into a story which is useful for determining historical and episode eruption in Pancanegara and its surrounding.

Diagenetic effect on reservoir quality of siliciclastic and volcaniclastic sandstones from a Paleogene volcanic rifted margin, East Greenland

ABSTRACT Siliciclastic and volcaniclastic sediments in a volcanic rifted-margin succession may experience a complex diagenetic history during burial that can have a large impact on sandstone reservoir properties. To understand such changes, variations in initial sediment composition and succeeding diagenetic changes have been studied for a Paleogene outcrop analogue in the Kangerlussuaq area, East Greenland. The nature of the mafic volcanics-bearing succession, which consists of intra-volcanic sandstones, accommodated over quartz-rich pre-volcanic fluvial sandstones, are comparable to the settings of recently discovered hydrocarbon-producing sandstones in the Faroe–Shetland Basin on the conjugate Atlantic margin. Our petrographic and provenance investigations of the pre- and intra-volcanic sandstones are supported by geochemical and X-ray diffraction analyses. The intra-volcanic sandstones were deposited in shallow marine environments with mixed siliciclastic and volcaniclastic input, the latter rich in felsic to mafic volcanic rock fragments and feldspar grains. Similar zircon age distributions of pre- and intra-volcanic sandstones support a continued supply from the same siliciclastic sediment source after the onset of volcanism. Variations in initial detrital grain and pore-fluid (fresh to marine) compositions resulted in different diagenetic changes in the pre- and intra-volcanic sandstones. However, where siliciclastic sandstones were overlain by volcaniclastic rocks rather than massive lava flows, the diagenetic changes resemble those of the intra-volcanic sandstones. The cementing phases are typically quartz, illite (probably illitized kaolinite), and rare anatase in the pre-volcanic sandstones. Chlorite, calcite, zeolite/feldspar, opal/quartz, and titanite are characteristic authigenic phases in the intra-volcanic sandstones. Precipitation of different minerals in the pre- and intra-volcanic sandstones show that the detrital composition (and to a lesser extent depositional environment) played a major role during early and late diagenesis after deep burial (up to 6–8 km). Inter-eruptive siliciclastic units may prove to form highly valuable reservoirs when they are composed of mixed siliciclastic and volcaniclastic material. In the stratigraphically youngest intra-volcanic sandstones and pre-volcanic sandstones overlain by hyaloclastite or tuff, there is a high potential for preservation of interparticle porosity during burial (&amp;lt; 5 km) due to early chlorite rims and the generation of secondary porosity after the dissolution of early zeolite cement.