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Middle Triassic beds exposed along the road between Mišji Dol and Poljane pri Primskovem (Posavje Hills) comprise marlstone, tuff, volcaniclastic sandstone, and thin- to medium-bedded limestone and dolostone. The succession was logged and sampled for conodonts. A relatively rich conodont assemblage was determined, consisting of Budurovignathus gabrielae Kozur, Budurovignathus sp., Cratognathodus kochi (Huckriede), Gladigondolella malayensis Nogami, Gladigondolella tethydis Huckriede, Gladigondolella sp., Neogondolella balkanica Budurov & Stefanov, Neogondolella cf. excentrica Budurov & Stefanov, Neogondolella constricta (Mosher & Clark), Neogondolella cornuta Budurov & Stefanov, Neogondolella sp., Paragondolella excelsa Mosher, Paragondolella liebermani (Kovacs & Kozur), Paragondolella trammeri (Kozur), Paragondolella cf. alpina (Kozur & Mostler), and Paragondolella sp. The assemblage correlates with the upper Anisian and lowermost Ladinian assemblages from the Global Boundary Stratotype Section and Point (GSSP) of the Ladinian at Bagolino in the Southern Alps in northern Italy. Along with conodonts, numerous specimens of benthic foraminifera Nodobacularia? vujisici Urošević & Gaździcki were recovered from the lowermost part of the succession. Previous research on this taxon is critically evaluated.

Pyroclastic density currents (PDCs) are hazardous, multiphase currents of heterogeneous volcanic material and gas. Moisture (as liquid or gas) can enter a PDC through external (e.g., interaction with bodies of water) or internal (e.g., initial eruptive activity style) processes, and the presence of moisture can be recorded within distinct deposit layers. We use analogue experiments to explore the behaviour of pyroclastic material with increasing addition of moisture from 0.00–10.00% wt. Our results show that (1) the cohesivity of pyroclastic material changes with the addition of small amounts of moisture, (2) small increases in moisture content change the material properties from a free-flowing material to a non-flowable material, (3) changes in moisture can affect the formation of gas escape structures and fluidisation profiles in pyroclastic material, (4) gas flow through a deposit can lead to a moisture profile and resulting mechanical heterogeneity within the deposit and (5) where gas escape structure growth is hindered by cohesivity driven by moisture, pressure can increase and release in an explosive fashion. This work highlights how a suite of varied gas escape morphologies can form within pyroclastic deposits resulting from moisture content heterogeneity, explaining variation in gas escape structures as well as providing a potential mechanism for secondary explosions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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This paper describes various soft-sediment deformation structures present in the Triassic deposits of the Betic External Zone (Southern Iberian). These structures, together with variations in deposit thicknesses, internal angular unconformities, and synsedimentary faults, point to intense tectonic activity from the Middle to Late Triassic related to a stage of rifting. The Middle–Late Triassic in the Betic External Zone shows a sedimentary record represented by Muschelkalk and Keuper facies. In the Ladinian Muschelkalk, carbonates appear slumps, breccias, load casts, slide and parallel shear surfaces, and tsunamites. In the sandstones of the Carnian Keuper facies, different seismite beds and ball and pillow structures can be discerned. Above these deposits, the carbonate Zamoranos Formation of the Rhaetian displays volcaniclastic rocks with conglomerates, slumps and synsedimentary faults. All these features and magmatism suggest some tectonic activity, possibly related to the breakup of Pangaea, especially at the end Triassic. We highlight the features that indicate this tectonic activity over time and discuss the factors that triggered the development of these structures, along with the conditions that made this possible.

• Bimodal grain size distribution increases sediments erodiblity. • Mineralogical composition and weathering processes are making unique badland site. • Volcaniclastic material are "bad" enough to make badlands. • Volcaniclastic material open a possibility for new badland classification. In the past few decades, terrains of accentuated roughness with variety of topographical features and, due to the diversity of lithology and colors, known as badlands attract great attention not only from the scientist, but from people in general and contribute to the touristic popularization of geosites. Badlands materials are mainly silty clays and clayey silts. However, they can be formed in volcaniclastics material too and one of the most prominent badlands developed in pyroclastic sediments is Cappadocia, Turkey. Less known are Kazar badlands, Hungary, developed in rhyolitic poorly-consolidated highly porous tuffs and Djavolja varos, Serbia developed in dacito-andesitic poorly-consolidated, poorly-sorted tuffs. Volcaniclastic rock samples from Kazar badlands, Hungary and Djavolja varos, Serbia were analyzed with the purpose to broaden existing knowledge on materials in which badlands can form. Through analysis of eight unweathered volcaniclastic sediment samples that included petrographic characterization, content of macroelements, pH, electrical conductivity, sodium adsorption ratio and immersion test an attempt was made to answer the question whether volcaniclastics are "bad" enough to make badlands. After all the analysis conducted, Kazar badlands and Djavolja varos materials have different properties, unique for each site, but are still more similar to each other than to, already known badlands materials. Similar bimodal grain size distribution of Kazar badlands and Djavolja varos reflects sediments erodibility and is making them similar to other badlands generally, while mineralogical composition and weathering processes are the main factors making these two sites a unique badlands group. Conclusions brought in this study are opening new scientific topic and they imply that volcaniclastic material, even though site-specific, make unique badlands and that, through future research, could bring the possibility of a new badlands classification that will include only volcaniclastics and will bring up small sites like these to the existent geotouristic map. [ABSTRACT FROM AUTHOR]

Jabal Farasan is located in the west central part of the Arabian Shield. The present study aims to reveal the stratigraphic setting and mineral paragenesis of the exposed volcano-sedimentary succession of the Samran Group in Jabal Farasan area. The succession of Samran Group is composed of three successive facies: the lower interbedded andesitic tuffs and tuffaceous andesites and trachyte’s (F1), the middle-altered quartz diorite/andesite (F2) and, an upper interbedded andesitic tuff, tuffaceous andesites and trachytes (F3). The vertical variations in the petrographic lithotypes depend mainly on the position of the depositional sites relative to the volcanic centers (proximal and distal). Both the volcanic rocks and the associated units are subjected to syn-and post-depositional diagenetic/metamorphic processes. These processes include the formation of the Fe2+-silicates: (i.e., chlorite instead of the volcanic ashes and the formation of plagioclase minerals). Post diagenetic recrystallization of the tuffaceous mudstones and the formation of microcrystalline quartz. The diagenetic oxidation of the Fe2+-silicates led to the formation of volcaniclastic red beds in certain stratigraphic horizons. [ABSTRACT FROM AUTHOR]

The N–S trending Neoarchaean to Palaeoproterozoic Dongargarh–Kotri belt in the Bastar Craton in central India exposes bimodal volcanics and volcaniclastics of the Nandgaon Group. In this contribution, lithofacies analysis of the Nandgaon Group has been attempted mainly based on distribution of rhyolites, basalts and pyroclastics in this ancient volcanic terrain, their field characteristics and petrography. The study area in the central part of the belt around Dongargaon–Gotatola area can be two distinct domains based on distribution and composition of volcanics and volcaniclastics. Domain-I comprises coherent and autoclastic rhyolite, and Domain-II with basic lava and pyroclastics. The rhyolites of Domain-I can be further divided into feldspar quartz phyric, quartz phyric, aphyric, and autoclastic rhyolites. Basic lava of Domain-II includes basalt and andesitic basalt. The associated volcaniclastics are mainly coarse lapilli tuff, fine lapilli tuff and ash beds. Field characteristics of coherent lavas and volcaniclastics attest to phreato-magmatically controlled plinian to sub-plinian style of eruptions. Effusive and explosive eruptive processes through multiple vents gave rise to the observed volcanic sequences. This study indicates that subaerial volcanism initially led to formation of felsic ignimbrites and ash deposits followed by effusive rhyolite lava flows. Subsequently, mafic volcanism occurred giving rise to pyroclastic flows and surges, followed by effusive mafic lava flows. [ABSTRACT FROM AUTHOR]

In the broader Caucasus region, multiple extrusive volcanic units are present within the Jurassic, Cretaceous, Eocene and Miocene sedimentary successions. Partial reworking of volcanic material from various provenance areas into Eocene, Oligocene and Miocene reservoir units is commonly observed in the Eastern Black Sea and in the Rioni, Kartli and Kura Basins of onshore Georgia. Reservoir quality has in general been negatively affected by volcanic rock fragments which may have undergone complex diagenetic alteration. However, despite concerns regarding reservoir quality, oil at the Samgori field, the largest field in Georgia (∼200 MM brl recovered), is hosted in altered Middle Eocene volcaniclastic sandstones interbedded with deep‐water turbidites. Previous studies of core material from numerous wells in this field showed that most of the oil is contained in altered, microfractured, laumontite‐rich tuffs which have fracture and cavernous net porosities averaging 12% and average permeability of 15 mD. The laumontite tuffs comprise only up to 20% of a tuffaceous sandstone section and occur as isolated lenses or pods on a sub‐seismic scale (i.e. 5‐10 m thick), causing highly variable oil productivity from one well to another. The petrographic analysis of samples of Middle Eocene volcaniclastic sandstones from outcrops in the central part of the Kartli Basin around Tbilisi broadly confirms the main conclusions of studies completed some 30 years ago which were based on the analysis of subsurface samples. However, the surface samples analysed show that zeolitization events typically did not improve, but actually reduced, reservoir quality due to extensive zeolite cementation. The poor reservoir properties of the plug samples, which are age‐equivalent to the proven subsurface Middle Eocene reservoir interval, highlight fracturing as a key factor controlling the presence of exceptional producers (up to 9000 b/d) in the Samgori field complex. The study therefore underlines the critical role of fracturing of the Middle Eocene volcaniclastic reservoir sequence in the Kartli Basin. [ABSTRACT FROM AUTHOR]

Many of the bentonite deposits of the Ankara-Çankırı Basin, Central Anatolia, Turkey were found within the Miocene Hancılı Formation, which comprises lacustrine sedimentary and volcaniclastic rocks that interfinger with Uludere pyroclastic rocks of the Miocene Galatean volcanic province. In the present study, the conventional K–Ar geochronological method was used to evaluate the contribution of volcanic materials to the K-bearing components of the bentonite clay fractions. Four dacite samples from near the southern end of the basin were indistinguishable in K–Ar age (average 18.4 Ma, standard deviation 0.3 Ma). K–Ar measurements of feldspar-enriched rock fragments and hydrobiotite separated from andesitic tuff from near the northern end of the basin indicated an age of 17 ± 1 Ma. The K–Ar age values of clay fractions of bentonites, which ranged from 77 ± 5 Ma to 162 ± 5 Ma, indicate that most of the K in the bentonite clay fractions occurs in minerals derived from the Mesozoic basement rocks adjacent to the Miocene basin. The K–Ar age values support field observations indicating that these bentonites are secondary bentonites formed by alteration of volcanic components during or after deposition of volcaniclastic phases. The K-bearing mineral components of these clay fractions consisted mostly of unaltered illitic material of detrital origin whereas the smectitic components were formed by alteration of Miocene pyroclastic materials. [ABSTRACT FROM AUTHOR]

Bimodal volcanism in the Cuddapah basin is associated with a cratonic rift setting. The Cuddapah basin consists of five sub-basins (viz., Papaghni, Nallamalai, Srisailam, Kurnool and Palnad) and a total thickness of ~12 km sediments and associated bimodal volcanics. The oval-shaped gravity high observed over the Papaghni sub-basin is due to lopolithic intrusions along listric faults. A basin evolution model is prepared in this context with signatures of active rifting. Mapping and geochemical sampling along the Tadpatri–Tonduru tract along with petrographic observations additionally supports the proposed model. The model presents the mechanism of bimodal volcanism during rifting and sedimentation. Basin evolution with tectonic modifications revealed a link with global tectonic events (e.g., ~1.8 Ga Hudsonian orogeny, ~1.3 Ga Grenville orogeny, ~0.9 Ga Enderbia docking). The stratigraphic disposition of the surge, flow, fall and volcaniclastic deposits in this old Proterozoic terrane indicate the magma history and eruption conditions. The felsic volcanic rocks are classified as rhyolite and rhyodacite. The mafic volcanics are mainly basaltic. Primordial mantle normalized trace element plots indicate enrichment of large ion lithophile elements (Rb, Th and K) along with negative Sr, P and Ti anomalies. The chondrite normalized REE patterns are characterized by LREE enrichment, negative Eu anomaly and flat HREE pattern. These features indicate origin of felsic volcanics through shallow crustal melting with plagioclase either as a residual or a fractionating phase. The mafic rocks of the area are product of shallow mantle melting related to asthenospheric upwelling followed by decompression melting and generation of basaltic magma. This was also associated with lithosphereic stretching, rifting and initiation of sedimentation. The less viscous mafic magma was probably channelized along the rift-related faults. The underplating and intraplating of hot mantle-derived magma supplied heat into the crust. The attendant partial melting of continental crust produced the felsic magma. Different sub-basins within the Cuddapah basin indicates a combined mechanism of rifting and orogenic events. [ABSTRACT FROM AUTHOR]

Two sedimentary basins are identified in the Turkana Depression (East African Rift System, Kenya). One of them, the Ekitale Basin, is presented in detail. Located on the western rift shoulder of the northern Turkana Depression, the preserved portion of the Ekitale Basin is 3–5‐km wide and bordered by N40°–50° normal faults. These normal faults were inherited from the reactivation of pre‐existing basement structures. The Ekitale Basin is filled by the ~75‐m‐thick Topernawi Formation. The lower portion of the formation provides evidence that the basin was occupied by a lake, bordered by alluvial fans, and into which river‐derived turbiditic complexes were deposited. The upper portion is comprised of pyroclastic deposits, originating from volcanic activity, and interbedded with fluvial deposits emplaced during periods of volcanic quiescence. The Ekitale Basin opened just after 28 Ma and was abandoned prior to 25 Ma, placing it after the deposition of the Oligocene Traps (ca. 33.9–27 Ma) and prior to the rift climax (after 14 Ma). This syn‐rift basin largely impacts our understanding of the Cenozoic rift evolution in the Turkana Depression. It helps to identify, for the first time, the first pulse of extension of the Cenozoic rifting, revealing a two‐step rifting scenario for the northern Turkana Depression. The Ekitale Basin, and analogous syn‐rift basins, is believed to have developed from the reactivation of pre‐existing structures during a period of extension marked by low differential stress and a low amount of extension. [ABSTRACT FROM AUTHOR]

Among other parameters, volcanic activity adjacent to shallow marine environments influences the development of ecosystems and their carbonate-producing communities. Volcaniclastic sediment influx in particular has potential to cause rapid and drastic environmental changes affecting biological systems in their composition and activity, and ultimately leading to changes to and breaks in carbonate sedimentation. Such sedimentary breaks that form in response to volcanic processes are rarely described in detail despite the common occurrence of carbonate platforms adjacent to active volcanoes both in the recent and past geological record. The Island of St. Bartholomew (St. Barths), French West Indies, exposes sections of middle Eocene limestones intercalated with thick volcaniclastic deposits and lavas. Theses carbonates provide an example of a low-latitude tropical platform where non-framework building biota were important, if not dominant, sediment contributors. The carbonate system records the repeated collapse and renewal of carbonate production, as a result of episodic volcaniclastic material input. The discontinuous nature of the carbonate sedimentation is reflected in contrasted depositional systems across sedimentary surfaces and gradational contacts. The studied Eocene deposits provide a sedimentary record of how volcanic events impacted warm-water carbonate factories, both in their disturbance, demise and recovery. [ABSTRACT FROM AUTHOR]

This study describes and interprets Upper Cretaceous volcaniclastics interbedded with hemipelagic to pelagic limestones, marls, and turbidites from the Western Pontides, northwestern Turkey. The Dereköy Formation, the Unaz Formation (red pelagic limestone unit), and the Cambu Formation can be distinguished, overlain by the turbiditic Akveren Formation. Biostratigraphic ages from the predominantly volcaniclastic Dereköy Formation indicate Turonian (Dicarinella concavata planktonic foraminifera zone, CC13/UC8-9 nannofossil zones) to middle/late Santonian ages up to CC17/UC13. The Unaz Formation, deposited during the late Santonian (UC13, Dicarinella asymetrica Zone), is overlain by the volcaniclastic Cambu Formation of latest Santonian (CC17b/UC13) to early/middle Campanian (CC20/UC15a) age. However, turbidite intercalations are already present diachronously from CC19/UC14d onwards, and the turbiditic Akveren Formation ranges up into the late Maastrichtian (Abathomphalus mayaroensis Zone). Geochemistry of the volcaniclastic units reveals information about the volcanic series and tectonic setting, although element mobility has to be considered. An overall trend of calc-alkaline to high-K calc-alkaline series and basaltic to basalt-andesitic rock types was identified. A negative Nb anomaly with respect to Th and Ce in all samples confirms the existence of a volcanic arc, also indicated by a negative Ti anomaly. Biostratigraphic age constraints give evidence for volcanic arc activity mainly between Turonian and early Campanian, ca. 91 - 79 Ma. Various geochemical data, especially element variations normalized to N-MORB, show two types of volcanic arc basalts (VAB): (1) Calc-alkaline to high-K calc-alkaline VAB have increased Nb and Zr values, (2) more tholeiitic VABs are depleted in Nb, Zr, Ti, V. The volcaniclastics successions were deposited in an arc setting triggered by different stages of subduction of the Neotethys Ocean to the south and contemporaneous spreading in the Western Black Sea Basin to the north. An extensional regime caused formation of small but deeper-water sedimentary basins along the southern shore of the Black Sea where volcaniclastic complexes interfingered within short lateral distances with pelagic and mass-flow deposits. [ABSTRACT FROM AUTHOR]

Underground mining and deep drilling of the richly diamondiferous ~1.2 Ga Argyle lamproite in Western Australia has prompted a re-evaluation of the geology of the pipe. Argyle is considered to be a composite pipe that formed by the coalescence of several diatremes and has been offset and elongated by post-emplacement faulting. Recent geological studies have recognised at least five distinct volcaniclastic lamproite lithofacies with differing diamond grades. The new data suggest that the centre of the southern (main) diatreme is occupied by well-bedded, olivine lamproite lapilli tuff with very high diamond grades (>10 ct/t). Characteristic features include a clast-supported fabric and high modal abundance of densely packed lamproite lapilli and coarse-grained, likely mantle-derived olivine now replaced by serpentine and/or talc. The persistence of small-scale graded and cross-bedding in this lithofacies to depths of ~1.5 km below the original surface prior to erosion suggests phreatomagmatic volcanism forming the diatreme was syn-eruptively accompanied by subsidence of the tephra, maintaining a steep-walled diatreme in the water-saturated country rock sediments. [ABSTRACT FROM AUTHOR]

DOI: 10.17014/ijog.v5i2.94Volcaniclastic rocks exposed in the Tanjung Balit area, West Sumatra, are red in color, loose, soft, and fractured. The rocks are strongly altered to be clay with calcium (CaO) and natrium (Na2O) contents extremely low (0.02 and maximum 0.30wt% respectively), and high loss of ignition (LOI) (4-15wt%). Mobile minor elements such as strontium (Sr), rubidium (Rb), and lanthanum (La) are also changed as their values do not fit to a normal contents range of fresh volcanic rocks in general. Geochemical analyses of the rocks resulted in the following oxide values: silica (SiO2) ranges from 58 – 68wt%, alumina (Al2O3) 15,90 – 21,46wt%, magnesium (MgO) 1, 36 – 1.61wt%, iron oxides (Fe2O3) 4,8-6,9wt%, potassium (K2O) 2,73 - 4,23wt% and titanium (TiO2) 0,60 - 0,70wt%. In general, the element contents especially the immobile ones (Ti, Mg and Fe) show that the rocks were originated from magmatic activity, which is also supported by petrographical characteristics that are still showing felspar and quartz minerals relicts. Based on SiO2 versus K2O diagram, these rocks are classified as high K-calc-alkaline series and belong to an intermediate composition. The rocks of the above criteria such as high alumina, very low magnesium and less than 1% titanium are one of the evidences that they are a magmatic arc product. The trace element of the rocks is summarized on the spider diagram; here their patterns strongly resemble to the typical of magmatic arc as well with enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and heavy REE (HREE). Trace element pattern and REE suggest they were originated from a high K- calc-alkaline magma source.

Volcaniclastic fall deposits in ICDP drilling cores from Lake Van, Turkey, contain sodium-rich sanidine and calcium-rich anorthoclase, which both comprise a variety of textural zoning and inclusions. An age model records the lake’s history and is based on climate-stratigraphic correlations, tephrostratigraphy, paleomagnetics, and earlier 40 Ar/ 39 Ar analyses (Stockhecke et al., 2014b). Results from total fusion and stepwise heating 40 Ar/ 39 Ar analyses presented in this study allow for the comparison of radiometric constraints from texturally diversified feldspar and the multi-proxy lacustrine age model and vice versa. This study has investigated several grain-size fractions of feldspar from 13 volcaniclastic units. The feldspars show textural features that are visible in cathodoluminescence (CL) or back-scattered electron (BSE) images and can be subdivided into three dominant zoning-types: (1) compositional zoning, (2) round pseudo-oscillatory zoning and (3) resorbed and patchy zoning (Ginibre et al., 2004). Round pseudo-oscillatory zoning records a sensitive alternation of Fe and Ca that also reflects resorption processes. This is only visible in CL images. Compositional zoning reflects anticorrelated anorthite and orthoclase contents and is visible in BSE. Eleven inverse isochron ages from total fusion and three from stepwise heating analyses fit the age model. Four experiments resulted in older inverse isochron ages that do not concur with the model within 2σ uncertainties and that deviate from 1 ka to 17 ka minimum. C- and R-type zoning are interpreted as representing growth in magma chamber cupolas, as wall mushes, or in narrow conduits. Persistent compositions of PO-type crystals and abundant surfaces recording dissolution features correspond to formation within a magma chamber. C-type zoning and R-type zoning have revealed an irregular incorporation of melt and fluid inclusions. These two types of zoning in feldspar are interpreted as preferentially contributing either heterogeneously distributed excess 40 Ar or inherited 40 Ar to the deviating 40 Ar/ 39 Ar ages that are discussed in this study. [ABSTRACT FROM AUTHOR]

[Display omitted] The West Koryak and Koryak fold-and-thrust belts (FTB) are typical accretionary orogens that formed during subduction of the Paleo-Pacific plate beneath eastern Asia. The geological histories of the basins that formed across supra-subduction volcanic belts remain poorly understood. To address this research gap, this study presents the petrographic compositions and U-Pb ages of detrital zircons from Late Paleozoic –Campanian sandstones and assessed the provenance and tectonic histories of the active margins in northeast Asia. The Tolovka thrust sheet of Ust'-Belaya terrane is composed of sandstones of different ages and origin. The quartz arenites were deposited in a passive margin environment in the Late Mesoproterozoic–Early Neoproterozoic (?) time. The most likely provenances for detrital zircons were the eastern part of the Siberian craton. The maximum depositional age of the lithic arenites is Middle Triassic. The source of zircons may constitute a coeval and Early Carboniferous supra-subduction magmatic rock of the Koni-Taigonos volcanic belt. Berriasian-Valanginian volcaniclastics of the Mavrina thrust sheet of Ust'-Belaya terrane formed in the forearc basin of the Uda-Murgal volcanic belt. Early and Late Jurassic complexes were the main source for detrital zircons. Albian-Campanian volcaniclastics of the Algan terrane were deposited in continental slope basins along the Okhotsk-Chukotka convergent margin. A possible source for Precambrian-aged zircons was cratonic terranes of the Verkhoyansk-Kolyma FTB. The Ediacaran–Early Cambrian detrital zircons were sourced from subducted-related complexes of the West- Koryak FTB. The Carboniferous-Late Cretaceous detrital zircons were derived from a supra-subduction of volcanic belts. [ABSTRACT FROM AUTHOR]

Strike-slip basins are one of the most important accumulation spaces for sediment of terrigenous, biogenic, and volcanic origins, and generally include large amount of event deposits. Although these event deposits are important basin filling process, research on this topic, particularly the effects of event deposits, is insufficient. In this study, we discuss sedimentation features based on grain composition and other properties for ca. 3000 year periods in Beppu Bay, which is strike-slip basin located at the western end of an arc-bisecting dextral fault known as Median Tectonic Line (MTL) associated with the northwestward subduction of the Philippine Sea Plate. This sediment is composed of hemipelagic clay and coarser event layers of turbidites referred to as types A, B, and C; ash layers referred to as type D; and other referred to as type E. The turbidite event layers, which accounted for 92% of the total major event layer, with >1 cm thickness, consist of particles related to volcanism, including hydrothermal activity. The events control the regional filling rate and transportation of coarse and heavy volcaniclastic materials. In particular, type A, which accounted for 73% of the total major event layer thickness, is likely induced by earthquakes related to the MTL, according to its age. As a result, the basin filling processes are controlled mainly by tectonics related to the subduction of the Philippine Sea Plate. [ABSTRACT FROM AUTHOR]

The geothermal potential of the Valley of Mexico has not been addressed in the past, although volcaniclastic settings in other parts of the world contain promising target reservoir formations. An outcrop analogue study of the thermophysical rock properties of the Neogene rocks within the Valley of Mexico was conducted to assess the geothermal potential of this area. Permeability and thermal conductivity are key parameters in geothermal reservoir characterization and the values gained from outcrop samples serve as a sufficient database for further assessment. The mainly low permeable lithofacies types may be operated as stimulated systems, depending on the fracture porosity in the deeper subsurface. In some areas also auto-convective thermal water circulation might be expected and direct heat use without artificial stimulation becomes reasonable. Thermophysical properties of tuffs and siliciclastic rocks qualify them as target horizons for future utilization of deep geothermal reservoirs. [ABSTRACT FROM AUTHOR]

In-situ soft sediment deformation structures (SSDS) are commonly used as paleoseismic indicators in marine and lacustrine sedimentary records. Earthquake-related shear can deform sediment in the shallow subsurface through Kelvin-Helmholtz instability. The SSDS related to Kelvin-Helmholtz instability have been used to quantify shaking strength of past earthquakes. However, the relative importance of i) lithology and physical properties, ii) potential basal shear surfaces (e.g. clastic deposits), iii) slope angle, and iv) seismic shaking strength (e.g. peak ground acceleration) for deformation related to Kelvin-Helmholtz instability remains poorly studied. Lake Riñihue (south-central Chile) is chosen as a natural laboratory for disentangling the effect of the aforementioned factors because i) the sediment composition of background sediment varies downcore and ii) volcanogenic clastic deposits are abundant within the sedimentary sequence. A previous study at lake Riñihue identified 25 SSDS intervals induced by historical earthquakes of varying rupture extent in 17 sediment cores taken at slope angles ranging from ~0.2° to ~4.9° (i.e. 16 slope sites and 1 basin site). Our study shows that deformation mostly occurs directly above volcanogenic deposits (i.e. 72 % of SSDS intervals), suggesting that volcanogenic deposits promote earthquake-induced deformation by strain softening, liquefaction or water film formation. Deformation thickness of SSDS increases with higher slope angles (i.e. strong positive correlation). Additionally, deformation thickness commonly corresponds to the stratigraphic depth of the youngest preceding volcanogenic deposit, but for steeper slope angles stratigraphically older volcanogenic deposits can function as basal shear surface. Therefore, we suggest that deformation thickness is primarily regulated by gravitational stress (i.e. slope angle) and secondarily by the stratigraphic depth of volcanogenic deposits. The earthquakes related to strongest shaking caused almost exclusively SSDS with highest deformation degrees (i.e. folds and intraclast breccia) as well as largest spatial extent of SSDS, resulting in highest numbers of related SSDS in the investigated cores. Thinner SSDS have higher deformation degrees at a given shaking strength, as seismically-induced shear energy acts more effectively on thinner deforming sequences. Therefore, we suggest that deformation degree is primarily controlled by shaking strength and secondarily modulated by the thickness of the deforming sequences. We infer that deformation thickness is not a reliable indicator of paleoseismic shaking strength as this relies on many preconditioning factors independent of shaking strength. On the other hand, deformation degree can be a good proxy for shaking strength also in settings with varying lithotypes and intercalated clastic event deposits, provided multiple cores are studied to avoid under- or overestimation of paleoseismic shaking strength. [ABSTRACT FROM AUTHOR]

Volcaniclastic horizons near the Guadalupian-Lopingian Boundary (G-LB) from southwest China have attracted much attention, not only due to the End-Guadalupian mass extinction near the boundary, but also to the unique and regionally extensive Nb-Zr-REY-Ga mineralization with potential economic significance (REY = rare earth elements and Y). Previous studies have suggested that these horizons were derived from volcanism associated with the terminal phases of the Emeishan mantle plume, which however was not the only contemporaneous volcanic activity in southeast Asia at this time (~260 Ma). Here we present a systematic analysis focusing on the petrological, mineralogical, and geochemical features of the volcaniclastics from the Yiliang and Weixin boreholes from the lowest strata of the Late Permian Xuanwei and Longtan formations, respectively, eastern Yunnan, SW China. In addition, previous geochemical data obtained for the correlative layers near the investigated boreholes were used for reference. The mineralogy of the volcaniclastics is dominated by mixed-layer illite/smectite, illite, berthierine, kaolinite, and quartz, and to a lesser extent, albite, calcite, siderite, anatase, and hematite, along with traces of chamosite, rutile, and florencite. Additionally, zircon, pyrite, chalcopyrite, sphalerite, galena, rhabdophane, parisite, goyazite, and barite were identified under SEM-EDS. The values of Al 2 O 3 /TiO 2 in the volcaniclastic samples are mostly greater than eight, consistent with the characteristics of intermediate-felsic rocks. The Nb/Yb and Zr/TiO 2 vs. Al 2 O 3 /TiO 2 diagrams, and the chondrite-normalized REY distribution patterns of the samples collectively indicate that the Nb-Zr-REY-Ga mineralization was not only derived from the ELIP alkaline rocks, but also from the arc-related intermediate-felsic magmatic rocks from the Paleo-Tethys. However, the latter source for Nb-Zr-REY-Ga mineralization in SW China has not been previously reported. The two sources of clastic materials, i.e., from both within-plate/anorogenic magmatism and arc-related/orogenic magmatism, agree with previously-reported discrimination diagrams of ε Hf (t) vs. age and Hf/Th vs. Th/Nb in the zircon grains from the correlative claystones. In addition, the modes of occurrence of critical metals (Nb, Zr, REY, Ga) are identified in detail in this study. The results show that most of the HREE and almost all the Zr and Hf are in zircon; the LREE are dominantly in REE-bearing carbonates and phosphates; the Nb is largely in former Fe Ti oxide phases; and the Ga is predominantly in the clays. • Volcaniclastic horizons near G-LB are an extensive Nb-Zr-REY-Ga ore deposit. • The horizons originated from within-plate and arc-related magmatism. • The minerals in the horizons were dominantly altered from volcanic ashes. • The modes of occurrence of critical metals (Nb, Zr, REY, Ga) are revealed. [ABSTRACT FROM AUTHOR]

Abstract: During IODP NanTroSEIZE Expedition 322, four packages of tuffaceous sandstones (TST 1, 2, 3a, 3b) were recovered within a moderately lithified and bioturbated silty claystone succession in the Late Miocene (>7.6 to ~9.1Ma) upper part of the middle Shikoku Basin deposits. To assess the emplacement processes of the tuffaceous sandstones we investigate modal and geochemical compositions of 24 thin sections that reveal systematic vertical changes within each bed. TST 1, 2 and 3b are single beds whereas TST 3a is composed of at least two beds suggesting several rapidly succeeding sedimentation events. The beds are density-graded such that low-density pyroclasts including pumice lapilli are enriched at the top whereas dense lithic components and minerals are enriched at the bottom. The volcanic glass particles (pumice and shards) that are the dominant modal constituents of each sandstone bed have homogeneous geochemical compositions in each bed. Moreover, TST 1, 2, and 3a glass compositions overlap completely but TST 3b glass has a different composition, as is analogously observed for the mineral compositions. This unique multistage approach of sedimentological and geochemical methods facilitated the detailed investigation of distal volcano-derived, probably tsunamogenic, turbidites in order to contribute to the distinction between primary and secondary induced mass flows. We interpret that all tuffaceous sandstones were emplaced by turbidity currents that were formed during major explosive volcanic eruptions. However, while TST 1, 2, and 3a turbidity currents formed by the entry into the ocean of voluminous pyroclastic flows erupted at a volcano on mainland Japan, TST 3b was emplaced by a turbidity current formed by a shallow submarine or subaerial volcanic eruption at the Izu–Bonin arc where it collided with Japan. These results regarding distal turbidites encourage the revisiting of older marine deposits in the scope of hazard evaluation through past events, especially in regions near to volcanic sources. [Copyright &y& Elsevier]

There are coarse-grained deposits, especially composed entirely of volcaniclastics in the central part of the Cretaceous Eumsung Basin, far away from the basinal margins. Primary volcanic masses are not exposed on the surface in the adjacent areas. For unraveling the origin of the volcaniclastics, subsurface magnetotelluric as well as surface sedimentological data were examined. Two resistivity profiles of crossed lines ES2 and ES9 represent subsurface basinal and basin-fill structures of the Eumsung Basin. In the basin fills, four high-resistivity bodies of A, B, C, and D were found. Considering the basin-scale structure and forming process of the pull-apart Eumsung Basin, it is reasonable to infer that these isolated high-resistivity bodies formed as a result of volcanic intrusion/ extrusion into/upon the basin-fill. Therefore, the coarse-grained volcaniclastic deposits in the central part of the Eumsung Basin can be interpreted as the product of syn-sedimentary deposition of volcaniclastic material that was shed from an exposed part of subsurface volcanics in a relatively short distance. [ABSTRACT FROM AUTHOR]

Abstract: In Laos (Southeastern Asia), Late Paleozoic sediments were identified by early French explorations across Indochina during the late 19th century (Pavie missions), but little work was undertaken to characterize the sedimentological and stratigraphical context until now. From detailed sedimentological and paleontological studies, we propose an interpretation of the depositional environment and of the stratigraphic context of series located on the right bank of the Mekong River in the Luang Prabang Basin where three main formations were described. The silicoclastic Red Claystone Formation, attributed to alluvial plain environment, contains large fragments of unidentified dicynodonts. The Limestones and Sandstones Formation preserves a new macrofloral assemblage displaying affinities with Middle to Late Permian Cathaysian floras of South China. This assemblage occurs as an intercalation within marine calcareous sandstones that have yielded a marine fauna, including the ammonoid Pseudotirolites sp. which indicates a Late Permian (Changhsingian) age. The well-developed Purple Claystones Formation yielded an abundant and well preserved Late Permian fauna composed of a carnivorous amphibian and numerous Dicynodon cranial and postcranial elements. This formation shows a vertical evolution from braided river to alluvial plain with sheet-flood sand bed and bed-load rivers, with a constant supply of volcanic clasts. Results from the analysis of the paleontological associations in the Luang Prabang Basin suggest that a continental communication between Laurussia and the Indochina Block existed during the Permian, allowing for migration of the terrestrial Dicynodon fauna. [Copyright &y& Elsevier]

The basal Ordovician Třenice Formation represents an initial unit of the preserved infill of the Prague Basin. Volcanic admixture in sediments preserved in the south-western part of the basin suggests subaerial volcanic activity during the deposition of the Třenice Formation. Three principal lithofacies associations were defined within sedimentary record of the Třenice Formation based on petrography and observed sedimentary structures: I) graded conglomerates, ii) lithic sandstones and iii) volcanigenic deposits. The studied sediments were mostly deposited as subtidal sand dunes, locally interbedded with volcaniclastic rocks. They are considered deposits of a marine lower shoreface influenced by ebb-tide currents. Volcaniclastic intercalations are interpreted as deposits of debris flows and turbidity currents that redeposited volcaniclastic material derived from subaerial Křivoklát-Rokycany and Strašice volcanic complexes. [ABSTRACT FROM AUTHOR]

Abstract: The study of the Late Triassic Zamoranos Formation and the comparison to coeval carbonate units provides new insights into the evolution and palaeogeography of carbonate platforms during major rifting phases in the Earth''s history. The platform carbonates of the Zamoranos Formation record the last major transgression during the Triassic, and document the initial phase of the CAMP volcanism in the external Zone of the Betic Cordillera. New palynological data from the lower part of the Zamoranos Formation indicate a Middle Norian age. The entire succession is built up by limestones, dolomites, and ferruginous red detrital deposits with volcaniclastic breccias. The carbonates are interpreted as tidal and shallow marine sediments, deposited under arid conditions. The red detrital deposits appear in coastal environments in relation to a volcanic event, which triggered hydrothermal processes in these deposits and started the massive magmatic event associated with the Central Atlantic Magmatic Province (CAMP). The Zamoranos Formation was also recognized in the SW part of the Valencia Triassic and is correlated to the Imón Formation (Iberian Ranges), to the Isábena Formation (Pyrenees) and to other carbonate units of the W Tethys realm (Aquitaine, Tunisian Atlas, West Carpathians). These units indicate that an extensive epicontinental platform developed during the Late Triassic. [Copyright &y& Elsevier]

The volcaniclastic Tepoztlán Formation (TF) represents an important rock record to unravel the early evolution of the Transmexican Volcanic Belt (TMVB). Here, a depositional model together with a chronostratigraphy of this Formation is presented, based on detailed field observations together with new geochronological, paleomagnetic, and petrological data. The TF consists predominantly of deposits from pyroclastic density currents and extensive epiclastic products such as tuffaceous sandstones, conglomerates and breccias, originating from fluvial and mass flow processes, respectively. Within these sediments fall deposits and lavas are sparsely intercalated. The clastic material is almost exclusively of volcanic origin, ranging in composition from andesite to rhyolite. Thick gravity-driven deposits and large-scale alluvial fan environments document the buildup of steep volcanic edifices. K-Ar and Ar-Ar dates, in addition to eight magnetostratigraphic sections and lithological correlations served to construct a chronostratigraphy for the entire Tepoztlán Formation. Correlation of the 577 m composite magnetostratigraphic section with the Cande and Kent (1995) Geomagnetic Polarity Time Scale (GPTS) suggests that this section represents the time intervall 22.8–18.8 Ma (6Bn.1n-5Er; Aquitanian-Burdigalian, Lower Miocene). This correlation implies a deposition of the TF predating the extensive effusive activity in the TMVB at 12 Ma and is therefore interpreted to represent its initial phase with predominantly explosive activity. Additionally, three subdivisions of the TF were established, according to the dominant mode of deposition: (1) the fluvial dominated Malinalco Member (22.8–22.2 Ma), (2) the volcanic dominated San Andrés Member (22.2–21.3 Ma) and (3) the mass flow dominated Tepozteco Member (21.3–18.8 Ma). [ABSTRACT FROM AUTHOR]

Geochemical and Sr-Nd isotope data for Mesozoic greywackes of New Caledonia terranes, indicate a forearc tectonic environment at the Eastern Gondwanaland margin, but they support only minor continental influences. Detrital-zircon U-Pb age patterns for the greywackes in these terranes similarly reflect an active-margin tectonic environment of Late Triassic, Late Jurassic, and in particular mid-Cretaceous, depocentres which comprise much contemporaneous volcanic detritus, but also include minor sediment inputs from Precambrian-Early Paleozoic continental clastic rocks. The contemporary volcanic sources are probably now hidden within a former hinterland to New Caledonia, such as Lord Howe Rise or Marion Plateau. The older, continental sediment sources were probably in northeasternmost Queensland, and beyond the northern extremity of the New England Orogen. Such sediments could have been supplied on long rivers, and submarine longshore current systems outboard of the orogen. Alternatively, the depocentres could have been consolidated close to the contemporary Gondwanaland margin and then tectonically transported, as suspect terranes, southwards in Early Cretaceous times to their present New Caledonia position. [ABSTRACT FROM AUTHOR]

Abstract: Large-scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material. The post-eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology, exemplified here by the 1.8 ka Taupo eruption in the central North Island of New Zealand. This eruption generated voluminous fall deposits, then climaxed with emplacement of a c. 30 km3 non-welded ignimbrite over a near-circular area of c. 20000 km2. Approximately 90% of the area, but <50% of the ignimbrite volume, is represented by a landscape-mantling unit that covered the pre-eruption topography to a depth varying from c. 10 m in proximal areas to less than 15–30 cm distally. The remainder of the ignimbrite deposit is represented by landscape-modifying material that ponded in valley bottoms and depressions to thicknesses of up to 70 m, with no systematic variation in thickness with distance from source. The headwaters of many of the North Island''s largest rivers were impacted by both the primary pyroclastic fall and flow material. Large-scale post-eruption remobilisation of this material, coupled with the re-establishment of fluvial systems, occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub-environments. Following an initial period dominated by mass flows, re-establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits, a process often associated with the break-out of temporary lakes. Aggradational streams developed in these channels rapidly evolved from shallow, ephemeral, sediment-laden outbursts associated with flash flood events to deeper, permanent braided rivers, before declining sediment yields led to retrenchment of single thread rivers and a return to pre-eruption gradients and bedloads years to decades later. Typically the modern profile of many streams and rivers follow closely their pre-eruption profiles, and incision and erosion is overwhelmingly confined to the deposits of the eruption itself. Although the general remobilisation pattern is similar for all impacted river systems, detailed studies of the Waikato, Rangitaiki, Mohaka, Ngaruroro and Whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment. These reflect differences in catchment physiography and hydrology, and the volume and type of pyroclastic material deposited in each. Ultimately, the landscape response reflects the relative spatial distributions of, and the volumetric ratios between, the volumes of pyroclastic debris, water, and accommodation space in the basin (cf. Kataoka and Manville, this volume). [Copyright &y& Elsevier]

Abstract: There have been few quantitative studies of the effects of siliciclastic and volcaniclastic sediment influx on carbonate producing organisms from the geological record. This study presents the results of quantitative field, petrographic and acid digestion analyses of samples from three Cenozoic shallow-water mixed carbonate-volcani/siliciclastic depositional environments—the Miocene Wonosari Formation of south Java, the Miocene Batu Putih Limestone of east Borneo, and the Eocene Collsuspina Limestone of northeast Spain. Carbonate production in these systems is dominated by larger benthic foraminifera, coralline algae and corals. Analyses of the quantity, grainsize and type of volcani/siliciclastic sediment within these mixed successions have allowed assessment of the influence of these factors on shallow-water carbonate producers. Larger benthic foraminifera and coralline algae exhibit the greatest tolerance to siliciclastic sediment influx (abundant up to 55 and 38 wt.%, respectively) at a range of grain sizes (to coarse sand). Platy corals are also present within sediments containing a large proportion of insoluble material (<80%); however, these are limited to clay-dominated horizons with a maximum siliciclastic size of fine sand grade. Branching and massive corals exhibit the least tolerance to large quantities of insoluble material (usually <40% up to medium sand, and usually <25% up to very fine sand, respectively). These variations probably reflect organism: 1) mobility, 2) ability to self clean, 3) morphology and 4) feeding mechanisms relative to: a) sediment settling, b) turbidity, c) abrasion, d) energy, e) water depth, f) light levels, and g) nutrients. The influx of volcaniclastic and siliciclastic grains of comparable size does not appear to have any differential effect on carbonate producers; although corals may be more susceptible to damage by angular volcanic shards. Geologically averaged rates of clastic accumulation and their potential influences on carbonate producers inferred herein may be difficult to compare directly with the daily and seasonal fluctuations experienced by modern clastic influenced systems. However, this study may aid our understanding of the likely effects of increased clastic influx (today commonly anthropogenically related) to marine carbonate environments over longer time periods. [Copyright &y& Elsevier]

The Miocene Eoil Basin, SE Korea, is a small half-graben basin that was rifted by both extensional and dextral strike-slip deformations during backarc opening of the East Sea (Sea of Japan). The basin was filled by fluviolacustrine sediments and abundant basaltic and dacitic volcanic deposits. The Paljori Tuff is a 2-20-m-thick, basinwide dacitic volcaniclastic unit that is intercalated in the topmost part of a fl uviolacustrine formation. The tuff consists of two pyroclastic units (units II and III), which are underlain and overlain by two resedimented volcaniclastic units (units I and IV). Unit I at the base is composed mainly of fine-grained resedimented tephra; unit II is a massive and stratifi ed tuff produced by a dense pyroclastic density current that was ponded in the southwestern part of the basin; unit III is a massive lapilli tuff emplaced by a voluminous and turbulent pyroclastic density current that swept across the basin toward the northeast without ponding or blocking by intrabasinal highs and basin-margin relief; and unit IV at the top is composed of coarse-grained resedimented tephra. The general coarsening-up of these units, the lack of nonvolcaniclastic sedimentary interbeds, and the offset stacking of the units toward the northeast suggest an episodic, short-duration eruption from the southwest that waxed in mass-eruption rate and changed eruption style from phreatomagmatic to magmatic. These units show basin-scale variations in geometry, including: (1) thick accumulations of unit I in the northeastern and southwestern extremities of the basin; (2) ponding of unit II in the southwestern part of the basin; (3) truncation of unit III in the same area; and (4) thickening of unit IV toward the northeastern basin margin. These provide important clues to the distribution of and temporal changes in accommodation space and, hence, the configuration and structural evolution of the Eoil Basin. It is inferred that the greatest subsidence occurred at the southwestern and northeastern corners of the basin; the southwestnortheast-trending axes of the basin plunge gently toward the northeast, and the major intrabasinal faults of the basin were produced before the eruption of the Paljori Tuff. The basinwide preservation of the tuff and its fairly uniform thickness suggest that the basin was undergoing rapid extension and subsidence because of the onset of the rift climax. The Paljori Tuff shows that important clues to, and high-resolution records of the large-scale configuration and structural evolution of a sedimentary basin can be obtained from the study of lithofacies variations and the architecture of a single basinwide volcaniclastic unit. [ABSTRACT FROM AUTHOR]

Jeju Island is a Quaternary shield volcano built upon the Yellow Sea continental shelf off the Korean Peninsula. Decades of borehole drilling reveals that the shield-forming lavas of the island are underlain by extensive hydrovolcanic deposits (the Seoguipo Formation), which are about 100 m thick and show diverse depositional features. This study provides criteria for distinguishing between hydrovolcanic deposits formed by primary (pyroclastic) and secondary (resedimentation) processes in subaerial and submarine settings based on the observations of several selected cores from the formation. Five facies associations are identified, including: (i) primary hydrovolcanic deposits formed by pyroclastic surges and co-surge fallouts in tuff rings (facies association PHTR); (ii) primary hydrovolcanic deposits formed by Surtseyan fallout and related pyroclastic transport processes in tuff cones (facies association PHTC); (iii) secondary hydrovolcanic deposits formed by debris flows, hyperconcentrated flood flows, sheet floods and rill flows in subaerial settings (facies association RHAE); (iv) secondary hydrovolcanic deposits formed in submarine settings under the influence of waves, tides and occasional mass flows (facies association RHMAR); and (v) non-volcaniclastic and fine-grained deposits formed in nearshore to offshore settings (facies association NVMAR). The primary hydrovolcanic facies associations (PHTR and PHTC) are distinguished from one another on the basis of distinct lithofacies characteristics and vertical sequence profiles. These facies differ from the secondary hydrovolcanic and non-volcaniclastic facies associations (RHAE, RHMAR and NVMAR) because of their distinctive sedimentary structures, textures and compositions. The depositional processes and settings of some massive and crudely stratified volcaniclastic deposits, which occur in many facies associations, could not be discriminated unambiguously even with microscopic observations. Nevertheless, these facies associations could generally be distinguished because they occur typically in packets or sequences, several metres to tens of metres thick and bounded by distinct stratigraphic discontinuities, and comprise generally distinct sets of lithofacies. The overall characteristics of the Seoguipo Formation suggest that it is composed of numerous superposed phreatomagmatic volcanoes intercalated with marine or non-marine, volcaniclastic or non-volcaniclastic deposits. Widespread and continual hydrovolcanic activity, together with volcaniclastic sedimentation, is inferred to have persisted for more than a million years in Jeju Island under the influence of fluctuating Quaternary sea-levels, before effusion of the shield-forming lavas. Extensive distribution of hydrovolcanic deposits in the subsurface of Jeju Island highlights that there can be significant differences in the eruption style, growth history and internal structure between shelfal shield volcanoes and oceanic island volcanoes. [ABSTRACT FROM AUTHOR]

Abstract: Recent studies have confirmed the important role played by magmatism during the Late Carboniferous–Permian transition. In this report, we describe the characteristics of this magmatism in the Central Iberian realm (Iberian Ranges and eastern Spanish Central System) and discuss its palaeoenvironmental impact. In the studied area, the late-Variscan transtensional to extensional tectonic regime favoured the emplacement of a calc-alkaline magmatism during the Late Stephanian–Permian. This magmatism is expressed both as pyroclastic rocks filling small half-graben basins and hypabyssal intrusions (sills and dykes). Pyroxenic- and amphibolic-andesites are the main rock compositions, while basalt, dacite and rhyolite are less represented. The available K/Ar isotopic data suggests a Lower Permian age for this magmatism, also supported by its complete macro- and microflora content and by features related to its emplacement (hypabyssal intrusions crosscut Stephanian rocks and are in turn overlain by late Permian–Triassic sediments). Frequent xenoliths of middle and lower crustal levels indicate considerable magma–crust interaction. This interaction may have led to substantial crustal assimilation during the first emplacement stages in conditions of a low extension rate. Crustal contamination barely affected the final magmatic products emplaced under conditions of greater extension. The palaeoecological effects of explosive manifestations of this volcanism are expressed in the varied macroflora record in volcaniclastic basins. The number and volume of hypabyssal intrusions suggest that the original geological record of explosive activity in these basins was much greater and was reduced by subsequent erosion processes. [Copyright &y& Elsevier]

The spatial patterns of the Hawaiian silversword (Argyroxiphium sandwicense DC.) were studied in Haleakala (Maui, HI). The silversword is a “giant” rosette plant nearly brought to extinction by human impact and goat browsing during the 1920s, but stern protection has resulted in the resurgence of plant populations. Silversword regeneration is occurring vigorously in soils with surficial layers of volcaniclastic fragments. Ten sites with sizable silversword populations and the associated substrates were examined in Haleakala''s crater between 2175 and 2755 m. At each site, the population structure of 100 plants was determined along wandering-quarter transects, which limit sampling bias. Substrates where rosettes were rooted and the size of the biggest stone fragments upslope and downslope from the plant''s base were determined. Volcaniclastic substrates were examined with photographs along 12-m-long transverse transects. Fine-debris samples (gravel and pebbles) were analyzed by mechanical sifting of surficial fragments gathered from 15×15 cm miniplots.Volcaniclastic fragments in silversword areas have different sources. (i) Most were ejected during eruptions yielding pyroclastic materials (ash to blocks) that built cinder cones on Haleakala''s crater. (ii) On steep slopes, weathering of (olivine alkali) basalt outcrops and subsequent mass wasting of rock fragments contributed a mantle of clasts to slopes below. (iii) On some cinder cones, welded spatter was produced during late eruptive stages; this coalesced into ruff-like agglutinate layers around crater rims, called Pohaku-o-Hanalei (“wreath of stones”). Agglutinate deposits weather gradually, supplying clasts that roll downhill and accumulate on cone flanks. (iv) On weathered aa lava flows, stone fragments and rocky crags abound along eroding lava-flow ridges, associated with vegetation; but the intervening troughs, covered with fine ash and cinder, remain bare.Silversword population structures indicate healthy regeneration. All populations display a typical pattern of decreasing silversword numbers with increasing size (=age). Nearly 65% of the rosettes are rooted near cobbles (5–10 cm long) or pebbles (2.5–5 cm), and ∼23% grow at the base of blocks (>10 cm) or outcrops; 9% of the plants are on gravel (<2.5 cm), but only 1% have germinated on sandy soil without granules or stones; 2% of the silverswords grow on organic litter of dead rosettes. Plants on six sites showed noticeable differences in clast size between their upslope and downslope sides; particles are significantly larger upslope from rosettes. This suggests that successful seedlings germinate below clasts, which deflect finer downslope-moving sediment, thus protecting young plants from burial by descending debris. Statistical tests indicate a few blocks above plants may have been stopped by adult rosettes. Such a relationship underscores the dynamic nature of steep cinder and rubble (talus) slopes, regularly affected by dry debris slides, frost creep, and other mass-wasting processes. Slope instability is also evinced by (i) common bending and deformation of silversword roots—particularly in seedlings—which trail upslope; (ii) pronounced downhill tilting and asymmetry of tall rosettes on steep gradients; (iii) presence of accumulated fine-debris steps (9.9–13.8 cm thick) upslope from plants and blocks; (iv) ubiquitous fine-earth flags exposed below embedded blocks, which intercept descending debris and deflect it laterally; (v) widespread miniature sorted stripes. [Copyright &y& Elsevier]

New data pertaining to the origin of volcaniclastic fan delta deposits (the El Time group) and previously unreported toreva remnants (intact landslide blocks) are presented in terms of their relationships with the Quaternary flank destruction of Bejenado volcano on La Palma, Canary Islands. Bejenado volcano is the heavily dismantled relic of a stratocone which developed at the confluence of the Cumbre Nueva embayment and the Caldera de Taburiente collapse amphitheatre. Both of these giant landslide structures formed at around 0.55 Ma after ∼0.2 Ma of gravitational spreading on the western and eastern flanks of the Taburiente–Cumbre Nueva shield volcanic complex. Evidence is presented on the basis of stratigraphic, photogeologic and Geographic Information System studies that both the toreva remnants and the El Time group can be related to the sequential collapses of the north flank and summit region of Bejenado inside the Caldera de Taburiente and the northernmost part of the adjoining Cumbre Nueva embayment. The collapses probably occurred between 0.44 and 0.4 Ma and they involved a volume of around 5 km3. The toreva remnants display a deformed volcanic architecture, traversed by discontinuities which developed during impact and post-collapse dislocation during slip. They are composed of layer-differentiated scoria with ancillary ankaramite and basanite–tephrite lavas and occasional dikes. They rest upon a thin veneer of sheared volcaniclastic deposits in relative proximity to the disfigured north flank of Bejenado. The collapse event(s) is distinguished by its extremely low mobility due to the deceleration of the debris avalanche mass within the confines of the Caldera de Taburiente. The high friction coefficient (H/L=0.22) reflects this topographic factor. Reworking of the avalanche matrix gave rise to the accumulation and offshore progradation of the fan delta deposits at the SW base of Bejenado. Contemporaneous fluvial sediments, sourced by the retrogressive erosion of the pre-Bejenado collapse scarps, were fed into the subaerial confines of the Cumbre Nueva embayment. Piecemeal scarp failure and the extrusion of substratum from beneath the scarps also contributed to the sediment budget. The fluvial sedimentation rates subsequently increased with the onset of Cumbre Vieja volcanism prior to 0.125 Ma. These processes have contributed to the development of the flat-floored submarine channels which extend onto the volcaniclastic apron west of La Palma. These new data give a fresh insight into the role of epiclastic processes, landsliding and volcanism in the morphology and sediment mass balance of an oceanic island volcano system. [Copyright &y& Elsevier]

The Falkland Islands lie in a critical location for our understanding of Gondwana supercontinent break-up. Subsurface data obtained during recent exploration activity provide important new insights into the structure and stratigraphy of the North Falkland Basin''s Late Jurassic syn-rift fill history. Results of seismic interpretation indicate that deposition was largely controlled by prominent planar normal faults, which divide the basin into a series of north-south trending half-grabens and minor grabens. Well data (in the form of exploration wireline logs, cores, petrographic thin sections, major and trace element analyses) indicate that their syn-rift fill was dominated by abundant volcaniclastic sediment supplied through debris flows, hyperconcentrated flows and pyroclastic ash-fall. The geochemical affinity of the volcanic sedimentary components shows a direct link to the widespread, Middle Jurassic to Early Cretaceous, silicic Chon Aike Large Igneous Province, in southern South America and Antarctica. Diagenesis has obscured provenance information and severely reduced porosity within the syn-rift sediments, causing them to have poor reservoir potential.The results enable a radically new interpretation of this key period in the North Falkland Basin''s evolution, which helps modify and unify previously disparate views. It is now suggested that basin development was the direct result of the Chon Aike back-arc stretching, influenced in part by the underlying Palaeozoic basement trends. This was followed by Cretaceous-Recent post-rift thermal subsidence of the basin, which was only arrested by local structural inversion related to Atlantic opening. Consequently, it is thought that the extension that created the North Falkland Basin was independent of both Early–Middle Jurassic rotation of the Falkland Islands microplate and the evolution of the South Atlantic Ocean in the Cretaceous and Cenozoic. [Copyright &y& Elsevier]