Formation Mechanism and Prediction Method for the Permian Fused Breccia Tuff Reservoir, Wuxia Region, Junggar Basin

Fused breccia tuff occurs globally, but its formation mechanism is very controversial. Volcanic reservoirs have developed at the bottom of the Permian Fengcheng Formation in the Wuxia region of the Junggar Basin, and here, the lithology is fused breccia tuff. The reservoir porosity is mainly vesicles, but the development and relative filling of the vesicles vary spatially, resulting in strong reservoir heterogeneity. Through core and thin section observations and structural analysis, and combined with reconstructions of the paleosedimentary environment, we discussed in detail the formation mechanism of the fused breccia tuff reservoir. Our conclusions are as follows. In the high-temperature and high-pressure environment of the deep crust, intermediate acidic lava containing volatile components rapidly rose to the earth’s surface along a fault. The volatile components in the lava foamed strongly and then exploded due to the sharp decline of pressure and temperature. A small part of the volcanic dust and pyroclastic material was erupted into the upper atmosphere. Most of the magma became magmatic pyroclast, vitric pyroclast, rock debris, dust, and other matter. This material was in a semimolten state and overflowed into a nearby low-lying lake. The extremely high-temperature pyroclastic flow quickly vaporized the water into high-pressure water vapor, which was squeezed into the pyroclastic flow and became mixed with other volatiles in the foam. On cooling, the pyroclastic material solidified into rock, and the vesicles were preserved. In a later period, due to strong tectonic movement, faults and fractures developed, surface water penetrated into the vesicles along the faults and fractures, and silica and other substances were deposited, filling the primary vesicles. To quantify the development and relative filling of vesicles, drilling parameters were used to establish different geologic models, and wave equation forward modeling was used to obtain a relationship between the development and filling of vesicles, and the seismic amplitude. The 3D seismic amplitude attributes were then extracted to predict the extent of the reservoir, yielding prediction results consistent with the drilling observations.

Resistivity Data Modeling for Subsurface Volcanostratigraphy Construction of Cibadak Sub-Watershed, Bogor, West Java, Indonesia.

In Mt. Salak, there are six volcanic facies divided by eruption time seen from geomorphology data analysis and to identified the subsurface layer DC Resistivity method is applied. Beside resistivity, geostatistical parameters also influence the result model interpretation, so for obtain best model correlation parameters such as tilting, surfacing, variogram, grid method, and logarithmic distribution is applied. Using 18 points of acquisition data subsurface model is produce and then section model made to describe vertical resistivity distribution then correlated with facies lithology model. Based on that, produce three facies resistivity type namely: 0 – 100 Ohm.m (Low Resistivity Value) Interpreted as pyroclastic material composed as tuff and breccia that lies under lava. 100 – 300 Ohm.m (Medium Resistivity Value) Interpreted as breccia lithology type. Harder that pyroclastic material due to by this product is avalanches of lava. And >300 Ohm.m (High Resistivity Value) Interpreted as lava lithology that lies at high elevation and the hardest lithology in this area. From the model, pyroclastic layer that is modeled found at low elevation and based on the direction it described as oldest facies layer, but at the bottom of this layer lies high resistivity value that unknown product. It can be Mt. Pangrango product due to at low elevation predicted as combine area product from product of Mt. Salak and Pangrango. High resistivity value show lava lithology and lava facies located in high elevation and medium resistivity describe breccia lithology as avalanche product of lava (youngest pyroclastic facies) and found at 500 – 100 meters msl.

Volcanogenic material in upper jurassic-lower cretaceous deposits of the Eastern Russian plate and its sources

. Widespread “camouflaged” pyroclastics including smectite, illite-smectite and heulandite are detected in the upper jurassic– lower cretaceous deposits of the Ulyanovsk-Saratov basin. Moreover, volcanic glasses are found in several stratigraphic units. The quantity of pyroclastic material in the study section (17–72%) is probably related to volcanic input in the basin. Concentrations of the trace and rare earth elements point to a predominantly acid source of ash material, except the Promzino and Ulyanovsk black shale formations linked to the mixed andesite-basaltic and felsic sources. Island arcs of the Northern Tethys basin and the High-Altitude Arctic Igneous Province are regarded as probable sources of the pyroclastic influx in the epeiric basin of the Russian Platform in the Jurassic-Early Cretaceous.

Results of 40Ar/39Ar dating of subvolcanic body in the vent tunnelKukurtly volcano

Эльбрус изучается с 1852 г., однако вопросы о времени его образования и временных этапах эволюции до сих пор остаются дискуссионными. По мере развития новых методов датирования геологических событий исследователями Эльбру- са применялись все более современные методы и методики. Так, на самых ранних этапах исследований время образования вулкана приблизительно оценивалось только по геологическим данным, затем стал очень широко применяться геолого-гео- морфологический метод относительной геохронологии, а с конца прошлого столетия – калий-аргоновый (K-Ar), аргон-арго- новый (40Ar/39Ar), иониевый (Io/234U) и радиоуглеродный (14C) методы датирования. В полученных вышеуказанными методами датировках (цифрах возрастов) по одному и тому же объекту часто имелись существенные различия. При 40Ar/39Ar датировании биотита из туфов риолитового состава раннего этапа кальдерной стадии было доказано, что при эксплозивных извержениях, приведших к формированию этих туфов и ассоциирующих с ними игнимбритов, был захвачен дезинтегрированный материал древнего гранитно-метаморфического основания Эльбруса, который после аэрального пере- носа стал составной частью туфов и игнимбритов. Следовательно, все изотопные датировки этого пирокластического материала (по биотиту, пироксену, плагиоклазу) не отражают время образования рассматриваемых пород, так как они со- держат мельчайшие обломки древнего гранитно-метаморфического фундамента и слагающего их породообразующего био- тита, что, естественно, искажает изотопный возраст пирокластики в неизвестном масштабе. Устойчивое плато при ступенчатом нагревании пробы № 542 мегакристалла санидина однозначно свидетельствует об от- сутствии избыточного аргона, а полученный аргон-аргоновый возраст (620.3±3.3 тыс. лет) отражает время остывания кри- сталла санидина при температуре закрытия системы ~ 300о С и свидетельствует об отсутствии значительного перерыва во времени между формированием пород раннего и позднего этапов кальдерной стадии. Ключевые слова: вулкан Эльбрус, 40Ar/39Ar датирования, субвулканическое тело дацитового состава, жерло вулкана Кюкюрт- ли, удревнение или омоложение изотопного возраста. Elbrus is under study since 1852 year, however the questions about time of it origin and temporal stage of evolution, up to now are remains as a discussional.So far as development of a new method for dating of geological events, investigators of Elbrus using all more current status of methods and procedures.So, on the very early stages of investigation, time of volcano origin approximately assessed by geological data only, then -geologo-geomorphological method of relative geochronology became in very regular use and from last century - potassium-argon (K-Ar), argon-argonian(40Ar/39Ar), ionic (Io/234U) and radio-carbon(14C) methods of dating. Inobtainedbytheabovementionedmethodsofdating (fi gureofage) oncommon poles object very often there was an fundamental dissimilarities. As a result of 40Ar/39Ar dating of biotite from tuff of the rhyolite composition of early period of calderian stage, it was proved, that during explosive eruption, lead to forming of these tuff and associated ignimbrites, the old disintegrated material of granite-metamorphic basement of Elbrus was encroach and which after aeral transportation became as a constituent part of tuff and ignimbrites. Consequently, all isotope age determination of this pyroclastic material (on biotite, pyroxene, plagioclase) do not take account of time origin of covered rocks, as they contain a very small debris of old granite-metamorphic basement and rock-building biotite, that natural, to distort of isotope age of pyroclastics in unknown scale. The tolerant plateau at scalariform heating sample № 542 - megacrystal of sanidine is uniquely testifi es about absence of excess argon and argon-argon age (620.3±3.3Ka) obtained is accounts time of cooling down ofsanidinemegacrystal at the temperature of clousing of the system - 3000 C and testifi es about absence of signifi cant interruption in time between rock forming of early and late periods of calderian stage

Plinian eruptions and their impact on human settlements: stratigraphy of the 79 AD Vesuvius fall deposits and detailed study of their downwind and substrate-induced variations inside the archaeological excavations of Pompeii and Stabiae (southern Italy)

<p>Plinian eruptions are highly energetic events that release cubic kilometres of magma in the form of pyroclastic material (pumice, lithic clasts and ash). These products tend to accumulate near the vent with considerable thickness. The rapid burial of the territory around the eruptive centre makes these eruptions extremely dangerous. For this purpose, the renowned 79 AD Vesuvius eruption, which destroyed the ancient cities of Pompeii and Stabiae (where Pliny the Elder founds his death) located respectively 10 and 15 km from the vent, was studied in detailed. The recent excavations carried out in collaboration with the Archaeological Park of Pompeii, both in Pompeii and in the Stabian villas, have shown the complete sequence of products of the 79 AD eruption that destroyed and covered these Roman cities. The discovery of thick sequences of reworked material accumulated during previous excavations, testifies for the presence of underground tunnels dug for the Royal House of Bourbon. Fall products of the 79 AD eruptive sequence, accumulated during the main Plinian phase and the successive sustained column phases, were studied in detail to investigate their sedimentological characteristics and how these were influenced by anthropic structures. Results from field investigation show that in both archaeological sites, fall deposits consist of white and grey pumice lapilli in the lower part of the eruptive sequence (units A and B), and of thin, lithic-rich layers interstratified to ash products emplaced by pyroclastic currents, in the highest part of the pyroclastic deposit (units D, G1, G3, I). A new thin lithic-rich layer (X2) has been observed near the top of the sequence at Stabiae. The internal structure of the Plinian pumice lapilli deposit appears weakly stratified in open areas, while it is strongly stratified near steep roofs (e.g., impluvium areas), where the deposit thickens. The observed stratification is confirmed by a significant variation of sedimentological parameters with the stratigraphic height (e.g., median ranging from -3.5 to -0.1), possibly related to fluctuations in the eruptive parameters. Locally, rolling of pyroclastic clasts on sloped roofs produced a well-stratified deposit with laterally discontinuous layers and rounded clasts. Several roofing-tiles, either intact or in fragments, were recovered at various stratigraphic heights in the pumice lapilli deposit both at Pompeii and Stabiae.  These tiles testify for the progressive collapse of the roofs under the increasing load of the falling lapilli clasts.</p>

The AD 79 Vesuvius eruption: stratigraphy, lithofacies variations and impact of the pyroclastic current deposits within the archaeological sites of Pompeii and Stabiae (southern Italy)

<p>Plinian eruptions are powerful explosive volcanic events that impact large areas with cubic kilometers of magma emplaced as pyroclastic material accumulated in thick blankets around the volcanic vents. The violence of the emplacement mechanism (i.e., fallout or pyroclastic density currents, PDC) and the sudden burial of the landscape, make these types of eruptions extremely dangerous. Aiming to fully understand these phenomena, an accurate reconstruction of the physical behaviour and the historical record of a volcano is critical as starting point for the assessment of volcanic hazard. In this scenario an excellent case is the worldwide-known Plinian AD 79 Vesuvius eruption, which destroyed Roman towns with large effects preserved in different sites around the volcano. This study reports the results of a collaboration between the Archaeological Park of Pompeii and the University of Napoli Federico II to document the stratigraphic sequence and the type and extent of damage and victims buried under meters of pyroclastic material within the Pompeii and Stabiae archaeological sites. A systematic survey of well exposed outcrops along the recent excavations front allowed us to study in detail the facies variations of the different PDC stratigraphic units and how their distribution is affected even by urban structures. At Pompeii, the stratified ash PDC succession ranges in thickness from few tens of centimetres to two metres and shows considerable vertical and lateral variations in its sedimentological features. The layer associated with the most destructive impact on the Roman buildings shows down-current variation in thickness (0 to 330 cm) and texture. Where it is less than 30 cm thick, the deposit is fine-grained and thinly stratified, with few rounded pumice clasts scattered inside the matrix. Where it thickens, the lower part is rich in coarse pumice lapilli and locally shows well-developed stratifications, while the upper part shows an internal arrangement of alternating layers of fine and coarse ash, forming progressive bedforms. Upwards, the sequence is made up of a succession of plane-parallel ash layers with rare pumice lapilli clasts and diffuse accretionary lapilli. This ash sequence is interstratified with four well-sorted, thin lithic-rich layers that exhibit mantling structures of fall deposits. All PDC layers, except the lowermost, are dispersed across the entire Pompeii area, although some are locally missing as a result of the erosive action of the following PDC. At Stabiae, the ash PDC sequence is 83 cm thick. In few rooms of the Roman villa the ash deposits thicken up to 150 cm. Most of the ash layers identified at Pompeii are recognized also at Stabiae. In the upper part of the sequence a new PDC layer, never reported at Pompeii, is here documented for the first time. Damages are documented inside the more destructive ash layer and even in the upper ash layers, providing new insights about the risk assessment in distal areas.</p>

Towards a better understanding of the role of glacier retreat and permafrost degradation in triggering secondary lahars

<p>As everywhere in the Andes, tropical glaciers have been rapidly retreating since several decades. The glaciers of Cotopaxi volcano, Ecuador, have been reduced in area by about 50% since 1976 (Cáceres, 2017). The Cotopaxi is mostly famous for its capacity to produce massive lahars during volcanic eruptions, but comparably smaller, secondary lahars generated in post-eruptive periods by heavy rainfall occur more frequently on the volcano’s flanks. However, since a few years, secondary lahars that originate in proglacial areas without any clear trigger mechanism are recorded at Cotopaxi. This raises the question of whether there exists a process-based link between the occurrence of secondary lahars and the retreat of cold-based glaciers with accompanied permafrost degradation in the former subglacial frozen pyroclastic material over the following years and decades.</p><p>Here, we present the data obtained from laboratory-calibrated Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT) conducted near the glacier margin between 5000 and 5300 m asl, which provide a better understanding of frozen/unfrozen conditions and the structure of the subsurface. In addition, data loggers have been recording surface air temperatures close to the glacier since May 2018. Our measurements show that permafrost cannot develop under current thermal conditions, but high electrical resistivities at depths of 10-20 m correspond to calibrated rock temperatures below 0 °C. The detected frozen lenses may act as detachment planes of periglacial secondary lahars in pyroclastic material recently exposed by glacier retreat.</p><p> </p><p>Cáceres, B. (2017). Goal workshop 2017 Mexico 135 Evolución de los glaciares del Ecuador durante los últimos 60 años y su relación con el cambio climático. Conference paper: The role of Geosciences to societal development: A German-Latin American Perspective. GOAL Geo-Network of Latin American-German Alumini. P. 149. México: UANL-Monterrey-México.</p>

Терригенное лавинное осадконакопление на примере пермских толщ Охотского и Аян-Юряхского бассейнов (Северо-Восток Азии)

Terrigenous avalanche sedimentation in Northeast Asia is considered on the example of the Permian strata of the Okhotsk and Ayan-Yuryakh basins. These deposits form a complicated sedimentary complex undergoing regular changes in the direction from the southwest (from the Okhotsk massif) to the northeast (to the Ayan-Yuryakh anticlinorium) - from continental and coastal-marine environments to deep-water, corresponding to the conditions of the foot of the continental slope. An important specific feature of this basins is the widespread development of deep-water deposits, primarily of various types of gravitites, among which facies of proximal and distal turbidites, grain and clay flows, and diamictites (debrites) can be distinguished. The facies of nepheloidites and disturbed-bedded deep-water siltstones also play a significant role. Shallower sediments are less widespread and were formed within the shelf of the Okhotsk massif. They are represented by facies of coastal sandstones, sandstones and siltstones of the inner part of the shelf and siltstones of the outer part of the shelf. Almost all types of rocks contain one or another fraction of pyroclastic material, the amount of which increases with approaching the Okhotsk massif, where some probable centers of eruptions of the Okhotsk-Taigonos volcanic arc were located. In the evolution of the basins under consideration, the general stages in the development of the entire system of northeast Asian basins are clearly established, which was obviously determined by reasons of a global scale. The first three stages correspond to the regional superhorizons (Munugudzhakian, Dzhigdalian, and Omolonian), the last three, to the Gizhigian Horizon and subhorizons of the Khivachian Horizon).

Controls on Associations of Clay Minerals in Phanerozoic Evaporite Formations: An Overview

Information on the associations of clay minerals in Upper Proterozoic and Phanerozoic marine evaporite formations suggests that cyclic changes in the (SO4-rich and Ca-rich) chemical type of seawater during the Phanerozoic could affect the composition of associations of authigenic clay minerals in marine evaporite deposits. The vast majority of evaporite clay minerals are authigenic. The most common are illite, chlorite, smectite and disordered mixed-layer illite-smectite and chlorite-smectite; all the clay minerals are included regardless of their quantity. Corrensite, sepiolite, palygorskite and talc are very unevenly distributed in the Phanerozoic. Other clay minerals (perhaps with the exception of kaolinite) are very rare. Evaporites precipitated during periods of SO4-rich seawater type are characterized by both a greater number and a greater variety of clay minerals—smectite and mixed-layer minerals, as well as Mg-corrensite, palygorskite, sepiolite, and talc, are more common in associations. The composition of clay mineral association in marine evaporites clearly depends on the chemical type of seawater and upon the brine concentration in the evaporite basin. Along with increasing salinity, aggradational transformations of clay minerals lead to the ordering of their structure and, ideally, to a decrease in the number of minerals. In fact, evaporite deposits of higher stages of brine concentration often still contain unstable clay minerals. This is due to the intense simultaneous volcanic activity that brought a significant amount of pyroclastic material into the evaporite basin; intermediate products of its transformation (in the form of swelling minerals) often remained in the deposits of the potassium salt precipitation stage.

Smectitization as a Trigger of Bacterially Mediated Mn-Fe Micronodule Generation in Felsic Glass (Livno-Tomislavgrad Paleolake, Bosnia and Herzegovina)

Miocene tuffs preserved in argillaceous sediment interbedded with lacustrine successions are commonly encountered throughout the Dinarides Lake System (DLS) in south-eastern Europe. In this contribution the volcanic glass degradation and co-genetic Mn-Fe precipitation were studied in a 14.68 Ma felsic tuff from DLS Livno-Tomislavgrad Basin. Microbial activity has been involved in both reactions thus adding the interest of revealing effects of biotic and abiotic processes taking place during tuff eogenesis. X-ray diffraction and electron microbeam analysis with energy-dispersive X-ray spectroscopy revealed the pitting or granular structures developed at glass rims along with smectite flakes protruding from a degrading glass. Mn-Fe mineralization emerges in the form of Mn-Fe coatings, an initial step to micronodule formation, where traces of biogenetic influence included a high content of phases rich in structural Mn (IV) (i.e., ranciéite and jacobsite) and presence of microbial microfossils. Co-genetic ties between glass degradation and Mn-Fe precipitation were established through the report of dioctahedral smectite formed out of altered glass; which then served as nuclei of the ongoing biotic and abiotic Mn-Fe mineralization. These processes manifest on a continuous involvement of microbial life in the course of eogenesis of pyroclastic material in lacustrine environments.