Tuffaceous Matrix Research Articles

Provenance of Volcanogenic Deposits from the Shanxi Formation of the Daniudi Gas Field, Ordos Basin, and Its Tectonic Implications

Through detailed drill-core description, petrography, cathodoluminescence imaging, and geochemistry analysis, sedimentary deposits with a high content of volcanogenic components (27.6%) were discovered in the Shanxi Formation of the Daniudi Gas Field, Ordos Basin. The volcanogenic components include volcanogenic quartz, lava fragments (dominated by rhyolite fragments), tuff fragments, and tuffaceous matrix. In addition, at least two volcanic ash layers were discovered. Although the metamorphic rocks of the Precambrian succession in the ancient land of Yin Mountain are usually considered the primary source of the Shanxi formation, it is most likely that the volcanogenic components were derived from intermediate-acid volcanic materials that accumulated in the Daqingshan area during the Late Carboniferous to Early Permian. Those volcanogenic components are mainly transported by flowing water rather than by air from origin to basin. In addition, the accumulation of volcanic materials in the Daqingshan area was controlled by volcanic eruptions occurring solely in this area, rather than by the Inner Mongolia Orogenic Belt. Those volcanic eruptions were related to the southward subduction of the Paleo-Asian Ocean Plate beneath the northern margin of the North China Plate in the Late Carboniferous to Early Permian. The active continental margin related to the subduction of the Paleo-Asian Ocean Plate lasted at least until the Early Permian, and the closure of the Paleo-Asian Ocean must have occurred later than the Early Permian.

Prediction of uniaxial compressive strength of the Kızılkaya ignimbrite with variable properties using MRA and ANN, Cappadocia (Turkey)

Cappadocia in Turkey is an important region with emphasis on ethnic and historic structures and geological features. Because of volcanic eruptions, ash flow materials deposited at different levels. These different colored ignimbrite levels have a wide range of geomechanical properties. In the region, the Kızılkaya ignimbrite covers a very large area and is frequently used as building dimension stone in for the restoration of old historical buildings such as churches, caravansaries and mosques as well as new buildings. It contains tuffaceous matrix with some minerals and rock fragments. The rock has variable character. In this study, the relationship between petrographic and physico-mechanical properties of the Kızılkaya ignimbrite was investigated. Rate of change between uniaxial compressive strength and the other index properties of the rock was statistically examined utilizing multiple regression analysis (MRA) and Artificial Neural Network (ANN) methods. The study has shown that uniaxial compressive strength (UCS) of the ignimbrite can be successfully estimated by the use of dry unit weight, effective porosity, sonic velocity, and grain matrix ratio (GMR) parameters. A new UCS prediction equation is proposed in this paper for the ignimbrite with variable character. Since properties of the ignimbrite at different distances from the eruption area changes significantly, the approach presented in this study can be considered for the ignimbrites especially covering a large area with different welding degrees and grains.

Diagenetic variations with respect to sediment composition and paleo-fluids evolution in conglomerate reservoirs: A case study of the Triassic Baikouquan Formation in Mahu Sag, Junggar Basin, Northwestern China

Understanding reservoir heterogeneity and associated diagenesis, have a paramount importance for efficient petroleum exploration and development strategies. Diagenetic variations and factors that control these processes have, therefore, been investigated in this study using petrographic and geochemical methods, including cathodoluminescence, scanning electron microscopy, x-ray fluorescence, electron probe microanalyses and stable isotope analysis. Mechanical compaction and chemical diagenesis trends have obviously varied as a function of rock types and geological locations. The conglomerate reservoirs with high content of tuffaceous matrix and characterized by poor sorting showed stronger compaction. The tuffaceous matrix displays a large degree of dissolution during the progressive burial diagenesis due to its thermodynamic instability. The tuffaceous matrix in Na-rich conglomerate reservoir rocks mainly transformed into analcite, while it transformed into illite in K-rich conglomerate reservoir rocks. In most conglomerate reservoirs far away from deep-rooted faults, calcite cements are indicated to have been sourced from the decarboxylation of organic matter in the interbedded mudstones. Carbonate cements in conglomerate reservoirs near the deep-rooted faults possibly formed from hydrothermal fluids or thermochemical oxidation of pre-existing methane accumulations. This study can serve us an excellent example for the control of sediment composition and paleo-fluid evolution on diagenetic variations in fan-delta conglomerate reservoirs.

Ediacaran post-collisional high-silica volcanism associated to the Florianópolis Batholith, Dom Feliciano Belt, southernmost Brazil: lithofacies analysis and petrology

The Cambirela Silicic Volcanic Sequence is the only Neoproterozoic volcanic manifestation in the Florianópolis Batholith. The sequence is associated with the late stages of the post-collisional magmatism emplaced in the Dom Feliciano Belt during the Brazilian/Pan-African Orogenic Cycle that was responsible for the amalgamation of the West Gondwana supercontinent. Distinct from other ignimbrite occurrence, that are generally associated with caldera and sedimentary sequences, the Cambirela Silicic Volcanic Sequence is associated with shallow granitic bodies in a plutono-volcanic system. The sequence is arranged along a high geomorphological feature with NNE-SSW orientation, distributed in a total area of 88 km2, and is constituted by effusive and pyroclastic units. The pyroclastic unit is dominant in the sequence and characterized by ignimbrites with 15–50% of quartz, K-feldspar and plagioclase crystals, crystal and lithic fragments immersed in a tuffaceous matrix, presenting incipient eutaxitic to parataxitic structure. Due to its geotectonic structure and the absence of associated caldera and sedimentary sequences, these ignimbrites were classified as fissure ignimbrites. The effusive unit is composed by rhyolites with 3% of quartz, K-feldspar and plagioclase phenocrysts immersed in an equigranular fine matrix. These units were divided into five lithofaceis: porphyritic rhyolite (pR), lapilli-tuff with low-crystal content and eutaxitic structure (lceLT), lapilli-tuff with high-crystal content and eutaxitic structure (hceLT), lapilli-tuff with parataxitic structure (pLT) and crystal-rich lapilli-tuff (crLT). Based on geochemical data, these were classified as high-silica rhyolites, related to the high-K calc-alkaline series, close to the shoshonitic series. The sequence has a slightly metaluminous to peraluminous character and high contents of alkalis, FeOt/(FeOt + MgO) and agpaitic indexes. These characteristics are associated to the A-type magmatism in post-collisional settings in southern Brazil. Regarding to the rheology, the sequence present glass transition temperatures ranging from 731 to 781 °C, liquidus temperatures from 940 to 968 °C and viscosities from 7.72 to 8.90 log Pa.s. These values are similar to the chronocorrelated Ilha Granite, but slightly different from the Ana Dias Rhyolite. The rheological and geochronological similarities between the Cambirela Silicic Volcanic Sequence and the Ilha Granite, together with the contact relationships and interaction observed in the field between these units, indicate that these melts probably belonged to the same magma chamber constituting a magma mush located in the shallow portion of the crust.

High‐silica Ediacaran volcanism in the Dom Feliciano Belt, southernmost Brazil

The Cerro Chato region is located in southernmost Brazil and is characterized by associations of acid volcanic and subvolcanic rocks. The region is affected by NW and NE‐ trending faults and is grouped into 2 geomorphologically distinct features: Cerro Chato and Cerro Partido. Cerro Chato is represented by ignimbrites that occur in 2 main facies: lithic‐rich ignimbrites and crystal‐rich ignimbrites. They are poorly sorted and consist of lapilli‐sized pyroclasts in a tuffaceous matrix with eutaxitic texture. Hemi‐crystalline rhyolitic flows represent effusive events, with porphyritic texture, flow structures, and spherulites. Cerro Partido is characterized by a subvolcanic rhyolitic body, with porphyritic texture, elongated in the NE–SW direction. Through geochemical data, the lithologies were characterized as high‐silica type rhyolites, correlated to the alkaline series, close to the subalkaline series limit; display metaluminous to peraluminous character and high contents of alkalis, FeOt/FeOt + MgO and agpaitic index. The Cerro Partido rhyolites were classified as high‐Ti with higher CaO, P2O5, FeOt, MgO, and K2O contents than the Cerro Chato low‐Ti rhyolites. The REE pattern is slightly enriched in LREE in relation to the HREE and has a strong negative Eu anomaly. U–Pb zircon dating indicates an age of 561 ± 2 Ma for Cerro Partido, suggesting contemporaneity with the granitoids of Dom Feliciano Suite. Additionally, Cerro Chato rhyolites indicate an age of 630.4 ± 2.8 Ma. These ages are in agreement with those obtained in the syn‐sedimentary volcanism at the base of the Maricá Formation, Camaquã Basin.

Micro-CT investigation of a seed fern (probable medullosan) fertile pinna from the Early Permian Petrified Forest in Chemnitz, Germany

A new bipinnate fertile pinna, Sterzelitheca chemnitzensis, bearing alternate synangia, is described from the Chemnitz Petrified Forest, Germany. The specimen occurs in the basal volcanic ash of the Zeisigwald Tuff Horizon, Leukersdorf Formation, Lower Permian. Because it is partially embedded in the tuffaceous matrix, X-ray micro-computer tomography was employed to investigate the complete morphology without mechanical preparation of the hand specimen. The pinna is 66mm long and branched once at least, the ultimate pinnae alternately positioned on the penultimate axis at angles of 45–55°. Stalked synangia are bell-like, borne alternately on both the terminal portion of the penultimate axis and the ultimate axes at angles of 25–60°. The smooth walled stalk is 3–7mm long, 1–1.5mm wide. Individual synangia are up to 6.5mm in diameter and 10mm long, and bear 12–14 elongated sporangia. Tubular sporangia are thin walled, circular in transverse section, arranged at the rim of the circular synangial pad around a central hollow. The unique preservational mould of the studied specimen is neither a permineralisation nor a compression–impression. It is three-dimensionally preserved, but lacks any organic remains. We provide the first detailed three-dimensional features of a probable medullosan male reproductive organ from the Chemnitz Fossil Lagerstätte. The relatively simple structure of the specimen offers a better understanding of the Palaeozoic seed ferns.

Deterioration mechanisms of tuffs in Midas monument

Slightly weathered white and pink tuffs of the Midas monument have deterioration problems. In this study, depths and characteristics of the weathering zones developed within the tuffs are investigated through optical microscopy, X-ray diffractometry (XRD), chemical analyses, scanning electron microscopy (SEM) and some index parameters. Accelerated weathering tests including wetting–drying, freezing–thawing and salt crystallization are performed, and durability assessment methods are used to predict the durabilities of the tuffs. The findings are compared with field observations. By examining quantitative weathering indices and comparing them with thin section studies, it is found that thin section analyses of the crystals, LoI, and WPI are good indicators to quantify the depth of weathering for the tuffs. However, thin section studies have limited value for fine-grained tuffaceous matrix. The chemical weathering of the tuffs produces weathered zones that are 4.5-cm thick within the white tuff and 2.5-cm thick within the pink tuff. Physical weathering causes scaling of outer layers of the tuffs and fracturing of feldspars along their cleavage planes. However, variations of the index properties of the tuffs due to weathering are not so significant to quantify the weathering depths in the tuffs. Among the accelerated weathering tests, salt crystallization is found to be the most destructive environmental condition. Pigeon droppings rich in NO 3 1− are found to be the main source of soluble salt at the Midas monument. The salt transported up by capillary rise due to surface water causes spalling of the tuffs in the capillary zone. Surface water and salt of any kind in the close vicinity of the monument should be totally eliminated for the purpose of conservation. Field observations and the durability equations reveal that the white tuff is less durable than the pink tuff. Wet-to-dry strength ratio yields a better stone durability assessment among various durability methods used in this study.

Quantification of weathering depths in slightly weathered tuffs

Slightly weathered white and pink tuffs of Midas monument have deterioration problems. In this study, depths of the weathering zones developed in the tuffs are investigated through optical microscopy, XRD, chemical analyses, SEM and some index parameters. By examining quantitative weathering indices and comparing them with thin section studies, it is found that thin section analyses of the phenocrysts, LoI and WPI are good indicators to quantify the depth of weathering for the tuffs. However, thin section studies have limited value for fine-grained tuffaceous matrix. The chemical weathering of the tuffs produces weathered zones that are 4.5 cm thick within the white tuff and 2.5 cm thick within the pink tuff. Physical weathering causes fracturing of feldspars along their cleavage planes. Variations of the index properties of the tuffs caused by weathering are not significant enough to quantify the weathering depths in the tuffs.

Tuffaceous Conglomerates: Syn-Eruptive Resedimented Debris Flow and Hyperconcentrated Flow Deposits from the "Rhyodacitic Formation", Gutai Mountains, Eastern Carpathians

The first volcanic products from Gutâi Mts, Eastern Carpathians belong to the Rhyodacitic Formation. The physical constituents of this formation are as follows: pyroclastic deposits (ignimbrites and fall tuffs), syn-eruptive resedimented volcaniclastic deposits, volcanogenic and non-volcanogenic sedimentary deposits. The tuffaceous conglomerates belong to the syn-eruptive resedimented volcaniclastics and represent the coarsest deposits. They outcrop in Baiţa area, west from Baia-Mare, being underlain by Lower Badenian (15.4±0.6 Ma) ignimbrites and overlain by Lower Sarmatian claystones. The main components of the conglomerates are boulders and cobbles of sedimentary and metamorphic rocks in a tuffaceous matrix. Scarse blocks eroded from the lower ignimbrite unit are present. In the frame of the study of the Rhyodacitic Formation, the conglomerates have been investigated using facies analysis. The facies model concludes that the studied deposits have been emplaced from debris flows and hyperconcentrated flows. They derived from subaerial channelized ignimbrite flows, which underwent strong flow separation while jumping in submarine basin and settling in deep water, below wave base. Such conditions, above the lower subaerial ignimbrite unit, were determined by the subsidence of Sasar-Dealu Crucii compartment, contemporaneously developed with the conglomerates emplacement.

飛騨外縁帯上広瀬層にみられる電気石の産状と化学組成

Tourmaline-bearing hydrothermal veins and metamorphic tourmalines occur in the Kamihirose Formation, circum-Hida terrane. The Kamihirose Formation was intruded by the Funatsu granitic rocks and underwent the contact metamorphism. Two types of tourmaline-bearing hydrothermal veins were distinguished: (1) tourmaline vein, which consists mostly of tourmaline with quartz and minor apatite; (2) potassium feldspar vein, which consists mostly of orthoclase with quartz, plagioclase and acicular tourmaline. Metamorphic tourmalines are found in sandstone and tonalite porphyry and tuffaceous sandstone clast of conglomerate. There are three types of sandstones that yield metamorphic tourmalines: black, white and acidic tuffaceous sandstones. In the black sandstone, the metamorphic tourmalines occur in shale fragments and occur as overgrowth on detrital tourmalines, whereas, in the white sandstone, those occur in acidic tuff fragments. In the acidic tuffaceous sandstone, metamorphic tourmalines occur in the tuffaceous matrix. The electron-microprobe analyses of tourmalines revealed the facts as follows ; (1) The tourmalines from the Kamihirose Formation are members of schorl-dravite solid solutions. (2) The tourmalines in the hydrothermal veins probably contain Fe3+, which substitutes for Al. (3) The metamorphic tourmalines have a wide compositional range reflecting various chemical features of host rocks.

Problems of recognition of olistostromes: An example from the lower Pit Formation, Eastern Klamath Mountains, California

The recognition of large olistostromes is difficult unless outcrop is nearly complete over broad areas. A previously unrecognized olistostrome in the lower Pit Formation was exposed on the shores of Shasta Lake, California, at a time of low water level. Blocks as much as 1000–2000 m across of diverse volcanic and sedimentary rocks are set in an unsheared tuffaceous matrix. The olistostrome formed in response to a Middle Triassic disturbance, possibly involving rifting, and it disrupted volcanogenic massive sulfide deposits.

A diatreme-hosted gold deposit at Montana Tunnels, Montana

A bulk-minable, gold-silver deposit at Montana Tunnels, southwestern Montana, is located in the central part of a diatreme. This diatreme was emplaced along the faulted contact between andesitic volcaniclastic rocks, assigned to the Late Cretaceous Elkhorn Mountains Volcanics, and a sequence of quartz latitic ignimbrites, which are part of the Lowland Creek Volcanics of middle Eocene age. A north-northeast-striking swarm of quartz latite porphyry dikes was emplaced during the waning stages of Lowland Creek volcanism. The two largest dikes, dated at 45 to 50 m.y. (middle Eocene), were intruded into the diatreme prior to the cessation of brecciation and mineralization.The diatreme underlies a 1-km 2 area and is known from drilling to extend steeply downward for at least 310 m. The principal rock type in the diatreme is a matrix-rich breccia. It is characterized by a sand-size tuffaceous matrix of quartz latitic composition containing fragments of contiguous volcanic wall rocks and intrusive rocks derived from the Late Cretaceous Boulder batholith. The batholith is inferred to underlie the Montana Tunnels area. Foundered blocks of volcanic wall rocks lie at various attitudes against the walls of the diatreme and within it. Those composed of Elkhorn Mountains Volcanics underwent hydraulic brecciation after they sank into the diatreme. Blocks interpreted to be composed of pyroclastic base surge deposits from a subaerial tuff ring and a piece of carbonized wood subsided into the diatreme from the palcosurface. The diatreme is separated into two unequal parts by a west-northwest-striking oblique slip fault.Sulfide minerals in the diatreme occur as disseminations in the breccia matrix and, in sub-ordinate amounts, as widely spaced, multidirectional veinlets and as the matrix to brecciated blocks of Elkhorn Mountains Volcanics. All forms of mineralization consist of pyrite, sphalerite, galena, minor chalcopyrite, and rare electrum accompanied by a gangue of manganocalcite, siderite, and minor quartz. Clastic grains and fragments of the sulfides and gangue minerals are common and attest to multiple alternating episodes of brecciation and mineralization. In the ore zone the introduction of abundant manganocalcite and siderite was accompanied by pervasive sericitic alteration but only weak kaolinization and silicification. Sericitization grades outward beyond the ore zone to chlorite-montmorillonite-carbonate alteration, an assemblage that also characterizes the interiors of the late mineral dikes in the diatreme. Gold occurs in electrum, with a fineness of about 550, as inclusions of less than 200 mu m in pyrite and sphalerite. Inclusions of electrum and galena were precipitated together. Silver is present mainly in solid solution in galena.The Montana Tunnels gold-silver deposit is characterized geochemically by anomalously high concentrations of zinc, lead, and manganese and, in comparison to many volcanic-hosted precious metal deposits, is low in arsenic, antimony, and mercury. This metal association and the low fineness of the gold are features shared by the Wau gold deposit in Papua New Guinea. It is suggested that the mineralized diatreme observable at Montana Tunnels was emplaced several hundred meters beneath the palcosurface, upon which a gold-bearing maar volcano, like that partly preserved at Wau, was constructed.

Volcanic geology of the Waipoua area, Northland, New Zealand

Abstract Waipoua Basalt Formation is closely associated with coeval mid Miocene sediments of Waipoua Subgroup. The formation consists of lava flows (2–25 m thick), typically separated by layers of tephra (up to 2 m thick), and intruded by dike swarms in a zone extending 15 km north from Maunganui Bluff. Lava from both flows and dikes is a glomeroporphyritic plagioclase-olivine-augite basalt. In the Kaihu area Whatoro Breccia Member (new) is a breccia of assorted igneous Hthologies, mostly of Waipoua Basalt origin, in a tuffaceous matrix. Although eruption may have occurred in the dike-intruded zone, evidence suggests that the main volcanic centre lay a short distance offshore from Maunganui Bluff.

A New and Important Occurrence of Sedimentary Analcime

ABSTRACT Considerable quantities of sedimentary analcime have been found in the rocks of the Chubutian Group (Senonian) of the anticline of the Senguerr River (Chubut, Argentina). These analcime-bearing rocks are pyroclastic, mostly tuffs that vary in grain size from claystones to conglomerates, sandstones being the most frequent type. Analcime occurs as replacement of the tuffaceous matrix, but also as crystals, fillings of cavities, veinlets, cement etc. Analcime distribution is concentrated in the lower or Castillo Formation, part of the Chubutian Group. The mineral is authigenic and its origin is closely related to environmental and climatic factors (lacustrine or paludal conditions under arid or semiarid climate); volcanic ashes, or their alteration products, seem to be essential in analcime formation. Sedimentary analcime may be more abundant in continental pyroclastic deposits than has hitherto been thought, since it can easily be mistaken for opal. Some partial references in the Argentine geological literature seem to point in this direction.