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, pp. 59 – 68 . Okumura , T. , A. Gucsik , H. Nishido , K. Ninagawa , S. Toyoda 2009 : Cathodoluminescence microcharacterization of ballen silica in impactites
. Streckeisen , B. Zanettin 1986 . A chemical classification of volcanic rocks based on the total alkali-silica diagram . – Journal of Petrology , 27 , pp. 745 – 750 . Lorenz
. Fournier , R.O. , J.J. Rowe 1966 : Estimation of underground temperatures from silica content of waters from hot springs and wet steam wells . — American Journal of Science , 264 , pp. 685 – 697
The Terebratel Beds of the Karlstadt section are composed of bioclastic grainstone revealing distinct layers of ooidal grainstone (Fig. 4 ). In thin sections, these layers show silicification of ooids and interparticle silica cement (Fig. 5a – c
shock-induced diaplectic glass; minor components are pyrrhotite, whitlockite, and titanomagnetite of magmatic origin ( Nyquist et al. 2001 ). In the terrestrial environment, similar silica-rich melt could form by melting along the grain boundaries of
South Gemerian Alsohegy (Silica nappe, Western Carpathians.) - Öslénytani Viták, 24, pp. 33-58 (in Hungarian with English abstract). A Dél-Gömöri Alsóhegy magyarországi részének földtani felépitése. (Geological buildup of the
-Jurassic silica-undersaturated and silica-saturated intrusions in the Cordillera of British Columbia: implications for arc magmatism Geology 23 451 454
Abstract
Large, irregular volumes of altered, friable Triassic dolomite with poorly recognizable depositional fabrics crop out in the Buda Mountains, Hungary. These rock volumes are characterized by powder-like, chalky, soft, whitish gray microporous carbonates, referred to as “pulverized dolomite”. This is interpreted as the result of corrosion of carbonates along microfractures. The pulverized dolomite is commonly associated with silica and clay cementation (“silicification”) and “mineralization” of ironrich minerals, barite, sphalerite, galena, fluorite, calcite, dolomite and others, clearly pointing out hydrothermal Mississippi Valley Type (MVT) conditions.
The pulverization, silicification and mineralization are considered to be a diagenetic facies association (PSM facies). Tectonic shear corridors played an important role in the development of PSM facies as carriers of hydrothermal fluids, but the geometry of the altered units is very irregular and cross-cuts different Triassic depositional facies in addition to Eocene limestone and Middle-Upper Miocene sediments. The PSM facies represents the early stages of hydrothermal alteration (i.e. the burial phase) that was later modified by thermal mixing zones. Pulverized dolomite bodies that reached the surface were strongly affected by meteoric fluids; peculiar speleo-concretions were formed by calcite cementation of the powdery dolomite clasts.
The altered carbonates show major porosity development whereas the unaltered carbonates present only minor porosity. The size and lithologic contrast of the altered geobodies makes them detectable by geophysical methods of mineral and hydrocarbon exploration.
Abstract
the Retezat Mountains, this study discusses radiocarbon chronology and sediment accumulation rate changes in two sediment profiles in relation to lithostratigraphy, organic content, biogenic silica and major pollenstratigraphic changes. A total of 25 radiocarbon dates were obtained from sediments of two lakes, Lake Brazi (TDB-1; 1740 m a.s.l.) and Lake Gales (Gales-3; 1990 m a.s.l.). Age-depth modeling was performed on TDB-1 using calibrated age ranges from BCal and various curve-fitting methods in psimpoll. Our results suggest that sediment accumulation began between 15,124–15,755 cal yr BP in both lakes and was continuous throughout the Late Glacial and Holocene. We demonstrated that local ecosystem productivity showed delayed response to Late Glacial and Early Holocene climatic changes in the subalpine and alpine zones most likely attributable to the cooling effect of remnant glaciers and meltwater input. However, regional vegetation response was without time lag and indicated forestation and warming at 14,450 and 11,550 cal yr BP, and cooling at ca. 12,800 cal yr BP. In the Holocene one major shift was detected, starting around 6300 cal yr BP and culminating around 5200 cal yr BP. The various proxies suggested summer cooling, shorter duration of the winter ice-cover season and/or increasing size of the water body, probably in response to increasing available moisture.
A. Streckeisen B. Zanettin 1986 A chemical classification of volcanic rocks based on the total alkali-silica diagram
