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  • Author or Editor: György Szakmány x
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Redeposited Eocene calcrete gravel was found in a Miocene conglomerate sequence in the Western Mecsek Mountains, S Hungary. The purpose of this paper is to describe the micromorphological and mineralogical characteristics of these rocks. A large number of calcrete thin sections were analyzed using a petrographic microscope. This study was supplemented by microchemical staining, cathode luminescence examination and X-ray diffraction methods.  The diagnostic features identified are rhizoliths (rhizocretion, root cast and root petrifaction), alveolar textures, in situ Microcodium grains, peloids, coated grains and pedogenic voids. According to these micromorphological results the studied calcrete belongs to the group of beta calcretes. The biofabric of this calcrete reflects an extensive vegetation cover and a relatively high degree of biological activity. Micromorphology and mineralogical composition of the calcrete gravels (i.e. dominance of calcite, quartz, illite±muscovite and illite/smectite) suggest a semi-arid/subhumid climate during calcrete pedogenesis. Within the Eocene calcrete gravel two main cement types have been distinguished: a meteoric vadose cement (vadose silt) and a phreatic one (drusy ferroan calcite spar). Drusy sparite is the typical cement of near-surface diagenesis, and this, together with its ferroan nature, leads to the conclusion that the main site of cementation of the Eocene calcrete was the meteoric phreatic zone.

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Twenty Roman Age home-made sherds from Central Italian San Potito locality were studied by petrographic microscopic method. The ceramics were divided into five petrographic groups on the basis of their composition and structural-textural features. Two groups of the ceramics were tempered with clasts of alkaline volcanic origin, which seem to originate from Central-Italian volcanic territory components. The ceramics belonging to the other three groups contained large amounts of limestone and carbonatic fossils, the origin of the raw material was a marine clayish sediment, perhaps flysch.

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In this paper, results of a bulk-rock geochemical study of silty and albitic claystone samples selected from the Upper Permian Boda Siltstone Formation (BSF) in the western part of the Mecsek Mountains (Tisza Mega-unit, Hungary) are presented. The high Na2O and P2O5 contents, relative to the post-Archean Australian average shale (PAAS) and the average Russian Paleozoic shale compositions, are the most striking features of the geochemistry of the Boda sediments. The samples studied are depleted in SiO2, TiO2 and Al2O3, and they are enriched in Fe2O3, MgO, CaO and K2O relative to the PAAS. The major element relations clearly show that the geochemistry of the BSF is strongly affected by post-depositional modification, corresponding to large-scale dispersal or addition of components. On the other hand, relatively high La content, low concentrations of V, Cr, Cu and Ni, and the result of the TiO2 versus Ni plot reflect a relatively felsic provenance of the BSF. By comparison with detrital mineralogy of the heteropic Cserdi alluvial fan system deposits, the authors assume that the Boda playa lake deposits had a similar immature primary composition consisting of quartz, plagioclase, K-feldspar, muscovite, biotite, chlorite and clay minerals. During weathering and transport in a semi-arid to arid climate, detrital mafic minerals were altered to yield chlorite and clay minerals plus Fe and Mg, and trace metals in solution. Mg was built into the structure of chlorite and of secondary carbonates such as dolomite and Mg-rich calcite. Based on previous geochemical studies, the BSF contains particularly sodic sedimentary rocks (up to 8 wt%) which may represent an addition of sodium in authigenic silicates from alkaline brine and/or evaporites in the playa deposits. In claystone, after albite formed, Na-depleted, Ca, K-enriched waters reacted with the clay minerals such as smectite and kaolinite to yield K-rich illitic sediments, Ca precipitated in calcite cement. P2O5 is enriched in some samples due to phosphorus mobilization during diagenesis.

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Upper Carboniferous (Westphalian) coal-bearing fluvial sediments (Téseny Sandstone Formation) of the Slavonian-Drava Unit and their reworked pebbles and cobbles occurring in the western part of the Mecsek Mountains in Miocene conglomerate sequences (Szászvár Formation) were studied.  Based on the petrographic and geochemical characteristics, the sandstone studied consists of arkose, subarkose, litharenite and sublitharenite. The main clastic source was a recycled orogenic area (collision suture and fold-thrust belt) dominated by metamorphic rocks. It was associated with a probably Variscan magmatic arc as indicated by the volcanic rock fragments. The original source area of these clastic sediments was felsic and the analyzed sandstone could correspond to a continental arc/active margin tectonic suite.  The pebble and cobble-sized clasts of the conglomerate were predominantly derived from acidic and intermediate volcanic rocks, low-grade regional metamorphic rocks (different types of schist, metasandstone, mylonite, metagranitoid, gneiss, quartzite, and metaquartzite) and siliceous sedimentary rocks. Among the sedimentary clasts, reworked black siltstone and fine-grained sandstone from older (possibly Carboniferous) deposits are common. Chert and contact metamorphic rocks are present in minor quantity. The extracted volcanic clasts consist of andesite, trachyandesite, dacite and rhyolite. Their geochemistry suggests convergent, active continental margin affinity. Upper Carboniferous siliciclastic successions are widely known at the southeastern margin of the European Variscides. In the area of the Upper Silesian Coal Basin, the Cracow Sandstone Series (Westphalian C and D) shows a similar petrographic composition to that of the Téseny Sandstone Formation. Additionally, volcanic clasts of the Upper Carboniferous conglomerate from southern Transdanubia and the calc-alkaline volcanites from the Intra-Sudetic Basin can be characterized by similar geochemical patterns.

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Authors: Andrea Varga, Béla Raucsik, Zsuzsanna Hartyáni and György Szakmány

Abstract

The clay mineralogical and chemical compositions of Upper Carboniferous siliciclastic rocks from the western flank of the Villány Mountains (Téseny Sandstone Formation) have been investigated to determine paleoweathering conditions, as well as to appraise the influence of the post-depositional processes upon source rock signature. The clay-mineral assemblage of the samples consists predominantly of illite±muscovite, suggesting a potassium metasomatism in the Téseny clastics. Therefore the use of the Chemical Index of Alteration (CIA), which provides a consistent quantitative framework for examining weathering, leads to erroneous conclusions without correction for K-metasomatism. When considered in Al2O3-CaO* + Na2O-K2O (A-CN-K) compositional space, orthogneiss and igneous rock clasts selected from the Téseny conglomerate reflect two different weathering trends; one (including orthogneiss, quartz diorite, and andesite samples) shows an ideal trend observed for granodioritic rocks, and the other (including aplite, rhyodacite, and rhyolite samples) follows a trend from a slightly more K-feldspar-rich fresh rock composition than that of average granite. Intermediate to intense chemical weathering of the source areas is indicated by premetasomatized CIA values of 77–84 for the samples from borehole Siklósbodony-1, suggesting that these rocks have gained about 6–7% K2O (in A-CN-K space) during metasomatism.

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On the territory Transcarpathian Ukraine, about 100 Palaeolithic localities are known up to our days. Most of them are surface finds. In spite of the rich archaeological heritage, the elaboration of the material, especially its petroarchaeological evaluation supported by professional scientific analytical methods, is in the initial phase as yet. The aim of the present study is to supply information on the lithic raw materials of the Palaeolithic settlements in Transcarpathian Ukraine, the detailed survey and description of the primary raw materials, their identification, description and terminology, as well as the outlining of the local raw material provinces and study of the distribution of the raw materials on archaeological sites.

In the archaeological literature of Transcarpathian Ukraine, lithic raw materials are still described under incorrect petrographical terms. For example, for the raw material of Korolevo Palaeolithic site is, correctly speaking, hyaline dacite, and the “flints” of Beregovo region are indeed rocks of volcanic origin which have undergone metasomatic processes. Field survey for collecting geological samples localized 19 different raw material sources all of which yielded hard rocks with conchoidal fracture that are suitable for tool making with knapping.

Out of the 19 raw material types 11 were actually found in archaeological assemblages of the studied area. The most popular raw materials of Transcarpathian Ukraine are the Korolevo hyaline dacite, Rokosovo obsidian, (Carpathian 3 type) and siliceous rhyolite tuff varieties (type I and II), siliceous tuffite (type I and II), siliceous and opalised rhyolite (type I and II) from the Beregovo Hills area, as well as silicified sandstone (type II) and the siliceous argillite. Certain types of potential raw materials were found in archaeological assemblages as yet. These are the Kriva limno-chalcedonite and limnoopalite, radiolarite of Svalyava type I, II and III, the siliceous limestone of Svalyava and Priborzhavske, and the hornfels of Suskovo.

The paper also points out patterns in lithic raw material circulation in the prehistoric period of Transcarpathia. In the Palaeolithic, the settlement system and location of sites was largely dependent on the lithic sources. Altogether 9 types of rocks played important role: Korolevo hyaline dacite, the Carpathian 3 type obsidian from Rokosovo, 6 types of metasomatites of Beregovo Hills, and the silicified sandstone (type II). Upper Palaeolithic communities settled close to the outcrops of primary and secondary geological positions and this phenomenon is observable at each important Palaeolithic settlement.

On the basis of the principal raw material circulation of the Palaeolithic three territorial groups have been formulated. These are named after the most abundant and used rock types of the given region. Three raw material regions are recognized in Transcarpathia: volcanic, metasomatic, and sedimentary. Furthermore, sub-regions were also established in the volcanic region (Rokosovo-Maliy Rakovets and Korolevo-Veryatsa sub-regions) and in the metasomatic region (Beregovo, Muzhiyevo and Bene- Kvasovo sub-regions).

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