Geological research (in Moravia and Silesia)

Výskyt hydroxylsynchyzitu-(Ce) na hydrotermální žíle ve vápencích z lomu cementárny Hranice

2025-02-12T09:58:10+01:00

A new occurrence of a mineral of the synchysite group was identified in a hydrothermal vein in the limestone quarry of the cement plant at the Hranice town (Moravo-Silesian Palaeozoic, Bohemian Massif, Czech Republic). The vein is formed by two chemically distinct generations of calcite (Cal_97-100Rdc_0-2Sid_0-1), Fe-rich dolomite (Dol_65-75Ank_21-31Ktn_2-6), quartz, pyrite and chalcopyrite. The synchysite-group mineral forms microscopic inclusions hosted by Fe,Mn-enriched calcite associated with pyrite and chalcopyrite. Since Ce predominates within the sum of REE+Y and the contents of F are low (0.14–0.29 apfu), the mineral can be classified as hydroxylsynchysite-(Ce). Chondrite-normalized REE distribution patterns show a decrease from La to Er and a distinct positive Eu anomaly. The La_CN/Sm_CN ratios of the mineral (1.51–2.49) are different from those of the host limestones (2.81–3.14). Similar discrepancy is observed also in case of two other synchysite occurrences from area of the Moravo-Silesian Palaeozoic hosted by Culmian siliciclastic sediments. Therefore, the exact source of REE cannot be identified on the basis of determined elemental ratios only. The fractionation of REE during synchysite crystallization was mostly negligible at all three above-mentioned sites, which suggests a low content of strong REE-complexing ligands (i.e., F^-, OH^-, or CO₃^2-) in the fluids and a dominant role of weak ligands (i.e., Cl^-, SO₄^2-,
HCO₃^-). The positive Eu anomaly indicates an increase of redox potential of fluids, but not up to strongly oxidizing conditions (as Ce anomaly is absent). The fluoride ions could act as a depositional anion, allowing the precipitation of REE into a mineral phase. The given parameters (chloride solutions, geochemically open system, mixing of brines with other types of fluids) reflect well the features of hydrothermal system of post-Variscan mineralizations, which is also consistent with mineral composition of veins at all discussed sites.

Pohyb skalních věží u Holštejna na severním okraji Moravského krasu

2025-01-10T11:53:03+01:00

Rock towers are in the Moravian Karst quite a rare phenomenon. The biggest group of seven is situated west of the Holštejn village near the Vaňous walls in the half blind valley of the Bílá voda stream. Surrounding area is made up of the Vilémovice Limestone of Frasnian age, which are folded into SW steeply inclined folds with subhorizontal fold axes, very gently dipping towards SSE. Three systems of cleavage were detected in the locality. The most prominent cleavage system K0 is NE–SW striking moderately dipping towards SW. Based on the orientation, it is likely that this system is the axial cleavage of the main folds. The other two cleavage systems are K1 and K2, which have very similar orientation. Both are W–E striking, dipping towards S, K2 is slightly steeper than K1. All rock towers show signs of toppling. This was proven via an orientation analysis of the two cleavage systems K1 and K2. More traditional bedding planes could not have been used, because there were none detected in any of the towers and because they are folded, they would be unreliable anyway. These two cleavage systems have an almost constant angle of 16° ±4° between them and can be therefore used as a rotation gauge instead. The rotation angle of these towers increases more or less systematically downslope up to 20°. The mean rotation axes for both cleavages are the same and have a very similar orientation as the NNE–SSW striking fault. Two structures control this toppling: the NNE–SSW striking fault system, which is the main subvertical separation plane of the towers forming a pronounced crest above the towers and bedding planes generally dipping gently towards E, which served as a “basal” plane of the limestones block on which they toppled. Opening of fault planes was detected also in the Sonda pod Jedničkou cave system located SW of the rock towers in the same slope. This, in combination with several small warm air exhalation spots near the crest around the rock towers, suggests quite a deep reach of the slope deformation (40 meters). This was possible because the Bílá voda stream valley was originally empty with much higher and steeper slopes than today and was subsequently filled by Quaternary sediments.

Provenienční studie eocenních sedimentů obsahujících jantar z belovežského souvrství u obce Študlov

2024-12-16T07:46:49+01:00

This study presents the mineralogical and textural characteristics of deposits of turbidity currents containing amber from the Beloveža Formation, located in the Bystrica Unit near the village of Študlov. Based on optical and microprobe analyses, the translucent heavy minerals present in the sandstone consist of 40% tourmaline, 25% zircon, and 15% garnet. Other heavy minerals are found in minor quantities, including spinel, staurolite, amphibole, apatite, members of the epidote group, kyanite, rutile, monazite, and barite. The chemical composition of the garnet has a range from pyrope to grossular-rich grains.
Dominated almandine-rich garnets with a higher content of the pyrope component (Alm_59–73 Prp_21–38 Grs_0–7 Sps₂ Adr_0–2), which is typical for most Cretaceous and Paleogene sediments in the Magura Sedimentary Basin. Additionally, the chemical composition of the spinelides suggests a contribution of materials from supra-subduction geotectonic settings and crustal metamorphic rocks. Tourmaline is derived from metamorphosed sediments and peraluminous granites, typical of the continental crust.
The chemical composition of the translucent heavy minerals in the studied sandstone sample indicates that the Southern Magura Ridge is the primary source of the sedimentary material. Chromium-rich spinels and pyrope-rich garnets indicate the presence of mafic to ultramafic, supra-subduction, or mantle rocks in the source region. The presence of coal and amber indicates the likely contribution of materials from forest-covered regions located to the south, specifically in the exposed areas of the active Western Carpathian accretionary wedge.

Strukturně-geologické nástroje a metody řešení geologické stavby pomocí nového doplňku GeoSol v ArcGIS Pro

2025-01-27T15:40:17+01:00

For understanding the structure of the Earth‘s crust, field surveys and the collection of localized data are crucial, such as compass measurements of oriented structures, detecting lithological boundaries and distinguishing types of lithology. In addition to these traditional methods, a detailed digital elevation model (DEM) created through airborne laser scanning is becoming a new foundation and guide for understanding geological structures, with ever-increasing levels of detail. To enable the analysis of these structural elements taking advantage of geographical information systems (GIS) and using established structural geology methods (such as orientation analysis, geological cross-section construction, down-plunge method, or three-point method), new tools were developed within the GeoSol add-in for ArcGIS Pro. GeoSol uses the position of three points belonging to a single lithological boundary or fault plane to calculate the plane‘s orientation (dip direction and dip) and sketches the intersection line of this plane with the DEM. Slope and shaded (illuminated) models derived from DEM are helpful to determine the position of outcrops, but also subtler morphological manifestations of layering with varying erosion resistence, which can reveal the presence of tectonic processes such as folds or faults. GeoSol can also construct cross sections and intersect structural planes with it. Also other available surface or borehole
data can be projected on the plane of cross section.
The GeoSol add-in thus combines the advantages of GIS with structural analysis methods, facilitating the construction of geological maps.

Cretaceous stratigraphy of the Silesisan and Subsilesian units in the D48 road cut of the road near Starý Jičín

2025-06-23T13:39:38+02:00

Nový silniční zářez ve vnější části karpatského flyše poblíž Starého Jičína odkryl tektonickou šupinu se složitou vnitřní strukturou, která je interpretována jako duplex tvořený různými souvrstvími slezské a podslezské jednotky. Slezská jednotka zahrnuje černé pelity hradišťského souvrství (barrem–apt) a vulkanické horniny těšínitové asociace. Podslezská jednotka je zastoupena šedými jílovci (cenoman), jíly a parakonglomeráty frýdeckého souvrství (campan) a jílovci s vápnitými pískovci frýdlantského souvrství (paleocén). Některých typicky albské a cenomanské vůdčí druhy aglutinovaných foraminifer byly zaznamenány v nevelkém počtu již v aptských sedimentech. Proto by zóny aglutinovaných foraminifer, navržené Gerochem a Nowakem (1984) jako zóny částečného rozsahu, měly být redefinovány jako akmezóny.

Spodnomiocénní fluviální sedimenty v okolí Nových Bránic

2025-07-15T07:42:35+02:00

Sedimentological study of the deposits at the locality near Nové Bránice provides data about Eggenburgian–Ottnangian deposits of the Carpathian Foredeep basin in the area. Altogether 9 lithofacies have been identified and deposits of the two facies associations/ depositional environment have been recognised in the outcrop. The first one is represented by deposits of the fluvial channel formed by traction currents of poorly confined waterflows. In-channel bedforms (2D and 3D gravelly and sandy dunes) represent their prominent part. Braided fluvial style is supposed with important role of variation in fluvial discharge. Paleocurrent data signalises transport towards SE, S or SSW. The deposits of the second facies associations (covering the deposits of the first facies association) are interpreted as proximal overbank deposits related to flood events with important role of aggradation.
Provenance analysis of the fluvial deposits is based on the evaluation of petrography of pebbles, transparent heavy mineral assemblages, composition of garnet and rutile, and zircon studies). The assessment of the gamma-ray spectra provides supplementary data. An important role of relatively local sources has been recognised represented dominantly by local granitoids and metamorphics of the Brno Massif (primary source). The role of the next crystalline complexes (Moldanubicum, Moravian Zone) in provenance was minor. Moreover, a role of intense reworking and redeposition of material from older deposits (as recycled secondary source) is supposed. Studied fluvial system continued towards the centre of the peripheral foreland basin.

Formation doubly terminated crystals of quartz in Carboniferous limestones from the Brañes site in northwestern Spain

2025-07-18T12:56:08+02:00

The Carboniferous limestones from the Brañes site in northwestern Spain contain dark, often doubly terminated authigenic quartz crystals. Optical microscopy and fluid inclusion studies of quartz crystals provide insights into the formation and thermal history of the surrounding limestones. The core of quartz crystals has been formed by filling voids created through the dissolution of sulphate. The morphology of the quartz crystals supports
this interpretation. The primary and pseudosecondary fluid inclusions within external zones in these quartz crystals are mostly two-phase, consisting of aqueous liquid and a vapor bubble. Cryometric measurements show an initial melting temperature (Tfm) of approximately −50 °C, with melting temperatures (Tmice) ranging from −18.1 °C to −21.8 °C and −42.4 °C to −45.0 °C, respectively. These melting temperatures indicate high
salinity, estimated between 20 mass% and 29 mass% CaCl2 equivalent. The homogenization temperatures of the fluid inclusions range from 60 °C to 147 °C, and suggest that the external zones of the quartz crystals were formed during peak temperature conditions of diagenesis in the Early Permian period.

Seasonal variations of water condensation in cave environment: A case study from the Výpustek Cave (Moravian Karst)

2025-06-11T11:03:40+02:00

Seasonal variations of water condensation were studied in the Výpustek Cave (Moravian Karst). Microclimatic data such as cave/external air temperatures and visitor numbers were monitored in the Škrapový Dome and exterior of the cave with one-hour step during an almost season-long monitoring campaign. Water condensation data were recorded at monthly intervals using a polished limestone tablet located in a dome near the thermometers. Long-term monitoring showed that the temperature of the cave air was controlled
by cave airflow driven by the temperature difference between the exterior and the cave, ΔT_AF. Anthropogenic temperature influence appeared as peaks superimposed onto natural cave air temperatures curves and corresponded to the number of visitors. Seasonality of water condensation based on cave airflow was identified: no condensation during the UAF mode and drops of condensed water on the tablet surface in the DAF mode. Traces of calcite recrystallization were found on the tablet surface as a consequence of dissolution by the condensed water.