Geologické výzkumy (na Moravě a ve Slezsku)

Ověření výsledků statistického modelu náchylnosti k sesouvání v oblasti Chřibů a severní části Kyjovské pahorkatiny

Vladimíra Krejčí — 2023-11-24

The aim of our work was to use a statistical model to determine the degree of susceptibility assessment in the area of the Chřiby Highland and northern part of the Kyjovská pahorkatina Hilly land and then compare the results with field verification of their actual occurrence in a part of this previously unmapped area. Studied part with a total area of 353,47 km² is frequently affected by landslides (580 landslides covering 9 % of the area). The mapped area and the results comparing with the final landslide susceptibility map showed that more than 85 % of the mapped landslides are located in areas of high and very high landslide susceptibility. For locations that were not detected by this statistical method, but where landslides were nevertheless subsequently mapped, it was found that their origin was initiated by phenomena other than the input conditions used for the analysis. The results of the analysis were verified by field research of the territory, which had not previously been comprehensively mapped (south part of the model area). A total of 98 landslides were newly identified or revised, covering a total area of 4 km², corresponding to 7.4 % of the area reconnaissanced.

Registrace seismických jevů stanicí VRAC v letech 2011 až 2022 v porovnání s globální seismicitou

Josef Havíř — 2023-11-24

Širokopásmová seismická stanice VRAC (Vranov u Brna), provozovaná ÚFZ (Ústav fyziky Země, Masarykova Univerzita), je jednou z certifikovaných stanic IMS CTBTO (International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization). Proto je velmi důležitá její schopnost zaznamenávat vzdálené seismické jevy. Tento článek se pokouší ukázat, pro jaké seismicky aktivní regiony může být využití stanice VRAC v rámci monitorování globální seismické aktivity výhodné. Za tímto účelem byla porovnána distribuce jevů registrovaných stanicí VRAC v letech 2011 až 2022 s celkovým rozložením projevů globální seismicity sledovaným na základě REB bulletinů (Reviewed Event Bulletin) CTBTO.

V letech 2011 až 2022 zaznamenala stanice VRAC 81110 seismických jevů, pro 60120 jevů je známa lokace (vypočtená v datovém centru ÚFZ anebo převzatá od jiných seismologických institucí). V případě 54314 z nich je epicentrální vzdálenost od stanice VRAC větší než 3°. Během stejného období lokalizovala IMS 440787 seismických jevů zařazených do REB bulletinů, data stanice VRAC byla využita při zpracování 21453 z těchto otřesů.

Nižší schopnost detekce seismických jevů stanicí VRAC byla pozorována nejen v případě regionů, vůči nimž se stanice VRAC nachází v zóně seismického stínu, ale také v regionech ve vzdálenostech 90° až 103° od stanice. Znamená to méně registrací jevů ze seismicky aktivních regionů Sumatry, Filipín a Střední Ameriky. Horši detekční schopnost vůči jevům ze vzdáleností 90° až 103° se očekávala, nikoli však v takové míře.

Naopak v důsledku kaustiky PKP vln je u stanice VRAC zjevný výrazně vyšší počet záznamů, a to i středně silných a slabých seismických jevů. Stanice VRAC tak dobře registruje otřesy z jižní části příkopu Nových Hebrid a z regionu Samoa.

Výzkum sedimentů zaniklého Leštinského rybníku na Zábřežsku

Lukáš Maloušek — 2023-11-24

Several ponds were built in the vicinity of the city of Zábřeh (Czech Republic) during the 15^th century, all of which disappeared over time, leaving only one (Oborník) that survived to the present day. Currently, the only proof of the existence of these ponds in the landscape are the dams, preserved in varying degrees of quality. Another potential proof of the presence of ponds is pond sediment, the existence and extent of which are the subject of this text. The abandoned Leštinský pond, located to the east of Zábřeh, was chosen for this research. This pond was only captured on the maps from the 1st military mapping, it is no longer depicted on newer maps. Its presence is indicated by a partially preserved dam, which is not very distinct in the landscape but is visible in Lidar images. The pond sediments were investigated through a combination of geological survey (shallow boreholes) and geophysical prospecting (electrical resistivity tomography and ground penetrating radar). A total of 5 drill cores were taken on which magnetic susceptibility, grain size, geochemical composition and spectral reflectance were measured. Four facies were identified based on the lithology and the used analyses. These facies are interpreted as a recent soil (facie P1), pond sediment (facie R) and buried alluvial soil developed on fluvial sediments (facie P2) and coarse-grained sands (facie F). The data from geophysical survey correlates with boreholes lithology and extends this information spacially. Above all, ground penetrating radar (GPR) of facie RF3, interpreted as the base of pond sediments, can be easily observed in GPR profiles. The obtained results provide information about the presence and thickness of the pond sediment. Pond sediment was captured in boreholes at thickness ranging from 12 to 38 cm, with no internal pond sediment stratigraphy being observed. The probable reason for such a limited sediment thickness could be the initially shallow depth of the pond or the pond’s summering process (“letnění”), during which no water was present in the pond and the removal of the pond sediment occurred in regular cycles.

Vyhodnocení fluviálních sedimentů a paleoekologická rekonstrukce prostoru ulice Křenová v Brně

Kristína Majorošová — 2023-12-19

Fluvial archives are a rich source of information about the environmental impact of the local industry in the past. This research is focused on Holocene fluvial sediments that were excavated in the area of Křenová Street in Brno, Czech Republic. The area was researched during the rescue archaeological excavations, which unearthed the defunct Svitava river channel and its banks together with wooden constructions and archaeological artifacts from the 13^th to the 16^th century. Three profiles were documented and lithostratigraphically described. Samples for the palaeoecological and chemical analyses and granulometry were taken from the excavated trench S11. The finding of the rivers´ point bar and the shape of the riverbed allowed us to determine that the river was meandering. Analysed pollen profile of the medieval riverbed shows species-rich vegetation in close proximity of the medieval town and progressing urbanization. Results from chemical analyses shows that the area was not significantly polluted. The source of most of the probable contamination were surrounding sumps, as is indicated by slightly elevated concentrations of phosphorus in the sediments.

Hydrogeologické poměry hydrogeologického rajonu 4232 Ústecká synklinála v povodí Svitavy z hlediska tvorby podzemní vody jako zdroje vody pitné

Jitka Novotná — 2023-12-19

Hydrogeological area 4232 Ústí syncline in the drainage basin of the Svitava river is producing very significant amounts of underground water. This water has been used as drinking water since 1914 for the Brno agglomeration. Two hydrogeological structures are exploited: aquifer C (Jizera formation) and aquifer B (Bílá hora formation). The Ústí syncline represents an asymmetrical graben, the deepest part of which is delineated by the Semanín and Svitava faults. The underground water of both structures is replenished by rainfall in the areas where they crop-out, namely in the eastern flank of the whole syncline. Systematical monitoring of the quality of the underground water has been running in the area for a very long time. It comprises mainly monitoring of the water quality in the individual production areas and monitoring of wells of the Czech Hydrometeorological Institute. Evaluation of all these data showed, that the whole area of the Ústí syncline, but especially the aquifer C, is threatened by areal pollution by nitrate compounds and locally by pesticide metabolites. Nitrate content reach up to 40 mg/l, which is the limit concentration set by the regulation 252/2004 Sb. Pesticides locally exceed the limit concentration. This shows, that the most dangerous compounds for the underground water as potential contaminants are clearly compounds closely connected with agriculture. The introduction of potential contaminants is of course controlled by the hydrogeological properties of rocks, i.e. whether it is a reservoir rock or a sealing rock. Sandstones of the aquifer C are separated by a layer of marl, sometimes called the Ca/Cb aquiclude. However, in the near-surface zone and in outcrops, this marl is heavily fractured and is very permeable. The Ústí syncline is also known for several pseudo-karst caves. Moreover, deeper pseudo-karst caverns were penetrated by boreholes by accident during the exploration of the Semanín fault zone. This karst permeability enables rapid spreading of infiltrating compounds including all possible pollutants. Based on tritium activity, freons and SF6 measurements, the mean delay times of the underground water in the Ústí syncline is estimated to be the first tens of years. One cannot presume any natural attenuation of very stable pesticides metabolites, just dilution. Based on this, there is a very real risk, that with increasing share of underground water younger than 2010, which has much higher concentration of pollutants, the concentration of these compounds will increase in exploited underground water.

Nový pohled na pozici slepenců od Starého Jičína ve slezské jednotce flyšového pásma Karpat

Lukáš Maceček — 2023-11-24

The conglomerates and sandstones on the castle hill of Starý Jičín Castle, assigned by previous authors to units of different age and tectonic position, were studied from the point of view of petrography and sedimentology in connection with detailed geological survey of the area. Thick-bedded conglomerates are characterized by sharp bases, massive or normal gradation and, in places, by imbrication of coarse clasts. They are product of high-density turbidite currents, debris flow, alternatively some layers may by products of hybrid sediment gravity flow deposits. The clastic component of the conglomerates is highly dominated by Štramberk-type limestones. Clasts of dolomitized limestones, Těšín-type detrital limestones and calcareous sandstones, and altered trachyte occur very rarely. Medium- and coarse-grained calcareous sandstones contain abundant lithoclasts and a relatively small proportion of quartz grains (20–30 %). A comparison with the conglomerate and sandstone of the Palkovice Formation from Kozlovice and Myslík showed considerable similarity. The sediments of both areas range within the upper Turonian–middle Coniacian interval based on previous micropalaeontological data. The conglomerates from Starý Jičín represent the proximal facies of the submarine fan in the lower slope (Kelč Facies Succession of the Silesian Unit), while the gravity flow deposits of the Palkovice Formation represent the more distal facies of the middle part of the submarine fan in continental rise (Baška Facies Succession). Based on sedimentological features, conglomerates from Starý Jičín can be classified as high-density turbidites, debris flow or hybrid sediment gravity flow deposits deposited in the upper part of a submarine fan. High-density and classical turbidites intercalated with claystone interlayers occurs in the Palkovice Formation of the Baška Facies Succession. Such an idea is in accordance with current knowledge on submarine fan architecture and with the assumed morphology of the former Silesian Basin.

New record of Middle Miocene (Badenian) brachiopods from Moravia, Czech Republic

Maria Aleksandra Bitner — 2023-11-24

This study presents the new record of brachiopods from the Middle Miocene deposits of the locality of Oslavany, Moravia, Czech Republic. The assemblage contains five species, i.e. Terebratula sp., Megathiris detruncata (Gmelin, 1791), Joania cordata (Risso, 1826), Argyrotheca cuneata (Risso, 1826), and Platidia sp. Apart from the species J. cordata, that dominates in the studied assemblage, the remaining species are reported for the first time from Oslavany. All species recognized here were already recorded from other localities in the Moravian part of the Carpathian Foredeep.

V příspěvku jsou prezentovány nové nálezy brachiopodů ze sedimentů středního miocénu na lokalitě Oslavany, Morava, Česká republika. Soubor zahrnuje 5 druhů, a to Terebratula sp., Megathiris detruncata (Gmelin, 1791), Joania cordata (Risso, 1826), Argyrotheca cuneata (Risso, 1826), a Platidia sp. Kromě druhu J. cordata, který ve studovaném materiálu dominuje, byly zbývající druhy zjištěny v Oslavanech poprvé. Všechny nalezené druhy jsou již známy z jiných lokalit moravské části karpatské předhlubně.