Moulting in Ordovician dalmanitoid and acastoid trilobites of the Prague Basin. Preliminary observation

A review of the supposed moulting positions of the Bohemian Ordovician dalmanitoid and acastoid trilobites is presented. Five main moulting positions are described, but some combinations of these are also widespread. The variability of the supposed moulting mechanisms is surprisingly high, especially in Middle Ordovician taxa. All and/or almost all moulting positions may occur together even within a single species. In advanced representatives, only a few of the described mechanisms prevail. Nevertheless, the occurrence of the moulting positions in the Bohemian Ordovician dalmanitoid and acastoid trilobites is considered to be constrained by the overall body morphology, rather than the result of phylogenetical relations. Functionality of the facial suture in these groups during the ontogeny and phylogeny is discussed

Observation of the influence which has the temperature of the surrounding on mechanical features of the core mixtures with respect to their type and the size of the grog

97 s. :obr., tab., grafy +CD ROMTato diplomová práce se zabývá sledováním vlivu teploty okolí na mechanické vlastnosti, konkrétně pevností ve střihu a ohybu, jádrových směsí s ohledem na druh ostřiva. V teoretické části je popsána výroba jader z různých druhů pojiv a ostřiv, vlastnosti jádrové formovací směsi a vliv teploty okolí závisející na ostřivu. V experimentální části diplomové práce se vyrábí různé typy jádrových směsí a zkouší se mechanické vlastnosti, které jsou závislé na teplotě okolí ostřiva. V závěru práce je zhodnocení výsledků mechanických vlastností na jednotlivých jádrových směsí a vyhodnocení vlivu teploty okolí na ostřiva. Tato diplomová práce byla vypracována v rámci řešení projektu SGS 28005

Production of zinc alloy castings

katedra: KSP; přílohy: 1 cd; rozsah: 48 s.This bachelor work deals with production of zinc alloy castings. Zinc, an easily fusible metal of blue-white colour, has lately been used more and more in industrial production and the automobile industry. The first part of this work concerns characteristics of zinc and its alloys, which are characterised in accordance with their application. Cast production and casting operations are characterised later in this study. The main part of this work includes summary of zinc alloy casting production, which consists of high-pressure castings. The main principles of zinc alloy casting production are discussed at the conclusion of this work.Tato bakalářská práce se zabývá výrobou odlitků ze slitin zinku. V poslední době se začíná tohoto lehce tavitelného, nepolymorfního, modrobílého kovu čím dál více uplatňovat v průmyslové výrobě, především v průmyslu automobilovém. První část bakalářské práce je zaměřena na charakteristiku zinku, jeho slitin, které jsou popsány dle použití. Dále je charakterizována výroba forem a následné odlévání. Hlavní částí práce je ucelený přehled výroby odlitků ze slitin zinku, které je založeno na vysokotlakém lití. V závěru práce jsou zmíněny hlavní zásady výroby odlitků ze slitin zinku

Ordovician conulariid monospecific assemblages (Czech Republic, Morocco)

A recently discovered locality of the Katian age near Erfoud (Morocco) supports an assumption that at least some conulariids lived preferably in monospecific associations. Thousands of skeletons belonging to Archaeoconularia consobrina (Barrande, 1867) were documented in an extensive accumulation within a 20 cm thick calcareous sandstone bed containing also rounded intraclasts of fine-grained sediments. The specimens are well exposed on the top surface of the bed due to weathering. The specimens have the same prevailing orientation throughout the entire bed. The preservation and distribution patterns of these conulariids suggest a parautochthonous origin of the accumulation that was likely deposited after a single, high water-energy event, such as a storm or turbidite flow. The same taphonomic situation was recently described for Anaconularia anomala (Barrande, 1867) from a Sandbian site in the Czech Republic and for Archaeoconularia cf. consobrina (Barrande, 1867) in a different Sandbian site in Bohemia, Czech Republic. Thus, the monospecific conulariid assemblages with abundant specimens seem not to be exceptional. Such mass occurrences of conulariids are similar in (1) alignment of specimens along the pre­vailing current direction, (2) limited content of other faunal elements, and (3) the presence of intraclasts and the sandstone matrix. These taxa are interpreted as originally inhabiting an offshore environment below the storm wave base, with erected skeletons firmly attached to the sandy bottom at some calm places, or more probably deeply anchored in sand with the apical part (similar mode of life has recently been shown in fan mussels, which are often accompanied by algae forming sea meadows). During a single catastrophic event, conulariid skeletons were first broken off. This resulted in prevalence of the rounded schott ending in the apical region of the specimens. The apertural endings, including lappets, were destroyed during rapid transport prior to final de­position as aligned monospecific mass accumulations. It is worth noting that some localities, especially those in Morocco, yielded mass accumulations, with tests densely covered by diverse epibionts like brachiopods and edrioasteroids, while others are typified by undisturbed skeletons without attached epizoans or traces of attachment scars. All these taphonomic and palaeoecological aspects, as well as association with mass occurrences of algae, are subject to further study

Preservation of fossils in the Šárka Formation (Darriwilian, Czech Republic)

The Šárka Formation is a well-known, fossiliferous Ordovician deposit in Bohemia. It has been targeted by fossil collectors since the 19th century due to the excellent preservation of many fossils. As a result, mainly well-preserved and interesting specimens have been deposited in collections. Many fragments, typical fossil accumulations but also complete specimens belonging to common taxa, have been ignored because they were considered poorly preserved compared to others. That is why some palaeoecological and taphonomical aspects of faunas are insufficiently represented in the existing collections. The Šárka Formation is early to middle Darriwilian in age and reflects an overall deepening of the Prague Basin, an Early Palaeozoic peri-Gondwanan basin, with a relic of its fill situated roughly between PlzeÅ and Prague as a part of the Teplá-Barrandian unit in Central Bohemia, Czech Republic. The Šárka Formation is typified by the prevalence of grey to dark grey shales that are 50 m thick in the south-western part of the basin and up to 300 m in the north-eastern part of it. Locally, these shales contain levels with predominantly siliceous nodules. Both, shales and nodules, are fossiliferous, but fossils demonstrate different modes of preservation, primarily resulting from different degrees of compaction accompanied by other processes such as the dissolution of shells. The highly diverse fauna in the formation is dominated by trilobites. Rhynchonelliformean brachiopods, bivalves, gastropods, cephalopods, ostracods, hyoliths, and echinoderms are very abundant; other groups such as conulariids, monoplacophorans, rostroconchs, machaeridans, and graptolites are less frequent. The fossils occur as isolated specimens, in clusters, or in larger concentrations of transported shells on the bedding planes. Fossils, the shells of which were originally composed of several parts (trilobite exoskeletons, bivalve molluscs, crustaceans, hyoliths, etc.), are often disarticulated. Disarticulated parts of skeletons are mostly complete, with a low degree of fragmentation. This is the prevailing mode of preservation, but some locali­ties yielded also abundant complete trilobites. In general, allochthonous material transported to short distances prevails in the Šárka Formation. Preservation in shales. The fossils in shales are variably compacted. Specimens of the groups producing organic protective structures, such as graptolites, range from predominantly flattened to relief when pyritized. The material of phosphatic shells (phyllocarid crustaceans, linguliformean brachiopods, conulariids) is usually preserved, primarily deformed depending on its solidity, and secondarily slightly flattened. Calcareous shells are often dissolved and the fossils cracked. Although primary cracking also occurs, many shells are collapsed indicating their deformation due to the sediment compaction before dissolution of a shell during late diagenesis. Preservation in nodules. Nodules are of early diagenetic origin and fossils in them are pre­served in full relief because they were protected from compaction. All deformations of fossils, such as cracking, can be considered primary, i.e. formed before the nodule formation. Only phosphatic shells occur in the nodules, organic and calcareous shells are not preserved with only minor exceptions. Thus, the dominating preservation mode of fossils in the nodules is as in­ternal and external moulds or only external moulds with a cavity inside. However, there is one special type of internal mould, which has been known for a long time but ignored because of its âworseâ preservation. This is related to many articulated brachiopods and bivalves but often also to some parts of trilobites, hyoliths and gastropods. It is formed by a porous spongiform material, sometimes forming irregular structures resembling the crumble. This taphonomic feature, unique for the nodules, represents a specific type of preservation. It can fully or partly fill in the cavities inside the closed two-valved shells, some enrolled trilobites, adapical parts of hyolith conchs, and gastropod shells but also glabellae, axes, or other parts of trilobites. This preservation is there­fore common in enclosed spaces of shells where the presence of organic substances, especially remains of tissues can be expected to occur even after their burial in the sediment. Subsequent decay of tissues in an open geochemical system, such as inside a muddy substrate that is a precursor of shales, would not be traced under normal conditions due to the migration of matters. The nodules were apparently of a very early diagenetic origin and their formation ceased the migration system of decaying tissue substances. The products of these processes remained in situ and fossilized in the form of the âtaphonomic crumbleâ, which has a considerable potential for several research directions

Subway into the Ordovician (Prague Basin, Czech Republic)

In the Late Ordovician, the Prague Basin was located at the high-latitude northwestern shelf of Gondwana. This period was characterised by profound environmental changes and ended by one of the most severe mass extinctions, which was caused by climatic changes. Although the end-Ordovician extinction is closely related to the Hirnantian glaciation, biodiversity started to decrease already in the late Katian. Decrease in temperatures and sea level drop are the main factors that affected these biodiversity changes. During the last years, construction of the new subway line D in Prague has provided a unique opportunity to study different aspects of the Upper Ordovician and Silurian of the Prague Basin. These tunnels have provided detailed information about the succession of fossil assemblages, facies variability and actual thicknesses of the upper Katian and Hirnantian formations (upper part of the Bohdalec, and entire Králův Dvůr and Kosov formations) in this part of the basin. Our study is based on material and data from several sites. We studied drill cores from vertical boreholes drilled from the surface and also horizontal boreholes drilled from the tunnel faces. The richest material came from an interim storage of excavated material near pitheads. In total, almost 700 m of sections in the tunnels were investigated. As the preliminary geo­logical exploration was carried out by various companies in connection with subway construction, intensive excavation and mining took place in several locations at the same time, and the frequency of our research activities and site visits were limited. Therefore, our palae­ontological and stratigraphical research was focused mainly on the Bohdalec Formation (upper Katian). The succession is, however, tectonised, apparently incomplete, and repetition of some parts cannot be excluded. The actual thickness of the investigated part of the Bohdalec Formation excavated so far is slightly less than 140 m (December 2022). The unit is dominated by fine-grained siliciclastics (dark grey shales and siltstones), except for the Michle Facies in the uppermost part of the Bohdalec Formation. This facies consists of calcareous sandstones alternating with siltstones and thin shaly interbeds. The section is regarded to be deposited in an offshore setting below the storm wave base. The Bohdalec Formation in the studied section is fossiliferous, and the abundance of fossils and composition of their associations are variable. Some subsections are typified by reduced fossil content. However, we also recorded several stratigraphical intervals (a few metres in thickness) with distinctly enriched fossil assemblages, notably with echinoderms, bryozoans, cnidarians, planktic graptolites, and sessile dendroid graptolites that are extremely rare anywhere else. Deposits of these specific intervals accumulated during gradual slowdown periods during the subsidence of the Prague Basin, which resulted in a decrease in the sedimentation rate and were followed by uplift, causing local shallowing. Also, global events, such as climatic and sea level fluctuations, influenced these changes of fauna and facies

Moulting in Ordovician dalmanitoid and acastoid trilobites of the Prague Basin. Preliminary observation

A review of the supposed moulting positions of the Bohemian Ordovician dalmanitoid and acastoid trilobites is presented. Five main moulting positions are described, but some combinations of these are also widespread. The variability of the supposed moulting mechanisms is surprisingly high, especially in Middle Ordovician taxa. All and/or almost all moulting positions may occur together even within a single species. In advanced representatives, only a few of the described mechanisms prevail. Nevertheless, the occurrence of the moulting positions in the Bohemian Ordovician dalmanitoid and acastoid trilobites is considered to be constrained by the overall body morphology, rather than the result of phylogenetical relations. Functionality of the facial suture in these groups during the ontogeny and phylogeny is discussed