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Ladislav Slavik - One of the best experts on this subject based on the ideXlab platform.
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in search of silurian devonian boundary conodont markers in carbonate environments of the prague Synform czech republic
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Aneta Hušková, Ladislav SlavikAbstract:Abstract Conodonts from two of the most representative sections in the Prague Synform were studied in search of alternative biostratigraphic markers of the Silurian/Devonian boundary. The Na Požarech and Praha-Radotin sections, with contrasting lithologies, were chosen to study changes in conodont faunas in relation to different carbonate facies – i.e., shallower- and deeper-water carbonates around the Silurian/Devonian boundary in the type area. Apart from icriodontids, the differences in bathymetry were also expected to affect the diversity of taxa of the family Spathognathodontidae, which is generally the most abundant and the most tolerant clade found in different carbonate environments at this stratigraphic level. Although the Scyphocrinites Horizon is developed at both study localities, the microfacies analysis confirmed significant differences in depositional environments at around the Silurian/Devonian boundary. Abundant conodont material from the two sections (more than one thousand elements) showed a high diversity and disparity in both the Spathognathodontidae and Icriodontidae. Altogether, 18 taxa were identified, but many forms still require a formal description. A new spathognathodontid taxon, Zieglerodina petrea sp. nov., described herein, is easily distinguishable because of its distinct morphology in denticulation of the blade, and its first occurrence is just above the base of the Devonian in both sections. It also has been identified in conodont collections from Morocco and the Carnic Alps, as such its biostratigraphic significance can be extended to peri-Gondwana. Although the stratigraphic occurrence and global significance of this promising conodont taxon still has to be tested in other areas, current data suggest it might have a great potential for identifying the base of the Devonian in sections where critical graptolite and icriodontid taxa are missing.
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early devonian lochkovian early emsian bioevents and conodont response in the prague Synform czech republic
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Ladislav Slavik, Jindřich HladilAbstract:Abstract The Devonian succession of the Prague Synform is characterized by two major lithofacies: shallow-water biodetrital, mostly crinoidal limestones that also include a reefal skeletal accumulation of Pragian age, and a more pelagic facies that is represented mostly by calcisiltites. Among the several Devonian prominent sea-level fluctuations, some can be traced globally, e.g., the Basal Pragian and Kacak events. In recent years, conodont biostratigraphy of the Early Devonian (Lochkovian, Pragian and early Emsian) of the Prague Synform has been refined. The regional subdivision of the Lower Devonian in its type area has been greatly improved by the integration of new biostratigraphic, chemostratigraphic, sedimentological, and petrophysical data that has, in turn, strengthened global correlations for this interval in Earth's history. The complete conodont biozonation of the Early Devonian interval (basal Lochkovian – earliest Emsian) in the Prague Synform includes 17 biozones, which can be applied to sections representing various depositional environments and have more global applicability than previously proposed ‘global’ conodont biozonations. The zonal scale enables a precise biostratigraphic delimitation of the major Early Devonian biotic events (Silurian-Devonian Boundary Event, Lochkovian-Pragian Event and Basal Zlichovian Event). There were major changes in the conodont fauna in response to the Silurian-Devonian Boundary and Lochkovian-Pragian events, however the Basal Zlichovian Event was only characterized by a very gradual transition in the conodont fauna. In parallel to the traditional events defined for the Prague Synform, seven other significant conodont events have been documented. These events represent major turnovers in the conodont fauna that have a direct impact on conodont biostratigraphy, specifically at a global scale. The Icriodus and Irregularis events are congruent with the lower boundaries of the Lochkovian and Pragian stages, respectively. The conodont events established in the Prague Synform largely reflect variations in the seawater depth but are generally independent of lithological changes within sections of the Prague Synform.
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the mid homerian silurian biotic crisis in offshore settings of the prague Synform czech republic integration of the graptolite fossil record with conodonts shelly fauna and carbon isotope data
Palaeogeography Palaeoclimatology Palaeoecology, 2019Co-Authors: Štěpán Manda, Ladislav Slavik, Petr Štorch, Jiři Frýda, Zuzana TasáryováAbstract:Abstract The middle Homerian biotic crisis resulted in the almost complete eradication of graptolites. The shale-dominated Kosov Quarry section, central Bohemia, preserves the most complete graptolite record across the crisis in peri-Gondwanan Europe. The pre-extinction graptolite assemblage of the upper lundgreni Biozone, composed of ten species vanished in three extinction phases recognized in an interval 1.6 m thick. The crisis commenced with the increasing dominance of generalist taxa and subsequent extinction of several abundant species including Cyrtograptus lundgreni. The second phase coincided with the extinctions of genera Cyrtograptus and Testograptus, whereas long-ranging, generalist monograptids prevailed before they became extinct as the crisis culminated in its third phase in the flemingii Biozone. The lower part of the overlying parvus Biozone contains only Pristiograptus parvus, which became abundant in the upper part of the biozone, together with incoming Gothograptus nassa. The recovery interval is marked by a moderate diversification of monograptids and retiolitids. The extinction did not affect the diversity of pelagic cephalopods although their abundance was reduced. A bivalve-dominated benthic fauna disappeared throughout the extinction interval and re-appeared not earlier than in the latest Homerian. It was temporarily replaced by a time-specific fauna of anachronistic trilobites and brachiopods. The extinction interval coincided with sea-level fall, indicated by limestone slump-beds in a generally shaly succession. The post-extinction interval corresponds with a lowstand systems tract with deposition of condensed shelly limestone and burrowed shale. A positive carbon isotope excursion started in the flemingii Biozone and δ13C values increased up to the lower parvus Biozone above which the plateau of the first peak started. The beginning of the graptolite extinction predated the early phase of the late Homerian carbon isotope excursion. The terminal phase of the extinction, nevertheless coincided with the onset of the carbon isotope excursion and change in benthic fauna.
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refining the early devonian time scale using milankovitch cyclicity in lochkovian pragian sediments prague Synform czech republic
Earth and Planetary Science Letters, 2016Co-Authors: A. C. Silva, Leona Chadimova, Jindřich Hladil, Frederik J Hilgen, Ondřej Bábek, Ladislav Slavik, Mark J. DekkersAbstract:Abstract The Early Devonian geological time scale (base of the Devonian at 418.8 ± 2.9 Myr , Becker et al., 2012 ) suffers from poor age control, with associated large uncertainties between 2.5 and 4.2 Myr on the stage boundaries. Identifying orbital cycles from sedimentary successions can serve as a very powerful chronometer to test and, where appropriate, improve age models. Here, we focus on the Lochkovian and Pragian, the two lowermost Devonian stages. High-resolution magnetic susceptibility ( χ in – 5 to 10 cm sampling interval) and gamma ray spectrometry (GRS – 25 to 50 cm sampling interval) records were gathered from two main limestone sections, Požar-CS (118 m, spanning the Lochkov and Praha Formations) and Pod Barrandovem (174 m; Praha Formation), both in the Czech Republic. An additional section (Branžovy, 65 m, Praha Formation) was sampled for GRS (every 50 cm). The χ in and GRS records are very similar, so χ in variations are driven by variations in the samples' paramagnetic clay mineral content, reflecting changes in detrital input. Therefore, climatic variations are very likely captured in our records. Multiple spectral analysis and statistical techniques such as: Continuous Wavelet Transform, Evolutive Harmonic Analysis, Multi-taper method and Average Spectral Misfit, were used in concert to reach an optimal astronomical interpretation. The Požar-CS section shows distinctly varying sediment accumulation rates. The Lochkovian (essentially equivalent to the Lochkov Formation (Fm.)) is interpreted to include a total of nineteen 405 kyr eccentricity cycles, constraining its duration to 7.7 ± 2.8 Myr . The Praha Fm. includes fourteen 405 kyr eccentricity cycles in the three sampled sections, while the Pragian Stage only includes about four 405 kyr eccentricity cycles, thus exhibiting durations of 5.7 ± 0.6 Myr and 1.7 ± 0.7 Myr respectively. Because the Lochkov Fm. contains an interval with very low sediment accumulation rate and because the Praha Fm. was cross-validated in three different sections, the uncertainty in the duration of the Lochkov Fm. and the Lochkovian is larger than that of the Praha Fm. and Pragian. The new floating time scales for the Lochkovian and Pragian stages have an unprecedented precision, with reduction in the uncertainty by a factor of 1.7 for the Lochkovian and of ∼6 for the Pragian. Furthermore, longer orbital modulation cycles are also identified with periodicities of ∼1000 kyr and 2000–2500 kyr.
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wenlock ludlow boundary interval revisited new insights from the offshore facies of the prague Synform czech republic
Canadian Journal of Earth Sciences, 2016Co-Authors: Petr Štorch, Ladislav Slavik, Štěpán Manda, Zuzana TasáryováAbstract:Wenlock–Ludlow boundary beds exposed near Nesvacily in the Prague Synform are documented in terms of their lithology, faunal content, high-resolution record of 19 graptolite species, graptolite biostratigraphy, and conodont record. This is the first time in Bohemia and peri-Gondwanan Europe that a continuous graptolite-bearing section through upper ludensis – middle nilssoni biozones is described in detail to refine high-resolution biostratigraphy and correlation of the Wenlock–Ludlow boundary. Organic-rich shale, relatively rare nongraptolite fauna, and absence of bioturbation indicate a stable deep-water offshore setting with sporadic, low-level bottom oxygenation. The uninterrupted succession revealed a series of origination events of principal graptolite taxa employed in determination of the Wenlock–Ludlow boundary strata worldwide. Bohemograptus represented by B. praecox appeared as early as in the uppermost Wenlock ludensis Biozone. Bohemograptus praecox is later accompanied and replaced by B. bohem...
Aneta Hušková - One of the best experts on this subject based on the ideXlab platform.
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in search of silurian devonian boundary conodont markers in carbonate environments of the prague Synform czech republic
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Aneta Hušková, Ladislav SlavikAbstract:Abstract Conodonts from two of the most representative sections in the Prague Synform were studied in search of alternative biostratigraphic markers of the Silurian/Devonian boundary. The Na Požarech and Praha-Radotin sections, with contrasting lithologies, were chosen to study changes in conodont faunas in relation to different carbonate facies – i.e., shallower- and deeper-water carbonates around the Silurian/Devonian boundary in the type area. Apart from icriodontids, the differences in bathymetry were also expected to affect the diversity of taxa of the family Spathognathodontidae, which is generally the most abundant and the most tolerant clade found in different carbonate environments at this stratigraphic level. Although the Scyphocrinites Horizon is developed at both study localities, the microfacies analysis confirmed significant differences in depositional environments at around the Silurian/Devonian boundary. Abundant conodont material from the two sections (more than one thousand elements) showed a high diversity and disparity in both the Spathognathodontidae and Icriodontidae. Altogether, 18 taxa were identified, but many forms still require a formal description. A new spathognathodontid taxon, Zieglerodina petrea sp. nov., described herein, is easily distinguishable because of its distinct morphology in denticulation of the blade, and its first occurrence is just above the base of the Devonian in both sections. It also has been identified in conodont collections from Morocco and the Carnic Alps, as such its biostratigraphic significance can be extended to peri-Gondwana. Although the stratigraphic occurrence and global significance of this promising conodont taxon still has to be tested in other areas, current data suggest it might have a great potential for identifying the base of the Devonian in sections where critical graptolite and icriodontid taxa are missing.
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The middle and upper Lochkovian (Lower Devonian) conodont successions in key peri-Gondwana localities (Spanish Central Pyrenees and Prague Synform) and their relevance for global correlations
Terra Nova, 2015Co-Authors: José Ignacio Valenzuela-ríos, Ladislav Slavik, Jau-chyn Liao, Helena Calvo, Aneta Hušková, Leona ChadimovaAbstract:Detailed correlation, based on conodont sequences, between middle and upper Lochkovian carbonate successions from two key peri-Gondwanan regions, the Spanish Central Pyrenees and the Prague Synform, is attained for the first time. This correlation facilitates the definition of tie points for further multidisciplinary studies that seek to establish high-resolution temporal subdivision and global correlation. Some intervals have a precision of less than 0.5 Ma, which is significantly greater than in previous studies. The estimated elapsed time considered herein is about 3.2 Ma and is subdivided into five major zones of global scope: transitanstrigonicus, trigonicus-kutscheri, kutscheri-pandora b, pandora b-gilberti and gilberti-steinachensis b. By providing tie points and globally applicable criteria, this research contributes to the international cooperative effort to subdivide the Devonian standard stages into globally recognised substages.
Leona Koptikova - One of the best experts on this subject based on the ideXlab platform.
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Subdivision of the Lochkovian Stage based on conodont faunas from the stratotype area (Prague Synform, Czech Republic)
Geological Journal, 2012Co-Authors: Ladislav Slavik, Peter Carls, Jindřich Hladil, Leona KoptikovaAbstract:Relatively rich conodont faunas from sections in the Prague Synform (Barrandian area, Czech Republic) include a number of indexes and other important guide conodonts that can be correlated with other regions, especially with Nevada and the Spanish Central Pyrenees. The collation and detailed correlation of conodont data from the Lochkovian in two parallel sections in the Požary quarries, together with biostratigraphic control of additional data from several (incomplete) sections with changing facies development, is the basis for a new detailed regional biozonal scale for the Lochkovian in the Prague Synform. The new subdivision follows, with modification, the global threefold conodont subdivision of the Lochkovian. Data from the Prague Synform enable further detailed subdivision of the lower, middle and upper Lochkovian into small-scale units. The conodont distribution shows a large proportional discrepancy between the late Lochkovian elsewhere; the conodont record in the latest Lochkovian in the Prague Synform area, which appears to be rather restricted and requires further discussion. Copyright © 2012 John Wiley & Sons, Ltd.
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precise position of the basal chotec event and evolution of sedimentary environments near the lower middle devonian boundary the magnetic susceptibility gamma ray spectrometric lithological and geochemical record of the prague Synform czech republic
Palaeogeography Palaeoclimatology Palaeoecology, 2011Co-Authors: Leona KoptikovaAbstract:Abstract The Basal Chotec Event, slightly above the Lower–Middle Devonian boundary in the Prague Synform, is significant not only for its faunal and lithological changes but also for its distinct and widely correlatable magnetic susceptibility (MS), gamma spectrometric (GRS), and geochemical patterns. The upper part of the Třebotov Limestone was composed of calcisiltic material deposited from distal storm or turbidite currents, which alternate with slowly deposited and condensed hemipelagic material. The lower part of the overlying Chotec Limestone was also composed of turbidite deposits. A more proximal depositional environment is recorded in the Na Skrabku Quarry whereas the Prastav Quarry represents a more distal environment. A decrease in the proportion of pelagic components was observed toward the event datum and an increase in the amount of recycled lithoclastic-skeletal detritus carbonate material. A similar trend is displayed by the shallow-water stratigraphic equivalents in the Cervený Quarry. The MS record across the studied interval produces a smooth curve below the first event-related beds (Třebotov and Suchomasty Limestone), a drop in MS values at the event base (base of the Chotec and Acanthopyge Limestone), and a rapid increase in MS values with high-magnitude and high-amplitude oscillations above the first event-related dark beds. The GRS record shows a reversal in the Th/U ratio at the event base from Th/U ≫ 1 to Th/U
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FINE-GRAINED NON-CARBONATE PARTICLES EMBEDDED IN NERITIC TO PELAGIC LIMESTONES (LOCHKOVIAN TO EMSIAN, PRAGUE Synform, CZECH REPUBLIC): COMPOSITION, PROVENANCE AND LINKS TO MAGNETIC SUSCEPTIBILITY AND GAMMA-RAY LOGS
Geologica Belgica, 2010Co-Authors: Leona Koptikova, Petr Cejchan, Jindřich Hladil, Ladislav Slavik, Ondřej BábekAbstract:Variations in non-carbonate impurities trapped in the Lower Devonian limestone stratal successions in the Prague Synform are studied, with particular emphasis on the composition and quantities of fine-mineral grain assemblages. Different assemblages are encountered for the Lochkovian, lower Emsian and Pragian. The Lochkovian (represented by the Lochkov Formation) is characterized by pyrite-pyrrhotite assemblages with lower abundance of iron oxides and oxyhydroxides (mostly goethite) whereas the Pragian (represented by the Praha Formation) shows relatively abundant iron oxides and oxyhydroxides (mostly hematite). Major changes in magnetic susceptibility and gamma-ray spectrometric logs also coincide with the Lochkovian/Pragian boundary. Maximum values of magnetic susceptibility and relatively high Th, K concentrations above the boundary correspond to the elevated amounts of barite and Ba concentrations. This level is interpreted as a significant interval with elevated delivery of impurities of aeolian origin, deceleration of sedimentation rate together with decreased carbonate productivity. REE distributions in the Lochkovian to lower Emsian are indicative of the aeolian origin of trapped impurities. Detrital zircons found in all three stages are considered to be also of aeolian origin.
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the dynamic time warping approach to comparison of magnetic susceptibility logs and application to lower devonian calciturbidites prague Synform bohemian massif
Geologica Belgica, 2010Co-Authors: Jindřich Hladil, Leona Koptikova, Petr Cejchan, Martin Vondra, Robert Vich, Ladislav SlavikAbstract:The effectiveness of alignment of magnetic susceptibility (MS) stratigraphic sections by means of the dynamic time warping (DTW) approach was tested with positive results. The DTW is a robust and effective tool for the alignment of the sequential MS data which is particularly sensitive to MS-log patterns, their details, successions, distortion or absence from logs. Moreover, the DTW performance proved to be appropriate for sections which involve a great deal of irregularly spread compacted or thick-bedded intervals and variously positioned and sized gaps. In view of the fact that the lateral changes in short- to medium-term sedimentation rates and local variations in diagenetic compaction are not exceptional but rather common features of the compared sedimentary sections, the DTW becomes a significant tool for stratigraphic comparison of sections with good potential of becoming an alternative to cyclostratigraphic correlation methods. Conditions governing the formation of Lower Devonian (Pragian) carbonate clinoforms obviously appear to be this case, and testing of the DTW on this type of MS sections suggests that the computationally robust results remain approximately the same, even if the importance of high values (peaks) is nonlinearly decreased or increased. In such cases the DTW outperforms the distortion-based vector quantisation (VQ), continuous density hidden Markov models (CDHMM), wavelet transformation (WT) or cross-correlation (CC) based approaches. The near absence of artificially introduced preconditions or predefined elements is also an advantage. The alignment of the sections using the DTW gives us warning about distorted intervals, thus reducing the risk of assembling quite different types of rhythmic patterns or cycles together. The overall ambition of this paper is to introduce the DTW alignment technique as an effective tool for MS log correlation. Extensive testing of the requirements for input data and constraints according to maximum differences between the compared stratigraphic segments are reserved for other studies. For the Pragian of the Barrandian area (specifically, calciturbidite-dominated clinoforms), the DTW-based interconnection between the relevant points of two sections has a resolution which is close to sampling distances (several cm) and is about two orders of magnitude higher compared to that which can be achieved by the bio-, chemo- or lithostratigraphic tools. The first results confirmed the presence of numerous visible and hidden gaps and condensations in the sections.
Jindřich Hladil - One of the best experts on this subject based on the ideXlab platform.
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early devonian lochkovian early emsian bioevents and conodont response in the prague Synform czech republic
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Ladislav Slavik, Jindřich HladilAbstract:Abstract The Devonian succession of the Prague Synform is characterized by two major lithofacies: shallow-water biodetrital, mostly crinoidal limestones that also include a reefal skeletal accumulation of Pragian age, and a more pelagic facies that is represented mostly by calcisiltites. Among the several Devonian prominent sea-level fluctuations, some can be traced globally, e.g., the Basal Pragian and Kacak events. In recent years, conodont biostratigraphy of the Early Devonian (Lochkovian, Pragian and early Emsian) of the Prague Synform has been refined. The regional subdivision of the Lower Devonian in its type area has been greatly improved by the integration of new biostratigraphic, chemostratigraphic, sedimentological, and petrophysical data that has, in turn, strengthened global correlations for this interval in Earth's history. The complete conodont biozonation of the Early Devonian interval (basal Lochkovian – earliest Emsian) in the Prague Synform includes 17 biozones, which can be applied to sections representing various depositional environments and have more global applicability than previously proposed ‘global’ conodont biozonations. The zonal scale enables a precise biostratigraphic delimitation of the major Early Devonian biotic events (Silurian-Devonian Boundary Event, Lochkovian-Pragian Event and Basal Zlichovian Event). There were major changes in the conodont fauna in response to the Silurian-Devonian Boundary and Lochkovian-Pragian events, however the Basal Zlichovian Event was only characterized by a very gradual transition in the conodont fauna. In parallel to the traditional events defined for the Prague Synform, seven other significant conodont events have been documented. These events represent major turnovers in the conodont fauna that have a direct impact on conodont biostratigraphy, specifically at a global scale. The Icriodus and Irregularis events are congruent with the lower boundaries of the Lochkovian and Pragian stages, respectively. The conodont events established in the Prague Synform largely reflect variations in the seawater depth but are generally independent of lithological changes within sections of the Prague Synform.
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refining the early devonian time scale using milankovitch cyclicity in lochkovian pragian sediments prague Synform czech republic
Earth and Planetary Science Letters, 2016Co-Authors: A. C. Silva, Leona Chadimova, Jindřich Hladil, Frederik J Hilgen, Ondřej Bábek, Ladislav Slavik, Mark J. DekkersAbstract:Abstract The Early Devonian geological time scale (base of the Devonian at 418.8 ± 2.9 Myr , Becker et al., 2012 ) suffers from poor age control, with associated large uncertainties between 2.5 and 4.2 Myr on the stage boundaries. Identifying orbital cycles from sedimentary successions can serve as a very powerful chronometer to test and, where appropriate, improve age models. Here, we focus on the Lochkovian and Pragian, the two lowermost Devonian stages. High-resolution magnetic susceptibility ( χ in – 5 to 10 cm sampling interval) and gamma ray spectrometry (GRS – 25 to 50 cm sampling interval) records were gathered from two main limestone sections, Požar-CS (118 m, spanning the Lochkov and Praha Formations) and Pod Barrandovem (174 m; Praha Formation), both in the Czech Republic. An additional section (Branžovy, 65 m, Praha Formation) was sampled for GRS (every 50 cm). The χ in and GRS records are very similar, so χ in variations are driven by variations in the samples' paramagnetic clay mineral content, reflecting changes in detrital input. Therefore, climatic variations are very likely captured in our records. Multiple spectral analysis and statistical techniques such as: Continuous Wavelet Transform, Evolutive Harmonic Analysis, Multi-taper method and Average Spectral Misfit, were used in concert to reach an optimal astronomical interpretation. The Požar-CS section shows distinctly varying sediment accumulation rates. The Lochkovian (essentially equivalent to the Lochkov Formation (Fm.)) is interpreted to include a total of nineteen 405 kyr eccentricity cycles, constraining its duration to 7.7 ± 2.8 Myr . The Praha Fm. includes fourteen 405 kyr eccentricity cycles in the three sampled sections, while the Pragian Stage only includes about four 405 kyr eccentricity cycles, thus exhibiting durations of 5.7 ± 0.6 Myr and 1.7 ± 0.7 Myr respectively. Because the Lochkov Fm. contains an interval with very low sediment accumulation rate and because the Praha Fm. was cross-validated in three different sections, the uncertainty in the duration of the Lochkov Fm. and the Lochkovian is larger than that of the Praha Fm. and Pragian. The new floating time scales for the Lochkovian and Pragian stages have an unprecedented precision, with reduction in the uncertainty by a factor of 1.7 for the Lochkovian and of ∼6 for the Pragian. Furthermore, longer orbital modulation cycles are also identified with periodicities of ∼1000 kyr and 2000–2500 kyr.
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Subdivision of the Lochkovian Stage based on conodont faunas from the stratotype area (Prague Synform, Czech Republic)
Geological Journal, 2012Co-Authors: Ladislav Slavik, Peter Carls, Jindřich Hladil, Leona KoptikovaAbstract:Relatively rich conodont faunas from sections in the Prague Synform (Barrandian area, Czech Republic) include a number of indexes and other important guide conodonts that can be correlated with other regions, especially with Nevada and the Spanish Central Pyrenees. The collation and detailed correlation of conodont data from the Lochkovian in two parallel sections in the Požary quarries, together with biostratigraphic control of additional data from several (incomplete) sections with changing facies development, is the basis for a new detailed regional biozonal scale for the Lochkovian in the Prague Synform. The new subdivision follows, with modification, the global threefold conodont subdivision of the Lochkovian. Data from the Prague Synform enable further detailed subdivision of the lower, middle and upper Lochkovian into small-scale units. The conodont distribution shows a large proportional discrepancy between the late Lochkovian elsewhere; the conodont record in the latest Lochkovian in the Prague Synform area, which appears to be rather restricted and requires further discussion. Copyright © 2012 John Wiley & Sons, Ltd.
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FINE-GRAINED NON-CARBONATE PARTICLES EMBEDDED IN NERITIC TO PELAGIC LIMESTONES (LOCHKOVIAN TO EMSIAN, PRAGUE Synform, CZECH REPUBLIC): COMPOSITION, PROVENANCE AND LINKS TO MAGNETIC SUSCEPTIBILITY AND GAMMA-RAY LOGS
Geologica Belgica, 2010Co-Authors: Leona Koptikova, Petr Cejchan, Jindřich Hladil, Ladislav Slavik, Ondřej BábekAbstract:Variations in non-carbonate impurities trapped in the Lower Devonian limestone stratal successions in the Prague Synform are studied, with particular emphasis on the composition and quantities of fine-mineral grain assemblages. Different assemblages are encountered for the Lochkovian, lower Emsian and Pragian. The Lochkovian (represented by the Lochkov Formation) is characterized by pyrite-pyrrhotite assemblages with lower abundance of iron oxides and oxyhydroxides (mostly goethite) whereas the Pragian (represented by the Praha Formation) shows relatively abundant iron oxides and oxyhydroxides (mostly hematite). Major changes in magnetic susceptibility and gamma-ray spectrometric logs also coincide with the Lochkovian/Pragian boundary. Maximum values of magnetic susceptibility and relatively high Th, K concentrations above the boundary correspond to the elevated amounts of barite and Ba concentrations. This level is interpreted as a significant interval with elevated delivery of impurities of aeolian origin, deceleration of sedimentation rate together with decreased carbonate productivity. REE distributions in the Lochkovian to lower Emsian are indicative of the aeolian origin of trapped impurities. Detrital zircons found in all three stages are considered to be also of aeolian origin.
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the dynamic time warping approach to comparison of magnetic susceptibility logs and application to lower devonian calciturbidites prague Synform bohemian massif
Geologica Belgica, 2010Co-Authors: Jindřich Hladil, Leona Koptikova, Petr Cejchan, Martin Vondra, Robert Vich, Ladislav SlavikAbstract:The effectiveness of alignment of magnetic susceptibility (MS) stratigraphic sections by means of the dynamic time warping (DTW) approach was tested with positive results. The DTW is a robust and effective tool for the alignment of the sequential MS data which is particularly sensitive to MS-log patterns, their details, successions, distortion or absence from logs. Moreover, the DTW performance proved to be appropriate for sections which involve a great deal of irregularly spread compacted or thick-bedded intervals and variously positioned and sized gaps. In view of the fact that the lateral changes in short- to medium-term sedimentation rates and local variations in diagenetic compaction are not exceptional but rather common features of the compared sedimentary sections, the DTW becomes a significant tool for stratigraphic comparison of sections with good potential of becoming an alternative to cyclostratigraphic correlation methods. Conditions governing the formation of Lower Devonian (Pragian) carbonate clinoforms obviously appear to be this case, and testing of the DTW on this type of MS sections suggests that the computationally robust results remain approximately the same, even if the importance of high values (peaks) is nonlinearly decreased or increased. In such cases the DTW outperforms the distortion-based vector quantisation (VQ), continuous density hidden Markov models (CDHMM), wavelet transformation (WT) or cross-correlation (CC) based approaches. The near absence of artificially introduced preconditions or predefined elements is also an advantage. The alignment of the sections using the DTW gives us warning about distorted intervals, thus reducing the risk of assembling quite different types of rhythmic patterns or cycles together. The overall ambition of this paper is to introduce the DTW alignment technique as an effective tool for MS log correlation. Extensive testing of the requirements for input data and constraints according to maximum differences between the compared stratigraphic segments are reserved for other studies. For the Pragian of the Barrandian area (specifically, calciturbidite-dominated clinoforms), the DTW-based interconnection between the relevant points of two sections has a resolution which is close to sampling distances (several cm) and is about two orders of magnitude higher compared to that which can be achieved by the bio-, chemo- or lithostratigraphic tools. The first results confirmed the presence of numerous visible and hidden gaps and condensations in the sections.
Zuzana Tasáryová - One of the best experts on this subject based on the ideXlab platform.
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the mid homerian silurian biotic crisis in offshore settings of the prague Synform czech republic integration of the graptolite fossil record with conodonts shelly fauna and carbon isotope data
Palaeogeography Palaeoclimatology Palaeoecology, 2019Co-Authors: Štěpán Manda, Ladislav Slavik, Petr Štorch, Jiři Frýda, Zuzana TasáryováAbstract:Abstract The middle Homerian biotic crisis resulted in the almost complete eradication of graptolites. The shale-dominated Kosov Quarry section, central Bohemia, preserves the most complete graptolite record across the crisis in peri-Gondwanan Europe. The pre-extinction graptolite assemblage of the upper lundgreni Biozone, composed of ten species vanished in three extinction phases recognized in an interval 1.6 m thick. The crisis commenced with the increasing dominance of generalist taxa and subsequent extinction of several abundant species including Cyrtograptus lundgreni. The second phase coincided with the extinctions of genera Cyrtograptus and Testograptus, whereas long-ranging, generalist monograptids prevailed before they became extinct as the crisis culminated in its third phase in the flemingii Biozone. The lower part of the overlying parvus Biozone contains only Pristiograptus parvus, which became abundant in the upper part of the biozone, together with incoming Gothograptus nassa. The recovery interval is marked by a moderate diversification of monograptids and retiolitids. The extinction did not affect the diversity of pelagic cephalopods although their abundance was reduced. A bivalve-dominated benthic fauna disappeared throughout the extinction interval and re-appeared not earlier than in the latest Homerian. It was temporarily replaced by a time-specific fauna of anachronistic trilobites and brachiopods. The extinction interval coincided with sea-level fall, indicated by limestone slump-beds in a generally shaly succession. The post-extinction interval corresponds with a lowstand systems tract with deposition of condensed shelly limestone and burrowed shale. A positive carbon isotope excursion started in the flemingii Biozone and δ13C values increased up to the lower parvus Biozone above which the plateau of the first peak started. The beginning of the graptolite extinction predated the early phase of the late Homerian carbon isotope excursion. The terminal phase of the extinction, nevertheless coincided with the onset of the carbon isotope excursion and change in benthic fauna.
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wenlock ludlow boundary interval revisited new insights from the offshore facies of the prague Synform czech republic
Canadian Journal of Earth Sciences, 2016Co-Authors: Petr Štorch, Ladislav Slavik, Štěpán Manda, Zuzana TasáryováAbstract:Wenlock–Ludlow boundary beds exposed near Nesvacily in the Prague Synform are documented in terms of their lithology, faunal content, high-resolution record of 19 graptolite species, graptolite biostratigraphy, and conodont record. This is the first time in Bohemia and peri-Gondwanan Europe that a continuous graptolite-bearing section through upper ludensis – middle nilssoni biozones is described in detail to refine high-resolution biostratigraphy and correlation of the Wenlock–Ludlow boundary. Organic-rich shale, relatively rare nongraptolite fauna, and absence of bioturbation indicate a stable deep-water offshore setting with sporadic, low-level bottom oxygenation. The uninterrupted succession revealed a series of origination events of principal graptolite taxa employed in determination of the Wenlock–Ludlow boundary strata worldwide. Bohemograptus represented by B. praecox appeared as early as in the uppermost Wenlock ludensis Biozone. Bohemograptus praecox is later accompanied and replaced by B. bohem...
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magnetic scanning and interpretation of paleomagnetic data from prague Synform s volcanics
Studia Geophysica Et Geodaetica, 2013Co-Authors: Štěpán Manda, Zuzana Tasáryová, Gunther Kletetschka, Petr Schnabl, Kristýna Sifnerova, Petr PrunerAbstract:Magnetic images have been produced at the distance of 0.1 mm from the polished basaltic thin sections of rocks from Prague Synform in Barrandian area. Three different magnetic textures were seen and when combined with optical imaging could be related to petrological features. The first magnetic texture revealed that most of the magnetic signature is localized within the amygdales formed later after the basalts became part of the sedimentary sequence. The second texture showed that the basaltic body contains large grain size distribution of magnetic carriers possibly with variable viscous magnetizations. The third texture suggested a presence of magnetic anisotropy of igneous origin. Such textural magnetic information along with the paleomagnetic characteristics of the basaltic rocks of Silurian age constrained the overall geological interpretation.
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the graptolite conodont and sedimentary record through the late ludlow kozlowskii event silurian in the shale dominated succession of bohemia
Geological Magazine, 2012Co-Authors: Štěpán Manda, Ladislav Slavik, Petr Štorch, Jiři Frýda, Jiři Křiž, Zuzana TasáryováAbstract:The shale-dominated hemipelagic succession exposed in the southwestern part of the Prague Synform preserves the most complete Ludfordian graptolite record so far encountered from peri-Gondwanan Europe. Four graptolite biozones – the Neocucullograptus inexpectatus , Nc. kozlowskii , Pseudomonoclimacis latilobus–Slovinograptus balticus and Pristiograptus fragmentalis biozones – are recognized in the middle and late Ludfordian, between the Bohemograptus tenuis Biozone and the base of the Pridoli Series. Conodont occurrences are restricted to scattered limestone beds, but enable tentative integration of the graptolite and conodont biozonal schemes. Particular attention was paid to faunal and sedimentary changes and the carbon isotope record across the middle Ludfordian Kozlowskii extinction Event. The Kozlowskii Event caused the almost simultaneous extinction of graptolites with ventrally curved rhabdosomes. The genera Bohemograptus , Polonograptus and Neocucullograptus , along with Pseudomonoclimacis dalejensis , disappeared from the fossil record. The offshore conodont fauna recorded in the section was not strongly affected and similarly the pelagic orthocerids and nektonic Ceratiocaris passed unaffected through the extinction interval. The abundant and widespread pelagic myodocopid ostracod Entomis , however, became extinct. The late Ludfordian graptolite recovery gave origin to a novel fauna of Pridoli type from taxa that emerged or just reappeared above the Kozlowskii crisis. In Vseradice and elsewhere in the Prague Synform, the recovery, manifested by the appearance of Pseudomonoclimacis latilobus and Slovinograptus balticus , closely postdates the end of the isotope excursion but pre-dates the first appearance of the conodont index ‘ Ozarkodina ’ snajdri . Here the graptolite recovery was delayed relative to the recovery of the benthic fauna. A canalized intraformational limestone conglomerate corresponds with a gap in the sedimentary record above the Kozlowskii extinction and just below the graptolite recovery. The benthic faunas from the conglomerate matrix and pebbles permit correlation with the shallower part of the basin indicating a distinct fall in sea-level. The present data demonstrate the coincidence of the graptolite crisis with benthic faunal change and eustatic fall in sea-level manifested by facies change and the carbon isotope excursion. Polonograptus chlupaci sp. nov., from the Nc. kozlowskii Biozone, is described and several other graptolite taxa are redescribed.
