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Short-term cyclic paleoenvironmental variations in Middle Turonian hemipelagic deposits, Bohemian Cretaceous Basin
Voženílková, Kristýna ; Uličný, David (advisor) ; Chadimová, Leona (referee)
The sedimentary record of the Turonian substage (Upper Cretaceous) offers an opportunity to examine climatic variations in a time of peak greenhouse climate. In the Bohemian Cretaceous Basin, recent cyclostratigraphic studies examined the cyclic variations of sedimentary environments of the Lower and Upper Turonian, while the cyclostratigraphy of the Middle Turonian substage has remained less understood. This thesis applied methods of spectral analysis to well logs and elemental composition data from several boreholes located in the central part of the Bohemian Cretaceous Basin, in order to better understand the environmental variations of the Middle Turonian substage and their possible astronomical forcing. A short eccentricity (~100 kyr) signature has been found in well log data, as well as the carbonate content of the Bch-1 borehole section and correlated over more than 20 km within the study area. Biogenic carbonate production is considered to be the cause of astronomically controlled cyclicity in content of Ca (proxy for CaCO3). For most of the substage, the carbonate cyclicity was shown to be decoupled from clastic sediment input variations, except the basal part of the Middle Turonian succession where clastic proxies are in phase with carbonate variations. It is proposed that the...
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Cyclic architecture of the Nýřany Member (Pennsylvanian) in the central part of the Kladno-Rakovník Basin
Páchová, Helena ; Opluštil, Stanislav (advisor) ; Pešek, Jiří (referee)
This master thesis studies cyclic pattern of the Nýřany Member (Middle Pennsylvanian, Moscovian) in the Slaný coalfield situated in the Kladno-Rakovník Basin. The main objective is to identify laterally persistent cycles and to find out their possible origin. Set of cross-sections constructed from boreholes proved lateral stability of 40 - 60 m thick units called the mesocycles. In all, eight mesocycles were identified (N0 - N7), of which the mesocycle N7 was newly defined. Maps of thickness and sand content constructed for each mesocycle provided additional information on subsidence rate and distribution of clastic sediments by fluvial processes. Lateral stability of the mesocycles suggests their allocyclic character and regionally operating mechanism responsible for their formation. Regularity in repetition of the mesocycles as indicated by their similar thicknesses and architecture may suggest that the mechanism could be periodic, possibly of climatic origin. This hypothesis is supported by calculated mean duration of the mesocycles to be ~ 400 ky, based on previously published high-precision CA-ID-TIMS radioisotopic ages of intercalated tonsteins. This "periodicity" approaches 413 ky periodicity of the long eccentricity, one of the Milankovitch orbital cycles, which, in turn, is considered here...
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Lithofacies and cyclic pattern of the upper part of the Poruba Member (Serpukhovian) in the eastern part of the Ostrava-Karviná coalfield
Michlová, Nikol ; Opluštil, Stanislav (advisor) ; Jirásek, Jakub (referee)
The diploma thesis studies lithofacies and cyclic pattern of about 200 m thick upper part of the Poruba Member (Serpukhovian) in the Karviná area of the Ostrava-Karviná coalfield. The objective of this thesis is to identify laterally persistent cycles from the local ones by the set of cross-sections and to better understand their formation, especially the role of glacio- eustatic sea level changes. Set of cross-sections constructed from boreholes were used for this study. The three genetic cycles were identified in the thesis based on previous studies of Gastaldo et al. (2009). From base to top the cycles are the (i) Max, (ii) Otakar a (iii) Gaebler. Their thickness fluctuates between 19.9 and 109.9 meters. The genetic cycles are bounded, with one exception, by a transgressive erosional surface of important faunal marine bands. From the set of cross-sections and maps of thickness and sand content (%), constructed for individual genetic cycles, it is obvious that the area of maximum thickness corresponds to area of increased content of medium- and coarse-grained sandstone. Maxima of sand content and thicknesses follow NNE-SSW direction, which is in agreement with basin axis. These maxima are interpreted as areas occupied by fluvial channels that are responsible for deposition of coarse- grained...
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