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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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