Climatic vs. tectonic controls on peat accretion in non-marine setting; an example from the Žacléř Formation (Yeadonian-Bolsovian) in the Intra-Sudetic Basin (Czech Republic)
Abstract
The Žacléř coalfield in the western part of the Intra-Sudetic Basin is an example of coal accumulation in an alluvial valley deposited under a long-term (~ 3 m.y.) stable tectonic regime, with climatic oscillations possibly operating on several time scales. The resulting sedimentary record, about 600 m thick, encompasses about 60 coal-bearing cycles formed in a relatively small and localized part of the valley, whereas elsewhere a higher clastic input and/or lower rate of subsidence resulted in deposition of strata with very little coal.
Available data suggest that tectonics produced accommodation for sediments and, via changes in topography and/or size of the source area, affected the volume and dispersal patterns of clastic material transported to the depocentre. Areas with long-term tectonic stability were suitable places for recognition of climatic signals in the sedimentary record, modified by the intensity of local clastic input.
Climatic fluctuations generated coal-bearing cycles, probably through a variable intensity of precipitation which affected the density of vegetation cover across the landscape along with evaporation and groundwater table. These factors influenced the intensity of chemical weathering and hence regulated the volume and composition of clastics delivered to the depocentre.
This in turn resulted in alternation of short periods of bedload-dominated deposition during the seasonally dry part of the cycle with periods of dominantly suspended load and organic (peat) deposition during the more humid (?everwet) part of the cycle. Estimated duration of the basic cycles (~ 46 k.y.) approximates the orbitally-driven axial tilt cyclicity.