Climatic and biotic changes around the Carboniferous/Permian boundary recorded in the continental basins of the Czech Republic
Abstrakt
The paper provides an overview of a several decades-long study of transitional Carboniferous-Permian (Stephanian C-Autunian) sedimentary successions in continental basins of the Czech part of the Bohemian Massif. These predominantly monotonous fluvial red beds intercalate with laterally widespread grey to variegated sediments of dominantly lacustrine origin.
Both, fossil and climatic records show that apart from a generally known long-term climatic shift to drier conditions in Early Permian, the climate oscillated on several time scales throughout the study interval. Climatic indicators in the red beds part of the succession include palaeosols ranging between red vertisols and vertic calcisols suggesting strongly seasonal dry sub-humid climate.
This is in agreement with the rarity of plant remains, which were mostly completely oxidised and only rarely preserved as plant impression in red mudstones or as silicified mostly gymnosperm woods in sandy channel fills. Silicification instead of coalification was the dominant fossilisation process during red-beds deposition.
Even drier, possibly semi-arid climate may be indicated by spatially and temporarily restricted bimodal sandstones, dominated by well-rounded quartz grains and interpreted as eolian in origin. Periods of moist sub-humid (or even humid) climate were accompanied by formation of perennial lakes containing grey laminated mudstones, dark grey bituminous mudstones or limestones, muddy limestones, chert layers or even spatially restricted coals, some of them, however, of economic importance.
Shorter climatic oscillations operating on a scale of tens to possibly hundreds of thousands of years are represented by transgressive-regressive lacustrine cycles followed by significant changes in lake water salinity reflected by boron content. The fossil record indicates the presence of dryland and wetland biomes in basinal lowlands although their proportions varied significantly as the climate changed.