A 25 million year macrofloral record (Carboniferous-Permian) in the Czech part of the Intra-Sudetic Basin; biostratigraphy, plant diversity and vegetation patterns
Abstract
The Intra-Sudetic Basin is essentially a post-orogenic (Variscan) continental basin with a depositional history that ranges from the late Visean to the Triassic. The fossil record in the Czech part of the basin, although discontinuous, spans the interval from the late Visean to the Asselian.
Middle Baskhirian (late Namurian) to Asselian adpression floras collected from boreholes, coal mines and outcrops permit reconstruction of the stratigraphic ranges of individual species in considerable detail, and reveal changes in plant diversity and vegetation patterns throughout this similar to 25 Myr interval at high resolution, even to the scale of individual coal-bearing cycles. Species diversity recorded in the rock record throughout the studied interval mainly was controlled by climatically-driven potential for preservation of plant material, which was highest in poorly drained/waterlogged habitats (wetlands, lakes) concentrated in basinal lowlands and representing major windows of preservation.
Low fossilization potential is typical for well-drained fluvial habitats, now represented by red beds deposited under drier (seasonal) climate. Diversity in major windows of preservation was highest during the late Langsettian and Duckmantian (>50 species), lower in the Late Pennsylvanian (25-40 species) and the lowest in the Asselian (similar to 20 species).
The diversity in red bed intervals with poor preservation potential varies between 11 and 21 species. The two distinct habitat types, with high and low preservation potential, were dominated by different plant groups.
Wetland habitats flourishing during the (per)humid to slightly seasonal intervals were colonized mainly by cryptogamic plants and some early gymnosperms, mainly pteridosperms and cordaitaleans. Habitats represented by red beds were dominated by cordaitaleans; from late Asturian time walchian conifers also occurred in these plant assemblages.
However, conifers only became common in red beds in the Cantabrian. In the Saberian, conifers are rarely found in discrete beds associated with coal-bearing strata, however, their common occurrences start in lacustrine rocks of Asselian age.
Temporal changes in vegetation patterns that show an increasing proportion of gymnosperms, in both wetland and dryland habitats are in agreement with the well known aridification trend in late Paleozoic tropical Pangea. Delays between the first appearance of walchian conifers in red beds (late Asturian) versus coal-bearing deposits (Saberian) supports the hypothesis that evolutionary innovations took place outside the windows of preservation, i.e. in well-drained, moisture-deficient areas.