Late Carboniferous vegetation change in lowland and intramontane basins in Germany

Abstract

Variations in species richness (alpha species diversity) have been determined for Westphalian and earliest Stephanian (Moscovian/Middle Pennsylvanian) macrofloras from the paralic Ruhr Basin and the intramontane Saarland Basin in Germany. In the Ruhr, species richness progressively increases through the Langsettian Substage, remains high in the Duckmantian and lower Bolsovian substages, and then undergoes a marked decline in the upper part of the Bolsovian Substage. This decline in macrofloral species richness coincides with a reduction in the number of coal seams present, and a change to upper delta and alluvial plain deposits. In Saarland, there are only a relatively few, impoverished macrofloras in the lower part of the succession, where high-energy braided fluvial deposits prevail. Species richness increases significantly in the very low Bolsovian Substage, somewhat below the stratigraphic level where the first thick coals appear. Species richness remains relatively high through the remainder of the Westphalian Stage in Saarland, except for a slight fall in the upper Bolsovian Substage. Most observed changes in species richness in both basins can be correlated with changes in facies resulting from shifting drainage patterns, which in turn were the result of Variscan tectonic activity in the surrounding hinterlands. The macrofloral species richness data provide no evidence of major change in the climate in late Westphalian and earliest Stephanian times, and the marked contraction of the coal forests taking place at this time must have been due to other, perhaps tectonic factors.