An evaluation of palaeogeography and palaeoecology in the Most Basin (Czech Republic) and Saxony (Germany) from the late Oligocene to the early Miocene
Abstrakt
This report concerns sediments in the Most Basin (NW Czech Republic) and coeval Northwest European Tertiary Basin (Germany) connected by a joint trunk river in the time period from the end of the Oligocene to the end of the early Miocene. The re-evaluation of older geochemical and palaeobotanical datasets and newly performed geochemical analyses supported by palaeomagnetic and cyclostratigraphic studies have brought a new insight into the evolution of the studied basins.
The relationship between the Most Basin and Saxony sites has been established on the basis of heavy mineral associations of coarse sediments and K, Ti and Al element ratios and cation exchange capacity of finer sediments. The results have allowed us to subdivide the Most Basin evolution into six distinct phases of palaeogeographic evolution related to tectonic and palaeoenvironmental changes.
The first palaeogeographic phase in the studied period, from the late Oligocene to the boundary of the Oligocene and Miocene, is characterised by a single trunk river transporting both fine and coarse clastics from the south-western part of the Bohemian Massif through the Most Basin to Saxony with a minor deposition of coarse clastics in the Most Basin. In subsequent phases of the Ohre (Eger) Rift development the export of coarser clastics from the Most Basin was hindered because the trunk river entered vast peat swamps via growing inland deltas.
In the final stages when lacustrine environment prevailed in the Most Basin, no clastics from the Bohemian Massif passed to Saxony although the lake was not hydrologically closed. Both magnetostratigraphic dating and palaeoclimatic analyses confirmed that the final stage of the Cenozoic deposition in the Most Basin occurred during the onset of the Mid-Miocene Climatic Optimum, i.e., during the end of the Early Miocene.