Print this pageOrigin, Geometry and Till Characteristics of Pennsylvanian Incised Valley Fills of North America and Europe
DAVIES, SARAH J., T. ELLIOTT, S. S. FLINT, and C. ATKINSON
Incised valley systems from the Carboniferous exhibit a suite of characteristics which are dependent on global and local controls. The high frequency marine band stratigraphy of the Lower Pennsylvanian in basins across western Europe and North America recognises truly global eustatic sea level rises. Below the Gastrioceras subcrenatum marine band widespread basal fluvial incision in tectonically-diverse basins from Poland through Germany, Belgium and Britain provides evidence for a global eustatic sea level fall. The stratigraphic framework enables a regional comparison of Lower Pennsylvanian sequence boundaries and their associated valley fills. Despite the differences in subsidence history of structurally separate basins, broadly coeval valley systems have very similar geometries. Early Morrowan incised valleys show the most variation between North America and Britain. In North America smaller incised valley widths probably reflect smaller drainage areas and substrate-controlled incision depths. Mid-Morrowan valley fills in the Appalachian Basin, South Wales and English Pennines have comparable dimensions (70-80 km in width and c.25 m thick) but differ in their internal fill characteristics. British examples are typically filled to capacity with fluvial deposits whereas the North American examples may have a significant component of tidal sedimentation. Stratigraphically younger (Atokan-Desmoinesian) incised valleys recognised from North America, including the Canadian Maritime area, are characterised by upward decreasing widths with a similar, but more complex pattern observed from Britain.