Drainage patterns in the Sudetes Mountains (Central Europe) – A clue to understanding polygenetic relief?

Abstract

The Sudetes range is a topographic unit of protracted history that can be traced back to the Variscan orogeny in the Palaeozoic. After marine inundation in the Late Cretaceous and uplift at the turn of the Cenozoic, a phase of long-term denudation ensued and rock-controlled morphology began to evolve. Differential uplift and subsidence resumed in the Neogene, producing the contemporary horst-and-graben relief with altitude differences exceeding 1000 m. Thus, the present-day topographic diversity is the combined outcome of structure-controlled denudation, vertical displacements, and variable erosional response to uplift modulated by rock resistance, over a timescale of ~60 Ma. However, no systematic attempts were made to disentangle this complex topography and to evaluate the role of lithology and structure versus differential uplift. Here we demonstrate that an analysis of regional fluvial network versus topography may provide important clues, allowing to discriminate between drainage patterns which are well-adjusted to lithology and structure, implicitly of long history, and river reaches that reflect fluvial response to younger tectonic forcing. Three lines of inquiry are explored. First, morphometric properties of main rivers in respect to plan and profile, and of their drainage basins, are analysed. Second, relationships of drainage patterns to the surrounding relief, including analysis of water gaps, styles of fluvial incision, and possible water-divide migrations, are investigated. Third, peculiarities in geometric patterns of drainage networks are identified. We propose that despite an important relief-forming role of the Neogene uplift, tectonic perturbations imposed on the drainage pattern were comparatively minor, no major reorganizations occurred, and much of the present-day fluvial network is inherited from the more distant history. The predominant fluvial response to uplift was continuous valley downcutting, perhaps with minor lateral shifts, although ongoing water-divide migrations are hypothesized for the most elevated parts of the Sudetes, which experienced asymmetric uplift.