Deciphering complexity of block-faulted topography – Insights from morphometric variables, drainage patterns and river profiles (Orlickie-Bystrzyckie Mountains Block, Central Europe)

Abstract

The Orlickie-Bystrzyckie Mountains Block (OBMB) is a medium-size, transboundary morphostructure within the Sudetes range in Central Europe, subject to non-uniform uplift in the late Cenozoic. Geologically, it consists of Variscan basement and Permian to Cretaceous sedimentary cover. This paper attempts to unravel its morphotectonic history and decipher the spatial pattern of uplift and erosional response, using several complementary, quantitative approaches to characterize topography. The focus is on: (1) general relief properties captured by selected topographic variables; (2) fault-generated escarpments, which define the eastern and northern limits of the study area; (3) drainage patterns and its peculiarities; (4) diversity of longitudinal river profiles and valley morphology. A LiDAR-based high-resolution digital terrain model was the primary source of elevation data. An important component of the study was examination of the role of lithological diversity on relief properties. A statistical approach generally revealed a secondary role of the rock factor and provided a foundation to interpret the macro-topography of the OBMB in terms of tectonic controls. Based on geomorphometric characteristics and information about the distribution of sedimentary rocks, which can be used as marker horizons to identify vertical displacements, four major and one secondary centres of surface uplift have been recognized. They are all asymmetric, being bounded by distinct fault-generated escarpments on one side and sloping gently in the opposite direction. Erosional response to uplift has been variable and includes, apart from simple incision into rising crustal blocks, the origin of epigenetic-antecedent water gaps, drainage diversions, headward erosion, and captures. This study also reveals that morphometric indices routinely used to extract the tectonic signal from landform patterns do not necessarily provide consistent information.