Deformation of terrace surfaces in the Bystrzyca River valley, central Sudetic Foreland, SW Poland

Abstract

This article addresses the development of Pleistocene terraces in the Bystrzyca River catchment (Sudetic Foreland, Southwestern Poland) in the vicinity of the Sudetic Marginal Fault, within the Roztoka–Mokrzeszów Graben. Nineteen research sites located within the Świdnica Plain are documented in this paper, representative of terraces of the Bystrzyca and its Piława and Witoszówka tributaries, with reporting on analyses of structure, grain size, petrography, quartz-grain morphoscopy, and heavy minerals. The Bystrzyca River, flowing in the largest and deepest valley in the Sowie Mountains, crossing the fault zone and extending into the Sudetic Foreland, has been influenced by significant tectonic and glacial events. During the Middle Pleistocene a fluvial piedmont fan was formed and survives as traces of higher-level (pre-Saalian) terraces. The main fluvial terraces are recognized as follows: an Upper Terrace, from the Saalian, a Middle Terrace from the Upper Pleistocene Last Glacial (Weichselian) and, in the valley bottom, a Lateglacial–Holocene Lower Terrace and a Holocene Lowermost Terrace. The sediments forming these terraces document a complex history of tectonic uplift, glacio-isostatic rebound, and climatic changes. Notable features include a sequence of alluvial fans and terraces shaped by neotectonic activity, particularly during the Late Quaternary.