PLEISTOCENE TECTONIC ACTIVITY OF THE POLISH WESTERN CARPATHIANS:INSIGHTS FROM FLUVIAL TERRACES

摘要

Fluvial archives of the Polish Carpathians bear a record of both climatic and tectonic signatures. The former consist in cyclic development of terrace covers interfingering with and/or overlain by soliluction and slopewash sediments; the latter include disturbances within strath long profiles and differentiated size of erosional downcutting. Valleys of the Outer Carpathians bear five to nine terrace steps of Pleistocene age. Most of these terraces are strath or complex-response ones; the Weichselian and Holocene steps are usually cut-and-fill landforms, except those located in the neotectonically elevated structures characterized by the presence of young straths. Long profiles of individual strath terraces frequently show divergence, convergence, upwarping, downwarping, or faulting that can be indicative of young tectonic control. Moreover, the size and rate of dissection of straths of comparable age are different in different morphotectonic units; a feature pointing to variable pattern of Quaternary uplift. Rates of river downcutting result mainly from climatic changes throughout the glacialinterglacial cycles, but their spatial differentiation appears to be influenced by tectonic factors as well. Examples based on detailed examination of deformed straths and fluvial covers in selected segments of the Polish Carpathian rivers appear to indicate Quaternary reactivation of both normal and thrust bedrock faults. The latter are mostly confined to the eastern portion of the Outer Carpathians. The Early Pleistocene, Holsteinian and Eemian stages of reactivated faulting dominated throughout the study area.