Comment on “Variable structural styles and tectonic evolution of an ancient backstop boundary: the Pieniny Klippen Belt of the Western Carpathians” by Plašienka et al. (2020)

Our comment is aimed to point out several controversial aspects of the paper Plašienka et al. (Int J Earth Sci (Geol Rundsch) 109:1355–1376, 2020). The Pieniny Klippen Belt marks a narrow zone at the boundary between the external and internal Western Carpathians. We appreciate efforts of the authors of the commented paper in advancing the understanding and interpretation of the geological structure of the Pieniny Klippen Belt as well as the surrounding tectonic units. However, it is essential to inform that the commented paper significantly modifies and deforms previously published maps and other data without any arguments, new data, or references to published material. We especially draw attention to the presence of the Šariš Unit and Gosau-type successions which has not been proven in the western segment of the Pieniny Klippen Belt. Due to the intricate structure and a number of unsolved fundamental questions, the Pieniny Klippen Belt area and its surroundings cannot be considered a model region of foreland–backstop boundary as is suggested by the commented paper.