Soft-sediment deformations in the Kleszczów Graben (central Poland)

Abstract

A wide variety of soft-sediment deformation structures is found in the Quaternary overburden of a giant open-cast browncoal mine near Bełchatów (SW of Łódź, central Poland), situated within a graben. The deformation structures range in size from tens of meters to only millimeters; it is remarkable that their size is often related to a specific type of genesis. Most large-scale deformations appear to result from tectonic activity. Other structures, commonly of intermediate size, result from exogenic processes such as glaciotectonism and overburden-induced diapirism. Penecontemporaneous and other early-diagenetic deformational processes (among which bioturbation and cryoturbation) are commonly of small size only; they are nevertheless important because their analysis allows a reconstruction of not only the depositional environment but also the deformational history of the sedimentary succession. In spite of the different types of genesis, many of the soft-sediment deformation structures are, in one way or another, related to the graben activity. Since the tectonic conditions in the Quaternary deposits within the graben are in many respects comparable to those in rift valleys, the deformation structures in the graben might be considered as representative for rift valleys as well. The analysis of the structures, resulting in an improved insight into their genesis, may thus contribute to a better understanding of the conditions to which sediments in rift valleys can be exposed.