Geometry and kinematics of glaciotectonic deformation superimposed on the Cenozoic fault-tectonic framework in the central Polish Lowlands

Abstract

The distribution of glaciotectonic structures can be controlled by the occurrence of tectonic or neotectonic faulting of the pre-Quaternary basement. The faulted and thus undulated pre-Quaternary basement influenced the thinning or pinching out of weak deformable surficial sediments and could play a role of buried obstacles to forcing by ice-sheets. In both cases, such faulting could result in a predisposition to the development of glaciotectonic deformations. The present study has demonstrated how the geometry and kinematics of the glaciotectonic structures was controlled by the pre-Quaternary framework related to the Kleczew graben tectonics (the central Polish Lowlands). The assumption has been made in this study that the tectonic fractures and faults could influence the reduction of strength and mechanical anisotropy within the pre-Quaternary sediments, which were also remobilised by glaciotectonic forces. The renewed stress build-up by the glaciotectonic forces assumed herein could reactivate the pre-existing fractures and faults at a lower stress level rather than produce new structures that require a higher stress level. The results presented in this study are focused on detailed structural and kinematic analysis of the glaciotectonic faults and fractures. For each glaciotectonic fault studied, the slip vector was directly calculated based on the orientation of the fault striations and indirectly calculated from analysis of the small fractures that developed along the fault. Additionally, the data from this analysis were integrated with the surface-based 3D structural model obtained from the borehole data. This approach revealed the relationships between the geometry, orientation and kinematics of the glaciotectonic structures and the tectonic framework of the pre-Quaternary basement. The different modes of glaciotectonic faulting were determined, depending on the geometry and orientation of the pre-existing reactivated faults and fractures with respect to the direction of the glaciotectonic contraction. In addition to reverse dip-slip displacements, the strike-slip and oblique-slip displacements were recognised. This study was performed in the Kleczew graben (the middle part of the Polish Lowlands) in which the Quaternary and the Miocene sediments are affected by glaciotectonic deformations. Moreover, the Miocene sediments were also tectonically deformed in response to the development of the graben.