Record of earthquake phenomena in a Lower–Middle Triassic sedimentary basin (North Sudetic Synclinorium, Lower Silesia, SW Poland)

Abstract

Deposits of the Röt Formation (Lower–Middle Triassic) in the eastern part of the North-Sudetic Synclinorium (Bolesławiec Syncline), SW Poland, include numerous synsedimentary deformation structures. Six boreholes with a total core length of ~434 m enabled macroscopic analysis and description of these deformation structures, supplemented by borehole log interpretation, calcimetric analysis, and interpretation of 2D surface seismics. An interval up to ~42 m-thick at the base of the Röt Formation showed both brittle and soft-sediment deformation structures. Their abundance and intensity decrease towards the top of the Röt Formation, and they completely disappear in the Muschelkalk (Middle Triassic). Both the number of boreholes and their locations indicate the presence of such structures across the entire study area. The occurrence of deformation structures in each borehole analysed and their large lateral range suggest that the uppermost part of the Lower Triassic and lowermost part of the Middle Triassic in the study area were influenced by seismic activity. As a result, tectonic reorganization of the study area is inferred for the latest Early/earliest Middle Triassic.