Joint systems in Devonian sandstones in the Kiidjärve-Taevaskoda area, southeastern Estonia

Data on the jointing of sandstone outcrops located in the area from Kiidjärve to Taevaskoda along the Ahja River are presented. Joints can usually be followed along the outcrop walls up to 15-20 m in the horizontal direction. In general, due to the stratification of the sandstone complex the vertical extent of joints is considerably smaller - 1.5-3 m. Along with the dominating vertical joints, a number of dipping (35%) joints are observed, having usually a dip between 60° and 70°. The majority of joints belong to a system made up of two sets with azimuth bearings of strikes 287° and 006°. The spacing of joints along the outcrops is variable, the average distance between them being 15-20 m. The cave structures of suffosional origin are formed mainly at the intersections of tilted and vertical joints. Because of the limited vertical extent of joints, most caves have a low arch-shaped cross section. Similar morphology of the caves is mostly due to the horizontally enlarging flow channel in the basal part of a joint. As a result the roof of the forming cave may collapse and give it a flat arch-shaped morphology. The research carried out in the Kiidjärve-Taevaskoda area gives a reliable basis for similar studies in other regions of Estonia.