The sandstones exposed in the Kaczawa Valley in Nowy Kościół are a record of a very interesting sedimentary environment. In the late Permian, about 250 million years ago, the warm sea covering a vast area of Central and Northern Europe began to dry up. Near the present-day eastern coast of Greenland, the connection of this reservoir with the global ocean closed. As the area of today’s Lower Silesia was then located near the tropics, in a hot and dry climate, the water quickly evaporated. Scanty rainfall over the vast expanses of the then supercontinent Gondwana did not compensate for the loss of water. The salinity of the sea gradually increased, and its level dropped. Near the centre of the reservoir, the precipitation of dissolved salts began: first calcium sulfate (gypsum), and later sodium chloride (rock salt). Closer to the coast, only small, shallow puddles remained from the sea on a vast, leveled terrain.
Such an area is called a sandy-mud plain. It is characteristic of leveled areas where a small change in water level in the reservoir brings about significant shifts in the shoreline. Material deposited by rivers or blown by the wind from the land side is spread across such a plain by currents and undulating, forming accumulating layers.
On the slopes starting at the crossroads of roads from Nowy Kościół to Jastrzębnik and to Złotoryja, sediments of such a plain are exposed. In the lower part, there are coarse-grained sandstones, and their upper (roof) surface has an erosional character. It is uneven, and in the exposure above the intersection, we can even notice a depression of almost a metre deep filled with finer sediment. This depression is a channel through which water flowed across the surface of the plain. The material filling it is almost homogeneous, devoid of layering. It may be due to the destruction of sedimentary structures by bioturbation, which is the activity of organisms burrowing in soft sediment.
Above the thick sandstone beds, the material forming the rocks becomes noticeably finer. Above the road to Jastrzębnik, we find exposures of dark, brownish-red silts. You can find septaria – disc-shaped, calcareous concretions – in them. The interior of the septaria is intersected by intersecting calcite veins. In a horizontal cross-section through such a disc, we can observe a polygonal arrangement of these veins. They formed as fillings with calcite, pure calcium carbonate, in cracks that occurred during the shrinking of the limestone sediment forming the concretions. The calcite in the veins is bicolored, white and dark brown to black, creating an interesting pattern on the cut surfaces. In some veins, you can also find pink barite. Due to the presence of septaria, the silts were named septarian silts.
Septarian concretions, or limestone precipitates in silty rocks, formed beneath the surface on an emergent plain. They formed at the then groundwater level, creating distinct horizons in the rocks. We can find other interesting structures in this part of the profile on the lower (basal) surfaces of thin sandstone layers occurring among the silts. These are small (usually less than a centimetre in edge length) cubes, as if growing from the rock. They formed as sandy fillings of voids created after the dissolution of halite (rock salt) crystals growing on the silty bottom during the drying of salty puddles. When rain brought water with sand onto the plain, the crystals dissolved, and the indentations left by them were filled with fine sand in the silt. Such structures are rare due to the transient nature of the environment in which they formed.
The septarian silts are overlain by sandstone beds. They are exposed in the upper parts of both slopes. In the sandstones, numerous sedimentary structures are well visible. Most commonly, these are layers: flat-parallel with good separation, indicating fast flow in shallow water, and small-scale cross-bedding (ripple marks) formed on the bottom in calmer currents. Sometimes, in the lower part of the sandstone beds, we can observe accumulations of flat pieces of silt, very similar to septarian ones. This is a trace of the erosion of silt layers, which must have been exposed somewhere near the site of our observations.
