Nearly 260 million years ago, the area where a beech forest now grows on the limestone hills between Stanisławów, Leszczyna, and Kondratów looked completely different. If someone wanted to see a similar landscape, they would have to visit one of the inhospitable, rocky deserts, such as Death Valley, the Saharan hamada, or the Danakil Depression. Especially the latter analogy would be apt—the temperatures often exceed 50°C, and water appears very rarely, only in the form of periodic rivers and rapidly drying pools. This area is located in a deep depression, exposed to flooding by ocean waters.
The region of our observations found itself in such a situation. 252 million years ago, in the late Permian period, the sun-scorched dry depression was flooded by a sudden deluge. From the southern Tethys Ocean, it was increasingly separated by an eroded but still mighty mountain chain, stretching about 1000 km wide, remnants of the Variscan orogeny. However, water surged in from the northwest. There, in the region of present-day Greenland, an opening occurred, enabling the flooding of the vast depression. The sea that formed at that time covered over a million square kilometres. Its southern shore was located several kilometres south of Kondratów. At the observation site, a shallow sea murmured. It was filled with cool water that had traveled almost 4,000 km and was now rapidly warming.
A large portion of the animals carried by the waves of the deluge did not survive such an extreme journey. Therefore, at the bottom, numerous shells of a poorly diversified community of organisms accumulated—mainly clams and snails, and in calmer times, brachiopods as well.
The sediment at the bottom was continually washed by storms. In deeper waters, where the turbulence of storm waves didn’t reach (below the storm wave base), material from crushed limestone shells was deposited by bottom currents generated during the storm. These currents left behind layers of limestone with a thickness of several to a dozen centimetres. During the periods between storms, the sediment settled from suspension. Evidence of this is seen in the marly layers between the limestones. Marls are rocks composed of fine particles of clay and limestone, intermediate between pure clays and limestone rocks. Very interesting structures formed during storms when the wave base touched the seabed. During such times, eddies carved basin-like depressions, between which domes were built up, consisting of thin layers with smooth surfaces. In even shallower waters, thick layers, several tens of centimetres (sometimes over a metre) in thickness, were formed, built from coarser grains that the turbulent water couldn’t carry away. These are shells and their fragments, sometimes pieces of limestone rock formed earlier and now being broken down.
When the sea retreated, the exposed limestone layers underwent dissolution – karstification. Evidence of this is the uneven surface covered with red and brown clay. The emergence of the seabed did not last long – the sea soon returned, and the cycle of sediment filling the basin resumed. This time, in the upper part of the profile of deposits in the shallower basin, we observe granular, sandy dolomitic limestones. This is a formation from a lagoon that formed after the creation of a barrier separating it from the open sea. The formations of the barrier can be observed in the quarries in Leszczyna. Between the barrier and the sandy shore, the water was calm. The isolation from the open sea resulted in increased salinity – the climate remained hot and dry, and the water continued to warm up. That’s why in the lagoon deposits, we will find even fewer remnants, although in the lower part, you may come across brachiopod twigs that filtered the lagoon water while searching for food.
The end of the formation of Carboniferous limestone carbonate deposits came with the closure of the connection to the global ocean. Thousands of kilometres away from this area, water ceased to flow into the vast, shallow sea, which dried up over thousands of years. The coastal region was exposed most rapidly, where beach sands buried the recent sea.
Later, the waters of the ocean returned and retreated several times. Their evaporation left behind massive deposits of rock salt, anhydrite, and gypsum, covering most of the Polish Lowland. But that’s material for a story in other places…