In the right slope of the Kamiennik Valley, near the water dam, there are rock layers characterized by red hues, which distinctively stand out from the green surroundings of grass and shrubs. These layers represent a record of geological events that occurred in this area during the transition between two geological periods – the Carboniferous and the Permian, with their boundary set nearly 300 million years ago.
At that time, the Sudetes and their foothills were divided into a series of elongated ridges separated by depressions, which generally had a NW–SE orientation. This character of the region was the result of regional extensional (stretching) processes, leading to the formation of faults, and consequently, the breakdown of the Sudetes mountain range into blocks – some uplifted (ridges), others subsided (depressions). The uplifted blocks formed regional watershed divides, while the subsided blocks created intramontane valleys where the accumulation of sedimentary material took place, derived from the erosion of the ridges directly adjacent to the valleys. In the depressions, the material was primarily transported by rivers and deposited either directly in riverbeds and their vicinity or in lake basins. One of such depressions was the Świerzawa Trench – bounded from the north by the Świerzawa Ridge and from the south by the Wleń Horst. In its axis, clastic sediments of varying grain size were deposited, predominantly gravels and sands, with smaller amounts of silts and clays. The site near the dam is a location where the deposits of the Świerzawa Trench are most prominently exposed.
The exposure is represented by a sequence of clastic rocks inclined at a relatively small angle in the southwest direction. It clearly divides into three distinct packages:
– the lower package, consisting of coarse-grained sandstones and conglomerates – in the main northern exposure, only its upper part is visible, while it is observable on the southern bank of the stream,
– the middle package, with a thickness of about 2 metres, composed of mudstones and sandstones with intense red hues,
– the upper package, with a thickness of nearly 5 metres, is mainly composed of a single, approximately four-metre-thick bed of conglomerate and sandstone, with the bottom of another bed visible in the highest part of the exposure.
Primarily, the exposure features a thick bed of conglomerate and sandstone. Its basal portion is composed of gravel material with fragments ranging in size from a few millimetres to approximately 7 cm. The gravel material is predominantly composed of quartz or fragments of quartzites, with a significant presence of black chert. Additionally, fragments of other sedimentary rocks (sandstones, mudstones, limestones) and igneous volcanic rocks are also present. The upper part of the bed is characterized by alternating layers and lenses of conglomerates and sandstones, with thicknesses typically around 20-30 cm. The diverse sedimentary character of this bed indicates a highly variable energy environment in which conglomerates and sandstones were deposited – a characteristic feature of braided river systems.
The mudstone-shale package directly below the described bed, on the other hand, represents sediment deposited in an environment where sediment-carrying currents had lower energy and were unable to transport gravel or sand particles. This package consists of three layers of mudstone, which transition into shale at the top of the layers, and along the lateral extent of the layers, they are replaced by sandstones. These layers represent material accumulated outside the main river channel, most likely during periods of high water levels, and thus, they are a record of flood events. The distinctive brick-red hues of these rocks are evidence of a very warm, dry climate during the period of their formation.
The described exposure serves as an excellent example of sedimentation in a braided river environment, characterized by a channel divided into a series of interwoven and braided flows separated by braid bars (islands). The exposed rocks here are characteristic of different elements of the braided depositional system – conglomerates and sandstones represent channel and mid-channel bar deposits, while mudstones and shales indicate floodplain environments.
In the exposure, in addition to depositional structures, one can observe interesting deformational structures. Namely, the base of the conglomerate bed is uneven and characterized by broad, bowl-shaped depressions separated by narrower convex forms. These depressions result from the slumping of the gravel sediment shortly after its deposition within the underlying shales and mudstones, as evidenced by the plastic deformations of the latter. The shales within the depression zones were bent, while in the convex areas, they were squeezed upward.