New Data on the Radiolarian Assemblage of the Dalny Tulkas Section (southern Urals)

The Dalny Tulkas section is located in the southern Urals, near the settlement of Krasnousolsky, and is situated within the transition zone between the Sakmarian and Artinskian stages of the Lower Permian. It has key stratigraphic significance, as it is officially designated as the Global Stratotype Section and Point (GSSP) for the base of the Artinskian Stage and serves as a reference section for regional and interregional correlations. This section represents a continuous sedimentary succession spanning from the Late Sakmarian to Early Artinskian interval and is characterized by abundant palaeontological samples. Geologically, the section is represented by two interconnected outcrops: the main quarry wall and a trench section at its base. The first comprehensive study of radiolarians was conducted using material from this trench (Afanasieva et al., 2022); however, it is currently largely inaccessible because of overgrowth and anthropogenic disturbance. Therefore, the focus of this study was on the main quarry wall, which allowed the collection of new material and provided more comprehensive coverage of the section. Twenty-three samples were collected during fieldwork. These samples originate from concretionary and dense siliceous horizons, which are considered the most favourable for the preservation of radiolarian skeletons. Abundant radiolarian assemblages were identified in several samples, whereas others contained only rare or fragmented remains, often affected by recrystallization. Scanning electron microscopy was used for detailed morphological analysis, enabling the acquisition of numerous high-resolution images and the identification of fine diagnostic skeletal features. More than 70 taxa were identified within the radiolarian assemblage. The greatest diversity is observed among the genera Copicyntra, Entactinia, and Latentifistula, which include species typical of Lower Permian deposits. Radiolarians of the order Albaillellaria play a particularly important role due to their high biostratigraphic potential and their usefulness in refining the stratigraphic position of the studied deposits. Their presence confirms that part of the section belongs to the Artinskian Stage. Thus, the obtained data significantly expand previously available information on the Dalny Tulkas section and enhance its stratigraphic resolution. These results are important for correlating Lower Permian sections of the southern Urals with coeval deposits in other regions and contribute to the further development of radiolarian biostratigraphy of the Late Palaeozoic.