Integrated Stratigraphy of the Tielongtan Group and Basin Evolution in the Western Kunlun Area, Northwestern Tibet

The uplift of the Tibetan Plateau has reshaped the geomorphic pattern of Eurasia and profoundly impacted the evolution of global climate, drainage systems, biology, and marine chemistry. In recent years, in-depth studies on the uplift history of different regions of the Tibetan Plateau have greatly promoted our understanding of its formation and environmental effects. However, in the western Kunlun area at the northwestern margin of the Tibetan Plateau, relevant stratigraphic and basin evolution studies remain relatively weak. For the first time, we establish a comprehensive stratigraphic framework for the Tielongtan Group in the Loqzung Mountains using integrated litho-, bio-, and isotope stratigraphy, and reconstruct the basin evolution from the Late Cretaceous to the Paleogene based on detailed provenance analysis. Based on 17 field sections and 7 sampling sites, the Tielongtan Group is shown to consist of two sets of “clastic rock–limestone” sedimentary sequences, with gypsum layers commonly intercalated in the strata above and below the clastic rocks. Biostratigraphically, 16 planktonic foraminifera species, 5 benthic foraminifera species, and 8 rudist species were identified, which firmly constrain the depositional ages. In the West Loqzung area, the lower sequence is dated to the Early Campanian, characterized by the rudist assemblage Radiolites aff.trigeri-Biradiolites fissicostatus-Vaccinites sulcatus and the benthic foraminifer Calveziconus lecalvezae. The upper sequence in this area is constrained to the Late Campanian-Early Maastrichtian by the rudist Radiolitella pulchellus. In the East Loqzung area, the widespread upper sequence yields Late Campanian-Early Maastrichtian assemblages, including planktonic foraminifera (Globotruncana cf. aegyptiaca, Contusotruncana plummerae, Globotruncana bulloides, Globotruncana falsostuarti, Globotruncana cf.ventricosa, Muricohedbergella holmdelensis) and rudists (Gorjanovicia acuticostata, Durania sp., Radiolitessp., Biradiolites boldjuanensis, Darendeella anatolica). Supported by detrital zircon U-Pb and shell strontium isotope data, the depositional age of the Tielongtan Group is constrained to ~86–66 Ma. Integrating this stratigraphic framework with provenance analysis reveals two major transgression-regression cycles from the Late Cretaceous to the Paleogene in the Western Kunlun area. During the Santonian to mid-Late Campanian (~86–74 Ma), continuous transgression resulted in coastal–shallow marine deposits sourced mainly from the Tianshuihai and South Qiangtang terranes. A brief tectonic inversion and regression occurred during ~74–73 Ma, accompanied by the input of volcaniclastic materials from the Shyok Suture. A second major transgression during the Late Campanian–Early Maastrichtian (~73–70 Ma) led to the widespread development of rudist-bearing carbonate platforms. This was followed by regression into a lagoonal environment in the Late Maastrichtian (~70–66 Ma), marking the final seawater retreat from the Western Kunlun area. During the Early Paleogene (~65–50 Ma), far-field effects of the India-Eurasia collision caused intense basin compression, forming arid evaporative lake deposits sourced from proximal recycling and Ladakh magmatic detritus.