Vertebrate fossils on the roof of the world: Biostratigraphy and geochronology of high-elevation Kunlun Pass Basin, northern Tibetan Plateau, and basin history as related to the Kunlun strike-slip fault
Résumé
The Kunlun Pass Basin, at the foothill of Yuzhu Mountain (6224 m asl and the highest peak of the Kunlun Range), records Plio-Pleistocene fine-grained sediments sandwiched between glacial moraines. We document a new vertebrate fossil assemblage, the Yuzhu Fauna, with 16 mammal and 2 fish species that provide insights into basin chronology as well as the paleoenvironment adjacent to alpine glaciations in the Pliocene, in which the mammals and fishes lived. The Yuzhu Fauna consists of the following eight small mammals: Petenyia sp., Aepyosciurus sp., Nannocricetus mongolicus, cf. Orientalomys sinensis, Mimomys n. sp., Prosiphneus cf. P. eriksoni, Ochotona minor, Ochotona cf. O. lagreli, and eight large mammals: Rhinocerotidae indet., Hipparion (Proboscidipparion) pater, Qurliqnoria sp., Bovidae indet., cf. Panthera blytheae, Hyaeninae indet., Vulpes qiuzhudingi, and aff. Arctomeles sp. Two cyprinid fishes are also included: Gymnocypris sp. and Triplophysa sp. The Yuzhu Fauna has a distinctly early–middle Pliocene appearance, substantially earlier than previous age estimates, sharing broad similarities with vertebrate fossil assemblages from North China in general and the Zanda Fauna in southern Tibet in particular, including three carnivorans (Vulpes qiuzhudingi, cf. Panthera blytheae, and aff. Arctomeles sp.), one artiodactyl (Qurliqnoria), and at least two rodents (Aepyosciurus and Prosiphneus) and a lagomorph (Ochotona). We re-interpret published magnetostratigraphy to arrive at a correlation of the Yuzhu Fauna to the lower part of Chron 2Ar (Gilbert Chron 4.2–3.6 Ma), and the entire basin sequence spanning part of chrons 1n through 3n.3n, i.e., ~ 4.9–0.5 Ma. Our revised magnetic age for the Kunlun Pass Basin strata implies a slip rate of 7.2–6.1 mm/year along this part of the Kunlun Pass strike-slip fault system, much slower than its modern rate of off set.