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A closed Quaternary saline paleolake, currently still a lake and named Dalangtan after one of its largest sub-basins, has widely distributed sediments in the western Qaidam Basin, NE Tibetan Plateau. Lacustrine salt minerals and fine sediments from this paleolake provide an environmental record for investigating paleoclimatic evolution in the Asian interior. However, detailed continuous Pliocene–Quaternary paleoclimatic records are broadly lacking from the NE Tibetan Plateau owing to poor exposure of the outcrops in section. For this study, we performed a detailed magnetostratigraphic dating and rock magnetic analysis on a 590-m-long core from the SG-5 borehole in the western Qaidam Basin. The results demonstrate that the lacustrine sediments in the SG-5 borehole were deposited more than ~3.0 Ma. Saline minerals began to increase at 1.2 Ma, and the magnetic susceptibility (χ) also changed at that time; the percentage frequency-dependent magnetic susceptibility was relatively low and uniform throughout the whole core. These observations, combined with the χ, pollen, salt ion, and grain-size records from other boreholes, indicate that the western Qaidam Basin and the greater Asian interior had a significant climate transition at 1.2 Ma during an extreme drought. [ABSTRACT FROM AUTHOR]

The Xining Basin lies in the transitional zone between the arid Asian interior and the East Asian monsoon region. The continuous Cenozoic sediments in the basin provide a unique archive recording the uplift of the Tibetan Plateau and its environmental effects on central Asian aridification and Asian monsoon evolution. However, sediments deposited since the middle Middle Miocene have not been precisely dated, hindering our ability to address these issues. Here we dated a 336 m-thick section containing many Late Miocene fossil mammals from the eastern basin. High-resolution paleomagnetism revealed 16 normal and 16 reversed zones that correlate well with chrons 3n to 5Ar.1r of the Geomagnetic Polarity Time Scale, constraining the section to ∼12.7-4.8 Ma. The changes in lithofacies from floodplain to braided river at ∼8.6 Ma and to thick alluvial fan at ∼6.3 Ma with predominantly southerly paleocurrent directions occur simultaneously with an increase in the sedimentation rates, representing two periods of rapid uplift in the eastern Qilian Shan to the north. Our results provide a robust oldest age constraint (<4.8 Ma) on the ancient Huang Shui and Yellow River terraces on the basin sediments and eolian deposits on the terraces. The presence of well-developed floodplain paleosols, shallow lake marls, and many large mammals in the lower section suggests that the monsoon climate in the late Middle Miocene to Late Miocene was more humid and stronger than that at present. [ABSTRACT FROM AUTHOR]

Intracontinental flexural (foreland) basin sediments are now frequently used as archives for detailed paleoclimatic and sedimentary environmental reconstruction, fossil and stratigraphic correlation, and tectonic evolution and uplift of basin and orogen. However, sedimentologic characteristics vary considerably in time-space with the evolution of flexural basin, apt to cause misinterpretation of climatic change and stratigraphic correlation. Based on high resolution fossil mammal and magnetostratigraphic constraints and sedimentary facies analysis, here we took the Linxia Basin at the front of the NE Tibetan Plateau as a case to demonstrate and figure out a model how sedimentology and stratigraphy vary temporospatially with the evolution of such flexural basin. The results show that the Linxia Basin is a type intracontinental foreland basin subjected to two phases of flexural deformation exerted by the West Qin Ling (Mts.) and NE Tibetan Plateau to the south. Phase I began latest at the beginning of the Miocene (23.3 Ma), indicated by a balanced fast flexural subsidence and mostly fine sediment infilling giving rise to the early underlying unconformity. It manifests as an obvious sediment wedge with high filling rate, thickening toward mountains and an occurrence of a mountains-parallel big river – shallow lake system along the foredeep, suggesting a less high mountain topography. In the late Phase I, from ~ 13 Ma to 8 Ma, the subsidence and thickening rates began to decrease, accompanied by faults and deformation propagating gradually into the basin, causing gradual basinward migration of the foredeep and its accompanying river-lake system. Since ~ 8 Ma in Phase II, the West Qin Ling and NE Tibetan began to uplift rapidly and thrust/load onto the Linxia Basin, causing strong mountain erosion, thrust-fold belt propagation and basin overfilling. This forced the mountains-parallel river - lake system to turn to the mountains-perpendicular alluvial - braided river system, and finally to an outflow system by the Quaternary onset of the Yellow River in the basin. Concurrent are rapid rotation of the basin, occurrence of growth strata and late unconformities, widespread expansion of boulder conglomerates, great decreasing and increasing sedimentation rates above and before the hanging wall of the fault-fold system and new supplementary provenance from the thrust-fold system. This demonstrates that in stable climate, same lithologic units such as distinct lacustrine sediments and alluvial conglomerates will migrate basinwards with the foredeep moving into basin, causing a great diachroneity and often misleads to recognize the same lithologic unit in space as one unit in time. A dynamic model is presented that should help to avoid such pitfalls in tectonic basin evolution, especially concerning stratigraphic correlation and paleoclimatic change research. [ABSTRACT FROM AUTHOR]

Late Cenozoic sediments in the Linxia Basin of China, on the northeastern Tibetan Plateau, bear abundant fossils of the Hipparion fauna. From late Miocene times, these sections record a history of aridification in the Asian Interior, the evolution of the east Asian monsoon, and multiple uplifts of the Tibetan Plateau. In this paper, a new detailed magnetostratigraphic study of a sedimentary sequence from the Duikang (DK) section containing the Hipparion fauna is presented, to better understand interconnected ecologic and environmental changes. The 90-m-thick section reveals nine normal and nine reversed zones that span from chron. C5n.2n to chron. C3Ar or from chron. C4n.2n to chron. C2Ar, yielding magnetostratigraphic ages of ~8.1 Ma - 3.7 Ma for the studied section and 5.3 Ma for the Hipparion fauna-bearing bed. Combined with all the previous magnetostratigraphic ages of the fauna-bearing sediments in the Linxia Basin, Hipparion can be distinguished as mainly having lived during five periods: Phase I (11.5 Ma), Phase II (8.2 Ma), Phase III (6.3 Ma), Phase IV (~5.3 Ma) and Phase V (2.5 Ma). Based on comparison of climate records in the Linxia Basin with aridification records from surrounding regions and global cooling during the late Cenozoic, we suggest that the evolution of Hipparion from the Linxia Basin was mainly driven by continuous global cooling and tectonic uplift of the northeastern Tibetan Plateau since the late Miocene. • Depositional age of the DK section in the Linxia Basin is between 8.1 Ma and 3.7 Ma. • Hipparion lived during five different periods (11.5, 8.2, 6.3, 5.3 and 2.5 Ma). • Linxia Basin experienced the stepwise aridification since the late Miocene. [ABSTRACT FROM AUTHOR]