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A comprehensive study of the sediment source-to-sink history of basins arranged along the Bangong-Nujiang Suture Zone (BNSZ) is critical for understanding the early Cenozoic topography and drainage systems of central Tibet and its implications for the uplift history of the Tibetan Plateau. Nevertheless, previous provenance analyses work mainly focused on the middle-eastern segment of the BNSZ, those Paleogene basins in the western segment have received less attention, which hinders a full understanding of the early Cenozoic topography of central Tibet. In this study, based on a chronostratigraphic framework developed for the lower Cenozoic continental redbeds of the Gaize Basin, we applied detrital zircon U-Pb geochronology to the well-exposed Paleogene Suonahu Formation in order to reconstruct the basin's source-to-sink history. Integrating these new data with detrital zircon U-Pb results from the underlying Kangtuo Formation, we recognize a major secular shift in sediment provenance characterized by inputs of Lhasa-derived clasts during the Late Eocene. Moreover, we applied statistical analysis to compare the U-Pb age spectra of Eocene strata in the Gaize-Nima-Lunpola basins in order to assess similarities between them and potential source regions. Our study confirms a paleogeographic scenario in which these Paleogene basins most likely were part of a low-elevation intermontane valley. • Analysis of detrital zircon U-Pb geochronology of Paleogene strata in Gaize Basin. • A major shift in provenance occurred between the Kangtuo and Suonahu formations. • Cenozoic clastic strata in the Gaize-Nima-Lunpola basins share a similar provenance. • The Gaize-Nima-Lunpola basins belonged to a Paleogene low-elevation valley. [ABSTRACT FROM AUTHOR]

Abstract The southeastern margin of the Tibetan Plateau (TP) is a key region for understanding the region's surface uplift mechanisms. This study focused on the Jiuziyan and Shuanghe Formations (Fms) in the Jianchuan Basin, both of which include lacustrine calcareous mudstones and marls. Ostracods of the genus Austrocypris found within the Jiuziyan and Shuanghe Fms constrain the age of strata to the Late Eocene. This study used two different proxies, i.e. fossil pollen coexistence and the δ18O (VPDB) values of carbonate (δ18O c), to reconstruct paleoelevation and the extant paleoenvironment from lacustrine calcareous mudstones and marls preserved in the Eocene stratigraphy of the Jianchuan Basin. The coexistence approach (CA) using pollen data from the Shuanghe Fm indicates a paleoelevation of 1.3–2.6 km above sea level (asl), which would most probably have been associated with a vegetation cover consisting of tropical-subtropical, deciduous, coniferous, broadleaf forests. The reconstructed mean annual air temperature (MAAT) had a value of 16.8–21.7 °C, warmer than today's MAAT (~6 °C). Oxygen isotope results from the Jiuziyan Fm, with/without modification between Eocene and modern Myanmar sea level, suggested that the surface of the Jianchuan Basin was at a paleoelevation between 0.5+0.8 –0.5 km asl and 2.5 ± 0.7 km asl (δ18O mw : −8.9 ± 1.3‰, 2σ). During the Shuanghe Fm sedimentation the paleoelevation was between 0.9 +0.7 –0.7 km asl and 2.9 ± 0.6 km asl (δ18O mw : −9.5 ± 1.1‰, 2σ). Our results suggest that a stepwise uplift of Jianchuan Basin and crustal thickening initiated during the Eocene was the cause of passive surface uplift of the southeastern Tibetan Plateau (TP) rather than Miocene lower crustal flow. Highlights • Use two different proxies, CA and O isotopes, to reconstruct paleoelevation in the Late Eocene Jianchuan Basin. • Age determination of the Shuanghe Fm from Chara ostracod index fossil, combined with zircon U/Pb ages from volcanics. • The elevation of the northwestern Yunnan Province had a stepwise uplift during the Late Eocene. [ABSTRACT FROM AUTHOR]

Abstract The Lhasa terrane is thought to be a key region for understanding the elevation history of the southern Tibetan Plateau after collision of continental India and Asia in early Paleocene. Stable isotopic studies consistently suggest that the Lhasa terrane had reached its near-present elevation before the Miocene. In this paper we report a plant megafossil assemblage from the Kailas Formation of the Kailas Basin in western part of the southern Lhasa terrane. Our U-Pb dating and magnetostratigraphic correlation show that the studied section of the Kailas Formation ranges from 25.1 Ma to 21.8 Ma in age, and that the fossil flora occurred at 23.3 Ma (latest Oligocene). The uppermost Oligocene Kailas fossil flora is low in diversity and dominated by Populus , Betulaceae and legume. It most likely represents a deciduous, broad-leaf vegetation and suggests a temperate, humid environment with a low to moderate palaeoelevation of 1500–2900 m in the Kailas Basin during the latest Oligocene, based on the co-existing range of the living analogues of the fossil plants. This conflicts with the existence of a continuous, high Gangdese Mountains stretching across the whole southern Lhasa terrane in the late Oligocene. Available evidence appears to suggest strong uplift of the southern Lhasa terrane after the latest Oligocene. Highlights • Plant fossils first reported from the uppermost Oligocene of Kailas Basin, Tibet • Fossils indicate temperate, humid environment and low to moderate paleoelevation. • Strong uplift of southern Lhasa terrane after the latest Oligocene [ABSTRACT FROM AUTHOR]

The freeze-up period is the pentad average temperature below or equal to 0 °C (≤0 °C), which belong to extreme low temperature events but more rigorous. And analyzing it will contribute to the sparse knowledge of the freeze-up period in the Tibetan Plateau and provide scientific base for animal husbandry production in pastoral area of Northern Tibet and agricultural production in Qaidam Oasis. This paper based on the daily average temperature from a 0.5° × 0.5° gridded data range from 1961 to 2015, the beginning pentad, the ending pentad and the pentads of freeze-up period over the Tibetan Plateau (TP) were calculated. In order to investigate the temporal–spatial variations of the freeze-up period, some methods were applied such as climatic trend rate, the non-parametric Mann–Kendall test, Kriging Interpolation method, wavelet transform and Power Spectrum, etc. The main results were as follows: the annual average beginning pentad had a delaying trend at the rate of 0.24 pentad/decade, the ending pentad was advanced at the rate of 0.35 pentad/decade, but the pentads of freeze-up period had a significant decreasing trend of 0.64 pentad/decade in recent 54 years, additionally, the most remarkable period appeared in 1990s when the freeze-up period shorten. The abrupt change revealed that the year of abrupt change for the beginning pentad and the pentads of freeze-up period was in 1994, and the year of abrupt change for the ending pentad was in 1994, 1995 and 1996. There existed significant regional differences for the freeze-up period, it is noteworthy that the freeze-up period showed a decreasing trend from northwest to southeast over the study region. The significant wavelet power spectra of the beginning pentad were 3.77 years, 4.57 years and 7.14 years and there were obvious periodic oscillations of 3.39 years, 6.49 years for the ending pentad, and the pentads of freeze-up period varied with period of 3.34 years, 4.57 years and 5.46 years, which were consistent with the atmospheric circulation quasi-period of 2–4 years. Furthermore, the correlation coefficient analysis presented that the freeze-up period were mainly controlled by the circulation factors, including the TPI, NHSHII, WPSHII, NHPVAI, NHPVII and APVAI. Moreover, altitude, latitude and longitude were the main influencing factors to the freeze-up period in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Charophytes from the middle to late Eocene Kangtuo Formation in the Gaize Basin, central Tibet, are studied from the perspectives of taxonomy, palaeoecology, and biogeography. In the upper member of the Kangtuo Formation of the Mengdangle (MDL) section, southern Gaize Basin, two charophyte species were studied, including Hornichara jianglingensis comb. nov. and Chara cf. wujinensis comb.nov. The flora lives in the temporary pond's depositional environment, based on sedimentological analysis and fossil species occurrence. A palaeobiogeographic analysis of the charophyte assemblage suggests that H. jianglingensis was widely distributed in China basins during the middle to late Eocene, and later as a regional species in the coastal area in the Oligocene. H. jianglingensis and C. cf. wujinensis disappeared during the Oligocene in the interior of the Tibetan Plateau, and it was likely attributed to the rapid uplift of the Central Tibetan Valley. • A middle to late Eocene charophyte flora on the central Tibetan Plateau was described. • Obtusochara jianglingensis was newly combined into Hornichara jianglingensis. • Charites wujinensis was newly combined into Chara cf. wujinensis. • This flora disappeared during the Oligocene in the interior of the Tibetan Plateau. • This local extinction was possibly related to the aridification following the rapid uplift of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The mechanisms and controls of the Middle-Late Miocene paleoenvironmental evolution of the northeastern Tibetan Plateau remain elusive. Here, we present an integrated multiproxy study of total organic carbon isotopes, lipid biomarkers, petrographic components and micropaleontological records in the well-dated Xigou section of the Xunhua Basin. Our data reveal a large decrease (−1.1 ‰) in bulk organic carbon isotopes (δ13C org) at ∼12.7 Ma, a broad minimum at ∼12.7–8.0 Ma, and a large increase (+1.3 ‰) at ∼8.0 Ma. The decline in δ13C org at 12.7 Ma was accompanied by pronounced changes in n -alkane indices, clay minerals, palynology, and ostracods, recording a major rise of lake level of paleo-Lake Xunhua due to increased precipitation in the regional catchment. Our inference of sustained elevated humidity in the Xunhua Basin at 12.7–8.0 Ma is contrary to previously reported cooling and drying trends on the NE Tibetan Plateau for the Middle-Late Miocene (∼14–8 Ma), thus precluding the role of global climate change as the dominant driver. Rather, we attribute the paleoenvironmental evolution of the Xunhua Basin to changes in regional rainfall patterns related to orogenic uplift. The Jishi Shan mountain range reached a critical threshold elevation at ∼12.7 Ma, becoming an orographic barrier to Westerlies-transported moisture and thus enhancing intensified precipitation within the Xunhua Basin. By ∼8 Ma, further uplift caused this orogen to become a barrier to the East Asian monsoon, resulting in aridification of the Xunhua Basin. • The Xunhua Basin sensitively recorded environmental changes on NE Tibetan Plateau. • Uplift of Jishi Shan since ∼13 Ma caused moister Xunhua Basin and drier Lixia Basin. • Regional humidity changes due to trapping of Westerlies moisture to west, rain shadow effect to east. • This environmental change recorded by d13C org , n -alkanes, ostracods, and palynology. • Two key environmental transition periods—at ∼12.7 Ma and ∼8.0 Ma. [ABSTRACT FROM AUTHOR]

Based on climate data from 68 meteorological stations over the Tibetan Plateau (TP) observed by the China Meteorological Administration in 1960–2012, temporal and spatial variations in aridity index (AI) and reference evapotranspiration (ET 0 ) were comprehensively investigated. The abrupt change and the period in AI and ET 0 were characterized using a comprehensive time series analysis conducted with Mann–Kendall test and Morlet wavelet. The results indicated that the regionally averaged value of AI significantly decreased by 0.04/decade during 1960–2012 period, with the maximum observed in 1972. Similarly, the regional trend for ET 0 was at the rate of −9.6 mm/decade with statistically significant at the 0.01 level. Most of these stations with positive value for AI were primarily distributed at the northern southwestern TP. Moreover, a majority of stations with low values of ET 0 were substantially distributed at the central and eastern TP, and amounts of the stations with high values of ET 0 were mainly located at a lower elevation. Abrupt changes of both AI and ET 0 primarily happened in 1980s. The major cycles of AI and ET 0 were 15 y and 17 y scale over the study period with apparent periodic oscillation characteristics, respectively, and together with other different scale cycles co-existing. The significant correlations between AI and East Asian Summer Monsoon Index (EASMI) indicated that AI over the TP was related to the EASMI. [ABSTRACT FROM AUTHOR]