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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]

As the largest intermontane basin in the northeastern Tibetan Plateau (TP), the Qaidam Basin provides unique insight into paleoclimatic change and its relationship with global change and uplift on the TP. In this study, based on morphological comparison, fossil fruit of Cyclocarya from the Early Oligocene Shangganchaigou Formation in the Qaidam Basin is assigned as Cyclocarya cf. weylandii. The discovery of Cyclocarya cf. weylandii demonstrates the occurrence of Cyclocarya in the Oligocene sediment in Qaidam Basin. This is the first record of Cyclocarya fossil of Early Oligocene Age in China and indicates that Cyclocarya has existed on the northeastern TP since at least the Early Oligocene. The living analogues of the current fossil now lives in sub-tropical China, where the East Asian Monsoon is prevalent. Integrating the new fossils and previously reported fossil remains of plants and fishes, it can be inferred that the Early Oligocene Qaidam Basin was primarily influenced by westerly circulation and had a relatively warm and humid climate, which was in sharp contrast to the present-day climate in Qaidam Basin. [ABSTRACT FROM AUTHOR]

Knowing the rotation and paleo-stress history in Qaidam Basin is a fundamental parameter to quantify the mechanism of intracontinental deformation in Tibetan Plateau. However, few studies have been conducted on tectonic rotation and stress evolution over long timescales in the Qaidam Basin. Here, we report new magnetic declination and the anisotropy of magnetic susceptibility (AMS) from a ∼52–7 Ma sequence of fluvial and lacustrine sediments in the Dahonggou (DHG) section in the northern Qaidam Basin. The magnetic declination revealed that the northern Qaidam Basin underwent a clockwise rotation 25.1° ±8.6° during ∼33–17 Ma, followed by a counterclockwise rotation 16.9°±6.8° during ∼17–13.5 Ma. The AMS results showed that the "earliest deformation" fabrics were interrupted by the "pencil structure" fabrics in the intervals of ∼52–45 and ∼21–15 Ma. The interruption, synchronous with the marked deceleration of the India-Asia convergence rate, indicates pulse of strong tectonic compressive stress. In addition, the AMS results documented a transition in stress direction from S-N to SW-NE at ∼15 Ma, suggesting a kinematic shift in the northeastern TP. Our constraints on the rotation and stress from the northern Qaidam Basin support the two-stage evolution of the Altyn Tagh Fault (ATF). The fast-rate slip motion on the ATF during the early Oligocene caused the clockwise rotation in the northern Qaidam Basin; the second stage with enhanced thrusting since the middle Miocene caused extensive crustal shortening and dispersive NW-trending folds and faults in the Qaidam Basin and the northeastern TP. [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]