Abstract:The uplifting of the Tibetan Plateau has significantly changed the environment in surrounding areas by delivering abundant water and sediment. The Heihe River draining the Qilian Shan in the NE Tibetan Plateau acts as a dominant sediment routing system from the uplifted NE Tibetan Plateau to the Hexi Corridor as well as the Badain Jaran Desert. Reconstructing the evolution of the Heihe River could provide evidence for the birth of the Badain Jaran Desert and enhance the understanding of sedimentary basin fill … Show more
“…In this sense the first order chronology of the GN200 is confirmed by findings of Pan et al (2016) and their cores from the Heihe fluvial/alluvial plains in the Hexi Corridor. Thus, the mega-sequence forming unit C in GN200 is a coarsening up succession that represents the arrival and progradation of the Heihe alluvial fan in the Ejina Basin.…”
Section: Discussionsupporting
confidence: 63%
“…An upcore enhanced chlorite load, which to some extent is paralleled by an enhanced dolomite load in units B and C, may support this interpretation; chlorite 465 is known to be exposed in basaltic bedrock outcropping in the Qilian Shan and so is dolomite; both minerals are interpreted to be indicative provenance minerals of the southern catchment (Song et al, 2009;Schimpf, 2019), which increase in the Ejina Basin with the arrival of Heihe river sediments. Pan et al (2016) discussed a previous study, which suggested that the Shiyang River (400 km SE from Heihe) formed approximately 1.2 Ma (Pan et al, 2007), based on studies of the highest fluvial terraces. This age is consistent with the 470 formation age of the Tengger Desert (Li et al, 2014).…”
Abstract. Central Asia is a large-scale source of dust transport, but also holds a prominent changing hydrological system during the Quaternary. A 223-m-long sediment core (GN200) was recovered from the Ejina Basin (synonymously Gaxun Nur Basin) in NW China to reconstructing the main transitional modes of water availability in the area during the Quaternary. The core has been drilled from the Heihe alluvial fan, one of the world's largest continental alluvial fan, which covers a part of the Gobi Desert. Grain-size distributions supported by endmember modelling analyses, geochemical-mineralogical compositions (based on XRF and XRD measurements), and bioindicator data (ostracods, gastropods, n-alkanes with leaf-wax δD) are used to infer the main transport processes and related environmental changes during the Pleistocene. Magnetostratigraphy supported by radionuclide dating provides the age model. Grain-size endmembers indicate that lake, playa (sheetflood), fluvial, and aeolian dynamics are the major factors influencing sedimentation in the Ejina Basin. Core GN200 reached the Pre-Quaternary quartz- and plagioclase-rich Red Clay Formation and reworked material derived from it in the core bottom. This part is overlain by silt-dominated sediments between 217 and 110 m core depth, which represent a period of lacustrine and playa-lacustrine sedimentation that presumably formed within an endorheic basin. The upper core half between 110 and 0 m is composed of mainly silty to sandy sediments derived from the Heihe River that have accumulated in a giant sediment fan until modern time. Apart from the transition from a siltier to a sandier environment with frequent switches between sediment types upcore, the clay mineral fraction is indicative for different environments. Mixed layer clay minerals (chlorite/smectite) are increased in the basal Red Clay Formation and reworked sediments, smectite is indicative for lacustrine-playa deposits, and an increased chlorite content is characteristic of the Heihe river deposits. The sediment succession in core GN200 based on the detrital proxy interpretation demonstrates that lake-playa sedimentation in the Ejina Basin has been disrupted likely due to tectonic events in the southern part of the catchment around 1 Ma BP. At this time Heihe river broke through from the Hexi Corridor through the Heli Shan ridge into the northern Ejina Basin. This initiated the alluvial fan progradation into the Ejina Basin. Presently the sediment bulge repels the diminishing lacustrine environment further north. In this sense, the uplift of the hinterland served as a tipping element that triggered landscape transformation in the Northern Tibetan foreland (i.e., the Hexi Corridor) and further on in the adjacent northern intracontinental Ejina Basin. The onset of alluvial fan formation coincides with increased sedimentation rates on the Chinese loess plateau, suggesting that the Heihe fluvial/alluvial fan may have served as a prominent upwind sediment source for it.
“…In this sense the first order chronology of the GN200 is confirmed by findings of Pan et al (2016) and their cores from the Heihe fluvial/alluvial plains in the Hexi Corridor. Thus, the mega-sequence forming unit C in GN200 is a coarsening up succession that represents the arrival and progradation of the Heihe alluvial fan in the Ejina Basin.…”
Section: Discussionsupporting
confidence: 63%
“…An upcore enhanced chlorite load, which to some extent is paralleled by an enhanced dolomite load in units B and C, may support this interpretation; chlorite 465 is known to be exposed in basaltic bedrock outcropping in the Qilian Shan and so is dolomite; both minerals are interpreted to be indicative provenance minerals of the southern catchment (Song et al, 2009;Schimpf, 2019), which increase in the Ejina Basin with the arrival of Heihe river sediments. Pan et al (2016) discussed a previous study, which suggested that the Shiyang River (400 km SE from Heihe) formed approximately 1.2 Ma (Pan et al, 2007), based on studies of the highest fluvial terraces. This age is consistent with the 470 formation age of the Tengger Desert (Li et al, 2014).…”
Abstract. Central Asia is a large-scale source of dust transport, but also holds a prominent changing hydrological system during the Quaternary. A 223-m-long sediment core (GN200) was recovered from the Ejina Basin (synonymously Gaxun Nur Basin) in NW China to reconstructing the main transitional modes of water availability in the area during the Quaternary. The core has been drilled from the Heihe alluvial fan, one of the world's largest continental alluvial fan, which covers a part of the Gobi Desert. Grain-size distributions supported by endmember modelling analyses, geochemical-mineralogical compositions (based on XRF and XRD measurements), and bioindicator data (ostracods, gastropods, n-alkanes with leaf-wax δD) are used to infer the main transport processes and related environmental changes during the Pleistocene. Magnetostratigraphy supported by radionuclide dating provides the age model. Grain-size endmembers indicate that lake, playa (sheetflood), fluvial, and aeolian dynamics are the major factors influencing sedimentation in the Ejina Basin. Core GN200 reached the Pre-Quaternary quartz- and plagioclase-rich Red Clay Formation and reworked material derived from it in the core bottom. This part is overlain by silt-dominated sediments between 217 and 110 m core depth, which represent a period of lacustrine and playa-lacustrine sedimentation that presumably formed within an endorheic basin. The upper core half between 110 and 0 m is composed of mainly silty to sandy sediments derived from the Heihe River that have accumulated in a giant sediment fan until modern time. Apart from the transition from a siltier to a sandier environment with frequent switches between sediment types upcore, the clay mineral fraction is indicative for different environments. Mixed layer clay minerals (chlorite/smectite) are increased in the basal Red Clay Formation and reworked sediments, smectite is indicative for lacustrine-playa deposits, and an increased chlorite content is characteristic of the Heihe river deposits. The sediment succession in core GN200 based on the detrital proxy interpretation demonstrates that lake-playa sedimentation in the Ejina Basin has been disrupted likely due to tectonic events in the southern part of the catchment around 1 Ma BP. At this time Heihe river broke through from the Hexi Corridor through the Heli Shan ridge into the northern Ejina Basin. This initiated the alluvial fan progradation into the Ejina Basin. Presently the sediment bulge repels the diminishing lacustrine environment further north. In this sense, the uplift of the hinterland served as a tipping element that triggered landscape transformation in the Northern Tibetan foreland (i.e., the Hexi Corridor) and further on in the adjacent northern intracontinental Ejina Basin. The onset of alluvial fan formation coincides with increased sedimentation rates on the Chinese loess plateau, suggesting that the Heihe fluvial/alluvial fan may have served as a prominent upwind sediment source for it.
“…Previous work suggested that alluvial/fluvial fan areas of the Heihe River and Shiyanghe River are the dominant source for sandy material in the Badain Jaran and Tengger Deserts (Yang et al, 2012;Wang et al, 2015;Hu and Yang, 2016). Thus, the formation of both deserts was to a large extent determined by the evolution of the Heihe River and Shiyanghe River, the formation ages of which were both dated to 1.2-0.9 Ma (Pan et al, 2003(Pan et al, , 2007(Pan et al, , 2016. In the case of the Hobq Desert, the aeolian sand mainly originated from the reworking of the fluvial-lacustrine sediments in the Hetao Basin.…”
Reconstructing the Cenozoic environmental history of Hetao Basin, in the northern part of the Ordos Plateau in North China, is important not only for revealing the evolution of the Yellow River, but also for understanding the formation of the Hobq Desert. Here we present the stratigraphic framework of drill core DR01 with length of 2503.18 m, and the results of magnetostratigraphic and ESR dating and multi-proxy analyses of drill core WEDP05 with length of 274.60 m, from the Hetao Basin. The magnetostratigraphic and ESR results indicate that core WEDP05 spans the last ~1.68 Ma. Stratigraphic sequence of core DR01 indicates that the Hetao area was uplifted and eroded during the early Cenozoic, before subsiding to form a sedimentary basin. Subsequently, the basin was a fluvio-lacustrine environment during the Pliocene and then experienced alternating desert and fluvio-lacustrine conditions during the Quaternary. Sedimentary facies and multi environmental-proxy analyses of core WEDP05 indicate that the basin was occupied by a fluvio-lacustrine system during the following intervals: ~1.47-~1.30 Ma, ~1.17-~1.07 Ma, ~0.68-~0.60 Ma and from ~0.47 Ma to the last interglacial; and that a desert environment developed during the lake regression phases of ~1.30-~1.17 Ma, ~1.07-~0.68 Ma and ~0.60-~0.47 Ma. The presence of aeolian sand at the base of core WEDP05 suggests that the origin of the Hobq Desert can be traced back to the early Pleistocene, and resulted from the erosion and transportation of exposed fluvio-lacustrine sediments by near-surface winds associated with the Asian winter monsoon. A large river channel in the Hetao Basin may have existed as early as the Pliocene, which was 3 occupied by the Yellow River when its upper reaches formed by at least ~1.6 Ma. Subsequently, at least since ~1.2 Ma, the Yellow River formed its drainage system around the Hetao Basin and controlled the paleoenvironment evolution of the basin.
“…The lack of long and continuous sedimentary records from the area has impeded paleoclimatic research of the transitional zone of the EASM and the westerlies. A sedimentary record from the Jiudong subbasin since ~1.8 Ma was presented previously (Pan et al, 2016), and the sediments clearly offer the opportunity to reconstruct the long-term climatic evolution of the area. Figure 1.(color online) Location of the NE Tibetan Plateau and the study area.…”
Section: Introductionmentioning
confidence: 92%
“…1). The annual rainfall is 80–130 mm (Pan et al, 2016), with 60% concentrated in June, July, and August. The annual pan evaporation is more than 1900 mm (Chen and Qu, 1992), and the annual temperature is approximately 7°C–8°C (Pan et al, 2016).…”
The thick sedimentary deposits of the Jiudong subbasin in the western Hexi Corridor of NW China can potentially provide important records of climate change in arid and semiarid areas subject to the interaction of the East Asian summer monsoon (EASM) and the westerlies. Here we present the results of a study of the clay mineralogy of the sediments of drill core DWJ from the Jiudong subbasin. The clay minerals consist mainly of illite, followed by chlorite, kaolinite, and smectite. The clay mineral assemblages are used to define four paleoclimatic stages since ~1.8 Ma: (1) During ~1.8–1.2 Ma, the climate was relatively cold and arid; (2) during ~1.2–0.9 Ma, it was relatively warm and wet, with strongly seasonal precipitation; (3) during ~0.9–0.3 Ma, there was a long-term trend of cooling and drying; and (4) during ~0.3–0.1 Ma, the climate was warmer and wetter than during the previous period, with strongly seasonal precipitation. The paleoclimatic record of the Jiudong subbasin since ~1.8 Ma is consistent with records from the Tengger Desert and typical monsoonal areas. This suggests that the EASM penetrated into the central regions of the North Qilian Shan and Zhangye–Jiudong subbasin during ~1.2–0.9 and ~0.3–0.1 Ma.
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