The Lunpola Basin distributed in the central part of the Banggong-Nujiang suture belt contains thick and continuous Cenozoic sediments, which have great potential for increasing our understanding of the tectonic uplift, paleoaltimetry, erosion, and depositional history of the Tibetan Plateau and climate environmental evolution. In this study, detailed investigations were carried on a Cenozoic continuous lacustrine sedimentary section, Lunpori (LPR), from the upper sequence of the central basin. Constrained by tie points of U-Pb zircon ages in the layers of tuffs and mammalian fossils of a rhinocerotid humerus, paleomagnetic methods yield ages of ~21.2 to 15 Ma for the section. In addition, we further select some parameters (e.g., magnetic susceptibility and saturation isothermal remanent magnetization (SIRM)) to establish a high-resolution magnetic record to explore the paleoclimate change. The magnetic susceptibility is measured by Kappabridge while the SIRM is measured by Mini spin and Impulse Magnetizer. The results suggest that magnetic susceptibility (χ) gradually increases during the period of semi-deep to the deep lake but shows a decrease in the stage of the shallow lake. Combining with the maximum values of χ often appearing in the layer of sandstones and no obvious correlation between the χ and SIRM, we preliminarily considered that the supply of detritus may dominate the variation of the χ. Lithofacies, pollen, and fossil records suggest that a relatively temperate, humid climate prevailed in the Lunpola Basin during the sedimentary period of the Dingqinghu Fm.
Clay minerals are the weathering products of the parent rocks, which was formed by a series of chemical processes under a specific climate, and they are also widely-used indicators to reconstruct the history of the regional paleochemical weathering process. In this study, we present a detailed mineralogical investigation of 76 clay samples collected from the Lunpori section (21-15 Ma) in the Lunpola Basin by using X-ray diffraction. The results show that illite-smectite mixed layers, illite, chlorite, and kaolinite are the common clay mineral types in this section. The illite-smectite mixed layers and illite are the most abundant ones, which account for 80-90% of the total clay content; while the content of kaolinite and chlorite is relatively low, only occupying ~10-20% of the total clay minerals. The variations of clay mineral content are relatively stable in the Lunpori section, thus indicating that the intensity of regional chemical weathering was less variable during this period.
Original information on the long-term dry-wet index (1500-2000) in western China is obtained by integrating data on dry-wet/drought-flood conditions and precipitation amounts in the western region published over more than a decade. The integrated data sets include tree rings, ice cores, lake sediments, historical materials, etc., and there are more than 50 such data sets. In addition to widely collecting representative data sets on dry-wet changes in the western region, this study also clarifies the main characteristics of the dry-wet changes and climate zones in the western region, and the long-term dry-wet index sequence was generated by extracting representative data from different zones. The data-based dry-wet index sequence has a 10-year temporal resolution for five major characteristic climate zones in the western region over nearly four hundred years and a high resolution (annual resolution) for three regions over the past five hundred years. The five major characteristic climate zones in the western region with a 10-year dry-wet index resolution over the last four hundred years are the arid regions, plateau bodies, northern Xinjiang, Hetao region, and northeastern plateau, and the three regions with a annual resolution over the last five hundred years are the northeastern plateau, Hetao region, and northern Xinjiang. For a detailed description of the data, please refer to the data file named Introduction of Dry-Wet Index Sequence Data for West China.doc.
The marine- and terrestrial-facies sediments from the southern piedmont of the Himalayan margin recorded the tectonic deformation and environmental evolution of the front edge of continental collision. To better understand the deformation mechanism of the southern Himalayan margin and constrain the continental collision age, we selected the three well exposed outcrop profiles from late Cretaceous to middle Eocene strata in the western Nepal and carried on rock magnetism. All the samples for the Palpa section with depth of 120 m had been performed on mass-specific magnetic susceptibility (χlf), anhysteretic remanent magnetization (ARM), and saturation isothermal remanent magnetization (SIRM). Meanwhile, the isothermal remanent magnetization (IRM) and the hysteresis loops was acquired from the fine sediments, and several important magnetic parameters were determined, including the saturation magnetization (Ms) and saturation remanent magnetization (Mrs).
The modern sporopollen identification results of five different geomorphic types in the middle reaches of Heihe River show that there are 39 sporopollen types, 22 main types, belonging to 6 different vegetation types in 45 topsoil samples distributed in the desert vegetation belt. The SPOROPOLLEN ASSEMBLAGES with high percentage of sporopollen in the sporopollen map were selected to represent different geomorphic types. It was found that five geomorphic types (dune, alluvial proluvial fan, flood plain, riverbed and wetland) could be expressed by different combinations of nine sporopollen.
This data set contains a deep drilling paleomagnetic age data near the open sea in the middle reaches of Heihe River. The borehole is located at 99.432 E and 39.463 n with a depth of 550m. The samples of paleomagnetic age were taken at the interval of 10-50 cm. The paleomagnetic test was carried out in the Key Laboratory of Western Ministry of environmental education of Lanzhou University. The primary remanence of the samples was obtained by alternating demagnetization and thermal demagnetization, and the whole formation magnetic formation was obtained by using the primary remanence direction of each sample, and then the sedimentary age of the strata was obtained by comparing with the standard polarity column. The results show that the bottom boundary of the borehole is about 7 Ma and the top boundary is 0 ma.
Since the formation of Heihe River, sporopollen data samples have been collected from the drilling strata of Da'ao well in the middle reaches of Heihe River. Drilling location: 39.491 n, 99.605 E. The drilling depth is 140 meters. 128 samples of sporopollen are collected from top to bottom. At present, there are 19 data of sporopollen results, which are distributed in each sedimentary facies from top to bottom. The sporopollen samples were removed from carbonate, organic matter, silicate and other impurities in the laboratory, and the species and data of sporopollen were identified under the microscope. Sporopollen results mainly include the percentage content and number of trees, shrubs, herbs, aquatic, ferns and other families and genera.
Based on the study of the terrace formation age in the upper reaches of heihe river, photoluminescence samples were collected from the sediments of grade 6 river terrace near the upper reaches of qilian river.The quartz particles (38-63 microns) in the sample were isolated in the laboratory, the equivalent dose and dose rate in the quartz particles were measured, and the photoluminescence age of the sample was finally obtained.The obtained ages range from 5ka to 82ka, corresponding to the years of cutting down the terraces of all levels.
Since the formation of heihe, palynology data samples were collected from the borehole formation of dasunken well in the middle reaches of heihe.Borehole location: 39.491 n, 99.605 e.The borehole has a depth of 140 meters and 18 palynological samples are collected from top to bottom. Currently, there are 3 palynological results, which are distributed in each sedimentary phase from top to bottom.Impurities such as carbonate, organic matter and silicate were removed from palynology samples in the laboratory, and the palynology types and data were identified under the microscope.Palynology results mainly included the percentage and number of trees, shrubs, herbs, aquatic and ferns.