Zihua Tang

Anisotropy of magnetic susceptibility of the Jingou River section: Implications for late Cenozoic uplift of the Tian Shan

Better constraints on the uplift history of Tian Shan will increase our understanding of both mountain building processes and deformation patterns related to the India-Asian collision. Anisotropy of magnetic susceptibility (AMS) holds great potential to track variations in tectonic strain, which is ultimately responsible for mountain uplift. Here we present an AMS record, spanning the interval of 28-4 Ma, from the fluviolucastrine Jingou River section in the Tian Shan foreland. Rock magnetic measurements show that the AMS are dominated by antiferromagnetic hematite and some paramagnetic minerals, both of which have a crystallographic preferred orientation, and therefore the AMS sequence may be applied to reconstruct tectonic strain. Although the principal minimum (K-min) direction is nearly perpendicular to the bedding plane, indicative of a predominantly sedimentary fabric for the section, the tightly grouped principal maximum (K-max) parallel to the fold axis suggests that the section was subject to an embryonic deformation at least since the Late Oligocene. The K-max direction is most likely associated with the N-S strain caused by the India-Asian collision. During the intervals of 23.3-20.0 Ma and 16.5-14.0 Ma, the strain markedly increased as evidenced by more tightly grouped K-max directions and K-min largely distributed within a clear N-S girdle. These two intervals are accompanied by changes in sedimentary facies (higher energy conditions and doubled sedimentation rates), and are interpreted as the periods when the Tian Shan experienced significant uplift. A conceptual model is tentatively proposed to reconcile various timings for the Tian Shan uplift.

Early Eocene carbon isotope excursions: Evidence from the terrestrial coal seam in the Fushun Basin, Northeast China

A series of transient global warming events between 56 and 50 Ma are characterized by a pronounced negative carbon isotope excursion (CIE). However, the documents of these hyperthermals, such as Eocene Thermal Maximum 2 and H2 events, have come chiefly from marine sediments, and their expression in terrestrial organic carbon is still poorly constrained. Here we yield a high-resolution carbon isotope record of terrestrial organic material from the Fushun Basin, which displays four prominent CIEs with magnitudes larger than 2.5‰. Based on age constraint and comparisons with deep-sea records, our data provide the first evidence of the four hyperthermals in coal seams and suggest a global significance of these events. Moreover, the difference of CIE magnitudes between marine and terrestrial records shows a significant linear correlation with the marine carbonate CIE, implying that these events are likely attributable to recurring injections of 13C-depleted carbon from submarine methane hydrates and/or permafrost.

Oligocene-Miocene magnetostratigraphy and magnetic anisotropy of the Baxbulak section from the Pamir-Tian Shan convergence zone

As the northernmost part of the Indo-Eurasian collision belt, the Pamir-Tian Shan convergence zone (PTCZ) is a strategic location for understanding intracontinental deformation. Here we present a magnetostratigraphic investigation of a continuous section from the Baxbulak region, to better constrain regional tectonic history. Rock magnetic analyses indicate that hematite and magnetite are the main carriers of characteristic remanent magnetization. The resulting polarity sequence allows a distinct correlation to the geomagnetic polarity time scale, showing that the section spans the interval of 29.1–20.7 Ma. Rock magnetic results further suggest that paramagnetic and antiferromagnetic minerals dominantly contribute to anisotropy of magnetic susceptibility (AMS) of the sequence. Thus, the AMS would indicate the preferred orientations of the mineral grains that are sensitive to tectonic strain. At around 26 Ma, the grouped principal minimum perpendicular to the bedding diverts to a girdle distribution in a N-S direction, demonstrating the overprint of tectonic fabric to previous weakly deformed sedimentary fabric. This would be interpreted as a marked increase in tectonic strain, consistent with various evidence from the Pamir and the neighboring basin that show the Pamir began to migrate northward. Moreover, the coincident changes in distribution of AMS principal axes, in both direction and magnitude, are comparable to the regional counterclockwise rotations observed from paleomagnetic data, likely related to orogenesis.

Strontium isotope evidence for a highly mobile population on the Pamir Plateau 2500 years ago

Archeological researches have proposed arguments for human mobility and long-distance trading over the Eurasia before the Silk Roads. Here we utilize biologically available strontium isotope analysis to assess the extent of pre-Silk Road population movements and cultural communications across the Asian interior. From an early Iron Age cemetery (ca. 2500 yr B.P.) on the eastern Pamir Plateau, mean 87Sr/86Sr ratios from 34 individuals display considerable isotopic variability, and 10 individuals are distinguished as migrants based on the local strontium isotope range of 0.710296–0.710572 defined by 12 ovicaprine bones. Comparison of the proportion (10/34) with the regional census data completed in 1909 A.D. (3% non-locals) suggests a highly migratory behavior on the plateau 2500 years ago. Furthermore, exotic mortuary objects, such as silk fabrics from eastern China and angular harp originated from the Near East, clearly demonstrate an interaction between different cultures on the plateau before the establishment of the Silk Road.

Wood Usage and Fire Veneration in the Pamir, Xinjiang,2500 yr BP

Located on the Pamir Plateau in Xinjiang Province, China, the Ji’erzankale Necropolis dates back to 2500 yr BP. Many materials that have been unearthed in this cemetery, including shoo konghou (musical instrument), bronze mirrors and glass beads, suggest cultural transference between East and West. Furthermore, small-sized and rounded fire altars made from sweet-scented Sabina were found for the first time and regarded as implements for fire veneration. We identified 70 wooden objects from 25 tombs within the Necropolis, and found that each object had been made from one of seven tree species. Analysis revealed that the inhabitants of the region mainly used the most widely available types of wood, namely Betula and Populus. People also specifically chose inflammable Populus wood to make hearth boards and hand drills (both are used for making fire by drilling), rigid Betula wood to craft wooden plates. Salix was used for fashioning wooden sticks, while sweet-scented Sabina was the preferred choice for making fire altars. Lonicera was selected for arrow shaft manufacture and Fraxinus syriaca, which has a beautiful grain, was chosen for making musical instruments. Conscious selection of different types of wood indicates that people of the Pamir Plateau were aware of the properties of various types of timbers, and were able to exploit these properties to the full. In turn, this demonstrates their wisdom and their ability to survive in, and adapt to, their local environment.

Distribution of strontium isotopes in river waters across the Tarim Basin: a map for migration studies

As the junction of the Silk Roads, the Tarim Basin played a critical role in human migration and cultural interaction between the East and the West. Recently, population migration patterns have been increasingly reconstructed from strontium isotope ratios (87Sr/86Sr) in archaeological human skeletons, and further constraints on their provenance require a bioavailable 87Sr/86Sr map across the basin. Based on measurement data from 44 river samples in this study and 29 samples from published data, we generate the first map of bioavailable 87Sr/86Sr values across the Tarim Basin and the neighbouring area. From the baseline map, three geologically distinct regions can be identified: (1) the Yili Block, Tian Shan orogenic belt and northern Tarim Block with lower ratios (0.7105 ± 0.0007 (1σ), n = 25); (2) the southern Tarim Block with higher ratios (0.7118 ± 0.0008, n = 29); and (3) the eastern Pamir Block with diverse values (0.7110 ± 0.0009, n = 19). This map is a promising tool for recognizing the origins of immigrants in the Tarim Basin and may aid understanding of the migration patterns and cultural communication along the Silk Roads.

Paleoweathering and paleoenvironmental change recorded in lacustrine sediments of the early to middle Eocene in Fushun Basin, Northeast China

Deciphering the long-term interaction among continental silicate weathering, global climate, and atmospheric CO2 concentrations is helpful in understanding the mechanisms of the Cenozoic climate change and accessing the future climatic and environmental response to anthropogenic carbon emissions. The Eocene, which is characterized by the Early Eocene Climatic Optimum (EECO) and the following global cooling, represents an ideal test case. Here we generate geochemical data of the Eocene lacustrine sediments from the Fushun Basin, northeast China, to explore the regional climatic response to the global climate change. The chemical index of alteration (CIA) and plagioclase index of alteration (PIA) consistently show a gradual, long-term decrease, indicating a climatic transition from warm and humid to relatively cold and arid during the Eocene in the Fushun Basin. This climatic trend is broadly coincident with the global cooling and decreasing CO2 concentration, implying that the regional climate is closely correlated with the global climate change over geological time scales. Additionally, the extreme silicate weathering and high lake productivity as reflected by relatively positive δ13C values of lacustrine organic matter are associated with the EECO. This consistency may demonstrate that enhanced continental weathering and lake productivity had served as effective sinks to lower atmospheric CO2 across the EECO. Collectively, our new geochemical data add supporting evidence for a long-term, close coupling among continental silicate weathering, climate, and global carbon cycle during the Eocene.