CMS physics technical design report : Addendum on high density QCD with heavy ions

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Vegetation and climate of the Lop Nur area, China, during the past 7 million years

Lop Nur in Xinjiang, Northwest China, is located in the lowest part of the Tarim Basin at an altitude of 780 m and experiences an extremely dry climate with an annual precipitation of only 17 mm and a high evaporation rate of 2,728 mm. The pollen and spores from the Late Miocene strata of a borehole in Lop Nur were analyzed with a view to interpreting the paleoenvironmental evolution of Lop Nur. Main types of pollen such as Chenopodiaceae, Nitraria, Ephedra and Artemisia reflect an arid climate. By collating the palynological data in this area as recorded in other literature and by applying the method of Coexistence Analysis, we have obtained the paleoclimatic parameters from Late Miocene to Holocene in Lop Nur. These suggest that temperatures increased from the Late Miocene (10.2A degrees C) to the Pliocene (13.4A degrees C), decreased from Pliocene to Pleistocene (4.7A degrees C), and were more stable from Holocene (12.1A degrees C) until now (11.5A degrees C). The precipitation was stable (about 900 mm) from Late Miocene to Early Pleistocene, then decreased markedly (to about 300 mm) in Middle and Late Pleistocene, and reached its lowest value (17.4 mm) in the Holocene. The changes in paleoclimate at Lop Nur provide new evidence for understanding the uplift of the Qinghai-Tibetan Plateau.</p

Wet climate during the 'Little Ice Age' in the arid Tarim Basin, northwestern China

A relatively cold period, the &#39;Little Ice Age&#39; (LIA), just prior to the current warm period, has been documented from many regions of the globe. However, hydrological changes (wet/dry conditions) during the LIA appear to be very different across different climatic regimes, suggesting that the position, strength and/or pattern of atmospheric circulation could have changed significantly in the past. Therefore, paleohydrological studies may have some implications for potential future hydrological changes in an anticipated warming world. In this study, we investigated hydrological changes over the last similar to 800 years in the arid Tarim Basin, northwestern China. We used carbon isotopes of plant remains (mainly leaves) from a 10.5 m long aeolian sand sediment section to evaluate changes in dry/wet conditions. The average value of carbon isotopes of plant remains during the LIA period (similar to AD 1490 to 1890) is -26.0%, ranging from -28.2% to -23.6%, much lower than values before (average of -24.3%, from -25.5% to -22.4%) and after this period (average of -22.8%, -24.6% to -21.6%). Although other environmental factors could also affect carbon isotopes to some degree, such consistent, large negative isotopic excursions of up to 6% strongly suggest a wetter climatic condition in the study area at that time, which is also consistent with two silty clay layers, indicating a wet depositional environment, found around ad 1560 and ad 1625 during the LIA period. This inference is consistent with previous studies suggesting a relatively wet period during the LIA in the Tarim Basin and possibly extending to the western central Asia region, but appears to be opposite to hydrological changes in regions that are today dominated by Asian monsoon systems. This pattern of regional hydrological changes may be related to possible changes in the trajectory or strength of the westerlies and/or the orographic effect in this region, as previous studies suggested.</p

Magnetostratigraphic evidence of a mid-Pliocene onset of the Nihewan Formation - implications for early fauna and hominid occupation in the Nihewan Basin, North China

The fluvio-lacustrine sediments in the Nihewan Basin of North China, known as the Nihewan Formation, are well-known for an abundance of Early Pleistocene mammalian fossils (known as the Nihewan Fauna sensu lato) and Paleolithic sites. The age at which the sedimentation started is thus crucial for our understanding of early fauna and hominid occupation and infilling history of the basin, but it is poorly constrained to date. Here we report on a detailed paleomagnetic investigation of the Yangshuizhan section that crops out in the northeastern Nihewan Basin, supplemented by rock magnetic analyses into the carriers of the natural remanent magnetization. Magnetite and hematite are shown to be the main carriers of the characteristic remanent magnetization. Magnetostratigraphic correlation to the geomagnetic polarity timescale indicates that the onset of the Nihewan Formation in this section occurs at &sim;3.7 Ma, just below the Gilbert-Gauss boundary and ca 1-Myr earlier than previously established evidence. This pushes the lower limit of the Nihewan Formation back in time from very late Pliocene (&lt;2.8 Ma) to (at least) the mid-Pliocene. Combining the previously established magnetostratigraphic data with the present study, we arrive at a better understanding of the chronological framework and spatio-temporal history of the deposition of the terrestrial Nihewan Formation. Furthermore, it provides new perspectives of early fauna and hominid occupation in the Nihewan Basin.</p

High-resolution record of geomagnetic excursions in the Matuyama chron constrains the ages of the Feiliang and Lanpo Paleolithic sites in the Nihewan Basin, North China

The Nihewan Basin (40 degrees N) in North China is a rich source of Early Pleistocene Paleolithic sites and thus a key area for studying early human evolution in high-latitude (from an early human perspective) East Asia. Here a high-resolution magnetostratigraphic investigation is carried out on a fluvio-lacustrine section in the northeastern Nihewan Basin, which contains the Feiliang and Lanpo Paleolithic sites. Paleomagnetic results suggest that this section records the lower portion of the Brunhes polarity chron and the upper Matuyama polarity chron. Furthermore, the Jaramillo polarity subchron and seven of the nine validated geomagnetic excursions within the Matuyama polarity chron are identified, including the Kamikatsura, Santa Rosa, Intra-Jaramillo, Cobb Mountain, Bjorn, Gardar and Gilsa excursions. The Feiliang artifact layer is located just at the bottom of the Cobb Mountain excursion, thus its age is estimated to be similar to 1.2Ma. The Lanpo artifact layer appears to be coeval with the Gilsa excursion, yielding an estimated age of similar to 1.6 Ma. This study provides new evidence for the presence of early humans in North China before 1.5 Ma and documents the powerful role of geomagnetic excursions: they provide valuable age control points for ongoing efforts to date the early Paleolithic sites.</p

Late Miocene episodic lakes in the arid Tarim Basin, western China

The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (delta O-18) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (delta B-11) and delta O-18 records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at similar to 4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period.</p

Qaidam Basin and northern Tibetan Plateau as dust sources for the Chinese Loess Plateau and paleoclimatic implications

The Chinese Loess Plateau of central Asia is composed of interbedded loess and paleosol layers, deposited during glacial and interglacial cycles, respectively, during the past similar to 2.5 m.y. Understanding the provenance of loess is fundamental to reconstructing wind patterns during Quaternary glacial periods. We determined and compared U-Pb ages on zircon crystals from Loess Plateau strata and potential source areas. The results indicate that the loess was largely derived from the Qaidam Basin and the northern Tibetan Plateau to the west, both of which exhibit spatially extensive geomorphic landforms indicative of past (interpreted as pre-Holocene) wind erosion and/or deflation by westerly winds. This challenges the current paradigm that the loess of the Chinese Loess Plateau was largely sourced from deserts located to the northwest, as observed in the modern interglacial climate. We propose that during glacial periods, the mean annual positions of the polar jet streams were shifted equatorward, resulting in more southerly tracks for dust-generating storms and suppression of the East Asian monsoon by inhibiting the subtropical jet from shifting northward across the Tibetan Plateau.</p

Controlling factors on heavy mineral assemblages in Chinese loess and Red Clay

Heavy-mineral analysis is a sensitive technique in constraining provenance of sandstone, but has rarely been applied to loess. Here we report a heavy-mineral study of selected samples from the Luochuan, Xifeng and Caoxian loess-Red Clay sections on the Chinese Loess Plateau, based on the novel QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) technique. We found that heavy mineral assemblages of loess deposited through the past 500 kyr are similar and unchanged by post-depositional chemical dissolution. In contrast, in samples deposited from 900 ka to 3 Ma, the relative proportion of stable minerals tends to increase down section. In addition, the Xifeng samples consistently display higher contents of unstable ferromagnesian minerals than the Luochuan samples. Detailed analysis of surface textures displayed by different minerals by optical methods indicates that such a compositional difference can be ascribed to more effective diagenetic dissolution for the Luochuan section, explained by more extensive percolation of interstitial waters in wetter climatic conditions. Interestingly, heavy-mineral assemblages in the underlying upper Miocene Red Clay from Xifeng (deposition age similar to 7 Ma) are similar to those of recent loess deposited since 500 ka. This similarity indicates that climate and/or local preservation conditions hampered dissolution reactions, thus helping to preserve an original provenance signal that remained largely unchanged throughout the considered time period. Our study demonstrates that climatically- and time-controlled diagenesis plays a key role in determining the composition of heavy-mineral assemblages contained in loess deposited several hundreds of thousands years ago. We also show that by using both QEMSCAN and traditional optical techniques on the same samples we can obtain fundamental complementary information for a correct interpretation of the heavy-mineral assemblage.</p