Guoqiao Xiao

Asian aridification linked to the first step of the Eocene-Oligocene climate Transition (EOT) in obliquity-dominated terrestrial records (Xining Basin, China)

Asian terrestrial records of the Eocene-Oligocene Transition (EOT) are rare and, when available, often poorly constrained in time, even though they are crucial in understanding the atmospheric impact of this major step in Cenozoic climate deterioration. Here, we present a detailed cyclostratigraphic study of the continuous continental EOT succession deposited between ∼35 to 33 Ma in the Xining Basin at the northeastern edge of Tibetan Plateau. Lithology supplemented with high-resolution magnetic susceptibility (MS), median grain size (MGS) and color reflectance (a) records reveal a prominent ∼3.4 m thick basic cyclicity of alternating playa gypsum and dry mudflat red mudstones of latest Eocene age. The magnetostratigraphic age model indicates that this cyclicity was most likely forced by the 41kyr obliquity cycle driving oscillations of drier and wetter conditions in Asian interior climate from at least 1 million year before the EOT. In addition, our results suggest a duration of∼0.9 Myr for magnetochron C13r that is in accordance with radiometric dates from continental successions in Wyoming, USA, albeit somewhat shorter than in current time scales. Detailed comparison of the EOT interval in the Tashan section with marine records suggest that the most pronounced lithofacies change in the Xining Basin corresponds to the first of two widely recognized steps in oxygen isotopes across the EOT. This first step precedes the major and second step (i.e. the base of Oi-1) and has recently been reported to be mainly related to atmospheric cooling rather than ice volCorrespondence to: H. A. Abels (abels@geo.uu.nl) ume growth. Coincidence with lithofacies changes in our Chinese record would suggest that the atmospheric impact of the first step was of global significance, while the major ice volume increase of the second step did not significantly affect Asian interior climate.

Spatial and glacial‐interglacial variations in provenance of the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) covers an extensive area over 440,000 km2 and provides an unprecedented terrestrial record of Neogene climate. However, it is still unclear whether the provenance of these loess deposits is uniform or contains spatial and temporal differences. Here this is addressed by comparing detrital-zircon age spectra of typical loess and paleosol samples from three distant sites located at the western, middle, and southeastern parts of the CLP. Our results reveal that the zircon age spectra not only change between loess and paleosol layers but also vary from the western to the eastern CLP, at least during the last glacial cycle. The discrepancies of the zircon age spectra among different sites suggest that the loess provenance of CLP is heterogeneous and spatially variable, although it has been suggested that the mineralogical, elemental and isotopic compositions of loess deposits on CLP are highly homogenous spatially and in glacial-interglacial cycles.

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.

New evidence for early presence of hominids in North China

The Nihewan Basin in North China has a rich source of Early Pleistocene Paleolithic sites. Here, we report a high-resolution magnetostratigraphic dating of the Shangshazui Paleolithic site that was found in the northeastern Nihewan Basin in 1972. The artifact layer is suggested to be located in the Matuyama reversed polarity chron just above the upper boundary of the Olduvai polarity subchron, yielding an estimated age of ca 1.7–1.6 Ma. This provides new evidence for hominid occupation in North China in the earliest Pleistocene. The earliest hominids are argued to have lived in a habitat of open grasslands mixed with patches of forests close to the bank of the Nihewan paleolake as indicated from faunal compositions. Hominid migrations to East Asia during the Early Pleistocene are suggested to be a consequence of increasing cooling and aridity in Africa and Eurasia.

Distribution of n -alkanes in Miocene loess in Qinan, western Chinese Loess Plateau, and its palaeoenvironmental implications

Neogene eolian successions are one of the most important terrestrial palaeoenvironmental archives in East Asia. However, they have received far less attention than Quaternary loess deposits, especially in the case of lipid biomarker analysis. In order to obtain a better insight into the early-middle Miocene palaeoenvironment, we conducted a study of n-alkane biomarkers from sediments of the QA-I section (Qinan) in the western Chinese Loess Plateau, and compared the results with those of previous n-alkane analyses of eolian and aquatic sediments of varying age. Our principal results are as follows: (1) All QA-I samples contain n-alkanes ranging from C14 to C35, among which the relative content of short-chain n-alkanes (C14–C20) from microorganisms is significantly greater than that of long-chain n-alkanes (C26–C35) from the waxes of terrestrial higher plants; the main peak is at C16–C18. All samples have a relatively lower abundance of medium-chain n-alkanes (C21–C25) than that of long- and short-chain n-alkanes, similar to strongly weathered palaeosols in Quaternary loess and Late Miocene-Pliocene Hipparion Red-Earth; however, this distribution is significantly different from that in weakly-weathered loess of Quaternary loess and Late Miocene-Pliocene Hipparion Red-Earth, as well as from aquatic sediments. (2) Despite some odd-over-even carbon predominance of long-chain n-alkanes in the QA-I samples, the carbon preference index (CPI) values are significantly lower than those of most of the weakly-weathered sediments. Our results show that strong weathering and microbial processes have significantly altered the n-alkanes in the Miocene eolian deposits in Qinan, and led to a significant oxidation and degradation of long-chain n-alkanes and the predominance of short-chain n-alkanes from bacteria. Therefore, the contribution of microorganism to total organic carbon (TOC) and its resulting in carbon isotopic composition should be carefully assessed in future studies.

History and Prediction of the Asian Monsoon and Glacial Terminations, Based on Records from the South China Sea

What caused the global ice sheets to come and go? Knowledge of this question is crucial for understanding global climate evolution and predicting future climate changes. Since the 1840s, when geologists firstly noted the expansion and retreat of ice sheets on land, scientists have been trying to solve this question. Although at present it is generally thought that the glacial cycles are driven by changes in solar insolation due to subtle variations in Earth’s orbit parameters (Milankovitch, 1941; Hays et al., 1976; Imbrie et al., 1992), the mechanism by which and the degree to which insolation plays a role on the glacial terminations remains unclear. For example, if glacial cycles vary directly in response to insolation, why do glacial terminations not occur at every time of increasing insolation? The benthic δ18O in the ocean is known to increase with glaciation and thus can be used to estimate the global ice-volume changes (Hays et al., 1976; Imbrie et al., 1984; Ruddiman, 2003). Therefore, precise timing of the benthic δ18O records is crucial for testing the exact relationship between glacial terminations and changes in insolation. Generally, a record of benthic δ18O versus depth was transformed into a record versus time by tuning the benthic δ18O record to the Earth’s orbital parameters (e.g. Imbrie et al., 1984; Ruddiman et al., 1986; Raymo et al., 1989; Shackleton et al., 1990; Lisiecki and Raymo, 2005). However, it is problematic to discuss the linkage between glacial termination and solar insolation based on the astronomical chronology because of the risk of circular reasoning. In the present study, therefore a different procedure independent of orbital tuning was adopted to establish the timescale for the late Quaternary benthic δ18O record retrieved from Ocean Drilling Program (ODP) Site 1143, southern South China Sea (Fig. 1). On the one hand, Zhang et al. (2007) recently published a high-resolution Asian summer monsoon record over the last 600 kyr using the ratio of hematite to goethite contents (Hm/Gt) from this site. On the other hand, the high-resolution (from orbital down to millennial) variations in Asian summer monsoon in South China over the last 350 kyr are now available from the δ18O of stalagmites from caves, which were accurately dated by high-resolution U-series analyses (Wang et al., 2001, 2005, 2008; Yuan et al., 2004; Zhang et al., 2008; Cheng et al., 2009). The stalagmite δ18O