Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: Guodong Zheng x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Three plant fragments were collected from two landslide profiles and were radiocarbon-dated by accelerator mass spectrometry. Results reveal that the two landslides occurred around AD 1646 and AD 1278, respectively. Mössbauer spectroscopy indicates that the sliding mud contains more ferrous iron species (para-Fe2+ and pyr-Fe2+) and less ferric iron (para-Fe3+ and hem-Fe3+) than do the overlying debris rock and the underlying bedrock. This suggests strong reductive condition within the slip zone relative to the underlying bedrock. Such a redox profile is different from the normal weathering profile whose oxidative conditions become reductive with increasing depth. The change of redox conditions in the sliding mud layer is most likely related to the percolated groundwater which is active in the slip zone.

Restricted access

Abstract  

Fission track dating was used to determine the ultimate rock-forming epoch of Mahanshan Group of metamorphic rocks and involved granitite in NW China. The quartz and hornblende fission tracks revealed that Mahanshan metamorphic rocks were formed during 3.66-3.56.108 years before. Xiaoshima granitite rock body was dated 3.30-3.41.108 years which present the migmatization time in Mahan Shan Mountains area. Geological and geographical features indicate that the latter regional geological process should be dominated with physical tectonic activities including uplifting and fracturing.

Restricted access

Abstract  

Mesozoic-Cenozoic reddish and green beds are widely distributed in northwest China. Mössbauer spectroscopy revealed that the composition of iron species varies with color in the middle-upper Jurassic sedimentary rocks from the Turpan Basin. Three main kinds of iron species were identified: (1) ferric iron of hematite (hem-Fe3+), (2) paramagnetic ferric iron (para-Fe3+), and (3) paramagnetic ferrous iron (para-Fe2+). Pyrite iron (pyr-Fe2+) was revealed only in a few samples. In general, there is a direct correlation between rock color, iron species and total iron content, however, in detail, this relationship is more complicated. The reddish rocks contain higher contents of total iron and hem-Fe3+, whereas the gray rocks contain much more para-Fe2+. However, relatively low hematite content cannot give red color to rocks, probably due to suppression by other pigments such as organic matter in black or chlorite in green. The dark or green rocks normally contain either only paramagnetic Fe2+ and paramagnetic Fe3+ species or these two species associated with hematite Fe3+, but the relative content of hematite species is lower. The variations of different iron species control lithological properties such as color and also may reflect the sedimentary conditions. Moreover, iron speciation in these rocks is one of the main factors, which result the color features of rocks in remote sensing imagery.

Restricted access

Abstract

Citrus reticulata cv. Chachiensis, a traditional Chinese herb, has extensive medicinal and edible effects. 3′,4′,5,6,7,8-Hexamethoxyflavone (HM) and 5,6,7,8,4′-pentamethoxyflavone (PM) are main bioactive compounds in Chachiensis, which have been reported to possess various biological properties. In this study, supercritical CO2 extraction (SCE) and high-speed countercurrent chromatography (HSCCC) were utilized to prepare HM and PM from Chachiensis. The contents of target compounds were determined by a high-performance liquid chromatography method with diode-array detection (HPLC-DAD), which was validated using the following parameters: linearity, sensitivity, repeatability, stability, precision and accuracy. The SCE conditions were optimized using response surface methodology with central composite design. Obtained optimum conditions were temperature of 37.9 °C, pressure of 26.3 MPa, and modifier volume of 81.0 mL. Under above conditions, the recoveries of target compounds were 92.52 ± 0.83 and 96.36 ± 0.43%, respectively. The most appropriate solvent system for HSCCC was selected as n-hexane/ethyl acetate/methanol/water (1:0.8:1:1.2, v/v). The HSCCC fractions were detected by HPLC-DAD, liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR). The results indicated that this method was successfully applied to obtain HM and PM with high purities and high recoveries from Chachiensis.

Open access