Organic carbon isotope and molecular fossil records of vegetation evolution in central Loess Plateau since 450 kyr

Significant uncertainties remain regarding the temporal evolution of natural vegetation during the Quaternary, and drivers of past vegetation change, on the Chinese Loess Plateau (CLP). This study presents analyses of total organic carbon isotopic composition (TOC) and n-alkane ratios (C31/C27) from the Lingtai loess-palaeosol sequence on the central CLP over the last 450 kyr. The results demonstrate that the vegetation in this region comprised a mix of C₃ and C₄ plants of herb and woody growth-form. C₃ plants dominated for most of the last 450 kyr, but this did not lead to extensive forest. C₃ woody plants were more abundant in MIS9 (S3 period) and MIS5 (S1 period) during warm and humid climate conditions. Herbs increased in the region since 130 kyr, possibly as a result of increased aridity. On the orbital timescales, there was a reduction of C₃ herbal plants in MIS11 (S4) than in MIS12 (L5), and in Holocene than in the last glacial period. Our isotope and n-alkane proxy records are in agreement with Artemisia pollen changes in the region, which is/was the dominant species in this area and varying due to different heat and water conditions between glacial and interglacial periods. Though the climate in MIS1 (S0) was similar to that in MIS11 (S4), a significant increase in woody plants during the Holocene suggests the impact of human activities and ecological effects of changes in fire activity.     

Application of Dispersive Liquid–Liquid Microextraction Based on Solidification of Floating Organic Droplet Multi‐residue Method for the Simultaneous Determination of Polychlorinated Biphenyls,Organochlorine, and Pyrethroid Pesticides in Aqueous Sample

Dispersive liquid–liquid microextraction based on solidification of floating organic droplet (DLLME‐SFO) technique was successfully applied for simultaneous assay of eight polychlorinated biphenyls, two organochlorine, and four pyrethroid pesticides multi‐residue in aqueous samples by using GC‐electron capture detection. The effects of various parameters such as kind of extractant and dispersant and volume of them, extraction time, effect of salt addition, and pH were optimized. As a result, 5.0 µL 1‐dodecanol was chosen as extraction solvent, 600 µL methanol were used as dispersive solvent without salt addition, pH was adjusted to 7. Under the optimized conditions, the limits of detection (LOD) were ranged from 1.4 to 8.3 ng L^?1. Satisfactory linear range was observed from 5.0 to 2000 ng L^?1 with correlation coefficient better than 0.9909. Good precisions were also acquired with RSD better than 13.6% for all target analytes. The enrichment factors of the method were ranged from 786 to 1427. The method can be successfully applied to simultaneous separation and determination of three class residues in real water samples and good recoveries were obtained ranging from 76 to 130, 73 to 129, and 78 to 130% for tap water, lake water, and industrial waste water, respectively.     

中天山卡瓦布拉克地区中-基性岩脉的年代学及岩石成因

中天山卡瓦布拉克地区侵入岩类广泛发育,并多处被中-基性岩脉穿插。LA-ICP-MS锆石U-Pb测年获得闪长岩和辉长岩脉年龄分别为296.1±2.5 Ma(MSWD=1.4),299.5±2 Ma(MSWD=1.07),均侵位于早二叠世。岩石学和岩石地球化学分析结果表明该区中-基性岩脉具有富集轻稀土元素(LREE)和大离子亲石元素(Rb,U,Th)、亏损高场强元素(Nb,Ta,Ti)的地球化学特征,SREE为69.19~234.62,LREE/HREE=3.97~11.18。闪长岩脉锆石(176Hf/177Hf)值为0.280 618~0.283 329,对应的εHf(t)值为-14.57^+25.06。研究数据表明,该区中-基性岩脉可能起源于亏损岩石圈地幔,原始岩浆在侵位过程中发生了分离结晶作用,同时还受到了地壳混染作用的影响。基于卡瓦布拉克地区中-基性岩脉的野外地质特征和地球化学分析结果,并结合区域地质资料,认为它们形成于南天山洋闭合之后的后碰撞伸展构造背景。