干旱区地理最新文献

{"title":"Magnetostratigraphy and provenance of the Qingzhou loess in Shandong province","authors":"Shuzhen Peng, Lijun Zhu, G. Xiao, Y. Qiao, Zhidong Gao, Dongdong Chen","doi":"10.3724/SP.J.1227.2011.00184","DOIUrl":"https://doi.org/10.3724/SP.J.1227.2011.00184","url":null,"abstract":"Loess deposits with varying thickness are widely distributed on the intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous regions. However, the basal ages and material resources of the loess deposits are not clear. The paper studied the Qingzhou loess profile in Shandong with magnetostratigraphic and optical stimulated luminescence (OSL) methods and further investigated its main provenances with the mineralogical methods. The magnetostratigraphic results showed that the Brun- hes/Matuyama (B/M) reversal boundary was not recognized, suggesting a basal age younger than 0.78 Ma. Ex- trapolations by sedimentation rates, based on the upper part depositional rate from the OSL age, the basal age of the Qingzhou loess is about 0.5 Ma. Until now, older loess deposits have not been reported on the northern side of the central Shandong mountainous regions. The results of the paper indicate that the loess deposits in this area might have strated from the Middle Pleistocene. The basal age of Qingzhou loess is approximately synchronous with the Xiashu loess in the middle-lower reaches of Yangtze River. Major components of clay minerals in the Qingzhou profile are dominated by illite. Other clay mineral compositions are mainly smectite, chlorite and kaolinite, which are similar with the Xifeng loess in the Loess Plateau. However, the contents of smectite and the ratios of illite and kaolinte in the Qingzhou loess samples are higher than those in the Xifeng loess samples of the Loess Plateau, indicating that the loess in the northern side of the central Shandong mountainous regions has different sources from that of the loess deposits in the Loess Plateau. The clay mineral analysis further reinforces the earlier conclu- sion that the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of Yellow River during the glacier periods are the main material sources for the Qingzhou loess deposits, which is an indicator to the local aridification of the lower reaches of the Yellow River. Loess deposition in the central Shandong mountainous regions started at around 0.5 Ma. The age of Qingzhou loess is approximately synchronous with the ongoing high-latitude cold since the Middle Pleistocene, which indicates that strengthened East Asian winter monsoon was sufficiently energetic to bring substantial quantities of material from the marine strata exposed in the Laizhou Bay and the fluvial plain of the lower reaches of the Yellow River to the central Shandong mountainous regions. The results therefore suggest that both regional geological process and global changes were responsible for the forma- tion of Qingzhou loess since Middle Pleistocene.","PeriodicalId":64574,"journal":{"name":"干旱区地理","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2011-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69936738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Climatic changes of semi-arid region over the northwest China in recent 50a.","authors":"Yao Yubi, X. Guo-ju, W. Runyuan, Zhang Xiuyun","doi":"10.3724/SP.J.1224.2009.00159","DOIUrl":"https://doi.org/10.3724/SP.J.1224.2009.00159","url":null,"abstract":"Using 33 stations temperature,precipitation,relative humidity,wind speed,evaporation in the semi-arid region of Northwest China from 1951 to 2004,some new characteristics of climatic changes were posted in virtue of statistics method.The result shows that precipitation displayed a descendant tendency in most areas of the semiarid region in Northwest China,the tendency rate was -59.168～-1.143 mm/10a,its maximum descendant tendency was in autumn and the second one in spring,but it displayed an ascendant tendency in some areas in summer and in most areas in winter,3a and 6～8a period was existed,whereas 3a period of oscillation was the strongest,as its centre during the period from 1962 to 1966,and 3a period of oscillation began to weaken from 1966,6～8a period of oscillation was the strongest,as its centre during the period from 1980 to 1985.The temperature showed an ascendant tendency,the tendency rate was 0.074～0.507℃/10a,it displayed anti-parabola type in most areas,and turning point was from the earlier stage of 1960s to the later stage of 1970s,its ascendant tendency was maximum in winter,the second one in spring and autumn,except for the common boundary of Shaanxi, Gansu and Ningxia Province,which showed a descendant tendency.The precipitation displayed a descendant tendency, whereas the temperature showed an ascendant tendency,which resulted in climate warming and drying in the semi-arid region of Northwest China.The relative humidity showed a wavelike variation.Evaporation also showed an ascendant tendency except for some individual areas in recent 50a.","PeriodicalId":64574,"journal":{"name":"干旱区地理","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69918280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}