景谷盆地低演化油气的同位素地球化学特征

对云南景谷盆地第三系原油及其伴生气的研究 ,共采集了油样 6个 ,气样 4个 ,进行了原油及其族组成、气体甲烷及其同系物的碳同位素测定 ,结果表明景谷盆地大牛圈原油富集轻碳同位素 ,其δ13 C1值为 - 32 .2‰～- 31.0‰ ,族组成碳同位素也偏轻 ,并具有δ13 C饱 <δ13 C芳 <δ13 C非 >δ13 C沥异常分布的类型曲线 ,各组成之间同位素组成的相对差值较小。这些都反映出原油主要来自湖相烃源岩 ,形成于低演化阶段的未熟—低熟原油。原油伴生气甲烷明显富集δ12 C ,δ13 C1值 - 5 7.8‰～ - 5 3.8‰ ,用低演化阶段油型气δ13 C1与Ro 模式计算景谷盆地烃源岩的成熟度约为Ro=0 .3%～ 0 .5 %,与景谷盆地地质背景基本一致。伴生气乙烷碳同位素偏重 ,甲烷同系物碳同位素出现反序列现象 ,可能有煤成气贡献的多源复合。上述特征表明 ,它是与盆地原油同型、同阶段的产物 ,即油为湖相烃源岩形成的未熟—低熟原油 ,气为同一演化阶段形成的油型气 ,其阶段和地球化学特征与天然气的“过渡带”气相当 ,因此主源为低演化阶段形成的油型气。

Temporal-Spatial Variances of Holocene Precipitation at the Marginal Area of the East Asian Monsoon Influences from Pollen Evidence

The woodland-steppe ecotone in the. southern Nei Mongol Plateau is located at the northern edge of the east Asian monsoon influences. A marked southeastern - northwestern (SE - NW) precipitation gradient exists in this region. Quantitative reconstruction of palaeo-precipitation of this region is helpful to reveal the development of monsoon climate and to predict die future desertification. Based on modern vegetation and surface pollen studies, a pollen-precipitation transfer function in the study region was established. Pollen data from three sediment sequences within the ecotone were used to reconstruct palaeo-precipitation during the Holocene. The processes of precipitation changes in the three sequences were quite different. There was a tendency of precipitation declined from the onset of the Holocene to 1 100 a BP in Haoluku. But, in Liuzhouwan and Xiaoniuchang, both located south of Haoluku, the annual precipitation reached highest values during 7 800 - 6 200 a BP and 7 200 - 5 000 a BP, respectively. The influences of southwestern (SW) monsoon and the variances of topographical conditions have possibly caused these temporal-spatial variances.

Boundary Shift of Potential Suitable Agricultural Area in Farming-grazing Transitional Zone in Northeastern China under Background of Climate Change During 20th Century

Climate change affected the agricultural expansion and the formation of farming-grazing transitional patterns during historical periods. This study analyzed the possible range of the boundary shift of the potential suitable agriculture area in the farming-grazing transitional zone in the northeastern China during the 20th century. Based on modem weather data, 1 km-resolution land cover data, historical climatic time series, and estimation by using similar historical climatic scenes, the following was concluded： 1） The climate conditions of suitable agriculture areas in the farming-grazing transitional zone in the northeastern China between 1971 and 2000 required an average annual temperature above 1℃ or ≥ 0℃ accumulated temperature above 2500℃-2700℃, and annual precipitation above 350 mm. 2） The northern boundary of the potential suitable agriculture area during the relatively warmer period of 1890-1910 was approximately located at the position of the 1961-2000 area. The northern boundary shifted back to the south by 75 km on average during the colder period of the earlier 20th century, whereas during the modem warm period of the 1990s, the area shifted north by 100 km on average. 3） The western and eastern boundaries of the suitable agricul^re area during the heaviest drought periods between 1920s and 1930s had shifted northeast by 250 km and 125 km, respectively, contrasting to the boundaries of 1951-2008. For the wettest period, that is, the 1890s to the 1910s, the shift of western and eastern boundaries was to the southwest by 125 km and 200 km, respectively, compared with that in the 1951-2008 period. This study serves as a reference for identifying a climatically sensitive area and planning future land use and agricultural production in the study area.

Response of Vegetation Cover to Climate Change and Influence of Dusty Weather in the Desertloess Transitional Zone of China

[Objective]This study aimed to analyze the relationships of the normalized difference vegetation index(NDVI)(1981-2006)in the desert-loess transitional zone of China with precipitation and temperature.[Method]The average method and the correlation function were applied in this study.[Result]The results indicated that during the growing season NDVI was positively correlated with precipitation in the current month,last month and the month before last,especially the last month.NDVI mostly negatively correlated with temperature,especially the temperature in the last month,which shows that the higher temperature,the more adverse the conditions for vegetation growth.[Conclusion]NDVI from August to October clearly is one of the significant factors influencing dust storm weather in spring of the next year.