西秦岭790铀金矿田成矿特征及铀,金成矿的异同性   总被引：1，自引：0，他引：1  

张忠达 《铀矿地质》1991,7(1):34-40

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云南蒙自五里冲水库区F1,F2断层新活动年代研究   总被引：1，自引：0，他引：1  

陈惠珠 《地震研究》1991,14(4):347-357

五里冲水库地处侵蚀山区,缺乏第四纪地层作为研究断层新活动年代的对比标志。本文以F_1、F_2断层带内发育的多期方解石脉和断层泥为研究对象,采用显微构造分析,热释光(TL)测年法和扫描电镜(SEM)分析,石英溶蚀速率测年法,对库区F_1、F_2断层新活动的年代进行综合判定。确认:F_1、F_2断层最后一次明显活动的年代分别为(2.93±0.31)×10~5年和(2.33±0.26)×10~5年以前,为评估五里冲水库构造稳定性,提供了可靠的数据。  相似文献   

固碳作用与地质时代的大冰期     

王自明 《冰川冻土》1991,13(1):61-66

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Oceanographic Change and Terrestrial Human Impacts in a Post A.D. 1400 Sediment Record from the Southwest Iceland Shelf     

A.E. Jennings  S. Hagen  J. Harðardóttir  R. Stein  A.E.J. Ogilvie  I. Jónsdóttir 《Climatic change》2001,48(1):83-100

Environmental proxies of soil erosion on Iceland, and oceanographic conditions on the adjacent shelf, were measured on a 50 cm box core taken from the southwest Iceland shelf in 1993 during cruise 93030 of the Canadian ship, CSS Hudson. These data, covering the last several centuries, are compared with the documentary record of sea-ice changes around Iceland since A.D. 1600. The site is under the influence of the Irminger Current, which carries warm, saline, Atlantic water northward along the shelf. Because of the relative warmth of this current, sea ice rarely occurs off southwest Iceland, even during the most severe sea-ice intervals of the historical record. In severe sea-ice years, however, the ice drifts clockwise around Iceland from the northeast and east and, in rare cases, reaches the southern coasts (Ogilvie, 1992). The chronology of the core was established by converting the basal radiocarbon date to calendar years and assuming a linear sedimentation rate from the base of the core to the year of collection, 1993. Organic carbon, stable C and O isotope ratios, planktonic foraminiferal assemblages, and sediment magnetic parameters were measured on samples from the core, plotted against calendar years and compared to the Icelandic sea-ice index. The environmental proxies suggest that increased soil erosion, reduced salinity, and, possibly, decreased marine productivity prevailed during the severe sea-ice interval lasting from the last quarter of the eighteenth century to around 1920. Such a situation could develop with climatic cooling, increased storminess, and loss of vegetation cover to stabilise the soil. Although the core site generally lies outside the sea-ice limits, the evidence clearly shows the influence of sea ice and fresh water, and is sensitive to the overall climatic deterioration manifested by the sea-ice record.  相似文献   

The Initiation of the "Little Ice Age" in Regions Round the North Atlantic   总被引：3，自引：0，他引：3  

J.M. Grove 《Climatic change》2001,48(1):53-82

The "Little Ice Age" was the most recent period during which glaciers extended globally, their fronts oscillating about advanced positions. It is frequently taken as having started in the sixteenth or seventeenth century and ending somewhere between 1850 and 1890, but Porter (1981) pointed out that the "Little Ice Age" may 'have begun at least three centuries earlier in the North Atlantic region than is generally inferred'. The glacial fluctuations of the last millennium have been traced in the greatest detail in the Swiss Alps, where the "Little Ice Age" is now seen as starting with advances in the thirteenth century, and reaching an initial culmination in the fourteenth century. In the discussion here, evidence from Canada, Greenland, Iceland, Spitsbergen and Scandinavia is compared with that from Switzerland. Such comparisons have been facilitated by improved methods of calibrating radiocarbon dates to calendar dates and by increasing availability of evidence revealed during the current retreat phase. It is concluded that the "Little Ice Age" was initiated before the early fourteenth century in regions surrounding the North Atlantic.  相似文献   

The "Little Ice Age" and its Geomorphological Consequences in Mediterranean Europe   总被引：1，自引：0，他引：1  

A.T. Grove 《Climatic change》2001,48(1):121-136

Alpine glacier advances in the "Little Ice Age" took place in the decades around 1320, 1600, 1700 and 1810. They were the outcome of snowier winters and cooler summers than those of the twentieth century. Documentary records from Crete in particular, and also from Italy, southern France and southeast Spain point to a greater frequency in Mediterranean Europe's mountainous regions of severe floods, droughts and frosts at times of "Little Ice Age" Alpine glacier advances. Deluges, when more than 200 mm of rain fall within 24 hours, are most frequent on mountainous areas near the coast. An instance is given of the geomorphological consequences of a great deluge which struck the Tech valley in the eastern Pyrenees on 17 October 1940. An increased frequency of deluges, probably at times when Alpine glaciers were advancing in the "Little Ice Age" and earlier in the Holocene, in areas known to be tectonically unstable and underlain by soft sediments, could better explain the occurrence of fluvial terraces in Mediterranean Europe sometimes known as the "younger fill", than soil erosion resulting from deforestation.  相似文献   

The Tallinn Temperature Series Reconstructed Back Half a Millennium by Use of Proxy Data     

A. Tarand  P.Ø. Nordli 《Climatic change》2001,48(1):189-199

In order to extend the Tallinn temperature series backward in time, three different climate proxies were used. These were: the first day of ice break-up in Tallinn port, a proxy for the mean winter air temperature (December to March); the first day of ice break-up on the rivers in northern Estonia, a proxy for the beginning of spring; and, the first day of the rye harvest, a proxy for the mean air temperature in spring and summer (April to July). On the basis of these proxies the mean winter temperature could be extended back to the year AD 1500, and the spring and summer temperature back to 1731. The series of winter temperatures was analysed for long-term trends and variations on different timescales. The most striking feature is the warming of the winters from about the mid nineteenth century to the present. The warming is especially noticeable over the latest decades. The climate from the start of the series (AD 1500) to the mid nineteenth century was in general somewhat colder, and should be recognised as a part of the Little Ice Age, though the period was intercepted by warmer winters in the first half of the eighteenth century.  相似文献   

小冰期以来中国十年尺度气候变化时空分布特征的初步研究   总被引：8，自引：2，他引：8  

杨保 《干旱区地理》2001,24(1):67-73

依据10年际的冰芯、树轮和历史文献记录，首先进行了聚类分析，近400年来中国温度变化大体上可分为两类：第一类包括高原南部、高原西部、东北和闽台地区；第二类包括西南、华南、华中、华东、西北和华北地区。接着分析了近600年、500年和400年三种不同时间尺度上中国气温的时空分布，第一特征向量显示中国东部温度值高于西部，第二特征向量中高原南部、高原东北部与高原西部的反位相变化趋势在不同时间惊讶的EOF结果中都有表现。西南、华南区与华北、华东区在后两种时间尺度上温度变化位相相反。以上这些变化型在近40年来的年际变化中同样发生。小冰期在不同时间尺度的第一特征向量的权重系数中均有明显表现。将中国温度变化与北半球和北极进行比较，发现它们变化非常类似，且以北半球和北级滞后中国温度20年时相关相关最好。  相似文献   

金沙江流域（云南段）砂金成因类型及其找矿前景     

黄仲权  史清琴 《云南地质》2001,20(3):270-278

根据成矿作用、成矿环境及矿床特征，金沙江流域（云南段）砂金矿床，可划分为：残坡积、洪积、冲洪积、冲积和冰碛等五种类型。成矿主要受碰撞带、深大断裂、大断裂及其派生断裂、基底岩石、地貌、水质和水化学环境等综合控制。以巨甸－大具及中江街－金江街两片区最具有找矿前景。  相似文献   

缅北中部脉金矿带控矿因素及成矿作用浅析     

何文举 《云南地质》2001,20(3):279-288

缅北中部，印缅岛弧及弧后盆地东侧、新生代造山带的前缘推覆构造带中，分布有许多脉金矿床及矿点，构成金矿带。矿带、矿田、矿床及矿体的形成、分布及其规模，受不同级别的近南北向逆冲断裂，及其间派生的北东向张性扩容断裂组成的剪切断裂带控制。可渗透的下麦尔组下部中一粗粒砂岩，起着很好的容矿作用。下麦尔组上部泥岩、细砂岩、粉砂岩和页岩互层单元，在携金热液的迁移、氧化硅的沉淀和矿质沉积定位等方面，可能起到圈闭作用。  相似文献