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ZHANG Chengjun ZHENG Mianping Alexander PROKOPENKO Steffen MISCHKE GOU Xiaohui YANG Qili ZHANG Wanyi FENG Zhaodong 《《地质学报》英文版》2009,83(6):1101-1115
Abstract: The Early Holocene paleoclimate in Bosten Lake on the northern margin of the Tarim Basin, southern Xinjiang, is reconstructed through an analysis of a 953 cm long core (BSTC2000) taken from Bosten Lake. Multiple proxies of this core, including the mineral components of carbonate, carbonate content, stable isotopic compositions of carbonate, Ca/Sr, TOC and C/N and C/S of organic matter, are used to reconstruct the climatic change since 8500 a B.P. The chronology model is made by nine AMS 14C ages of leaves, seeds and organic matter contained in two parallel cores. The climate was cold and wet during 8500 to 8100 a B.P. Temperature increased from 8100 to 6400 a B.P., the climate was warm and humid, and the lake expanded. The lake level was highest during this stage. Then from 6400 to 5100 a B.P., the climate became cold and the lake level decreased slightly. During the late mid-Holocene, the climate was hot and dry from 5100 to 3100 a B.P., but there was a short cold period during 4400 to 3800 a B.P. At this temporal interval, a mass of ice and snow melting water supplied the lake at the early time and made the lake level rise. The second highest lake level stage occurred during 5200 to 3800 a B.P. The climate was cool and wet during 3100 to 2200 a B.P., when the lake expanded with decreasing evaporation. The lake had the last short-term high level during 3100 to 2800 a B.P. After this short high lake level period, the lake shrank because of the long-term lower temperature and reduced water supply. From 2200 to 1200 a B.P., the climate was hot and dry, and the lake shrank greatly. Although the temperature decreased somewhat from 1200 a B.P. to the present, the climate was warm and dry. The lake level began to rise a little again, but it did not reach the river bed altitude of the Konqi River, an outflow river of the Bosten Lake. 相似文献
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The Etendeka Formation of north-western Namibia consists of a sequence of interbedded quartz latites and tholeiitic basalts and forms part of the Karoo Igneous Province in southern Africa. The age of the Etendeka Formation is approximately 130–135 Ma. The quartz latites make up a significant proportion of the stratigraphic succession (<25% of the total stratigraphic thickness) and form as much as 60% of the outcrop area in the southern Etendeka. Apart from some systematic differences between pitchstones and devitrified quartz latite, largely explained by alteration processes, individual quartz latite units exhibit remarkably uniform compositions with no significant vertical or lateral variation. Geochemistry can be used as a primary criterion for the correlation of major quartz latite units over much of the southern Etendeka area enabling the reconstruction of the Etendeka Formation stratigraphy in this region. Individual quartz latite units occur as voluminous (400–2600 km3), widespread (up to 8800 km2), sheet-like deposits typically between 40 and 300 m thick. Each unit consists of basal, main and upper zones. The main zone generally constitutes over 70% of the thickness of the unit and typically consists of texturally featureless devitrified quartz latite. In contrast the basal and upper zones of the flow are characterised by flow banding, pitchstone lenses and breccia, with rare occurrences of pyroclastic textures. The quartz latites are sparsely porphyritic (<10% phenocrysts) with glassy or devitrified groundmass textures. The phenocrysts consist of plagioclase, pyroxene, titanomagnetite and rare ilmenite. Pyroxene geothermometry indicates high (1000–1100°C) temperatures of crystallisation which, coupled with the absence or primary hydrous phases, indicates that the quartz latites were relatively hot, H2O-undersaturated magmas. The quartz latites display features common to both rhyolite lavas and ignimbrites and are clearly the products of an unusual eruption style. The local preservation of pyroclastic textures and the broad areal extent of these units lead to the conclusion that the quartz latites are high-temperature rheomorphic ignimbrites (i.e. rheoignimbrites). A combination of high eruption temperature and relatively low viscosity helps to explain the often completely welded and homogeneous textures observed in most quartz latite outcrops in the Etendeka area. 相似文献
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An Analysis of Spatial and Temporal Dimension of Drought Vulnerability in Turkey Using the Standardized Precipitation Index 总被引：3，自引：1，他引：2
F.?KEMAL.?S?NMEZEmail author ALI?üMRAN?K?MüSCü AYHAN?ERKAN ERTAN?TURGU 《Natural Hazards》2005,35(2):243-264
Drought has become a recurrent phenomenon in Turkey in the last few decades. Significant drought conditions were observed during years of late 1980s and the trend continued in the late 1990s. The countrys agricultural sector and water resources have been under severe constraints from the recurrent droughts. In this study, spatial and temporal dimensions of meteorological droughts in Turkey have been investigated from vulnerability concept. The Standardized Precipitation Index (SPI) method was used to detail geographical variations in the drought vulnerability based on frequency and severity of drought events at multiple time steps. Critical (threshold) rainfall values were derived for each station at multiple-time steps in varying drought categories to determine least amount of rainfall required to avoid from drought initiation. The study found that drought vulnerability portrays a very diverse but consistent picture with varying time steps. At regional scale, south-eastern and eastern Anatolia are characterized with moderate droughts at shorter time steps, while the occurrence of severe droughts at shorter time steps is observed at non-coastal parts of the country. A similar picture was observed with very severe droughts. The critical (threshold) values exhibited rising numbers during the growing season at 3-month step in the South-eastern Anatolia, which might have significant consequences considering presence of large irrigation projects under-development in the region. In general, rainfall amounts required for non-drought conditions decrease from the coastal parts toward the interiors with increasing time steps. 相似文献
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The bloom forming dinoflagellate, Ceratium furca, has been linked with coastal eutrophication worldwide in tropical and subtropical locations. During the summer of 2007, an unusual 6-month long bloom of C. furca was observed in Pago Pago Harbor, Tutuila Island, American Samoa. Incidents of dinoflagellate blooms in this area have not been previously reported. The bloom was first reported in May and dissipated in November 2007. In February-March 2009, a similar C. furca bloom was observed. During both blooms,... 相似文献
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The development of an effective artificial larval diet has been a major stumbling block for advancing the aquaculture of spiny lobsters internationally. Attempts to determine the natural diet of spiny lobster larvae have been impeded by their small size and sparse distribution in the open ocean, making these larvae difficult to study using conventional methods. Recent advances in molecular genetic techniques have provided a novel route for identifying the natural prey of spiny lobster larvae (phyllosoma). In this study, sequences from zooplankton found associated with phyllosomas, along with sequences from GenBank, were used to design a suite of group-specific primers. These primers were able to amplify via the polymerase chain reaction (PCR) a short (100–200 base pair) DNA fragment from the 16S or COI locus of potential prey but not from lobster. These methods were applied to four wild-caught phyllosomas of Jasus edwardsii and two phyllosomas of Scyllarus sp. Z. Gadiforme, Cnidaria, Gastropoda and Decapoda crustacean (non-lobster) DNA sequences were obtained from the gut contents of these lobster larvae and inferred as prey. These initial results confirm previous studies using other less definitive methods which have indicated that phyllosomas are opportunistic predators of a wide range of zooplankton taxa. 相似文献
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