Ant assemblages at their dry limits: the northern Atacama Desert, Peru, and the Chott El Djerid, Tunisia     

Harold Heatwole 《Journal of Arid Environments》1996,33(4):449-456

Ants do not occur in the rocky desert of the Nazca Plain, Peru, except in the vicinity of shrubs in outwash gulleys, where there are two species that have similar activity periods and microhabitats and exhibit interference competition. Only one species of ant was found on the Chott El Djerid, Tunisia, a large, dry salt lake, devoid of vegetation.  相似文献   

晚古生代特提斯区热带、亚热带植物群的东西分异   总被引：3，自引：0，他引：3       下载免费PDF全文

江新胜  潘桂棠  李兴振 《沉积与特提斯地质》1996,16(2):34-41

从早石炭世开始，地球出现明显受气候带控制的植物分区现象，产生了分别代表南、北温—寒带的冈瓦纳植物区和安加拉植物区以及夹在其间的代表热带、亚热带的欧美植物区（广义）。随着南、北大陆在特提斯西部的汇聚，广义的欧美植物区在晚石炭世产生了东西分异，形成了西部狭义的欧美植物区和东部的华夏植物区。本文从分析东、西两植物区的生态特征、演化阶段、古构造格局的重组和古地理环境等因素入手，探讨了两植物区之间的区别及其分异的原因。可以认为植物区的东西分异是由气候的东西分异造成的，而气候的东西分异则是由于特提斯西部的板块汇聚造成的，它促使西部特提斯地区转变为干旱的大陆性气候，而东部特提斯地区为裂解阶段，保持着潮湿的海洋性气候。  相似文献   

沅陵县沃溪金锑钨矿床网状细脉型矿体地质特征     

王锋  杨仁双 《湖南地质》1990,9(1):52-53

沃溪金锑钨矿床中网状细脉型矿体是一种容易被忽略的有价值的矿体,探明矿石量120万吨。这种矿体赋存于主脉(层状含矿石英脉)间蚀变板岩中,与主脉有着密切的关系,严格受主脉旁的次级构造控制。矿体呈楔状、透镜状、囊状。有白钨矿-自然金、白钨矿-辉锑矿-自然金、单一自然金三种矿化类型。  相似文献   

四川龙门山石炭纪珊瑚组合序列   总被引：2，自引：0，他引：2  

叶干  杨菊芬 《地球科学》1988,(5)

四川龙门山地区石炭系发育完整,生物化石丰富,是研究石炭系良好的地区之一。本文依据珊瑚化石演化序列,提出本区石炭系8个珊瑚组合序列。本区石炭系厚约220m,以碳酸盐岩沉积为主。上界与二叠系为假整合;下界和泥盆系连续沉积。在其下伏的地层中发现有孔虫Quasiendothyra Communis(Rauser),可归入上泥盆统,相当于西欧的艾特隆层。因此本区的下界和西欧的泥盆—石炭界线是接近的。  相似文献   

The relationships of seabird assemblages to physical habitat features in Pacific equatorial waters during spring 1984-1991   总被引：1，自引：0，他引：1  

Ribic  Christine A.; Ainley  D. G. 《ICES Journal of Marine Science》1997,54(4):593-599

  相似文献   

Singularities in NCKFMASH (Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O)     

B. WORLEY  & R. POWELL 《Journal of Metamorphic Geology》1998,16(2):169-188

A new petrogenetic grid is presented for the system NCKFMASH (Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O), in which Ca is incorporated in garnet, and CaAlNa₋₁Si₋₁ solid solution is considered for both the plagioclase and white-mica structures. A compatibility diagram for plagioclase-bearing metapelitic assemblages within the NCKFMASH system also has been derived. A dominant feature of the NCKFMASH grid is the singularities and associated singular reactions which occur along plagioclase+margarite- and plagioclase+paragonite-bearing univariant equilibria. The singularities represent compositional coplanarities which occur in response to the CaAlNa₋₁Si₋₁ substitution occurring at different rates in plagioclase and white-mica. This is controlled by a fundamental difference in the mixing within the two mineral structures. The singularities give rise to a number of intriguing phase diagram features, including azeotropes. From the results presented here, it is predicted that the occurrence of margarite and paragonite in pelitic rocks is controlled by equilibria related to the singularities. The presence of these white-micas is strongly dependent upon bulk composition, and plagioclase-bearing, margarite/paragonite-free assemblages, typical of Barrovian-type terranes, are predicted for bulk compositions of Mg/(Mg+Fe)≈0.4 and Ca/(Ca+Na)≈0.4 at for example 5.5  kbar.  相似文献   

苏鲁人类扰动区表土花粉组合与植被关系的研究     

李永飞  李春海  许斌  舒军武  李月丛  许清海 《地球科学进展》2019,(4):333-345

利用江苏和山东地区70个农田和非农田表土样品研究不同土地类型的花粉特征,为使用孢粉作为研究手段分析古代农业提供重要参考资料。结果表明所有植被类型的花粉谱均以草本花粉为主,但是含量明显不同,表现为农田>荒地>林地。其中禾本科谷物类型含量的变化最大,农田最高达41%,荒地高于11%,林地低于8%。谷物类禾本科花粉传播距离很短,其百分含量在10~20m内急剧衰减至27.6%,500m以外降低至20%以下;十字花科花粉也有相似的变化规律。藜科花粉对农田和荒地具有同等指示意义,可能与人类活动强度与方式有关。中华卷柏含量增加表明人类活动加强。油菜、水稻、小麦和玉米等谷物类花粉产量或者在土壤中保存存在差异:十字花科>玉米型禾本科>水稻型禾本科>小麦型禾本科。降趋势对应分析(DCA)结果表明,通过花粉相对百分含量,可以较好地区分水田、麦田和非农田,但油稻田与麦稻田、荒地与林地难以区分。  相似文献   

新疆且末地区中侏罗世杨叶组孢粉化石的发现及其地质意义     

赵志刚  张雄华  李晓阳  孙志佳  曾蛟  王运良 《地质通报》2019,38(10):1603-1614

新疆且末县江尕勒萨依村杨叶组首次发现了大量孢粉化石。经鉴定共计37属81种,根据孢粉化石组合特征及地层分布将其命名为Cyathidites-Neoraistrickia-Disacciatrileti组合,时代为中侏罗世早期,与西北区、华北区同时代地层中孢粉组合可以很好的对比。通过研究孢粉组分与母本植物的亲缘关系,得出中侏罗世早期江尕勒萨依地区植被主要由真蕨类植物、石松类植物和乔木的松柏类及苏铁类组成,反映古气候为热带-亚热带湿润气候。  相似文献   

Can severely fragmented patches of riparian vegetation still be important for arid-land bird diversity?     

C.L. Seymour  R.E. Simmons 《Journal of Arid Environments》2008,72(12):2275-2281

The vegetation of riparian habitats is often distinct from that of the surrounding landscape, thus representing unique habitat for a variety of biota. Although highly mobile, birds often exhibit distinct species assemblages associated with habitat. Therefore, degradation or removal of riparian habitat, particularly in arid environments, may threaten bird diversity. Along the Vaal River, South Africa, mining and agriculture have reduced natural riparian habitat to ca. 9% of its former extent in the Northern Cape Province. We surveyed bird assemblages within intact riparian, savanna and bush-thickened habitats along the Vaal River to ascertain their importance to bird diversity. Avian abundance and species richness did not differ between the three habitats. Species composition of riparian bird assemblages was significantly different to that of savanna and bush-thickened habitats, however, which were not significantly different from each other, and more species were characteristic of riparian habitat (17 species) than bush-thickened (seven species) or savanna (one species) habitats. Of three species reaching the south-western limit of their African distribution, all occurred in riparian habitat. Thus, despite its fragmented nature, the riparian vegetation on the Vaal still supports an important component of avian diversity, and a landscape-level approach is required to manage this relatively rich, arid-land, river.  相似文献   

两种鹤虱属短命植物的繁育系统及其对荒漠环境的适应   总被引：2，自引：1，他引：1  

赵学杰  谭敦炎  李新蓉 《中国沙漠》2008,28(2):294-300

两形果鹤虱（^{Lappula duplicicarpa}）和异形狭果鹤虱（^{L. semiglabra}）是两种广泛分布于新疆准噶尔荒漠的具异形果实的早春短命植物。两种植物同一花中均能产生两种形态、脱落及扩散方式明显不同的小坚果,且同一花序上不同部位的花中产生的异形果实比例不同。重点对两种植物的繁育系统与异形果实的产生是否存在联系,以及它们与准噶尔荒漠环境相适应的特点进行了观察。结果表明：①二者花均为两性,植株上同一花中以及花序上产生不同比例异形果实的花之间在花各部的数目与形态、单花花粉量(P)、胚珠数(O)和P/O值上表现均很稳定,与异形果实的产生没有直接联系。②单花花期一般在24 h左右,开花时间不受气候因素的影响。③两种植物的花粉育性均很高,花粉可育率分别为(91.0±4.7)％和(93.2±4.3)％。④散粉时二者的花粉活力均不高,散粉后花粉活力的动态变化基本一致,最佳授粉期分别在2 h和3 h以内,柱头的最佳可授期均在3 h以内,花粉的最佳授粉期与柱头的最佳可授期高度吻合。⑤ 两种植物的P/O值分别为1 222±197和3 419±426,属于混合式繁育系统,这与套袋实验及自花授粉的荧光显微观察结果相一致。⑥ 两种植物在繁育系统上所表现出的特点,避免了准噶尔荒漠的多风、温湿度变化大等恶劣环境条件对其开花、传粉过程的不利影响,保障了繁殖成功。这些结果将为探讨短命植物对准噶尔荒漠的生态适应机制提供重要的理论依据。  相似文献