Late-glacial and early-Holocene Coleoptera assemblages as indicators of local environment and climate at Kråkenes Lake, western Norway     

Geoffrey Lemdahl 《Journal of Paleolimnology》2000,23(1):57-66

Thirty-six Coleoptera (beetle) taxa and other insects were identified from the late-glacial and early-Holocene sediments at Kråkenes Lake. Compared with other Scandinavian late-glacial sites, this is a rather sparse record. The water beetles found in the Allerod are characteristic of a poorly vegetated clear-water lake. The terrestrial fauna is indicative of dwarf-shrub and moss vegetation. A marked decline in the number of species at the start of the Younger Dryas was rather rapid, probably over less than 80 calendar yrs. No obligate tundra species replaced the Allerod fauna. Most of the Younger Dryas is virtually devoid of beetles. The increase in numbers and diversity of both aquatic and terrestrial species at the Younger Dryas/Holocene transition is very rapid. After an initial pioneer stage, beetles associated with dwarf-shrub heath and willow scrub appeared, but no obligate tree or forest taxa were recorded.Mutual Climatic Range (MCR) temperature reconstructions suggest that the Allerod was colder and more continental than present. The near absence of beetles in the Younger Dryas probably reflects very cold conditions. A rapid temperature rise at the start of the Holocene resulted in a warmer and more continental climate than present.  相似文献   

对松辽盆地钱家店凹陷铀成矿作用的重新认识   总被引：1，自引：0，他引：1  

陈晓林  方锡珩  郭庆银  夏毓亮  庞雅庆  孙晔 《地质学报》2008,82(4):553-561

钱家店凹陷中的含矿层位主要为上白垩统姚家组,前人认为其中的红色砂岩为原生成因,但大量的证据证实砂岩原生应以灰色为主,红色砂岩为后生氧化蚀变造成,并控制着钱家店铀矿床铀矿化的产出。在此基础上建立该矿床的后生蚀变分带,依次为红色蚀变带、黄色蚀变带、灰白色蚀变带、过渡带、原生带,红色蚀变带为主要的氧化带,铀矿化主要集中在过渡带。平面上铀矿化主要分布于层间氧化带前锋线附近的位置,并在氧化舌状体的前端和两个氧化舌状体之间存在铀的富集。文章最后还建立了该矿床的成矿模式,并对区域上层间氧化带的展布进行了讨论。  相似文献   

太白山北坡成土因素及不同土壤垂直带谱的比较   总被引：1，自引：2，他引：1  

雷梅  陈同斌  冯立  常庆瑞  阎湘 《地理研究》2001,20(5):583-592

在系统地考察太白山北坡地质、地貌、气候和植被等成土因素的基础上,总结和回顾了用土壤发生分类和土壤系统分类两种分类体系划定的太白山北坡土壤垂直带谱。根据最新的土壤系统分类,太白山北坡的土壤垂直带谱是:暗瘠寒冻雏形土(3500～3767m)———暗沃寒冻雏形土(3300～3500m)———酸性湿润雏形土(2500～3300m)———简育湿润淋溶土(1400～2500m)———简育干润淋溶土(<1400m)。分析、比较表明:两种体系有密切联系,均以成土因素为依据,建立在土壤发生学理论之上;与土壤地理发生分类相比,土壤系统分类用可以度量的诊断层和诊断特性进行土壤分类,不仅能够反映出山地土壤成土因素的垂直变化趋势,而且避免了太白山北坡土壤类型鉴定上的许多歧义。  相似文献   

山西地堑系强震的活动规律和危险区段的研究   总被引：16，自引：3，他引：16       下载免费PDF全文

徐锡伟  邓起东 《地震地质》1992,14(4):305-316

山西地堑系是我国著名的历史强震活动带之一。作者系统地分析了山西地堑系历史强震的重复和迁移现象、M≥7级地震前中强地震的活动特征、蠕变曲线的线性分段性,并根据近期地震活动的特点,判断了现今地震活动暂态和未来地震活动性;最后,在现有的形变测量资料、历史地震和古地震研究成果的基础上,确定了山西地堑系内可能发生强震的危险区段  相似文献   

The higher grade metamorphic zonation of the Sambagawa metamorphic belt in central Shikoku, Japan   总被引：5，自引：1，他引：5  

T. HIGASHINO 《Journal of Metamorphic Geology》1990,8(4):413-423

The higher grade metamorphic zonation of the Sambagawa (= Sanbagawa) belt is established for the first time for the whole area of central Shikoku. As discontinuous reactions to define the isograd are absent, the metamorphic grade is primarily determined by the Mg-Fe partitioning between garnet and chlorite along representative traverses. However, for regional mapping, mineralogical features of the pelitic schists, such as using mineral assemblages of more than divariant equilibrium, the modal garnet to chlorite ratio, and the optical properties of chlorite, are employed as auxiliary criteria.
The presence of the highest grade mineral zone in the middle of the structural level is confirmed, but its spatial distribution is far more complex than hitherto accepted. Thermal axes are now confirmed at three different structural levels. A model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress. Thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets. Tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re-equilibrated. Local anomalies of metamorphic grade, represented by mixing of schists of different metamorphic grade, exist, but they are due to a later stage event.  相似文献   

Inoceramid bivalves and biostratigraphy of the upper Albian and lower Cenomanian of the United States Western Interior Basin     

《Cretaceous Research》2016

Inoceramid bivalves of the upper Albian and lower Cenomanian of the United States Western Interior are revised, Eleven species-level taxa and three genera are described. Two new species, Gnesioceramus mowriensis, characterizing the Mowry Shale of the early, but not the earliest, Cenomanian, and Posidonioceramus merewetheri, of the lower Cenomanian, and on new genus, Posidonioceramus, are recognised. The Western Interior inoceramid species from this interval are strongly endemic and are not good tools for long-distance correlations, although they are very effective in regional dating.In terms of the inoceramid biostratigraphy, middle and upper parts of the upper Albian can be referred to the Gnesioceramus Biozone, represented by G. comancheanus (Cragin) and G. bellvuensis (Reeside). These taxa are endemic to the Western Interior and some adjacent areas (Gulf Coast; Greenland?), but are closely allied to the cosmopolitan species, Gnesioceramus anglicus (Woods). At approximately the Albian-Cenomanian boundary, the endemic clade of ‘Inoceramus’ nahwisi appears, now referred to the newly erected Posidonioceramus, resulting in a distinct P. nahwisi biozone. This zone corresponds to the lower part of the ammonite Neogastroplites’ stratigraphic range. Gnesioceramids re-appear in the early Cenomanian. Close to base of the Cenomanian, for the first in the Western Interior, the genus Inoceramus, represented by Inoceramus irenensis Warren and Stelck, 1958, apparently immigrated into the Western Interior Basin.The Western Interior inoceramids do not allow for direct correlation to chronostratigraphic standard subdivision. The Albian-Cenomanian boundary, as earlier recognized on geochronologic correlations and confirmed, to some extent, based on ammonites, may approximately be located close to the appearance level of the genus Posidonioceramus.  相似文献   

Symbiodinium (internal transcribed spacer 2) diversity in the coral host Agaricia lamarcki (Cnidaria: Scleractinia) between shallow and mesophotic reefs in the Northern Caribbean (20–70 m)          下载免费PDF全文

Matthew Q. Lucas  Michael Stat  Matthew C. Smith  Ernesto Weil  Nikolaos V. Schizas 《Marine Ecology》2016,37(5):1079-1087

This study investigated differences in Symbiodinium diversity in the scleractinian coral species Agaricia lamarcki between shallow (20–25 m) and mesophotic (50–70 m) depths in the Northern Caribbean. Corals were sampled in each of four shallow sites (20–25 m; n = 18) and three mesophotic sites (50–70 m; n = 18) from Mona Island (Puerto Rico) and the US Virgin Islands during a mesophotic exploratory cruise and from the La Parguera shelf edge, off Southwestern Puerto Rico. Symbiodinium diversity was assessed using internal transcribed spacer 2 sequences clustered into operational taxonomic units (OTUs). Clustering resulted in eight clade C OTUs and one clade D OTU. Of these, there were three common Symbiodinium OTUs consisting of C3 and D1a.N14 in shallow reefs and C11.N4 in mesophotic reefs. Statistical tests (permutational multivariate analysis of variance and analysis of similarity) showed significant differences between clade C Symbiodinium OTUs in A. lamarcki colonies located at shallow and mesophotic depths, indicating symbiont zonation. Symbiodinium diversity in A. lamarcki from the Northern Caribbean is comparable to previous reports in the Southern Caribbean for this species. This is the first report of the thermal tolerant species Symbiodinium trenchii (D1a) in A. lamarcki.  相似文献   

Alteration of naruo porphyry Cu (Au) deposit in the duolong ore-concentration area,tibet北大核心CSCD     

Gao K.  Duo J.  Tang J.-X.  Zhang Z.  Song J.-L.  Ding S.  Song Y.  Lin B.  Feng J. 《矿物岩石地球化学通报》2016,(6):1226-1237

The Naruo Cu( Au) deposit is a large porphyry deposit in Bangonghu-Nujiang suture, and it is an important part of Duolong ore •concentration area. In this study, alteration and mineralization zoning were constrained by detailed field investigation and indoor petrography observation in order to characterize the alteration and establish alteration-zoning model for exploration. The deposit has typical porphyry hydrothermal alteration system with successively alteration zoning of potassium silicate zone( with later propylitization) to sericite zone( with later propylitization) , propylitic zone, and hornfel zone from inner outward. The mineralization is closely related to potassium silicification and sericitization.  相似文献   

The Distribution of Polychaetes Along Environmental Gradients: An Example from the Or betel I o Lagoon, Italy     

C. Lardicci    M. Abbiati    R. Crema    C. Morri    C. N. Bianchi  A. Castelli 《Marine Ecology》1993,14(1):35-52

  相似文献   

Habitat Selection and Space Partitioning among two Mediterranean Blenniid Species   总被引：4，自引：0，他引：4  

Veronika H.  Koppel 《Marine Ecology》1988,9(4):329-346

Abstract. The utilization of the spatial resources of two syntopic blenniid species - Blennius cunevue and Blennius incognitas - has been investigated in silu and under laboratory conditions. Both species occupy bore holes of the mussel Lithophugu in the sublittoral zone. B. cunevue dominates the more shallow zone (= 0.68 m) and prefers smaller (= 12.76 mm diameter) and horizontal bore holes. B. incognitus inhabits the same depth range as B. cunevue but occupies larger bore holes (= 14.57 mm) in a deeper zone (= 0.86 m). Individuals of B. incognitus do not prefer a special inclination angle. The two blenniid species defend territories with different intraspecific sizes: the mean territory radius of B. cunevue is 6.87 mm, of B. incognitus = 10.95. Mechanisms to reduce competition include different activity rhythm, interspecific social dominance, and differences in territoriality. B. cunevue is the dominant species; its territories arc defended against conspecifics and against B. incognitus.  相似文献