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1.
哲杜斯贝是一种以高丰度和低物种分异度为显著特征、在全球广泛独立分布的小嘴贝类。笔者对华南台地相和台间盆地相5个含哲杜斯贝类上泥盆统剖面进行沉积环境和埋藏特征研究,确定华南哲杜斯贝类的原生沉积环境为台地的正常浅水,这与美国和摩洛哥生长在冷泉环境中的哲杜斯贝不同,表明其既可在浅海环境中生长,也可以在冷泉环境中生长,具有较强的生态可塑性。台地相(原地埋藏)的3个哲杜斯贝种群具有以下特征:(1)均呈现出壳体呈层状紧密堆积、集群生长特点,丰度极高,并且有相当数量的个体呈现出由于拥挤生长而导致的壳体生长畸形现象;(2)缺乏其他底栖后生生物,显示了极低的生物多样性;(3)壳体大小—频率分布和生存曲线揭示了3个哲杜斯贝种群都具有非常低的幼年期死亡率特点,同时同一介壳层内哲杜斯贝个体大小均一,表明绝大多数的个体能够达到或接近自然寿命后死亡。上述证据表明,哲杜斯贝具有密集群居生活的习性,其生活在一个独特的、不适合其他后生底栖生物生存的环境。 相似文献
2.
前人对鄂西地区大隆组页岩气资源潜力调查评价较少。本文通过研究区地层剖面测量及钻探等方法,对大隆组储层特征及沉积环境进行了分析。结果表明,大隆组纵向上可分为三段,横向上有由西向东厚度减薄的趋势。大隆组有机质类型主要为腐泥型,热演化处于过成熟阶段,TOC值含量较高且非均质性分布特征明显。大隆组矿物成分以长英质矿物为主,属于低孔-特低孔特低渗储层。微量元素分析显示大隆组下段处于厌氧环境,上段处于富氧环境。TOC变化曲线与V/(V+Ni)和Ni/Co所指示的氧化还原条件具明显相关性,厌氧环境TOC含量高。综合研究表明,西部建始一带为页岩气成藏有利区,大隆组下段为有利的勘探层位。 相似文献
3.
四川盆地上二叠统大隆组富有机质硅质泥岩是页岩气勘探的一套重要目的层系.利用扫描电子显微镜和元素地球化学等方法探究大隆组有机质类型、分布特征及富集因素,对该地区非常规油气勘探具有指导意义.根据扫描电镜图片,上寺剖面大隆组有机质按形态可分为形态有机质、弥散有机质和沥青.三者成因不同,形态有机质是选择性保存的结果,以离散状分布在所有岩性样品中;弥散有机质是大隆组有机碳总量(total organic carbon,TOC)的主体,主要分布在硅质泥岩样品中,硅质灰岩样品中极少,体现了粘土矿物的吸附作用;沥青是可溶有机质运移进入孔、缝系统,经高热演化后形成的块状有机质,主要分布于硅质灰岩和灰岩样品中.该剖面地球化学数据显示缺氧沉积环境有利于有机质保存,但海洋表层生产力才是控制TOC含量变化的主要因素.研究表明,晚二叠世海平面上升导致上寺剖面大隆组表层生产力增加及底层海水缺氧,该组富有机质黑色硅质泥岩段高TOC是沉积环境与矿物吸附共同作用的结果,同时也反映了原生有机质保存情况.更好的理解泥质烃源岩中有机质赋存类型有助于烃源岩评价及非常规油气勘探开发工作. 相似文献
4.
以汾湖镇为研究区,采用GIS和RS方法分析了全镇及典型圩区近15年来河网结构的变化特征。结果表明:等级最低的圩内河道的河网结构变化显著,而村级以上的骨干河网结构基本没有变化,河网结构趋于稳定;不同圩区河网结构变化存在明显的时空差异。快速城镇化过程中,经过及时规划和治理的圩区河网结构得到了一定的改善,反之,河网结构受到了较大破坏;根据河网结构演变特征及原因,快速城镇化圩区河网结构演变的主要原因是对水系的保护、整治和破坏等人类活动的影响,据此识别圩区河网演变的几种主要模式为:主动引导型、被动改造型、修复完善型和保护优先型。 相似文献
5.
T. V. Klets 《Stratigraphy and Geological Correlation》2008,16(5):467-489
Geographic differentiation of conodontophorids between northern and southern latitudes commenced in the Triassic since the early Induan. Cosmopolitan long-lived genera of predominantly smooth morphotypes without sculpturing were characteristic of high-latitude basins of the Panboreal Superrealm. Since the early Olenekian until the Carnian inclusive, this superrealm consisted of the Siberian Realm that extended over Northeast Asia and the Canada-Svalbard Realm that included the Svalbard Archipelago and northern regions of Canada. Throughout the Triassic period, conodontophorids characteristic of the Tethys-Panthalassa Superrealm spanning the Tethys and low-latitude zones of the Pacific were highly endemic, very diverse in taxonomic aspect, having well-developed sculpturing and tempos of morphological transformations. Distinctions between the Early-Middle Triassic conodontophorids from northern and southern zones were not as great as afterward, and their impoverished assemblages from southern Tethyan basins were close in some respects to the Boreal ones. Their habitat basins of that time can be grouped into the Mediterranean-Pacific and India-Pakistan realms. Hence, the extent of geographic differentiation of conodontophorids was not constant and gradually grew, as their taxonomic diversity was reducing in northern basins but relatively increasing in southern ones. The Panboreal e Tethys-Panthalassa superrealms of conodontophorids, which are most clearly recognizable, are close to first-rank paleobiochores (superrealms) established earlier for ammonoids and bivalve mollusks. Main factor that controlled geographic differentiation of Triassic conodontophorids was climatic zoning. Initially lower diversity of southern Tethyan assemblages points probably to relatively cooler water regime in the peri-Gondwanan part of the Tethys. The established patterns in geographic distribution of conodontophorids characterize most likely the real trend of their differentiation and evolution, i.e., the distribution area contraction prior to complete extinction at the end of the Triassic 相似文献
6.
7.
W. E. Schaaf D. S. Peters L. Coston-Clements D. S. Vaughan C. W. Krouse 《Estuaries and Coasts》1993,16(4):697-702
Pollution effects on fish populations were estimated with a simulation model, using Leslie matrices. Results from changing only first-year survival rate (So) have already been published (Schaaf et al. 1987). This paper explores the effects of perturbing both So and the adult survival rate (Si) for 12 spatial-temporal stocks. Most stocks examined are more sensitive to permanent change in Si than to changes in So. The relative importance of these two rates in determining the population growth rate (λ) depends upon the age distribution of the expected lifetime egg production of age i females (Vi). In turn, the vector Vi, as measured by its mean and standard deviation, is shown to vary among geographic or temporal stocks of a single species. Hence, we quantify the impact on population size of destroying a fixed percentage of habitat, relative to where and when it occurs (i.e., relative impact on Si and So). For example, destroying 1% of the Atlantic menhaden habitat would reduce λ by 0.8% and the population by 8.0% in 10 yr, if the impact affected only adults (e.g., offshore in winter). If the 1% habitat destruction all occurred in the estuaries, affecting juveniles as well, λ would be reduced by almost 5%, and in 10 yr drive the population down to 58% of its former equilibrium. We show that knowledge of the mean and variance of the age distribution of Vi permits prediction of relative sensitivity among species to pollution. Within species, this knowledge of Vi permits comparison of the effects of impacting different life stages and at different times and places. 相似文献
8.
南京汤山直立人头骨的复原和更新世中期直立人的地理变异 总被引：7，自引：0，他引：7
现代中国人体质特征可分为南北两大地区类型。这两大类群的形成可追溯到全新世的新石器时代 ,甚至更新世晚期。 1993年在南京汤山发现一具更新世中期的带有面骨的直立人头骨。为追索中国人群南北两大类型的形成历史 ,对汤山头骨作了重新复原 ,对汤山头骨与周口店头骨作了形态比较。结果表明 ,汤山头骨与周口店头骨相同的特征几乎全是直立人共有的形态特征。汤山头骨不同于周口店头骨的诸特征 ,如浅的眶上圆枕上沟、不呈发髻状的枕骨水平轮廓、较短宽的面部、特宽的鼻型和接近低眶的眶型等 ,提示中国人群南北两大类型的形态差别可能早在更新世中期汤山直立人生存时已显出端倪 相似文献
9.
Ramona L. Walls 《Estuaries and Coasts》2010,33(4):902-918
Japanese knotweed s.l. (Fallopia spp.) is a highly invasive clonal plant, best known from roadside and riparian habitats. Its expansion into beaches on Long
Island, NY, USA, represents a major habitat shift. I surveyed populations from beaches and wetlands and conducted a common
garden experiment to test for variation in drought tolerance and phenotype among populations and habitats. All populations
were composed mostly of first- and later-generation hybrids. I found significant variation among populations in growth, lamina
size, specific leaf area (SLA), and biomass allocation, in both the field and the common garden. Lamina size, growth, and
root-to-shoot responded plastically to drought treatment. Wetland populations tolerated drought as well as beach populations.
Differentiation in SLA between habitats suggests that some selection for beach genotypes may have occurred. It appears that
both hybridization and phenotypic plasticity are contributing to the expansion of Fallopia spp. into novel habitat. 相似文献
10.
贵州安顺新民二叠系-三叠系界线剖面磁化率测试结果表明,该剖面二叠系磁化率整体偏低（平均6.4×10-8 m3/kg）,界线之上磁化率快速增加并相对稳定在1.3×10-7 m3/kg附近,与华南其他二叠系-三叠系剖面磁化率变化趋势相同;与陆源孢粉丰度、TiO2曲线的同步变化趋势表明,新民剖面磁化率主要来自陆源物质。结合磁化率、地球化学指标的变化特征,将源区P-T之交古气候划分为3个阶段:阶段Ⅰ（1 2层中部）为化学风化作用较强的温暖潮湿的气候条件;阶段Ⅱ（2层上部 P-T界线）整体处于较强化学风化作用条件下温热潮湿的气候环境,变化较为频繁,表现为温润/湿热交替;阶段Ⅲ（P-T界线之上）物理风化加强,化学风化明显减弱,经短暂“过渡段”,气候总体转变为干热的条件。 相似文献
11.
以湘中坳陷涟源凹陷上二叠统龙潭组和大隆组海陆过渡相泥页岩为研究对象,重点选取12块典型泥页岩钻井岩心样品开展有机碳含量、岩石热解、X射线衍射、密度法孔隙度、高压压汞、二氧化碳和氮气吸附等测试分析,利用氩离子抛光-场发射扫描电镜（FE-SEM）观察了泥页岩孔隙特征,通过定性描述和定量测定相结合的方法研究了海陆过渡相泥页岩纳-微米级孔隙结构特征及孔隙发育影响因素.研究结果表明:龙潭组和大隆组泥页岩有机碳含量均较高,热演化程度处在凝析油和湿气生成阶段早期,对应Ro为1.22%~1.43%;泥页岩孔隙类型主要为粒间孔、粒内孔、有机孔和微纳米缝.龙潭组与大隆组样品在孔隙形态、孔隙大小和影响因素上均有差异:龙潭组样品氮气吸附滞回环开口宽,有机孔形态多为圆形和椭圆形,孔径较大;大隆组样品氮气吸附滞回环开口窄,有机孔形态多为不规则状,孔径较小;龙潭组泥岩和大隆组泥页岩样品有机碳含量与黏土矿物含量呈正相关关系,2套样品的微孔孔隙积体与有机碳和黏土矿物含量均呈正相关性;龙潭组样品介孔+宏孔的孔隙体积与有机碳和黏土矿物含量呈正相关性,与石英+长石含量呈负相关性;大隆组样品中的碳酸盐矿物对其孔隙性有明显影响,大隆组样品介孔+宏孔孔隙体积与有机碳、黏土矿物和石英+长石含量相关性不明显. 相似文献
12.
喀斯特区常见的出露石牙对水分和养分的再分配影响了植物物种的分布与适应特征。为了解出露石牙对中国特有珍稀濒危植物四药门花(Loropetalum subcordatum)的分布与叶表型性状的影响,用样带法对贵州茂兰国家自然保护区内四药门花个体根部和周边最近石牙与土表连接处的距离进行调查、并选择距石牙不同距离的乔木植株叶片进行表型特征测量。根据四药门花植株的分布特征,将其与石牙距离分为三组（0 cm、0.1~10 cm、≥10 cm）进行分析。结果表明:①本次共调查到四药门花个体515株,其中胸径≥1 cm的388株（75.3%）。胸径最大值为17.5 cm,该植株距石牙7 cm。胸径≥1 cm植株距石牙0 cm、0.1~10 cm、≥10 cm植株数分别为89株平均胸径3.44±2.26 cm、21株平均胸径4.38±4.55 cm和278株平均胸径3.93±2.75 cm;幼苗和幼树距离石牙0 cm有19株、0.1~10 cm有62株、≥10 cm有46株。②茂兰四药门花种群叶长106.60±19.28 mm、叶宽47.53±10.10 mm、叶宽/长0.45±0.08、叶厚0.32±0.05 mm、叶柄长12.82±3.35 mm、叶柄径1.43±0.35 mm。距石牙0 cm组、0.1~10 cm组和≥10 cm组四药门花的叶长、叶宽、叶柄径差异不显著（P>0.05）,叶厚、叶宽/叶长、叶柄长差异极显著（P<0.01）。石牙出露深刻影响了四药门花的分布和植物的适应特征。 相似文献
13.
《Precambrian Research》2006,144(1-2):52-68
Acritarchs are a group of organic-walled vesicular microfossils interpreted as protists, and are among the first eukaryotes preserved in the fossil record. Taxonomic inconsistencies amongst acritarch workers have made it difficult to address the evolutionary history of this group through more traditional methods (i.e., biodiversity through species counts). We have constructed an empirical morphospace to examine the first 1.3 billion years of acritarch evolution. We show that protist morphologic evolution is broadly correlated with major environmental and biologic revolutions in Earth history such as late Neoproterozoic global glaciations, the first appearance of the Ediacaran metazoans and the Cambrian explosion. Our results also show that protist morphologic expansion precedes their taxonomic diversification; this pattern, similar to that seen in Phanerozoic animal clades, suggests that early morphospace saturation and convergence are common occurrences in eukaryote macroevolution. In addition, our data do not support a monotonic increase in maximum diameter of acritarch vesicles through the Proterozoic; instead, maximum vesicle diameter appears to fluctuate in the Proterozoic before decreasing significantly in the early Cambrian. 相似文献
14.
S. Mahmood A. Ahmed A. Hussain M. Athar 《International Journal of Environmental Science and Technology》2005,2(3):193-199
Variability among populations was analyzed in five provenances of Acacia nilotica from spatially variable habitats. Populations of A. nilotica developed in response to their habitat conditions. The level of variability was significantly high among the populations. Phenotypic variability was extremely high for leaf and stipular spine characteristics. The nature of morphological variability for vegetative traits appeared environmentally controlled. The differentiation of leaf and stipular spine expression seems to have an adaptive significance for the species in terms of water economy. Although, seed and pod characteristics are genetically controlled showing a lower proportion of variability but these traits supported r and k-selection that may allow the species to survive under a wide array of contrasting habitats. The study suggested that populations of A. nilotica are differentiated in relation to the heterogeneity of environment. These populations became adapted to their habitat through the variability of morphological expressions. The morphologically differentiated populations of the species had allowed them to maintain themselves in a wide array of environmental situations enabling A. nilotica to occupy ample ecological ranges. 相似文献
15.
In its evolution through geologic time, the oceanic plankton has reflected many changes in the physical environment while both causing and being affected by evolutionary change in the associated biota. Temporal variations in the vertical and latitudinal habitat partitioning also affected geochemical balances in the oceans and accumulation rates of biogenic sediments, and perhaps the atmospheric oxygen pressure. Advantages of the oceanic plankton habitat that led to its occupation by a varied sequence of organisms include its extensive geographic area, the possibility for rapid dispersal by currents, the availability of resources (ranging from light, carbon dioxide, and dissolved nutrients for the autotrophic organisms to the various lower trophic levels required by the heterotrophs), and the better oxygenation of the upper water layers.Convergent morphology of the plankton represents adaptations for suspension in the water column, for movement within this water mass to increase nutrient uptake, and for protection against grazing or predation. Necessary attributes for cosmopolitan species include eurythermy and euryhalinity. The patchiness of plankton diversity results from small-scale variations in water masses, the low level of interorganism contact or competition, and the possibility of rapid exploitation of favorable conditions by species present in the local area.Parallel evolution, radiation, and extinction of the various components of the oceanic plankton are similar in pattern to an ecologic succession — early evolution and conditions following major periods of extinction being homologous with the physically controlled or immature modern ecosystem associated with high stress levels and characterized by high net but low gross productivity, low diversity but great intraspecific variability, and small biomass. Evolutionary radiation is associated with more stable physical conditions and, like the seral progression, of an ecosystem, results in high diversity but less intraspecific variability. Increased biological interaction leads to higher gross but lower net productivity, hence more efficient energy and resource utilization. The drop in gross oceanic productivity at times of major extinction is associated with low diversity and decreased rate of accumulation of biogenic ooze, hence the apparent worldwide disconformities, as at the Cretaceous-Tertiary boundary, even in the deep sea. 相似文献
16.
Robert J. Livingston 《Estuaries and Coasts》1984,7(4):377-390
Continuous, long-term studies of coastal grassbed assemblages in the N.E. Gulf of Mexico indicate complex relationships between physical controlling factors and biological response. Such seagrass systems are physically unstable over short periods. Seasonal ranges of temperature, salinity, and natural water quality conditions are considerable with periodic, recurrent “catastrophic” events such as floods and cold winters. These factors control the distribution and productivity of the seagrasses and algae which constitute the habitat and organic substrate for diverse assemblages of organisms. In addition, the benthic plants mediate predator-prey relationships and competitive interactions. Despite the physical instability, timed sequences of distinct ontogenetic feeding populations are generally stable from year to year as are other population and community characteristics. Thus, physical processes determine overall habitat conditions and productivity cycles whereas biological processes such as predation and competition define specific community relationships. However, seemingly minor changes in the physical environment due to anthropogenous activities can lead to major reorganization of the biological system; the observed biological stability of the seagrass beds can be ephemeral if important habitat features are altered in a way that exceeds the adaptive response of the system. Concepts are discussed which relate observed sequences of ontogenetic feeding units to food web patterns and geographic differences of population-niche relationships from one estuary to another. 相似文献
17.
A study was conducted to define winter distribution patterns of blue crabs,Callinectes sapidus, in the lower Chesapeake Bay and to relate these patterns to environmental variation. During February 1986 a stratified random survey was conducted to examine the distribution of blue crabs with respect to three major habitat types: 1) high energy, wave- and tide-dominated, spits and shoals; 2) moderate energy, tide-dominated basins; and 3) variable energy, tide-dominated or quiescent channels (natural or cut). Each major habitat type was further stratified on the basis of location (to account for possible salinity effects), resulting in a total of 17 habitat-stratum combinations. Blue crabs exhibited significant differences in abundance among habitats. Crabs were most abundant in the basin habitat and least abundant in the shoal and spit habitat. A posteriori evaluations of abundance patterns in relation to sediment type and depth showed that crabs were significantly more abundant where sediments contained between 41 and 60% sand and at depths exceeding 9 m. The sampled population of blue crabs was dominated by mature females. There were no significant differences in crab sex ratios between habitats, but significant differences between two fixed sites sampled through the winter showed that there were proportionately more male crabs at the western site than there were at the eastern site. The observed patterns indicate that some differential habitat utilization occurs and that overwintering female crabs are found preferentially in areas characterized by moderate energy regimes and fine, but sandy sediments. 相似文献
18.
应用地质统计学方法研究剖面沉积物化学组分的含量变化规律和相互关系,以了解剖面沉积物及其化学组分的影响因素和剖面地层的古环境演化。从R型和Q型因子分析结果得出,剖面沉积物及其化学组分含量主要受陆源物质影响,其次受火山源物质的影响,成岩作用及生物源物质也发挥了一定的作用。剖面的古环境演化以陆源物质、火山源物质和生物源物质混合沉积为主,其间至少经历了7次火山喷发。短期频繁的火山喷发及大量的火山喷发物可能严重影响该时期剖面位置的爬行动物及其他生物的生活环境,这可能是它们在这段时间大量死亡的重要原因之一。 相似文献
19.
Although the elderly are commonly thought to be disproportionately vulnerable to natural hazards, the elderly populations of coastal communities are continuing to grow. Because there is little to no empirical hazards work specifically addressing the vulnerable elderly in coastal communities, this paper uses Sarasota County, Florida, as a case study to analyze how vulnerable the elderly are to hurricane hazards and whether all elderly people are equally vulnerable. To explore the spatial variations in degree and composition of vulnerability among this population, the analysis maps physical exposure to hurricane storm-surge inundation and precipitation-induced flooding and creates social vulnerability indices by applying principal components analysis to census block group data in a geographic information system. The results show that elderly inhabitants of barrier islands face a considerable physical threat from hurricane-induced storm surge and flooding but are less socially vulnerable because of their wealth; the elderly living inland are far less physically vulnerable but are poorer and consequently demonstrate high socioeconomic sensitivity and limited adaptive capacity to these hurricane hazards. The paper concludes that the elderly are not equally vulnerable: there are many different types of elderly living in many different locations, and their vulnerability varies by type and over space. Effective vulnerability reduction measures should account for these differences between the elderly populations. 相似文献
20.
The exploration of the spatial association between Medicare physician spending and population densities and sizes could possibly facilitate the investigation of the causal mechanisms beneath the variation in medical care. We acquired the U.S. Medicare physician expenditures and regional demographic and geographic data in 2006 from the Dartmouth Atlas of Health Care. Six geographic units—states, counties, Hospital Referral Regions, Hospital Service Areas, Metropolitan Statistical Areas, and state non-Metropolitan Statistical Areas—were used as units of study. Pearson correlation analysis, multivariable regression, and partial correlation analysis were employed. Among six geographic units, Pearson correlation coefficients between Medicare physician expenditures and logarithmic population densities ranged from 0.42 to 0.63 (p < 0.05 for all), and between the expenditures and logarithmic population sizes from 0.31 to 0.65 (p < 0.05 for all). When population health, differential demand, market structure, and data reporting bias were controlled, population densities and sizes were positively associated with Medicare physician expenditures in most models. Population densities and sizes could explain considerable amounts of regional variation in Medicare physician spending. We concluded that Medicare physician spending was contingent on population densities and sizes. Because population densities and sizes are produced by more fundamental qualities such as natural environments and resources and thus are not easily manipulated, they are suggestive in health policy studies. Further research might investigate population distribution associated properties such as geographic distribution of health care resources, spatial dynamics of medical technology distribution, and cultural and psychological factors. 相似文献