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1.
伟齿蛤化石研究现状与存在问题 总被引：6，自引：0，他引：6
晚三叠世非常繁盛的伟齿蛤类是一种奇特的双壳类软体动物 ,以其个体巨大、壳壁厚实 (骨骼/躯体比率高 )、铰板厚重、铰齿粗壮且强烈突出、铰齿变化大而著称。但以往发现的这类化石主要为内核和印模 ,因此迄今对伟齿蛤类的了解还十分贫乏 ,其属种分类混乱 ,生态与演化关系不清 ,是双壳纲目前研究最薄弱的科之一。文中评述了伟齿蛤类的研究现状和存在的问题 ,并指出中国长江源区新发现的伟齿蛤化石保存完好数量丰富 ,为研究解决这些问题提供了目前世界上最完备的材料。 相似文献
2.
Polygnathus costatus partitus(肋多颚牙形石分亚种)是国际地层委员会(ICS)确定的中泥盆统底部的标准化石,但它与共存的Polygnathus lingui formisbultyncki在形态上难以区分,造成地层划分的困难。经过认真研究,Polygnathuscostatus partitus依据基腔位置可以划分出幼年期和成年期两个发育阶段。Poly-gnathus linguiformis bultyncki依据表面形态可以划分为幼年期、青年期和老年期三个发育阶段;通过两者不同发育阶段的比较研究,笔者提出了三点不同以在鉴定中将两者加以区别,从而提高化石鉴定的精度。 相似文献
3.
西秦岭地球物理场的地质解释 总被引：7，自引：0，他引：7
西秦岭及邻区，由区域重力异常反映的地壳深部构造和剩余重力异常反映的区域地质构造呈明显的立体交叉。以通渭—武都近南北向重力梯级带反映的隐伏深断裂是划分东、西秦岭和祁连、北秦岭构造单元的分界，亦是秦岭复合型造山带向西拓展为祁连、西秦岭和松潘—甘孜各造山带的转折枢纽。西秦岭北缘断裂带在不同地质历史阶段，其边界位置、断裂性质不同，深部产状和浅部产状不同，因此伴随Ａ型俯冲形成大陆碰撞型花岗岩，并出现岩体磁性分带现象。 相似文献
4.
《International Geology Review》2012,54(12):2204-2213
The author equates paleontology and phylogeny and discusses principles and problems of transitions found in the phylogentic approach to taxonomy. opics discussed include: subspecies and species (time needed for new species to become isolated is 500 to 1,000 years); the morphological exclusiveness of genera in the differential diagnoses of species, evolutionary patterns of transition in time, the biogenetic law (“Ontogenesis in compressed form reflects the phylogeny of a long series of ancestors, retaining everything that was especially useful for life, but preserving in it generalized form, without the details characterizing the adult states”); ability of changes in early ontogenetic stages to produce sudden large phylogenetic changes, and monophyletic and polyphyletic evolution. — R. S. Boardman. 相似文献
5.
The intense study of coleopteran inclusions from Spanish(Albian in age) and French(Albian-Santonian in age) Cretaceous ambers,both of Laurasian origin,has revealed that the majority of samples belong to the Polyphaga suborder and,in contrast to the case of the compression fossils,only one family of Archostemata,one of Adephaga,and no Myxophaga suborders are represented.A total of 30 families from Spain and 16 families from France have been identified(with almost twice bioinclusions identified in Spain than in France);13 of these families have their most ancient representatives within these ambers.A similar study had previously only been performed on Lebanese ambers(Barremian in age and Gondwanan in origin),recording 36 coleopteran families.Few lists of taxa were available for Myanmar(Burmese) amber(early Cenomanian in age and Laurasian in origin).Coleopteran families found in Cretaceous ambers share with their modern relatives mainly saproxylic and detritivorous habits in the larval or adult stages,rather than wood-boring behavior.Fifteen of the coleopteran families occur in both the Lebanese and Spanish ambers;while only five are present in both Spanish and French.Considering the paleogeographic proximity and similarity of age of the Spanish and French ambers,the small number of taxa found in common at both areas is surprising.The ancient origin for the Lebanese and Spanish ambers,the paleogeography(including some barriers for terrestrial biota) and the local paleohabitats are factors that may explain the dissimilarity with the French specimens.Wildfires are believed to be a more likely cause of resin production during the Cretaceous than infestation by beetles.Current knowledge of the beetle species found in the Cretaceous ambers is introduced. 相似文献
6.
本文描述了采自新疆准噶尔地区石炭纪的海扇类标本,认为它们具有一种新的韧带组合类型,即韧带区由两个三角形弹体窝和细弱的韧带槽组成,并建立一新科(Binipectinidae)。 相似文献
7.
普弄巴金矿床黄铁矿的标型特征 总被引：1，自引：0，他引：1
笔者对本地区金矿床中黄铁矿的晶体结构形态、物理性质、微量元素及同位素进行了研究，结果表明：黄铁矿晶形呈五角十二面体，八面体－五角十二面体、立方体－五角十二面体聚晶富Ａｕ；黄铁矿的晶胞参数（ａ）、热电系数（α）与砷、金关系密切，基本上成正相关关系；黄铁矿质变热电系数的测定表明本区金矿床为中低温矿床；本区金矿床中的黄铁矿多数为空穴型，据其空间分布特征，认为本区金矿床深部可能有一定勘探远景；同位素研究表 相似文献
8.
Surfaces of phosphorite nodules and pebbles from the “Cambridge Green Sand” (Cenomanian, South England) yielded several discernible types of scratches. These originated before the burial of nodules/pebbles as evidenced by fossil epibiotic oysters cemented to cover the scratches. The individual forms of scratches differ in size and shape; therefore, the set of “scratching instruments” also had to be different. The scratches described differ from scratches generated by glacial processes, namely by the regularity of length and intervals, parallel orientation, existence of recurrent forms and placement along the nodule edges. We interpret the scratches as trace fossils of the ichnogenus Machichnus. Three new species, namely M. normani, M. harlandi and M. jeansi, are erected for them herein. The series of scratches originated probably by teeth on a couple of jaws; the makers possibly scraped bacterial or algal film off the surface of nodules that were covered with the phosphate gel. Both homodont and heterodont animals (probably fish) were involved. 相似文献
9.
Steven G. Morgan Jennifer L. Fisher Skyli T. McAfee John L. Largier Seth H. Miller Megan M. Sheridan Joseph E. Neigel 《Estuaries and Coasts》2014,37(5):1269-1283
The effectiveness of larval behavior in regulating transport between well-mixed, low-inflow estuaries and coastal waters in seasonally arid climates is poorly known. We determined the flux of an assemblage of benthic crustacean larvae relative to physical conditions between a shallow estuary and coastal waters on the upwelling coast of northern California (38°18′N, 123°03′W) from 29 to 31 March 2006. We detected larval behaviors that regulate transport in adjacent coastal waters and other estuaries for only two taxa in the low-inflow estuary, but they were apparent for taxa outside the estuary. Vertical mixing in the shallow estuary may have overwhelmed larvae of some species, or salinity fluctuations may have been too slight to cue tidal vertical migrations. Nevertheless, all larval stages of species that complete development in nearshore coastal waters were present in the estuary, because they remained low in the water column reducing seaward advection or they were readily exchanged between the estuary and open coast by tidal flows. Weak tidal flows and gravitational circulation at the head of the estuary reduced seaward transport during development for species that completed development nearshore, whereas larval release during nocturnal ebb tides enhanced seaward transport for species that develop offshore. Thus, nonselective tidal processes dominated larval transport for most species back and forth between the low-inflow estuary and open coastal waters, whereas in adjacent open coastal waters, larval behavior in the presence of wind-induced shear was more important in regulating migrations between adult and larval habitats along this upwelling coast. 相似文献
10.
纵弯褶皱叠加机制和类型的研究现状 总被引：1，自引：0，他引：1
叠加褶皱的研究是以叠加机制和叠加类型为基础的。从变质岩构造研究中形成的叠加褶皱理论是以剪切褶皱为基础,而沉积岩的纵弯褶皱叠加机制和类型均与之不同。国外有学者分别指出再褶皱时的斜纵弯褶皱机制和早期褶皱枢纽的迁移机制以及四种基本叠加类型。我国有人论述了早期褶皱的枢纽、拐线的迁移是正纵弯再褶皱的一种机制,依此提出了正纵弯叠加褶皱的三种基本类型。本文对这些成果的主要认识和依据予以介绍。 相似文献
11.
晋宁期变质侵入岩是大别山造山带主体组成部分，从地质、地球化学及同位素年龄等方面阐述了其基本特征，源岩属壳幔重熔型钙碱性岩浆组舍，受纬向伸展、经向挤压力控制剪切侵住。受加里东期、印支期、燕山期三期强烈改造，以大型穹状、隆滑韧性剪切带为特征．提出了非深俯冲板块构造演化基本思路。 相似文献
12.
Habitat use by larval fishes was investigated in a tidal creek of the Swartkops estuary, South Africa, during a trial study using light traps. A total of 12 fish families represented by 28 species were recorded during October and November 2000. Fishes caught were predominantly in a postflexion stage of larval development although preflexion larvae and some early juveniles were also recorded. The distribution of larval fishes indicated that fishes were influenced by proximity to either channel or littoral regions of the creek rather than showing specific preferences for eelgrass covered areas. Estuary-dependent marine species were caught in higher numbers along the margins of the estuary. Length frequencies of both estuary-resident and estuary-dependent marine fishes showed that larger individuals were found in the littoral regions suggesting active migration of these fishes to the margins. Catches of straggler marine species were higher in the channel areas and showed no difference in size distribution between littoral and channel sites. Estuary-dependent species may be using marginal areas as a means of avoiding high flow in the channel and as a predator avoidance mechanism. Light traps were found to be a useful sampling device for localized studies on the early life stages of fishes in an estuary. 相似文献
13.
辽宁铁法盆地早白垩世植物群中的真蕨植物新材料及其原位孢子 总被引：4，自引：0，他引：4
铁法植物群产于辽宁北部铁法盆地下白垩统小明安碑组含煤地层中。该植物群由45属79种组成。真蕨是其中最繁盛的类别,计15属29种,占植物群种数的36.7％,并且有较高的分异度,覆盖了9个科别,在我国同期植物群中很有特色。本文在形态对比和原位孢子囊、孢子研究的基础上建立了Coniopteris longpinnate sp.nov.,Dryopterites triangularis sp.nov.,Asplenivm tiefanvm sp.nov.3个新种,还对保存了生殖羽片的其它8种真蕨作了原位孢子分析,大大提高了这些属种的研究程度。 相似文献
14.
腕足类新科Spinochonetidae(fam.nov.)建立在宜昌地区志留系兰多维列统罗惹坪组下段中部(上埃隆阶)的Spinochonetes Rong,Xu et Yang(1974)和Spinolella(gen.nov.)两个属,以及一个属、种未定的分类单元的基础上。新科成员仅有从腹壳喙部伸出一根直的腹喙刺,这与Chonetoidea超科内的Strophochonetidae科以及Chonestrophiidae科众成员的铰合缘刺都是从腹壳铰合缘上伸出来的有着本质差别。另外,本文还对Spinochonetes以及它的属型种S.notata Rong,Xu et Yang(1974)进行重要图解和补充描述。与此同时,对Spinolella(gen.nov),以及S.minuta(gen.et sp.nov.)进行系统描述和对比。据目前所知,新科成员只分布于我国鄂西、黔东北、陕南和川北等地,属于上扬子台地的土族居民。因为Spinochonetidae(fam.nov.)属于腕足类独特的一个类型,演化快,贝体极小,保存精美,因此具有分类学、地层对比,以及恢复古环境等方面的重要意义。 相似文献
15.
A. B. RONOV 《Sedimentology》1968,10(1):25-43
The initial geological facts are considered on which the author bases on of the possible variants of the evolutionary scheme of the stratisphere, ocean and atmosphere composition from the Early Precambrian to the Recent. Some general tendencies and causal relationships in the development of these external shells of the earth are traced. The object of this paper is to trace the evolution of the compositions of the sedimentary shell, the world ocean and the atmosphere from the Early Precambrian to the Recent period. Further, an attempt is made to elucidate some general tendencies in the development of these outer shells of the earth, in the changes of magmatic rock composition and in the history of tectonic movements and to establish causal relationships between them. The solution suggested is one of the possible variants, as the data used and the assumptions that have been made are not uniformly reliable for the different stages of geological history. 相似文献
16.
唐口区煤中微量元素的分布特征 总被引：4，自引：1，他引：3
在大量化验测试资料的基础上,分析了唐口区煤中微量元素在平面上的变化特征和在不同煤中或同一煤层在垂向上的变化规律,并初步研究了微量元素在不同粒度和不同密度煤中的分布特征,探讨了煤中微量元素富集的原因,为今后煤的综合开发和利用提供了参考资料。 相似文献
17.
Simultaneous development of noncylindrical folds and transcurrent fractures has been studied using model techniques. A plasticine model was compressed in one direction and an initial formation of folds was followed by the initiation of conjugate sets of transcurrent fractures. It was recorded that with progressive deformation the length of each fracture and the displacement along it increase steadily and the rate of displacement varies at different stages of deformation. Individual fold geometries vary along their hinge lines and these geometrical variations appear to be due to interference of folds with the transcurrent fractures. These interference effects also change the amount of rotation of fractures. Fold structures are different on either side of the fault plane. A natural example from the Bude area, England, shows similar geometrical features.The method of determining fault displacement by comparing the positions of fold hinge lines on either side of a fault is discussed in the light of the above results. 相似文献
18.
Cleiothyridina obmaxima McChesny的个体发育、生态特征及进化途径 总被引：2，自引：1，他引：1
本文通过对Cleiothyridina obmaxima在同一化石点产出的大量个体的统计研究,讨论了该种个体发育的阶段及其种群动力学特征,并做出了相应的解释。同时根据该种个体形态的特征及其在个体发育不同阶段的变化,结合其所赋存的群落及其围岩特征,讨论了其个体生态学及其环境意义,进而探讨了该种的演化途径。 相似文献
19.
海扇类（pectinoids (s.l)）是一类具浮游异养幼虫类型生态特征的表生双壳类。这种生态特征决定了其大部分组成分子具世界性分布。但是,在侏罗纪原大西洋地区海扇类中仍有不少属/亚属显示出地区性特征,其地理分布主要受纬度气候带控制,即显示出南北差异。这些地区性海扇贝类是认识侏罗纪生物地理分区的重要标志。主要分布于高纬度地区的北方型分子由Buchiidae、Pectinidae和Oxytomidae 3科的一些属/亚属组成,它们于中侏罗世晚期和晚侏罗世常见于格陵兰东部,往南止于英格兰南部,是北方生物区的重要代表。适于热带－亚热带的特提斯型分子分异度较高,组成分子来自Pectinidae,Spondylidae和Entoliidae 3科,主要分布于法国以南的较低纬度地区。但是,在特提斯海扩张时期,如侏罗纪巴通期,随着特提斯生物大区北界的北移,特提斯双壳类可散布至英格兰北部。 相似文献
20.
Crab larval dispersal and, thus, adult population size can be influenced by oceanographic conditions, especially in highly dynamic and variable environments such as high-latitude estuaries. This study's primary goal was to understand larval timing, abundance, and distribution in relation to oceanographic effects between the more estuarine inner and more oceanic outer part of the subarctic estuary of Kachemak Bay (south-central Alaska, USA). Temperature and salinity measurements and plankton tows were taken along the boundary between the two bay parts from 31 March to 28 October 2008 on spring and neap tides. Summer water flow and stratification in Kachemak Bay were chiefly buoyancy driven, and predominant flow patterns were not affected by the large tidal range in the region. Larvae of seven brachyuran species were found over the sampling period, with seasonally different peak abundances. Larval spatial distribution patterns, presence of most larval stages for each species, and their seasonal timing and persistence within the water column suggest that most species are locally transported within or close to Kachemak Bay. The larval assemblage was correlated with seasonal changes in water temperature, and peak abundances of some species coincided with spring tides and/or frontal systems between the in- and outflow regions of the bay. The strong influence of freshwater on the local circulation pattern in the summer indicates that larval transport will likely be strongly affected by future changes in glacial melt and precipitation. 相似文献