Recent environmental changes inferred from the sediments of small lakes in Yellowstone's northern range (Engstromet al., 1991)

Sedimentation rate data of Engstromet al. (1991) were analyzed in relation to the elevation of the eight ponds studied. The ... asynchroneity of the stratigraphic changes among the lakes ... that they noted was transformed into a pattern of time-transgressive change of sedimentation rate with elevation. Sediment units representing increasing (and decreasing) sedimentation rate and accelerating (and decelerating) sediment accumulation were correlated from pond to pond, suggesting that the sediment-producing condition somehow moved upslope over time at a rate of 3.4 to >5 m yr^–1. Climatic data appear not to explain this monotonic pattern, but dendrochronological data and elk population numbers suggest that ungulate foraging patterns might. Engstromet al. (1991) concluded that ...the lake-sediment records in the northern range do not convincingly show systematic direct or indirect effects of ungulate grazing during the history of the Park. Reinterpretation of these sediment data suggests that detailed reanalysis might lead to a different conclusion.     

Review of the use of Péclet numbers to determine the relative importance of advection and diffusion in low permeability environments

In low permeability environments, transport by advection is often neglected based on a Péclet number criterion. Such a criterion usually states that if the Péclet number (Pe) is much smaller than 1, diffusion dominates over advection and transport may be modeled considering diffusion only. Unfortunately, up to 10 different Péclet number definitions exist and for a particular case these different definitions lead to very diverse Péclet number values, differing several orders of magnitude from each other. In this paper, the different Péclet number definitions are therefore evaluated on their ability to determine the relative importance of transport by advection and by diffusion in low permeability environments. This is done by comparing the results of the analytical solution for pure diffusion with the analytical solution for diffusion, advection and dispersion for a large number of different input parameter values. The relation between the different Péclet numbers and the difference between the calculated concentration considering diffusion only and the calculated concentration considering both diffusion and advection is studied. These calculations show that some Péclet number definitions are not well suited to decide whether advection may be neglected in low permeability media.

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Resumen Frecuentemente se descuida el transporte por avección en ambientes de baja permeabilidad sobre la base del criterio del número de Péclet. Dicho criterio usualmente sostiene que si el número de Péclet (Pe) es mucho menor a 1, la difusión domina sobre la avección y es posible modelar el transporte considerando la difusión únicamente. Desafortunadamente existen 10 definiciones diferentes del número de Péclet y para un caso en particular estas diferentes definiciones conducen a valores de número de Péclet muy diversos los cuales difieren entre sí en varias magnitudes. Por lo tanto, en este artículo se evalúan las diferentes definiciones en base a su habilidad para determinar la importancia relativa del transporte por avección y difusión en ambientes de baja permeabilidad. Esto se lleva a cabo mediante la comparación de los resultados de la solución analítica para difusión pura con los de la solución analítica por difusión, avección y dispersión para un número amplio de diferentes valores como parámetro. Se ha estudiado la relación entre los diferentes números de Péclet y las diferencias entre la concentración calculada considerando difusión únicamente y considerando tanto difusión como avección. Estos cálculos muestran que algunas de las definiciones de los números de Péclet no son muy apropiadas par decidir si se puede descuidar la avección en medios de baja permeabilidad.

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Résumé Dans les milieux à faible perméabilité, le transport par advection est souvent négligeable lorsquon se base sur le critère du nombre de Péclet. Un tel critère suggère habituellement que pour un nombre de Péclet beaucoup plus petit que 1, la diffusion domine sur ladvection et que le transport peut être modélisé par diffusion seulement. Malheureusement, il existe jusquà environ dix définitions du nombre de Péclet et pour un cas spécifique, ces différentes définitions mènent à des valeurs du nombre de Péclet très différentes, et qui varient entre elles de plusieurs ordres de grandeur. Dans cet article, les différentes définitions du nombre de Péclet sont évaluées en fonction de leur habileté à déterminer limportance relative du transport par advection et par diffusion dans les milieux à faible perméabilité. Ceci est fait en comparant les résultats de la solution analytique pour la diffusion pure à la solution analytique pour la diffusion, ladvection et la dispersion, et ce, pour un grand nombre de valeurs différentes comme paramètre dentrée. La relation entre les différents nombres de Péclet et la différence entre la concentration calculée en considérant la diffusion seulement et la concentration calculée considérant simultanément la diffusion et ladvection est étudiée. Ces calculs prouvent que certaines définitions de nombre de Péclet ne sont pas appropriées afin de décider si ladvection peut être négligée dans les milieux à faible perméabilité.

     

辽西三十家子一带张家口组的发现及意义

利用“八五”期间开展的１∶５万区域地质调查获得的新资料,确认了辽西三十家子盆地张家口组的存在,就其岩相类型、岩石组合特征、时代归属、与上下地层之间的接触关系等问题进行了论述。并探讨了张家口组的建立对冀北辽西中生代岩石地层单位划分与对比的地质意义。     

变质岩区构造地层单位划分及鉴别标志探讨

文章提出了构造地层单位中“岩群 -岩组 -岩段”和“片麻岩套 -片麻岩”实质上就是正常的“群 -组 -段”或“超单元 -单元”与杂岩之间的过渡类型。以此认识为基础 ,根据变质岩系遭受改造和再造作用的主因、方式、强烈程度以及原岩类型等的不同 ,把构造地层单位划分为两大套 4种基本类型 ,并对其鉴别标志、等级体系划分等予以总结和探讨。     

福建省地层多重划分,对比研究（续）

福建省地层多重划分、对比研究（续）李兼海，王国平，郑铁藩，梁诗经（福建省区域地质调查队，三明，３６５００１）３晚三叠世一新第三纪印支运动后，福建地壳发生了重大变革，全境由海转变成陆地。晚三叠世一中佛罗世，除闽西南局部地区有海湾泻湖相沉积外，皆为河流一...     

Mesozoic evolution of the Tisza Mega-unit

The south-eastern part of the basement of the Pannonian Basin is made up of Variscan crystalline complexes and early Mesozoic formations showing striking affinity with the corresponding formations in the southern margin of the European Plate. This large composite structural unit, which is actually an exotic terrane of European Plate origin, has been named the Tisza Mega-unit. Based upon relevant data of the pre-Tertiary basement of southern Hungary the reconstruction of the position of the Tisza Terrane in the early Alpine evolutionary stages, the process of its separation and break-off from the European Plate, and results of its Eo-Alpine deformations are summarised in the present paper. In the Variscan and early Alpine evolutionary stages the area of the later Tisza Mega-unit was located at the margin of the European Plate. During Variscan orogeny terrane accretion led to intensive deformation and metamorphism in this belt. This was followed by transpressional tectonics and the development of molasse basins in the late and post-Variscan stages, and passive margin evolution after the Neotethys opening in the Middle Triassic. The separation of the Tisza Mega-unit began with incipient continental rifting along the axis of the later Ligurian–Penninic–Vahic oceanic branch in the Late Triassic. The end of terrigenous material deposition in the most external zones, and a coeval change in fossil assemblage, point to the separation of the Tisza Block from the European Plate in the Early Bathonian. Significant rotation of the Tisza Mega-unit and coeval paroxysm of alkaline rift-type basalt volcanism took place in the Early Cretaceous. In the mid-Cretaceous, due to the northward motion of the Adria Block and the related closure of the westernmost Neotethys basin, the extensional regime changed to a compressional one, leading to onset of the nappe stacking and low-grade regional metamorphism within the Tisza microplate. In the foreland of the nappe systems flexural basins came into existence that are characterised by flysch-type sedimentation. In the Early Tertiary the north-eastward motion of the Alcapa and Tisza + Dacia Blocks led to the formation of the present-day heterogeneous basement of the Pannonian Basin.     

Deciphering the geologic memory of a Permian conglomerate of the Southern Alps by pebble <Emphasis Type="Italic">P</Emphasis>–<Emphasis Type="Italic">T</Emphasis> estimates

The volcano–clastic sequence of Trompia Valley, which caps the Tre Valli Bresciane Variscan basement (TVB), comprises the Dosso dei Galli Conglomerate (DGC), the oldest deposit containing up to metre-sized metamorphic pebbles. This Lower Permian formation of the Trompia Basin was fed by the erosion products of the Variscan chain. We used microstructural and mineral chemical data on metamorphic pebbles of the DGC to infer a quantitative tectono-thermal evolution of the eroded pre-Permian basement and to compare them with those of TVB and the surrounding Southalpine basement units (tectono-metamorphic units = TMUs). Metapelitic and metaintrusive pebbles record a polyphase metamorphism with two metamorphic re-equilibrations: the first under epidote amphibolite facies (M1, ) and the second under greenschist facies (M2) conditions. Rock types and metamorphic data largely match those of TVB basement unit. The structural and metamorphic records in the pebbles are pre-Permian, and the conglomerate matrix is non-metamorphic. The DGC deposition age (283 ± 1–280.5 ± 2 Ma) constrains the minimal exhumation age of its basement source. The lack of staurolite bearing assemblages in metamorphic pebbles suggests that the DGC basement source was already exhumed to shallow structural levels (greenschist facies conditions) before the thermal equilibration consequent upon continental crust thickening induced by the Variscan collision.     

伊宁地块构造单元划分——来自火山岩浆作用的证据

伊宁地块不是一个之前一贯认为的"均匀地块"或"均一地块",而是以乌孙山-塔勒得近东西向区域性大断裂为界的南、北两大次级构造带（"弧-盆"体系）叠加拼贴增生而成,火山岩浆作用为这一新的构造单元划分与建立提供了佐证。南构造带由喀拉峻岛弧带和其北的阿腾套弧后盆地构成,主要发育于晚泥盆世-早石炭世早期,火山岩同位素年龄峰值为355~350Ma,17个年龄平均值为351Ma;北构造带由北而南可再细分出清水河-苏布台弧后盆地→阿吾拉勒叠加岛弧带→特克斯-新源弧前盆地,主要发育于早石炭世中-晚期,同位素年龄峰值集中于345~329Ma,18个火山岩年龄平均值为340Ma。这两个"弧-盆"体系以大哈拉军山组钙碱性火山岩为主体,共生早石炭世海相阿克沙克组弧前及弧后沉积岩组合。大哈拉军山组火山岩主体以岛弧火山岩为主,见有富Nb玄武岩、高镁安山岩等,共生埃达克岩和高分异Ⅰ型花岗岩等小岩体;在弧后还见有碱性火山岩、碱性球泡流纹岩,共生双峰式火山岩。不仅大哈拉军山组火山岩在各构造相中显著有别,而且共生的阿克沙克组在各构造相中差异极为显著。两大次级构造带具有独立的基底建造史,差异显著的盆地沉积史,独特的火山岩浆史和构造演化史。早晚石炭世之间的鄯善运动使南、北两个次级构造带叠加拼贴,构成统一的伊宁地块,晚石炭世进入统一的陆内构造发展演化阶段,发育以伊什基里克组碱性双峰式火山岩为代表的裂谷火山岩浆建造。     

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)

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.