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Considerable Distances (considerable + distance)
Selected AbstractsTHE PALEOCENE SANDY SIRI FAIRWAY: AN EFFICIENT "PIPELINE" DRAINING THE PROLIFIC CENTRAL GRABEN?JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2006S.E. Ohm A new petroleum charge model is presented for the sand-dominated Paleocene channel system known as the Siri Fairway in the Central Graben of the North Sea. The Siri Fairway is located in the platform area along the Danish - Norwegian border and extends from the Norwegian palaeo shelf into the Tail-End Graben and Søgne Basin. The nearest known expelling source rocks are located in the Central Graben. The discovery of the Siri oilfield and later the Cecilie and the Nini fields proves that petroleum has migrated through these Paleocene sandstones for up to 70 km, which is a considerable distance in the North Sea. If the Siri Fairway has acted as a "pipeline" for petroleum migrating from the Graben to the platform area, the chemical composition of the hydrocarbons discovered in the Graben and within the Fairway itself should be similar in terms of maturity and organic facies signature. This study shows this not to be the case. The Graben oils have a mature signature, whereas the oils from the Siri field have an early mature signature and are mixed with biogenic gas generated in situ. The biogenic gas "signature", which was inherited from gas which accumulated in the trap before the arrival of the oil charge, should have disappeared if petroleum had continuously been introduced to the Fairway. It therefore appears that hydrocarbon charging to the Fairway ceased for some reason before the source rocks in the Graben entered the main oil window; the Siri Fairway therefore represents an aborted migration route, and limited charging of the Paleocene sandstone deposits in the platform has occurred. The chemical composition of the oils from the Siri field indicates that the Fairway was charged from two different basins with different subsidence histories. The Siri-2 trap is thus interpreted to have been filled with the same oil as that found in Siri-1 and Siri-3, but this oil was later partly displaced by oil generated in a shallower sub-basin. The sandstones in the Siri Fairway were deposited as turbidites and/or gravity slides in the Late Paleocene, and consist of stacked interfingering sandstone lobes which are encased to varying degrees in fine-grained sediments. Although long distance migration through the sandstones has been proved to occur, connectivity between individual sandlobes may be problematic. The number of dry wells drilled in the Fairway and the early-mature character of the analysed oils, together with the general absence of more mature later petroleum, indicate that migration routes in this region are limited and difficult to predict. [source] THE STRUCTURE AND NANOMECHANICAL PROPERTIES OF THE ADHESIVE MUCILAGE THAT MEDIATES DIATOM-SUBSTRATUM ADHESION AND MOTILITY,JOURNAL OF PHYCOLOGY, Issue 6 2003Michael J. Higgins We investigated the adhesive mucilage and mechanism of cell-substratum adhesion of two benthic raphid diatoms, the marine species Craspedostauros australis E. J. Cox and the freshwater species Pinnularia viridis (Nitzsch) Ehrenberg. SEM images of P. viridis and C. australis cells revealed the presence of multistranded tethers that appear to arise along the raphe openings and extend for a considerable distance from the cell before forming a "holdfast-like" attachment with the substratum. We propose that the tethers result from the elongation/stretching of composite adhesive mucilage strands secreted from raphes during the onset of cell adhesion and reorientation. Atomic force microscopy (AFM) force measurements reveal that the adhesive strands originating from the nondriving raphe of live C. australis and P. viridis are highly extensible and accumulate to form tethers. During force measurements tethers can be chemically stained and are seen to extend between the cantilever tip and a cell during elongation and relaxation. In most cases, AFM force measurements recorded an interaction with a number of adhesive strands that are secreted from the raphe. The force curves of C. australis and P. viridis revealed a sawtooth pattern, suggesting the successive unbinding of modular domains when the adhesive strands were placed under stress. In addition, we applied the "fly-fishing" technique that allowed the cantilever, suspended a distance above the cell, to interact with single adhesive strands protruding from the raphe. These force curves revealed sawtooth patterns, although the binding forces recorded were in the range for single molecule interactions. [source] The Twannberg (Switzerland) IIG iron meteorites: Mineralogy, chemistry, and CRE agesMETEORITICS & PLANETARY SCIENCE, Issue 2 2009Beda A. HOFMANN Five additional masses (12 to 2488 g) were recovered between 2000 and 2007 in the area. The different masses show identical mineralogy consisting of kamacite single crystals with inclusions of three types of schreibersite crystals: cm-sized skeletal (10.5% Ni), lamellar (17.2% Ni), and 1,3 × 10 ,m-sized microprismatic (23.9% Ni). Masses I and II were compared in detail and have virtually identical microstructure, hardness, chemical composition, cosmic-ray exposure (CRE) ages, and 10Be and 26Al activities. Bulk concentrations of 5.2% Ni and 2.0% P were calculated. The preatmospheric mass is estimated to have been at least 11,000 kg. The average CRE age for the different Twannberg samples is 230 ± 50 Ma. Detrital terrestrial mineral grains in the oxide rinds of the three larger masses indicate that they oxidized while they were incorporated in a glacial till deposited by the Rhône glacier during the last glaciation (Würm). The find location of mass I is located at the limit of glaciation where the meteorite may have deposited after transport by the glacier over considerable distance. All evidence indicates pairing of the six masses, which may be part of a larger shower as is indicated by the large inferred pre-atmospheric mass. [source] Reproductive ecology of the freshwater red alga Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in three tropical streamsPHYCOLOGICAL RESEARCH, Issue 3 2005Orlando Necchi Junior SUMMARY Batrachospermum delicatulum specimens from three stream segments were analyzed from a tropical region in south- eastern Brazil (20°18,, 20°49,S, 49°13,, 49°46,W). Physical and chemical parameters and the spatial placement of thalli were investigated along with the reproductive characteristics of the gametophytic phase. Sequence data of the cox 2- 3 spacer region was also utilized to evaluate genetic variation in individuals within and among stream segments. Gametophyte occurred under relatively diverse environmental conditions, whereas thalli abundance was weakly or not correlated to environmental variables within the stream segments. All specimens examined were dioecious. The ratio of male/female plants was relatively low (0.5 to 1.3) and male plants tended to occur as clumps (two or three plants together). High reproductive success was observed, as indicated by the occurrence of 100% fertilized (carposporophytic) female plants. This is similar to previous reports for this and other dioecious species, which is remarkable considering the relatively low proportion of male/female plants. Results support the two hypotheses to explain the high reproductive success in dioecious species. The occurrence of male plants in clumps was evidence for a strict spatial relationship (i.e. male plants located in upstream position of female plants in order to release spermatia, which would be carried by eddies through female plants). In contrast, the occurrence of male and female plants adjacent to each other allowed outcrossing among neighboring plants with intermingled male and female branches, which seemed more applicable to some situations (low turbulence habitats). The cox 2- 3 spacer region from the 18 individuals sequenced was 376 bp and the DNA sequence was identical with no base pair substitutions. Likewise, a previous study of another Batrachospermum species showed that the same haplotypes were present in all stream segments from the same drainage basin, even though the stream segments were a considerable distance apart. Short distance dispersal either by small birds or waterway connectivity might explain these findings. [source] Overwintering of the sycamore aphid, Drepanosiphum platanoidisENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2-3 2002F.A. Wade Abstract Spatial and temporal aspects of overwintering in the holocyclic sycamore aphid Drepanosiphum platanoidis (Schrank) (Homoptera: Callaphididae) were investigated. Eggs of D. platanoidis were principally laid on trunks and branches of Acer pseudoplatanus L., at considerable distances from the buds. Trunks with rough bark, followed by branches with moderate roughness supported more overwintering eggs than the relatively exposed smooth surfaces of twigs and terminal buds. Eggs were aggregated on rough bark. Aspect had no effect on the number of eggs laid. Experimental manipulations varying ovipara densities showed intra-specific competition among oviparae for optimal oviposition sites. Overwintering egg mortality was a function of time, with the greatest mortality rate occurring in late winter. Egg mortality varied from 80.4% to 76.9% on trunks and 83.0% to 65.9% on branches in 1996 and 1997. [source] Mineral chemical provenance of Neolithic pitchstone artefacts from Ballygalley, County Antrim, Northern IrelandGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 3 2002Jeremy Preston A large number of pitchstone fragments and artefacts have recently been discovered at a Neolithic settlement site in Ballygalley, Co. Antrim, Northern Ireland. They consist predominantly of flakes and un-reworked lumps and cores, with only one complete tool being found. Since no sources of workable pitchstone exist in Ireland, the source must have been the abundant pitchstone volcanic rocks found on the Hebridean Islands of northwest Scotland. The composition of the glass from a number of artefacts is highly siliceous, indicating that they were derived from pitchstones on the Island of Arran; pitchstones from all other Scottish locations are less silica-rich. In addition, analysis of pyroxene and amphibole microcrystallites within the pitchstone suggests that the Corriegills area of Arran is the most likely source of the Ballygalley artefacts, although the precise outcrop has proved elusive. These finds, and others across Ireland, show that raw materials were being transported and probably traded over considerable distances despite there being suitable alternative sources of material for making tools (flint, etc.) available in the local area. This suggests that the pitchstone had a very specialist use. © 2002 Wiley Periodicals, Inc. [source] The Azores diversity enigma: why are there so few Azorean endemic flowering plants and why are they so widespread?JOURNAL OF BIOGEOGRAPHY, Issue 1 2010Mark A. Carine Abstract Aim, Endemism in the flora of the Azores is high (33%) but in other respects, notably the paucity of evolutionary radiations and the widespread distribution of most endemics, the flora differs markedly from the floras of the other Macaronesian archipelagos. We evaluate hypotheses to explain the distinctive patterns observed in the Azorean endemic flora, focusing particularly on comparisons with the Canary Islands. Location, Azores archipelago. Methods, Data on the distribution and ecology of Azorean endemic flowering plants are reviewed to ascertain the incidence of inter-island allopatric speciation and adaptive, ecological speciation. These are contrasted with patterns for the Canary Islands. Patterns of endemism in the Azores and Canaries are further investigated in a phylogenetic context in relation to island age. beast was used to analyse a published molecular dataset for Pericallis (Asteraceae) and to investigate the relative ages of Azorean and Canarian lineages. Results, There are few examples of inter-island allopatric speciation in the Azorean flora, despite the considerable distances between islands and sub-archipelagos. In contrast, inter-island allopatric speciation has been an important process in the evolution of the Canary Islands flora. Phylogenetic data suggest that Azorean endemic lineages are not necessarily recent in origin. Furthermore, in Pericallis the divergence of the Azorean endemic lineage from its closest relative pre-dates the radiation of a Canarian herbaceous clade by inter-island allopatric speciation. Main conclusions, The data presented do not support suggestions that hypotheses pertaining to island age, age of endemic lineages and ecological diversity considered individually explain the lack of radiations and the widespread distribution of Azorean endemics. We suggest that palaeoclimatic variation, a factor rarely considered in macroecological studies of island diversity patterns, may be an important factor. Palaeoclimatic data suggest frequent and abrupt transitions between humid and arid conditions in the Canaries during the late Quaternary, and such an unstable climate may have driven the recent diversification of the flora by inter-island allopatric speciation, a process largely absent from the climatically more stable Azores. Further phylogenetic/phylogeographic analyses are necessary to determine the relative importance of palaeoclimate and other factors in generating the patterns observed. [source] Marine nematode deep-sea biodiversity , hyperdiverse or hype?JOURNAL OF BIOGEOGRAPHY, Issue 4 2003P. John D. Lambshead Abstract Nematodes have been identified as a potentially hyperdiverse group and the deep sea as a potentially hyperdiverse environment (i.e. > 1 million species). A large-scale data set from the equatorial central Pacific is used to estimate regional diversity with results that challenge this view; regional diversity is higher in some coastal waters despite lower sample diversity in coastal waters than in the deep sea. The data suggests a paradigm where the deep sea has modest regional diversity, despite high local diversity through patch dynamics, because similar patches in a similar habitat are repeated for considerable distances. Disturbance in shallow water dominates over patch-dynamic mechanisms reducing local diversity but regional diversity is high because of the close packing of multiple habitats within a single region. The Pacific data are also used to demonstrate the pitfalls of extrapolating from local to global diversity. There is no reason to conclude that nematodes are less diverse than other benthic groups, indeed where direct comparison is possible the Nematoda appear to be as diverse as the Polychaeta, the most diverse macrofaunal taxon. This analysis is not consistent with the hypothesis that either marine nematodes or the deep-sea benthos are hyperdiverse raising the question whether any environment or metazoan taxon has more than a million species. [source] Partitioning nuclear and chloroplast variation at multiple spatial scales in the neotropical epiphytic orchid, Laelia rubescensMOLECULAR ECOLOGY, Issue 9 2004DORSET W. TRAPNELL Abstract Insights into processes that lead to the distribution of genetic variation within plant species require recognition of the importance of both pollen and seed movement. Here we investigate the contributions of pollen and seed movement to overall gene flow in the Central American epiphytic orchid, Laelia rubescens. Genetic diversity and structure were examined at multiple spatial scales in the tropical dry forest of Costa Rica using nuclear (allozymes) and chloroplast restriction fragment length polymorphism (RFLP) markers, which were found to be diverse (allozymes, P = 73.3%; HE = 0.174; cpDNA, HE = 0.741). Nuclear genetic structure (FSTn) was low at every spatial scale (0.005,0.091). Chloroplast markers displayed more structure (0.073,0.254) but relatively similar patterns. Neither genome displayed significant isolation-by-distance. Pollen and seed dispersal rates did not differ significantly from one another (mp/ms = 1.40) at the broadest geographical scale, among sites throughout Costa Rica. However, relative contributions of pollen and seeds to gene flow were scale-dependent, with different mechanisms determining the dominant mode of gene flow at different spatial scales. Much seed dispersal is highly localized within the maternal population, while some seeds enter the air column and are dispersed over considerable distances. At the intermediate scale (10s to 100s of metres) pollinators are responsible for substantial pollen flow. This species appears capable of distributing its genes across the anthropogenically altered landscape that now characterizes its Costa Rican dry forest habitat. [source] Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus)MOLECULAR ECOLOGY, Issue 7 2001D. J. Girman Abstract African wild dogs are large, highly mobile carnivores that are known to disperse over considerable distances and are rare throughout much of their geographical range. Consequently, genetic variation within and differentiation between geographically separated populations is predicted to be minimal. We determined the genetic diversity of mitochondrial DNA (mtDNA) control region sequences and microsatellite loci in seven populations of African wild dogs. Analysis of mtDNA nucleotide diversity suggests that, historically, wild dog populations have been small relative to other large carnivores. However, population declines due to recent habitat loss have not caused a dramatic reduction in genetic diversity. We found one historical and eight recent mtDNA genotypes in 280 individuals that defined two highly divergent clades. In contrast to a previous, more limited, mtDNA analysis, sequences from these clades are not geographically restricted to eastern or southern African populations. Rather, we found a large admixture zone spanning populations from Botswana, Zimbabwe and south-eastern Tanzania. Mitochondrial and microsatellite differentiation between populations was significant and unique mtDNA genotypes and alleles characterized the populations. However, gene flow estimates (Nm) based on microsatellite data were generally greater than one migrant per generation. In contrast, gene flow estimates based on the mtDNA control region were lower than expected given differences in the mode of inheritance of mitochondrial and nuclear markers which suggests a male bias in long-distance dispersal. [source] The effect of a binary source companion on the astrometric microlensing behaviourMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001Cheongho Han If gravitational microlensing occurs in a binary source system, both source components are magnified, and the resulting light curve deviates from the standard one of a single source event. However, in most cases only one source component is highly magnified and the other component (the companion) can be treated as a simple blending source: this is a blending approximation. In this paper we show that, unlike the light curves, the astrometric curves, representing the trajectories of the source image centroid, of an important fraction of binary source events will not be sufficiently well-modelled by the blending effect alone. This is because the centroid shift induced by the source companion endures to considerable distances from the lens. Therefore, in determining the lens parameters from astrometric curves to be measured by future high-precision astrometric instruments, it will be important to take the full effect of the source companion into consideration. [source] The Flight Heights of Chalcid Wasps (Hymenoptera, Chalcidoidea) in a Lowland Bornean Rain Forest: Fig Wasps are the High Fliers,BIOTROPICA, Issue 3 2000Stephen G. Compton ABSTRACT Tropical rain forests are characterized by their rich plant diversity and highly diverse insect faunas containing mainly rare species. Phytophagous and parasitoid insects utilizing such fragmented resources often must travel considerable distances to find suitable hosts. For small, weak-flying insects, entry into the fast-flowing air above the canopy can provide one way by which long-distance dispersal is achieved. Using sticky traps placed at different heights in a lowland rain forest of Borneo, we compared the diurnal and nocturnal flight heights of chalcids, a group of mainly very small parasitoids and phytophages, to determine if the air above the canopy was used for dispersal. Most families were represented throughout the range of trap heights, including those above the general canopy. A higher proportion of individuals were trapped above the canopy at night than during the day. Fig wasps were exceptional in that they were trapped almost entirely above the canopy. They included species associated with host trees that do not fruit in the canopy, suggesting that these short-lived, slow-flying insects actively fly up above the canopy and then use the wind to passively carry them the long distances needed to reach their highly localized and ephemeral hosts. Once the fig wasps detect the species-specific volatiles released by their host figs, they then may fly down into the canopy, where the lower wind speeds would allow them to fly actively upwind to their hosts. [source] | ||||||||||||||||