bluuebunny/crossref_metadata_2025 huggingface dataset:
The spread of gray birch (Betula populifolia) in eastern Quebec: landscape and historical considerations
Authors: Lavoie Claude , Saint-Louis Annie
Published: April 2011

The understanding of recent changes of the spatial distribution of tree species occurring in agricultural landscapes is essential to realistically predict future positions of the range limit of tree species. In Quebec (Canada), it has recently been suggested that gray birch (Betula populifolia Marsh.) is spreading rapidly eastward. We tested the hypothesis that this tree migration is strongly facilitated by human activities. Herbarium specimens, historical landscape reconstructions, botanical surveys in mined peatlands and old fields, and dendrochronological data were used to reconstruct past and recent distribution limits of gray birch in the study area (Bas-Saint-Laurent region). Gray birch has been present in the Bas-Saint-Laurent region since at least 1945. However, herbarium specimens and botanical surveys indicate that gray birch individuals were scarce before 1970. The introduction of gray birch in the Bas-Saint-Laurent region seems to be associated with peat mining activities. All mined peatlands located between Rivière-Ouelle and Isle-Verte were colonized by gray birch, but only 11% of old fields surveyed contained at least one gray birch individual. This suggests that the spread of an early successional tree species in an agricultural landscape is facilitated more by the presence of a few large patches favorable to the growth of the species (mined peatlands) than by numerous small patches (old fields). The recent expansion of gray birch populations in the Bas-Saint-Laurent region could be a major concern for peat mining companies because massive invasions of gray birch in abandoned mined bogs may impede successful restoration of these ecosystems.Key words: Betula populifolia, gray birch, Quebec, peatland, old field, landscape ecology.
Estimates of structural complexity in clonal plant morphology: comparisons of grazed and ungrazed Acaena magellanica rhizomes
Authors: Moen Jon , Ingvarsson Pär K , Walton David WH
Published: April 2011

The aim of this study is to examine the information given by various indices of rhizome morphology that describe grazed and ungrazed rhizome systems of Acaena magellanica (Rosaceae). Internode lengths, branching probabilities, and branching angles were estimated from grazed and ungrazed rhizomes in the field. These parameter values were then used in computer simulations of rhizome growth, and the structural complexity of the simulated rhizomes were described using size, topology, and fractal dimensions. Grazed rhizomes had shorter internodes, higher probabilities of branching, and more open branching angles than ungrazed rhizomes. This resulted in a more directional growth (herring-bone pattern) in the simulated ungrazed rhizomes, whereas the grazed rhizomes had a more space-filling growth pattern. Most indices, even though they are based on different mathematical and theoretical backgrounds, were highly correlated and thus equally good at describing the structural complexity exhibited by the rhizomes. However, indices have different relationships to theories about function, and we suggest that any study of structural complexity of branching systems should use several different indices of shape depending on the questions asked.Key words: Acaena magellanica, fractal dimension, grazing, growth simulation, topology.
Plants colonized by AM fungi regulate further root colonization by AM fungi through altered root exudation
Authors: Pinior Alexandra , Wyss Urs , Piché Yves , Vierheilig Horst
Published: April 2011

The effect of root exudates from non-mycorrhizal and mycorrhizal cucumber (Cucumis sativus L.) plants colonized by one of three arbuscular mycorrhizal fungi (Gigaspora rosea Nicolson & Schenck, Glomus intraradices Smith & Schenck, or Glomus mosseae (Nicolson & Gerdemann) Gerd. & Trappe) on hyphal growth of Gi. rosea and G. intraradices in axenic culture and on root colonization by G. mosseae in soil was investigated. Root exudates from non-mycorrhizal cucumber plants clearly stimulated hyphal growth, whereas root exudates from all mycorrhizal cucumber plants tested showed no stimulation of the hyphal growth of Gi. rosea and only a slight stimulation of the hyphal growth of G. intraradices. Moreover, root exudates from all mycorrhizal cucumber plants inhibited root colonization by G. mosseae compared with the water-treated controls. These results suggest that plants colonized by AM fungi regulate further mycorrhization via their root exudates.Key words: Glomales, Gigaspora rosea, Glomus intraradices, Glomus mosseae, root exudates, regulation.
Localization ofCasuarina-infectiveFrankianearCasuarina cunninghamianatrees in Jamaica
Authors: Zimpfer J F , Kennedy G J , Smyth C A , Hamelin J , Navarro E , Dawson J O
Published: April 2011

Soil sampled along a 100-m linear series of plots extending from the stems of three Casuarina cunninghamiana Miq. trees was bioassayed to estimate the number of infective units (IU) of the symbiotic diazotroph Frankia per gram of soil using native Myrica cerifera L. and exotic C. cunninghamiana as Frankia traps. Casuarina-infective Frankia was detected only in soils within 20 m of Casuarina host trees. Myrica-infective Frankia was found in all of the plots assayed even though none of the native M. cerifera occurred on or near the site. Polymerase chain reaction - restriction fragment length polymorphism characterization of nodule microsymbiont DNA from both host species indicates that Casuarina were nodulated by a different group of Frankia than the groups nodulating Myrica. The Casuarina-infective Frankia is in the same taxonomic group as most other Casuarina-infective Frankia found where Casuarina trees were introduced outside of Australia. Soil collected near the C. cunninghamiana trees had higher total N, NO3, organic matter, P, Mg, K, Ca, pH, and cation exchange capacity. Homogenates ofC. cunninghamiana leaves and stems increased the number of IUs of Frankia CjI82 001 when inoculated and incubated for 3 months in an artificial soil. Thus, it seems that C. cunninghamiana is able to alter soil chemical properties and possibly favor its specific microsymbiont in soil.Key words: Frankia, Casuarina, Myrica, symbiosis, allelopathy, N-fixation.
Antibiotic resistance patterns ofFrankiastrains
Authors: Tisa Louis S , Chval Matthew S , Krumholz Glenn D , Richards Joel
Published: April 2011

A major hurdle in the development of a genetic system for Frankia is the lack of genetic markers. To identify potential genetic markers, 12 strains of Frankia were screened for resistance to antibiotics by the use of a growth inhibition assay. All of the strains demonstrated sensitivity to tested antibiotics. Several strains had distinctive patterns of antibiotic resistance that are potentially useful as genetic markers. Novobiocin was the antibiotic to which the most strains were resistant.Key words: genetics, genetic markers, Frankia, actinorhizal, nitrogen fixation, vesicles.
Genomic fingerprinting ofFrankiamicrosymbionts fromCeanothuscopopulations using repetitive sequences and polymerase chain reactions
Authors: Jeong Soon-Chun , Myrold David D
Published: April 2011

Specificity between Ceanothus species and their microsymbionts, Frankia, were investigated with nodules collected from three geographically separated copopulations of Ceanothus species. Nodules were analyzed using DNA sequencing and repetitive sequence polymerase chain reaction (rep-PCR) techniques. DNA sequencing of the intergenic spacer region between 16S and 23S rRNA genes suggested that Ceanothus-microsymbiotic Frankia are closely related at the intraspecific level. Diversity of the microsymbionts was further analyzed by genomic fingerprinting using repetitive sequences and PCR. A newly designed direct repeat (DR) sequence and a BOX sequence were used as PCR primers after justification that these primers can generate Frankia-specific fingerprints from nodule DNA. Analysis of the nodules using BOX- and DR-PCR showed that Ceanothus-microsymbiotic Frankia exhibited less diversity within each copopulation than among copopulations. These data suggested that geographic separation plays a more important role for divergence of Ceanothus-microsymbiotic Frankia than host plant.Key words: Frankia, Ceanothus, rep-PCR, diversity.
Cytoplasmic bridge formation in the nodule apex of actinorhizal root nodules
Authors: Berg R Howard
Published: April 2011

High-pressure frozen - freeze-substituted actinorhizal root nodules of several distantly related plant genera were used to document the sequence of structural changes in cortical cells of the nodule apex that happened prior to their infection. The sequence of mobilization of the plant cell cytoplasm requisite to infection by Frankia was (i) penetration of the parenchyma cell vacuole by cytoplasmic strands, which contained microtubules; (ii) movement of the nucleus and other organelles (Golgi stacks, endoplasmic reticulum, mitochondria), involved later in growth of the infection thread, to the cell center on these strands; (iii) thickening of some of these strands generally located at midpoints of the wall, forming cytoplasmic bridges (preinfection threads); and (iv) infection of the cell by initiation of infection threads (containing Frankia) within the cytoplasmic bridges. The infection thread was caged in microtubules that were oriented along its axis, suggesting the cytoskeleton had a major role in the infection process, perhaps guiding the growth of the infection thread across the cell. The coalignment of cytoplasmic bridges, along several cells, towards the advancing microsymbiont suggested Frankia secretes a diffusible signal eliciting this host response.Key words: actinorhiza, cryofixation, development, infection, microtubules, symbiosis.
Phylogenetic placement of unculturedCeanothusmicrosymbionts using 16S rRNA gene sequences
Authors: Ritchie Nancy J , Myrold David D
Published: April 2011

Full-length 16S rDNA sequences were amplified directly from the nodules of Ceanothus americanus L. and Ceanothus thyrsiflorus Eschsch. using the polymerase chain reaction. Sequences were determined using an automated sequencer, compared against those in GenBank, and assembled into consensus sequences. The sequences were aligned with other full-length Frankia 16S rDNA sequences available from the data base. Phylogenetic trees were obtained using three different algorithms: neighbor joining, parsimony, and the maximum-likelihood method. All three methods showed that these Ceanothus L. microsymbionts were most closely related to the microsymbiont associated with Dryas drummondii Richardson ex Hook. Lvs. rather than Frankia isolated from the Elaeagnaceae.Key words: Frankia, Ceanothus, 16S rDNA.
Development of flood-induced lenticels in red alder nodules prior to the restoration of nitrogenase activity
Authors: Batzli Janet McCray , Dawson Jeffrey O
Published: April 2011

Red alder (Alnus rubra Bong.) is a nitrogen-fixing woody plant that is common on wetland sites and tolerates flooding through a variety of induced morphological and physiological changes. Among these changes are the formation of hypertrophied nodule lenticels and the subsequent full restoration of nitrogenase activity after 50 days of flooding. The objective of this study was to examine fine structural changes within red alder nodules during lenticel development that correspond to changes in nitrogenase activity during a 50-day experimental flood. Nodulated seedlings of red alder were grown under greenhouse conditions and then exposed to root flooding for 1, 20, 35, or 50 days. At each harvest, estimates of nitrogenase activity were made via acetylene reduction, and nodule samples were taken for light-microscope examination. Only after 50 days of flooding did red alder show restoration of nitrogenase to pretreatment levels. At this time, Frankia vesicles were found to be directly adjacent to developing lenticel tissue and large intercellular spaces. Intercellular space within the nodule increased from 0.6% in nonflooded tissue to 5.7% after 50 days of flooding. Our results demonstrate the sensitivity of the nitrogenase enzyme to low oxygen soil conditions and indicate that substantial morphological change within the nodule must occur before red alder can regain the capacity to fix nitrogen under flooded conditions.Key words: Alnus rubra, Frankia, waterlogged, biological nitrogen fixation, hypertrophied lenticels, intercellular space.
Phylogenetic analysis of chloroplast rps16 intron sequences reveals relationships within the woody southern African Apiaceae subfamily Apioideae
Authors: Downie Stephen R , Katz-Downie Deborah S
Published: April 2011

Evolutionary relationships among 48 genera of Apiaceae (Umbelliferae) were inferred using maximum parsimony, maximum-likelihood, and neighbor-joining analyses of chloroplast DNA rps16 intron and adjacent rps16 3prime exon sequences. Emphasis was placed on woody members of Apiaceae subfamily Apioideae endemic to southern Africa, a region hypothesized to be the place of origin of this largely herbaceous subfamily. The resultant phylogenies were highly concordant and indicate that the apioid genera Polemanniopsis and Steganotaenia form a clade sister to Apiaceae subfamily Saniculoideae. The African genera Anginon, Dracosciadium, Glia, Heteromorpha, and Polemannia also comprise a clade and likely represent the most basal elements within Apioideae. Heteromorpha, however, is not monophyletic, with Heteromorpha arborescens (Spreng.) Cham. & Schltdl. var. abyssinica (A. Rich.) H. Wolff and Heteromorpha arborescens (Spreng.) Cham. & Schltdl. var. arborescens arising in separate subclades. Progressing up the trees, Annesorhiza then Bupleurum fall as successive sister taxa to all remaining Apioideae. The major clades recognized within subfamily Apioideae are largely congruent with those inferred using other types of molecular evidence. Sequence divergence is similar to that of other chloroplast introns, including being generally low among congeners and woody taxa. While the rps16 intron has seen very little use in molecular systematic studies to date, this study demonstrates its ability to discern high-level relationships within Apiaceae.Key words: Apiaceae, Apioideae, chloroplast rps16 intron, phylogeny, southern Africa, Umbelliferae.
Phenotypic plasticity in hybridizing Carpobrotus spp. (Aizoaceae) from coastal California and its role in plant invasion
Authors: Weber Ewald , D'Antonio Carla M
Published: April 2011

Carpobrotus edulis (L.) N. E. Br., an exotic perennial that invades the coastal habitats of California, hybridizes with the presumed native Carpobrotus chilensis (Mol.) N. E. Br. To investigate the potential role of hybrids in the invasion process by C. edulis, we compared the growth and plasticity of clones of hybrids and parental species. Ramets of three hybrid classes and both parental species were grown in a common garden with four different environments. Both the parental species and the hybrids exhibited strong plastic responses to the test environments for characters describing clonal growth and physiology. Carpobrotus edulis consistently had the largest biomass, but C. chilensis produced longer branches. Carbon isotope ratios (<$QFD0E00000010446D80BFFEFF88A6750DA8D9C8282ADCC6210090483DA6ECD7658F80>13C) showed only weak differences among morphotypes. Hybrids were mostly intermediate relative to parental species in both growth and physiological characters. The intermediacy of hybrids in their response to environmental variation indicates that they do not have inferior growth compared with parental species. The high amount of plasticity of the hybrids and C. edulis, as well as their overall similarity, may account for their invasion success in different habitats of coastal California.
Arbuscular mycorrhizae of American ginseng (Panax quinquefolius) in cultivated field plots: plant age affects the development of a colonization lag phase
Authors: McGonigle T P , Hovius J P , Peterson R L
Published: April 2011

Temporal patterns of colonization of roots of perennials by arbuscular mycorrhizal fungi are poorly understood because annual crops are more often studied. The objective was to monitor in detail the growth and mycorrhizae of the perennial American ginseng (Panax quinquefolius L.) over the first 2 years after seeding. In particular, the extent of carry-over of colonization into the second year was examined. Delayed germination of some seeds caused by chance-driven variability in the time needed for seed maturation after seed collection provided an opportunity to compare first- and second-year plants under identical conditions in the second year. For all plants, development of arbuscules rose to a maximum in mid-August, falling partially thereafter. Production of hyphal coils proceeded more slowly but steadily, so that end-of-season colonization was composed equally of arbuscules and hyphal coils. Between seasons, taproot dry mass was reduced by 18%, whereas lateral root length increased by 15%. These changes were probably caused by root turnover, which left little initial colonization of roots at the start of the second year. Strikingly, second-year plants did not exhibit a colonization lag phase, whereas a lag of 43 days was seen for the first-year plants alongside. Possible reasons for this difference are discussed.Key words: perennial, arbuscules, hyphal coils, taproot, Ontario.
The pattern of seed formation in cauliflower (Brassica oleracea L. var. botrytis) with special reference to seed abortion
Authors: Gurusamy C
Published: April 2011

In cauliflower Brassica oleracea L. var. botrytis cv. Kibo Giant, patterns of seed abortion and development within developing siliques are nonrandom. All ovules were fertilized from 14 days after anthesis. However, only 70% of the ovules produced mature seeds. Cryptic seed abortion started early in silique ontogeny and reached a maximum at 28 days after anthesis. Ovules located in the middle zone of a silique produced more mature seeds than ovules in stylar and basal zones in that order. Ovules in the first three positions in the stylar zone (positions 1, 2, and 3) and ovules in the last four positions in basal zone (positions 19, 20, 21, and 22) showed higher rates of seed abortion. The nonrandom pattern of seed abortion within a silique is mainly due to partiality in the allocation of maternal resources to the developing ovules at different positions, which enhances maternal fecundity through resource conservation. It may also be due to temporal differences in fertilization, spatial advantage of seeds within the ovary, and superiority of the parental lineage.Key words: Brassica oleracea L. var. botrytis, seed development, seed abortion, maternal regulation, seed to ovule ratio.
Estimated nitrogen concentrations in humus based on initial nitrogen concentrations in foliar litter: a synthesis. XII. Long-term decomposition in a Scots pine forest
Authors: Berg Björn , Laskowski Ryszard , Santo Amalia Virzo
Published: April 2011

The final (limit) values for litter decomposition were estimated and, by extrapolating a linear relationship between accumulated litter mass loss and litter N concentration, the N concentration at the limit value (Nlimit) was estimated. The values for Nlimit were compared with those of the A01 layer (Nhumus) and of newly shed litter (Ninit). No difference was found between the A01 and A02 layers when their N concentrations were compared with the values for Nlimit. There was a highly significant linear relationship between Nlimit and Ninit (R2 = 0.769 and p < 0.001). Likewise, there was a highly significant linear relationship between Nhumus and Ninit. When these two linear relationships were compared, there was no significant difference in slope, while there was a significant difference in the intercepts of 6.76 and 7.25 mg·g-1 for Nhumus and Ninit, respectively. Thus, for a given site in our investigation, the estimated value for N concentration in humus would be 6.8% lower than the measured one.
Aphid fitness on 13 grass species: a test of plant defence theory
Authors: Fraser Lauchlan H , Grime J Philip
Published: April 2011

The growth rate hypothesis, which states that fast-growing plants support more herbivores than slow-growing plants, was tested with 12 native and 1 naturalized British grasses using the grain aphid (Sitobion avenae). Five aphids were enclosed with grasses for two weeks in a growth chamber. After 2 weeks, fast-growing plants had 38 aphids, whilst slow-growing plants had 6, which supports the growth-rate hypothesis. When aphid numbers were analysed on plants according to "CSR" theory (Grime 1977, 1979), ruderals (R) had 54, competitors (C) had 18, and stress tolerators (S) had 6. This supports the predictions of CSR theory. Furthermore, aphid numbers increased significantly with grass growth rates and a mollusc palatability index, although this largely resulted from a single outlier, Poa annua. Aphid number was not affected by hairs on grasses. Finally, the effect of aphid feeding on grasses was tested. Generally, the greatest change in total and aboveground biomass of the grasses was found in the ruderals, whilst stress tolerators had the least amount of change.
Leaf trichome morphology and density in West African Trema spp. (Ulmaceae: Celtidoideae)
Authors: St-Laurent Luc , Baum Bernard R , Akpagana Koffi , Arnason John T
Published: April 2011

Leaf trichome morphology and density are described for three species belonging to the genus Trema from West Africa: T. africana (Planch.) Blume, T. orientalis (L.) Blume, and T. nitens (Hook. & Planch.) Blume. Leaves of specimens collected in West Africa were observed using scanning electron microscopy. Unicellular trichome morphology was assessed, and a 3 × 3 two-way contingency table analysis showed dependence between the trichome type and species identity. Density of unicellular and multicellular trichomes on both leaf surfaces as well as the number of cells composing the stalk of multicellular trichomes were measured and subjected to nonparametric analysis of variance. Kruskal-Wallis tests yielded significant results (p < 0.05) among the three species for all characters except unicellular trichome density on the adaxial leaf surface. Wilcoxon two-sample tests showed that all species were different, except for the density of multicellular trichomes on the abaxial leaf surface where densities in T. africana and T. orientalis were not significantly different. The number of cells composing the stalk of multicellular trichomes was significantly different among each species on the adaxial leaf surface, but on the abaxial one, T. africana and T. orientalis exhibited no significant differences. The value of these characters in the discrimination between the three species is discussed.Key words: Trema spp., Ulmaceae, West Africa, leaf trichomes, morphology, density.
Phylogenetic studies of Saprolegniomycetidae and related groups based on nuclear large subunit ribosomal DNA sequences
Authors: Riethmüller Alexandra , Weiß Michael , Oberwinkler Franz
Published: April 2011

To reveal phylogenetic relationships within the Peronosporomycetes (Oomycetes), we sequenced a part of the nuclear rDNA coding for the ribosomal large subunit of 46 Peronosporomycetes species and one representative of the Xanthophyta. The main emphasis of our study was put on the phylogenetic relationships within the Saprolegniomycetidae. We supplemented our data with a sequence of Phytophthora megasperma Drechsler from GenBank. Two sets of sequences were analysed using the neighbor-joining method, statistically supported by the bootstrap method, as well as the maximum parsimony method. Our results are well compatible with the tripartite subclassification of the Peronosporomycetes into Saprolegniomycetidae, Rhipidiomycetidae and Peronosporomycetidae, as well as with the placement of the orders Saprolegniales and Leptomitales in the Saprolegniomycetidae. Pachymetra chaunorhiza Croft & Dick, which has been placed in the Sclerosporales, was grouped within the Saprolegniales. Within the Peronosporomycetidae, the orders Peronosporales and Pythiales could not be separated. There are indications that Phytophthora de Bary and the Peronosporales form a common natural group. The genus Achlya Nees proved to be a heterogeneous group.
The influence of clear-cutting on ectomycorrhizal fungus diversity in a lodgepole pine (Pinus contorta) stand, Yellowstone National Park, Wyoming, and Gallatin National Forest, Montana
Authors: Byrd Kristin B , Parker V Thomas , Vogler Detlev R , Cullings Ken W
Published: April 2011

Effects of clear-cutting on the ectomycorrhizal (EM) fungus community in a Pinus contorta Dougl. ex Loud. forest near Yellowstone National Park, Wyoming, U.S.A., were assessed using molecular techniques. Samples were taken by soil core in both undisturbed and clear-cut sites by randomized block design. Species overlap was compared between clear-cut and undisturbed sites and ascomycete-basidiomycete ratio was determined, using PCR-RFLP methods. Fifty species of EM fungi were detected in the clear-cut sites, the most common being Cenococcum geophilum Fr., Suillus sp., a member of the suilloid group, a Russulaceae species, and a Thelephoraceae species. Sixty-six species were detected in the undisturbed sites, which were dominated by a Suilloid species, a Tricholomataceae species, Cortinarius sp., and Cenococcum geophilum. Species composition in the clear-cut sites differed significantly from that in the undisturbed sites (P = 0.0001). However, 9 of the 14 species most commonly found in the clear-cut sites were also found in the undisturbed sites, but in much lower abundance, while species rank curves of both stand types mirrored each other. There were no significant differences in species richness, root-tip abundance, or ascomycete-basidiomycete ratio between the clear-cut and undisturbed sites. However, species richness was lower in the clear-cut sites than in the undisturbed sites. An overall loss of species richness after clear-cutting and significant changes in species composition indicate that clear-cutting can negatively alter the EM fungal community, and this may have profound effects on ecosystem function.Key words: ectomycorrhizae, community structure, clear-cutting, molecular techniques.
Small subunit rDNA phylogeny shows the lichen families Caliciaceae and Physciaceae (Lecanorales, Ascomycotina) to form a monophyletic group
Authors: Wedin Mats , Döring Heidi , Nordin Anders , Tibell Leif
Published: April 2011

A phylogenetic analysis based on small subunit (SSU) rDNA sequences shows the lecanoralean lichen families Caliciaceae and Physciaceae form a well-supported monophyletic group within the order Lecanorales (Ascomycotina). Support for this relationship is present from anatomical data, in particular data from spore ontogeny, where close similarities between the pattern of development of spore surface structures in the two families are pointed out. The Caliciaceae-Physciaceae group is characterized by having thick-walled, pigmented spores, often with a distinctive ornamentation which is usually formed either from strongly melanized parts of the perispore, separated by nonmelanized, gelatinous parts that eventually dissolve, or by cracks in the perispore. The relationship to the Teloschistaceae, sometimes suggested as a possible sister-group to the Physciaceae, was not supported by jackknifing, but cannot be rejected with the present data. There is no support for the suggested order Teloschistales. A brief discussion of the evolution of the prototunicate ascus in the Lecanorales is given. New SSU rDNA sequences were produced from Buellia disciformis (Fr.) Mudd. and Physcia aipolia (Humb.) Fürnr. (Physciaceae), Cladonia sulphurina (Michx.) Fr. (Cladoniaceae), Cyphelium tigillare (Ach.) Ach. (Caliciaceae), and Caloplaca flavorubescens (Huds.) J.R. Laundon and Xanthoria parietina (L.) Th.Fr. (Teloschistaceae).Key words: 18S, fungi, lichens, molecular phylogeny, ribosomal DNA.
Skeletal remains of a small theropod dinosaur with associated soft structures from the Lower Cretaceous Santana Formation of northeastern Brazil
Authors: Martill David M , Frey Eberhard , Sues Hans-Dieter , Cruickshank Arthur RI
Published: April 2011

Associated well-preserved, uncrushed skeletal remains, comprising the pelvic girdle, partial sacrum, both femora, and parts of the right tibia and fibula, from the Romualdo Member of the Lower Cretaceous Santana Formation of northeastern Brazil record the presence of a previously unknown coelurosaurian theropod dinosaur in that formation. The pelvic girdle is noteworthy for the bilaterally asymmetrical development of various bony features. The specimen also preserves a segment of lithified intestinal tract. While still in the matrix, the fossil preserved a vacuity behind the pubic apron that may indicate the existence of a postpubic air sac.
A U-Pb and 40Ar/39Ar time scale for the Jurassic
Authors: Pálfy J , Smith P L , Mortensen J K
Published: April 2011

Published time scales provide discrepant age estimates for Jurassic stage boundaries and carry large uncertainties. The U-Pb or 40Ar/39Ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration. A radiometric age database consisting of fifty U-Pb and 40Ar/39Ar ages was compiled to construct a revised Jurassic time scale. Accepted ages have a precision of ±5 Ma (2σ) or better and are confined to no more than two adjacent stages. The majority of these calibration points result from integrated bio- and geochronologic dating in the western North American Cordillera and have not been previously used in time scales. Direct dates are available only for the Triassic-Jurassic boundary and the initial boundary of the Crassicosta chron and the Callovian stage. The chronogram method was used to estimate all Early and early Middle Jurassic zone boundaries (attempted here for the first time), late Middle Jurassic substage boundaries, and Late Jurassic stage boundaries. Significant improvement is achieved for the Pliensbachian and Toarcian, where six consecutive zone boundaries are determined. The derived zonal durations are disparate, varying between 0.4 and 1.6 Ma. The latest Jurassic isotopic database remains too sparse, therefore chronogram estimates are improved using interpolation based on magnetochronology. The initial boundaries of Jurassic stages are proposed as follows: Berriasian (Jurassic-Cretaceous): 141.8+2.5– 1.8 Ma; Tithonian: 150.5+3.4– 2.8 Ma; Kimmeridgian: 154.7+3.8– 3.3 Ma; Oxfordian: 156.5+3.1– 5.1 Ma; Callovian: 160.4+1.1– 0.5 Ma; Bathonian: 166.0+3.8– 5.6 Ma; Bajocian: 174.0+1.2– 7.9 Ma; Aalenian: 178.0+1.0– 1.5 Ma; Toarcian: 183.6+1.7– 1.1 Ma; Pliensbachian: 191.5+1.9– 4.7 Ma; Sinemurian: 196.5+1.7– 5.7 Ma; Hettangian (Triassic-Jurassic): 199.6 ± 0.4 Ma.
Spatial distribution of surficial sediments in part of the Kingston basin of northeastern Lake Ontario, Canada
Authors: Härtling Joachim W , Gilbert Robert
Published: April 2011

The distribution of surficial sediments in the interisland area of northeastern Lake Ontario is characterized by a generally homogeneous composition of fine grained muds with some local exceptions at the gaps leading into Kingston basin and in parts of North Channel. This pattern reflects principally differing levels of wave energy from the exposed areas of outer Kingston basin and Upper and Lower gaps to the more protected interisland area. Additional processes responsible for the distribution are currents at the Upper and Lower gaps and local slumping. The observed deposition of surficial sediments in the northern Kingston basin shows generally good agreement with the wave base calculations employing wind speeds of 60 km·h-1. The study region consists of three sedimentary environments. Above the wave base related to winds of less than 60 km·h-1 continual erosion and transport of all grain sizes leads to a constant source of sediment to the deeper parts of the Kingston basin. Above the wave base related to infrequent strong winds of more than 60 km·h-1, episodic removal of the fine grain sizes leads to winnowing of the fines and their being transported into North Channel and Kingston Harbour while the sands are left in place. Below the wave base the sediments are undistributed. Thus, there is no proximal-distal differentiation outward from the coasts nor along the channels. The sediment is transported with currents moving through North Channel and Kingston Harbour with similarly low velocities across the entire section.
Isotopic evidence for the sources of Cretaceous and Tertiary granitic rocks, east-central Alaska: implications for the tectonic evolution of the Yukon-Tanana Terrane
Authors: Aleinikoff John N , Farmer G Lang , Rye Robert O , Nokleberg Warren J
Published: April 2011

Magnetotelluric traverses across the southern Yukon-Tanana terrane (YTT) reveal the presence of a thick conductive layer (or layers) beneath Paleozoic crystalline rocks. These rocks have been interpreted to be flysch of probable Mesozoic age, on the basis of the occurrence of Jurassic-Cretaceous flysch in the Kahiltna assemblage and Gravina-Nutzotin belt flanking the YTT to the southwest and southeast, respectively. The Pb, Nd, Sr, and O isotopes in Cretaceous and Tertiary granitic rocks that crop out throughout the YTT were measured to determine if these rocks do in fact contain a component of flysch. Previous limited analyses indicated that the Pb isotopes of the granitic rocks could be a mixture of radiogenic Pb derived from Paleozoic crystalline rocks of the YTT with an increasing component of relatively nonradiogenic Pb with decreasing age. Our Nd, Sr, and O data, along with additional Pb isotope data, eliminate flysch as a likely source and strongly suggest that the nonradiogenic end-member was derived from mafic rocks, either directly from mantle magma or by melting of mafic crust. The lack of a sedimentary component in the granitic plutons suggests either that the plutons did not incorporate significant amounts of flysch during intrusion or that the conductive layer beneath the YTT crystalline rocks is not flysch.
Characterization, identity, distribution, and source of late Cenozoic tephra beds in the Klondike district of the Yukon, Canada
Authors: Preece Shari J , Westgate John A , Alloway Brent V , Milner Michael W
Published: April 2011

A large number of distal, silicic tephra beds have been preserved in the late Cenozoic deposits of the Klondike region, Yukon Territory. Forty-one tephra samples, representing twelve distinctive beds, are detailed in this study. They range in composition from basaltic andesite to high-silica rhyolite, and were deposited during the late Pliocene to Late Wisconsinan time interval. Seven tephra beds are derived from volcanoes in the Wrangell volcanic field, and four come from the more distant eastern Aleutian arc - Alaska Peninsula region, but the source of the single andesitic tephra is unknown. The widespread and well known Old Crow and Sheep Creek tephra beds have been identified in the Klondike district, but all the other tephra units are characterized in detail for the first time. The ages of most tephra beds are poorly constrained, but will undoubtedly become better known with the application of recently developed glass fission-track methods. Hence, prospects are favourable for the eventual development of a comprehensive and reliable time-stratigraphic framework that will support on-going studies on the late Cenozoic geology, geomorphology, paleontology, and paleoenvironments of the Klondike area.
Petrology, geochemistry, and diabase-granophyre relations of a thick basaltic sill emplaced into wet sediments, western Montana
Authors: Poage Michael A , Hyndman Donald W , Sears James W
Published: April 2011

The Plains Sill is a thick diabase-granophyre body that intruded the wet sediments of the Middle Proterozoic Prichard Formation of the Belt-Purcell Supergroup. The diabase is a high-iron tholeiite geochemically compatible with large-volume mantle melting in an intracratonic rift environment. Evidence of emplacement into wet sediments includes thick zones of homogenized granosediments adjacent to the sill, soft-sediment deformation at sill contacts, and sedimentary ovoid structures possibly formed by local fluidization of sediments. Utilizing sediment pore water and driven by heat from the sill, the diabase was metamorphosed during crystallization and cooling, leaving hornblende as the dominant mafic phase. Continued retrograde alteration resulted in overgrowths of secondary hornblende and variable alteration of plagioclase to epidote. A miarolitic granophyre layer, up to 150 m thick, caps the diabase and appears igneous in origin. Locally the granophyre is anomalously thick, perhaps reflecting updip migration of granophyric fluid where the Plains Sill cuts upsection through the Prichard Formation stratigraphy.
Emplacement of the Nain anorthosite: diapiric versus conduit ascent
Authors: Royse K R , Park R G
Published: April 2011

Estimation of settling velocities of large orthopyroxene megacrysts, found within anorthosite intrusions, are calculated and compared with ascent rates achieved by diapirism and conduit propagation. Calculations suggest that diapirism is far too slow to be an appropriate ascent mechanism for anorthositic crystal mush and favour conduit emplacement. The intrusions of the Nain Plutonic Suite (NPS) are located along the Abloviak shear zone, which marks the boundary between the Nain and Churchill provinces, and within the zone of juxtaposition of the Saglek and Hopedale blocks of the Nain Province. These crustal weaknesses have probably controlled the emplacement and distribution of the intrusions. Contact relations between intrusions of anorthosite and their gneissic host rock provide evidence for two emplacement styles within the NPS, the first typified by strongly deformed and recrystallized rocks, and the second by an outer border zone of mafic rocks. It is proposed that these differences in intrusive style are due to differences in ductility contrast between the magma and its surrounding host rocks, such that those intrusions emplaced into the thermally softened shear zone have deformed margins, whereas those intruded into the cooler Archaean crust have undeformed margins.
Taltson basement gneissic rocks: UPb and Nd isotopic constraints on the basement to the Paleoproterozoic Taltson magmatic zone, northeastern Alberta
Authors: McNicoll Vicki J , Thériault Réginald J , McDonough Michael R
Published: April 2011

The Taltson magmatic zone is a 300 km long, northerly trending belt of Archean to Paleoproterozoic granitic basement gneiss, amphibolite, supracrustal gneissic rocks, and voluminous Paleoproterozoic magmatic rocks underlying northeastern Alberta and the southwestern portion of the Northwest Territories. Taltson basement gneissic rocks exposed in the southern Taltson magmatic zone in northeastern Alberta are composed of a lithologically diverse suite of banded gneissic rocks, including amphibolitic gneiss, paragneiss, and metaplutonic gneiss. Metaplutonic gneissic rocks are predominant; six new UPb ages range from 2.4 to 2.1 Ga. Taltson basement also contains tectonic slices and layers of Archean gneissic rocks dated at 3.2 Ga, 3.1 Ga, and 2.6 Ga. εNd(2.2 Ga) values of 1.6 to 14.3 and TDM ages of 2.593.73 Ga from Taltson basement rocks (27 new analyses) overlap with values for the western Churchill Province and are interpreted to represent Paleoproterozoic recycling of the latter. The similarity in UPb ages and partial overlap in Nd isotopic compositions of the Taltson basement gneissic rocks and the Buffalo Head terrane are consistent with the two domains representing a single Paleoproterozoic crustal entity, which evolved from variable contributions of depleted mantle and preexisting Churchill Province crust. Greater contributions from a depleted mantle component in the Buffalo Head terrane are suggested by the Nd data. Taltson basement gneissic rocks and Buffalo Head terrane may represent earliest Paleoproterozoic magmatism associated with breakup of the western Churchill Province prior to ThelonTaltson orogenesis.
Petrology of a supra-subduction zone ophiolite (Elaz1g, Turkey)
Authors: Beyarslan Melahat , Bingöl A Feyzi
Published: April 2011

The Elaz1g region in eastern Taurus, Turkey, exposes Paleozoic-Tertiary metamorphic, magmatic, and sedimentary units. Contacts between the different units are mostly tectonic, but there are also primary sedimentary, and intrusive contacts. The metamorphic rocks of the Elaz1g region are the Bitlis-Pütürge and Keban-Malatya massifs, which are a single tectonostratigraphic unit that has been tectonically disrupted and fragmented during the Upper Cretaceous. Magmatic rocks in the region are represented by ophiolitic units, magmatic arc products, and young volcanic rocks. The sedimentary units are represented by Upper Cretaceous - Tertiary marine and lacustrine sedimentary rocks. In the study area, the metamorphic units are represented by the Paleozoic Pütürge metamorphic rocks composed of phyllite, slate, mica schist, quartz-muscovite schist, calc-schist, and low-grade metamorphite. The ophiolite that is described in this paper is composed of wehrlite-pyroxenite, gabbro, diabase dykes, and dykes cutting gabbro. These units are cut by the granitic rocks of the Upper Cretaceous Elaz1g magmatic suite. The lithological and geochemical data on the rocks of Kömürhan ophiolite indicate that these rocks were derived from crystallization of an enriched mid-ocean ridge basalt (MORB)-type magma. The Kömürhan ophiolite formed in a supra-subduction spreading zone during the Cretaceous; related to this event is the north-dipping subduction of the southern branch of Neo-Tethys ocean, which began spreading in the Late Triassic. The crust was thickened by the development of an island arc and by the thrusting of the Pütürge metamorphic rocks onto this island arc in response to north-south compression during the Late Cretaceous. The magma formed by partial melting of the subducted slab giving rise to granitic rocks that cut the upper parts of the ophiolite. The ophiolite and the Elaz1g magmatic suite attained their present position after the Middle Eocene.
Geology and U-Pb geochronology of the Island Lake greenstone belt, northwestern Superior Province, Manitoba
Authors: Corfu Fernando , Lin Shoufa
Published: April 2011

Mapping and U-Pb geochronology have been used to examine the tectonic and depositional history of the Archean Island Lake greenstone belt in the northwestern Superior Province. The Island Lake greenstone belt comprises two main supracrustal successions, the older Hayes River Group and the younger Island Lake Group. Zircon data for two volcanic units from the Hayes River Group provide identical ages of 2852 ± 1.5 Ma, whereas a turbidite of this group contains a detrital zircon population with ages between 2858 and 2847 Ma. Younger intrusive events include the emplacement of tonalite in the southern batholith at 2825 ± 2 Ma and the Whiteway Island gabbro at 2807 ± 1 Ma. A wacke at the base of the Island Lake Group is dominated by detrital zircon grains yielding ages between 2830 and 2821 Ma, the latter defining a maximum age of sedimentation. A relatively early time of deposition of the lower stratigraphic sections of the Island Lake Group is also supported by an age of 2744 ± 2 Ma obtained for a crosscutting tonalite. By contrast, two turbidite horizons from higher stratigraphic levels of the Island Lake Group contain detrital zircon populations with ages mostly younger than 2730 Ma, the youngest zircon grains providing maximum ages of sedimentation at 2722 and 2712 Ma, respectively. Our results confirm the protracted evolution of the greenstone belt and show in particular that major sedimentary processes were active throughout the main stages of volcanism of the belt. This pattern of protracted sedimentation is comparable to that observed in other greenstone belts of the northwestern Superior Province, all of which developed on pre-Kenoran crust.
Evolution and extinction of the North American Hiscobeccus brachiopod Fauna during the Late Ordovician
Authors: Jin Jisuo
Published: April 2011

The earliest rhynchonellid brachiopods were small-shelled and preferred cool-water conditions in both siliciclastic and carbonate environments. Relatively large shells of Rhynchotrema evolved in mid-Caradoc time and rapidly became widespread in Laurentia. Hiscobeccus probably evolved from Rhynchotrema during the late Caradoc by developing a large, globular, strongly lamellose shell. The earliest form of Hiscobeccus shows transitional characteristics between Rhynchotrema and typical Hiscobeccus, most notably in its nonglobular shell that is wrinkled by growth lamellae only on the anterior two thirds of the shell. By early Ashgill time, Hiscobeccus became widespread in North American inland basins, although it remained common in marginal carbonate platforms and basins. During the Ashgill, Hiscobeccus, Lepidocyclus, and Hypsiptycha represented a distinct North American fauna, characterized by large, globular, and completely wrinkled shells. These morphological features were adaptations to the shallow, well-circulated, epicontinental, tropical seas with a soft muddy substrate. The gigantism exhibited by the Hiscobeccus Fauna is also shown by orthid and strophomenid brachiopods, gastropods, nautiloids, and trilobites. Extinction of the Hiscobeccus Fauna was probably related to its narrow range of environmental tolerance, especially during the Gondwana continental glaciation, which brought a major global sea-level drawdown and lowered ocean temperature. The cool-water Rostricellula and Rhynchotrema were uncommon in inland seas during the Ashgill and were represented by several opportunistic species in the Anticosti Basin during the Hirnantian and Llandovery, and most of these preferred siliciclastic-rich or deep-water shelf carbonate environments.
Records of geomagnetic secular variation since 1200 AD and the potential for chronological control of lake sediments in northern Alberta
Authors: Larsen C PS , Morris W A , MacDonald G M
Published: April 2011

We assess whether absolutely aged declination changes can be used to date recent, massive lake sediments at the sub-century scale. Three issues limiting such studies are addressed: recovery of undisturbed recent lake sediments, assessment of the reliability of the geomagnetic record, and the comparison of lake-sediment records with historic records. A 793-year long geomagnetic chronology was obtained from the annually laminated sediment of Rainbow Lake A. Sediment disturbance was minimized by freezing the sediment in situ and maintaining this state for geomagnetic analyses. Geomagnetic chronologies ca. 600 years long from the massive sediments of Fariya Lake and Ninisith Lake were collected in removable plastic tubes using a piston-corer. Sediment disturbance was minimized by ex situ draining of water from the plastic tubes. The reliability of the geomagnetic record was assessed using a measure of internal coherence with an absolute cutoff of 15°. By further separating the samples at coherence values of 5° and 7.5°, it was possible to identify zones of disturbance and reduced compaction. The most reliable samples had a high magnetic intensity due to high inputs of magnetic minerals, sediment compression, and inputs of stable magnetic minerals. Neither freezing nor dewatering of the sediments appeared to decrease reliability of the geomagnetic record. The declination chronology from the annually laminated sediments was significantly correlated with a 230-year long historical record from Churchill, Manitoba, and with the massive lake sediment chronology from Fariya Lake. Geomagnetic dating was not possible, however, because of the large amplitude in the annually laminated sediment declination record, the large number of years of sediment in many specimens, and the lack of reliability for samples that contain few years of sediment per specimen.