Search results for "ero"
showing 10 items of 33096 documents
Modern pollen and non-pollen palynomorphs along an altitudinal transect in Jammu and Kashmir (Western Himalaya), India
2021
Pollen and non-pollen palynomorphs were analysed from 35 modern moss cushions collected along an altitudinal gradient (2225–2552 m a.s.l.) from the Baramulla District of Jammu and Kashmir State (Western Himalaya), India. The selected sampling altitude is at the elevation of appearance of blue pine (Pinus wallichiana) and West Himalayan spruce or morinda spruce (Picea smithiana). We used cluster analysis and principal component analysis (PCA) to reveal trends and characteristics in the modern pollen and non-pollen palynomorph composition within this zone. Tree taxa mainly correlated positively with the altitudinal gradient, i.e. tree pollen is more abundant at higher altitudes. The presence …
Using growth and geochemical composition of Clathromorphum compactum to track multiscale North Atlantic hydro-climate variability
2020
International audience; Records of ocean/atmosphere dynamics over the past centuries are essential to understand processes driving climate variability. This is particularly true for the Northwest Atlantic which is a key region with an essential role in global climate regulation. Over the past two decades, coralline red algae have been increasingly used as environmental and climatic archives for the marine realm and hold the potential to extend long-term instrumental measurements. Here, we investigate the possibility to extract climate and environmental information from annual growth patterns and geochemical composition of the coralline red algae, Clathromorphum compactum, from Saint-Pierre …
Stage boundaries, global stratigraphy, and the time scale: towards a simplification
2004
International audience; This paper examines four facets of stratigraphic terminology and usage considered faulty and proposes corrective measures. The four perfectible areas are: (1) The system of dual nomenclature requiring discrete terminologies for the superpositional and temporal aspects of rock units. (2) The premise that a GSSP establishes the base of a stage as being coincident with the top of the preceding stage rather than simply defining it as the boundary between stages. (3) The rejection of supplementary (auxiliary) sections that would broaden the knowledge of a GSSP and enlarge the area in which it is easily usable. (4) The current dual system of nomenclature for Precambrian an…
The metamorphic rocks of the Nunatak Viedma in the Southern Patagonian Andes: Provenance sources and implications for the early Mesozoic Patagonia-An…
2019
The Nunatak Viedma within the Southern Patagonian Icefield has been considered as a volcanic center based on its geomorphologic features, despite the fact that field explorations by Eric Shipton determined its metamorphic nature 70 years ago. We carried out fieldwork to characterize this isolated outcrop and performed the first U-Pb dating in detrital zircons from the basement rocks located inside the Southern Patagonian Icefield. We recognized very-low grade metamorphic rocks, corresponding principally to metapelites and metapsammites, and scarce metabasites. Detrital zircons in three metapsammitic samples (composite group of 240 grains) yielded prominent age population peaks at ∼1090, ∼96…
Quaternary marine and continental unconformity-bounded stratigraphic units of the NW Sicily coastal belt
2017
In the coastal sector of NW Sicily, the regional correlation of relevant unconformities recognised within the Quaternary sedimentary successions allowed the mapping of seven unconformity-bounded stratigraphic units (UBSUs). The regional unconformities are marine or subaerial erosional surfaces, as well as non-depositional surfaces, locally marked by paleosoils. The erosional surfaces were produced from marine abrasion, surface water overland/concentrated flow, river erosion, karst solution, mass movement, or wind erosion. The main lithofacies of the Quaternary UBSUs consist of: (a) marine and coastal bioclastic calcarenites, (b) aeolian sandstones, (c) river deposits, (d) colluvial deposits…
Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK
2009
Abstract: The Late Jurassic was a time of increasing aridity in NW Europe. Here, a new clay mineral dataset is presented from a 600 m thick composite core through the Kimmeridge Clay Formation, southern England. Clay mineral assemblages comprise mainly illite and kaolinite, with minor randomly interstratified illite–smectite mixed-layer clays. SEM observations indicate that clay minerals are mainly detrital, except in silty strata of late Tithonian age, which contain abundant pore-filling kaolinite aggregates. Th/K ratios determined from gamma-ray spectrometry mirror palaeoclimatically significant variations in kaolinite/illite ratios, with notable exception where diagenetic kaolinite occur…
Radial Symmetry, the Anterior/Posterior Axis, and Echinoderm Hox Genes
2008
20 pages; International audience; The strangeness of echinoderm pentaradiality results from superposition of radial symmetry onto ancestral deuterostome bilaterality. The Extraxial- Axial Theory shows that echinoderms also have an anterior/posterior (A/P) axis developed independently and ontogenetically before radiality. The A/P axis is first established via coelomic stacking in the extraxial region, with ensuing development of the pentamerous hydrocoel in the axial region. This is strongly correlated with a variety of gene expression patterns. The echinoid Hox cluster is disordered into two different sets of genes. During embryogenesis, members of the posterior class demonstrate temporal, …
L’origine des Imerites Rouchadze, 1933 : résultat d’une innovation chez les Gassendiceratinae Bert, Delanoy et Bersac, 2006 (Ammonoidea, Ancylocerati…
2009
15 pages; La découverte récente de plusieurs spécimens remarquables d'Imerites dichotomum (Ammonoidea, Ancyloceratina) apporte de nouvelles précisions paléontologiques sur ce genre. L'étude du développement ontogénétique montre que les Imerites dérivent directement du genre Pseudoshasticrioceras. Leur origine se situe donc parmi les Gassendiceratinae et non chez les Heteroceratidae comme il était généralement admis. Par ailleurs, la cohabitation de formes macroconques et microconques au sein des espèces du genre Imerites confirme l'hypothèse du dimorphisme. Les nouvelles données paléontologiques obtenues montrent que le taxon « Crioceras » cristatus est un nomen dubium et qu'il doit être ab…
<p><strong><em>Chilocoris</em> <em>serratus</em> n. sp., the first burrower bug species (Hemiptera: Heteroptera: …
2016
The first burrower bug species recorded in Guinea-Bissau, Chilocoris serratus n. sp., is described and compared with morphologically related species. Additionally, an annotated checklist of Afrotropical species of the genus Chilocoris is provided.
First Perigondwanan record of actinolepids (Vertebrata: Placodermi: Arthrodira) from the Lochkovian (Early Devonian) of Spain and its palaeobiogeogra…
2011
Different palaeogeographic models have been proposed for the position of Laurussia ( including Baltica) and Gondwana-derived microcontinents ( including Ibero-Armorica) during Ordovician to Late Carboniferous times. Principal differences concern the presence and duration of a large ocean, the Rheic Ocean, acting as a faunal barrier between these areas. The timing of the collision of Laurussia with Gondwana and/or Gondwana-derived terranes continues to be debated. Here we present new faunal data revealing close biogeographical relations between Ibero-Armorica ("Perigondwanan" or Gondwanan derivate terranes) and Podolia (SE margin of Baltica, in Laurussia). The placoderm assemblage found in t…