Search results for "Devonian"
showing 10 items of 77 documents
New insights into the reading of Paleozoic plant fossil record discontinuities
2011
Studying the discontinuity patterns of Paleozoic vascular plants provides a global vision of these key events from the multivariate methods viewpoint. Non-metric multidimensional scaling, detrended correspondence analysis and cluster analysis have been employed together with a set of diversity and abundance measures and an evaluation of the geologic constraints from the plant fossil record data. The results reveal four clear significant discontinuities in terms of taxonomic composition and record representativeness during the early-middle Devonian, Devonian–Carboniferous, Mississippian–Pennsylvanian and early-late Permian. Due to the controversial character of the plant fossil record data a…
Adaptation to environmental changes: communities need more time than species
1998
Effects of environmental changes on communities and on species have been studied with two different types of animals: mammals and conodonts. This analysis was conducted on mammals from the ’Ubeidiya Sequence (Israel) dated to the Lower Pleistocene, and on conodonts from the quarry of Coumiac (France) dated to the Frasnian/Famennian boundary (Devonian). The main result of the analysis is that an ecological event can be subdivided. First of all there is a change in the environment that corresponds to a physical signal, the species react to this change, and afterwards the communities respond. Thus, a delay in time can be observed between the reaction of the species and the reaction of the comm…
Ostracod and conodont faunal changes across the Frasnian-Famennian (Devonian) boundary at Els Castells, Spanish central Pyrenees
2008
Diverse conodont and silicified ostracod assemblages were found in the Spanish Pyrenees (Els Castells section), in the Frasnian/Famennian boundary beds (laterhenana and/orlinguiformis to latetriangularis zones), in strata below and above the well-known Kellwasser Extinction Event. Many of the ostracods studied here are conspicuous elements of the “Thuringian Mega-Assemblage”, and show maximum affinities with faunas from the southeastern Cantabrian Mountains (Spain), eastern Thuringia and the Harz (Germany). The composition of the faunas, however, is not uniform through the Els Castells section. A rather sharp break exists, roughly coinciding with the Frasnian/Famennian boundary. The break i…
Timing and selectivity of the Late Mississippian mass extinction of brachiopod genera from the Central Appalachian Basin
2008
The seventh largest mass extinction of the Phanerozoic Era occurred in the Late Mississippian and coincided with the onset of the late Paleozoic ice age. Analyses of brachiopod genera from Mississippian strata of the Central Appalachian Basin reveal that the regional expression of the mass extinction occurred after the development of high-amplitude glacioeustasy by several million years and occurred instead during low-latitude cooling and the expansion of glaciation near the Mississippian-Pennsylvanian boundary. The Late Mississippian mass extinction was even more severe for genera in the Central Appalachian Basin than global metrics would predict; in addition to the genera of this basin th…
Discovery of a Lochkovian flora (Lower Devonian) in the Iberian Peninsula
2011
ABSTRACT The Lower Devonian represents an important episode in plant life history, which was marked by the diversification of land plants. Unfortunately, remains of early Devonian plants in the Iberian Peninsula are scarce. In the present paper, we describe a small assemblage of early land plants from the Lochkovian (Lower Devonian) of the Teruel Province in Spain. The main element consists of Taeniocrada-like sterile stems that are predominandy dichotomous and ribbon-like with a narrow central strand. An unidentified fossil formed by dichotomous axes together with an uncertain globular structure were also observed. This finding increases our knowledge of the palaeogeographical distribution…
Taphonomical peculiarities and formation conditions of Baltic Devonian vertebrate fossil assemblages
2013
Devona mugurkaulnieku atrodņu tafonomiskais raksturojums un veidošanās apstākļi dienvidaustrumu Baltijā Pirmo reizi paleontoloģisko pētījumu vēsturē Baltijā ir veikta detalizēta Živetas, Franas un Famenas mugurkaulnieku atrodņu tafonomisko īpašību analīze, izmantojot mūsdienu metodiku. Savā starpā ir salīdzinātas vidējā un augšējā devona oriktocenozes Latvijas teritorijā, bet Baltijas (Galvenā devona lauka) fosiliju atrodnes ir salīdzinātas ar sakopojumiem Dienvidu Timanā. Ir secināts, ka, neskatoties uz tafonomisko pazīmju atšķirībām, Franas un Famenas klastiskās slāņkopas, kā arī vidus- un augšdevona mugurkaulnieku sakopojumu veidošanās mehānismi Baltijā ir bijuši visai līdzīgi. Ir noteik…
Palaeozoogeographical connections of the Devonian vertebrate communities of the Baltica Province. Part II. Late Devonian
2010
Abstract Late Devonian vertebrate communities within the Baltica zoogeographical Province are analysed for intra- and interprovincial connections. Components within the category of provincial endemics are used to assign the communities to a particular zoogeographical province. Marine and continental, presumably freshwater types of vertebrate dispersal are outlined. During the Late Devonian marine dispersal is displayed by ptyctodonts, struniiforms, and some dipnoans, and continental dispersal by psammosteids, acanthodians, and some arthrodires. Isolation of communities is reflected by predominance of local and provincial endemics; the majority of polydemics and cosmopolitans records wider c…
Timing of granitoid magmatism in the eastern mid-German crystalline rise
2001
Abstract The eastern parts of the mid-German crystalline rise (MGCR) are exposed in the Spessart, Ruhla and Kyffhauser crystalline complexes and known from boreholes in the region of Dessau. In this study we determined igneous formation ages of granitoid intrusives and orthogneisses from this part of the MGCR using the Pb/Pb single zircon dating technique. The intrusion ages of the granitoids range from ∼489 to ∼302 Ma (i.e. from lower Ordovician to upper Carboniferous). The grouping of these ages marks several distinct magmatic episodes during the Variscan orogeny, with a major peak at the end of the lower Carboniferous. We tentatively suggest the following geodynamic scenario for the orig…
Geochronology of the mid-German crystalline rise west of the River Rhine
1996
The mid-German crystalline rise has its westernmost exposures at the western margin of the Rhine graben in the southern Pfalz and the northern Alsace. The outcrops are made up of granitoid rocks and minor volcano-sedimentary sequences. Radiometric ages obtained by U/Pb, Pb/Pb, Sm/Nd and Rb/Sr analyses of the igneous rocks from this area range from ∼433 to ∼325 Ma thus covering a time span from the Silurian to the end of the lower Carboniferous. Because the investigated rocks are — according to their chemical composition — largely related to subduction zone environments, the following three geodynamical scenarios are postulated, always taking subduction of oceanic crust beneath the mid-Germa…
Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Ahnet and Mouydir basins, Central Saha…
2018
Abstract. The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The structural framework of the platform results from the accretion of Archean and Proterozoic terranes during the Pan-African orogeny (750–580 Ma). The Ahnet and Mouydir basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches, bounded by inherited Precambrian sub-vertical fault systems which were repeatedly reactivated or inverted during the Paleozoic. Major unconformities are related to several tectonic events …