Search results for "Ordovician"
showing 10 items of 50 documents
Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations
2022
Abstract The Ordovician (∼487 to 443 Ma) ended with the formation of extensive Southern Hemisphere ice sheets, known as the Hirnantian glaciation, and the second largest mass extinction in Earth History. It was followed by the Silurian (∼443 to 419 Ma), one of the most climatically unstable periods of the Phanerozoic as evidenced by several large scale ( > 5 ‰ ) carbon isotope (δ13C) perturbations associated with further extinction events. Despite several decades of research, the cause of these environmental instabilities remains enigmatic. Here, we provide osmium (187Os/188Os) and lithium (δ7Li) isotope measurements of marine sedimentary rocks that cover four Silurian δ13C excursions. Osmi…
Student Author of the Year Award 2009
2009
The ‘‘Student author of the Year Award’’ is made for an outstanding paper in which an undergraduate or graduate student played a key role in the research and publication. The recipient of this award for 2009 is Ruben Diez Fernandez for his contribution, co-authored with Jose R. Martinez Catalan 3D Analysis of an Ordovician igneous ensemble: A complex magmatic structure hidden in a polydeformed allochthonous Variscan unit Journal of Structural Geology, Volume 31, Issue 3, March 2009, Pages 222–236. The Editors have selected this paper out of many student submissions in 2009. The basis of this paper is detailed field mapping, metamorphic petrology and structural analysis. These clearly establ…
Evolution of Cambrian and Early Ordovician arcs in the Kyrgyz North Tianshan: Insights from U-Pb zircon ages and geochemical data
2019
Abstract Geochronological, geochemical, and structural studies of magmatic and metamorphic complexes within the Kyrgyz North Tianshan (NTS) revealed an extensive area of early Palaeozoic magmatism with an age range of 540–475 Ma. During the first episode at 540–510 Ma, magmatism likely occurred in an intraplate setting within the NTS microcontinent and in an oceanic arc setting within the Kyrgyz-Terskey zone in the south. During the second episode at 500–475 Ma, the entire NTS represented an arc system. These two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature, which led to obduction of ophiolites from the Kyrgyz-Terskey zone onto the microcont…
The trace fossil gyrochorte: ethology and paleoecology
2021
Specimens of the trace fossil Gyrochorte from the Ordovician, Jurassic and Cretaceous of Utah, and the Pliocene of Spain are described. These occurrences expand the stratigraphic range of the ichnogenus, and allow for a reexamination of this paleoenvironmentally sensitive and puzzling trace fossil. The recognition of the penetrative characteristic of the trace is essential for a correct identification, as some trace fossils have been erroneously ascribed to Gyrochorte in the past. The producer must have been a detritus-feeding worm-like animal, probably an annelid, that created a bilobed, vertically penetrating and sometimes plaited meandering trace. Gyrochorte typically occurs in sandy f…
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…
<p class="HeadingRunIn"><strong>Reinterpretation of the enigmatic Ordovician genus <em>Bolboporites </em>(Echinodermata)</…
2019
Bolboporites is an enigmatic Ordovician cone-shaped fossil, the precise nature and systematic affinities of which have been controversial over almost two centuries. For the first time, a wide range of techniques (CT-scan, SEM, cathodoluminescence, XPL, UV epifluorescence, EBSD, FT-IR and XRF spectrometry) were applied to well-preserved specimens of Bolboporites from Norway and Russia. Our main finding confirms its echinoderm affinities, as shown by its stereomic microstructure and by the first definitive evidence of its monocrystalline nature. Each cone consists in a single, microporous calcitic crystal with a narrow longitudinal internal canal. These results are combined with all previous …
New trepostomate bryozoans from the Upper Ordovician of Morocco and the temperature influence on zooid size
2015
AbstractNew Upper Ordovician trepostomate bryozoans from the eastern Anti-Atlas of Morocco have been identified. They have been collected from the lower and intermediate units of the Khabt-el-Hajar Formation, late Katian in age, representing, respectively, bryozoan-pelmatozoan meadows with siliciclastic input, degraded by wave activity in a mid-ramp setting, and outer-ramp environments with marly substrates. Ten species of the generaCyphotrypa,Calloporella,Diplotrypa,Parvohallopora,Dekayia, andAostiporaare described. Of them, three species are new:Cyphotrypa regularisJiménez-Sánchez,Parvohallopora cystataJiménez-Sánchez, andAostipora elongataJiménez-Sánchez. Univariate statistical analyses …
LATEST CAMBRIAN CORNUTES (ECHINODERMATA: STYLOPHORA) FROM THE TAEBAEKSAN BASIN, KOREA
2005
The oldest echinoderms and first cornute stylophorans ever reported from Korea are described, based on more than 40 specimens collected from the Late Cambrian of the Taebaeksan Basin. New material doubles the number of stylophorans described from Asia and the number of specimens of Late Cambrian stylophorans recorded throughout the world. Three different cornutes are identified: Sokkaejaecystis serrata n. gen. and sp. and two genus and species indeterminate forms A and B. Sokkaejaecystis serrata and indeterminate form B are assigned to the Chauvelicystinae, while the systematic position of indeterminate form A within cornutes is difficult to assess. This new material suggests paleobiogeogra…
Morphometric analysis of Tremadocian (earliest Ordovician) kirkocystid mitrates (Echinodermata, Stylophora) from the Taebaeksan Basin, Korea
2004
Abstract Abundant isolated remains of stylophoran echinoderms (cornutes and mitrates) are reported for the first time in the late Tremadocian (Asaphellus Zone) Tumugol Formation of Korea. Mitrate remains include numerous adorals of Kirkocystidae. Several new important anatomical features have been observed on these adorals, as an internal calcitic layer that is associated to s2 and possibly also to the palmar complex. This observation suggests that the palmar complex would be present not only in mitrocystitid mitrates, but also in peltocystitids. For the first time, several morphometric analyses have been undertaken based on isolated kirkocystid adorals, so as to explore the morphological d…
Sedimentation in the Kandi extensional basin (Benin and Niger): fluvial and marine deposits related to the Late Ordovician deglaciation in West Africa
2003
Abstract The Lower Paleozoic detrital succession of the half-graben Kandi Basin in West Africa (Niger-Benin) is about 600 m thick and rests unconformably on the Pan-African basement. Along the western edge of the basin, the base of the succession locally features large glacial fault-bounded paleovalleys. These valleys are filled by the lowermost continental deposits of the Were Formation characterized by massive diamictites with dropstones, and coarse to conglomeratic sandstones associated with large-scale channel structures and internal erosional truncations. The uppermost braided-river deposits of the Were Formation deposited across the entire basin are overlain by the Late Ordovician–Ear…