Search

The Sommerodde positive organic carbon isotope excursion (SOCIE) within the Oktavites spiralis graptolite Biozone (Telychian, Silurian) was first identified in the Sommerodde-1 core, Bornholm, Denmark, where it is the largest positive excursion within the Upper Ordovician–lower Silurian part of the core. Other published occurrences of the SOCIE are discussed here, including new δ 13Corg data from the Jabalón River section, Corral de Calatrava, central Spain, where the SOCIE is only a very minor positive excursion. Very unusually, the SOCIE is best developed in deeper water settings, contrary to the typical pattern of declining excursion magnitude offshore. In the Sommerodde-1 core (Bornholm), and where it has been tentatively identified in the Vežaičiai-2 core (Lithuania), the SOCIE is developed in pale, organic-poor mudstones. It is considered likely that the magnitude of the SOCIE has been enhanced in the Sommerodde-1 core record by a change in organic matter composition in the deep-marine environment that did not have such a significant effect in shallower marine environments. Supplementary material: A table of organic carbon isotope data from the Jabalón River section, Corral de Calatrava, central Spain is available at https://doi.org/10.6084/m9.figshare.c.6769514 Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system [ABSTRACT FROM AUTHOR]

The present-day distribution of the Ossa-Morena, Central Iberian, West Asturian-Leonese, and Cantabrian tectono-metamorphic Zones resulted from the complex Variscan evolution, juxtaposing along the Eurasian margin domains formerly located at the Gondwana margin in Early Palaeozoic times. Characterized by mainly thick detrital Cambrian and/or Ordovician sediments, all four regions with their different sedimentary evolution indicate specific emplacements along the Gondwana margin. The elaboration of tectonic subsidence curves for each region and their comparison during the Cambrian, result in a time-space relationship characterized by the following stages: Late Proterozoic to Early Cambrian Cadomian active margin setting (Ossa-Morena and Central Iberian Zones), potential accretion to Gondwana; since the Early Cambrian extending continental crust, leading to an initial subsidence in the Ossa-Morena Zone and to a strong subsidence in the West Asturian-Leonese Zone lasting until the Late Cambrian, related to the opening of the Prototethys. A new pulse of subsidence is recorded since the Arenigian, during the deposition of the "Armorican Quartzite" in the Central Iberian Zone, which is thought to represent a rim-basin forming behind the shoulder of the opening Rheic Ocean. The moderate subsidence in the Cantabrian Zone could be the expression of its evolution of a hinterland between the two passive margins. GermanDie heutige Zonengliederung des Iberischen Massivs in die Südportugiesische, Ossa-Morena, Zentraliberische, Westasturisch-Leonesische und Kantabrische Zone ist Folge einer komplexen variszischen Entwicklung, die verschiedene frühpaläozoische Kontinentaleinheiten des ehemaligen Gondwanarandes am Südrand von Eurasien zusammenführte. Durch eine mächtige detritische Entwicklung während des Kambriums und Ordoviziums charakterisiert, zeigen alle der vier letztgenannten Blöcke unterschiedliche Sedimentationsbedingungen und damit unterschiedliche Ablagerungsbedingungen am Gondwanarand an. Die Sedimentation ist in allen vier Gebieten durch spezifische tektonische Subsidenzkurven charakterisiert, und es lassen sich für die Zeit des Kambriums und Ordoviziums folgende plattentektonische Entwicklungsabschnitte unterscheiden: neoproterozoisch bis frühkambrischer aktiver Plattenrand (Ossa-Morena und Zentraliberische Zonen) und mögliche Akkretion an den Gondwanarand; seit dem Unterkambrium Dehnung der kontinentalen Kruste mit initialer Subsidenz in der OssaMorena Zone, und mit starker Subsidenz im Bereich der Westasturisch-Leonesischen Zone bis zum oberen Kambrium im Zusammenhang mit der Öffnung der Prototethys. Mit der Ablagerung des Armorikanischen Quarzits seit dem Arenig wird in der Zentraliberischen Zone eine neue Subsidenzphase erkennbar, die auf eine ,,Rim-Basin" Situation hinter der Riftschulter des sich öffnenden Rheischen Ozeans gedeutet werden kann. Die relativ geringen Subsidenzraten in der Kantabrischen Zone könnten Ausdruck einer Entwicklung zwischen zwei passiven Rändern im Hinterland des Riftsystems sein. SpanishLa distribución actual de las Zonas tectonometamórficas Cantábrica, Asturoccidental-Leonesa, Centroibérica y Ossa-Morena es el resultado de una compleja evolución que yuxtapuso, durante la deformación varisca, dominios emplazados en distintos lugares del margen de Gondwana durante el Paleozoico Inferior. La diferente evolución sedimentaria de estas cuatro regiones, caracterizadas principalmente por su potente sedimentación detrítica durante el Cámbrico-Ordovícico, indica un emplazamiento específico para cada una de ellas dentro del margen gondwánico. La reconstrucción de las curvas de subsidencia tectónica de cada zona y su comparación den-tro del marco de la evolución cambro-ordovícica perigondwánica, permite distinguir varias etapas en sus relaciones espacio-temporales. Así, en la primera (Neoproterozoico-Cámbrico inicial), un margen activo sobre corteza de tipo cadomiense se desarrollaba en la periferia de Gondwana (Zonas de Ossa-Morena y Centroibérica). La segunda etapa supuso la extensión de dicha corteza entre el Cámbrico Inferior a Superior, con subsidencia incipiente en Ossa-Morena, y fuerte subsidencia en la Zona Asturoccidental-Leonesa. Finalmente y a partir del Arenigiense, se registra un nuevo pulso subsidente en la Zona Centroibérica, ligado al depósito de la Cuarcita Armoricana, lo que permite interpretarla como una cuenca marginal ("rim basin") a espaldas del borde sobreelevado ("shoulder") creado en la apertura del Océano Rheico. La subsidencia moderada durante esta época en la Zona Cantábrica puede ser el resultado de su evolución como un traspaís ("hinterland") situado entre dos márgenes pasivos.

Aus Tonschiefern des Mittel- und Oberordovizium der Zentral-Iberischen Zone (Provinzen Toledo, Ciudad Real und Cáceres, Spanien) werden vier neue Arten von mitrocystitiden Mitraten beschrieben. Eine neue Rekonstruktion von Ovocarpus moncereti aus dem Mittel-Arenig der Montagne Noire, die auf gut erhaltenen Exemplaren von der Typuslokalität beruht, wird vorgestellt. Ovocarpus wird zum ersten Male von der Iberischen Halbinsel erwähnt; das neue Spanische Material ist das jüngste bekannte Vorkommen der Gattung. Eine Neubearbeitung eines früher als Mitrocystites? sp. (= Mitrocystitida gen. et sp. indet. 1) beschriebenen Exemplares hat ergeben, dass es sich vermutlich um eine Übergangsform zwischen Mitrocystites und Promitrocystites handelt. Ein weiteres unvollständiges Exemplar, das als Mitrocystitida gen. et sp. indet. 2 bestimmt wurde, entspricht vermutlich einer neuen Gattung und einer Zwischenform zwischen primitiven Mitrocystitiden (Mitrocystites, Promitrocystites) und Anomalocystitiden. Weiterhin wird mit Barrandeocarpus sp. zum ersten Mal eine Stylophore aus dem Hirnantium von SW-Europa nachgewiesen. Es handelt sich dabei um eines der seltenen Fossilien aus den zwischengelagerten Quarziten der Fazies der 'pelites with fragments' (Lederschiefer), die mit der oberordovizischen Gondwana-Vereisung zusammenhängt.

Limestones from the Silurian succession of the Moncorvo synclinorium (NW Central Iberian Zone, Portugal) have yielded, in two distinct localities, the first Portuguese Silurian conodonts. In the first locality, Kockelella cf. variabilis, K. cf. absidata, Ozarkodina confluens, Oz. excavata and Pseudooneotodus beckmanni indicate the Ludlow s.l. (or also possibly the late or latest Wenlock). In the second, Oulodus elegans, O. cf. cristagalli and Ozarkodina ex gr. remscheidensis indicate a Pridolian age, which is confirmed by the presence, in the same level, of cirrus-type loboliths of scyphocrinoids. Graptolites from the black-shales with nodules that underlie the limestones indicate the existence of Llandovery (Aeronian to Telychian) and Wenlock deposits. The Silurian succession from Moncorvo thus appears as a condensed sequence, especially similar to those of the Ossa Morena Zone, Sardinia and parts of North Africa. These successions clearly differ from those which characterize the central and southern parts of the Central Iberian Zone, where shallow-water uppermost Silurian deposits are much thicker and comprise abundant coarser terrigenous material. These data suggest that, during the Silurian, the northwestern part of the Iberian Peninsula (including part of the West Asturian-Leonese Zone) belonged to a special paleogeographic domain with deeper distal shelf characteristics.

A fourth occurrence of Caradoc diplograptaceans in the French Armorican Massif is recorded from the uppermost part of the Schistes d'Angers Formation. Three-dimensional graptolite molds preserved in nodules apparently belong to one (or ?two) different taxa, whose overall morphology and dimensions suggest an affinity with the Climacograptus antiquus group (resembling C. antiquus lineatus), and with some Bohemian taxa (C. tectus), respectively. The new data evidence a close correlation with a similar horizon occurring in the Kermeur Formation of the Crozon Peninsula, and suggest the existence of a probable stratigraphic gap within the upper part of the Schistes d'Angers.

A new rostroconch mollusk (Tolmachovia babini nov. sp.) is described from the early MiddleOrdovician shales of Central Spain. It can be distinguished from other technophorids by its prominent concentric ornament and by the absence of traces of radial elements on both surfaces of the conch. The species could have arised from a similar form, which lacks radial ornament, known from the Argentine Lower Ordovician, and whose SW European derivatives probably represent inmigrants arrived crossing the perigondwanan shelf. A brief analysis of previous references on Ordovician ribeirioids from north and northwestern Gondwana is also presented.

Within the Lower Ordovician of SW Europe, lingulid beds are frequently recorded in the uppermost part of the Armorican Quartzite Formation or at the base of the overlying unit of dark shales. They have a broad geographical extension, particularly in the Hesperian and Armorican Massifs. The lingulid horizons occur within littoral fine to medium sands deposited on flat and relatively stable areas, without tide, however under storm influence. The large lingulids which characterize these facies were living in conditions similar to those of the extant lingulides. Two types of lingulid beds are described. Type A forms lags with lamination, from some millimetres to several centimetres thick, at the base of or within quartzo-sandstone strata. It originated through sedimentary floods of coarse particles, probably transported by rivers during periods of heavy rains which also induced large salinity decreases. Type B, the most common, consists of conglomeratic coquinoid beds, associated with sandstone and quartzitic layers, containing phosphatic and sideritic pebbles and heavy minerals, embedded in a matrix with a huge concentration of fragments of lingulid valves and sometimes of some other fossils, i.e. bivalves and microarthropods. The coquinas are related to erosive discontinuities at the base of sandstone sequences with hummocky cross stratification. They originated during very short catastrophic events which induced unconformable deposits of valve fragments in the littoral zone. Most of the most widespread beds of type B were probably deposited during hurricanes or tsunamis, the latter related to explosive volcanism on the perigondwanan shallow shelves. Numerous evidences of acid volcanism of explosive type at the end of the Arenig are documented in the upper part of the Armorican Quartzite in the Iberian Peninsula. Nevertheless, at least one of the thickest deposits of type B does not belong to a tempestite but could have formed through a coastal upwelling of phosphate-rich waters in which large lingulid populations could develop.