Enrique Villas

Universidad de Zaragoza

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J. C. Gutiérrez-Marco

Universidad Complutense de Madrid

Jorge Colmenar

Instituto Geológico y Minero de España

Isabel Rábano

Instituto Geológico y Minero de España

Andrea Jiménez-Sánchez

Centre de Géosciences

Zarela A. Herrera

Universidad de Zaragoza

Emmanuelle Vennin

Université de Bourgogne

Jaime Reyes-Abril

Instituto de Geociencias

J. Javier Álvaro

Instituto de Geociencias

Enrique Bernárdez

Instituto Superior de Investigaciones Biológicas

David A. T. Harper

Durham University

Cooperative Institutions

Universidad de Zaragoza

Universidad Complutense de Madrid

Universitat de València

Instituto Geológico y Minero de España

Consejo Nacional de Investigaciones Científicas y Técnicas

Instituto de Geociencias

Universidad de Oviedo

Centre National de la Recherche Scientifique

Natural History Museum

Consejo Superior de Investigaciones Científicas

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The late Ordovician carbonate sedimentation as a major triggering factor of the Hirnantian glaciation

BSGF – Earth Sciences Bulletin (2002)

Enrique Villas Emmanuelle Vennin J. Javier Álvaro W. Hammann Zarela A. Herrera

Abstract A new approach explaining the main forcing factor of Hirnantian glaciation is proposed herein. It follows the models associating occurrences of continental glaciations with periods of low atmospheric CO2 levels. The accumulation of great volumes of carbonates during pre-Hirnantian late Ordovician, in regions where these deposits were previously absent, is suggested as a major sink of atmospheric CO2. This would have caused an important lowering of the average temperature in the early Hirnantian, after CO2 values had attained a certain threshold. This process was maintained by other positive feedbacks, such as the short-term carbonate weathering CO2 sink. An increase of the direct flux of CO2 from the atmosphere to the oceans by means of dissolution would have been driven by the enhancement of carbonate deposition. The great inundation of the low latitude Laurentia craton during Cincinnatian times and the establishment of a temperate-water carbonate sedimentation on the North Gondwana margin during pre-Hirnantian Ashgill allowed the burying of more than 840 × 1015 kg (1.9 × 1019 mol) of dissolved CO2. This mass is equivalent to nearly 350 times the present values of atmospheric CO2. This is important enough to have greatly altered the equilibrium between the CO2 dissolved in the oceans and the partial pressure of CO2 in the air, eventually causing an important reduction of the latter. The new model also offers a simple explanation for the end of the glaciation after a short time-span. Glacioeustatic lowering of the sea level, concomitant with the glaciation, would have stopped the extra-sedimentation of carbonate due to the retreat of the oceans from the platforms, closing this CO2 sink. Pre-glacial CO2 levels would then recover, due to volcanic and metamorphic CO2 outgassing. After subsequent melting of the ice cap, oceanic circulation did not recover pre-Hirnantian Ashgill strength, resulting in a strong stratification of ocean waters and precluding the recovery of an extensive carbonate deposition. The well-known positive shift in the δ13C at the base of the Hirnantian is assumed to have been caused by weathering and dissolution of carbonates, relatively enriched in 13C, during the glacioeustatic regression and exposure of the platforms.

Sink (geography)

10.2113/173.6.569

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New bryozoans from the Upper Ordovician of Morocco and their place in the temperate-to-cool water Mediterranean Province

Bulletin of Geosciences (2016)

Andrea Jiménez-Sánchez Andrej Ernst Emmanuelle Vennin Enrique Villas

A new study of the Upper Ordovician bryozoans belonging to the families Aisenvergiidae, Amplexoporidae, Arthrostylidae, Enalloporidae, Halloporidae, Heterotrypidae, Mesotrypidae, Ptilodictyidae, Rhinidictyidae and Trematoporidae from the eastern Anti-Atlas of Morocco is presented here.These bryozoans come from the calcarenitic levels of the Khabt-el-Hajar Formation, upper Katian, where for the first time the orders Fenestrata and Cryptostomata are described in this formation.This fauna inhabited an upper offshore environment and represent high-energy deposits, typical of a shore face environment, as well as storm-induced deposits.A total of 15 species included in 13 genera, 10 of them only identified in the calcarenitic levels of the Khabt-el-Hajar Formation, and two incertae sedis taxa are described.A new species, Trematopora vesiculata, is defined.An update of the Upper Ordovician bryozoan presence/absence database, including the 22 genera described in total in the Khabt-el-Hajar Formation, has been carried out.The augmented database has been analysed with two multivariate statistical techniques: detrended correspondence analysis (DCA) and principal coordinate analysis (PCO), in order to assess the palaeogeographic affinity of this fauna, and the results show that Moroccan bryozoans, in spite of belonging to the fauna developed in the highest latitudes during the upper Katian, have a clear Mediterranean affinity.•

10.3140/bull.geosci.1569

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Revisión bioestratigráfica de las pizarras del Ordovícico Medio en el noroeste de España (zonas Cantábrica, Asturoccidental-leonesa y Centroibérica septentrional)

Acta Geologica Hispanica (1999)

J. C. Gutiérrez-Marco C. Aramburu Milena Cecilia dos Santos Arbizu Enrique Bernárdez Matilde Peinado Rodríguez

La revision completa de mas de un centenar de localidades fosiliferas del Ordovicico Medio situadas en el noroeste del Macizo Hesperico, muestra que el deposito de las pizarras y limolitas oscuras (Formacion Luarca y equivalentes), que siguen a las cuarcitas del Arenig, no fue tan uniforme como se consideraba hasta ahora. Las pizarras se sedimentaron esencialmente durante el Oretaniense en la Zona Asturoccidental-Leonesa y en la parte septentrional de la Zona Centroiberica (Dominio del Ollo de Sapo), donde el techo de la unidad se situa muy proximo al limite Oretaniense / Dobrotiviense, sin existir ningun yacimiento paleontologico de probada edad dobrotiviense (= Llandeilo inferior en sentido clasico). En la Zona Cantabrica, la sedimentacion arcillosa se inicia en el Oretaniense superior tardio y prosigue durante el Dobrotiviense. Para el conjunto del area estudiada se caracterizan, o proponen, diversas lagunas estratigraficas de alcance local o regional, y se discuten las circunstancias paleogeograficas generadas por las hipotesis mas recientes, que son contrastadas a la luz de los nuevos datos paleoecologicos y paleobiogeograficos. Estos indican que la sedimentacion tuvo lugar en areas externas y abiertas de la plataforma, relativamente mas profundas que en la region surcentroiberica, con areas de surco donde ingresan elementos mesopelagicos. Desde el punto de vista paleontologico, se reconocieron un total de 97 formas distintas (67 especies presentes en el Oretaniense y 45 en el Dobrotiviense), entre las que destaca la primera aparicion conocida de determinadas especies de trilobites y ostracodos, el registro mas moderno de otros, y algunos taxones en comun con Avalonia y Baltica, desconocidos hasta el presente en otras areas del suroeste de Europa

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Ashgill bryozoans from the Iberian Chains (NE Spain) and their contribution to the Late Ordovician biodiversity peak in North Gondwana

Ameghiniana (2007)

Andrea Jiménez-Sánchez Nils Spjeldnæs Enrique Villas

Abstract. In the lower-middle Ashgill Cystoid Limestone Formation of the Iberian Chains (NE Spain) twenty one bryozoan genera have been identified, which belong to the four Stenolaemata orders that were already spread worldwide by the Mid Ordovician: Cryptostomata, Cyclostomata, Cystoporata and Trepostomata. Five of them: Cyclophaenopora Spjeldnaes, Glauconomella Bassler, Orbignyella Ulrich and Bassler, Phaenopora Hall and Pseudostictoporella Ross have been identified here for the first time in the Mediterranean Province. This list increases the number of bryozoan genera known to sixty six, making it the most diversified group in the region for that period. Resumen. BRIOZOOS DEL ASHGILL DE LAS CADENAS IBERICAS (NE ESPANA) Y SU CONTRIBUCION AL PICO DE BIODIVERSIDAD DEL ORDOVICICO SUPERIOR EN EL NORT EDE GONDWANA. En la Formacion Calizas de Cistideos, de edad Ashgill inferior-medio, de las Cadenas Ibericas (NE de Espana) se han identificados veintiun generos de briozoos pertenecientes a los cuatro ordenes Stenolaemata que ya se habian expandido a nivel mundial en el Ordovicico Medio: Cryptostomata, Cyclostomata, Cystoporata y Trepostomata. Cinco de ellos: Cyclophaenopora Spjeldnaes, Glauconomella Bassler, Orbignyella Ulrich y Bassler, Phaenopora Hall y Pseudostictoporella Ross son reconocidos por primera vez en la Provincia Mediterranea. Esta lista permite ampliar a sesenta y seis el numero de generos de briozoos conocidos alli, convirtiendolos en el grupo mas diversificado de la region para ese periodo.

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Brachiopods from the Upper Ordovician of Erfoud (eastern Anti-Atlas, Morocco) and the stratigraphic correlation of the bryozoan-rich Khabt-el Hajar Formation

Geological Society London Special Publications (2018)

Enrique Villas Jorge Colmenar

Abstract The Khabt-el-Hajar Formation, very rich in bryozoans and echinoderms but relatively poor in other fossil groups, has provided a brachiopod association that allows an improvement in the stratigraphic correlation of this Moroccan eastern Anti-Atlas unit with those from the Upper Ordovician of SW Europe and the rest of the Anti-Atlas. The intermediate marly beds, with bryozoan and echinoderm patches, of the Khabt-el-Hajar Formation have yielded Streptis ? sp., Paucicrura catalanica and Drabovia sp. Of these, P. catalanica , the richest in the association and known up to now exclusively from the Catalonian Coastal Ranges in NE Spain, is dated as mid to late Katian (Ka2–Ka4), since it occurs in the La Mora Slates, correlatable with horizons of that age from Iberia, Sardinia or the Montagne Noire. The analysis of the stratigraphic and palaeobiogeographical ranges of the bryozoans from the same formation agrees with the correlation above. The quartzitic sandstones that underlie the Khabt-el-Hajar Formation in the surroundings of Erfoud have yielded a different brachiopod association, including Kiaeromena ? chouberti and Rostricellula termieri among other forms more poorly represented. K. ? chouberti allows its yielding horizon to be dated as mid Katian (Ka2) and supports the identification of the sandstone-dominated unit where it occurs as the Tiouririne Formation.

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10.1144/sp485.2

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Citations (4)

Cronoestratigrafía del Ordovícico ibérico

Geotemas ( Madrid ) (2016)

J. C. Gutiérrez-Marco A.A. Sá Enrique Villas Enrique Bernárdez Jorge Colmenar

La nuevas divisiones de la escala global del Sistema Ordovicico, con excepcion de los pisos Tremadociense e Hirnantiense, son dificiles de aplicar en la Peninsula Iberica, pues sus estratotipos de limite radican en facies y faunas de aguas profundas, desconocidas en las plataformas someras y de paleolatitud elevada del ambito peri-gondwanico. Antes de ello, la escala regional britanico-avalonica fue utilizada en Iberia durante todo el siglo XX, pero presenta serios inconvenientes de correlacion vinculados con la propia evolucion, conceptual y de criterio, registrada en las areas tipo britanicas durante los ultimos 40 anos. Sin embargo, la escala regional bohemo-iberica es la que actualmente aporta una mayor precision a las correlaciones, pues se basa en elementos bioestratigraficos y biocronologicos de distribucion comun a todo el margen peri-gondwanico europeo y norteafricano, y la que mantiene vinculos episodicos con otras escalas regionales, que permitiran resolver progresivamente las equivalencias con la escala global.

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Braquiópodos Ordovícicos del Perú: revisión de antecedentes, diversidad y aspectos paleobiogeográficos

Instituto Geológico, Minero y Metalúrgico – INGEMMET (2010)

Enrique Villas J. C. Gutiérrez-Marco César Augusto Chacaltana Budiel Víctor Santiago Carlotto Caillaux José Dionicio Cárdenas Roque

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Foliomena Fauna (Brachiopoda) from the Upper Ordovician of Sardinia

Palaeontology (2002)

Enrique Villas W. Hammann David A. T. Harper

The late Ordovician brachiopod assemblage from Sardinia is one of the youngest members of the deep‐water Foliomena fauna and is characterized by the following core taxa: Christiania , Cyclospira , Dedzetina and Foliomena . The fauna also contains Epitomyonia , Leangella , Glyptorthis and Skenidioides , which are more typical of shallower‐water environments during the late Ordovician but occupied deeper‐water niches during the Silurian following the termination of the Foliomena fauna. The suprafamilial placement of the family Chrustenoporidae is discussed and the new species Dedzetina serpaglii and Leangella ( Leangella ) fecunda are established. In common with many mid‐Ashgill Foliomena faunas the Sardinian assemblage shows significant differences from other faunal developments of this type, reflecting its geographical position and shallower water conditions than those of the classic early Ashgill Foliomena faunas. The brachiopods occur with abundant trilobites belonging to a variant of the cyclopygid fauna. The faunas developed on part of a complex of microcontinents derived from peri‐Gondwana during the Ordovician.

Assemblage (archaeology)

10.1111/1475-4983.00237

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Rasgos estratigráficos de la sucesión del Ordovícico Superior en Portilla de Luna (Zona Cantábrica, noroeste de España)

Geogaceta (1996)

J. C. Gutiérrez-Marco Carlos E. Aramburú Miguel Arbizu I. Méndez-Bedia Isabel Rábano

Upper Ordovician rocks have been characterized for the first time in the Cantabrian Zone of the Hesperian Massif. The sequence consists of a lower siliciclastic unit of Caradoc-(‘basal Ashgill age developed as an alternation of shales, siltstones and sandstones, overlain by an upper unit of fossiliferous limestones with marly intercalations, of pre-Hirnantian (mainly Cautleyan-Rawtheyan) age. Ashgill fossils are fairly abundant in the limestone unit, and there have been identified brachiopods of the «Nicolella fauna», echinoderms of the «Heliocrinites fauna» and trilobites of the Qvalocephalus biofacies

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Informe preliminar sobre la presencia de trilobites hirnantienses (Ordovícico terminal) en las Pizarras de Orea de las Cadenas Hespéricas (NE de España)

Geotemas ( Madrid ) (2004)

Daniel Vizcaïno Enrique Villas Zarela A. Herrera José Javier Álvaro Blasco

Hirnantian trilobites have been recovered from the glaciomarine Orea Shales, in the Hesperian Chains of the Iberian Ranges (NE Spain). They occur in the lowermost strata of the unit, in poorly stratified, grey to black claystones lacking the quartz grains and pebbles typical of other outcrops of the formation. The trilobites have been collected in one locality from the Tremedal massif, which has yielded Mucronaspis mucronata. This species is pandemic and constitutes the most frequent trilobite of the Hirnantia fauna, although its origin is slightly earlier. The presence of trilobite fauna in this point may be related to the extremely fine-grained character of the Orea Shales by comparison with other areas where the input of coarser grained clasts has been recorded, and would represent hemipelagic deposition in the distal part of the Hesperian platform.

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Baltica

Hesperian

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