Enrique Villas

High‐latitude pelmatozoan–bryozoan mud‐mounds from the late Ordovician northern Gondwana platform

Mud-mound complexes identified within the early to middle Ashgill Cystoid Limestone Formation of northeastern Spain are the first fossil build-ups to be described in the high latitude north-facing margin of Gondwana. Mud-mound complexes comprise individual lenticular mounds (composed of floatstones, cephalopod-rich mudstones and cementstones), flanks and intermound deposits (including pelmatozoan packstones and floatstones). The small mounds are mainly composed of bryozoans, cystoids and crinoids, and were developed on outer ramp environments. Mound initiation depended upon the stabilization and colonization of densely packed lenses of pelmatozoan-rich sediments. In a mid-ramp setting, pelmatozoan–bryozoan meadows were episodically degraded by common wave- and storm-induced processes, the development of semi-consolidated substrates, and the periodic influx of terrigenous material. Finally, during the Hirnantian regression, the Iberian mixed (carbonate–siliciclastic) platform was exposed to subaerial conditions sufficiently for erosion and karstification to occur. From a palaeogeographical point of view, the pattern of the Ashgill Iberian platform deposition is characterized by episodic exclusion of carbonates from most nearshore environments by a shoreline source of siliciclastic sediments. A similar interpretation to that made on the Iberian Cystoid Limestone Formation, in terms of gradual proximality–distality changes, is proposed for comparable facies types in Ashgill limestones described in southwestern Europe.

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

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 [omega]13C 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.

Chapter 11 Biodiversity, biogeography and phylogeography of Ordovician rhynchonelliform brachiopods

Abstract The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopods through the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) is characterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitude porambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblages mostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displays a steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoidea and Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician (Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmly installed the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response to an early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New clades rapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related to intense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the role of gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents. The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilized by the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the other hand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Biodiversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were disrupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying a more cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latest Katian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; possibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well established with especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun, regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas, anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts. Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667

Caradoc through Early AshgillBrachiopods from the Central-Iberian zone (Central Spain)

Abstract Caradoc through early Ashgill brachiopods from the Central-Iberian Zone, representing the latest cold water brachiopodassociations of the West European Platform developed on the North-African Gondwana margin, have been studied. Twenty one brachiopod taxa, including two new species ( Tafilaltia brevimusculosa and Hedstroemina almadenensis ), collected from stratigraphic sections in Corral de Calatrava, Almaden, Guadalupe and Valencia de Alcantara (Ciudad Real and Caceres provinces in Spain) are described and their stratigraphic significance is assessed. The oldest brachiopods studied, from the ironstone above the “ Neseuretus Sandstone” and the basal “Cantera Shales”, are considered coeval with those from the Soudleyan iron oolite widely spread in Ibero-Armorica. The youngest brachiopods have been collected from the uppermost “Bancos Mixtos” and the “ Calymenella Quartzite”, of Pusgillian age. All those associations are dominated by Mediterranean forms of the families Heterorthidae, Draboviidae, Orthostrophiinae and Aegiromeninae, but the highest horizons of the “Bancos Mixtos” have also yielded rare occurrences of forms more typical of the northern temperate continents (Strophomenidae, Sowerbyellinae, Leptestiidae) within a typically Mediterranean association. Those northern forms are considered to represent a first pulse of immigration, occurring shortly before the environmental turnover that promoted the final replacement of the cold waters associations by the Nicolella Community across the West European Platform.

The Upper Tremadoc fauna from Vogtendorf and the Bavarian Ordovician of the Frankenwald (Germany)

The description of the Upper Tremadocian fauna from Vogtendorf is used as an opportunity to replace the provisional term ‘Randschiefer-Serie’ of the Bavarian Ordovician of the Frankenwald by the terms Vogtendorf Formation for the lower part with a predominance of volcanic rocks and Gösmes Formation for the upper part in which sediments predominate. The Vogtendorf fauna comprises articulate and inarticulate brachiopods, a paragastropod, trilobites and cystoids. New species arePoramborthis vonhorstigi n. sp.,Ranorthis franconica n. sp.,Parapilekia vogtendorfensis n. sp.,Agerina alkleini n. sp.,Macrocystella greilingi n. sp. andEchinosphaerites henkleini n. sp. Lithology and biofacies indicate shallow marine conditions. The fauna is dominated by Mediterranean elements, but shows relations to Baltica. Closely comparable faunal associations and the joint occurrence ofKvania kvanica (Mergl 1984) are evidence of a correlation in age with the Milina Formation of Bohemia and of a close biogeographical relationship of the Bavarian type of facies with the Barrandian during the Lower Ordovician. Further,Euloma ornatumAngelin 1854 allows direct correlation of the Vogtendorf Formation and indirect correlation of the Milina Formation with the late Tremadocian (Shumardia pusilla Zone of the Alum Shale Formation and the Bjørkåsholmen Formation) of Scandinavia. The absence of any species of the Mílina and Vogtendorf faunas in the Leimitz Shales excludes even a partial correlation in age.KurzfassungDie hier beschriebene Fauna aus artikulaten und inartikulaten Brachiopoden, einem Paragastropoden, Trilobiten und Cystoideen gehört ins Ober-Tremadoc und ist damit eindeutig älter als die mit Conodonten als Arenig-Llandeilo? datierten vorherrschenden Sedimente der ‚Randschiefer-Serie‘. Es ist daher vernünftig, den 1964 eingeführten Begriff Vogtendorf-Schichten auf den unteren, vorherrschend vulkanischen Teil der Randschiefer-Serie auszudehnen und für den vorherrschend sedimentären höheren Teil der Randschiefer-Serie die neue Bezeichnung Gösmes-Schichten zu verwenden. Neue Arten sindPoramborthis vonhorstigi n. sp.,Ranorthis franconica n. sp.,Parapilekia vogtendorfensis n. sp.,Agerina alkleini n. sp.,Macrocystella greilingi n. sp. undEchinosphaerites henkleini n. sp. Lithologie und Biofazies weisen auf ein Flachwassermilieu hin. Die Fauna enthält überwiegend mediterrane Elemente, zeigt aber auch deutliche Beziehungen zu Baltica. Die weitgehende Übereinstimmung der Gattungen, sowie das gemeinsame Vorkommen vonKvania kvanica (Mergl 1984), beweisen eine altersmäßige Korrelation mit der Milina Formation Böhmens und deuten auf enge paläogeographische Beziehungen der Bayerischen Fazies mit dem Barrandium im Unterordovizium hin.Euloma ornatumAngelin 1854 erlaubt eine direkte Korrelation der Vogtendorf-Schichten und damit auch eine indirekte Korrelation der Mílina Formation mit dem höheren Tremadoc (Shumardia pusilla Zone der Alum Shale Formation und der Bjørkåsholmen Formation) Skandinaviens. Das völlige Fehlen von Arten der Mílina- und Vogtendorf-Fauna in den Leimitz-Schiefern spricht auch gegen eine teilweise Korrelation.

Foliomena Fauna (Brachiopoda) from the Upper Ordovician of Sardinia

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.

First record of a Hirnantia Fauna from Spain, and its contribution to the Late Ordovician palaeogeography of northern Gondwana

A new occurrence of the Hirnantia brachiopod fauna is documented from the Criadero Quartzite of Almaden, Ciudad Real Province, Spain. This unit is the regional development of a largely unfossiliferous sandy facies that frequently overlies the typical Late Ordovician diamictitic glaciomarine formations in the Iberian Peninsula and the Armorican Massif. The new occurrence establishes palaeontologically the latest Ashgill age of the quartzite, at least for its lowest horizons, and adds new data on a fauna that, although widespread, has been very rarely documented from peri-Gondwanan Europe. The new collection contains only Hirnantia sagittifera and Plectothyrella crassicosta chauveli . The subspecific status of the latter and its inclusion within Plectothyrella crassicosta is discussed herein, based on the continuous variation in rib thickness of several samples of both forms. The extremely low diversity and the occurrence of the key form P. c. chauveli , are both typical of the Bani Province that developed on the subpolar margins of Gondwana. This contrasts with other occurrences of the Hirnantia Fauna in peri-Gondwanan Europe, such as those from Sardinia and the Carnic Alps, which are characteristic of the more temperate Kosov Province.

Orthid brachiopods from the Middle Ordovician of the Central Iberian Zone, Spain

The present study of a large collection of orthid brachiopods from Middle Ordovician (middle Darriwilian) strata of Spanish regions of the Central Iberian Zone of the Iberian Massif, as well as the type collection of Portuguese species from the same Zone, revealed the occurrence of five genera of the family Orthidae, two of them new, and to which most of the seven previously reported species of Orthis from the same areas can be assigned. Besides the two new genera and species Almadenorthis auriculata Reyes-Abril and Villas gen. et sp. nov., and Gutiorthis incurvata Reyes-Abril and Villas gen. et sp. nov., three further new species are erected: Paralenorthis estenaensis Reyes-Abril and Villas sp. nov., Paralenorthis lolae Reyes-Abril and Villas sp. nov., and Sivorthis calatravaensis Reyes-Abril and Villas sp. nov. Paralenorthis alata and Orthambonites sp. are also identified in the same beds. Orthis noctilio is ascribed to the genus Sivorthis, and the species Orthis lusitanica and Orthis miniensis are restricted to only their type specimens. Orthis duriensis is poorly described and illustrated, its type material missing, and actually it may belong to Sivorthis noctilio. These brachiopod taxa invaded the cold waters of the Afro-South European Gondwanan margin from lower latitudes, coincident with the mid Darriwilian transgression, as they belonged to a family that diversified in temperate and tropical seas during the early Mid Ordovician.

BRACHIOPODS FROM VOLCANOCLASTIC MIDDLE AND UPPER ORDOVICIAN OF ASTURIAS (NORTHERN SPAIN)

In the El Castro Formation, cropping out on the Asturian coast of northern Spain, two fossiliferous horizons have been studied. Above the basal one, containing the Llandeilian brachiopods Tissintia cf. T. convergens and Howellites? sp., a new horizon of estimated Ashgillian age has been identified that has yielded the new brachiopod species Mcewanella vulcanica and Hesperinia asturica. The new species of Mcewanella, close to the Irish Rawtheyan Mcewanella dorsisulcata, is characterized by a great delay of the insertion of costellae, which gives many adults a strikingly costate ornament for this genus. Hesperinia was, up to now, poorly known from a small number of specimens from the Llanvirnian Tank Hill Formation in Nevada; thus, the new record, besides allowing a better understanding of the genus and its relationship with other oepikinids, extends its known time span to the Late Ordovician. These two species were dwellers on a low-energy bottom formed of loose sand and gravel supplied by nearby volcanic eruptions. The ash-flow depositional pattern of these sediments would have had lethal effects on the brachiopod communities, periodically causing their destruction. These species of the genera Mcewanella and Hesperinia are new representatives of the immigration of North American and Northern European warm-water faunas into the circumpolar Mediterranean Province during

Lingulate brachiopods from the Lampazar Formation (late Cambrian) of the Cordillera Oriental of northwestern Argentina

Abstract The Angosto de Lampazar, a classic locality for the study of lower Paleozoic successions in the Cordillera Oriental, NW Argentina, has yielded a late Cambrian relatively diverse, lingulate brachiopod fauna. Sandy lenses with calcareous cement from the uppermost levels of the Lampazar Formation have yielded abundant remains of articulate and phosphatic brachiopods. Among the latter, the new species Eurytreta harringtoni Mergl and Herrera, Lingulella? melonica Mergl and Herrera, Libecoviella lenticularis Mergl and Herrera, and Schizambon cardonalis Mergl and Herrera, as well as the new genus and species Saltaia lampazarensis Mergl and Herrera are formally introduced. Trilobites and conodonts from the same horizons characterize the Cordylodus proavus Zone, allowing a correlation with Stage 10 of the Furongian Series. Although the information on lingulate brachiopods from the C. proavus Zone is scarce across the world, the composition of the studied association displays a relationship with coeval and slightly younger faunas of Utah and Kazakhstan. The Argentine brachiopods, the first described from the late Cambrian Proto-Andean margin of Gondwana, are more closely related to temperate Laurentian faunas than to those from the high latitude North African margin of Gondwana.