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The Anti-Atlas contains a thick, volcanic-free Ordovician succession that originally deposited in a passive-margin basin. Three main sedimentary packages are bounded by major unconformities: (i) the Tremadocian–Floian Lower Fezouata and Upper Fezouata formations, which unconformably overlie a palaeorelief of Cambrian rifting volcanosedimentary complexes, and are subsequently topped by a Dapingian para-conformable gap; (ii) the Darriwilian–Katian Tachilla Formation and First Bani and Ktaoua groups, the latter unconformably overlain by a Hirnantian glaciogenic succession; and (iii) the Second Bani Group, which subsequently infilled the former glaciogenic palaeorelief. Due to the scarcity of carbonate interbeds for etching analyses, leading to rare references of conodonts, the global Ordovician chart is interpolated on the basis of microphytoplancton (acritarchs and chitinozoans), regional graptolites and brachiopods. The Ordovician counter-clockwise rotation of Gondwana led its Moroccan margin from mid-to high-latitude positions, leading to the onset of a siliciclastic, wave-and storm-dominated platform. Flooding surfaces are marked by shelly silty carbonate interbeds that reflect the episodic development of echinoderm–bryozoan meadows during Katian times; in areas protected from siliciclastic input, they reached massive and bedded bioaccumulations (Khabt-el-Hajar Formation). The Hirnantian glaciation controlled the incision of numerous tunnel channels, infilled with both alluvial to fluvial sediments and glaciomarine diamictites. The Hirnantian palaeorelief was definitively sealed during Silurian times.

The western Iberian Chain of NE Spain represents a lateral prolongation of the West Asturian-Leonese Zone. As other proximal sectors fringing NW Gondwana, the chain comprises a con-formable and continuous Furongian-Tremadocian transition, comprising a thick (3600-4500 m) Lower Ordovician sedimentary succession, exclusively composed of siliciclastic strata and deposited in mid-latitude (temperate) waters. Although the shelly fossil record is not abundant, some key trilobites and brachiopods allow the identification of distinct biogeographic links with the Argentinian margin of West Gondwana, Oaxaca (Mexico), and the neighbouring Montagne Noire (France), with which a common biostratigraphic biozonation can be envisaged. Two phosphoritic interbeds rich in linguliformean brachiopods punctuate the Valconchán and Borrachón formations, and represent event beds related to condensation processes and sedimentation of explosive ignimbritic tuffs, respectively.

This study presents a new geochemical, petrological, and geochronological U–Pb dataset from Ediacaran metabasites of the Canigó and Cap de Creus massifs, Eastern Pyrenees. The rocks are composed of calcic amphibole + plagioclase + chlorite + epidote ± quartz plus titanite + apatite + ilmenite ± biotite ± rutile as accessory phases and show relict igneous textures. Peak pressure-temperature determinations share common conditions, ranging 452–482ºC and 5.2–7.7kbar. These intermediate P-T conditions suggest Barrovian-type metamorphism, most likely related to a collisional setting. The metabasites correspond to evolved basaltic rocks (Mg#<0.55) with moderate TiO2 content (up to 2.08wt.%) and relatively low Cr (43–416ppm). The rocks are moderately enriched in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) (average (La/Lu)n of 2.7) and the N-MORB normalized multi-element patterns show negative slopes, with prominent negative Nb anomalies ((Nb/La)NMORB=0.33–0.78). These variations are akin to island arc tholeiites generated in back-arc basins and to other metabasites described in the Eastern Pyrenees with a putative Ediacaran age, and they differ from the Ordovician tholeiitic metabasites from the Canigó massif, which derived from a contaminated E-MORB source. The positive ƐNd(T) values (0.82–3.05) of the studied metabasites preclude a notable contribution from an older continental crust. U-Pb dating (LA-ICP-MS) of one chlorite-rich schist sample in contact with the metabasites from the Canigó massif yielded a main peak at ca. 632Ma. We argue that the Cadomian metabasites from the Pyrenees formed during back-arc extension in the continental margin of Gondwana and were later affected by (probably early Variscan) medium-P metamorphism before the HT-LP metamorphism classically described in the Pyrenees

This study presents a new geochemical, petrological, and geochronological U–Pb dataset from Ediacaran metabasites of the Canigó and Cap de Creus massifs, Eastern Pyrenees. The rocks are composed of calcic amphibole + plagioclase + chlorite + epidote ± quartz plus titanite + apatite + ilmenite ± biotite ± rutile as accessory phases and show relict igneous textures. Peak pressure-temperature determinations share common conditions, ranging 452–482ºC and 5.2–7.7kbar. These intermediate P-T conditions suggest Barrovian-type metamorphism, most likely related to a collisional setting. The metabasites correspond to evolved basaltic rocks (Mg#<0.55) with moderate TiO2 content (up to 2.08wt.%) and relatively low Cr (43–416ppm). The rocks are moderately enriched in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) (average (La/Lu)n of 2.7) and the N-MORB normalized multi-element patterns show negative slopes, with prominent negative Nb anomalies ((Nb/La)NMORB=0.33–0.78). These variations are akin to island arc tholeiites generated in back-arc basins and to other metabasites described in the Eastern Pyrenees with a putative Ediacaran age, and they differ from the Ordovician tholeiitic metabasites from the Canigó massif, which derived from a contaminated E-MORB source. The positive ƐNd(T) values (0.82–3.05) of the studied metabasites preclude a notable contribution from an older continental crust. U-Pb dating (LA-ICP-MS) of one chlorite-rich schist sample in contact with the metabasites from the Canigó massif yielded a main peak at ca. 632Ma. We argue that the Cadomian metabasites from the Pyrenees formed during back-arc extension in the continental margin of Gondwana and were later affected by (probably early Variscan) medium-P metamorphism before the HT-LP metamorphism classically described in the Pyrenees.

This study presents a new geochemical, petrological, and geochronological U-Pb dataset from Ediacaran metabasites and associated rocks of the Canigó and Cap de Creus massifs, Eastern Pyrenees. Metabasites are composed of calcic amphibole + plagioclase + chlorite + epidote ± quartz plus titanite + apatite + ilmenite ± biotite ± rutile as accessory phases and show relict igneous textures. Peak pressure-temperature determinations share common conditions, ranging 452-482ºC and 5.2-7.7kbar, which suggest Barrovian-type metamorphism, most likely related to a collisional setting. The metabasites correspond to evolved basaltic rocks (Mg#<0.55) with moderate TiO content (up to 2.08wt.%) and relatively low Cr (43-416ppm). The rocks are moderately enriched in Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE) (average (La/Lu) of 2.7) and the N-MORB normalized multi-element patterns show negative slopes, with prominent negative Nb anomalies ((Nb/La)=0.33–0.78). These variations are akin to island arc tholeiites generated in back-arc basins and to other metabasites described in the Eastern Pyrenees with a putative Ediacaran age, and they differ from the Ordovician tholeiitic metabasites from the Canigó massif, which derived from a contaminated E-MORB source. The positive Ɛ values (0.82-3.05) of the studied metabasites preclude a notable contribution from an older continental crust. Detrital zircon U-Pb dating Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) of one chlorite-rich schist sample in contact with the metabasites from the Canigó massif yielded a main peak at ca. 632Ma and apparent maximum age of deposition at ca. 550Ma. We argue that the Cadomian metabasites from the Pyrenees formed during back-arc extension in the continental margin of Gondwana and were later affected by (probably early Variscan) medium-P metamorphism before the Low-Pressure High-Temperature (LP-HT) metamorphism classically described in the Pyrenees.

A comprehensive review and phylogenetic analysis of genera and species presently assigned to the rhynchonelliform superfamily Nisusioidea and family Nisusiidae suggests that this short-lived but important group of brachiopods first appeared in peri-Gondwana during the second half of the Cambrian Series 2, before going extinct by the end of Drumian times. Nisusiides achieved their maximum morphological disparity and geographical distribution during the Wuliuan Age, and Laurentia was probably the major centre of their dispersal. A new phylogenetic analysis suggests an early separation of the lineages of spinose and non-spinose nisusiids. The non-spinose nisusiids probably evolved in Laurentia by the end of Cambrian Series 4. The new nisusiid genus Bellistrophia is described. The new species Nisusia multicostata represents the first documented rhynchonelliform (kutorginide) brachiopod from the Miaolingian (Drumian) of the Alborz Mountains, Iran.

Esta tesis doctoral presenta un estudio comparativo sobre la conservación de fábricas ytexturas microbianas en dos complejos vulcanosedimentarios: (1) la caldera de Oued Dar’a,en el en el Ediacárico terminal del Supergrupo de Ouarzazate (Anti-Atlas oriental,Marruecos), que representa la fase terminal de la Orogenia Pan-Africana, y (2) el campogeotermal de Seltún en la península de Reyjkanes (Islandia), situada en la parte septentrionalde la dorsal atlántica actual. El objetivo incluye la caracterización de los mediossedimentarios de calderas volcánicas, en los que se han registrado varios procesos debiomineralización, principalmente relacionados con la silicificación de biofilms, tapices yestromatolitos microbianos, a partir del estudio de sus facies sedimentarias, fábricas ytexturas microbianas y el registro de procesos diagenéticos, en su aspecto petrológico,mineralógico y geoquímico. Para ello se ha realizado un estudio analítico y microscópico, aescala centimétrica, milimétrica y nanométrica, de los restos microbianos a partir de losmicroscopios petrográfico y electrónico de barrido (MEB), acoplados a espectrómetros deenergía dispersiva de rayos X (Energy Dispersive X-Ray Spectrometry, EDS),catodoluminiscencia (CL) y difracción de rayos X (DRX)..., This PhD thesis documents a study that aims to make a comparison about the preservationof microbial fabrics and textures in two volcanosedimentary complexes: (i) the Oued Dar’acaldera exposed in the uppermost Ediacaran Ouarzazate Supergroup (eastern Anti-Atlas,Morocco), which represents the end of the Pan-African Orogeny, and (ii) the Seltungeothermal area of the Reyjkanes Peninsula (Iceland), located in the present-day exposuresof the northern Mid-Atlantic Ridge. The aim of this work is the characterization of thesedimentary environments recorded in both volcanic calderas, which exhibit a wide varietyof biomineralization processes, mainly related to silicification of biofilms, mats andstromatolites. The study is based on the analysis of sedimentary facies, microbial fabricsand textures and the record of diagenetic processes, focused on their petrologic,mineralogical and geochemical features. The latter include a dataset of analytical andmicroscopic results, at the cm, mm and nm scale yielded by the petrographic and ScanningElectron Microscopy (SEM) microscopies, Energy-Dispersive X-Ray Spectroscopy (EDS),cathodoluminescence (CL) and X-Ray Diffraction (XRD) analyses...

Esta tesis doctoral presenta un estudio comparativo sobre la conservación de fábricas ytexturas microbianas en dos complejos vulcanosedimentarios: (1) la caldera de Oued Dar’a,en el en el Ediacárico terminal del Supergrupo de Ouarzazate (Anti-Atlas oriental,Marruecos), que representa la fase terminal de la Orogenia Pan-Africana, y (2) el campogeotermal de Seltún en la península de Reyjkanes (Islandia), situada en la parte septentrionalde la dorsal atlántica actual. El objetivo incluye la caracterización de los mediossedimentarios de calderas volcánicas, en los que se han registrado varios procesos debiomineralización, principalmente relacionados con la silicificación de biofilms, tapices yestromatolitos microbianos, a partir del estudio de sus facies sedimentarias, fábricas ytexturas microbianas y el registro de procesos diagenéticos, en su aspecto petrológico,mineralógico y geoquímico. Para ello se ha realizado un estudio analítico y microscópico, aescala centimétrica, milimétrica y nanométrica, de los restos microbianos a partir de losmicroscopios petrográfico y electrónico de barrido (MEB), acoplados a espectrómetros deenergía dispersiva de rayos X (Energy Dispersive X-Ray Spectrometry, EDS),catodoluminiscencia (CL) y difracción de rayos X (DRX)...

ian magmatic events. Based on U–Pb zircon dating constraints, palaeotopographic relationships linked to onlap geometries and distance from vent sources, three volcanosedimentary edifices can be distinguished, the so-called Tregurà (ca. 565–552 Ma), Cap de Creus (ca. 558 Ma) and Coll d’Ares (ca. 542–532 Ma) edifices. The top of their palaeoreliefs recorded locally the nucleation of centres of microbial carbonate productivity (Puig Sec Member) linked to synsedimentary tilting and karstification. Throughout West Gondwana, the presence of carbonate production across the Ediacaran–Cambrian transition is exclusively located in back-arc settings (Central-Iberian Zone) and areas far from the Cadomian subduction trench and devoid of significant terrigenous input, such as those reported in the Eastern Pyrenees and the neighbouring Montagne Noire.

ian magmatic events. Based on U–Pb zircon dating constraints, palaeotopographic relationships linked to onlap geometries and distance from vent sources, three volcanosedimentary edifices can be distinguished, the so-called Tregurà (ca. 565–552 Ma), Cap de Creus (ca. 558 Ma) and Coll d’Ares (ca. 542–532 Ma) edifices. The top of their palaeoreliefs recorded locally the nucleation of centres of microbial carbonate productivity (Puig Sec Member) linked to synsedimentary tilting and karstification. Throughout West Gondwana, the presence of carbonate production across the Ediacaran–Cambrian transition is exclusively located in back-arc settings (Central-Iberian Zone) and areas far from the Cadomian subduction trench and devoid of significant terrigenous input, such as those reported in the Eastern Pyrenees and the neighbouring Montagne Noire.

In the Toledo Mountains of the Central-Iberian Zone (CIZ), some scattered outcrops with volcanic and metavolcanic rocks occur interbedded across Cambro-Ordovician strata (Martínez Escorza, 1976; Ramírez-Merino et al., 2000). The authors differentiated two volcanic suites: (i) some volcanic rocks underlying the Cambrian Cortijos Sandstone Formation (VR1), and (ii) a volcanosedimentary complex (VSC) sandwiched between the Valdehierro and the Purple Series. Thirteen samples of both volcanic suites were selected for geochemical analysis. According to geochemical characteristics, VSC can be subdivided into two sets: (i) VSC1 displays similar geochemical characters than suite VR1 and is composed of andesite to subalcaline basaltic andesites in the Pearce (1996) diagram; whereas (ii) VSC2 exhibits a dacitic to rhyolitic composition (Fig. 1). Because of their stratigraphic position and age, VR1 and VSC are associated with the volcanic events of the Toledanian Phase, a widespread Furongian Lower Ordovician tectono-magmatic episode related to generalize tilting, uplift and subaerial erosion in the Central-Iberian Zone.