Eladio Liñán

The Lower—Middle Cambrian stages and stratotypes from the Iberian Peninsula: a revision

Lower-Middle Cambrian regional stages of the Iberian Peninsula (Cordubian, Ovetian, Marianian, Bilbilian, Acadoparadoxides and Solenopleuropsidae stages) are now reconsidered in the light of new stratigraphic and palaeontological (trace fossils, trilobites and archaeocyaths) studies. These stages are re-described with selected stratotypes and chronostratigraphic boundaries. The names Leonian and Caesaraugustian are formally proposed to replace the provisional stages of Acadoparadoxides and Solenopleuropsidae, respectively. A correlation chart of the Lower-Middle Cambrian lithostratigraphic units from the Iberian Peninsula is also presented. Two regessive-transgressive cycles are proposed to explain the lithological and palaeontological peculiarities through the Lower-Middle Cambrian sequence in the Iberian Peninsula.

Late Neoproterozoic crustal growth in the European Variscides: Nd isotope and geochemical evidence from the Sierra de Córdoba Andesites (Ossa-Morena Zone, Southern Spain)

Abstract Because the Hercynian overprint was extremely weak, the Sierra de Cordoba (southeastern Ossa-Morena Zone, OMZ) provides an excellent opportunity to study the tectonic evolution of sequences deposited close to the Late Neoproterozoic–Early Palaeozoic boundary. In order to put constraints on the sources and geodynamic significance of the Late Proterozoic magmatism, a representative set of 18 igneous rocks, and 3 interbedded sedimentary rocks from the San Jeronimo Formation have been studied for major and trace element geochemistry and for the Sm–Nd isotopic systematics. The igneous rocks are generally porphyritic to microporphyritic andesites, with abundant plagioclase (±amphibole) phenocrysts. With the exception of two intrusive rocks, possibly not related to the Late Proterozoic episode, all the samples display positive eNd550 Ma values, ranging from +2.9 to +7.6. Most of them, with +4

Precambrian-Cambrian boundary and correlation from southwestern and central part of Spain

This paper comprises the first palaeontological correlation between the Upper Proterozoic–Lower Cambrian Series of Ossa-Morena, Luso-Oriental-Alcudica and Galaico-Castellana Zones of the Iberian Peninsula. The authors show the palaeontological events on acritarchs, stromatolites, cyanophyta, soft-bodied metazoa, trilobites, archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the Precambrian–Cambrian boundary in the sequences. The Sierra de Cordoba general Series (Ossa-Morena Zone) has an erosive discontinuity between the rocks with the first record of Cambrian metazoan activity ( Skolithos sp., Monomorphichnus sp., Phycodes pedum and Rusophycus sp.) and the rocks with a palynological association ( Bavlinella faveolata, Protosphaeridium flexosum, Trachisphaeridium sp., aff. Octoedryxium truncatum, Phycomicetes ? sp. and cf. Ooidium sp.) which suggests a Lower–Middle Vendian age. For this reason we suggest that the Precambrian–Cambrian boundary be placed at this unconformity. The upper part of the Sierra de Guadalupe Series (Luso-Oriental-Alcudica Zone) includes detrital beds with Phycodes pedum, Planolites sp. and Treptichnus sp. which are also the first record of Cambrian metazoan activity. In the middle part of the sequences, acritarchs attributed to the genus Micrhystridium are found at the top of the Calcareous Beds. This is taken to indicate an early Cambrian age. Vendotaenids and Bavlinella faveolata are found in abundance, thus indicating a Late Vendian age for the middle part of this unit. Thus, we propose the Precambrian–Cambrian boundary be located in the upper part of the Calcareous Beds. In the Rio Uso Series (Galaico-Castellana Zone), the Azorejo Sandstones contain Rusophycus gr. radwanskii, Planolites sp. and Gordia sp. Trace fossils produced by trilobite-like arthropoda ( Monomorphichnus ) have been cited in the upper part of the underlying Pusa Shales. Moreover, Octoedryxium truncatum and Bavlinella faveolata are found in the lower part of this unit which suggest that the Precambrian–Cambrian boundary could be situated in the Pusa Shales. Calcareous microfossils related to annelid polychaetes are found associated with Upper Vendian acritarchs in the Calcareous Beds of Sierra de Guadalupe. They are the oldest record of skeletal metazoa in the Spanish Series. The medusoids found are associated with a Vendian flora and they are also the oldest non-skeletal metazoa record known in the Iberian Peninsula.

The first record of Dinesus (Trilobita, Dinesidae) in the Cambrian of the Mediterranean region

An important problem facing inter-regional correlation in the Cambrian is the scarcity of shared taxa between different palaeogeographic domains. Currently, species of the Corynexochida are proposed as tools to define the base of Cambrian Series 3. However, few Mediterranean Corynexochida species are known. A specimen of Dinesus truyolsi comb. nov. from the middle Cambrian of Spain represents the first record of this genus in the Acadobaltic province. Erbia and Tingyuania are accepted as junior subjective synonyms of Dinesus, and we now recognize 22 species within this genus. Dinesus has been found previously in lower to middle Cambrian strata of Australia, Russia, Kazakhstan, North America and China providing the potential for improved global correlation for this interval.

A New Early Cambrian Lobopod-Bearing Animal (Murero, Spain) and the Problem of the Ecdysozoan Early Diversification

A new xenusian, Mureropodia apae gen. and sp. nov., is found in the lower Cambrian of the Murero Lagerstatte in the Cadenas Ibericas, NE Spain. In Mureropodia, the lobopod length/body width ratio reveals that this animal hardly was able to walk on the bottom surface. Possibly, it could use the limbs for anchoring the body to the substrate. A well-developed dermomuscular sac of circular and longitudinal muscular systems as well as probably retractile proboscis fit such an interpretation. The ground plan of the Xenusia includes a vermiform body; a proboscis or mouth cone; paired lobopods with claws; a cuticle displaying a repeated anatomical patterning; a straight digestive tract with terminal mouth and anus. Morphologically heterogeneous xenusians, which crawled with their lobopods along the bottom, might give rise to four morphofunctional lineages – to cephalorhynch worms by adaptation for burrowing with retractable proboscis; to tardigrades by adaptation for interstitial habitat; to euarthropods by adaptation to walking on joint appendages; and to anomalocaridids by adaptation to swimming with lateral flaps.

Biostratigraphical significanceof the genus Ferralsia (Lower Cambrian, Trilobita)

Abstract Ferralsia is known from the southern side of the Montagne Noire (France), the Gorlitz Synclinorium(Germany), and the Ossa-Morena zone (Iberian Peninsula). The finding of Ferralsia saxonica in the reference section of the Marianian stage (a Lower Cambrian chronostratigraphic unit of the Iberian Peninsula) allows us to consider it as a potential taxon for correlation within the Cambrian Mediterranean Subprovince. The stratigraphical position and associated trilobites suggest a middle to late Marianian age for Ferralsia saxonica, whereas a middle Marianian to earliest Bilbilian age may be suggested for Ferralsia blayaci.

The middle lower Cambrian (Ovetian) Lunagraulos n. gen. from Spain and the oldest trilobite records

The type material of Agraulos antiquus Sdzuy, 1961 from the La Herreria Formation, northern Spain, is revised together with additional material and included in the new genus Lunagraulos . The stratigraphical range of Lunagraulos antiquus (Sdzuy, 1961) – occurring below that of the trilobite species of the genera Lunolenus , Metadoxides and Dolerolenus in the type locality of Los Barrios de Luna in the province of Leon, northern Spain – and the accompanying ichnofossil assemblage demonstrate an Ovetian age (lower part of Cambrian Stage 3, currently being discussed by the International Subcommission on Cambrian Stratigraphy) for this species. Moreover, the trilobite Lunagraulos tamamensis n. gen. n. sp. is found in the Tamames Sandstone near the village of La Rinconada in the province of Salamanca, central Spain. The biostratigraphical position of this new taxon and its accompanying ichnoassemblage is also analysed and assigned to the lowermost Ovetian Stage. The genus Lunagraulos is therefore the oldest agraulid found in the fossil record. The exceptional presence of Lunagraulos in a marine coarse siliciclastic succession – a facies rather typical for the ichnofossils Cruziana and Rusophycus , some of the oldest signs of trilobite activity – suggests that first trilobite representatives may have inhabited high- to middle-energy, marine environments. This hypothesis may also explain both the taxonomic and biostratigraphic heterogeneity of the first trilobite genera appearing across the world, due to preservation problems in this type of facies. Comparison of the Lunagraulo s biostratigraphy with other coeval Spanish fossil assemblages allows us to propose its intercontinental correlation with the oldest records of currently known trilobites.

Les flores du bassin lacustre de Rubielos de Mora. Nouvelles données sur les conditions climatiques au Miocène inférieur dans la région de Teruel (Espagne)

Abstract The stratigraphie and floristic studies of two sections in the lacustrine deposits of the Miocene basin of Rubielos de Mora increase our knowledge of palaeoenvironmental and palaeoclimatic conditions and specify the biochronology of these sites. The lowlands are inhabited by a swampy, or lacustrine, vegetation ( Botryococcus, Sparganium, Potamogeton , Taxodiaceae, Myrica, Nyssa… ), whereas the uplands are covered by a Zelkova mesophilous forest with other temperate elements ( Acer, Betula, Carya… ). The scarcity of thermophilous taxa in this vegetation indicates that the climatic conditions were not the warmest in the Miocene. The rodents faunas of this basin suggest a Ramblian-basal Aragonian age (Lower Miocene).

Upper Vendian-lowest Ordovician sequences of the western Gondwana margin, NE Spain

Abstract The intra-Vendian (Ediacaran)–intra-Tremadocian succession of the Cadenas Ibéricas in NE Spain is divided into nine sequences. Overall, these are interpreted as second-order sequences. Those that encompass Lower and lower Middle Cambrian carbonates, with identified transgressive systems tract (TST) and highstand systems tract (HST) phases, may constitute elements of composite sequences. The lowermost sequence is of Late Vendian age. In Lower and lower Middle Cambrian units, sequence tops indicate drowning, reflecting extensional tectonics. Rifting effects are traceable up to mid-Mid Cambrian times. The remaining sequences probably represent a sag phase, either accentuating the preceding extensional local basin regime or heralding the Gondwana passive margin stage. Of the southerly Gondwana deposits those of other areas of the Iberian Peninsula and of the Moroccan Anti-Atlas fold belt show similar conditions during the Early Cambrian, that is, an Early Cambrian extensional regime, and, as for the Moroccan fold belt, four sequences imaging TST and HST phases.

Paradoxides brachyrhachis Linnarsson, 1883 versus Paradoxides mediterraneus Pompeckj, 1901: a problematic determination

A revision of paradoxidid trilobites reveals that previous identifications of specimens from Sardinia and Spain as the Nordic trilobite species Paradoxides brachyrhachis Linnarsson, 1883, are mistaken. The southern species, occurring also in France, is here referred to Eccaparadoxides mediterraneus (Pompeckj, 1901). Main differences are seen in the preocular field, pleural furrow and pygidium. The species P. brachyrhachis is referred with question to the genus Mawddachites Fletcher 2007.