Permian-Triassic of the Tethys: Carbon isotope sudies

Profiles of carbon isotopes were studied in marine limestones of Late Permian and Early Triassic age of the Tethyan region from 20 sections in Yugoslavia, Greece, Turkey, Armenian SSR, Iran, Pakistan, India, Nepal, and China. The Upper Permian sections continue the high positive values of 13C previously found in Upper Permian basins in NW Europe and western USA. In the more complete sections of Tethys it can now be demonstrated that the values of 13C drop from the Murgabian to the Dzhulfian Stages of the Upper Permian, then sharply to values near zero during the last two biozones of the Dorashamian. These levels of 13C sample the Tethys Sea and the world ocean, and equal values from deep-water sediments at Salamis Greece indicate that they apply to the whole water column. We hypothesize that the high values of 13C are a consequence of Late Paleozoic storage of organic carbon, and that the declines represent an episodic cessation of this organic deposition, and partial oxidation of the organic reservoir, extending over a period of several million years. The carbon isotope profile may reflect parallel complexity in the pattern of mass extinction in Late Permian time. Des profils isotopiques du carbone ont été établis dans des calcaires marins d'âge tardi-permien à  éo-triasique répartis dans 20 endroits du domaine téthysien: Yougoslavie, Grèce, Turquie, République d'Arménie, Iran, Pakistan, Inde, Népal et Chine. Les profils établis dans le Permien supérieur montrent les mêmes valeurs positives de 13C observées antérieurement dans des bassins de même âge en Europe occidentale et dans l'ouest des USA. Dans les profils les plus complets de la Téthys, il est maintenant établi que les valeurs de 13C décroissent depuis le Murgabien jusqu'au Dzhulfien (Permien supérieur) pour devenir proches de zéro dans les deux dernières biozones du Dorasharmen. Ces valeurs de 13C sont caractéristiques de la Téthys et de l'Océan mondial; elles s'appliquent à toutes les profondeurs d'eau, comme en témoignent les valeurs fournies par des sédiments de mer profonde à Salamis (Grèce). Nous formulons l'hypothèse que les hautes valeurs de 13C sont la conséquence du stockage du carbone organique au Paléozoïque supérieur et que leur décroissance traduit un arrêt épisodique de cette sédimentation organique, accompagné d'une oxydation partielle de la matière organique s'étendant sur une période de plusieurs Ma. L'influence parallèle des phénomènes d'extinction massive à le fin du Permien se refléterait également dans les profils isotopiques du carbone.

Estratigrafía del Paleógeno en la zona de tránsito entre la Cordillera Prelitoral Catalana y el Prepirineo

La serie de Eoceno y Paleoceno de El Far (provincia de Gerona), presenta un gran interés por servir de punto de enlace entre el Paleógeno de la Cordillera Prelitoral Catalana (en la zona de la Plana de Vic) y el Prepirineo. Es por ello que lieinos considerado interesante el pulilicar una serie detallada que sirva de jalón para poder correlacionar el Eoceno de la Plana de Vic con el de La Salut, Bellmunt y Puigsacalm, sobre todo en los tramos inferiores. Ambas series eocénicas poseen diferencias muy notables en su litología (cainbios laterales de facies) y potencia (aumento pogresivo hacia el surco paleógeno prepirenaico), lo que influye en la misma fauna...

On the Upper Ordovician unconformity in the Pyrenees: New evidence from the La Cerdanya area

In recent years, contradictory reports about whether or not an unconformity exists at the base of the Upper Ordovician succession of the Pyrenees have been made. In the Cerdanya area (Central Pyrenees), good outcrop evidence for this unconformity is displayed at the base of the Rabassa conglomerates. In this area, the Upper Ordovician rocks overlie a tilted Cambro-Ordovician sequence, displaying an angular unconformity and indicating a break in the stratigraphic series. Moreover, the existence of such an unconformity is supported by the distribution of Variscan minor structures, suggesting that the Cambro-Ordovician and the Upper Ordovician strata initially had different orientations before the main Variscan folding.

Estudio tectónico del Paleozoico inferior del Pirineo entre la Cerdaña y el río Ter (resumen)

El análisis estructural del domo del río Freser (Pirineos Orientales, España) permite poner de manifiesto una sucesión de tres fases de plegamiento hercinianas. Se describen las características de las mismas y se comparan con las descritas por otros autores en regiones vecinas.

Sobre una discordancia en el Paleozoico inferior de los Pirineos orientales

Se describe una discordancia de los materiales atribuidos al caradoc sobre las formaciones Canavelles y Jujols en la zona axiai pirenaica, entre la Cerdanya y el ro Freser (prov. dc Gerona, Espaa) y en Andorra. Se discute su importancia y significado, as como la edad de los materiales de las foririacioms Canavelles y Jujols

Corte compensado del Pirineo oriental: Geometría de las cuencas del antepaís y edades de emplazamiento de los mantos de corrimiento

El manto del Pedraforca se ha dividido en dos unidades: el manto superior del Pedraforca predominantemente constituido por materiales del Cretftcico inferior y el manto inferior del Pedraforca formado principalmente por una serie de Cretacico superior discordante por encima del Jurásico. La parte aflorante del manto superior del Pedraforca se ha interpretado como una rampa de bloque superior. Su edad de emplazamiento es Maastrichtiense terminal...

Volcanic stratigraphy of Hannah Point, Livingston Island, South Shetland Islands, Antarctica

The Upper Cretaceous volcanic succession of Hannah Point is the best exposure of the Antarctic Peninsula Volcanic Group on L ivingston Island. The aim of the present paper is to contribute to the characterisation of the stratigr a p hy and petrogr a p hy of this little studied succession, and briefly discuss some aspects of the eru p t ive style of its volcanism. The succession is about 470 m thick and is here subdivided into five lithostratigraphic units (A to E from base to top). Unit A, approximately 120 m thick, is mainly composed of polymict clast-supported volcaniclastic breccias and also includes a dacitic lava laye r. Interstratified in the breccias of this unit, there is a thin laminated devitrified layer which shows some degree of welding. Unit B, approx imately 70 m thick, is almost entirely composed of volcaniclastic breccias, and includes a volcaniclastic conglomerate laye r. Breccias in this unit can be subdivided into two distinct types; polymict clast-supported breccias, and monomict matrix-supported breccias rich in juvenile components and displaying incipient welding. Unit C, about 65 m thick, is mainly composed of basaltic lavas, which are interlayered with minor vo lcaniclastic breccias. Unit D, approximately 65 m thick, is lithologically similar to unit B, composed of an alternation of polymict clasts upported breccias and matrix-supported breccias, and includes a volcaniclastic conglomerate laye r. Unit E, about 150 m thick, is mainly formed of thick andesitic lava layers. Minor basaltic dykes and a few normal faults cut the succession, and the contact betwe e n units A and B can be interpreted both as an unconformity or a fault. The matrix-supported breccias included in the succession of Hannah Point have high contents of juvenile components and incipient welding, which suggest that part of the succession is the result of pyroclastic fragmentation and emplacement from pyroclastic flows. In contrast, the polymict clast-supported breccias suggest reworking of previous deposits and deposition from cool mass flows. The lavas indicate eff u s ive volcanic eruptions, and the absence of features indicative of subaqueous volcanism suggests that at least these portions of the succession were emplaced in a subaerial environment .

Magmatismo paleozoico en el Macizo del Roc de Frausa (Pirineos Orientales)

En el Macizo del Roc de Frausa se han diferenciado mediante criterios geoquímicos dos tipos diferentes de anfibolitas. El primer tipo lo forman metabasitas de afinidad toleitica y composición próxima a los E-MOIIB. Proceden de magmas poco evolucionados moderadamente bajos en potasio. Forman sills intercalados entre los metasedimentos cambro-ordovícicos y están asociadas a porfiroides gneísicos. Los porfiroides gneisicos representan términos ácidos subaluminicos de carácter explosivo y afinidad calcoalcalina con un contenido medio en potasio. Su relación genética con las metabasitas es poco clara; se interpretan como diferenciados ácidos de estas con una importante mezcla de material cortical. Se sugiere para este magmatismo un ámbito geodinámico continental fini-compresivo en relación con cucncas marginales.

A Variscan pressure-temperature-time path for the N-E Mont Blanc massif

The northeastern portion of the Mont Blanc massif in western Switzerland is predominantly comprised of the granitic rocks of the Mont Blanc intrusive suit, and the Mont Blanc basement gneisses. Within these metamorphic rocks are a variety of sub-economic Fe skarns. The mineral assemblages and fluid inclusions from these rocks have been used to derive age, pressure, temperature and fluid composition constraints for two Variscan events. Metamorphic hornblendes within the assemblages from the basement amphibolites and iron sk:lms have been dated using Ar-40/Ar-39, and indicate that these metamorphic events have a minimum age of approximately 334 Ma. Garnet-hornblende-plagioclase thermobarometry and stable isotope data obtained from the basement amphibolites are consistent with metamorphic temperatures in the range 515 to 580 degrees C, and pressures ranging from 5 to 8 kbar. Garnet-hornblende-magnetite thermobarometry and fluid inclusion studies indicate that the iron skarns formed at slightly lower temperatures, ranging from 400 to 500 degrees C in the presence of saline fluids at formational pressures similar to those experienced by the basement amphibolites. Late Paleozoic minimum uplift rates and geothermal gradients calculated using these data and the presence of Ladinien ichnofossils are on the order of 0.32 mm/year and 20 degrees C/km respectively. These uplift rates and geothermal gradients differ from those obtained from the neighbouring Aiguilles Rouges massif and indicate that these two massifs experienced different metamorphic conditions during the Carboniferous and Permian periods. During the early to late Carboniferous period the relative depths of the two massifs were reversed with the Aiguilles Rouges being initially unroofed at a much greater rate than the Mont Blanc, but experiencing relatively slower uplift rates near the termination of the Variscan orogeny.

El Paleozoico de les Guilleries

El macizo de Les Guilleries está formado por materiales metasedimentarios e ígneos de edad paleozoica. Los niveles mas bajos que afloran han sido atribuidos al Cambro-Ordovícico y consisten en dos tramos esencialmente pelíticos bien diferenciados separados por un nivel de ortogneises de varios centenares de metros de espesor. Por encima, se situa una serie vulcano-detrítica, con abundantes niveles de rocas volcánicas ácidas, y que ha proporcionado braquiópodos de edad Caradoc. El Silúrico y el Devónico, muy fragmentarios han sido también datados mediante fósiles. Toda la sucesión fue deformada y metamorfizada durante la orogenia herciniana. La deformación es polifásica y ha dado lugar al desarrollo de foliacions generalizadas en el brea. En las zonas mis profundas, la foliación regional es una crenulación que pliega una foliación anterior. En las zonas mas superficiales solo se observa una foliación de tipo ccslaty cleavagen. El metamorfismo hercinico afecta en mayor o menor grado a toda la serie. En las zonas mis profundas alcanza la facies anfibolitica de alto grado, con el desarrollo en las metapelitas de cordierita y feldespato potásico, mientras que en las zonas más superficiales s610 se alcanza la formación de clorita. En la región se han producido una serie de intrusiones ligadas a la orogenia herciniana. Las mis antiguas son unos filones de diorita y cuarzodiorita que se encuentran intensamente deformados. Posteriormente se produjo la intrusión de leucogranitos de dos micas, que son muy abundantes en las zonas más metamórficas y que en ocasiones se encuentran también algo deformados. Finalmente, se elnplazaron 10s granitoides tardios, que han originado extensas aureolas de metamorfismo de contacto.

Playas fósiles sumergidas en la Costa Brava Meridional (Girona)

This paper describes petrologic and morphologic characteristics of fossil beaches submerged in the sector of the Costa Brava located between the Pals Beach and Blanes (Girona). These submerged beaches are composed of large-grain sandstone andconglomerate platforms, situated at a depth between 0.5 and 2.5 meters. These platforms are slightly inclinated towards the open sea. These deposits have been formed very recently, and date from Holocene, as noted by the presence of fragments of roman ceramics inside sandstone

A new classification of the Turkish terranes and sutures and its implication for the paleotectonic history of the region

The Turkish part of the Tethyan realm is represented by a series of terranes juxtaposed through Alpine convergent movements and separated by complex suture zones. Different terranes can be defined and characterized by their dominant geological background. The Pontides domain represents a segment of the former active margin of Eurasia, where back-arc basins opened in the Triassic and separated the Sakarya terrane from neighbouring regions. Sakarya was re-accreted to Laurasia through the Balkanic mid-Cretaceous orogenic event that also affected the Rhodope and Strandja zones. The whole region from the Balkans to the Caucasus was then affected by a reversal of subduction and creation of a Late Cretaceous arc before collision with the Anatolian domain in the Eocene. If the Anatolian terrane underwent an evolution similar to Sakarya during the Late Paleozoic and Early Triassic times, both terranes had a diverging history during and after the Eo-Cimmerian collision. North of Sakarya, the Küre back-arc was closed during the Jurassic, whereas north of the Anatolian domain, the back-arc type oceans did not close before the Late Cretaceous. During the Cretaceous, both domains were affected by ophiolite obduction, but in very different ways: north directed diachronous Middle to Late Cretaceous mélange obduction on the Jurassic Sakarya passive margin; Senonian synchronous southward obduction on the Triassic passive margin of Anatolia. From this, it appears that the Izmir-Ankara suture, currently separating both terranes, is composite, and that the passive margin of Sakarya is not the conjugate margin of Anatolia. To the south, the Cimmerian Taurus domain together with the Beydağları domain (part of the larger Greater Apulian terrane), were detached from north Gondwana in the Permian during the opening of the Neotethys (East-Mediterranean basin). The drifting Cimmerian blocks entered into a soft collision with the Anatolian and related terranes in the Eo-Cimmerian orogenic phase (Late Triassic), thus suturing the Paleotethys. At that time, the Taurus plate developed foreland-type basins, filled with flysch-molasse deposits that locally overstepped the lower plate Taurus terrane and were deposited in the opening Neotethys to the south. These olistostromal deposits are characterized by pelagic Carboniferous and Permian material from the Paleotethys suture zone found in the Mersin mélange. The latter, as well as the Antalya and Mamonia domains are represented by a series of exotic units now found south of the main Taurus range. Part of the Mersin exotic material was clearly derived from the former north Anatolian passive margin (Huğlu-type series) and re-displaced during the Paleogene. This led us to propose a plate tectonic model where the Anatolian ophiolitic front is linked up with the Samail/Baër-Bassit obduction front found along the Arabian margin. The obduction front was indented by the Anatolian promontory whose eastern end was partially subducted. Continued slab roll-back of the Neotethys allowed Anatolian exotics to continue their course southwestward until their emplacement along the Taurus southern margin (Mersin) and up to the Beydağları promontory (Antaya-Mamonia) in the latest Cretaceous-Paleocene. The supra-subduction ocean opening at the back of the obduction front (Troodos-type Ocean) was finally closed by Eocene north-south shortening between Africa and Eurasia. This brought close to each other Cretaceous ophiolites derived from the north of Anatolia and those obducted on the Arabian promontory. The latter were sealed by a Maastrichtian platform, and locally never affected by Alpine tectonism, whereas those located on the eastern Anatolian plate are strongly deformed and metamorphosed, and affected by Eocene arc magmatism. These observations help to reconstruct the larger frame of the central Tethyan realm geodynamic evolution.

Response to the comments on "The formation of Pangea" by D.A. Ruban

The Variscan structures of the Caucasus region are still quite difficult to decipher, they certainly deserved some in depth investigations in the future. Thus, it is right to question any paleogeographic models proposed in that area, as made by D.A. Ruban. We present here the arguments that we used to decide on the distribution of the terranes in that region. The Transcaucasus massif is regarded as pertaining to the Galatian super-terrane, whereas, the Great Caucasus terrane belongs to the Hanseatic ribbon terrane. The latter was a part of Hunia, detached from Laurussia in the Devonian.

Basement lithostratigraphy of the Adula nappe: implications for Palaeozoic evolution and Alpine kinematics

The Adula nappe belongs to the Lower Penni- nic domain of the Central Swiss Alps. It consists mostly of pre-Triassic basement lithologies occurring as strongly folded and sheared gneisses of various types with mafic boudins. We propose a new lithostratigraphy for the northern Adula nappe basement that is supported by detailed field investigations, U-Pb zircon geochronology, and whole-rock geochemistry. The following units have been identified: Cambrian clastic metasediments with abundant carbonate lenses and minor bimodal magmatism (Salahorn Formation); Ordovician metapelites associated with amphibolite boudins with abundant eclogite relicts representing oceanic metabasalts (Trescolmen Formation); Ordovician peraluminous metagranites of calc-alkaline affinity ascribed to subduction-related magmatism (Ga- renstock Augengneiss); Ordovician metamorphic volcanic- sedimentary deposits (Heinisch Stafel Formation); Early Permian post-collisional granites recording only Alpine orogenic events (Zervreila orthogneiss). All basement lithologies except the Permian granites record a Vari- scan ? Alpine polyorogenic metamorphic history. They document a complex Paleozoic geotectonic evolution consistent with the broader picture given by the pre- Mesozoic basement framework in the Alps. The internal consistency of the Adula basement lithologies and the stratigraphic coherence of the overlying Triassic sediments suggest that most tectonic contacts within the Adula nappe are pre-Alpine in age. Consequently, me ́lange models for the Tertiary emplacement of the Adula nappe are not consistent and must be rejected. The present-day structural complexity of the Adula nappe is the result of the intense Alpine ductile deformation of a pre-structured entity.