Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The pre-Variscan rocks of the Pyrenees exhibit a polyphase deformation linked to the Variscan crustal shortening and a low-pressure–high-temperature metamorphism. However, there is scarce chronostratigraphic evidence of this Variscan deformation. In the Pyrenean low-grade metamorphic domains, maximum ages have been provided by the synorogenic Carboniferous Culm deposits. In medium- to high-grade metamorphic areas, the Variscan regional metamorphism or intrusive magmatic bodies constrain the age of the main Variscan deformation structures. However, these data usually provide a minimum age. Here, we present new palaeobotanical records that assign a Namurian age to the base of the Culm deposits of la Cerdanya in the eastern Pyrenees. This dating is based on the co-occurrence of the sphenopsids Archaeocalamites radiatus, Mesocalamites cistiiformis and the seed of Cardiocarpus sp. The plant remains were found in sandstone facies produced by high-density turbidity flows of a deep-sea fan system. The new biostratigraphic information constrains the age of the Carboniferous Culm succession in the eastern Pyrenees.

In this short note, we present the first data on stable isotope composition of the oilfield waters from Carabobo area of the Faja Petrolífera del Orinoco “Hugo Chávez” (Orinoco Oil Belt). From a chemical point of view, the formation waters show a main Na-Cl level (TDS up to 30g/l) with a dilution trend toward Na-HCO3 composition (down to 1g/l). Until now, such a clear net chemical compositional trend was ascribed to a meteoric dilution (fresh/ brackish bicarbonate) of the seawater endmember (the saltiest chloride). The isotope results of this study reveal that the seawater mother water was modified during a high-temperature thrusting event (120–125°C), forming 18O-enriched diagenetic water (up to +4‰), which was diluted in recent times by glacial meltwater and presentday meteoric water. The hypothetical presence of flood by a meteoric paleo-water also offers new hints to explain the low API gravity (<10°API biodegraded, extra heavy oil) and composition of the local crude.

This paper presents a new model of the subsurface structure of the eastern Jaca flexural basin of the west-central southern Pyrenees, by means of subsurface structural maps and four new balanced cross-sections. The study is based on the interpretation of a set of publicly available seismic reflection profiles tied to deep exploration well logs, which constitute a unique database in the southern Pyrenees associated to the gas discovery of the Serrablo field. Investigation of the deep basin structure highlights strong mechanical-stratigraphic contrasts between basement, a competent Upper Cretaceous-Eocene carbonate sequence in the deep basin and a weak infill of Eocene to lower Miocene synorogenicclastic deposits. These contrasts promote the occurrence of various décollement levels and a decoupled style of deformation between intervals of different competence. A contour map for the top of basement reveals a complex structure with lateral variations of the number of thrusts and the displacement on these and local transverse elements.Between the Gavarnie thrust at the southern edge of the Axial Zone and the Guarga thrust at the leading edge of the basement thrust system, three main other basement thrusts are defined below the north-eastern Jaca Basin, from South to North the Fiscal, Yésero and Broto thrusts. In the Meso-Cenozoic sedimentary cover, two low-angle thrusts are mappedin the subsurface across the Upper Cretaceous-Eocene carbonates: i) the deep Oturia thrust, connected upsection to the emerging Oturia thrust known at the surface, and ii) the deep Jaca thrust, drilled by the Serrablo wells, and connected to the emerging Jaca thrust and Yebra de Basa anticline through a zone of disharmonic deformation. The deducedsubsurface geometrical relationships are consistent with the connection of the Gavarnie and Broto basement thrusts to the Priabonian-Rupelian Oturia and Jaca thrusts while the younger Yésero, Fiscal and Guarga basement thrusts emerge at the South Pyrenean thrust front of the Sierras Exteriores, active until the early Miocene. This study highlights the complex structural pattern that characterizes the deep structure of the South Pyrenean basin and the role of disharmonic deformation that challenges the resolution of the deeper thrust system without the help of seismic profiles.

The activity of normal faults in the Central-Western Pyrenees is mainly detected by the disruption of paleic landforms surviving to Plio-Quaternary incision: the remnants of a Low-Relief Topography (LRT) that probably originated asynchronically during the Oligocene and Miocene. We propose a new method for mapping the LRT remnants that combines automatic analysis of digital topography and cross-checking with regional databases of Quaternary landforms. We focus on an area where the location of the main-drainage divide seems to be influenced by the activity of the Bedous-Pic de Midi du Bigorre set of faults and by the North Maladeta Fault. Neotectonic markers defined by the remnants of LRT envelops are tectonically displaced up to ~700m by the previously identified faults, but also along new faults observed in between them. A western prolongation of the North Maladeta Fault has been identified for the first time, implying a 75km total trace length, almost twice thepreviously published value. A restoration of the fault block motion was performed assuming a regional uplift across the range, enhanced in the northern part of the Axial Zone. This uplift leads to an outer arch extension along the Maladeta-Bedous Fault System. The resulting paleo-topography shows a broad southern paleo-flank (up to ~120km long) with a gentle regional gradient (~1º) and a much shorter and steeper northern paleo-flank (~4º gradient, up to 30km-long). This configuration suggests that the LRT remnants now located North of the main divide were connected to the Ebro Basin. The results are supported by previous studies on age and source provenance of major alluvial systems mantling the northern and southern flanks of the chain.

The interpretation of the available seismic lines of the South-Central-Pyrenean fold and thrust belt, conveniently tied with the exploration wells, define the main structural features of this realm of the Pyrenees. In particular, they define the geometry and areal extension of the autochthonous foreland underneath the sole thrust. The mapping ofseveral selected structural lines brings constraints for the structural interpretation of the South-Central Pyrenees, including the cut-off lines between selected stratigraphic horizons of the autochthonous foreland and the branch line between basement-involved thrust sheets and the sole thrust. The thrust salient which characterizes at surface the geometry of the South-Pyrenean fold and thrust belt contrasts with the linear trend of these structural lines at subsurface. This salient has been the result of a secondary progressive curvature developed since Middle Eocene times by thrust displacement gradients during verthrusting of the South-Pyrenean thrust sheets above a Paleogene autochthonous sequence. Displacement gradients resulted from the uneven distribution of weak salt layers, mostly the Triassic and the Upper Eocene ones. The minimum amount of South-directed displacement from early MiddleEocene times to Late Oligocene is 52km, which would be significantly higher if internal shortening by folding and cleavage/fracture development as well as hanging-wall erosion is added.

The Iberian Chain is a complex intraplate fold-and-thrust belt resulting from the convergence between the Eurasian, Iberian and African plates during the late Eocene to the Miocene. The main trend of its contractionalstructures is NW-SE, but E-W, NE-SW and N-S-trending structures are also present. The boundaries of the chain with its surrounding foreland basins are always thrusts. The North-Iberian Thrust separates thechain from the Ebro Basin to the North, while the Serranía de Cuenca Thrust makes the SE boundary of the chain, separating it from the Tajo Basin and La Mancha foreland areas. Between these thrusts, thecontractional structure is basement-involved, while South of the Serranía de Cuenca Thrust only Mesozoic and Cenozoic rocks are involved in the thrust-system, detached in the evaporitic Triassic materials. Twoparts can be differentiated considering the major structure of the chain. The western and central areas hold two major anticlinoriums separated by the Almazán Synclinorium. East of the Teruel Depression, E-WstrikingN-verging thrusts in the North, and NW-SE-striking S-verging thrusts in the center and South are the dominant structures.The crust thickened during the Cenozoic contraction generating a mean crustal thickening of about 5km. The horizontal shortening obtained from cross-sections is 32km, and from a density-gravity section of 57.5km.These two values may be considered end values.The relief of the Iberian Chain has a strong areal coincidence with the contractional structures and the thickened crust, indicating that they are genetically related.

The Ediacaran-Lower Ordovician successions exposed in the Eastern Pyrenees are updated and revised based on recent U-Pb zircon radiometric ages, intertonguing relationships of carbonate-dominated strata, and onlapping patterns marking the top of volcano-sedimentary complexes. A stratigraphic comparison with neighbouring pre-Variscan outcrops from the Montagne Noire (southern French Massif Central) and Sardinia is related to i) the absence of Cadomian deformation close to the Ediacaran-Cambrian boundary interval; ii) the presence of an episodic, Cadomian-related, acidic-dominant volcanism related to carbonate production punctuating the Ediacaran-Cambrian transition, similar to that recorded in the northern Montagne Noire; and iii) the lack of Guzhangian (Late Cambrian Epoch 3) regressive shoal complexes present in the Montagne Noire and probably in Sardinia.

We studied Cenozoic sedimentary rocks in the NE Ebro foreland Basin using the Anisotropy of Magnetic Susceptibility (AMS) as a proxy for grain preferred orientation. Our new data, in combination with existing results, reveal that penetrative strain by layer-parallel shortening extends well beyond the Pyrenean thrust-wedge front into the Ebro foreland Basin, challenging the concept of the location of “deformation front” in the Southern Pyrenees. Penetrative strain, as revealed by the magnetic fabrics, seems to reach larger distances into the Ebro foreland Basin where stiffer layers constitute the main detachment level, whereas to the East strain dissipates closer to the deformation front when the detachment is mostly due to salt deposits.

The Konservat-Lagerstätte Menat (Puy-de-Dôme, France) is an outstanding archive of a Paleocene ecosystem, which was deposited in a former maar lake. Excavations during the last century have yielded an extensive flora and fauna record, therefore an overview of the current state of paleontological investigations is given in this paper. Additionally, new results based on excavations from the years 2012 to 2014 are presented. The preservation of organic matter differed strongly between excavation sites, probably influenced by weathering processes. The stratigraphic succession consists mostly of organic-rich clays, intercalated with hard, silicified claystones. In 2013 and 2014 both impression and compression fossils were collected from different outcrops. Compression fossils from organic-rich clays were exceptionally well-preserved and included three-dimensional plant remains. A new database on insect paleobiodiversity was compiled. The occurrence of charcoal in almost all horizons investigated suggests that paleowildfires were frequent during the Paleocene in the vicinity of the paleolake. The results confirm the high potential of the Konservat-Lagerstätte Menat for future paleontological research.

Despite forming part of the Balearic group of islands, Minorca differs stratigraphically and structurally from Majorca and Ibiza: i) Paleozoic rocks are abundant in Minorca but are very scarce in Majorca and are absent in Ibiza. Eocene-Oligocene sediments are virtually absent in Minorca but crop out extensively in Majorca, ii) Contractional structures in Minorca differ in direction (aligned SW-NE in Majorca and Ibiza and N-S in Minorca) and in age from those in Majorca and Ibiza. In addition, Paleozoic deposits of Minorca do not correlate with those of Sardinia, where in addition the Triassic sediments are not very abundant. Contractional deformation in Sardinia is in part older (late Eocene-early Miocene) than in Minorca (early Miocene?). Given its Neogene clockwise rotation, Minorca cannot be considered a small block dragged by the early Miocene counter clockwise rotation of the Corsica-Sardinia block. Furthermore, the Paleozoic and Mesozoic stratigraphy of Minorca (siliciclasticlate Paleozoic rocks, Triassic Germanic facies and Jurassic carbonates) has affinities with that of the southern part of the Catalan Coastal Ranges. Thus, of all the Balearic islands, Minorca seems to have traveled the farthest during the Valencia Trough rifting with the result that it resembles an exotic island forming part of the Balearic foreland.