Antonio Teixell

The tectonic evolution of the Eastern Pyrenees from the orogenic mountain building to the post‐orogenic dismantling is still debated. Since the Oligocene, the Gulf of Lion rifting in the Western Mediterranean superimposed crustal extension in this eastern part of the Pyrenean belt, while compressional tectonics persisted in the Central Pyrenees. In this study we use low‐T thermochronology to reconstruct the thermal history of the Eastern Pyrenees to provide insights on the distribution and timing of the transition from shortening to extension, which was still poorly resolved. We provide a new data set of (U‐Th)/He cooling ages and thermal history models of basement rocks of the Axial Zone of the Pyrenees east of the Tet normal fault. Cooling ages and histories, coupled with an analysis of the lag time between zircon and apatite (U‐Th)/He central ages, help in the differentiation of tectonic units (i.e., basement‐involved thrust sheets) in the Eastern Pyrenees. Our results support a marked exhumation period during the early Oligocene (35–28 Ma), that we interpret as the last compressional phase. The first extension‐related exhumation/cooling occurred during the early Miocene (24–18 Ma) in the footwall of the Tec fault, which was reactivated and propagated south‐westwards during the late Miocene (11–5 Ma). Thus, the transition to extension in this region did occur until the late Oligocene, in an interval bracketed between 28 and 24 Ma of relative quiescence or at least slower exhumation rate.

The study of new collected, stratigraphically constrained ammonites from the uppermost Pliensbachian to Toarcian succession in three basinal sections of the Rich area (Central High Atlas, Morocco) allows refinement of the regional biochronostratigraphy for this interval and recognition of several unconformities with associated hiatuses of variable extent. Two of the sections (Azag and Ait el Abbas), located on the flanks of former diapiric anticlines, display relatively reduced thicknesses (110 and 91 m, respectively), whereas the Agounou section, situated within a syndepositional, halokinetic-related syncline (minibasin), is nearly seven times thicker. Hiatuses are identified by the absence or condensation of stratigraphic intervals ranging from ammonite subzones to entire stages. Ammonites from the Azag section enabled characterization of the Polymorphum, Levisoni, Bifrons, Gradata, Bonarelli, and Speciosum zones beneath an erosional surface capped by a condensed, decimetric-thick calcarenitic-conglomeratic bed with a ferruginous hardground of early Bajocian (Discites–Laeviuscula zones) age. This indicates a hiatus spanning at least the upper part of the late Toarcian to the Aalenian. In Ait et Abbas, the hiatus related to erosional truncation is even larger, encompassing at least from the Gradata Zone (Middle Toarcian) to the Aalenian. Moreover, the Semicelatum Subzone appears to be absent or only partially developed in the studied sections, suggesting an additional hiatus affecting the upper part of the Polymorphum Zone, as observed in other Tethyan and European sections. These hiatuses are interpreted as resulting primarily from erosion and/or sedimentary thinning toward diapiric highs, as well as from gravity-driven sliding related to the synsedimentary mobility of Triassic evaporites. The interplay of these regional halokinetic processes with supraregional tectonic events, climatic perturbations, and sea-level fluctuations shaped the stratigraphic evolution of the area. The chronostratigraphic framework and interpreted Toarcian–Lower Bajocian tectonosedimentary evolution of the Rich area are likely applicable to the Central High Atlas basin as a whole.

The Ouarzazate Basin is located between the southern flank of the Central High Atlas and the Anti-Atlas mountains (in Morocco). The Neogene is primarily represented by the Aït Ouglif and Aït Kandoula alluvial formations, which are exposed in the Amekchoud section. Magnetostratigraphic data indicate a Middle to Late Miocene age for this sequence, from the upper Langhian to the Messinian. Despite extensive sampling, significant paleontological results were only obtained at level PAM 207, situated 773 m above the base of the Aït Kandoula formation. This level, characterized by reversed polarity, yielded a microvertebrate assemblage preliminarily described by Tesón et al. (2010). In this work we present a revised study of the small vertebrates from PAM 207, providing updated information on its faunal composition as well as new insights into the biostratigraphy and paleoenvironment of the locality. The assemblage includes fishes, amphibians, reptiles, insectivores, and rodents. Based on the rodent association, PAM 207 is slightly younger than Guefait 1 (Morocco) and close in age to Sidi Salem (Algeria), representing one of the oldest early Turolian localities in North Africa. It postdates Tafna 2 (9.1–8.7 Ma) and predates Amama 2 (7.7 Ma), supporting its correlation with chron C4r (8.77–8.12 Ma). Paleoenvironmental evidence suggests temperate freshwater habitats within an open landscape with a certain degree of vegetative cover, under relatively arid conditions. Overall, PAM 207 provides new evidence that contributes to the establishment of a chronologically constrained Late Miocene biochronological scheme for North Africa and enhances our understanding of paleoenvironments during this interval.

The Eaux‐Chaudes massif provides keys to unravel the deep‐seated deformation of the Iberian rifted margin during the Alpine orogeny in the Pyrenees. The massif conforms to an inlier of upper Cretaceous carbonate rocks within the Paleozoic basement of the western Axial Zone, originally deposited in the upper margin shelf before the Cenozoic collision. New geological mapping and cross‐section construction lead to the description of the lateral structural variation from a km‐scale fold nappe in the west to a ductile, imbricate fold‐thrust fan in the east. The transition from a Variscan pluton to Devonian metasediments underlying the autochthonous Cretaceous induced this structural change. Recumbent folding, which involved upper Paleozoic rocks, was facilitated by a lower detachment in Silurian slates and an upper detachment in an overlying Keuper shale and evaporite thrust sheet. Remnants of this allochthonous sheet form shale and ophite bodies pinched within the upper Cretaceous carbonates, conforming unusual tertiary welds. Ductile shear in the overturned limb of the Eaux‐Chaudes fold nappe imparted strong mylonitic foliation in carbonate rocks, often accompanied by N‐S stretching lineation and top‐to‐the‐south kinematic indicators. The burial of the massif by basement‐involved thrust sheets and the Keuper sheet, along with their Mesozoic‐Cenozoic cover, account for ductile deformation conditions and a structural style not reported hitherto for the Alpine Pyrenees. A hypothesis for the tectonic restoration of this part of the Pyrenean hinterland is finally proposed.

The Eaux-Chaudes massif provides keys to unravel the deep-seated deformation of the Iberian rifted margin during the Alpine orogeny in the Pyrenees. The massif conforms to an inlier of upper Cretaceous carbonate rocks within the Paleozoic basement of the western Axial Zone, originally deposited in the upper margin shelf before the Cenozoic collision. New geological mapping and cross-section construction lead to the description of the lateral structural variation from a km-scale fold nappe in the west to a ductile, imbricate fold-thrust fan in the east. The transition from a Variscan pluton to Devonian metasediments underlying the autochthonous Cretaceous induced this structural change. Recumbent folding, which involved upper Paleozoic rocks, was facilitated by a lower detachment in Silurian slates and an upper detachment in an overlying Keuper shale and evaporite thrust sheet. Remains of this allochthonous sheet form shale and ophite bodies pinched within the upper Cretaceous carbonates, conforming unusual tertiary welds. Ductile shear in the overturned limb of the Eaux-Chaudes fold nappe imparted strong mylonitic foliation in carbonate rocks, often accompanied by N-S stretching lineation and top-to-the-south kinematic indicators. The burial of the massif by basement-involved thrust sheets and the Keuper sheet, along with their Mesozoic-Cenozoic cover, account for ductile deformation conditions and a structural style not reported hitherto for the Alpine Pyrenees. Two hypotheses for the tectonic restoration of this part of the Pyrenean hinterland are proposed in this work.

We describe a singular structure in Upper Cretaceous rocks of the Eaux‐Chaudes massif of the western Pyrenees, consisting of a kilometre‐scale fold nappe with a sheared overturned limb. High ductile strain attests a deformation style rarely reported for the alpine Pyrenees, and peak temperature in Upper Cretaceous carbonates is estimated by Raman spectroscopy of carbonaceous material palaeothermometry in the lower greenschist facies (>300°C). The normal fold limb retains the original sedimentary textures, while the overturned limb shows calcite crystal‐plastic deformation and dynamic recrystallization, with crystallographic preferred orientation. The observed ductility and metamorphic temperature bear similarities with the lower Helvetic nappes of the Alps, suggesting deep burial and/or possibly high geothermal gradient in this part of the Pyrenees.

Apatite (U‐Th)/He (AHe) thermochronometric results are integrated with geologic cross sections, structural relationships, and stratigraphic data to reconstruct the growth of the NW Zagros orogenic belt in the Kurdistan region of Iraq. Prolonged exhumation is documented across the belt with deformation advances and retreats from ~14 Ma onward. After in‐sequence propagation of deformation during middle to late Miocene times, preserved growth strata and AHe data show a deformation retreat by latest Miocene time (~5 Ma). In the NW Zagros, the Phanerozoic succession contains two principal décollements in Lower Triassic and middle Miocene units. The Triassic strata are interpreted as the main décollement for a thin‐skinned system that was dominant during most of the Cenozoic. By ~8–5 Ma, the fold‐thrust belt shifted to basement‐involved deformation in association with growth of the mountain front flexure and reactivation of frontal structures. The shift from thin‐skinned to a hybrid thin‐ and thick‐skinned mode of shortening may reflect variations in the mechanical behavior of the upper crust and the presence of inherited basement discontinuities. On the basis of two NE‐SW balanced cross sections spanning the NW Zagros, the estimated total minimum horizontal shortening is ~18.2 km (6%) in the central and ~16 km (7%) in the southern sectors of the Kurdistan region of Iraq. These findings suggest that the evolution of the NW Zagros orogenic belt was likely driven by the mechanical stratigraphy of the sedimentary cover, inherited basement discontinuities, and the dynamic and thermomechanical effects of potential slab breakoff and lithospheric mantle delamination events.

The Moroccan Atlas developed through a multiphase tectonic history including Permian‐Jurassic continental rifting and Cretaceous‐Cenozoic intracontinental shortening. New detrital zircon (DZ) U–Pb geochronologic results from the Ourika‐Zat region in the Marrakech High Atlas constrain the sediment provenance of prerift sediment sources and synrift and postrift basin fill. Prerift Precambrian‐Cambrian units contain Neoproterozoic DZ from the Pan‐African orogeny. Ordovician rocks contain diagnostic 0.95‐ to 1.28‐Ga DZ that are absent in the West African Craton, suggesting distal sediment sources. Permian rift basin fill contains Permian zircons that constrain maximum deposition age and diagnostic of northern Meseta domain sediment sources. New mapping and cross‐section construction demonstrate that Permian basin fill accumulated in a half‐graben above a southward dipping normal fault that likely guided subsequent inversion. Triassic rift basin fill thickens southward, above a likely northward dipping normal fault. The change in rift basin geometry was accompanied by catchment reorganization, the introduction of southern rift flank sediment sources, and subbasin integration. The southern catchment expanded to encompass Meso‐Archean rocks of the Reguibat Shield situated >800 km southward. Existing and new provenance results from postrift strata document onset of recycling of Atlas rift basin fill during the mid‐Cretaceous and before the onset of compressional inversion. These results highlight the interaction between deformation and sediment routing in an extensional basin and sediment dispersal patterns across continental margins during multiphase deformation. Stratigraphic, structural, and provenance characteristics reveal that the Atlas rift shares similarities with high‐angle and supradetachment basin models, emphasizing the diverse nature of extensional styles.

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.