Prebetic Zone Research Articles

Early Aptian development and OAE 1a-linked demise of a carbonate platform in the Western Tethys: Lower Cretaceous of Sierra Mariola (South Iberian Paleomargin, SE Spain)

A carbonate platform succession of early Aptian age is described from the Sierra Mariola, which is located within the Prebetic Zone of the Betic External Zones (BEZ) of the Southern Iberian Palaeomargin, in SE Spain. The facies and stratigraphic architecture of the studied succession are described and analysed from multiple logged sections to characterize different depositional environments.The cyclic stacking of facies observed suggests a possible orbital forcing of climate transmitted to sedimentation. Superbundles are recognized describing two sequences of Regressive-Transgressive (R-T) evolution. Analysis of carbon-isotope data identifies both the interval before the hyperthermal event of the early Aptian Oceanic Anoxic Event (OAE 1a) and the onset of the latter event, with an abrupt change in sedimentation marking the demise of the carbonate platform. The field outcrop thus preserves a record of the transition from a greenhouse world to a hothouse event.

Evolution of the Júcar-Cabriel fluvial system on the Mediterranean watershed of the Iberian Peninsula (Valencia, eastern Spain)

This study presents the characterization and chronology of the Quaternary terrace sequence developed in the confluence zone of the Júcar and Cabriel river valleys. The study area covers a radius of 10 km from the confluence of the two valleys near the locality of Cofrentes (Valencia). It is located in the northern zone of the Ayora-Cofrentes Graben in the northeastern sector of the External Prebetic Zone adjacent to southern Iberian Chain. This N-S graben is an inherited tectonic feature with an axial salt wall subject to different periods of fluvial dissection and refilling since at least the end of the Messinian Salinity Crisis (MSC). Regional isostatic uplift and local uplift and subsidence processes related to salt flow and dissolution during the Quaternary period, favored by fluvial entrenchment and terrace development. The terrace system and the previous pre-incision erosional and depositional surfaces are analyzed from a geomorphological point of view. The terrace system only develops within the soft Mio-Pliocene sedimentary fill of the graben, whilst upstream and downstream this zone the studied valleys develop important gorges (canyons) carved in the Cretaceous tablelands (Caroch Massif) and Mio-Pliocene deposits (Llanura Manchega). The geochronological control is established from 20 numerical ages obtained by different dating methods, such us Electron Spin Resonance (ESR), Optically Stimulated Luminescence (OSL) in detrital sequences and Th/U series in calcareous tufa deposits. Additionally, four K/Ar dates available for volcanic materials disrupting the upper and oldest terrace have been considered. A total of 14 terrace levels were identified between +130–135 m (T1) and +3–4 m (T14) of relative height above the river thalwegs. The T1 has an approximate age of c. 1.6–2.0 M.a. as indicate the age of the volcanic materials from the Agras Volcano intruded in the terrace, marking the onset of Quaternary fluvial dissection in the zone. The obtained geochronological data indicate that the Lower-Middle Pleistocene boundary is slightly above T6 (+60–65 m), which has an ESR age of 577 ± 43 ka. This terrace also documents the onset of the most important period of rise of the salt within the graben interfering drainage development. The geochronological data indicate the occurrence of a second eruptive event during the second half of the Middle Pleistocene related to the terraces T7 (+50 m) and T8 (+35–40 m), updating the volcanic activity in the zone. The beginning of the Upper Pleistocene is recorded by the top sequences of the T9 terrace (+25–30 m) where numerous OSL and Th/U data have been obtained with ages between ca. 105 and 81 ka (MIS 5). However, these young terraces (T8 to T13) are thickened (8–10 m) recording Middle Pleistocene sediments in their basal sequences with ages between ca. 193 and 137 ka (MIS 6). The study provides important data on valley evolution under the interference of volcanic activity, salt –related deformation (diapirism, solution subsidence) and fluvial incision fostered by the rise of the axial diapir (salt wall) protruding the graben since at least the Brunhes-Matuyama boundary. The analyzed fluvial evolution documents interesting cases of river capture, drainage antecedence and tectonic adaptation of the drainage throughout the Quaternary Period. The paper also poses interesting geochronological data on the long-term Quaternary evolution of Mediterranean valleys in the Iberian Peninsula, poorly explored to the date.

Middle Cenomanian coral fauna from the Roßsteinalmen (Northern Calcareous Alps, Bavaria, Southern Germany) – a revised and extended version

In the Northern Calcareous Alps, relics of a formerly widely distributed shallow marine facies belonging to the Branderfleck Formation (upper Albian to lower Turonian) crop out and contain locally abundant corals. The fauna described here derives from Middle Cenomanian sediments. This study complements a former revision. In total, the fauna includes 98 species in 46 genera, belonging to 16 scleractinian superfamilies and two octocorallian families. One species – Enallhelia octasepta – is described as new. The fauna that was formerly located at the northern part of the Apulian plate (Austroalpine unit), south of the Penninic Ocean, shows palaeobiogeographic relationships to Cenomanian faunas from the Basque-Cantabrian Basin, the Prebetic zone, the Pelagonium, and the Quillan Basin, indicating stronger connections to Tethyan rather than Boreal faunas. The fauna also shares species with Aptian and Albian, but also with Late Cretaceous faunas of the Gosau Basin. Eight genera experienced a range extension; five genera have their last occurrence in the Middle Cenomanian fauna, and three genera have their first occurrence. Although the fauna presents numerous genera that became widespread in the Late Cretaceous, its generic composition is more closely related to late Early Cretaceous corals than to post-Cenomanian corals. The faunal turnover at the Cenomanian/Turonian boundary was not marked by the sudden appearance of new faunal elements, but rather by the disappearance of taxa. Some faunal elements that constitute post-Cenomanian faunas already existed in the Cenomanian, but they were very rare. The increase of taxa after the Cenomanian/Turonian boundary took place during the Coniacian and Santonian.

A new enigmatic lacustrine trackway in the upper Miocene of the Sierra de las Cabras (Jumilla, Murcia, Spain)

A new fossil trackway is described in the upper lacustrine Miocene in the Prebetic Zone of the Iberian Peninsula, in Jumilla town (Murcia region) called Aenigmatipodus jumillensis nov. ichnogen. nov. ichnosp. This trackway consists of a pattern made up of sets of three tracks or triads, which are subparallel to each other, arranged in alternate groups. Each track presents a depression formed by a central body that is three times as long as it is wide, with straight or slightly curved walls, with two shorter bodies placed at the ends, one of the ends being shorter and more pronounced than the opposite, which is longer and stretched. All the biomechanical possibilities compatible with an anatomical design that could leave the impression of three alternate triads of tracks are analysed. The supports are only from the extremities on one side of the organism (left or right), the displacement being by translation. It is concluded that it had to be a large arthropod (metre scale), with a hexapod or decapod (less probably octopod), which had to be dragged laterally by a current in a very shallow lake or wetland environment. To date, no fossil organism is known, nor its current equivalent, that corresponds to these characteristics.

Progradation of a shallow carbonate platform developed on a fault-block in the Western Tethys (lower Aptian, Sierra de Bedmar-Jódar, Prebetic of Jaén, Spain)

The Middle Member of the Llopis Fm in the Sierra de Bedmar-Jódar Unit of the Prebetic Zone of Jaén (southern Spain) was deposited on a shallow-marine platform of the Southern Iberian Continental Margin during the earliest Aptian. Detailed field logging of nine stratigraphic sections and facies mapping have allowed seven lithofacies associations (L1–L6) to be distinguished, one siliciclastic (L1) and five carbonate facies (L2–6). The succession is composed of eight consecutive elemental sequences of lithofacies associations L1–L6. Each elemental sequence is interpreted as representing one episode of shallowing-upwards carbonate deposition in a very shallow platform-lagoon that was bounded shoreward by clastic/ooid bars and passed seaward either to stromatoporoid bioconstructions (bioherms and biostromes) or rudist biostromes. The successive elemental sequences show north-eastward progradational geometries. Three phases of platform development are identified: (1) installation of the shallow platform; (2) development of a lagoon bounded by a stromatoporoid barrier and (3) development of an Urgonian-type platform dominated by rudists. During the early Aptian, the Bedmar-Jódar platform was partially isolated from the rest of the Prebetic platform and showed overall progradation towards the NE, in contrast to the general south-eastward progradational trend of the Prebetic platform. Sedimentation was controlled by rift-generated extensional tectonics that resulted in tilting of the platform block, causing the deviation of progradation from the general trends of the Prebetic Platform. In addition, climatic influence is inferred from the presence of siliciclastic sediments derived from weathering of the hinterland, which restricted the carbonate factory.

Geology and evolution of the Cortes de Pallás diapir (Eastern Iberia)

ABSTRACT This paper presents an 1:20,000 geological map and cross-sections of the Cortes de Pallás diapir (eastern Iberia). This structure is located at the junction of the Iberian Chain and the Betic Cordillera, in the northernmost part of the eastern Prebetic Zone. The diapir is an ENE to NE oriented saltwall, parallel to the regional structural trend of the Betic Cordillera. Our results support the hypothesis of a polyphase tectonic evolution from Oligocene to Pliocene times: (a) An extensional phase, Oligocene–Early Miocene in age, in which the graben system formed and the diapir rose. (b) A Middle Miocene compressive phase characterized by at least the partial closure of the diapir and thrusting of its old southern margin over the previous half-graben infill. (c) Finally, a Late Miocene–Pliocene extensional phase in which, synchronous to the normal faulting in the graben system, the diapir was reactivated and cut the previous structures.

Upper Valanginian to Lower Hauterivian coral faunas from the Sierra Larga (Prebetic zone, SE Spain)

From the Upper Valanginian and Lower Hauterivian of the Sierra Larga (Prebetic zone, SE Spain) two small faunas of colonial corals are taxonomically described. The Valanginian fauna encompasses 23 species and the Hauterivian fauna 11 species. The family diversity with 11 families or informal groups is high. Most species-rich are the families Latomeandridae, Microsoleniidae, and Stylinidae. Whereas the Hauterivian fauna contains only few common genera, the Valanginian fauna represents more and more rare genera. The faunas differ in age and facies and represent a low coincidence in their taxonomic composition. The species of both faunas are known from other areas with a range of Oxfordian to Turonian in age, but most species occurred from the Hauterivian to the Lower Aptian. Palaeobiogeographically, both faunas show a relationship with Lower Cretaceous faunas of the Western Hemisphere and nearby located faunas of the Tethys and Boreal. Two genera – Actinastraeopsis and Polyphylloseris – experience a range extension in their first occurrence.

Geology of the Eastern Prebetic Zone at the Jumilla region (SE Iberia)

ABSTRACTThis article presents a geological map and cross-sections at 1:50,000 scale covering an area of 609 km2 of the Eastern Prebetic Zone (SE Iberia). The structure of the studied area is characterized by an NW-directed fold-and-thrust belt and inactive salt diapirs that are parallel to the ENE- to NE-regional trend of the eastern Betic Cordillera. This regional trend is locally disrupted by the NW-trending Matamoros Basin, which is flanked by the active Jumilla and La Rosa diapirs. The geological map, the cross-sections and the outcrop observations support the hypothesis that the major Mesozoic rifting phase affecting the Eastern Prebetic Zone occurred during the Upper Jurassic to Santonian times coeval to the development of extensional basins in the Western Tethyan area. The proximal part of this passive margin was subsequently incorporated into the external part of the Betic thin-skinned fold-and-thrust belt. The Upper Cretaceous to Cenozoic tectonic evolution of the study area encompassed the following stages: a Campanian to Aquitanian NW-directed contraction; a Burdigalian to upper Miocene extensional reactivation of the main subsalt faults; and a Serravallian NW-directed contractional reactivation. In this scenario, the combined effect of the previous contractional reactivation of pre-existing salt structures together with the Miocene subsalt extension triggered passive salt extrusion of the La Rosa and Jumilla diapirs.

Testing thin-skinned inversion of a prerift salt-bearing passive margin (Eastern Prebetic Zone, SE Iberia)

Detailed geologic mapping combined with well and seismic data from the Eastern Prebetic Zone (SE Iberia) reveal extensional and contractional structures that permit characterization of passive margin development and its incorporation into a thin-skinned fold-and-thrust belt. The study area is represented by NW-directed, ENE-trending folds and thrusts faults locally disrupted by the NW-trending Matamoros Basin and the active Jumilla and La Rosa diapirs. These structures resulted from the thin-skinned inversion of the proximal part of the Eastern South Iberian passive margin containing prerift salt. Here, Upper Jurassic to Santonian thick-skinned extension controlled the accumulation of sediment over mobile prerift salt. This in turn defined the style of salt tectonics characterized by monoclinal drape folds, suprasalt extensional faults and diapirs. The structural and sedimentological analysis suggests that during extension, salt localizes strain thus decoupling sub- and suprasalt deformation. Thick-skinned extension controls suprasalt deformation as well as its location and distribution which changes over time. Salt also localizes strain during inversion. The preexisting salt structures, weaker than adjacent areas, preferentially absorb the contractional deformation. In addition, the stepped subsalt geometry that results from thick-skinned extension also controls the shortening propagation. Therefore, the degree of strain localization depends on the thickness of the suprasalt cover and on the dip of subsalt faults relative to the thin-skinned transport direction.

Sulfur and lead isotope systematics: Implications for the genesis of the Riópar Zn-(Fe-Pb) carbonate-hosted deposit (Prebetic Zone, SE Spain)

The Zn-(Fe-Pb) deposits of the Riópar area (Prebetic Zone, SE Spain) are hosted by dolostones that replace Berriasian to Valanginian (Upper Jurassic-Lower Cretaceous) limestones. Mineralization consists of hypogene sphalerite, marcasite and galena, and supergene calamine zones. The hypogene ores are associated with a saddle dolomite gangue. The ore bodies occur as discordant and stratiform lenses, ore-cemented breccias, cm- to mm-wide veins and veinlets, disseminations and stylolite porosity filling within the host dolomites. The main ore controls include stratigraphy and/or lithology, tectonics (faults, fractures and breccias) and availability of metals and sulfur. The morphologies and epigenetic character of the hypogene ore bodies are consistent with the classification of this mineralization as a Mississippi Valley-type (MVT) deposit. The Ga/Ge geothermometer in sphalerite yielded a temperature range of 194–252°C, which represents the temperature of the source region of the ore solution. This value is comparable to the temperature obtained in the ore deposition site, 159±15°C from the Δ34S geothermometer in sphalerite galena pairs. This similitude points to a hydrothermal fluid that did not cool down significantly during flow from the fluid reservoir area to the precipitation site. δ34S values of base-metal sulfides (−7.5 to +3.5‰) are consistent with thermochemical reduction of Triassic sulfate (seawater and/or derived from dissolution of evaporites) by interaction with organic compounds (e.g., hydrocarbons, methane), which reduced sulfate to sulfide in the deposition site. The lead isotope ratios (206Pb/204Pb=18.736–18.762; 207Pb/204Pb=15.629–15.660; 208Pb/204Pb=38.496–38.595) of galena suggest that Pb, and probably other metals as Zn, is derived from continental crustal rocks. On the other hand, these relations points to a unique metal source probably derived from the Paleozoic basement rocks. The relationship between bedding-parallel stylolites, dolomitization, sulfide precipitation and Alpine tectonic affecting the MVT ore, suggests a relative timing range for the mineralization in the Riópar area of 95–20Ma (Upper Cretaceous-Tertiary). The sulfide mineralization and the associated dolomitization are thus explained by the contribution of two fluids that mixed in different proportions during dolomitization and mineralization: i) a fluid probably derived from Cretaceous seawater saturating Mesozoic sediments (Fluid A), characterized by being dilute and initially low temperature, which should have contained organic rich compounds in the ore deposition site (e.g., hydrocarbons and CH4 dissolved gas); and ii) a high salinity hydrothermal brine (Fluid B) rich in both metals and sulfate, circulated through the Paleozoic basement. During the pre-ore dolomitizing stage the fluid phase was dominated by the diluted fluid (Fluid A>Fluid B), whereas in a later fluid pulse, the proportion of the high salinity fluid increased (Fluid A<Fluid B) which allowed sulfide precipitation. MVT exploration in the Prebetic Zone should focus towards the SW of the Riópar mines, in the vicinity of the Alto Guadalquivir-San Jorge fault.

REE and Sm-Nd Clues of High-temperature Fluid-rock Interaction in the Riópar Dolomitization (SE Spain)

REE geochemistry and Sm-Nd isotope data of Mesozoic stratabound and patchy dolostones of the Riópar area (Prebetic Zone, SE Spain) are presented. The results, combined with previously published data, suggest the dolomitizing fluid was a warm brine that interacted with siliciclastic rocks of Triassic age and with the host carbonates at low fluid-rock ratios. The positive Eu anomaly, negative ɛNd values and MREE patterns confirm that the dolostones were formed by interaction with warm acidic crustal fluids. C-O isotopic interaction models indicate that these fluids were characterized by δ18O-enriched and δ13C-depleted compositions, pointing to low ratios of fluid to rock volumes. The studied dolostones show two Sr sources: one Sr signature is close to the host carbonate values and the other one is more radiogenic, indicating that fluids became enriched in 87Sr after interacting with siliciclastic rocks. Furthermore, the Sr-Nd isotope data systematic depicts a positive correlation, thus probably the same rock sources are shared for both elements. Moreover, the warm fluids interacted with regional limestones achieving a negative Ce and positive La anomalies, low δ18O compositions and similar δ13C values than the host carbonates.

New drilling of the early Aptian OAE1a: the Cau core (Prebetic Zone, south-eastern Spain)

Abstract. The Cretaceous was punctuated by several episodes of accelerated global change, defined as Oceanic Anoxic Events (OAEs), that reflect abrupt changes in global carbon cycling. The Aptian Oceanic Anoxic Event (OAE1a; 120 Ma) represents an excellent example, recorded in all major ocean basins, and associated with massive burial of organic matter in marine sediments. The OAE1a is concomitant with the "nannoconid crisis", which is characterized by a major biotic turnover, and a widespread demise of carbonate platforms. Many studies have been published over the last decades on OAE1a's from different sections in the world, and provide a detailed C-isotope stratigraphy for the event. Nevertheless, new high-resolution studies across the event are essential to shed light on the precise timing and rates of the multiple environmental and biotic changes that occurred during this critical period of Earth history. Here we present a new drill core recovering an Aptian section spanning the OAE1a in southern Spain. The so-called Cau section was drilled in the last quarter of 2015. The Cau section is located in the easternmost part of the Prebetic Zone (Betic Cordillera), which represents platform deposits of the southern Iberian palaeomargin. The lower Aptian deposits of the Cau section belong to a hemipelagic unit (Almadich Formation), deposited in a highly subsident sector of the distal parts of the Prebetic Platform. Previous work on the early Aptian of the Cau succession has focused on stratigraphy, bioevents, C-isotope stratigraphy, and organic and elemental geochemistry. A more recent study based on biomarkers has presented a detailed record of the pCO2 evolution across the OAE1a (Naafs et al., 2016). All these studies reveal that the Cau section represents an excellent site to further investigate the OAE1a, based on its unusually high sedimentation rate and stratigraphic continuity, the quality and preservation of fossils, and the well-expressed geochemical signatures.

Mineralogical and geochemical characterization of the Riópar non-sulfide Zn-(Fe-Pb) deposits (Prebetic Zone, SE Spain)

The present paper reports the first detailed petrological and geochemical study of non-sulfide Zn–(FePb) deposits in the Riópar area (Prebetic Zone of the Mesozoic Betic Basin, SE Spain), constraining the origin and evolution of ore-forming fluids. In Riópar both sulfide and non-sulfide Zn–(FePb) (“calamine”) ores are hosted in hydrothermally dolomitized Lower Cretaceous limestones. The hypogene sulfides comprise sphalerite, marcasite and minor galena. Calamine ores consist of Zn-carbonates (smithsonite and scarce hydrozincite), associated with abundant Fe-(hydr)oxides (goethite and hematite) and minor Pb-carbonates (cerussite). Three smithsonite types have been recognized: i) Sm-I consists of brown anhedral microcrystalline aggregates as encrustations replacing sphalerite; ii) Sm-II refers to brownish subhedral aggregates of rugged appearance related with Fe oxi-hydroxides in the surface crystals, which replace extensively sphalerite; and iii) Sm-III smithsonite appears as coarse grayish botryoidal aggregates in microkarstic cavities and porosity. Hydrozincite is scarce and appears as milky white botryoidal encrustations in cavities replacing smithsonite. Also, two types of cerussite have been identified: i) Cer-I cerussite consists of fine crystals replacing galena along cleavage planes and crystal surfaces; and ii) Cer-II conforms fine botryoidal crystals found infill porosity. Calcite and thin gypsum encrustations were also recognized. The field and petrographic observations of the Riópar non-sulfide Zn–(FePb) revealed two successive stages of supergene ore formation under meteoric fluid processes: i) “gossan” and “red calamine” formation in the uppermost parts of the ore with deposition of Fe-(hydr)oxides and Zn- and Pb-carbonates (Sm-I, Sm-II and Cer-I), occurring as direct replacements of ZnPb sulfides; and ii) “gray calamine” ore formation with deposition of Sm-III, Cer-II and hydrozincite infilling microkarst cavities and porosity. The stable isotope variation of Riópar smithsonite is very similar to those obtained in other calamine-ore deposits around the world. Their CO isotope data (δ18O: +27.8 to +29.6‰ V-SMOW; δ13C: −6.3 to +0.4‰ V-PDB), puts constrains on: i) the oxidizing fluid type, which was of meteoric origin with temperatures of 12 to 19°C, suggesting a supergene weathering process for the calamine-ore formation under a temperate climate; and ii) the carbon source, that resulted from mixing between two CO2 components derived from: the dissolution of host-dolomite (13C-enriched source) and vegetation decomposition (13C-depleted component).

Petrography and geochemistry of fault-controlled hydrothermal dolomites in the Riópar area (Prebetic Zone, SE Spain)

The present paper reports the first detailed petrographical and geochemical studies of hydrothermal dolomites related to MVT Zn-(Fe–Pb) deposits in the Riópar area (Mesozoic Prebetic Basin, SE Spain), constraining the nature, origin and evolution of dolomitizing and ore-forming fluids. Mapping and stratigraphic studies revealed two stratabound dolostone geobodies connected by other patchy bodies, which replace carbonate units of Upper Jurassic to Lower Cretaceous ages. These dolostones are associated to the W–E trending San Jorge fault, indicating a main tectonic control for fluid flow. Seven different dolomite types were identified: i) matrix-replacive planar-s (ReD-I); ii) matrix-replacive planar-e (ReD-II); iii) planar-e sucrosic cement (SuD); iv) non-planar grey saddle dolomite cement (SaD-I) pre-dating Zn-(Fe–Pb) sulfides; v) non-planar milky to pinkish saddle dolomite cement (SaD-II) post-dating Zn-(Fe–Pb) ores; vi) ore-replacive planar-e porphyrotopic (PoD); and vii) planar-s cloudy cement (CeD). Meteoric calcite types were also recognized. The different dolomite types are isotopically characterized by: i) depleted δ18O (from +25.1 to +27.6‰ V-SMOW) and δ13C (from −2.3 to +0.9‰ V-PDB) values compared to Upper Jurassic to Lower Cretaceous limestone signature (δ18O: +27.6 to +30.9‰ V-SMOW; δ13C: +0.5 to +3.2‰ V-PDB); and ii) 87Sr/86Sr ratios for the main dolomitization phases (ReD and SuD: 0.70736–0.70773) close to the Jurassic and Cretaceous carbonate values (0.70723–0.70731) whereas more radiogenic values (0.70741–0.70830) for saddle dolomites (SaD) related to the Zn-(Fe–Pb) sulfide mineralization prevailed after fluid interaction with Rb-bearing minerals. Microthermometrical studies on two-phase liquid and vapor fluid inclusion populations in planar and non-planar dolomites and sphalerite show homogenization temperatures between 150 and 250 °C. These data indicate that both planar and non-planar dolomite textures formed at high-temperatures under hydrothermal conditions in deep-burial diagenetic environments. The main dolomitizing phase (ReD-I/ReD-II and SaD-I) shows low to moderate fluid inclusions salinity (5–14 wt.% eq. NaCl), whereas the dolomitization related to ore precipitation (sphalerite and SaD-II) spreads to higher salinity values (5–25 wt.% eq. NaCl). These data may respond to a mixing between a low salinity fluid (fluid A, less than 5 wt.% eq. NaCl) and a more saline brine (fluid B, more than 25 wt.% eq. NaCl) at different fluid proportions.

Description of a new species of Offneria (Hippuritida, Caprinidae) from the lower Aptian of southeast Spain. Stratigraphic, evolutionary, palaeobiogeographic and palaeoenvironmental implications

A new species of Offneria (Caprinidae) Offneria prebetica nov. sp., is described from the Murcia region (Prebetic zone, SE Spain). Its type level is the upper Bedoulian. The key diagnostic character of the new species is the presence on the ventral side of the left valve of an inner row, or double row, of polygonal canals flanked by outer piriform canals with one or two orders of bifurcations. Offneria prebetica nov. sp. is the most advanced species of the genus. Cluster analysis shows the placement of the new species in the monophyletic group of European species, in agreement with its geographic location. Offneria appears to be the most prolific genus of the Caprinidae with species having contrasting ages and palaeobiogeographic distributions. Stratigraphic data from SE Spain indicate that the Offneria lineage was resilient to the environmental perturbations recorded during the late Bedoulian, Offneria prebetica nov. sp. may be used as a time marker for this interval, and its last occurrence was coeval with the “Mid-Aptian extinction event”.

Applicability of magnetic fabrics in rocks associated with the emplacement of salt structures (the Bicorb–Quesa and Navarrés salt walls, Prebetics, SE Spain)

This work assesses the applicability of the analysis of the anisotropy of magnetic susceptibility (AMS) to rocks associated with salt structures. Magnetic fabrics from 16 sites sampled on Upper Triassic clays (Keuper facies) interbedded within the salt layers of the Bicorb–Quesa and Navarrés salt walls (Prebetic Zone, SE Spain) are mostly characterized by oblate magnetic ellipsoids with their magnetic foliation parallel to the bedding and magnetic lineation contained in the bedding plane but without a constant relationship with dip direction. To evaluate the quality and significance of the low-field AMS, several experiments were carried out to characterize the magnetic mineralogy of representative samples and enable separation of the contributions from paramagnetic and ferromagnetic (s.l.) minerals. The comparison between the orientation of the observed magnetic lineation and that of the structural elements characterizing the internal geometry of the studied salt structures (antiforms, minor folds, faults and shear zones) and flanks indicates that the magnetic fabric is controlled by deformation processes affecting the salt walls during their growth and/or evolution. Samples were also analyzed from sixteen sites from Miocene rocks outcropping in several syn-diapiric Miocene half-grabens related to the salt walls studied. Their magnetic fabric is interpreted to reflect the dominant stretching direction at the syn-diapiric half grabens during and/or shortly after deposition. Our results indicate that caution is required in interpreting magnetic lineations related to salt flow mechanics from rocks associated with salt structures.

Late Albian Scleractinian corals from the Prebetic Zone (SE Spain)

Late Albian Scleractinian corals from the Prebetic Zone (SE Spain)

Paleomagnetic and inner diapiric structural constraints on the kinematic evolution of a salt-wall: The Bicorb-Quesa and northern Navarrés salt-wall segments case (Prebetic Zone, SE Iberia)

Paleomagnetism together with an analysis of the internal structure of the Bicorb-Quesa and northern Navarrés salt-wall segments (Prebetic Zone in SE Iberia) were used to constrain their kinematics and driving mechanisms. Paleomagnetic data from Upper Triassic red beds of the selected salt-related structures and from the Miocene rocks belonging to adjacent syn-diapiric half-grabens reveal 15–30° counter-clockwise vertical-axis rotations of the salt-wall rocks and a 20° clockwise rotation of the Jurassic-Miocene cover block located south of the salt-wall. This, together with the salt-wall structure, indicates that the origin of the salt-wall was linked to the motion of a late Miocene thin-skinned extensional fault system, which detached on the Upper Triassic evaporites. Specifically, the salt-wall formed by the south-southwest displacement with a 20° clockwise rotation component of a cover block bounded northwards by the detachment disruptions generated by the motion of pre-existent basement faults. The Upper Triassic detachment level was first affected by a counter-clockwise vertical axis rotation and, during the Paleogene-earliest Miocene building of the Iberian Chain, by tight WNW-trending folds and SSE-directed minor thrusts. This study also shows that Paleomagnetism together with the analysis of the internal structure can successfully depict the geometry and kinematic evolution of complex salt-wall structures.

Ascription of the island of Ibiza to the Prebetic of Alicante (Betic Range, Spain) after correlation of Lower Cretaceous sedimentary successions

The lithostratigraphic succession of the Tithonian – Albian interval of the island of Ibiza shows a great similarity with that of the Internal Prebetic Zone in the Alicante area (Betic Range), with only slight differences in age and stratigraphic distribution. This similarities are based on the correlation of the following units: i) the Punta Jondal Formation of Ibiza with the Sierra del Pozo Formation of Alicante (Tithonian – early Valanginian); ii) the Port Sant Miquel Formation (Aptian) with the Arroyo de los Anchos Formation; iii) the Torre des Molar (early Aptian), Penyal de s’Águila (late Aptian) and Cala d'en Sardina (late Aptian) members of the Port Sant Miquel Formation with the Llopis, Almadich and Seguilí formations in Alicante; and iv) the Es Cubells Formation (Tithonian – earliest Cenomanian) with several marly units of the Prebetic of Alicante.The Ibiza Tithonian – Albian sedimentary succession was deposited within a NNW–SSE trending basin related to the Tethyan domain of SE Iberia. It is organized in three sedimentary successions (named Aubarca, San José and Ibiza successions, from NNW to SSE), which were tectonically stacked towards the NNW during the Alpine inversion of the basin. These sedimentary successions were deposited within the distal regions of a carbonate platform opened towards the southeast. In the SE sector of the island, the Ibiza succession is characterized by a thick and rhythmic alternation of basinal marls and marly limestones. Northwestwards, the San José succession is characterized by the presence of inner platform carbonate deposits at the base of the succession (Tithonian – early Valanginian). Finally, the presence of shallow-water rudist-bearing limestones (Aptian) in the northwestern sector, defines the Aubarca succession. The NNW–SSE evolution of the stratigraphic architecture from the Aubarca – San José – Ibiza successions is clearly similar to the tectonostratigraphic and palaeogeographic N–S zoning previously recognized from the Sierra de Mariola – Cabezón de Oro – Fontcalent successions in the Prebetic of Alicante, respectively.Stratigraphical sequence analysis of the sedimentary successions of the island of Ibiza allows recognizing a depositional stacking pattern defined by four long-term depositional megasequences, which can also be correlated with equivalent megasequences in the Prebetic of Alicante. The three lower megasequences (Tithonian – Albian) show a transgressive–regressive evolution, revealed by the deposition of transgressive hemipelagic facies in the lower part and the development of prograding shallow-water carbonate platforms during regressions. The fourth megasequence (Albian) is not as well developed as the previous megasequences, showing siliciclastic levels instead of the shallow-water carbonate platform facies, thus suggesting a development during major sea-level fall. Nevertheless, in the Ibizan successions, high resolution sequence stratigraphy and accurate biostratigraphic scales have not yet been established; consequently, the chronostratigraphy of megasequence boundaries and the maximum flooding surfaces are less accurate than in their Prebetic counterparts.

Paleoseismic and geomorphologic evidence of recent tectonic activity of the Pozohondo Fault (Betic Cordillera, SE Spain)

Instrumental and historical seismicity in the Albacete province (External Prebetic Zone) has been scarcely recorded. However, major strike-slip faults showing NW-SE trending provide geomorphologic and paleoseismic evidence of recent tectonic activity (Late Pleistocene to Present). Moreover, these faults are consistently well oriented under the present stress tensor and therefore, they can trigger earthquakes of magnitude greater than M6, according to the lengths of surface ruptures and active segments recognized in fieldwork. Present landscape nearby the village of Hellin (SE of Albacete) is determined by the recent activity of the Pozohondo Fault (FPH), a NW-SE right-lateral fault with 90 km in length. In this study, we have calculated the Late Quaternary tectonic sliprate of the FPH from geomorphological, sedimentological, archaeoseimological, and paleoseismological approaches. All of these data suggest that the FPH runs with a minimum slip-rate of 0.1 mm/yr during the last 100 kyrs (Upper Pleistocene-Holocene). In addition, we have recognized the last two major paleoearthquakes associated to this fault. Magnitudes of these paleoearthquakes were gretarer than M6 and their recurrence intervals ranged from 6600 to 8600 yrs for the seismic cycle of FPH. The last earthquake was dated between the 1st and 6th centuries, though two earthquakes could be interpreted in this wide time interval, one at the FPH and other from a far field source. Results obtained here, suggest an increasing of the tectonic activity of the Pozohondo Fault during the last 10,000 yrs.