Integrated calcareous nannofossil biostratigraphy and magnetostratigraphy from the uppermost marine Eocene deposits of the southeastern Pyrenean foreland basin : evidences for marine Priabonian deposition

An integrated magneto-biostratigraphic study, based on calcareous nannofossils, was carried out on the Eocene uppermost marine deposits of the southeastern Pyrenean foreland basin. The study was performed along six sections of the upper portion of Igualada Formation, cropping out in the Vic area. Common late Middle/Upper Eocene nannofossil assemblages allow recognizing, within a normal magnetozone or immediately below, the FO of Istmolithus recurvus, which identifies the base of NP19 Zone, in the Priabonian. This event occurs within C16n.2n magnetozone in several oceanic and Mediterranean sections, which allows the correlation of the normal magnetozone in the Vic area to chron C16n.2n. This challenges previous magnetostratigraphic interpretations in the Vic area that correlated the uppermost marine sediments to chron C17n. The estimated age for the FO of I. recurvus is 36 Ma and collectively with the magnetostratigraphic data indicates that the uppermost marine sediments in the basin are of Priabonian age. The new results indicate that the entire chronology of the marine strata needs reassessment. The thickness of chron C16n.2n varies from 45 m in the Collsuspina area (southern sector) to about 270-290 m in the Sant Bartomeu del Grau area (northern sector), which is indicative of a marked asymmetry in the basin deposition

Datos paleomagnéticos del sustrato rocoso de la isla de Livingston (Península Antártica): implicaciones tectónicas en la evolución neógena

Se presentan resultados paleomagnéticos de la Fo rmación Miers Bluff y de los diques terciarios y andesitas de la Isla de Livingston (Islas Shetland del Sur, Península A n t á rtica). La mayoría de las rocas estudiadas son portadoras de magnetización estable, que reside en una fase de baja coercividad, probablemente Ti-Magnetita. La restitución tectónica progresiva de las direcciones de magnetización remanente característica revela que la magnetización en las turbiditas de la Fm. Miers Bluff fue adquirida después del plegamiento. Las direcciones medias de los diques y de la Fm. Miers Bluff no ofrecen una diferencia significativa, sugiriendo una misma edad para la magnetización. Se propone que el origen de la misma es una remagnetización de edad terciaria. Asimismo, la posición de los polos paleomagnéticos obtenidos sugiere un basculamiento tectónico que estaría relacionado con la apertura y extensión en el Estrecho de Bransfield.We report paleomagnetic results from the Miers Bluff Formation and Tertiary dykes and andesites in Livingston Island (South Shetland Islands, Antarctic Peninsula). Most of the samples carry stable magnetization, residing in a low coercivity phase, most likely (Ti)magnetite. Progressive untilting of the Characteristic Remanent Magnetization directions reveals that the magnetization of the turbidites (Miers Bluff Fm.) is post-folding. Miers Bluff and the dyke mean directions do not show any significant difference, suggesting the same magnetization age. Thus, a local Cenozoic remagnetization is proposed. Also, the paleomagnetic poles suggest a tectonic tilting that would explain the observed discrepancies between the produced paleopoles and the APWP for the Antarctic Peninsula

Palaeomagnetic chronology of the evaporitic sedimentation in the Neogene Fortuna Basin (SE Spain): early restriction preceding the 'Messinian Salinity Crisis'

The magnetostratigraphic study of the evaporitic Río Chicamo section (240 m) in the Neogene Fortuna Basin (Murcia, southeast Spain) has identified the record of five magnetozones. The most probable correlations with the standard geomagnetic polarity time scale (GPTS) imply that the marine evaporitic sedimentation of this basin was not coeval with the Messinian evaporites of the Sorbas Basin (Almeria, southeast Spain) and the Caltanissetta Basin (central Sicily) (assigned to the reverse Chron C3r, late Messinian by Gautier et al., 1994). The marine evaporites and diatomites from the Fortuna Basin are older (late Tortonian to early Messinian) than the evaporites of those basins. The chronological framework for the sedimentation in the Fortuna Basin together with the isotopic data from the sulphates in these evaporitic units indicate the following. (1) Restriction and confinement in the basin initiated as early as uppermost Tortonian, leading to deposition of evaporites under mixed (marine-continental) conditions. (2) The subsequent sedimentation of marine evaporites and diatomites in this basin occurred in a period between the Tortonian and Messinian transition and the early Messinian: the onset of this sedimentation pre-dates similar sediments of restricted marine environments in the eastern Betics basins, and possibly of the western Mediterranean region also. (3) Episodes of restriction and reflooding in the basin would have occurred in response to periodic fluctuations of the oceanic level under local tectonic controls. In the Fortuna Basin, the global base level drop associated with the late Messinian Salinity Crisis was recorded by the progradation of alluvial fans leading to thick clastic deposits overlying the youngest evaporites. These observations hint to: (a) the peculiar characteristics and sensitiveness of some of the marginal intramontane basins in the eastern Betics to reflect structural controls framed in the late Neogene global climatic changes; and (b) the diachronism of the beginning of the marine evaporitic deposition in the Mediterranean region linked to the salinity crisis during the Messinian

Paleomagnetic dating of non-sulfide Zn-Pb ores in SW Sardinia (Italy): a first attempt

A first paleomagnetic investigation aimed at constraining the age of the non-sulfide Zn-Pb ore deposits in the Iglesiente district (SW Sardinia, Italy) was carried out. In these ores, the oxidation of primary sulfides, hosted in Cambrian carbonate rocks, was related to several paleoweathering episodes spanning from the Mesozoic onward. Paleomagnetic analyses were performed on 43 cores from 4 different localities, containing: a) non-oxidized primary sulfides and host rock, b) oxidized Fe-rich hydrothermal dolomites and (c) supergene oxidation ore («Calamine»). Reliable data were obtained from 18 samples; the others show uninterpretable results due to low magnetic intensity or to scattered demagnetization trajectories. Three of them show a scattered Characteristic Remanent Magnetization (ChRM), likely carried by the original (i.e. Paleozoic) magnetic iron sulfides. The remaining 15 samples show a well defined and coherent ChRM, carried by high-coercivity minerals, acquired after the last phase of counterclockwise rotation of Sardinia (that is after 16 Myr), in a time interval long enough to span at least one reversal of the geomagnetic field. Hematite is the main magnetic carrier in the limestone, whereas weathered hydrothermal dolomite contains goethite or a mixture of both. The results suggest that paleomagnetism can be used to constrain the timing of oxidation in supergene-enriched ores

First biostratigraphic data of the evaporitic groups in the Fortuna Basin (Betic Cordillera)

The present work offers the first biostratigraphic calibration based on calcareous nannoplankton of the three evaporitic assemblages in the Rio Chicamo section. The A. primus FAD is registered at the upper part of the Sanel marls, above the lower gypsum, and bellow the Tale gypsum. The A. delicatus FAD, and the A. amplificus FAD occurs in the lower and upper part of the Chicamo Cycles, respectively, which allow to calibrate the Chicamo Cycles reversal as the chron C3Ar. The Tortonian/Messinian boundary is found at the Tale gypsu

The Bajo Segura Basin (SE Spain): implications for the Messinian salinity crisis in the Mediterranean margins

The analysis of the Messinian and Pliocene stratigraphy of the Bajo Segura Basin (a marginal basin of the western Mediterranean) has revealed three synthems deposited in a high sea-level context: T-MI (late Tortonian-Messinian), MII (Messinian), and P (early Pliocene), bounded by two lowstand erosional surfaces (intra-Messinian and end-Messinian unconformities). With respect to the salinity crisis, we propose the following series of events: 1) pre-evaporitic or pre-crisis phase (T-MI synthem); 2) first sea-level fall and subaerial exposure (intra-Messinian unconformity), possibly related to the precipitation of the Lower Evaporites; 3) syn-evaporitic phase (MII synthem), recorded both by selenitic gypsum (Upper Evaporites) as well as by lagoon deposits (Lago-Mare); 4) second sea-level fall and subaerial exposure (end-Messinian unconformity), characterized by deeply incised palaeovalleys; and 5) postevaporitic or post-crisis phase (P synthem), which coincides with the definitive restoration of open marine conditions in the basin. A combined biostratigraphic and magnetostratigraphic study revealed that all the events linked to the salinity crisis (from the end of the pre-evaporitic phase to the beginning of the post-evaporitic phase) occurred within the chron C3r (c. 5.9-5.2 Ma).Financial aid was provided by Research Projects BTE2003-05047, CGL2005-06224BTE (MEC), CGL2007-65832/BTE (MEC), GV04B-629 (Generalitat Valenciana) and “Paleoenvironmental Changes” Group (UA)

Integrated multi-stratigraphic study of the Coll de Terrers late Permian-Early Triassic continental succession from the Catalan Pyrenees (NE Iberian Peninsula): A geologic reference record for equatorial Pangaea

The most severe biotic crisis on Earth history occurred during the Permian-Triassic (PT) transition around 252 Ma. Whereas in the marine realm such extinction event is well-constrained, in terrestrial settings it is still poorly known, mainly due to the lack of suitable complete sections. This is utterly the case along the Western Tethys region, located at Pangaea's equator, where terrestrial successions are typically build-up of red beds often characterised by a significant erosive gap at the base of the Triassic strata. Henceforth, documenting potentially complete terrestrial successions along the PT transition becomes fundamental. Here, we document the exceptional Coll de Terrers area from the Catalan Pyrenees (NE Iberian Peninsula), for which a multidisciplinary research is conducted along the PT transition. The red-bed succession, located in a long E-W extended narrow rift system known as Pyrenean Basin, resulted from a continuous sedimentary deposition evolving from meandering (lower Upper Red Unit) to playa-lake/ephemeral lacustrine (upper Upper Red Unit) and again to meandering settings (Buntsandstein facies). Sedimentary continuity is suggested by preliminary cyclostratigraphic analysis that warrants further analysis. Our combined sedimentological, mineralogical and geochemical data infer a humid-semiarid-humid climatic trend across the studied succession. The uppermost Permian strata, deposited under an orbitally controlled monsoonal regime, yields a relatively diverse ichnoassemblage mainly composed of tetrapod footprints and arthropod trace fossils. Such fossils indicate appropriate life conditions and water presence in levels that also display desiccation structures. These levels alternate with barren intervals formed under dry conditions, being thus indicative of strong seasonality. All these features are correlated with those reported elsewhere in Gondwana and Laurasia, and suggest that the Permian-Triassic boundary might be recorded somewhere around the Buntsandstein base. Consequently, Coll de Terrers and the whole Catalan Pyrenees become key regions to investigate in detail the Permian extinction event and the Triassic ecosystems recovery