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

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

Error de inclinación paleomagnética en materiales aluviales del Oligoceno superior del sector Suroriental de la Cuenca del Ebro (Región Surpirenaica, NE de España)

Alluvial red-beds of two Oligocene succesions in the Southeastem Ebro Basin (Southem Pyrenean foreland, NE Spain) show inclination shallowing, taking into account the reference Oligocene palaeolatitude expected for this region. This fact is interpreted to reflect an inclination error due to either these factors: hydrodynamic control of magnetic particles in the depositional environment, differential compaction of sediment during burial and tectonic deformation. The studied lithofacies are split into five groups: gray sandstones, red sandstones, red siltstones, red mudstones and limestones. A strong positive correlation between the relative amount of phyllosilicates and the magnitude of the inclination error has been established. Lithofacies with low percentage of phyllosilicates (limestones and gray sandstones) display a statistically not significant error of 5" with respect to the magnetic palaeofield inclination, whereas the sediments with a higher phyllosilicate content (siltstones and mudstones) show significant errors of up to 25". This observation has not a major consequence for the interpretation of the magnetic polarity but is crucial for palaeogeographic and palinspastic reconstmctions based on palaeolatitudinal data. The obtained results in this study highlight that the interpretation of paleolatitude based on paleomagnetic data is sometimes not straightfonvard and it requires a detailed evaluation of the rock magnetic parameters (AMS in particular) to reveal the presence of such inclination deflection

Nuevos datos magnetoestratigráficos del tránsito Oligoceno-Mioceno en el sector SE de la Cuenca del Ebro (provincia de Lleida, Zaragoza y Huesca, NE de España)

The study of two late Oligocene-early Miocene stratigraphic sections of alluvial and shallow lacustrine facies in the SE Ebro Basin has enabled the establishment of a high-resolution magnetostratigraphy for the Oligocene-Miocene boundary. The studied samples include alluvial sandstones and mudstones as well as shallow lacustrine limestones. A total of 121 stratigraphic levels, with an average sample spacing of -2.5 m, were sampled in two sections, using a portable gasoline powered dril1 machine. Core samples were cut in the laboratory into two or three standard specimens of 2.54 cm diameter X 2.1 cm in length. A minimum of two specimens per site were thermally or AF demagnetized in 8-9 steps at intervals of 50°C or 30°C, and intervals of 2.5 mT and 5 mT, respectively. The magnetic polarity zonation of the sections have been correlated to the Geomagnetic Polarity Time Scale (GPTS) allowing the recognition of Chrons 9r, 9n, 8r and 8n in the Mina Pilar section, and Chrons 6Cr, 6Cn, 6Br, 6Bn and 6AAr in the Valcuerna section. On the basis of magnetostratigraphic correlation it is deduced an interval of sedimentation time of -1.6 Ma for the Mina Pilar section, and 1.7-1.9 Ma for the Valcuerna section

Cinemática rotacional del cabalgamiento basal surpirenaico en las Sierras Exteriores Aragonesas: Datos magnetotectónicos

The magnetotectonic analysis of 32 sites located along the External Sierras (mainly in Middle Eocene marls) shows the primary character of the magnetisation and pennits the differences between the paleovectors obtained to be interpreted as a result of the rotational kinematics of the southpyrenean floor thrust in the study area. The constancy of the directions of the defined unblocking intervals (300"-425°C for the thermal treatment) and the homogeneity of the magnetic carriers (these were always low coercitivity phases, probably sulphides andlor magnetite) prove the stability of the magnetisation. On the other hand, the primary character of the magnetisation (Middle Eocene) can be demonstrated by: a) the constancy of the magnetic inclination (47.3 +/- 1.7) and its similarity with the reference direction; b) the occurrence of reversals, and the positive result of the fold-test made in the Pico del Águila anticline; c) the consistency between the reference direction (DEC = 005", INC = 51°, a95=6 ") and the direction obtained for the authocthonous footwall (DEC = 005", INC = 38", a95= 8") which crops out in the western sector of the Sierras Exteriores thrust front. The interpretation of the paleomagnetic data within the External Sierras structural framework clearly shows that the kinematics of individual thrust sheets involves a clockwise component, at least during a period of their evolution. The maximum rotation values were found in the western and central sectors (42" and 30" respectively). The age of the rotation decreases towards the west along with the age of deformation of the cover rocks. Starting in late Priabonian the kinematics of the thrust front resulted in a lack of rotation in the central sector of the Sierras, while the western sector undenvent a clockwise rotation. The differential movement between both sectors gave rise to the development or reactivation of structures (i. e. Rasal-Anzáñigo anticlines) that articulated the deformation of adjacent zones with different rotational components

Magnetocronología de las sucesiones cenozoicas de la cuenca de As Pontes (La Coruña, Noroeste de España)

The Terciary Basin of As Pontes (Northwest Spain) is associated with an onshore NW-SE dextral strike-slip fault system. A total of 900 specimens from the sedimentary infill have been demagnetized, using thermal and alternating field demagnetization procedures. Paleomagnetic data indicate that the duration of sedimentation in the basin was about 6,2 My, lasting from the latest Early Oligocene until the Early Miocene. The magnetostratigraphy of the basin successions allows us to establish a very precise chronological correlation within the basin. In addition, the overall pattern of declinations shows a clockwise rotation (9º±4º in the sedimentary infill) with respect to the Oligocene-Miocene reference declination, coherent with a NW-SE dextral strike-slip faults system. The dating of the sedimentary infilling of the As Pontes basin establishes that the NW-SE dextral strike-slip faults system of NW Iberian Plate were highly active from the uppermost Early Oligocene to the Early Miocene. This implies that the end of the main tectonic activity in both NW Iberian offshore and onshore took place during the same time span

IFCP Riemann solver: Application to tsunami modelling using GPUs

In this work, we present a simplified two-layer model of Savage-Hutter type to simulate tsunamis generated by landslides (see (Fern´andez et al. 2008)). A layer composed of fluidized granular material is assumed to flow within an upper layer composed of an inviscid fluid (e.g. water). The sediment layer ismodelled by a Savage-Hutter type model where buoyancy effects have been considered. The system is discretized using IFCP finite volume scheme. The first order IFCP scheme was introduced in (Fern´andez et al. 2011) and it is constructed by using a suitable decomposition of a Roe matrix by means of a parabolic viscosity matrix, that captures information of the intermediate fields (Intermediate Field Capturing Parabola). Its extension to high order and two-dimensional domains is straightforward. To conclude, some numerical examples are presente

Las cuevas de la Sierra de Atapuerca y el uso humano del paisaje kárstico durante el Pleistoceno (Burgos, España)

El karst de la Sierra de Atapuerca representa un interesante sistema multinivel, inactivo y heredado de antiguos niveles de base plio-pleistocenos, que alberga los enclaves prehistóricos más importantes para el conocimiento del poblamiento antiguo en Eurasia, y que fue declarado Patrimonio de la Humanidad en 2000 por la UNESCO. Estas cuevas se originan a partir de conductos subhorizontales con paleodrenajes en sentido SN, localizándose la zona de descarga en la cabecera del río Pico. Los conductos están organizados en tres niveles principales que aparecen colgados entre 90 y 60 m sobre el actual cauce del río Arlanzón, coincidiendo con los niveles de base generados por sus terrazas fluviales T2, T3 y T5. La incisión fluvial liberó de las aguas los conductos superiores mientras se excavaban los niveles inferiores del karst. Las cuevas que iban quedando accesibles fueron utilizadas por la fauna y los homininos, conservando un registro arqueo-paleontológico de más de 1,2 Ma

Site 1220

Site 1220 (10°10.600´N, 142°45.503´W; 5218 meters below sea level (mbsl); Fig. F1) forms a southerly component of the 56-Ma transect drilled during Leg 199. It is situated about midway between the Clipperton and Clarion Fracture Zones in typical abyssal hill topography. On the basis of regional magnetic anomalies, we anticipated basement age at Site 1220 to be equivalent to Chron C25n (~56 Ma; Cande et al., 1989), slightly older than at Site 1219. At the outset of drilling at Site 1220, our estimate for total sediment depth was ~225 meters below seafloor (mbsf) (Fig. F2). Based upon a fixed hotspot model (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles), Site 1220 should have been located ~3° south of the equator at 56 Ma and in an equatorial position at 40 Ma. Thus, Site 1220 should have been situated underneath the South Equatorial Current in the early Eocene. A nearby piston core (EW9709-13PC) taken during the site survey cruise recovered >16 m of red clay, with the base of the core dated as middle-early Miocene on the basis of radiolarian biostratigraphy (Lyle, 2000). Site 1220 will be used to study equatorial ocean circulation from the late Paleocene through the late Eocene during the early Cenozoic thermal maximum. Sediment records from this site will help to define the calcite compensation depth (CCD) and lysocline during the Paleocene-Eocene and Eocene-Oligocene transitions. In this and other respects, Site 1220 will act as an interesting analog to Site 1218. Both sites are thought to have been located on the equator at ~40 Ma, but the older crustal age anticipated at Site 1220 dictates a greater paleowater depth than for contemporaneous sediments accumulating at Site 1218

Site 1216

Site 1216 (21°27.16´N, 139°28.79´W; 5152 meters below sea level [mbsl]; Fig. F1) is situated in abyssal hill topography south of the Molokai Fracture Zone and two small associated unnamed parasitic fracture zones (Fig. F2). Based on magnetic lineations, Site 1216 appears to be situated on normal ocean crust formed during the C25r magnetic anomaly (~57 Ma; Atwater and Severinghaus, 1989). Site 1216 was chosen for drilling because it is near the thickest section of lower Eocene sediments along the 56-Ma transect, which was based upon the seismic stratigraphy of seismic reflection data acquired on site survey cruise EW9709 during transits between the proposed drill sites (Lyle et al., this volume; Moore et al., 2002). The Cenozoic history of sedimentation in this region was poorly constrained prior to Leg 199, being largely based on two Deep Sea Drilling Project (DSDP) drill sites (40 and 41) and piston core data (EW9709-3PC) from ~1.5° in latitude to the south. Based on data from these drill sites, we expected the sedimentary sequence at Site 1216 to comprise red clays (a mixture of wind-blown dust and authigenic precipitates) overlying a biogenic sediment section composed of an upper middle Eocene radiolarian ooze and lower carbonate ooze deposited when the site was near the ridge crest in the late Paleocene and early Eocene. The broad paleoceanographic objectives of drilling the sedimentary sequence anticipated at Site 1216 are as follows: (1) to help define the shift in the Intertropical Convergence Zone through the Paleogene by following the change in eolian-dust composition and flux through time (red clays) and (2) to help define the latitudinal extent, composition, and mass accumulation of plankton communities in the north equatorial Pacific region thereby constraining ocean circulation patterns and the extent of the equatorial high-productivity belt in the Eocene ocean. Results from Site 1216 will also provide important information to test whether there was significant motion of the Hawaiian hotspot with respect to the Earth's spin axis during the early Cenozoic. At 56 Ma, the backtracked location of Site 1216 based upon a hotspot reference frame (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) is about 9°N, 108°W. If significant hotspot motion or true polar wander occurred since 57 Ma (Petronotis et al., 1994), this drill site could have been much nearer to the equator

Site 1217

Site 1217 (16°52.02´N, 138°06.00´W; 5342 meters below sea level [mbsl]; Fig. F1) is one of seven sites drilled to target upper Paleocene crust along a latitudinal transect during Leg 199 and will be used to investigate paleoceanographic processes in the northern tropical early Eocene Pacific Ocean. Site 1217 is situated ~1° north of the Clarion Fracture Zone on abyssal hill topography typical of the central Pacific. Based on magnetic lineations, basement age at Site 1217 should be in magnetic Anomaly C25r or ~57 Ma (Cande et al., 1989; timescale of Cande and Kent, 1995). The Cenozoic history of sedimentation in this region was poorly constrained prior to Leg 199 drilling because the nearest drill site (Deep Sea Drilling Project [DSDP] Site 162) is situated ~300 km south and west on 48-Ma crust. Based on data from this early rotary-cored hole, magnetic anomaly maps, a shallow-penetration piston core near Site 1217 (EW9709-4PC), and seismic profiling (Fig. F2), we expected the sedimentary sequence at Site 1217 to comprise a relatively thick (25 to 35 m thick) section of red clays overlying a radiolarian ooze and a basal carbonate section with possible chert near basement (estimated total depth ~125-150 meters below seafloor [mbsf]) deposited when the site was near the ridge crest in the late Paleocene and early Eocene. Site 1217 was chosen because it is anticipated to have been located just outside of the equatorial region at 56 Ma, ~5°N, 106°W based upon a fixed hotspot model (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles). On the same basis at 40 Ma, the site was located at ~8°N, 111°W. Thus, Site 1217 should help define the paleoceanography of the northern tropical Pacific, in particular locating the ancient North Equatorial Countercurrent (NECC) region. General circulation-model experiments for the early Eocene (see Huber, this volume) suggest that the NECC was a well-developed current during this time period. Other paleoceanographic and paleoclimatic objectives of drilling the sedimentary sequence anticipated at Site 1217 are as follows: (1) to help define the shift in the Intertropical Convergence Zone through the Paleogene by following the change in eolian dust composition and flux through time (red clays); (2) to help constrain the middle-late Eocene calcite compensation depth (CCD); and (3) to sample the Paleocene/Eocene (P/E) boundary, one of the most climatologically critical intervals of Cenozoic time. Recovery of deep-sea sediments from this time interval during Leg 199 is a high priority because the P/E boundary has never before been sampled in the central tropical Pacific Ocean. Results from Site 1217 will also provide important information to test whether there was significant motion of the Hawaiian hotspot, with respect to the Earth's spin axis during the early Cenozoic. At 56 Ma, the backtracked location based upon a hotspot reference frame is ~5°N, 106°W, and at 40 Ma is ~8°N, 106°W. If significant hotspot motion or true polar wander occurred since 57 Ma (Petronotis et al., 1994), this drill site could have been much nearer to the equator