The History of the El Niño - Southern Oscillation according to lacustrine and marine sediments

El gran impacte que El Niño — Oscil·lació del Sud (ENSO) té en la nostra societat industrialitzada ha esperonat la comunitat científica d'arreu a entendre quins són els mecanismes físics que el controlen, així com clarificar quina ha estat la seva història. El registre sedimentari de sensors naturals, com els llacs o la mar, ha permès reconstruir la història de l'ENSO. En aquest article, els autors donen una visió sintètica de la història d'aquest fenomen climàtic al llarg dels darrers quatre milions d'anys.The large impact of the El Niño – Southern Oscillation (ENSO) in our industrial society has spurred the scientific community to understand the physical processes that trigger this climate phenomenum and to elucidate its history. The sedimentary record of natural sensors, such as lakes and seas, was used to reconstruct the history of the ENSO and to obtain a comprehensive history of this climate phenomenon throughout the last 4 million years

A statistical approach to disentangle environmental forcings in a lacustrine record: the Lago Chungará case (Chilean Altiplano)

A high resolution multiproxy study (magnetic susceptibility, x-ray diffraction, XRF scanner, gray-colour values, Total Organic Carbon, Total Inorganic Carbon, Total Carbon and Total Biogenic Silica) of the sedimentary infill of Lago Chungará (northern Chilean Altiplano) was undertaken to unravel the environmental forcings controlling its evolution using a number of different multivariate statistical techniques. Redundancy Analyses enabled us to identify the main provenance of the studied proxies whereas stratigraphically-unconstrained cluster analyses allowed us to distinguish the 'outsiders' as result of anomalous XRF scanner acquisitions. Principal Component Analysis (PCA) was employed to identify and isolate the main underlying environmental gradients that characterize the sedimentary infill of Lago Chungará. The first eigenvector of the PCA could be interpreted as an indicator of changes in the input of volcaniclastic material, whereas the second one would indicate changes in water availability. The chronological model of this sedimentary sequence was constructed using 17 AMS 14C and 1 238U/230Th dates in order to characterize the volcaniclastic input and the changes in water availability in the last 12,300 cal years BP. Comparison of the reconstructed volcaniclastic input of Lago Chungará with the dust particle record from the Nevado Sajama ice core suggested that the Parinacota volcano eruptions were the main source of dust during the mid and late Holocene rather than the dry out lakes as has previously been pointed out. The comparison of the water availability reconstruction of Lago Chungará with three of the most detailed paleoenvironmental records of the region (Paco Cocha, Lake Titicaca and Salar Uyuni) showed an heterogeneous (and sometimes contradictory) temporal and spatial pattern distribution of moisture. Although the four reconstructions showed a good correlation, each lacustrine ecosystem responded differently to the moisture oscillations that affected this region. The variations in the paleoenvironmental records could be attributed to the dating uncertainities, lake size, lake morphology, catchment size and lacustrine ecosystem responses to the abrupt arid events

Lacustrine sedimentation in active volcanic settings: the Late Quaternary depositional evolution of Lake Chungará (northern Chile)

Lake Chungara´ (18 15¢S, 69 09¢W, 4520 m above sea-level) is the largest (22Æ5 km2) and deepest (40 m) lacustrine ecosystem in the Chilean Altiplano and its location in an active volcanic setting, provides an opportunity to evaluate environmental (volcanic vs. climatic) controls on lacustrine sedimentation. The Late Quaternary depositional history of the lake is reconstructed by means of a multiproxy study of 15 Kullenberg cores and seismic data. The chronological framework is supported by 10 14C AMS dates and one 230Th/234U dates. Lake Chungara´ was formed prior to 12Æ8 cal kyr bp as a result of the partial collapse of the Parinacota volcano that impounded the Lauca river. The sedimentary architecture of the lacustrine succession has been controlled by (i) the strong inherited palaeo-relief and (ii) changes in the accommodation space, caused by lake-level fluctuations and tectonic subsidence. The first factor determined the location of the depocentre in the NW of the central plain. The second factor caused the area of deposition to extend towards the eastern and southern basin margins with accumulation of high-stand sediments on the elevated marginal platforms. Synsedimentary normal faulting also increased accommodation and increased the rate of sedimentation in the northern part of the basin. Six sedimentary units were identified and correlated in the basin mainly using tephra keybeds. Unit 1 (Late Pleistocene-Early Holocene) is made up of laminated diatomite with some carbonate-rich (calcite and aragonite) laminae. Unit 2 (Mid-Holocene-Recent) is composed of massive to bedded diatomite with abundant tephra (lapilli and ash) layers. Some carbonate-rich layers (calcite and aragonite) occur. Unit 3 consists of macrophyte-rich diatomite deposited in nearshore environments. Unit 4 is composed of littoral sediments dominated by alternating charophyterich and other aquatic macrophyte-rich facies. Littoral carbonate productivity peaked when suitable shallow platforms were available for charophyte colonization. Clastic deposits in the lake are restricted to lake margins (Units 5 and 6). Diatom productivity peaked during a lowstand period (Unit 1 and subunit 2a), and was probably favoured by photic conditions affecting larger areas of the lake bottom. Offshore carbonate precipitation reached its maximum during the Early to Mid-Holocene (ca 7Æ8 and 6Æ4 cal kyr bp). This may have been favoured by increases in lake solute concentrations resulting from evaporation and calcium input because of the compositional changes in pyroclastic supply. Diatom and pollen data from offshore cores suggest a number of lake-level fluctuations: a Late Pleistocene deepening episode (ca 12Æ6 cal kyr BP), four shallowing episodes during the Early to Mid-Holocene (ca 10Æ5, 9Æ8, 7Æ8 and 6Æ7 cal kyr BP) and higher lake levels since the Mid-Holocene (ca 5Æ7 cal kyr BP) until the present. Explosive activity at Parinacota volcano was very limited between c. >12Æ8 and 7Æ8 cal kyr bp. Mafic-rich explosive eruptions from the Ajata satellite cones increased after ca 5Æ7 cal kyr bp until the present

Interplay between tectonics and diagenetic modification of the Natih Formation carbonates in Jabal Qusaybah (Oman), with special emphasis on dolomitisation

The Natih Formation (Cenomanian-Turonian) constitutes giant oil fields in North Oman. For this reason this formation has been extensively studied both in outcrops and analogues in the Oman foothills and in subsurface. Studies in subsurface have proven that reservoir properties were controlled by fracturing, late leaching and late dolomitization. Late dolomitization has been recorded as volumetrically insignificant, although relevant higher permeabilities along dolomitized pressure solutions favoured circulation of late leaching fluids, which enhanced reservoir properties. The results that are presented in this poster are integrated in a three year project that aims to characterise the interplay between fault and fracture dolomitization, their spatial patterns and the source of the dolomitization fluids in the Jabal Qusaybah outcrop analogues. The Jabal Qusaybah is affected by major NE-SW and N-S fault zones. The latter dominantly occur in the central part of the structure, creating displacements of tens of meters between individual fault blocks. The N-S and NE-SW fault system is relatively young. Along these major faults, the circulation of different fluids is recorded by several events of calcite and dolomite cementation. Dolomitisation is virtually not affecting the host rock, apart from selective dolomitisation of bioturbated facies close to the faults, the top Natih C cross-bedded grainstones and the top Natih A. The dolomitised top Natih C interval is locally up to 2,5m thick and possesses good reservoir characteristics. Whether the fault related and the replacive dolomite in the top Natih C grainstones are of the same origin is under investigation. The interplay between tectonics and diagenetic modification of the Natih Formation carbonates in Jabal Qusaybah will be based on the integrated multiscale structural and diagenetic evolution including the paragenetic evolution of cement fill of the recognised fault and fracture zones. Specific points that will be addressed include: 1) possible role of salt movements in the formation of the Jabal Qusaybah structure; 2) source and temperature of dolomitising fluids; 3) evolution of the fluid system.status: publishe

Fault-controlled dolomitization in the Montagna dei Fiori Anticline (Central Apennines, Italy): record of a dominantly pre-orogenic fluid migration

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Correlación magnetoestratigráfica y bioestratigráfica en la cuenca Miocena de Lorca (Murcia, SE de España)

[EN] The Lorca basin is one of the Neogene basins OS South Eastern Spain. The infilling Tortonian-Messinian deposits are mainly composed OS marls and reach up to 1,200 m in thickness. A biostratigraphic survey OS these deposits, assisted by the determination OS the magnetic polarity reversal pattern Sor most OS these deposits (900 m), has enabled the Tortonian-Messinian chronostratigraphy to be precised. The close sampling space for biostratigraphic determination has enabled the accurate location OS Sour main biostratigraphic events than can be correlated with charactenstic events of the Mediterranean biostratigraphic Zones. In addition, the location OS the TortonianNessinian boundary has been accurately placed at some 150 m below the main gypsurn unit outcropping in the basin. The integrated bio-magnetostratigraphic data fiom the studied section allows a tentative interpretation OS the identified magnetozones. Thus, a correlation to the Geomagnetic Polarity Time Scale is presented for more than 900 m of pre-evaporite Miocene stratigraphic succession fiom the Lorca basin. Moreover, about 15" OS anticlockwise rotation has been detected. Its significance is evaluated in the basin geodynamic framework.[EN] La cuenca de Lorca es una de las cuencas neógenas del sureste de España. Los depósitos de edad Tortoniense-Messiniense son mayoritariamente margosos y llegan a alcanzar hasta 1.200 m de espesor en el depocentro. Se ha refinado la estratigrafía para los sedimentos de esta edad, a partir de los resultados de un estudio biostratigráfico de toda la sucesión, y de la determinación del modelo de inversión de polaridad magnética para la mayor parte de los depósitos (900 m). La alta resolución en el espaciado del muestreo biostratigráfico ha permitido detectar cuatro eventos biostratigráficos principales que pueden ser correlacionados con eventos característicos de las Zonas Biostratigráficas del Mediterráneo. Además, se ha precisado la posición del limite Tortoniense/Messiniense a unos 150 m por debajo de la unidad evapontica (yesos de la Serrata) aflorante en la cuenca. La integración de los resultados bio- y magnetostratigráficos ha permitido una interpretación tentativa de las magnetozonas identificadas. Así pues, se presenta la correlación de más de 900 m de la sucesión estratigráfica del Mioceno preevapontico aflorante en la cuenca de Lorca con la Escala Temporal de Polaridad Magnética. Además, se han detectado unos 15' de rotación antihoraria, el significado de la cual se evalúa en el marco geodinámico de la cuenca.This work has been funded by the Human Capital and Mobility U.E. contract ERBCH RXCT930309 (NATENMAR) and -GRQ94-1049 and 1996SGR-0070 funds from the Catalan Governrnent. Carlos Santisteban and Marie Russell are acknowledged for helpful discussions in the field and on the manuscript.Peer reviewe

Preliminary integrated magnetostratigraphic and biostratigraphic correlation in the Miocene Lorca Basin (Murcia, SE Spain).

The Lorca basin is one of the Neogene basins OS South Eastern Spain. The infilling Tortonian-Messinian deposits are mainly composed OS marls and reach up to 1,200 m in thickness. A biostratigraphic survey OS these deposits, assisted by the determination OS the magnetic polarity reversal pattern Sor most OS these deposits (900 m), has enabled the Tortonian-Messinian chronostratigraphy to be precised. The close sampling space for biostratigraphic determination has enabled the accurate location OS Sour main biostratigraphic events than can be correlated with charactenstic events of the Mediterranean biostratigraphic Zones. In addition, the location OS the TortonianNessinian boundary has been accurately placed at some 150 m below the main gypsurn unit outcropping in the basin. The integrated bio-magnetostratigraphic data fiom the studied section allows a tentative interpretation OS the identified magnetozones. Thus, a correlation to the Geomagnetic Polarity Time Scale is presented for more than 900 m of pre-evaporite Miocene stratigraphic succession fiom the Lorca basin. Moreover, about 15' OS anticlockwise rotation has been detected. Its significance is evaluated in the basin geodynamic framework

Fault-related dolomitization in the Vajont Limestone (Southern Alps, Italy): photogrammetric 3D outcrop reconstruction, visualization with textured surfaces, and structural analysis

The Vajont Gorge (Dolomiti Bellunesi, Italy) provides spectacular outcrops of Jurassic limestones (Vajont Limestone Formation) in which Mesozoic and Alpine faults and fracture corridors are continuously exposed. Some of these faults acted as conduits for fluids, resulting in structurally-controlled dolomitization of the Vajont Limestone, associated with significant porosity increase. We carried out a 3D surface characterization of the outcrops, combining high resolution topography and imaging to provide a quantitative framework for structural analysis and 3D characterisation of the dolostone geobodies, enabling interdisciplinary reconstruction of coupled brittle deformation and fluid flow processes. 3D imaging of outcrop surfaces has been carried out by means of photogrammetric techniques. This methodology has advantages with respect to Lidar-based projects in terms of arbitrary spatial resolution, quality of imagery, acquisition and processing timing and cost. The survey resulted in a “virtual outcrop” dataset (700 m x 350 m x 300 m) consisting of continuous triangulated surfaces representing the outcrop surfaces textured with high resolution images (c.f. Bistacchi et al., 2011). Interpretation and modelling work performed on this dataset include: (1) georeferencing of structural measurements and sampling stations; (2) tracing of stratigraphic boundaries, structural surfaces, and dolomitization fronts (partly performed in the field for direct comparison with outcrops); (3) correlation and extrapolation of realistic 3D surfaces from their traces; and (4) development of a 3D geological model at the scale of the Vajont Gorge, including stratigraphy, faults, dolomitization fronts, and volumetric meshes suitable for the statistical analysis of structural, diagenetic and geochemical parameters. The model allows reconstruction of subtle offsets (10-30 m range) across faults which provided the main pathways for Mg-rich fluids, but which are now heavily masked by the dolomitization process. This was particularly important in the development of a tectonic and geochemical scenario to explain dolomitization. As a further development, we plan to populate the model (e.g. as in Smith et al., 2013) in terms of: morphological features of individual structure sets (orientation statistics, mean length of fractures, displacement/length ratios for faults, etc.), and aggregated parameters of the fracture/fault network (clustering/anticlustering, terminations, interconnection, fracture density in 1D or 2D, etc.). These parameters will be used in subsequent modelling steps, including a DFN approach. References Bistacchi A., Massironi M., Menegon L., 2010. Three-dimensional characterization of a crustal-scale fault zone: The Pusteria and Sprechenstein fault system (Eastern Alps). Journal of Structural Geology, 32 (12), 2022-2041, doi: 10.1016/j.jsg.2010.06.003. Bistacchi A., Griffith W.A., Smith S.A., Di Toro G., Jones R., and Nielsen S., 2011. Fault Roughness at Seismogenic Depths from LIDAR and Photogrammetric Analysis. Pure and Applied Geophysics, 168 (12), 2345-2363. doi: 10.1007/s00024-011-0301-7. Smith S.A.F., Bistacchi A., Mitchell T.M., Mittempergher S., Di Toro G., 2013. The Structure of an Exhumed intraplate Seismogenic Fault in Crystalline Basement. Tectonophysics, in press.status: publishe