Consecuencias del dragado y vertido de arena estuarina en la Reserva de la Biosfera de Urdaibai (Golfo de Bizkaia): el caso de la “ola izquierda de Mundaka”

ABSTRACT. In the spring of 2003, 240,000 m3 of sand were dredged from the main channel of the lower Oka estuary (Urdaibai Reserve of the Biosphere) and dumped on the southern area of Laida beach located at the estuary mouth. After few months, strong erosion of the deposited sediments occured as a consequence of the northwards migration of the final meander of the main estuarine channel before it reached the estuary inlet. At the same time, the estuarine inlet abandoned its original position near the rocky western margin and migrated eastwards cutting and eroding the sandy ebb delta (Mundaka sand bar). This caused a change in the way the incident wave broke as it reached the shallow water of the ebb tidal delta and beach and made surfing impossible under the same optimal conditions previously enjoyed due to the production of a wave that gradually broke from right to left as it reached shallow water, the so called “Mundaka left wave”. As a consequence, the Billabong Pro surf championship was cancelled in 2005. This paper describes the results obtained during a study of the outer estuary carried out during the period May 2005-April 2006 to characterize the processes operating on the most dynamic area of the estuary throughout the year and to evaluate the influence that the anthropogenic activities in the estuary had on the wave characteristics. No corrective measures were taken in the outer estuary during the study period and the environment recovered its normal morphological features naturally. This natural restoration it is hoped will be more stable, long lasting and reliable to ensure the continuing future of the “Mundaka left wave”.RESUMEN. En primavera del año 2003, la necesidad de mayor calado condujo a la realización de un dragado con la extracción de aproximadamente 240.000 m3 de arena del canal principal del estuario inferior del Oka (Reserva de la Biosfera de Urdaibai) y su vertido en la zona supramareal sur de la playa de Laida situada en la desembocadura del mismo. Desde la finalización de este vertido, se observó en la zona una fuerte erosión debido a la migración lateral del último meandro del canal estuarino antes de su desembocadura. Paralelamente, se produjo una variación morfológica del canal de desembocadura, con el paulatino abandono de su posición original junto al margen rocoso oeste de la ría y la aparición de un canal alternativo hacia el este que seccionaba el delta de reflujo (barra arenosa de Mundaka). Esta variación provocó un cambio en las características del oleaje incidente imposibilitando la práctica del surf en las condiciones idóneas que se disfrutaban hasta entonces y obligando a la cancelación en 2005 de una de las pruebas de surf más importantes del mundo, el Billabong Pro. Este trabajo muestra una síntesis de los resultados obtenidos en el estudio de la zona más externa del estuario del Oka durante el período Mayo 2005-Abril 2006 con el fin de caracterizar los procesos que operan durante todo el año en la zona más dinámica de este estuario y evaluar la influencia que el dragado efectuado tuvo sobre la rotura del oleaje. Como consecuencia de no haber adoptado ninguna medida correctora en la zona exterior de la desembocadura, el propio sistema sedimentario y sus diferentes elementos constitutivos consiguieron de modo natural unas características morfológicas similares a las habituales en esa zona. Esta restauración natural será previsiblemente mucho más estable, duradera y segura de cara a garantizar el futuro de la “ola izquierda de Mundaka”

Rift-margin extensional forced folds and salt tectonics in the eastern Basque-Cantabrian rift basin (western Pyrenees)

In this paper we present and discuss Cretaceous extensional folds of the eastern Basque-Cantabrian Basin (Northern Spain). Geometry and kinematics of folds is constrained by means of structural and sedimentological fieldwork integrated with geological mapping, revealing an intimate link between coeval folding, extensional faulting, and salt mobilization. In detail, the Mesozoic succession of the northwestern and southern borders of the Palaeozoic Bortziriak-Cinco Villas massif (eastern margin of the BCB) host late Albian–early Cenomanian syn-rift forced folds. The studied forced fold axes trend parallel and are located above main and inferred Cretaceous syn-sedimentary basement faults. Structural data indicate that these folds formed during the late Albian − early Cenomanian interval. The presence of Upper Triassic clay and evaporite outcrops along and/or close to the axes of folds and their stratigraphic relationship with Upper Cretaceous strata indicate their halokinetic origin and extrusion during folding. The trigger of salt tectonics is attributed to a basement extensional pulse during the Bay of Biscay – Pyrenean rifting. Related high subsidence-rates allowed salt to flow towards faults, forming salt walls and causing the inflation and folding of the overburden.grant BFI05.398 from the Basque Government to A. Bodego and grant AP98-44159606 from the Spanish Science Ministry to E. Iriarte. Funds were also supplied by Ministerio de Educación y Ciencia (MEC) – Ministerio de Ciencia e Innovación (MICINN) (projects CGL2006-05491/BTE and CGL2009-08545) and Euskal Herriko Unibertsitatea (UPV/EHU) (projects EHU06/62, UNESCO06/03 and EHUA15/18

Rift-margin extensional forced folds and salt tectonics in the eastern Basque-Cantabrian rift basin (western Pyrenees)

In this paper we present and discuss Cretaceous extensional folds of the eastern Basque-Cantabrian Basin (Northern Spain). Geometry and kinematics of folds is constrained by means of structural and sedimentological fieldwork integrated with geological mapping, revealing an intimate link between coeval folding, extensional faulting, and salt mobilization. In detail, the Mesozoic succession of the northwestern and southern borders of the Palaeozoic Bortziriak-Cinco Villas massif (eastern margin of the BCB) host late Albian–early Cenomanian syn-rift forced folds. The studied forced fold axes trend parallel and are located above main and inferred Cretaceous syn-sedimentary basement faults. Structural data indicate that these folds formed during the late Albian − early Cenomanian interval. The presence of Upper Triassic clay and evaporite outcrops along and/or close to the axes of folds and their stratigraphic relationship with Upper Cretaceous strata indicate their halokinetic origin and extrusion during folding. The trigger of salt tectonics is attributed to a basement extensional pulse during the Bay of Biscay – Pyrenean rifting. Related high subsidence-rates allowed salt to flow towards faults, forming salt walls and causing the inflation and folding of the overburden.This research was funded by grant BFI05.398 from the Basque Government to A. Bodego and grant AP98-44159606 from the Spanish Science Ministry to E. Iriarte. Funds were also supplied by Ministerio de Educación y Ciencia (MEC) – Ministerio de Ciencia e Innovación (MICINN) (projects CGL2006-05491/BTE and CGL2009-08545) and Euskal Herriko Unibertsitatea (UPV/EHU) (projects EHU06/62, UNESCO06/03 and EHUA15/18)

Hiperestentsioa: kontinenteen apurketa ulertzeko eredu berri bat

Kontinenteen apurketa luzaroan ikertu den prozesu geologikoa da. Rifting deritzon prozesu horrek milioika urte irauten ditu, eta kontinente-ertzetan, mendikateetan eta bestelako ingurune geologikoetan topatzen dira fenomeno tektoniko horren aztarnak. Plaka tektonikoen banaketaren interpretazioa, ordea, eboluzionatuz doa ikertzaileen ulermenaren eta aurrerapen teknologikoen arabera. Hiperestentsioaren ideia da interpretazio horren azken berrikuntza. Ideia hori litosfera kontinentalaren deformazio polifasikoan barneratzen da, litosferaren muturreko luzapenean oinarrituz, hain zuzen. Ertz egonkorretan eta gerriko orogenikoetan identifikaturiko egitura geologiko eta eremu estruktural bereizgarriek ahalbidetzen dute fenomeno horren bilakaeraren nolakotasuna definitzea. Magman txiroak bezala ezagutzen diren ertz egonkorretako eremu horiek dira hurbileko domeinua, necking domeinua, urruneko domeinua edo hiperluzatua eta kanpoko domeinua. Domeinu horietako bakoitza riftingaren deformazio faseekin lotzen da; fase horiek litosfera kontinentalaren luzapena, mehetzea, mantuaren azaleratzea eta lurrazal ozeanikoaren zabaltzea dira. Esan bezala, iraganean hiperluzatutako arroetan ari da garatzen ikerketa, eta hipotesi horren bitartez ulertzen hasia da, honezkero, Euskokantauriar arroa (EKA) barneratzen duen Iberia eta Eurasia arteko Mesozoikoko rift-sistemaren garapena. Urteetan arroan bildutako datuek, behintzat, horretara bultzatzen dute. Pirinioen mendebaldean deskribaturiko mantuaren azaleratzeak eta arroan deskribaturiko hamaika prozesuk indartu dute Kretazeoko riftingean hiperestentsioak izan zezakeen garrantzia; azken horrek, gainera, garai hartako EKAren eboluzio geologikoaren paradigma argitu dezake.; Continental breakup is a geological process which has been deeply learnt. The keys of that tectonic phenomena, the so-called rifting process that lasts millions of years, can be found worldwide within rifted margins, mountain chains and other geological settings. However, the interpretation of tectonic plate rupture evolves while researcher´s comprehension and technology advance. Hyperextension is the last update within that interpretation. This revolutionary idea involves the extreme polyphasic extensional deformation of the continental lithosphere. Characteristic geological structures and structural domains identified within passive margins and orogenic belts, allow to define the evolution of this phenomena. Domains such as the proximal domain, necking domain, distal or hyperextended domain and outer domain are distinguishing features within magma poor rifted margins. These domains are linked to specific deformation phases during rifting, being stretching and thinning of continental lithosphere, mantle exhumation and oceanic crust spreading part of these process. As said, research is being carried out in hyperextended basins, and the evolution of the Iberia-Eurasia Mesozoic rift system, which involves the Basque-Cantabrian Basin (BCB), is already being understood within that hypothesis. Data collected over years in the BCB, at least, suggest that. Mantle exhumation described in the western Pyrenees and several processes linked to that within the BCB, reinforces the significance that hyperextension could have occurred during the Cretaceous rifting, shedding light to the paradigm concerning the evolution of the BCB

Reconstructing the sedimentary history of Lezetxiki II cave (Basque Country, northern Iberian Peninsula) using micromorphological analysis

Micromorphological analysis is an invaluable research tool for reconstructing detailed depositional and post-depositional processes of cave infill sequences and for providing paleoenvironmental insight. In this work, we present the results of a micromorphological and mineralogical study of the sedimentary sequence at the Lezetxiki II cave (northern Iberian Peninsula). The cave forms part of the Lezetxiki archaeological complex which has yielded early Middle Palaeolithic tools and archaic human remains. We have identified three main clastic sedimentary processes as being significant at Lezetxiki II: 1) fluviokarst or runoff processes, which are characterised by yellow sandy illite-rich microfacies; 2) infiltration processes, which produce a massive red silty-clay vermiculite-rich microfacies; and 3) inwash processes, which generate a reworked illite and vermiculite rich silty sand microfacies. The most common post-depositional processes observed are calcite precipitation infilling pore spaces, and compression structures derived from specific vertical loading events. In order to improve the chronological framework of the sedimentary sequence at Lezetxiki II, we have revised previous radiometric and relative dating results from faunal and archaeological remains and have dated the lowermost stratigraphic level using single-grain thermally-transferred optically-stimulated luminescence dating. Sedimentation at the Lezetxiki II cave started during Marine Isotope Stage (MIS) 7 through fluviokarst processes. We interpreted that runoff prevailed during MIS 6, while soil infiltration processes became more significant towards the MIS 5 optimum. Gradually, inwash processes prevailed over infiltration until the end of the interglacial phase. During the following glacial phases, runoff and erosion dominated but were subsequently replaced by inwash processes during MIS 1.PALEOGATE project, funded by the Spanish Ministry of Economy and Competitiveness (HAR2014-53536-P) as well as the US14/16 project funded by the University of the Basque Country and Basque Coast Geopark, and Basque Government (IT1029-16-GBV6). We would also like to thank Tim Nicholson for his work in translating and editing different versions of the English text. Additional financial support for this research was provided by Australian Research Council (ARC) Future Fellowship project FT130100195, ARC Discovery Early Career Researcher Award DE16010074

Tracer test in the vadose zone of Praileaitz Cave (Deba, Guipúzcoa). Application for protection of karstic cavities

Se ha realizado un ensayo de trazador en la zona no saturada de la Cueva de Praileaitz (Bajo Deba, Guipúzcoa) para ayudar a la delimitación del área de protección de la cavidad. Dicho ensayo se ha efectuado con 14.000 L de agua desionizada y una masa de 500 gr de LiCl. El trazador analizado (Li+) ha permitido deducir un tránsito de entre 18 y 19 horas desde el momento de la inyección. Esta primera detección corresponde a una ve locidad de flujo no saturado de entre 4-5 m/h. La concentración máxima al canzada de litio fue de 11’28 µg/L.A tracer test has been performed in the vadose zone of the Cave of Praileaitz (Bajo Deba, Guipúzcoa) for helping in the delimitation of its protection area.The test was done with 14.000 L of deionized water and a mass of 500 gr of LiCl. The detection of the tracer substance (Li+) has allowed deducing a transit time between 18 and 19 hours since the injection. This first detection corresponds to a non-saturated flow between 4-5 m/h. The maximum lithium concentration was 11’28 µg/L

Evidencias de ocupación antigua en núcleos rurales actualmente habitados: el proyecto arqueológico de Aizarna (Gipuzkoa)

El estudio arqueológico de las comunidades rurales actualmente habitadas ofrece la posibilidad de abordar una serie de problemas historiográficos hasta ahora poco explorados. Este artículo discute los problemas, los métodos y los resultados que pueden derivarse de la investigación arqueológica de los pueblos actuales y presenta la metodología transdisciplinar que ha sido aplicada en las recientes intervenciones llevadas a cabo en el área de Erretorekoa (Aizarna, Gipuzkoa). Lejos de los marcos interpretativos tradicionales, los resultados obtenidos revelan que una parte del poblamiento rural actual pudo originarse en época antigua, evidenciando la resiliencia del mismo. En este sentido, es necesario desarrollar marcos conceptuales adecuados para el reconocimiento, estudio e interpretación de este tipo de registros, mediante el diseño de metodologías específicas que permitan superar las limitaciones impuestas por la propia continuidad de la ocupación en estos contextos

Geoarchaeological Core Prospection as a Tool to Validate Archaeological Interpretation Based on Geophysical Data at the Roman Settlement of Auritz/Burguete and Aurizberri/Espinal (Navarre)

Geophysical survey methods are broadly used to delimit and characterize archaeological sites, but the archaeological interpretation of geophysical data remains one of the challenges. Indeed, many scenarios can generate a similar geophysical response, and often interpretations can not be validated without access to the subsoil. In large geophysical surveys many anomalies are detected and validation through archaeological trenches can not be afforded. This paper analyses the validity of geoarchaeological core survey to check the archaeological interpretations based on geophysical results. The Roman site located at Auritz/Burguete and Aurizberri/Espinal (Navarre), provides a great case of study as many investigations have been carried out. After the gradiometer survey performed in 2013 a sediment core survey was designed. 132 cores were drilled using a hand-held coring machine and the sediments were analysed in situ. Site delimitation and archaeological interpretations based on magnetic data could be improved or corrected. In this regard, the core survey proved to be an useful methodology as many anomalies could be checked within reasonable time and resources. However, further geophysical investigations trough GPR revealed unexpected remains in areas where no archaeological deposits were identified through coring. Excavations showed poor conservation level in some of those areas, leading to thin archaeological deposits hard to identify at the cores. The sediment core survey, therefore, was proved to be inconclusive to delimit the archaeological sit

Datos paleoflorísticos en la Cuenca media del Nalón entre 40-32 Ka. BP: antracoanálisis de la Cueva del Conde (Santo Adriano, Asturias)

RESUMEN.Presentamos los datos antracológicos de los niveles de ocupación de la Cueva de El Conde fechados entre 40-32 Ka. BP, procedentes del área de excavación denominada “Plataforma”. Pinus sylvestris, Sorbus aria, Betula, aparecen como principales táxones arbóreos. El estrato arbustivo presenta una gran variabilidad florística procedente tanto de substratos calcáreos: Arbutus, Rhamnus, Crataegus, Prunus como silíceos: Erica, Leguminosae (Ulex, Cytisus). La configuración topográfica de este territorio así como la variabilidad de substrato entre áreas geográficamente próximas, explicaría la proximidad de estas comunidades vegetales con afinidades ecológicas diversas. Asimismo la posición de la cueva a media ladera habría facilitado el aprovechamiento alternativo de todas ellas en lo referente a la gestión del combustible por parte de los grupos humanos que habitaron estacionalmente dicho yacimiento.ABSTRACT.Anthracological data coming from the Cueva del Conde “Plataforma” excavation area, dated between 40-32 Kyr. BP, are presented in this work. Pinus sylvestris, Sorbus aria, Betula, appear as main arboreal taxa. Shrub stratum presents a great floristic variability coming from calcareous: Arbutus, Rhamnus, Crataegus, Prunus as well as siliceous substrats: Erica, Leguminosae (Ulex, Cytisus). Topographic characteristics of this area and discontinuity of substrats geographically closed, explain the proximity of these vegetal communities with diverse ecological affinities. Futhermore, the position of the cave in the middle part of the slope has made possible the alternative firewood management made among these vegetal communities by human groups that have seasonally inhabited this site