Datación por luminiscencia de depósitos fluviales y eólicos en el margen occidental de Galicia

Programa Oficial de Doutoramento en Ciencia e Tecnoloxía Ambiental . 5006V01[Resumen] La aplicación y desarrollo de la técnica de datación absoluta por luminiscencia durante de los últimos años ha permitido conocer el tiempo de enterramiento de sedimentos a lo largo del Holoceno y el Pleistoceno Superior, dentro del propio limite de la técnica, de unos 150 o 200ka para la señal OSL a partir de granos de cuarzo, y de 500ka o más para la señal pIR-IRSL, extraída a partir de granos de feldespato. Estas señales se generan por la redistribución de cargas a través de la red cristalina de Jos granos de los minerales debido a la radiación natural que incide sobre los mismos dentro del sedimento, hasta un nivel de saturación que no permite alcanzar edades más antiguas de las mencionadas. Existen una serie de condicionantes que deben ser considerados para aplicar el procedimiento de datación más adecuado. Por ejemplo, y a diferencia de lo que ocurre con sedimentos eólicos cuya señal de luminiscencia es bien blanqueada por la luz del sol al ser transportados por el viento antes de su deposición, los sedimentos de tipo fluvial pueden sufrir un blanqueamiento incompleto de la señal debido a las condiciones de turbidez del agua que los transporta antes de su deposición, que podría dar lugar a la presencia de una carga residual que se suma a la que se genera durante el tiempo de enterramiento y que podría tener como consecuencia una sobre-estimación de la edad. Para este trabajo de tesis doctoral se han aplicado técnicas de luminiscencia en depósitos fluviales y eólicos, de edad desconocida hasta el momento, desarrollados en el margen atlántico del noroeste de la Península Ibérica. Esto ha permitido poner a prueba la aplicación de la técnica y ampliar el conocimiento de la evolución costera en esta región durante las últimas etapas glaciales e interglaciales del Cuaternario. Con esta finalidad se han seleccionado algunos de los depósitos fluviales costeros desarrollados en el curso bajo de la cuenca del río Mero (A Coruña, Galicia, España) y en la desembocadura del río Ulla a la altura de Catoira (Pontevedra, Galicia España), así como algunos de los afloramientos correspondientes a antiguas dunas presentes a lo largo de la fachada atlántica de Galicia en las provincias de A Coruña y Pontevedra.[Abstract] The use and development ofthe technique of absolute dating by luminescence over the last years has alJowed to know the burlal time of sediments along the Holocene and the Upper Pleistocene, within the limits of the technique, up to 150 or 200ka for the OSL signal from quartz grains, and 500 ka or more, for the pIR-IRSL signal from feldspars. Those signals are generated through crystal-Iattice charge redistribution in mineral grains due to their exposure to natural radiation within sediments, until a saturation level that does not alJow reaching older ages than referred above. There exist a number of constraints that must be considered in order to apply the most approprlate dating procedure. For instance, and unlike what happens in aeolian sediments whose luminescence signal is completely-bleached by sunlight during wind transport befare deposition, fluvial sediments can ove reame incomplete bleaching of the luminescence signal due to turbidity conditions of the water transporting them prior to their deposition, which could lead to the presence of an inherited residual charge added to these generated during the burial time and which would result in an age overestimation. In this PhD. Thesis, luminescence techniques were applied in fluvial and aeolian sediments of unknown age until now, developed in the Atlantic margin of the Northwest of the Iberian Península. This allowed to test the technique as wel! as to ¡ncrease the knowledge of the coastal evolution in this region during the last glacial and interglacial Quaternary phases. To this end, some of the coastal-fluvial deposits developed in the lower Mero river basin (A Coruña, Galicia, Spain) and the mouth of the Ulla river at Catoira (Pontevedra, Galicia, Spain) have been selected, as well as so me outcrops corresponding to ancient dunes along the Atlantic coastline of Galicia in the provinces of A Coruña and Pontevedra.[Resumo] A aplicación e desenvolvemento da técnica de datación absoluta por luminescencia nos últimos anos permitiu coñecer o tempo de enterramento de sedimentos durante o Holoceno e o Pleistoceno Superior, dentro dos límites da técnica, de uns 150 ou 200ka para o sinal OSL a partir de grans de cuarzo, e de 500ka ou máis, para o sinal pIR-IRSL de feldespatos. Estes sinais son xerados por a redistribución de cargas a través da rede cristalina dos grans dos minerais debido a radiación natural que incide sobre os mesmos dentro do sedimento, até un nivel de saturación que non permite atinxir idades mais antigas das mencionadas. Existen unha serie de condicionamentos que deben ser considerados para aplicar o procedemento de datación mais axeitado. Por exemplo, ao contrario do que acontece cos sedimentos eólicos, cuxa sinal de luminescencia é ben branqueada pola luz solar cando son transportado polo vento antes da sua deposición, os sedimentos de tipo fluvial poden sufrir un branqueamento incompleto do sinal debido as condicións de turbidez da auga que os transporta antes da súa deposición, que podería levar á presenza dunha carga residual herdada que é engadida a aquela xerada durante o tempo de enterramento, e que resultaría nunha sobre-estimación da idade. Para este traballo de tese de doutoramento aplicaranse técnicas de luminescencia en depósitos fluviais e eólicos desenvolvidos, de idade descoñecida ate o de agora, na marxe atlántica da Península Ibérica. Isto permitiu por a proba a aplicación da técnica e ampliar o coñecemento da evolución da costa nesta rexión o langa dos últimos estadías glaciais e interglaciais do Cuaternario. Para este fin foron seleccionados algúns dos depósitos fluviais costeiros desenvoltos no curso baixo da bacía do río Mero (A Coruña, Galicia, España) e na desembocadura do río Ulla na localidade de Catoira (Pontevedra, Galicia, España), así como algúns dos aflora mentas correspondentes a antigas dunas presentes o langa da fachada atlántica de Galicia, nas provincias de A Coruña e Pontevedra

Chronology of Four Climbing Dune Outcrops on the Atlantic Coast of Galicia (NW Spain) Linked to the Sea Level Fall during the MIS6 and MIS4 Isotopic Stages

[Abstract] Numerous sandy deposits, interpreted as the remains of old climbing dunes, are preserved on the cliffy coast of Galicia (northwest Spain). These deposits can be found both in open coastal areas and in the interior of the Galician Rias. In this paper, a formation age is established for four aeolianite outcrops dating back to 166 ± 9 ka, 131 ± 6 ka, 128 ± 18 ka and 62 ± 3 ka, using the IRSL290 signal of feldspars. These sands were mobilised by coastal winds from a sea level lower than the current one during MIS6 and MIS4. The sea level fall during these regressive episodes shifted the coastline several kilometres away from its current position. This favoured the action of the wind blowing over the emerged coastal strip, which acted as a source area for aeolian sands. During warmer episodes, such as the Eemian and the Holocene, the advance of the sands onto the coast was progressively reduced as the sea level rose and the oceanic waters flooded the continental shelf.This research was funded and supported by Xunta de Galicia (programmes ED431B 2018/47 and ED431B 2021/17) through the Grupo Interdisciplinar de Patrimonio Cultural e Xeolóxico (CULXEO)Xunta de Galicia; ED431B 2018/47Xunta de Galicia; ED431B 2021/1

New Model of Coastal Evolution in the Ria de Vigo (NW Spain) from MIS2 to Present Day Based on the Aeolian Sedimentary Record

This article belongs to the Special Issue Recent Advances in Geological Oceanography[Abstract] Galician Rias are fluvial valleys that were flooded during the last marine transgression in the Atlantic margin. The study of fossil dunes in the Cies Islands, a small archipelago in the mouth of the one of the rias (Ria de Vigo), allowed us to reconstruct the coastal evolution from the end of the Late Pleistocene to the present day. During this period, sea-level was 100 metres below the present one and the shoreline located about 5–10 kilometres away. About 15,000 years ago, sea-level rise began, radically modifying the coastline. This started with a gradual advance of large dune fields on both sides of the valley. The aeolian accretion continued until the Late Holocene, finishing when the sea reached its present level.This research was funded and supported by Xunta de Galicia (programmes ED431B 2018/47 and ED431B 2021/17) through the Grupo Interdisciplinar de Patrimonio Cultural e Xeolóxico (CULXEO)Xunta de Galicia; ED431B 2018/47Xunta de Galicia; ED431B 2021/1

Chronology of Coastal Alluvial Deposits in The Ria de Coruña (NW Spain) Linked to the Upper Pleistocene Sea Level Regression

This article belongs to the Special Issue Novel Approaches for Exploring Geological Processes on Both Earth and Planetary[Abstract] The Ria de Coruña (NW Spain) is a wide estuary recently formed by the flooding of the Mero fluvial valley lowlands during the last postglacial transgression. During the last glacial episode, with the sea level located more than 100 m below the current one, the final section of the Mero river and lateral tributaries contributed numerous deposits that the postglacial rise in sea level has partially flooded. Until now, the presence of these alluvial deposits disconnected from the main network by the Holocene marine transgression had been misinterpreted, especially for lack of an absolute chronology that would place them in an adequate paleoclimatic context. For the first time, a deposition age was assessed in this work by optically stimulated luminescence (OSL) dating back from 128 ka to 51 ka.This research was funded and supported by Consellería de Cultura, Educación y Ordenación Universitaria, Xunta de Galicia (programmes ED431B 2018/47 and ED431B 2021/17) through the Grupo Interdisciplinar de Patrimonio Cultural e Xeolóxico (CULXEO)Xunta de Galicia; ED431B 2018/47Xunta de Galicia; ED431B 2021/1

Sediment Beta-Microdose Variability as Main Cause of Dispersion in OSL-Quartz Dating Of Upper-Pleistocene Coastal Fluvial-Deposits Preserved at Mero-River Basin (A Coruña, Galicia, Spain)

[Abstract] In this work, we have estimated the equivalent dose (De) from the OSL signal from quartz, for fluvial deposits of the Upper Pleistocene in the Mero River basin (A Coruña, Galicia, Spain) and preserved in the Ria of Coruña coastal margin (NW Iberian Peninsule). Such deposits show De distributions more scattered than expected, providing unexpected high over-dispersion percentages of the mean (OD> 20%). These values are usually correlated to incomplete-bleaching of the OSL signal due to the transport of quartz grains under turbulent conditions as a consequence of high suspended sediment loads. However, both distribution plots and normality-test show normal, symmetric and central distributions. No evidence of two or more populations in aliquots due to two groups of grains, namely y (i) one group of grains with well-bleached signals before the last burial event and (ii) another group of grains which an inherited signal from a previous burial episode. Moreover, Dose-Recovery experiments on quartz grains show that the high dispersion is due to external and not internal factors. Thus, we have analyzed the activity concentration of radioisotopes in samples and the concentration of potassium in several grain-sizes, to assess if the origin of over-dispersion is microdosimetry caused by 40K from potassium, given the low dose rates (Dr) measured in samples. Results show that this is the most probable cause of dispersion, and no evidence of partial bleaching is found.[Resumen] En este trabajo se han estudiado las dosis equivalentes (De) obtenidas de la señal OSL del cuarzo, para depósitos fluviales del Pleistoceno Superior de la cuenca del río Mero (A Coruña, Galicia, España) y conservados en el margen costero de la Ría de A Coruña (NO Península Ibérica). Estas De muestran distribuciones con una dispersión mayor a la esperada, obteniéndose porcentajes de sobre-dispersión elevados (OD>20%). Estos valores suelen asociarse al blanqueamiento incompleto de la señal OSL, debido al transporte de los granos de cuarzo en un medio turbio, debido una caga finos en supresión. No obstante, los gráficos y test de bondad de ajuste describen distribuciones normales, simétricas y centradas en la media. Tampoco indican evidencias de dos o más poblaciones de alícuotas conformadas por dos clases de granos de cuarzo agrupadas: (i) un grupo donde la señal de los granos ha sido bien blanqueada antes del último episodio de deposición y enterramiento y (ii) otro grupo que muestran señal heredada (residual). Sin embargo, los experimentos de Dose Recovery realizados indican que la dispersión se debe a factores extrínsecos y no intrínsecos al tipo de cuarzo estudiado. Por ello, se han analizado las concentraciones de radioisótopos en las muestras y la concentración de potasio en diferentes granulometrías, para estimar si el origen de la sobre-dispersión es la micro-dosimetria causada por el 40K del potasio, dada las bajas tasas de radiación y dosis anual medidas en las muestras. Los resultados obtenidos muestran que esta es la causa más probable de la dispersión, no encontrándose evidencias de blanqueamiento parcial

Estimating the radioactive heat production of a granitic rock in the University of A Coruña (Galicia, Northwest Spain) by gamma-ray spectrometry

Geothermal energy is a form of renewable energy with a long tradition in European countries, although it is scarcely used in Spain. One of the reasons for this is the poorly studied geothermal potential of the Spanish territory. In recent years, data published on terrestrial gamma radiation and the geochemistry of radioisotopes in rocks have suggested that the radiogenic heat production (RHP) in some areas of Spain is high. In this work, we assessed the RHP by analysing the U, Th, and K contents of the rocks underlying the most important campus of the University of A Coruña (northwest Spain), using in situ handheld gamma-ray spectrometry (GRS) and X-ray fluorescence spectrometry (XRF). Our results provide a good fit of the radioisotope contents and unexpectedly high RHP, compared with average data observed in similar rocks (granodiorite). These results reveal that GRS is a very reliable tool for studying the RHP of rock surfaces, and that geothermal energy can be used in the area (i.e., the studied campus, but also most of the city of A Coruña, as it is built on the same underlying rock) for central heating in buildings using ground-source heat pumps (GSHPs).This research has been funded by the Consellería de Cultura, Educacion, e Ordenacion Universitaria, Xunta de Galicia, Spain (programmes ED431B 2018/47 and ED431B 2021/17)

Cronología finipleistocena de los depósitos fluviales costeros en la desembocadura del Río Ulla en la Ría de Arousa (Galicia, NO de España) mediante datación OSL.

This work establishes the age of an outcrop of fluvial deposits located at the current mouth of the Ulla River in the Ría de Arousa (Galicia, NW Spain), at +40 m and +30 m above present sea level. The deposits are formed by braided siliciclastic materials. Although they have been known for a long time their age had never been determined, being considered successively from Upper-Tertiary to Quaternary and even Holocene undifferentiated material. Using the optically stimulated luminescence (OSL) technique, a burial age has been calculated for the quartz grains included in the sediment of 180 ky for the lower level and between 70 ky and 60 ky for the upper levels. The chronology established here is consistent with that obtained for other fluvial deposits studied on the Galician and northern Portuguese coast.Este trabajo establece la edad de un afloramiento de depósitos fluviales situados en la desembocadura actual del Río Ulla en la Ría de Arousa (Galicia, NO de España), a +40 m y +30m sobre el nivel del mar actual. Los depósitos están formados por materiales siliciclásticos de tipo trenzado (braided). Aunque conocidos desde hace mucho tiempo, no se había determinado nunca su edad, considerándose sucesivamente desde finiterciaria a cuaternaria e incluso material indiferenciado holoceno. Utilizando la técnica de luminiscencia ópticamente estimulada (OSL) se ha calculado una edad de enterramiento para los granos de cuarzo incluidos en el sedimento de 180 ka para el nivel inferior y entre 70 ka y 60 ka para los niveles superiores. La cronología aquí establecida es coherente con la obtenida para otros depósitos fluviales estudiados en la costa gallega y del norte de Portugal

Datos paleoambientales de depósitos fluviales asociados a antiguas presas de pesca en el río Miño, NW Iberia

[Abstract] Fluvial sediments provide environmental records of the Quaternary. In some cases, fluvial deposits are caused by anthropogenic processes that cause changes in the water regime of some river stretches. This is the case of dams. It has been reported that some dams or partial damming systems existed in the past, at least from some thousands of years ago. Such dams were used for fishing purposes and are referred as fishing weirs. In a recently published work it has been demonstrated that a fluvial thick deposit was caused by a damming system in a river of NW Iberia (River Miño, Pontevedra). Optically stimulated luminescence (OSL) provided the burial age of such fluvial deposit, showing a 1300-year-old fluvial record. The sedimentation rates of the record did not match with known climate fluctuations in the area. In this work, the sedimentation phases of such record are identified, and the detrital and organic matter content is studied to assess any change occurred in the environmental and fluvial conditions during the deposition period of the record that ranges from 814±134 to 1837±11 AD.[Resumen] Los sedimentos fluviales pueden proporcionar registros ambientales del Cuaternario. En algunos casos, los depósitos fluviales pueden ser causados por procesos antropogénicos que provocan cambios en el régimen hídrico de algunos tramos de los ríos. Este es el caso de los actuales embalses. Algunos estudios han mostrado que en el pasado existieron algunas presas o sistemas de represas parciales, desde hace al menos algunos miles de años. Esas presas se utilizaban con fines pesqueros y se denominan fishingweirs o en Galicia pesqueiras. En un trabajo reciente se ha estudiado un depósito fluvial causado por un sistema de embalses en un río del noroeste de la Península Ibérica (rio Miño, Pontevedra). Utilizando luminiscencia estimulada ópticamente (OSL) se pudo datar la edad de deposición de estos sedimentos, obteniéndose un registro fluvial de 1300 años de antigüedad. Las tasas de sedimentación del registro no coincidían con las fluctuaciones climáticas conocidas en la zona. En este trabajo se identifican las fases de sedimentación de ese registro y se estudia el contenido detrítico y la materia orgánica para evaluar los posibles cambios que se hayan producido en las condiciones ambientales y fluviales de ese tramo del río durante el período de deposición del registro, que va de 814±134 a 1837±11 d.C

Aeolization on the Atlantic Coast of Galicia (NW Spain) From the End of the Last Glacial Period to the Present Day: Chronology, Origin and Evolution of Coastal Dunes Linked to Sea-Level Oscillations

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] The Atlantic coast of Galicia (NW Spain) is a high-energy environment where shingle beaches are currently developing. These coarser sediments alternate with sandy deposits which are also considered as beaches typical of a low-energy environment. The physical association of both types of sediment with contrasted sedimentary significance raises problems of interpretation. The study of four outcrops of fossil aeolianites on this coast has allowed us to reconstruct their evolution from the end of the Upper Pleistocene to the present day. Their chronology, estimated by optically stimulated luminescence between 35 and 14 ky at the end of the last glaciation (MIS2), coincides with a local sea level 120 m below the present one. This implies a coastline shifted several kilometres from its current location and the subaerial exposure of a wide strip of the continental shelf covered by sands. The wind blew sand to form dunes towards the continent, covering the coastal areas, which then emerged with no other limitation than the active river channels. Sea-level rise during the Holocene transgression has progressively swamped these aeolian deposits, leaving only flooded dunes, relict coastal dunes and climbing dunes on cliffs up to 180 m high. The aeolian process continued as long as there was a sandy source area to erode, although accretion finished when the sea reached its current level (Late Holocene). Since then, the wind turned from accretion to erosion of the dunes and sand beaches. This erosion exposes the older shingle beaches (probably of Eemian age) buried under the aeolian sands, as well as old, submerged forest remains and megalithic monuments. The destruction of sand beaches and dunes currently observed along the Galician coast is linked, according to most researchers, to anthropogenic global warming. However, their management should consider these evolutive issues.This research has been funded and supported by Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia (programmes ED431B 2018/47 and ED431B 2021/17) through the Grupo Interdisciplinar de Patrimonio Cultural e Xeolóxico (CULXEO). Thanks to Universidade da Coruña/Consorcio Interuniversitario del Sistema Universitario de Galicia (CISUG) for Open Acces fundingXunta de Galicia; ED431B 2018/47Xunta de Galicia; ED431B 2021/1

Cíes Islands: a wind trap in the Ria of Vigo (Galicia, Spain) at the end of the Last Glacial

Las Islas Cíes han constituido un obstáculo para los intensos vientos costeros del Atlántico Norte, especialmente durante las fases glaciares del Cuaternario. Al final del último glaciar el mar descendió más de 100 m por debajo de su nivel actual. Este descenso transformó el archipiélago en un relieve emergido de 300 m de alto, capaz de deflectar el viento y atraer, al mismo tiempo, sedimentos eólicos procedentes de una franja de plataforma continental también emergida. Bajo esta hipótesis, estos materiales eólicos se depositaron cubriendo el contorno de Cíes. Un ejemplo de estos episodios de acreción eólica es el afloramiento de eolianitas situado en la Isla de Monteagudo (Islas Cíes, Galicia, España), interpretado como una duna rampante que estuvo activa desde el final del Pleistoceno Superior, cubriendo parcialmente la vertiente oriental. Con un espesor de más de 3 metros y una edad (OSL) de 35 ka (b2k) en el muro y de 17 ka en el techo de la formación, este depósito es una prueba de la eolización desarrollada en la costa de Galicia durante miles de años, interrumpida al cesar los aportes durante el postglaciar holocenoCies Islands have been an obstacle to the intense coastal winds from the North Atlantic, especially during the Quaternary glacial cycles. At the end of the Last Glacial period, the local sedimentary-record shows that sea-level decreased more than 100 m below present level. This sea-level drop transformed the archipelago into an emerged relief 300 m high, which probably deflected the wind and, at the same time, was able to capture aeolian sediments coming from a strip of the continental shelf also emerged. Under this hypothesis, these aeolian materials were deposited covering the contour of Cies Islands. An example of these aeolian accretion processes is the eolianites outcrop located at Monteagudo Island (Cies Islands, Galicia, Spain) interpreted as a climbing-dune which was active from the end of the Upper Pleistocene, partially covering the eastern slope. This deposit more than 3 meters thick with an OSL age of 35 ky (b2k) at the base and 17 ky at the top, is an evidence of the aeolisation developed in the Galician coast for thousands of years, finally disrupted when aeolian-supplies were suspended during Holocene post-glacia