The microstratigraphic record of human activities and formation processes at the Mesolithic shell midden of Poças de São Bento (Sado Valley, Portugal)

Shell midden formation is largely controlled by an-thropogenic processes, resulting from human exploitation of aquatic resources. This makes shell middens archives of bothhuman behaviour and palaeoenvironmental records.However, their often complex stratigraphy hampers the isola-tion of individual anthropogenic events. In the central/ southern coast of Portugal, extensive inland estuaries were preferential settings for Mesolithic groups from c. 6200 calBC. Here, we present a microstratigraphic approach to theshell midden of Poças de São Bento, one of the largest and best-knownsitesintheSadoValley.Themicrofaciesapproachwas based on sedimentary components, their abundance andarrangement, and post-depositional processes. Anthropogenic processes identified as tossing events and anthropogenicallyreworked deposits allowed inferences on spatial organisation, preferential refuse areas, occupational surfaces, and temporal-ity of the occupations. The presence of calcareous pebbles inthe anthropogenic, shell-rich sediments, together with forami-nifera, presumably from the estuarine marshes, is compared with the regional geology, providing a hypothetical location of the shellfish gathering. The microstratigraphy described reveals a full internal dynamic in the formation of the apparently homogeneous shell midden layer. The human activities inferred at Poças de São Bento have many similarities with those reported for Cabeço da Amoreira in the nearby Tagus palaeo-estuary. This evidence points to the need for further micro-morphological approaches in similar deposits. The study of shell midden formation processes, through integrative microcontextual approaches, plays a major role in understanding Mesolithic societies in the large early Holocene estuary environments of Atlantic Iberia.info:eu-repo/semantics/publishedVersio

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

Evidencias de albitización de carbonatos mesozoicos: estudio petrológico de albitas autigénicas al noroeste del Macizo Bortziriak-Cinco Villas, este de la Cuenca Vasco-Cantábrica

The presence of authigenic Na-feldspars in sedimentary carbonate rocks is unusual and its origin is controversial in terms of genesis and timing. The use of optical microscopy, cathodoluminescence and in situ semi-quantitative EDX analysis techniques, has allowed the identification and characterization of authigenic albite crystals in the Mesozoic pre- and syn-rift carbonates of the northwestern margin of the Bortziriak-Cinco Villas Massif, in the northeastern Basque- Cantabrian Basin (western Pyrenees). The euhedral habit, crystal size, spatial distribution and crosscutting relationships, together with the pure albitic composition, suggest a relatively early replacement origin. Compaction of sediments during burial, besides possible fluid migration linked to the intense syn-rift halokinetic activity, may have been decisive for the mobilisation of cations, and hence, for the albitization of the carbonate rocksLa presencia de feldespatos sódicos autigénicos en rocas sedimentarias carbonáticas es inusual y su origen es controvertido en términos de génesis y cronología. El empleo de la microscopía óptica, catodoluminiscencia y los análisis semi-cuantitativos in situ por EDX, han permitido la identificación y caracterización de albitas autigénicas en los carbonatos pre- y sinrift del Mesozoico, en el margen noroeste del Macizo de Bortziriak-Cinco Villas, al noreste de la Cuenca Vasco-Cantábrica (Pirineos occidentales). El hábito euhédrico, el tamaño de cristal, la distribución espacial y las relaciones de corte, junto a la composición albítica, sugieren un origen relativamente temprano por remplazamiento. La compactación por enterramiento de los sedimentos además de la posible migración de fluidos relacionada con la intensa actividad halokinética syn-rift, pudo ser decisiva para la movilización de cationes, y, por lo tanto, para la albitización de las rocas carbonatada

Caracterización y bioestratigrafía de foraminíferos planctónicos de la transición del Grupo Flysch Negro - Flysch Calcáreo entre Usurbil y Hernani, Pirineo occidental

La realización de una cartografía de detalle junto al análisis sedimentológico y bioestratigráfico del contacto entre las unidades del Grupo Flysch Negro y el Flysch Calcáreo entre las localidades de Usurbil y Hernani ha permitido caracterizar el tránsito entre ambas unidades estratigráficas. Los datos indican la existencia de una disconformidad entre ambas unidades y no un contacto por falla inversa tal y como habían sugerido autores anteriores. Un análisis bioestratigráfico de detalle de las rocas subyacentes y suprayacentes al contacto deposicional indica la presencia de un hiato de duración variable a lo largo del mismo: en el sector oeste un hiato intra-Zona R. globotruncanoides (Cenomaniense Inferior) y en el sector este un hiato entre las Zonas R. appenninica – R. globotruncanoides (Albiense Superior-Cenomaniense Inferior

Influence of salt-antiform growth on a mid-Cretaceous braidplain delta system: Oiartzun Formation, NE margin of the Basque-Cantabrian Basin

Los depósitos siliciclásticos y carbonatados de la Formación Oiartzun (Albiense superior-Cenomaniense inferior) al sureste de Donostia-San Sebastián (margen NE de la Cuenca Vasco-Cantábrica) registran la evolución de la formación de pliegues forzados causados por la tectónica salina coetánea dentro de un contexto de rifting . El análisis de facies indica la localización espacial de distintos ambientes sedimentarios dentro de un sistema deposicional de tipo braidplain delta en un espacio relativamente reducido debido a la evolución y formación de los antiformes de Txoritokieta y Oiartzun. Asimismo, el crecimiento de estos pliegues modifica el relieve deposicional, condicionando notablemente el espesor estratigráfico sobre cada uno de los flancosThe siliciclastic and carbonate deposits of the upper Albian to lower Cenomanian Oiartzun Formation, which crop out to the southeast of Donostia-San Sebastián (NE margin of the Basque-Cantabrian Basin), record the evolution of the coeval growth of salt-influenced forced-folds (anticlines), in an extensional rifting context. Facies analysis indicates the distinct spatial distribution of sedimentary environments in a braidplain delta depositional system over a relatively reduced area, due to the synsedimentary growth of the Txoritokieta and Oiartzun forcedfolds. The growth of these folds conditions the depositional relief and impact not only in the facies distribution but also in stratigraphic thicknesses in the fold limb

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)

Palaeoenvironment and formation processes of a Palaeolithic deposit: The Mendieta site (Sopelana, Biscay province)

An urgent archaeological excavation on the Mendieta area (Sopelana, Biscay province) has evidenced the presence of lithic industry within an original stratigraphic context of possible lower Palaeolithic age. The materials containing the lithic industry exhibit stratigraphic and sedimentary features derived from fluvioalluvial and pedogenic processes. The formation procedures of this open-air site took place under warm and humid palaeoenvironmental climatic conditions. This characterization supplies an important information in order to understand the genesis and location of the scarce open-air archaeological sites of lower Palaeolithic age present in the Cantabrian regio