La secuencia aluvial a palustre-lacustre del Mioceno de Faido-Samiano (cuenca Miranda – Treviño, Pirineos occidentales)

This work presents the results from the study of the lower to middle? Miocene continental succession exposed in the Faido-Samiano section, on the south-east flank of the Miranda – Treviño piggy-back basin. Facies analysis allowed accurate interpretation of the constituent deposits and the corresponding depositional settings they characterize, from alluvial to varied palustrine-lacustrine sub-environments. Logging and mapping across an area of about 15 km2 revealed a distinct recurrent stratigraphic arrangement that reflects successive cycles of progressive expansion and abrupt subsequent retraction of the km-wide palustrine-lacustrine wetlands developed on the basin depocentre. The scale and distinct asymmetry of the successive stratigraphic cycles point to an origin likely related to high-frequency pulsating tectonic activity affecting the rising basin marginsEste trabajo expone los resultados del estudio de la sucesión continental del Mioceno inferior-medio? aflorante en la sección de Faido-Samiano, en el flanco sureste de la cuenca piggy-back de Miranda-Treviño. El análisis de facies ha conducido a la interpretación de un sistema sedimentario integrado por ambientes de abanico aluvial, palustre y lacustre. El levantamiento de la sección estratigráfica y la cartografía de los diferentes tramos ha permitido reconocer un patrón de facies recurrente, que refleja varios ciclos de expansión progresiva y retracción brusca de los humedales palustres-lacustres desarrollados en el centro de la cuenca. La escala y la asimetría de estos ciclos estratigráficos se ha relacionado con pulsos tectónicos de alta frecuencia afectando a los márgenes activos de la cuenc

Why Do Bio-Carbonates Exist?

Calcium carbonate precipitation associated with biotic activity is first recorded in Archaean rocks. The oldest putative fossils related to hydrothermal vents have been dated at ~3.77 Ga (possibly 4.29 Ga). Stromatolites, the oldest dated at 3.70 Ga, have since occurred through Earth history, despite dramatic changes in physical and chemical conditions in aquatic environments. A key question is: what advantages do photosynthesizing aquatic prokaryotes and algae gain by precipitating carbonates? We propose the Phosphate Extraction Mechanism (PEM) to explain the benefits of biomineralization in warm, oligotrophic, alkaline, euphotic environments. Carbonate precipitation enhances access to otherwise limited carbon dioxide and phosphate in such environments. This mechanism also provides an explanation for prolific production of carbonates during times of elevated atmospheric carbon dioxide at intervals in the Phanerozoic.JIB acknowledges funding from the Basque Government to the Research Group IT1602-22. L.P., P.H. and G.M.-V. participation did not involved external funding aside from their academic institutions

Magnetic properties of cherts from the basque-cantabrian basin and surrounding regions: Archeological implications

We present the first rock magnetic study of archeologically-relevant chert samples from the Basque-Cantabrian basin (BCB) and surrounding regions, which was conducted in order to test the usefulness of non-destructive magnetic properties for assessing chert quality, distinguishing source areas, and identifying heated samples in the archeological record. Our results indicate that the studied BCB cherts are diamagnetic and have very low amounts of magnetic minerals. The only exception is the chert of Artxilondo, which has a median positive magnetic susceptibility associated with larger concentrations of magnetic minerals. But even in this case, the magnetic susceptibility is within the lower range of other archeologically-relevant cherts elsewhere, which indicates that the studied BCB cherts can be considered as flint. The similar median values for all magnetic properties, along with their associated large interquartile ranges, indicates that rock magnetic methods are of limited use for sourcing different types of flint except in some specific contexts involving the Artxilondo flint. With regards to the identification of chert heating in the archeological record, our results indicate only a minor magnetic enhancement of BCB natural flint samples upon heating, which we attribute to the low amount of non-silica impurities. In any case, the diamagnetic behavior of most BCB natural flints, along with the local use only of the Artxilondo type, suggests that any flint tool within the core of the BCB with positive magnetic susceptibility values is likely to have been subjected to heating for improving its knapping properties. Further studies are necessary to better identify the type, origin and grain size of magnetic minerals in BCB natural flints, and to apply non-destructive magnetic properties to flint tools in order to identify the use of heat treatment in the BCB archeological record. © 2016 Larrasoaña, Beamud, Olivares, Murelaga, Tarriño, Baceta and Etxebarria.This study was funded by project GUI15/34 of the Universidad del País Vasco.Peer reviewe

Multi-aged social behaviour based on artiodactyl tracks in an early Miocene palustrine wetland (Ebro Basin, Spain)

We present a new locality with at least 880 vertebrate tracks found at the top of a limestone bed from the lower Miocene Tudela Formation (Spain). The trampled surface was formed by artiodactyls that crossed a muddy carbonate accumulated under the influence of water level variations in a palustrine environment. The tracks reflect different types of morphological preservation. The well-preserved tracks have tetradactyl digit impressions caused by both manus and pes, and are the type series of a new artiodactyl ichnotaxon, Fustinianapodus arriazui ichnogen. nov. and ichnosp. nov. The rest of the tracks, which are not as well preserved, are didactyl and were classified as undetermined artiodactyl tracks. According to their preservation, morphology, size, arrangement and orientation, we propose that this tracksite is the product of a social behaviour, particularly gregariousness, of a multi-age group of artiodactyls ~19Ma ago. The morphologic and palaeoecologic data presented here suggest that the trackmakers were a group of anthracotheres with a livelihood similar to current hippos. They crossed, periodically, a fresh water palustrine area along some preferential pathways (trails)

Estratigrafía y sedimentología del Mioceno de la Plana Negra-Sancho Abarca (sector central-occidental de la Cuenca del Ebro)

Este trabajo abarca el estudio sedimentológico y estratigráfico de los depósitos del Burdigaliense (Mioceno inferior) y Langhiense (Mioceno medio) de la Plana Negra y la Plana de Sancho Abarca, sector central-occidental de la Cuenca del Ebro (NE de la Península Ibérica). Se han identificado un total de 5 litofacies (unidades cartografiables) constituidas por areniscas, lutitas, margas y calizas en variables proporciones, equiparables a miembros (informales) de la Formación Tudela. Se han realizado dos perfiles estratigráficos que abarcan las unidades tectosedimentarias T5 y T6 definidas para la Cuenca del Ebro; dicho límite es una conformidad que se reconoce como el paso de lutitas con intercalaciones de areniscas y calizas a predominio de calizas, y constituye un nivel excelente de correlación. Los depósitos de T5 tienen 130 m de espesor y los de T6 tienen 63 m. Las paleocorrientes medidas en la unidad T5 señalan procedencia del margen pirenaico. Se han caracterizado 17 facies sedimentarias (detríticas, mixtas y carbonatadas) que muestran gran variedad biótica (ostrácodos, carófitos y gasterópodos) y rasgos pedogenéticos. Se agrupan verticalmente en 5 asociaciones de facies que caracterizan los ambientes fluvial-aluvial distal, palustre y lacustre somero. El modelo de sedimentación propuesto se basa en la distribución espacial de esas asociaciones y expresa la relación entre dichos ambientes. La correlación de las secciones estudiadas con otras tres de áreas adyacentes que disponen de datación magneto-bioestratigráfica ha permitido datar con precisión la sucesión estudiada y el límite T5/T6 (C5Cn.1n, entre 16,062 y 16,099 Ma). La integración de las cinco secciones permite distinguir cuatro estadios evolutivos, definidos por la progradación-retrogradación del medio aluvial o retracción-expansión de los ambientes palustres y lacustres. Se relacionan con la tectónica y el clima, que controlaron la evolución de los sistemas sedimentarios a través de variaciones de los aportes y del nivel lacustre en el área estudiada.<br /

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

The stratigraphic and sedimentologic study of Miocene deposits in the Plana Negra-Sancho Abarca area fills a gap in the Ebro Basin knowledge. Five main lithofacies were characterized and mapped. The boundary between regional tectosedimentary units T5 and T6 is recognized as a conformity at a major facies change. Unit T5, up to 130m thick, consists of mudstones with interbedded sandstones and limestones. Unit T6, with 30 to 62m of preserved thickness, is made of limestones, marls and minor mudstones. Correlation of the studied outcrops with nearby sections that already had detailed magnetoestratigraphic and biostratigraphic data allows dating the studied succession as Burdigalian (early Miocene)-Langhian (middle Miocene), from C5Dr to C5Cn, and the boundary between units T5 and T6 to be located at 16.062-16.099 Ma. Seventeen sedimentary facies associated in seven vertical facies sequences document deposition in fluvial-distal alluvial, palustrine and lacustrine environments. A shallow (2-4m deep) lake body was locus for charophytes, ostracods, bivalves and gastropods to thrive. Occasional bottom currents reworked and transported allochems and fine-siliciclastic sediment offshore, forming laminated limestones. Bioturbation and desiccation features are abundant, indicating wide palustrine areas and episodic exposure. Low-sinuosity channels associated to the Pyrenean-derived Luna fluvial system run across the alluvial-plain. Four evolutionary stages of alluvial progradation-retrogradation and retraction-expansion of the palustrine-lacustrine system, likely related to Pyrenean tectonic activity, are distinguished. Maximum lacustrine expansion took place at the beginning of unit T6 deposition. This is consistent with initial conditions of increasing humidity of the Middle Miocene Climatic Optimum (MMCO)

K/T muga euskokantauriar arroan

Kretazeo eta Tertziarioaren arteko mugan gertatu zen suntsipen masiboak Lurreko espezieen hiru laurden baino gehiago desagertarazi zuen eta gaur egun zientzia-eremu ezberdinetako zientzialarien interesa suspertzen du; haien artean paleontologoak, geokimikoak, astrofisikoak eta abarrak. Ikertzaileok, Biziaren historiaz gain Lur planetaren eboluzioaz arduratzen dira. Euskokantauriar Arroan K/T muga ebaki anitzetan gorde da, Kretazeoaren amaierako krisiari buruzko ikerketak garatzeko leku aparta izanik

Preliminary study of the ostracods from the Lower Eocene Loza site (Álava, Basque-Cantabrian Basin)

In this paper the preliminary study of ostracods preserved in a distinct fossiliferous level within the poorly-known lower Eocene lacustrine-palustrine succession of Loza (Álava, Basque-Cantabrian Basin) is developed. The studied level is a 28cm thick marly interval including a thin whitish chalky level, interbedded between fine-grained limestones with variable proportions of gastropods and characean remains.With the aim of knowing the richnes of the ostracods and the prevailing palaeoenvironmental conditions during deposition of the lacustrine succession, two samples (L1 and L2), located within the marly interval respectively below and above the chalky level, have been studied. In L1 the most abundant genus is Limnocythere Brady, while in L2 the principal genera are Limnocythere and Cyclocypris Brady and Norman. According to the successive change in the ostracods, the fossiliferous level was deposited in a lacustrine environment,which was more saline and, probably, restricted over timeEn este trabajo se desarrolla un estudio preliminar de los ostrácodos preservados en un nivel fosilífero distintivo dentro de la pobremente conocida sucesión de origen palustre-lacustre del Eoceno inferior de Loza (Álava, Cuenca Vasco-Cantábrica). El nivel estudiado contiene un espesor de 28cm de margas incluyendo una fina banda calcítica blanca, intercalada entre calizas de grano fino con proporciones variables de gasterópodos y carofitas. Con el propósito de conocer la riqueza de ostrácodos y las condiciones paleoambientales predominantes durante el depósito de la sucesión lacustre, se han estudiado dos muestras (L1 y L2), situadas respectivamente por encima y por debajo de la banda blanca. En L1 el género más abundante es Limnocythere Brady, mientras que en L2 los géneros mayoritarios son Limnocythere y Cyclocypris Brady y Norman. De acuerdo a la variación de los ostrácodos identificados, el nivel fosilífero se depositó en un medio lacustre que fue más salino y, posiblemente, restringido con el tiemp

Los ostracódos de las arenas con "Heterostegina" de la formación "calcarenita de Niebla" (Depresión del Guadalquivir, S.O. de España)

El estudio de las asociaciones de ostrácodos de las arenas basales con microforaminíferos de la Formación "Calcarenita de Niebla" (Civis et al., 1987) indican una edad Tortoniense para estos materiales. Su depósito se produjo en un medio infralitoral muy somero, bien oxigenado y con una importante vegetación.The ostracod assemblages of the basal sands with Heterostegina of the "Calcarenita de Niebla" Formation (Civis et al, 1987) indicates a Tortonian age. These materials were deposited in an infralittoral environment, well oxigenated and vegetate