Glauconitic laminated crusts from hydrothermal alteration of Jurassic pillow-lavas (Betic Cordillera, S Spain): a microbial influence case

The green crusts infilling the spaces among pillow-lava bodies from the Median Subbetic (Betic Cordillera, S Spain) are the subject of this textural, mineralogical and geochemical study. The exceptional laminated morphology and mineral composition made it possible to establish the genetic conditions and different phases of the infilling, while also interpreting the possible influence of microbial activity in the origin and growth of the laminated crusts. Two types of crusts were discerned: green laminated crusts and black crusts. The green crusts are mostly composed by glauconite and celadonite, and a minority by smectites, whereas black crust and lens-shaped nappes are saponitic. The record of filaments and coccoid-shaped forms at different scales from the glauconitic crusts indicates the potential implication of chemoorganotrophic microbes in the precipitation of the glauconite and the development of laminated textures under low-temperature hydrothermal conditions. In an early stage, alteration of pillow-lava surfaces with influence of hydrothermal reducing fluids results in black films of saponite and calcite filling the void spaces. During a cooling phase, green laminated crusts composed by glauconite and celadonite grow under oxic conditions due to the circulation and diffusion of oxygenated sea-water along inter-pillow spaces and the chemoorganotrophic microbial activity. A new stage of saponite formation with calcite occurs under higher T and confined-reducing conditions resulting from deposition of marine sediments, and finally calcite and quartz crystallise as the latest product closing the remaining space (or producing geodes) among the pillow-lava bodies.Las costras verdes localizadas entre las lavas almohadilladas del Subbético Medio (Cordillera Bética, S España) presentan una morfología laminada excepcional. La caracterización textural, geoquímica y mineralógica de estas costras ha permitido establecer las condiciones bajo las que se formaron e interpretar la posible influencia de la actividad microbiana en el origen, crecimiento y morfología de las mismas. Se han diferenciado dos tipos de costras: costras laminadas verdes y costras negras. Las costras verdes están formadas mayoritariamente por glauconita y celadonita y, en menor proporción, por esmectitas. Las costras negras, sin embargo, son de naturaleza saponítica. La presencia de filamentos y formas cocoidales a diferentes escalas de observación en las costras verdes, sugiere la mediación de microbios quimiorganotróficos en la precipitación de la glauconita así como en el desarrollo de texturas laminadas en un ambiente hidrotermal de baja temperatura. En un primer momento, la alteración de las superficies de las lavas almohadilladas, bajo la influencia de fluidos hidrotermales de carácter reductor que siguieron al depósito de las lavas almohadilladas, produjo láminas negras de saponita y calcita. En una fase de enfriamiento posterior, bajo condiciones oxidantes favorecidas por la circulación y difusión de agua marina oxigenada a lo largo de los huecos entre las lavas almohadilladas y con la participación de actividad microbiana quimiorganotrófica, tuvo lugar la precipitación de glauconita y celadonita generando las costras verdes laminadas. Como consecuencia del enterramiento de la pila volcánica debido al depósito de sedimentos marinos, se produjo una confinación del medio que favoreció el incremento de temperatura y un ambiente reductor que propició nuevamente la génesis de saponita y calcita. Finalmente, en el hueco entre las lavas cristalizó calcita y cuarzo, que en algunos casos dieron lugar a geodas y en otros al cierre total del espacio entre las mismas

Jurassic Fe-Mn macro-oncoids from pelagic swells of the External Subbetic (Spain) : evidences of microbial origin

Ferromanganesiferous macro-oncoids are distinctive from the External Subbetic Zone (Betic Cordillera, SE Spain) in relation to a major heterochronic unconformity, with a Middle Bathonian-Lower Oxfordian minimum hiatos and a Lowest Bathonian-Lowest Kimmeridgian maximum hiatus. The Fe-Mn macro-oncoids (43 mm mean-size) consist of microbial laminae with planar and arborescent to dendrolitic morphologies. Under petrographic microscopy, the planar morphologies are made up by condensed fibrillar meshworks whereas the dendrolitic ones are similar to Frutexites. Alternation between these two types of laminae reveals a rhythmic growth in the Fe-Mn macro-oncoids. Bacterial and fungal filaments are observed in SEM analyses as microbial mats constituted by a disperse web of filaments exhibiting a branching tube-like morphology with diameters ranging between 2 and 10 µm. Aggregates of coccoid-shaped forms are also registered by SEM analyses. Taxonomical approximation of the microbiota is complex, though in the thin section the condensed fibrillar meshworks look like cyanobacteria, and in SEM images the morphology of the filaments resembles fungal hyphae and green algae, whereas coccoids are assigned to cyanobacteria. The precipitation of Fe-Mn is related to the chemoorganotrophic behaviour of the benthic microbial communities, probably corresponding to the fungal mats and other chemosynthetic microbes. Inorganic precipitation mechanisms are regarded as insufficient for the accumulation of a significant amount of MnO. An efficient precipitation of Mn from natural water largely depended on the presence of Mn-oxidizing microorganisms. Sediment-starved zones of pelagic swells of the External Subbetic, located in the deep euphotic zone, were the best places for microbially mediated authigenesis

Costras laminadas glauconíticas de depósitos de lavas almohadilladas del Jurásico (Cordillera Bética, Sur de España)

An exceptional record of Jurassic glauconitic laminated crusts is reported from veins of spaces among pillow-lava bodies in the Middle Subbetic (Betic Cordillera). The veins are composed by green crusts with planar (<36 mm thick), columnar (<130 mm length) and oncoid-like morphologies growing from the pillow-lava walls. Mineralogical and geochemical analyses of the green crusts led us to identify lath-like crystals of glauconite and minority filmy veil-like smectites (saponite and beidellite), calcite and iron oxides. The composition of clay minerals and their association with carbonates reveal whether the alteration occurred under oxidizing or reducing conditions. The main phase of hydrothermal alteration occurred under low temperature oxidizing conditions with a high sea-water/rock ratio, in an open-circulation regime, with precipitation of glauconite. The late phase of alteration is typified by the formation of saponite and calcite, and took place under confined conditions due to the burial of pillow-lava by marine sedimentSe ha puesto de manifiesto que los materiales que rellenan el espacio entre las lavas almohadilladas jurásicas del Subbético Medio (Cordillera Bética) son costras verdes constituidas mayoritariamente por glauconita. Las costras crecen desde las paredes de las lavas almohadilladas con morfología planar (<36 mm de espesor), columnar (<130 mm de altura) y concéntrica. El análisis mineralógico y geoquímico ha permitido identificar cristales micrométricos de glauconita tabular, esmectitas de naturaleza saponítica y beidellítica, calcita y óxidos de hierro. El tipo de minerales de la arcilla (glauconita y esmectitas) y su asociación con carbonatos sugiere una primera fase de alteración hidrotermal con precipitación de glauconita que aconteció a baja temperatura en un régimen de circulación abierta con alta proporción de agua marina (condiciones oxidantes). Una segunda fase de alteración, bajo condiciones de confinamiento resultado del enterramiento de las lavas por sedimentos marinos carbonatados, dio lugar a la precipitación de saponita y calcit

Primer registro de sauropterigios fósiles del Triásico Superior del suroeste de España (Ayamonte, provincia de Huelva)

This work reports the first record of a sauropterygian reptile remain from the uppermost Triassic of the westernmost part of the South Iberian Palaeomargin. The fossil bone, found in the Upper Triassic carbonate succession of Ayamonte (Huelva, Spain), corresponds to a neural arch of a sauropterygian. The carbonate succession was deposited in very shallow marine environment simultaneous with igneous activity during the Rhaetian (latest Triassic). The studied remain is isolated, disarticulated and presents fractures that evidence transport but also potential activity of scavengers. The neural arch is preserved as calcium phosphate enriched in some elements (e.g. Sr) relative to the surrounding carbonate sediment. The anatomic features do not allow a detailed taxonomic identification. This remain extends the record of sauropterygians to the westernmost end of the Tethys following the South Iberian Palaeomargin and evidences the colonization of the Algarve Basin during the extensional phase related with the progress of the rifting of Pangaea and the opening of the Tethys to the west. &nbsp;Este trabajo se centra en el estudio del primer registro de un resto fósil de sauropterigio procedente del Triásico superior del sector oriental del Paleomargen Suribérico. El resto, encontrado en la sucesión sedimentaria carbonatada del Triásico que aflora en Ayamonte (Huelva, España), corresponde a un arco neural de un sauropterigio. La sucesión carbonatada se depositó en un ambiente marino muy somero simultáneamente a cierta actividad ígnea durante el Rhaetiense (Triásico superior). El resto fósil aparece aislado, desarticulado y presenta algunas fracturas que evidencian cierto transporte por corrientes, sin descartar la posible interacción de organismos carroñeros. El arco neural está conservado como fosfato cálcico con enriquecimiento en Sr, de acuerdo con los mapeos composicionales realizados sobre el resto fósil y el sedimento circundante. Los rasgos anatómicos no han permitido su identificación taxonómica detallada. El resto estudiado extiende el registro de reptiles sauropterigios hacia el occidente colonizando el Paleomargen Suribérico, en este caso la Cuenca del Algarve, conforme se producía la rotura (rifting) de Pangea y el Tethys se abría paso hacia el oeste con la progresiva inundación de nuevas cuencas

Ostrácodos del tránsito Cenomaniense-Turoniense en los Montes Ksour y Amour (Atlas Sahariano): sistemática e implicaciones paleobiogeográficas

The study of ostracods from the Cenomanian-Turonian transition in the Ksour and Amour Mountains (Saharan Atlas, Algeria) has allowed the identification of fossil assemblages characterising this relevant time interval characterised by global environmental changes. The ostracod assemblages consist of fifteen species and seven genera, and are dominated by the Family Cytherellidae (mainly genus Cytherella), and secondarily by the families Paracyprididae (exclusively Paracypris) and Trachyleberididae (mainly Cythereis). Less common are components of families Bairdiidae, Bythocypridae and Macrocyprididae. The studied ostracod assemblages were compared with those assemblages from basins belonging to palaeobiogeographic provinces of North Africa-Middle East (Gondwana Palaeomargin) to search for possible similarities among basins. Thus, the results obtained show the proximity of the ostracod fauna of the Moroccan and Egyptian basins, to which the two basins belonging to the Middle East (Jordan and Oman) are related, the strong similarity between the basins of the Saharan Atlas (Algeria and Tunisia) and finally, the isolation of the ostracod fauna of the Lebanese Basin. This palaeobiogeographical topology shows the probable existence of communication routes during the Cenomanian-Turonian transition or equivalent palaeoenvironmental conditions in different basins.El estudio de los ostrácodos de la transición Cenomaniense-Turoniense (Cretácico superior) en los Montes Ksour y Monte Amour (Atlas Sahariano, Argelia) ha permitido la identificación de asociaciones fósiles típicas de este periodo caracterizado por cambios ambientales a escala global. La asociacion de ostrácodos consiste en 15 especies y 7 géneros, y se encuentra dominada por la familia Cytherellidae (principalmente el género Cytherella), y en menor medida por las familias Paracyprididae (exclusivamente Paracypris) y Trachyleberididae (principalmente Cythereis). Las formas menos comunes corresponden a las familias Bairdiidae, Bythocypridae y Macrocyprididae. Las asociaciones de ostrácodos del Atlas Sahariano fueron comparadas con las asociaciones de cuencas vecinas pertenecientes a la provincia paleobiogeográfica del Norte de África y Oriente Medio (margen septentrional de Gondwana) con el fin de encontrar similitudes entre cuencas. Así, el resultado obtenido muestra una gran similitud entre la fauna de ostrácodos de las cuencas del Atlas Sahariano en Argelia y Túnez. Por otro lado, existe similaridad entre las asociaciones de las cuencas de Marruecos y Egipto, y de ambas a su vez con las cuencas de Oriente Medio (Jordán y Omán). Finalmente, la fauna de la Cuenca Libanesa aparece relativamente aislada. Estas similaridades entre distintas cuencas desde el punto de vista palaeobiogeográfico pueden evidenciar cierta comunicación entre las mismas o condiciones ambientales equivalentes durante el tránsito Cenomaniense-Turoniense

New deep-water brachiopod resilient assemblage from the South-Iberian Palaeomargin (Western Tethys) and its significance for the brachiopod adaptive strategies around the Early Toarcian Mass Extinction Event

The Pliensbachian-Toarcian transition was a period of changes in long-term environmental conditions leading up to the Early Toarcian Mass Extinction Event (ETMEE), which resulted in a noticeable extinction and turnover in the marine biota. The westernmost Tethyan basins, especially the peri-Iberian platforms, provide an exceptional brachiopod record to better understand the adaptive strategies and the severe ecological effects of these faunas within the marine ecosystems. This event marks a critical interval in the evolutionary history of the Phylum Brachiopoda as two orders, the Athyridida and Spiriferinida, became extinct. Evolutionary patterns displayed by several taxa from these groups and some rhynchonellids typifying deep-water habitats are analyzed across this biotic crisis spanning several Mediterranean and NW-European basins. New work performed in La Cerradura section, a deep pelagic trough from the South-Iberian palaeomargin, reveals two new taxa (Koninckodonta sumuntanensis and Atychorhynchia falsiorigo) herein described. This newly documented fauna supports pre-extinction dwarfing and resilience in deep refugia linked to the ETMEE, and an episode of speciation which is interpreted in terms of a pre-extinction radiation. In the ETMEE repopulation phase an opportunistic strategy occurs typified by Soaresirhynchia bouchardi, and a case of homoplasy involving post-extinction pioneers (Elvis taxon) is detected. Similar adaptive strategies occurred associated with other mass extinctions such as the Permian/Triassic and the Cretaceous/Paleocene events, supporting a possible standard pattern in the response of the brachiopod fauna to such biotic crises and shedding light on the ecological effects of the mass extinction events.This research is a contribution to the IGCP-655 Toarcian Oceanic Anoxic Event: Impact on marine carbon cycle and ecosystems and was also supported by projects RYC-2009-04316 (Ramón y Cajal Program), P11-RNM-7408 (Junta de Andalucía), CGL2015-66604-R (MINECO, Government of Spain), and the Research Group VIGROB-167 (University of Alicante)

Comparison of the Calcareous Shells of Belemnitida and Sepiida: Is the Cuttlebone Prong an Analogue of the Belemnite Rostrum Solidum?

The microstructure of the rostrum solidum of Jurassic belemnites is compared with that of Sepia cuttlebones, in order to examine possible convergences in their style of growth. For this study, transmitted and polarized light, cathodoluminescence, epifluorescence, scanning electron and backscattered electron microscopy have been employed. Despite differences in the primary mineralogy of the studied belemnites and sepiids, calcite and aragonite, respectively, many similarities have been observed between the microstructure of the belemnite rostra and the prong of Sepia cuttlebone: (1) In both, crystals start growing from successive spherulites, from which crystals emerge radially towards the apex and the external walls, displaying internally micro-fibrous texture. (2) Both display concentric growth layering, comprising an alternation of organic-rich and organic-poor layers, which, in turn, is traverse by the radially-arranged micro-fibrous crystals. (3) The highest organic matter content and porosity have been observed along the apical area of the Sepia prong, similarly to that interpreted for belemnite rostra. The strong convergences observed suggest that the growth of belemnites occurred similarly to that of the prong of sepiids and that the Sepia prong is the analog of the belemnite rostrum. Additionally, non-classical crystallization processes are proposed to be involved in the formation Sepia endoskeleton

Primer registro de Palaeoloxodon cf. antiquus (Proboscidea, Pleistoceno Medio) del sector oriental de la Cuenca del Guadalquivir (SE España): tafonomía y relación con otros yacimientos

The first record of a proboscidean from the Eastern Guadalquivir Basin is located in the alluvial fans developed during an intense erosive phase of the reliefs of the outermost mountain front of the Betic Cordillera. The remain is a fragment of a fossil tusk (74 cm length) transported by water streams during the Middle Pleistocene and deposited with high energy detritic sediments (coarse sands to boulders). The fossil is coated by a laminated crust (&lt; 2 cm) composed by carbonate. Detailed analysis of this crust evidences it was a cover of mosses around the bone that was cemented early and preserved as a thin phytoherm. The presence of this coating favoured the preservation of the bone in a high energy environment, and its fast burial also favoured preservation. Analysis of the Schreger lines in the internal structure of the tusk allow us to assign this remain to the straight-tusked elephant Palaeoloxodon cf. antiquus. The studied specimen from the Eastern Guadalquivir Basin is found between populations of P. antiquus from the Western Guadalquivir Basin and from the Guadix-Baza Basin. Seasonal migrations of P. antiquus between low lands of the Western Guadalquivir Basin (&lt; 200 m above sea level) and high lands of the Guadix-Baza Basin (&gt; 900 m above sea level) are not discarded.El primer registro de un proboscídeo en el sector oriental de la Cuenca del Guadalquivir se ha localizado en los abanicos aluviales desarrollados durante una etapa intensa de erosión de los nuevos relieves del frente montañoso más externo de la Cordillera Bética. El fósil estudiado es un fragmento de defensa de 74 cm de longitud que fue transportado por las corrientes que alimentaban el abanico deltaico durante el Pleistoceno medio. Este resto se encuentra dentro de unos depósitos detríticos de alta energía que varían entre tamaño arena gruesa y bloques. El fragmento de defensa se encuentra revestido por una costra carbonatada laminada de un espesor inferior a 2 cm. El análisis detallado de esta costra ha permitido identificar estructuras asignables a briofitas fósiles. Por lo tanto, se interpreta que la defensa fue recubierta casi completamente por musgo que experimentó una cementación temprana. Posiblemente la formación de esta costra favoreció que el fragmento de defensa se preservara. Un posterior enterramiento rápido también debió favorecer la preservación. El análisis de las líneas de Schreger en superficies de fractura de la defensa ha permitido asignar el resto a la especie de elefante Palaeoloxodon cf. antiquus. El ejemplar estudiado en el sector oriental de la Cuenca del Guadalquivir se encuentra entre las poblaciones del sector occidental de la Cuenca del Guadalquivir y las de la Cuenca de Guadix-Baza. No se descarta la posibilidad de que existieran migraciones estacionales de P. antiquus entre las tierras bajas de la Cuenca del Guadalquivir a menos de 200 m de altura sobre el nivel del mar, y el altiplano de la Cuenca de Guadix-Baza, por encima de 900 m de altura

Bioestratigrafía de Foraminíferos del Toarciense del Atlas Medio (Marruecos). Correlación con las regiones vecinas

Los depósitos del Toarciense del Atlas Medio, generalmente de tipo hemipelágico, presentan características de plataforma y de cuenca. Son depósitos margosos, confinados en los depocentros, y depósitos condensados calcáreo-margosos, en los altos de la cuenca. Los estudios micropaleontológicos de foraminíferos bentónicos nos permiten seguir la extensión bioestratigráfica de las diferentes especies encontradas. Se han establecido las siguientes cuatro biozonas: biozona con Lingulina. gr. tenera y Marginulina gr. prima; biozona con Lenticulina obonensis mg Planularia; biozona con Lenticulina pennensis mg Marginulinopsis, Ichtyolaria hauffi, Dentalina utriculata, Citharina longuemari var. angusta-gradata y espectro de Lenticulina chicheryi; y biozona con Lenticulina d’orbignyi mg Lenticulina, Astacolus y Planularia, Nodosaria pulchra y Lenticulina ferruginea mg Falsopalmul

Foraminiferal assemblages as palaeoenvironmental bioindicators in Late Jurassic epicontinental platforms: relation with trophic conditions

Foraminiferal assemblages from the neritic environment reveal the palaeoecological impact of nutrient types in relation to shore distance and sedimentary setting. Comparatively proximal siliciclastic settings from the Boreal Domain (Brora section, Eastern Scotland) were dominated by inner−shelf primary production in the water column or in sea bottom, while in relatively seawards mixed carbonate−siliciclastic settings from the Western Tethys (Prebetic, Southern Spain), nutrients mainly derived from the inner−shelf source. In both settings, benthic foraminiferal assemblages increased in diversity and proportion of epifauna from eutrophic to oligotrophic conditions. The proximal setting example (Brora Brick Clay Mb.) corresponds to Callovian offshore shelf deposits with a high primary productivity, bottom accumulation of organic matter, and a reduced sedimentation rate for siliciclastics. Eutrophic conditions favoured some infaunal foraminifera. Lately, inner shelf to shoreface transition areas (Fascally Siltstone Mb.), show higher sedimentation rates and turbidity, reducing euphotic−zone range depths and primary production, and then deposits with a lower organic matter content (high−mesotrophic conditions). This determined less agglutinated infaunal foraminifera content and increasing calcitic and aragonitic epifauna, and calcitic opportunists (i.e., Lenticulina). The comparatively distal setting of the Oxfordian example (Prebetic) corresponds to: (i) outer−shelf areas with lower nutrient input (relative oligotrophy) and organic matter accumulation on comparatively firmer substrates (lumpy lithofacies group) showing dominance of calcitic epifaunal foraminifera, and (ii) mid−shelf areas with a higher sedimentation rate and nutrient influx (low−mesotrophic conditions) favouring potentially deep infaunal foraminifers in comparatively unconsolidated and nutrient−rich substrates controlled by instable redox boundary (marl−limestone rhythmite lithofacies).This research was carried out with the financial support of projects CGL2005−06636−C0201 and CGL2005−01316/BTE, and University of Oslo, Norway−Statoil cooperation. M.R. holds a Juan de la Cierva grant from the Ministry of Science and Technology of Spain