On the microstructure, growth pattern and original porosity of belemnite rostra: insights from calcitic Jurassic belemnites

[EN] Calcitic belemnite rostra are usually employed to perform paleoenvironmental studies based on geochemical data. However, several questions, such as their original porosity and microstructure, remain open, despite they are essential to make accurate interpretations based on geochemical analyses. This paper revisits and enlightens some of these questions. Petrographic data demonstrate that calcite crystals of the rostrum solidum of belemnites grow from spherulites that successively develop along the apical line, resulting in a “regular spherulithic prismatic” microstructure. Radially arranged calcite crystals emerge and diverge from the spherulites: towards the apex, crystals grow until a new spherulite is formed; towards the external walls of the rostrum, the crystals become progressively bigger and prismatic. Adjacent crystals slightly vary in their c-axis orientation, resulting in undulose extinction. Concentric growth layering develops at different scales and is superimposed and traversed by a radial pattern, which results in the micro-fibrous texture that is observed in the calcite crystals in the rostra. Petrographic data demonstrate that single calcite crystals in the rostra have a composite nature, which strongly suggests that the belemnite rostra were originally porous. Single crystals consistently comprise two distinct zones or sectors in optical continuity: 1) the inner zone is fluorescent, has relatively low optical relief under transmitted light (TL) microscopy, a dark-grey color under backscatter electron microscopy (BSEM), a commonly triangular shape, a “patchy” appearance and relatively high Mg and Na contents; 2) the outer sector is non-fluorescent, has relatively high optical relief under TL, a light-grey color under BSEM and low Mg and Na contents. The inner and fluorescent sectors are interpreted to have formed first as a product of biologically controlled mineralization during belemnite skeletal growth and the non-fluorescent outer sectors as overgrowths of the former, filling the intra- and inter-crystalline porosity. This question has important implications for making paleoenvironmental and/or paleoclimatic interpretations based on geochemical analyses of belemnite rostra. Finally, the petrographic features of composite calcite crystals in the rostra also suggest the non-classical crystallization of belemnite rostra, as previously suggested by other authors.[ES] Los análisis geoquímicos obtenidos en rostros de los belemnites se utilizan habitualmente para llevar a cabo estudios paleoambientales. Sin embargo, hay cuestiones esenciales, como la porosidad y la microestructura original de los belemnites, que están todavía en discusión y que hay que tener en cuenta si se quieren realizar interpretaciones geoquímicas adecuadas. Los datos petrográficos obtenidos en este trabajo demuestran que los cristales de calcita del rostrum solidum de los belemnites crecen a partir de esferulitos que sucesivamente se desarrollan a lo largo de la línea apical, dando lugar a una microestructura “esferulítica prismática regular”. Los cristales de calcita surgen y divergen radialmente desde los esferulitos: hacia el apex, hasta que se forma un nuevo esferulito y hacia los bordes externos del rostro donde los cristales se van haciendo progresivamente mayores y prismáticos. La ligera variación de la orientación del eje-c de los cristales adyacentes explica la extinción ondulante. Al patrón radial, que da lugar a la textura micro-fibrosa de southlos cristales de calcita del rostro, se le superpone un bandeado de crecimiento concéntrico. Los datos petrográficos también indican que los rostros de los belemnites eran originalmente porosos como lo demuestra la naturaleza compuesta de los cristales de calcita que están formados sistemáticamente por dos zonas distintas que están en continuidad óptica: 1) la zona interna es fluorescente, tiene relieve óptico bajo, en microscopia de luz transmitida (TL), color gris oscuro en microscopia electrónica con electrones retrodispersados (BSEM), morfología triangular y contenidos en Mg y Na relativamente altos; 2) la zona exterior no es fluorescente, tiene relieve óptico alto (TL), color gris claro (BSEM), y contenidos en Mg y Na relativamente bajos. La zona fluorescente interior se formó primero, durante el crecimiento de los belemnites y la zona no fluorescente precipitó como un cemento rellenando la porosidad intra- e intercristalina. Las características petrográficas de los cristales de calcita también sugieren que la cristalización no clásica del esqueleto de los belemnites, como han sugerido algunos autores previamente.This research was carried out with the financial support of the projects CGL2011-22709, CGL2014-52670-P and RYC- 2009-04316 (Ramón y Cajal Program, Ministerio de Ciencia e Innovación), and by the “Sedimentary Basin Analysis” and “Paleoclimatology and Global Change” research groups of the Complutense University of Madrid.Peer reviewe

Comparación entre foraminíferos bentónicos e indicadores geoquímicos en depósitos de plataforma del Jurásico superior del Prebético (Sur de España)

Comparison of the stratigraphic distribution of major and trace elements, used as proxies for palaeoproductivity and redox conditions, and benthic foraminifera from Oxfordian shelf deposits of the External Prebetic (Betic Cordillera, South Spain) allows us to recognise two sedimentary cycles, both characterised by initial enhanced productivity and decreasing oxygen availability in the seabottom, and a subsequent decreasing productivity with a recovering in oxygenation during the second half of each cycle. Dysoxic conditions appear to coincide with maximums in marine surface productivity, thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation. The boundary between the two cycles is characterised by low contents of redox-sensitive elements and lower TOC content and Sr/Al, P/Ti, Ca/Al and Ba/Al ratios, indicating well oxygenated sea-bottom, lower productivity and lower organic matter accumulation. The geochemical proxies have also revealed as a valuable tool for interpreting the stratigraphic fluctuations of benthic foraminiferal assemblages, as well as for evaluating the palaeoecology of the main genera. Spirillina is adversely influenced by oxygen depletion independently of food availability. Ophthalmidium presents very good correspondence with palaeoproductivity fluctuations, and tolerated low oxygen levels in the sediment-water interface. Reophax was an opportunist that proliferated after adverse conditions when oxygenation and food availability were limiting factors. The variability in the microhabitat depth inside the sediment of Reophax favoured adaptation to adverse conditions. Lenticulina shows behaviour similar to Reophax. Finally, Ammobaculites shows a low degree of relation with the palaeoproductivity proxies, and is intolerant with respect to low oxygen values in shallow infaunal microhabitatsLa comparación de la distribución estratigráfica de indicadores geoquímicos de paleoproductividad y condiciones redox junto con foraminíferos bentónicos en los depósitos de plataforma del Oxfordiense (Jurásico superior) del Prebético Externo (Cordillera Bética, SE España) permite reconocer dos ciclos caracterizados por un incremento inicial de la productividad y una disminución de la oxigenación en el fondo y una posterior disminución en productividad y aumento de la oxigenación. Las condiciones disóxicas coinciden con máximos en la productividad marina superficial sugiriendo que la disminución de la oxigenación pudo estar relacionada con un mayor consumo relacionado con la oxidación de la materia orgánica más que por una circulación restringida. El límite entre ambos ciclos se caracteriza por valores bajos de elementos indicadores de condiciones reductoras, carbono orgánico total y las relaciones Sr/Al, P/Ti, Ca/Al y Ba/Al, indicando buena oxigenación del fondo marino, baja productividad y baja acumulación de materia orgánica. Los indicadores geoquímicos han mostrado ser una valiosa herramienta para interpretar fluctuaciones estratigráficas en las asociaciones de foraminíferos bentónicos, así como para evaluar la paleoecología de los principales géneros de foraminíferos. Spirillina es sensible a las disminuciones en el grado de oxigenación independientemente de la disponibilidad de alimento. Ophthalmidium presenta muy buena correspondencia con las fluctuaciones en paleoproductividad y toleró bajos niveles de oxigenación en la interfase agua-sedimento. Reophax fue un organismo oportunista que proliferó bajo condiciones adversas cuando la oxigenación o el alimento fueron factores limitantes. La variabilidad en la profundidad del microhabitat dentro del sedimento de Reophax favoreció su adaptación a condiciones adversas. Lenticulina muestra un comportamiento similar a Reophax. Finalmente, Ammobaculites muestra una escasa relación con las variaciones de los indicadores de paleoproductividad, pero se muestra intolerante con respecto a valores bajos de oxigenación en los microhábitats infaunales someros

Registro de Carcharocles megalodon en el sector oriental de la Cuenca del Guadalquivir (Mioceno superior, Sur de España)

Tortonian diatomites of the San Felix Quarry (Porcuna), in the Eastern Guadalquivir Basin, have given isolated marine vertebrate remains that include a large shark tooth (123.96 mm from apex to the baseline of the root). The large size of the crown height (92.2 mm), the triangular shape, the broad serrated crown, the convex lingual face and flat labial face, and the robust, thick angled root determine that this specimen corresponds to Carcharocles megalodon. The symmetry with low slant shows it to be an upper anterior tooth. The total length estimated from the tooth crown height is calculated by means of different methods, and comparison is made with Carcharodon carcharias. The final inferred total length of around 11 m classifies this specimen in the upper size range of the known C. megalodon specimens. The palaeogeography of the Guadalquivir Basin close to the North Betic Strait, which connected the Atlantic Ocean to the Mediterranean Sea, favoured the interaction of the cold nutrient-rich Atlantic waters with warmer Mediterranean waters. The presence of diatomites indicates potential upwelling currents in this context, as well as high productivity favouring the presence of large vertebrates such as mysticetid whales, pinnipeds and small sharks (Isurus). These large vertebrates recorded in the Eastern Guadalquivir Basin were potential prey of C. megalodon.Las diatomitas tortonienses de la antigua Cantera de San Félix (Porcuna, Jaén), en el sector oriental de la Cuenca del Guadalquivir, han proporcionado restos aislados de vertebrados marinos entre los que destaca un gran diente de tiburón (123.96 mm desde el ápice hasta la línea basal de la raiz). La altura de la corona (92.2 mm), su forma triangular con bordes aserrados, la presencia de una cara lingual convexa y una labial plana, conjuntamente con la raíz angulosa y robusta, permiten determinar que este diente perteneció a un ejemplar de Carcharocles megalodon. La alta simetría de la pieza, su tamaño y su relación longitud/anchura de la corona permiten afrimar que se trata de un diente superior anterior. La longitud total estimada para este tiburón, es calculada a partir de diferentes métodos basados principalmente en la comparación con el tiburón blanco Carcharodon carcharias. La longitud total inferida finalmente para este ejemplar ronda los 11 m, lo que permite incluir este ejemplar dentro del rango de los ejemplares de C. megalodon de gran tamaño. La paleogeografía de la Cuenca del Guadalquivir próxima al Estrecho Nordbético que conectaba el Océano Atlántico con el Mar Mediterráneo, favoreció la interacción de aguas atlánticas frías y ricas en nutrientes con las aguas más cálidas del Mediterráneo. La presencia de diatomitas indica la actividad potencial de corrientes de upwelling en este contexto, así como la alta productividad que suele favorecer a grandes cetáceos y pinnípedos. Estos mamíferos marinos, registrados en el sector oriental d la Cuenca del Guadalquivir fueron potenciales presas de pequeños tiburones como Isurus el gran C. megalodon

The abrupt onset of the modern South Asian Monsoon winds

The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system

Palaeoenvironmental turnover across the Cenomanian-Turonian transition in Oued Bahloul, Tunisia: Foraminifera and geochemical proxies

The integrated analysis of foraminiferal assemblages, geochemical proxies, and stable isotopes in the Oued Bahloul section (Tunisia) allowed us to reconstruct the environmental turnover across the Cenomanian–Turonian boundary. An increase in palaeoproductivity proxies (P/Ti, U/Al, Sr/Al) and in d13C values, and a decrease in foraminiferal diversity and d18O values mark the beginning of the Oceanic Anoxic Event 2 (OAE2) at the Rotalipora cushmani and Whiteinella archaeocretacea biozones boundary. Eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist Rotalipora by eutrophic opportunist Hedbergella. The enrichment in organic matter and redox sensitive elements, together with the abundance of low-oxygen tolerant benthic foraminifera, indicate dysoxic conditions in the deep-water column and at the seafloor (higher Uaut than Moaut). Among planktic foraminifera, deep- and intermediate-dwellers disappear (Rotalipora and Globigerinelloides), and surface-dwellers proliferate (Hedbergella). The persistency of the poorly oxygenated conditions during the W. archaeocretacea Biozone locally produced euxinic conditions where MoEF and Moaut reach high values, diversity presents minimum values, and benthic foraminifera temporarily disappear. The maximum percentage of heterohelicids indicates a stratified water column with a well-developed oxygen minimum zone. Improved oxygen conditions returned in the upper part of the W. archaeocretacea Biozone and Helvetoglobotruncana helvetica Biozone, with a slow recovery of foraminiferal assemblages, decrease in eutrophic genera (Heterohelix) and increase in mesotrophic genera (Whiteinella). A gradual increase in d18O values suggests decreased temperatures in surface waters. The OAE2 has been attributed to global temperature changes and palaeoceanographic reorganization. The poor mixing of surface and deep waters and enhanced primary productivity related to global warming – associated with increasing continental weathering and nutrient runoff – may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

Lower/Middle Ordovician (Arenigian) shallow-marine trace fossils of the Pochico Formation, southern Spain: palaeoenvironmental and palaeogeographic implications at the Gondwanan and peri-Gondwanan realm

Nineteen ichnospecies belonging to thirteen ichnogenera (Archaeonassa, Catenichnus, Cochlichnus, Cruziana, Didymaulichnus, ?Diplichnites, Gordia, Lingulichnus, Lockeia, cf. Monocraterion, Planolites, Ptychoplasma, and Rusophycus) occur in the Pochico Formation (Arenigian) in the Aldeaquemada section, Sierra Morena, southern Spain, just above the Armorican Quartzite. They belong to the archetypal Cruziana ichnofacies, indicating a lower shoreface-upper offshore zone. The low degree of sediment reworking may be due to a high rate of sedimentation. The trace fossil assemblage, rich in large Cruziana, is typical of the Armorican Quartzite that developed on the margins of Gondwana and peri-Gondwanan microcontinents. The distribution of ichnofauna during the Early Ordovician was partly palaeogeographically controlled, although ichnological data from the literature point to paths of migration between Gondwana, Baltica and Laurentia. Differences between the ichnofauna of Gondwana and Baltica could be conditioned by facies (clastics in Gondwana and carbonates in Baltica) causing a taphonomic filter, because Cruziana requires diversified clastic deposits for preservation. The ichnofauna would also be influenced by trophic group amensalism between filter feeding and deposit feeding fauna, the former prevailing in Baltica and the latter in Gondwana.Se presenta el análisis sedimentológico/icnológico de los materiales de la Formación Pochico (Arenigian) de la sección de Aldeaquemada, Sierra Morena, Sur de España, provincia de Jaén, justo por encima la Cuarcita Armoricana. Se han reconocido diecinueve icnoespecies pertenecientes a trece icnogéneros (Archaeonassa, Catenichnus, Cochlichnus, Cruziana, Didymaulichnus, ?Diplichnites, Gordia, Lingulichnus, Lockeia, cf. Monocraterion, Planolites, Ptychoplasma, y Rusophycus). Las características icnológicas junto con los rasgos sedimentológicos permiten asignarlas a las icnofacies arquetípicas de Cruziana, comunes de las zonas de shoreface inferior a offshore superior. El grado de bioturbación relativamente bajo puede estar relacionado con una alta tasa de depósito. La asociación registrada, dominada por grandes Cruziana, es típica de la Cuarcita Armoricana desarrollada en los márgenes de Gondwana y peri-Gondwana. La distribucción de icnofósiles del Ordovícico temprano posee, en gran medida, un control paleogeográfico, aunque datos icnológicos procedentes de la literatura indican la existencia de migraciones entre Gondwana, Baltica y Laurentia. Las diferencias entre las asociaciones de Gondwana y Báltica pueden estar asociadas a las diferentes facies, con el dominio de materiales clásticos en Gondwana y de carbonatados en Báltica, causando un filtro tafonómico ya que el potencial de conservación de Cruziana es mucho mayor en las facies clásticas heterolíticas. A estos factores habría que añadir las estrategias de alimentación asociadas, diferenciando entre filtradores y aquellos que se alimentan de las partículas existentes en el sedimento, los primeros podrían verse favorecidos en Báltica y los segundos en Gondwana.Research by R.-T. was supported by Projects CGL2008-03007, and CGL2012-33281 (Secretaría de Estado de I+D+I, Spain), Project RNM-3715 and Research Group RNM-178 (Junta de Andalucía)

Agglutination of benthic foraminifera in relation to mesoscale bathymetric features in the abyssal NE Atlantic (Porcupine Abyssal Plain)

Abyssal hills, small topographic features rising above the abyssal seafloor (< 1000 m altitude), have distinct environmental characteristics compared to abyssal plains, notably the presence of coarser-grained sediments. As a result, they are a major source of habitat heterogeneity in the deep sea. The aim of this study was to investigate whether there is a link between abyssal hills and the test characteristics of selected agglutinated benthic foraminiferal species. We analysed 1) the overall morphometry, and 2) the granulometric and chemical (elemental) characteristics of the agglutinated tests of ten common foraminiferal species (Adercotryma glomerata, Ammobaculites agglutinans, Cribrostomoides subglobosus, Lagenammina sp.1, Nodulina dentaliniformis, Portatrochammina murrayi, three Reophax sp. and Recurvoides sp. 9) at four sites (two on top of abyssal hills and two on the adjacent plain) in the area of the Porcupine Abyssal Plain Sustained Observatory, northeast Atlantic. The foraminiferal test data were compared with the particle size distribution and elemental composition of sediments from the study sites in order to explore possible grain size and mineral selectivity. We found differences in the visual appearance of the tests (i.e. the degree of irregularity in their shape), which was confirmed by morphometric analyses, related to seafloor topography. The agglutinated foraminifera selected different sized particles on hills and plains, reflecting the distinct granulometric characteristics of these settings. These characteristics (incorporation of coarse particles, test morphometry) could provide evidence for the recognition of ancient abyssal hill environments, as well as other palaeoceanographic settings that were characterised by enhanced current flow. Furthermore, analyses of sediment samples from the hill and plain sites using wavelength dispersive X-ray fluorescence (WD-XRF) yielded different elemental profiles from the plains, probably a result of winnowing on the hills, although all samples were carbonate-rich. In contrast, the majority of the agglutinated tests were rich in silica, suggesting a preferential selection for quartz

A new type of Halimeda bioherm on the Queensland Plateau, NE Australia

Morphology, internal structure, and in situ facies distribution of mesophotic Halimeda bioherms from the Queensland Plateau (NE Australia) are presented based on hydroacoustic and oceanographic data, seafloor observations, and discrete sediment sampling carried out during RV SONNE cruise SO292 in 2022. Halimeda buildups consist of cone-like mounds up to 500 m in diameter and 3–10 m high, with gentle slopes (2°–5° on the top of Tregrosse Bank). Bioherms occur in water depths of 10–70 m, with most bioherm between 50 and 65 m. Their internal structure consists of aggrading low-amplitude reflections at the core of the bioherm interfingering with high-amplitude reflections to the flanks. Surface facies distribution displays one to four facies belts, from distal to proximal: Halimeda rudstone, Halimeda rudstone with living plants, Halimeda rudstone with coralgal debris, and coralgal boundstone (when present, occupied the top of the bioherms). It is proposed that the alternation of two key processes contributes to the formation of these bioherms: (1) in situ accumulation of Halimeda debris and (2) episodic dismantling of the mesophotic coralgal boundstone at the centre of the bioherm by severe storms. These storms may dismantle the mesophotic reef and export coralgal rubble to the flanks. Flanks may be recolonized by Halimeda during fair-weather periods. Due to their different geomorphic expressions, complex internal structure, and surficial facies distribution, we suggest that the buildups of the Queensland Plateau represent a new Halimeda bioherm morphotype, distinct from previously described bioherms on the adjacent Great Barrier Reef and elsewhere globally.03G0292A—ICECARB from the Bundesministerium für Bildung und Forschung (Germany) to CBSpanish Ministry of Science and Innovation (MCIN) through the Ramón y Cajal Project RYC2021-034362-I (MCIN/ AEI/https:// doi. org/ 10. 13039/ 50110 00110 33 and NextGenerationEU/ PRTR)Parks Australia for the research permit for Cruise SO292 (permit EPBC 2022/9168)The Schmidt Ocean Institute is thanked for the RV Falkor multibeam data acquired during cruises FK200429 and FK200802

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