The calcareous nannofossil crisis in Northern Spain (Asturias province) linked to the Early Toarcian warming-driven mass extinction

Quantitative analysis of Late Pliensbachian–Early Toarcian calcareous nannofossil assemblages from the West Rodiles section (Asturias, Northern Spain) has been performed in order to interpret the paleoenvironmental changes that occurred during this time interval, characterized by a major extinction event, and especially around the Lower Toarcian Tenuicostatum/Serpentinum zonal and extinction boundary. Nannofossil data were statisti- cally treated: the Shannon diversity index was calculated, and results were compared to the stable isotope data and the total organic carbon content. To determine the changes recorded in the entire nannofossil communities, a principal component analysis was applied. During the latest Pliensbachian, the nannofossil assemblages were dominated by Schizosphaerella sp. and Tubirhabdus patulus, followed by the dominance of Calcivascularis jansae, taxa that probably thrived in rather cold waters. The progressive decrease in the relative abundances of both Schizosphaerella sp. and C. jansae coincides with a progressive increase in paleotemperatures during the extinc- tion interval, as indicated by the δ18O values measured on diagenetically screened belemnite calcite. Biscutum spp. dominated the nannofossil assemblages during the Early Toarcian Tenuicostatum Ammonite Zone, when seawaters were warm. In the West Rodiles section, the extinction boundary coincides with the deposition of the laminated shales, where especially high relative abundances of Calyculus spp. were recorded. After the extinction boundary, C. jansae becomes extinct, the relative abundance of Biscutum spp. sharply decreases, and the nannofossil assemblages become dominated by the Crepidolithus and Lotharingius species, which have been interpreted as opportunistic taxa. The Shannon Index fluctuates throughout the studied section, although it is especially high after the extinction boundary. The covariance between the nannofossil crisis and the evolu- tion of δ18Obel-based seawater paleotemperatures, as well as the fact that none of the explanations proposed by other authors seems to explain our observations, suggest a clear relationship between the increase in paleotemperature and the changes recorded in our nannofossil assemblages. Nevertheless, we do not discard possible changes in other paleoenvironmental parameters related or not to warmin

La influencia de la temperatura en los cambios de abundancia de los nanofósiles calcáreos del Plienbachiense de E Rodiles (Asturias)

En los últimos años, los estudios sobre la paleoecología de los nanofósiles se han centrado en materiales pertenecientes al Toarciense inferior, caracterizado por una calentamiento global y anoxia en algunas cuencas del Centro y Norte de Europa (Mattioli et al., 2008; Fraguas et al., 2012; Casellato et al., 2015; Clémence et al., 2015). Sin embargo, los trabajos sobre la paleoecología de los nanofósiles del Pliensbachiense son escasos, destacando el de Reggiani et al. (2010) en la Cuenca Lusitánica. Recientemente, Gómez et al. (2016) describieron una serie de cambios paleoclimáticos registrados en Asturias durante el Pliensbachiense, que pudieron afectar al nanoplancton. El objetivo principal de este trabajo es arrojar luz sobre esta hipótesis, realizando un análisis cuantitativo sobre los nanofósiles calcáreos del Pliensbachiense de la sección de Este (E) Rodiles, que durante el intervalo temporal estudiado estaba situada en la zona de conexión entre el Dominio Boreal y el Tethys

Geodivulgar: Geología y Sociedad 2018

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasFALSEsubmitte

GEODIVULGAR: Geología y Sociedad

Fac. de Ciencias GeológicasFALSEsubmitte

Geodivulgar: Geología y Sociedad

Con el lema “Geología para todos” el proyecto Geodivulgar: Geología y Sociedad apuesta por la divulgación de la Geología a todo tipo de público, incidiendo en la importancia de realizar simultáneamente una acción de integración social entre estudiantes y profesores de centros universitarios, de enseñanza infantil, primaria, de educación especial y un acercamiento con público con diversidad funcional

Los nanofósiles calcáreos del Pliensbachiense de la sección de Tudanca (Cuenca Vasco-Cantábrica, España)

Se estudian los nanofósiles calcáreos identificados en materiales del Pliensbachiense de la sección de Tudanca (Cuenca Vasco-Cantábrica, España). Se han reconocido doscientos catorce niveles estratigráficos constituidos, fundamentalmente, por una alternancia de margas y calizas, de los que se han tomado un total de sesenta y cinco muestras. Se ha realizado un análisis semicuantitativo sobre las smear slides preparadas observándose, en la mayoría de ellas, un estado de preservación de malo a moderado y una abundancia total de nanofósiles calcareos de rara a frecuente. Se han identificado dos divisiones, dos clases, cinco órdenes, siete familias, una subfamilia, trece géneros y veintiséis especies. Los datos obtenidos han permitido establecer una bioestratigrafía de detalle con nanofósiles calcáreos, calibrada con las zonas de ammonites y marcar con precisión la primera y la última aparición de las especies más abundantes e índices de zona. Se han identificado las zonas de nanofósiles calcáreos, NJ4 Similiscutum cruciulus y NJ5 Lotharingius hauffii completas, así como la parte superior de la Zona NJ3 Crepidolithus crassus. Se han reconocido algunos cambios significativos en la composición de las asociaciones de nanofósiles. El primero de ellos, la aparición del género Similiscutum en la Zona Jamesoni de ammonites. Otro cambio relevante en la composición tiene lugar en el Pliensbachiense Superior, e incluye la primera aparición del género Biscutum, un incremento en la abundancia de C. jansae, la primera aparición del género Lotharingius, y una disminución en la abundancia de los géneros Similiscutum, Crucirhabdus, Crepidolithus y Parhabdolithus. El mayor cambio registrado en las asociaciones de nanofósiles calcáreos durante la Zona Spinatum es el fuerte aumento en la abundancia de L. hauffii. Los eventos principales en la sección de Tudanca son: 1. FO de S. cruciulus; 2. FO de L. hauffii. Los eventos secundarios son: 1. FO de B. novum; 2. FO de B. finchii; 3. FO de B. grandis; 4. FO de L. barozii; 5. FCO de C. jansae; 6. FCO de L. hauffii

Pliensbachian calcareous nannofossils of the Santotis section (Basque-Cantabrian Basin, N Spain).

The target of this paper is to study the succession of the Pliensbachian calcareous nannofossil assemblages recovered from the Santotis section (Northern Spain) in order to calibrate the biohorizons against the ammonite zones. In this section, one hundred nineteen marly and carbonate-dominated levels have been recognized and forty-one of them have been sampled. The semiquantitative analysis has been carried out on smear slides and reveals that the majority of the assemblages show a bad to moderate degree of preservation and the species abundance varies from rare to frequent. In the studied section, the most relevant Pliensbachian composition changes of the assemblages are the first appearances of the genera Similiscutum (Jamesoni Zone) and Lotharingius (Stokesi Zone). The assemblages further change due to the appearance of the species belonging to the genus Biscutum. The succession of the assemblages have allowed the identification of two main events, the FOs of Similiscutum cruciulus (Jamesoni Zone) and Lotharingius hauffii (Stokesi Zone) as well as four secondary events, the FOs of Biscutum novum (Davoei Zone), Biscutum grandis (Stokesi Zone), Biscutum finchii (Stokesi Zone) and Lotharingius barozii (Stokesi Zone). Assemblages and biohorizons have allowed the identification of the upper part of the NJ3 Crepidolithus crassus Zone, the complete NJ4 Similiscutum cruciulus Zone and the almost complete NJ5 Lotharingius hauffii Zone

Pliensbachian calcareous nannofossil paleoecology in the E Rodiles section (Asturias, N Spain): A key location connecting the Boreal and Tethyan realms

Here, we present the results of a quantitative analysis performed on Pliensbachian calcareous nannofossil assemblages from the E Rodiles section (northern Spain), which allowed us to determine their changes in response to paleoenvironmental variations in a key connection between the Boreal and Tethyan realms. Nannofossil data are compared to published carbon and oxygen stable isotope data and organic matter content. During the Early Pliensbachian, when seawater temperatures were around the Pliensbachian average value, calcareous nannofossil assemblages were dominated by the nannolith Schizosphaerella punctulata and the ancestral coccoliths Crucirhabdus primulus and Parhabdolithus liasicus. Mitrolithus elegans, Similiscutum avitum, Similiscutum cruciulus and, to a minor extent, Schiszosphaerella show peaks in their abundances coinciding with the deposition of black-shales and, probably, they thrived in periods of enhanced marine primary productivity and under eventually poorly oxygenated and water stratified conditions. A significant change in calcareous nannofossil assemblages is observed in the Late Pliensbachian, with the dominance of Tubirhabdus patulus, the newly emerged species Lotharingius hauffii and a sharp increase in the abundance of Calcivascularis jansae, coinciding with the rise in the δ18Obel values due to a cooling event that led to the increase of taxa with affinities for rather low temperatures. The species of Crepidolithus, interpreted as opportunistic, show fluctuations in their abundances throughout the studied section, although they are more abundant during the Early Pliensbachian warming, together with the species of Similiscutum, and especially coinciding with the δ13Cbel positive peak in organic-poor carbonates, in opposition to Similiscutum spp., which show their abundance peaks in organic-rich layers

GEODIVULGAR: Geología y Sociedad

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasFALSEsubmitte

Geodivulgar: Geología y Sociedad

Depto. de Geodinámica, Estratigrafía y PaleontologíaDepto. de Química InorgánicaDepto. de Didáctica de las Ciencias Experimentales , Sociales y MatemáticasFac. de Ciencias GeológicasFac. de Ciencias QuímicasFac. de EducaciónFALSEsubmitte