Foraminiferal assemblages from the bajocian global stratotype section and point (GSSP) at Cape Mondego (Portugal)

A detailed study of the benthic foraminiferal assemblages at the Bajocian Global Stratotype Section and Point (GSSP— Murtinheira section, Lusitanian Basin, western Portugal) presented herein increases the correlation potential of this relevant global geological time reference. The recorded assemblages are relatively abundant and diverse, and are composed of wellpreserved taxa typical of the Boreal Realm. The most abundant suborders are Lagenina and Spirillinina. Representatives of the Suborder Textulariina are also abundant in some assemblages, while those of the suborders Robertinina and Rotaliina are scarce. Lenticulina specimens are the most abundant in all assemblages, but at the specific level, there are differences between Aalenian and Bajocian assemblages, with Lenticulina muensteri being most abundant in the former and Spirillina orbicula in the latter. Two biozones, based on calcareous foraminifers, have been established and calibrated to the standard ammonite zonation: 1) the Lenticulina quenstedti Zone, ranging from the upper part of the Gigantea Subzone, Bradfordensis Biozone, upper Aalenian, to the lower part of the Discites Biozone, lower Bajocian, and 2) the Ramulina spandeli Zone, beginning at the top of the preceeding zone and having an undefined upper boundary. In addition, 11 bioevents are defined on first occurrences, last occurrences, changes in abundances of some taxa, or changes in assemblage diversity. After a severe impoverishment at the Aalenian–Bajocian transition, an important foraminiferal turnover takes place in the early Bajocian, where some Lower Jurassic and Aalenian forms are replaced by typical Middle Jurassic tax

Seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the Toarcian (Early Jurassic) in Central and Northern Spain. Comparison with other European sections

The Early Toarcian mass extinction marks one of the critical events in the history of the Earth. Many of these events have been linked to important climate changes. Two sections of the Toarcian showing high-resolution ammonite-based biostratigraphy are studied in Central and Northern Spain. Stable isotope datasets, based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates, allowed the construction of δ13C curves and a δ18O-based palaeotemperature. Comparison of the extinction pattern with other sections in Europe and northern Africa shows that the Early Toarcian mass extinction boundary occurred at the Tenuicostatum–Serpentinum transition, and that the organic-rich facies linked to the Oceanic Anoxic Event and the associated negative δ13C excursion are diachronous. From a latest Pliensbachian cooling interval, a first increment of seawater temperature averaging about 4.5 °C, started around the Pliensbachian–Toarcian boundary and developed during the earliest Toarcian Tenuicostatum Biochron, marking the beginning of the main extinction interval. From the Tenuicostatum–Serpentinum transition up to the Bifrons Biochron, a rise in seawater temperature averaging 5.7 °C to 7.8 °C was recorded. This warming interval, which started rapidly and which seems to be synchronous at least in Western Europe, is considered one of the main factors responsible for mass extinction. For some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere, but it does not seem to be recorded in belemnite calcite, and the origin of these possible gases is largely debated in the literature. Additional isotope excursions were found in the studied sections in Spain during the Middle and Late Toarcian. A negative δ13Cbel excursion has been recorded at the latest Bifrons Biochron. Above this shift, the Illustris–Vitiosa subzones thermal peak, which represents a 2–3 °C ΔT, could be linked to one of the tectonomagmatic activity peaks recorded in the Karoo Basin. A renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in NW Europe and Western Tethys. An interesting thermal peak has also been detected in belemnites of the Insigne Subzone. ΔT is in the order of 3 °C, and in both sections the thermal peak is included into a δ13Cbel negative excursion of about −1.5‰. Relative synchrony with the new age for the Karoo main magmatic activity (178–180 Ma) indicates that the δ13C negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases. At this short interval, noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of NW Europe and Tethys are observed. The uppermost Levesquei Subzone thermal peak has only been recognized in the deposits of the section located in Central Spain and coincides with a positive δ13C excursion

Ostracods from the global stratotype section for de base of the Aalenian stage, Jurassic, at Fuentelsaz section (Cordillera Ibérica, Spain)

The Toarcian/Aalenian Global Stratotype Section and Point (GSSP) have been recently placed in the Fuentelsaz section, northeastern Spain. This paper is part of a long-term project that attempts to describe for the first time the fossil ostracod assemblages present in the Toarcian-Aalenian boundary GSSP, and to assess their palaeobiogeographical significance. The study of the Late Toarcian-Early Aalenian Turmiel and Casinos formations at the Fuentelsaz section has produced a detailed stratigraphy and a large collection of stratigraphically constrained ostracod faunas. Twenty benthic ostracod species have been identified and for the first time described in Spain. Higher part of the Mactra Subzone, Late Toarcian, have yielded abundant ostracod faunas, including mostly species of the genera Praeschuleridea, Cytherelloidea and Kinkelinella; fossiliferous marls of the Late Toarcian and part of the Early Aalenian and poorly fossiliferous marls at the beginning of the Opalinum Zone are dominated by Praeschuleridea and Cytherelloidea. The boundary between the Toarcian and Aalenian is not characterized by any radical change in the ostracod faunal composition. The Fuentelsaz sequence exhibits ostracod assemblages comparable to those recorded in western Europe, with many of their species having similar stratigraphical distributions

El mar subtropical del Jurásico en Guadalajara

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Educación y Ciencia. Españapu

Abrupt diatom responses to recent climate and land use changes in the Cantabrian Mountains (NW Spain)

The multi-proxy study of sediment cores from Lake Isoba (43° 02′ N, 5° 18′ W; 1400 m a.s.l.) allows a detailed assessment of the past hydrological and environmental dynamics in north-western Iberia resulting from the interplay between climate variability and anthropogenic impact. The combination of diatom stratigraphy, sedimentology and high-resolution elemental geochemistry along with a robust chronological framework (established by 210Pb, 137Cs and 14C dating) provides a detailed environmental reconstruction for the past ~ 500 years. Abrupt changes in the fossil diatom assemblages indicate a high sensitivity of this small lake to past environmental change and allow identifying four major stages related to the main climate fluctuations of the Little Ice Age (LIA) and recent warming. High lake levels, enhanced runoff and higher productivity characterised the middle phase of the LIA (~ 1550 to 1630 CE), indicating an overall wet climate. Conversely, shallow lake levels, decreased runoff and relatively low productivity prevailed during the last phase of the LIA and the onset of the Industrial Era (~ 1630 to 1925 CE), likely due to colder and drier conditions. High lake levels and higher carbonate input occurred after ~ 1925 CE until the 1980s CE, when our data show an abrupt drop in lake levels probably caused by a regional negative rainfall anomaly related to climate warming during the past decades. Finally, since ~ 1997 CE a remarkable and abrupt increase in the lake nutrient load and turbidity is detected, probably associated with the replacement of transhumant sheep flocks with staying cattle. The main environmental changes reconstructed at Lake Isoba mostly agree with other palaeoclimatic records from northern Spain. However, the hydrological patterns reconstructed are opposed to those observed on the northern slopes of the Cantabrian Mountains. The recent and strong impact of land-use changes on the lake, causing more ecological disruptions than previous climate changes, is noteworthy and demonstrates the high sensitivity of mountain lakes to human activities in a global change context

Stratigraphic and structural interpretation of the San Pedro Basin (south-eastern Dominican Republic offshore margin)

La cuenca de San Pedro (CSP) se define como una depresión batimétrica con tendencia E-O y una extensión aproximada de 6000 km2, situada en el margen sureste de la isla de La Española (República Dominicana y Haití). Estructuralmente se ubica en la parte trasera del Cinturón Deformado de los Muertos (CDM). Considerada tradicionalmente como una cuenca de edad Mioceno medio, cuyo relleno ha sido depositado en el espacio de configuración generado por la progresiva deformación del CDM. Sin embargo, gracias a la integración de los trabajos de cartografía geológica (Proyectos SYSMIN I y II) con datos de geofísica de subsuelo (sísmica de reflexión, registros de pozo y campos potenciales), ha sido posible proponer un nuevo modelo evolutivo de la cuenca que abarca desde el inicio de la sedimentación en un contexto de retro-arco desde el Cretácico Superior hasta la inversión de la cuenca en el Eoceno medio y la posterior evolución del conjunto CSP-CDM hasta la actualidad, pudiendo correlacionar las principales secuencias estratigráficas y estructuras con los datos de afloramiento y pozo.The San Pedro Basin (SPB) consists of an E-W bathymetric depression with an extension of 6000 km2, located in the south-eastern margin of Hispaniola Island (Dominican Republic and Haiti). Structurally, the SPB is situated at the rear zone of the Muertos Thrust Belt (MTB). The basin has been dated as middle Miocene in the bibliography, with the infill deposited in the configuration space generated by the progressive deformation of the MTB. Nevertheless, the integration of the new systematic geological mapping (SYSMIN I&II Programs) with geophysical data (reflection seismic, well logs and potential fields) led us to propose a new evolution model of the basin from the start of sedimentation in Upper Cretaceous in a retro-arc context to the inversion of the basin in middle Eocene and the later evolution of the SPB-MTB system until present, establishing the correlation between main sequences with outcrops and well data.Depto. de Geodinámica, Estratigrafía y PaleontologíaDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

GEODIVULGAR: Geología y Sociedad

Fac. de Ciencias GeológicasFALSEsubmitte

Geodivulgar: Geología y Sociedad 2018

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. 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