Representantes de Helicosphaera en sedimentos del Neógeno en el Atlántico oriental

RESUMEN: El presente trabajo se centra en el estudio de los helicolitos que se reconocen en diferentes secciones de las cuencas del Guadalquivir y Surrifeña (España y Marruecos), así como en sondeos oceánicos del Atlántico Oriental. De dicho morfotipo se lleva a cabo un estudio sistemático; asimismo se muestra otro de carácter cuantitativo con el que se trata de evidenciar su variabilidad en función de cambios ambientales que pudieran haber tenido lugar. Por comparación con la distribución de otros táxones indicadores, se observa que el morfotipo en general —del que es especie dominante Helicosphaera carteri (Wallich)— sufre una reducción con un supuesto descenso de las temperaturas de las masas de agua. El cambio cuantitativo más importante tiene lugar en el Tortoniense superior. Hacia el Messiniense superior parece iniciarse una cierta recuperación, probablemente relacionado con un relativo calentamiento. También se tratan aspectos preservacionales. La relativa fácil disolución de los representantes de Helicosphaera determina que, en base a su ausencia, presencia y estado particular de los nanolitos, puedan emplearse para evaluar el grado de alteración de una asociación en una determinada muestra. Palabras Clave.— Nanoplancton calcáreo, Helicolitos, Sistemática, Paleocología, Conservación, Neógeno, Cuenca del Guadalquivir (España), Cuenca Surrifeña (Marruecos), D.S.D.P., Atlántico

Late miocene calcareous nannofossils and biostratigraphy of the sw tumaco onshore basin (colombian pacific)

Se presenta el estudio bioestratigráfico semicuantitativo de nanofósiles calcáreos para tres secciones estratigráficas del Mioceno superior de la costa Pacífica de Colombia (SW de la Cuenca Tumaco costa adentro). Para establecer la biocronología de las asociaciones de nanofósiles recuperadas se identificaron las biozonas estándar y se compararon los bioeventos reconocidos con las edades obtenidas en otros estudios (e.g. ODP leg 138, ODP Leg 165). Un total de seis bioeventos fueron reconocidos, incluyendo los primeros registros o lower occurrence (LO) de Amaurolithus primus, Reticulofenestra rotaria, Amaurolithus delicatus, Amaurolithus amplificus y Amaurolithus tricorniculatus, y el último registro o highest occurrence (HO) de Reticulofenestra rotaria. Los resultados sugieren que las secciones abarcan un intervalo de tiempo entre el Tortoniense y el Mesiniense, correspondiente a las biozonas NN11a - NN11b de Martini (1971) y CN9a - CN9b de Okada and Bukry (1980).Fil: Bedoya Agudelo, Erika Lorena. Universidad de Caldas; Colombia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Flores, José Abel. Universidad de Salamanca; EspañaFil: Pardo, Andrés. Universidad de Caldas; Colombi

Origin and evolution of the Neogene calcareous nannofossil Ceratolithus

Sediment samples of deep marine oceanic ODP boreholes from sites 999 in the Caribbean Sea and 1237 in the Eastern Pacific Ocean covering the period between 6 and 4.5 Ma have been studied with a focus on ceratolith evolution. Orthorhabdus rugosus is a nannolith with three blades (sinistral, median, and dextral) that first appeared during the Serravallian, it is not-birefringent in its stable orientation. It shows a high morphological variability time-interval at the end of the Messinian to the basal Pliocene (5.5 to 5 Ma) during which Ceratolithus (5.484 Ma) evolved. Changes occurred in the sinistral and median blades, whilst the dextral blade was reduced. Ceratolithus finifer n. comb is the first species of the evolutionary line. The nannolith stable position changed during its evolution, resulting in the older forms showing low birefringence and the younger ones moderate to high birefringence in the most stable orientation. Ceratolithus acutus, with an arrowhead shape, Ceratolithus armatus, and the morphologically distinct C. larrymayeri evolved from C. finifer with all three species showing high birefringence. The previous O. rugosus and C. finifer continued. Finally, C. armatus gives rise to C. cristatus. Ceratolithus atlanticus and C. tricorniculatus also evolved from C. finifer. All the species mentioned become extinct during the Pliocene except Ceratolithus cristatus that lives today. Detailed observations permit the analysis of the evolutionary trends of the group, possible mechanisms, patterns, and processes of speciation, and establish new criteria to define the species that, by their relative abundance and short geologic range, have permitted adjustment of biostratigraphic markers for this period.This work was supported by the projects RTI2018-099489-B-I00 and PID2020-114381GB-I00 (Spanish Ministry of Science, Innovation, and Universities). This study was funded by the European Union NextGenerationEU (PRTR-C17.I1) project GVA-THINKINAZUL/2021/039

Origin and evolutionary trends of the Neogene genera Amaurolithus and Nicklithus (calcareous nannofossils)

Sediment samples from Ocean Drilling Program (ODP) Sites 999 and 1237 in the Caribbean Sea and Eastern Pacific Ocean were studied to monitor the evolution of ceratoliths from 7.4 Ma to 6 Ma. Orthorhabdus rugosus shows high variability at the end of the Tortonian to the Early Messinian (7.35 Ma to 6.91 Ma), resulting in the Amaurolithus (7.354 Ma) and Nicklithus branches (6.985 Ma). Orthorhabdus rugosus is an ortholith with three blades (sinistral, median, and dextral). The first ceratholith, A. primus, has two arms and a horseshoe shape with marked laths, and is stable and concave upwards. Its sinistral arm is formed from the sinistral blade of O. rugosus and the right arm is formed from the other blades. Early robust A. primus evolved into stylised forms and then to A. delicatus (7.226 Ma), an almost plain horseshoe ceratolith with two arms. The left arm, usually the longer one, comes from the sinistral wing of A. primus and has a characteristic flattened omega section (Ω) without laths. There is a distribution overlap between A. primus and A. delicatus; the highest occurrence of the first one, at 6.282 Ma, is a newly proposed bioevent for the Messinian. After this, Amaurolithus does not have laths in its longer left arm and should be included in A. delicatus. The second branch has only one species, Nicklithus amplificus, which became extinct at 6.049 Ma. In addition, the dextral and median blades of O. rugosus form N. amplificus dextral arm and the sinistral arm, which has the characteristic beak, hook, or hawk's bill, which is the main difference between the development of this horseshoe and that of the previous one. The descriptions of A. primus, A. delicatus, and N. amplificus were specified based on the proposed evolutionary genesis.This work was supported by projects RTI2018-099489-B-I00 and PID2020-114381GB-I00 (Spanish Ministry of Science, Innovation and Universities). This study was funded by the European Union NextGenerationEU project GVA-THINKINAZUL/2021/039

Variation in calcification of Reticulofenestra coccoliths over the Oligocene–Early Miocene

Coccolithophores are calcifying marine phytoplankton whose intracellularly produced calcite plates, coccoliths, have been the dominant source of calcium carbonate in open-ocean settings since the Cretaceous. An open question is whether their calcification has been affected by changing environmental conditions over geological timescales such as variations in the ocean carbon system. Previous methods using circular polarized light microscopy allowed for only the thickness of small coccoliths thinner than 1.5 µm to be quantified, but prior to the Pliocene, a significant fraction of the coccoliths exceeded this thickness and have not been quantifiable. Here, we implement a new approach for calibration of circular polarized light microscopy enabling us to quantify coccoliths which feature calcite up to 3 µm thick. We apply this technique to evaluate the evolution of calcification in the Reticulofenestra from the early Oligocene to Early Miocene in exceptionally well-preserved sediments from the Newfoundland margin. Through this time interval, coccolith thickness and the scale-invariant shape factor kse vary by about 20 % around the mean thickness of 0.37 µm and mean kse of 0.16. Lower shape factors characterize samples with a higher relative abundance of dissolution-resistant nannoliths, suggesting that dissolution may contribute to thinning of placoliths. We therefore define temporal trends in calcification only in samples in which the assemblage suggests minimal dissolution. The lowest kse characterizes the middle Oligocene, and the highest kse around 18 Ma is in the Early Miocene. High ocean dissolved inorganic carbon (DIC) concentrations have been proposed for this period of the Miocene and may be one factor contributing to high coccolith kse.</p

Astrobiochronology of Late Neogene deposits near the Strait of Gibraltar (SW Spain). Implications for the tectonic control of the Messinian Salinity Crisis

[EN]The main objective of this work is to explore the Guadalquivir basin and the Gulf of Cadiz to obtain continuous sediment records for the interval of the Messinian Salinity Crisis on the Atlantic side of the Iberian peninsula so as to analyse the possible paleoenvironmental, tectonic or paleoclimatic changes in a region which was only a few kms away from the Mediterranean coasts during this time period

Sea surface temperature reconstruction in the southeastern Iberian Margin during the Last Glacial period by means of coccolithophore analyses

4 pages, 2 figures.Detailed quantitative analyses of coccolithophore assemblages have been carried out in three sediment cores recovered from different locations in the Atlantic and Mediterranean sectors of the Iberian Peninsula. Biostratigraphical and oxygen isotope analyses show that these cores provide a high-resolution record of most of the last glacial period. Joint interpretation of the results reveals that higher sea surface temperatures (SST) were recorded in the Atlantic side during that interval. Dansgaard-Oeschger Interstadials are the warmer periods, while during Heinrich Events and Dansgaard-Oeschger Stadials SSTs suffered a substantial decrease, probably due to the appearance of turbid, fresher and colder surface water masses. These quantitative differences in the response of coccolithophore assemblages between the Atlantic and the Mediterranean cores indicate that the Mediterranean Sea shows a more intense response to climatic and oceanographic changes than the Atlantic area.La realización de esta investigación ha sido posible gracias a la concesión de una beca predoctoral del Programa Nacional de Formación de Profesorado Universitario (FPU, Ministerio de Educación, Cultura y Deportes) a E. Colmenero Hidalgo, y a la financiación de los proyectos REN2003-08642-CO2/CLI y BTE2002-04670 (Ministerio de Ciencia y Tecnología), SA088/04 (Junta de Castilla y León) y PROMESS 1 (EVR1-T-40024, Comisión Europea). Los autores también agradecen a Jesús Roncero y a José Ignacio Martín Cruz su ayuda en la preparación de muestras.Peer reviewe

Impact of suborbital climate changes in the North Atlantic on ice sheet dynamics at the Mid-Pleistocene Transition

Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic delta O-18 time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 (similar to 940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic delta O-18 time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic delta O-18) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator