Browsing by Author "Ventura, C."
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- Data report: diatom and silicoflagellate records of marine isotope Stages 25-27 at IODP Site U1387, Faro DriftPublication . Ventura, C.; Abrantes, Fatima; Loureiro, I.; Voelker, Antje; Stow, Dorrik A. V.; Hernandez-Molina, F. Javier; Alvarez Zarikian, Carlos A.; Expedition 339 ScientistsDuring Integrated Ocean Drilling Program Expedition 339, the shipboard micropaleontological studies of Site U1387 core catcher samples revealed the preservation of diatoms and radiolarians in specific depths from early Pleistocene age (900–1000 ka). To evaluate the ecological significance of those diatoms, we analyzed 98 samples from the intervals of 244 to 274 m along the corrected splice, corresponding to marine isotope Stage (MIS) 25 to MIS 29, for the abundance of diatoms and silicoflagellates. In 6 samples, the composition of the diatom assemblage was determined as well. Although most samples were barren of siliceous microfossils, the downcore record revealed two intervals, 249–252 corrected meters composite depth (cmcd) and 263–265 cmcd, where diatoms and silicoflagellates reach their maximum values. These maxima occurred from the MIS 26/25 transition to interglacial MIS 25, and again during early MIS 27. The diatom assemblage includes 27 identified taxa with Chaetoceros (Hyalochaete) resting spores being dominant and Thalassionema nitzschioides and Paralia sulcata significant. The Chaetoceros spores clearly indicate strong influence of seasonal upwelling and associated high primary productivity. Special to the diatom record is, however, the occurrence of the large-diameter (>125 µm) centric diatoms Coscinodiscus asteromphalus, Coscinodiscus apiculatus, and Coscinodiscus cf. gigas that imply incursions of low-nutrient, open-ocean water into the southern Portuguese coast during MIS 25.
- Data report: IODP Expedition 339 Site U1391: an improved splice and preliminary age model on the basis of XRF dataPublication . Abrantes, Fatima; Santos, C.; Ventura, C.; Voelker, Antje; Röhl, U.; Stow, Dorrik A. V.; Hernandez-Molina, F. Javier; Alvarez Zarikian, Carlos A.; Expedition 339 ScientistsWith the objective to reconstruct past primary production on the southwest Portuguese margin at orbital and millennial timescales through the Pleistocene, we chose to compare two sites recovered during Expedition 339 at similar latitude but different distances to the coast (Sites U1385 and U1391). Site U1385 has a well-established chronology, but for Site U1391 no isotope data are yet available. In order to develop a correct chronology without isotope data, we performed XRF analysis of cores from Holes U1391A and U1391B between 76.51 and 205.77 mbsf. With these data, in particular using log(Ca/Ti) and log(Ca/Fe), it was possible to enhance the Site U1391 splice and to establish an age model based on the correlation to the well-defined and robust Site U1385 age model.