1,721,075 research outputs found
The Global Standard Stratotype-section and Point (GSSP) of the Piacenzian Stage (Middle Pliocene)
No full textThe base of the Piacenzian Stage, representing the Lower Pliocene-Middle Pliocene boundary, has been recently defined and ratified by IUGS. The boundary stratotype is located in the Punta Piccola section (Sicily, Italy)
Late Miocene calcareous nannofossil biostratigraphy and astrobiochronology for the Mediterranean region
No full textResults are presented of a quantitative biostratigraphic study of the calcareous nannofossils from the upper Miocene Metochia section (Gavdos Island, Greece) located in the eastern Mediterranean. The study allows the completion of the calcareous nannofossil Zonal Scheme for the Mediterranean Neogene. Parts of the scheme have already been proposed earlier for the Pliocene-Pleistocene (Rio et al. 1990b) and for the latest Oligocene to early late Miocene (Fornaciari and Rio 1996, Fornaciari et al. 1996).
The Metochia section proved to be a suitable section for high-resolution biostratigraphic studies. It has a detailed planktonic foraminiferal biostratigraphy and a robust chronology based on the astronomical calibration of the sedimentary cycles (Krijgsman et al. 1995, Hilgen et al. 1995). Age estimates for the nannofossil biohorizons recognized in the section were obtained through direct correlation to this astrochronology. Five out of seventeen biohorizons were selected for biostratigraphic purposes and to define the (sub)zonal boundaries. They are (in stratigraphic order): LO (Last Occurrence) of Discoaster hamatus Martini and Bramlette 1963, equivalent to the base of Subzone MNN10a, dated at 9.53 Ma; FCO (First Consistent Continuous Occurrence) of Discoaster pentaradiatus (Tan 1927) Bramlette and Riedel 1954, equivalent to the base of Subzone MNN10b, at 9.37 Ma; PB; (Paracme Beginning) of Reticulofenestra pseudoumbilicus (Gartner 1967) Gartner 1969, equivalent to the base of Zone MNN11a, at 8.76 Ma; FO (First Occurrence) of Amaurolithus spp. (A. primus (Bukry and Percival 1971) Gartner and Bukry 1975), equivalent to the base of Subzone MNN11b, at 7.42 Ma. and FO of Nicklithus amplificus (Bukry and Percival 1971) Raffi Backman and Rio 1998, equivalent to the base of Subzone MNN11c, at 6.69 Ma. We compared our biochronology with data available from other Mediterranean sections (Sprovieri et al. 1996, Negri et al. 1999, Negri and Villa 2000, Bonomo 200 1), and with the nannofossil biochronology from low-latitude oceanic reference sections (Raffi et al. 1995, Backman and Raffi 1997). Our results evidence differences and similarities: some of the recently proposed events in the Tortonian-Messinian (e.g., FO and FCO of Reticulofenestra rotaria Theodoridis 1984, FO of Amaurolitus delicatus Gartner and Bukry 1975) proved not to be reliable and do not improve the biostratigraphic resolution by calcareous nannofossils in the time interval under consideration. On the other hand, the five selected biohorizons can easily be reproduced elsewhere in the Mediterranean. and are considered useful for correlations to the extra-Mediterranean realm
Base of large Gephyrocapsa and astronomical calibration of early Pleistocene sapropels in Site 967 and Hole 969D: solving the chronology of the Vrica section (Calabria, Italy)
No full textCalcareous plankton biochronology and the astronomical calibration of sapropels are presented for the early Pleistocene in Ocean Drilling Program (ODP) Site 967 and Hole 969D with the aim to solve the existing chronology problem in the Pliocene/Pleistocene boundary stratotype section of Vrica, Italy. Detailed sapropel correlations between these ODP sites and the Vrica and Singa sections, corroborated by calcareous plankton biostratigraphy, indicate that the Vrica section is continuous and that the base of the large Gephyrocapsa is diachronous on a global scale
Astrochronology of the Burdigalian-Langhian in the Mediterranean: understanding climatic and environmental changes
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Integrated stratigraphy of La Vedova section (Conero Riviera, Italy), a potential candidate for the Langhian GSSP.
No full textINTEGRATED STRATIGRAPHY AND ORBITAL TUNING OF THE RAS IL PELLEGRIN SECTION ON MALTA: EC-CENTRICITY AND OBLIQUITY CONTROL ON MIDDLE MIOCENE CLIMATE COOLING AND OXYGEN ISOTOPE EVENT MI-3
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