Completing the Neogene geological time scale between 8.5 and 12.5 Ma |
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| Institution: | 1. Dept. de Geología, University of Salamanca, Plaza de los Caídos s/n, 37008 Salamanca, Spain;2. Dept. of Biogeosciences, JAMSTEC, Yokosuka 237-0061, Japan;3. Dept. Earth Sciences, Royal Holloway Univ. London, Egham, Surrey TW20 0EX, UK;4. BRIDGE, School of Geographical Sciences, Cabot Institute, University of Bristol, University Road, Bristol BS8 1SS, UK;5. Dept. Geography and Geology, Sam Houston State University, Huntsville, TX 77341-2148, USA;6. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, D-24148 Kiel, Germany;7. Inst. für Erdwissenschaften, Karl-Franzens-Universität Graz, NAWI-Graz, Heinrichstrasse 26, 8010 Graz, Austria;8. Leibniz-Laboratory for Radiometric Dating and Isotope Research, Christian-Albrechts-Universität Kiel, Max-Eyth-Str. 11-13, 24118 Kiel, Germany;1. Department of Earth Sciences, Utrecht University, 3584CD, Utrecht, The Netherlands;2. Université Hassan II Mohammedia, Fac. Sci. Ben M''Sik, BP7955 Casablanca, Morocco;3. BRIDGE, School of Geographical Sciences and Cabot Institute, University of Bristol, Bristol BS8 1SS, UK;4. Department of Geology, University of Salamanca, 37008 Salamanca, Spain;5. ONHYM, 10050 Rabat, Morocco;1. Istituto di Scienze Marine (ISMAR) – CNR, sede di Napoli, Calata Porta di Massa, Napoli 80133, Italy;2. Istituto di Geoscienze e Georisorse, C.N.R. - Area della Ricerca di Pisa, Via G. Moruzzi 1, Pisa 56124, Italy;3. Dipartimento di Scienze Fisiche, della Terra e dell’Ambiente, Università di Siena, Via Laterina 8, Siena 53100, Italy;4. Dipartimento di Scienze Chimiche, della Vita e della Sostenibilità Ambientale, Università di Parma, Parco Area delle Scienze 11/a, Parma 43124, Italy;5. Dipartimento di Scienze della Terra e del Mare, Università di Palermo, Via Archirafi 20-22, Palermo 90123, Italy;6. Department of Geology, University of Salamanca, Salamanca 37071, Spain |
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| Abstract: | A much improved high-resolution magnetostratigraphy is presented for the interval between 8.5 and 12.5 Ma in the deep marine astronomically tuned Monte dei Corvi Beach section in northern Italy. This section contains the formally designated boundary between the Middle and Upper Miocene defined by the Tortonian GSSP. The natural remanent magnetization is carried by an unusual low-temperature component of primary origin. According to interpretations of isothermal remanent magnetization (IRM) acquisition curves, the palaeomagnetic signal is most probably carried by iron sulphides, such as greigite or pyrrhotite. The resultant magnetostratigraphy is reliable and can be straightforwardly calibrated to the Astronomically Tuned Neogene Time Scale (ATNTS2004) showing that the section ranges from Chron C5An.2n up to C4.2r-1. The inferred correlation of the Tortonian GSSP to the older part of Chron C5r.2n is confirmed, thereby guaranteeing global correlation potential. In addition, the Monte dei Corvi Beach section has been re-tuned to the new numerical solution La2004 for the interval between 8.5 and 12.9 Ma. This exercise shows that the characteristic cycle patterns are not consistent with a single solution with fixed values for dynamical ellipticity and tidal dissipation. For the younger part of the section, sedimentary cycles show an excellent fit with intricate details of precession/obliquity interference in the nominal La2004(1,1) solution. However, this solution produces serious mismatches between the sedimentary cycles and the precession/obliquity interference in the interval older than ∼ 10.2 Ma. For this interval changes in tidal dissipation value (while keeping dynamical ellipticity constant at its present-day value) are necessary to maintain a perfect fit. A detailed visual comparison reveals a very good to excellent fit with La2004(1,1.2) and, to lesser extent, with La2004(1,0.5). However, La2004(1,1.2) is the preferred tuning target for the moment in the interval older than 10.2 Ma. The astronomical (re)tuning on precessional scale to La2004(1,1) yielded slightly different astronomical ages for each basic cycle and, hence, also for the calcareous plankton events and magnetic reversal boundaries with uncertainties ranging within a few thousand years. The age of the Tortonian GSSP turns into 11.625 Ma instead of the previously published 11.608 Ma. Our ages should replace existing ages in the Astronomically Tuned Neogene Time Scale (ATNTS2004). |
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