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Liddicoat, J. C.
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- PublicationOpen AccessOn the reliability of the Matuyama–Brunhes record in the Sulmona Basin—Comment to ‘A reappraisal of the proposed rapid Matuyama–Brunhes geomagnetic reversal in the Sulmona Basin, Italy’ by Evans and Muxworthy (2018)(2019)
; ; ; ; ; ; ; ; ; ; ; The Matuyama–Brunhes Boundary (MBB) recorded in the lacustrine sequence in the Sulmona basin (central Apennines, Italy) raised considerable scientific interest and has been the focus of various papers (Giaccio et al. 2013; Sagnotti et al. 2014; 2016). The interest comes from evidence for a very sharp geomagnetic polarity transition, that is radioisotopically dated. A paper recently published by Evans and Muxworthy (2018) questions the reliability of the Sulmona palaeomagnetic record. With new measurements on companion samples from the same stratigraphic block studied by Evans and Muxworthy, we show that directional results obtained by different demagnetization treatments (AF, thermal and thermal + AF) are in close agreement.We here propose a different interpretation of the magnetostratigraphy, and confirm that the palaeomagnetic record of the MBB geomagnetic reversal in the Sulmona basin is properly documented371 100 - PublicationRestrictedExtremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal(2014-09-18)
; ; ; ; ; ; ; ;Sagnotti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Scardia, G. ;Giaccio, B. ;Liddicoat, J. C. ;Nomade, S. ;Renne, P. R. ;Sprain, C. J.; ; ; ; ; ;We report a palaeomagnetic investigation of the last full geomagnetic field reversal, the Matuyama-Brunhes (M-B) transition, as reserved in a continuous sequence of exposed lacustrine sediments in the Apennines of Central Italy. The palaeomagnetic record provides the most direct evidence for the tempo of transitional field behaviour yet obtained for the M-B transition. 40Ar/39Ar dating of tephra layers bracketing the M-B transition provides high-accuracy age constraints and indicates a mean sediment accumulation rate of about 0.2 mm yr–1 during the transition. Two relative palaeointensity (RPI) minima are present in the M-B transition. During the terminus of the upper RPI minimum, a directional change of about 180 ◦ occurred at an extremely fast rate, estimated to be less than 2 ◦ per year, with no intermediate virtual geomagnetic poles (VGPs) documented during the transit from the southern to northern hemisphere. Thus, the entry into the Brunhes Normal Chron as represented by the palaeomagnetic directions and VGPs developed in a time interval comparable to the duration of an average human life, which is an order of magnitude more rapid than suggested by current models. The reported investigation therefore provides high-resolution integrated palaeomagnetic and radioisotopic data that document the fine details of the anatomy and tempo of the M-B transition in Central Italy that in turn are crucial for a better understanding of Earth’s magnetic field, and for the development of more sophisticated models that are able to describe its global structure and behaviour.301 65 - PublicationOpen AccessControllo climatico sull'accumulo di sedimenti di margine Olocenici e Pleistocenici del Mar Tirreno Orientale(2007)
; ; ; ; ; ; ;Iorio, M.; IAMC, CNR, Napoli ;Sagnotti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Budillon, F.; IAMC, CNR, Napoli ;Liddicoat, J. C.; Columbia University, New York, USA ;Coe, R. S.; California University, Santa Cruz, USA ;Marsella, E.; IAMC, CNR, Napoli; ; ; ; ; ; ; ; ; ; ;Carli, B.; CNR ;Cavarretta, G.; CNR ;Colacino, M.; CNR ;Fuzzi, S.; CNR; ; ; Dati di paleovariazioni secolari (PSV) del campo geomagnetico sono stati ottenuti negli ultimi 25.000 anni da diverse carote recuperate nel Golfo di Salerno (Mar Tirreno orientale). Le curve composte di PSV, sono comparate con le “ PSV Master Curves” britanniche e francesi. La comparazione fornisce uno strumento cronologico per determinare un trend di accrescimento del tasso di sedimentazione nell’ Olocene superiore e di variazione ad intervalli di circa 1000 anni nell’ Olocene medio della piattaforma. Inoltre durante i due principali episodi caldi del Mediterraneo a circa 3.3 e tra 6-9 ka sia la piattaforma che la scarpata superiore registrano un aumento con successiva diminuzione del tasso di sedimentazione, mentre ulteriori diminuzioni si registrano, in scarpata superiore, durante l’ ultimo picco Glaciale (LGM) e l’interstadio Bølling-Allerød, suggerendo cosi un’ influenza climatica sui processi di accumulo dei sedimenti del margine del Golfo di Salerno.197 162 - PublicationRestrictedHow fast was the Matuyama-Brunhes geomagnetic reversal? A new subcentennial record from the Sulmona Basin, central Italy(2016-02-02)
; ; ; ; ; ; ; ;Sagnotti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Giaccio, B.; IGAG, CNR ;Liddicoat, J. C.; Barnard College, Columbia University, USA ;Nomade, S.; IPSL, CEA/CNRS/UVSQ et Universit´e Paris–Saclay, France ;Renne, P. R.; Berkeley Geochronology Center, Berkeley, USA ;Scardia, G.; Universidade Estadual Paulista, Brazil ;Sprain, C. J.; Berkeley Geochronology Center, Berkeley, USA; ; ; ; ; ; A recent study of the Matuyama–Brunhes (M-B) geomagnetic field reversal recorded in exposed lacustrine sediments from the Sulmona Basin (Italy) provided a continuous, highresolution record indicating that the reversal of the field direction at the terminus of the M-B boundary (MBB) occurred in less than a century, about 786 ka ago. In the sediment, thin (4–6 cm) remagnetized horizons were recognized above two distinct tephra layers—SUL2- 19 and SUL2-20—that occur ∼25 and ∼35 cm below the MBB, respectively. Also, a faint, millimetre-thick tephra (SUL2-18) occurs 2–3 cm above the MBB.With the aim of improving the temporal resolution of the previous Sulmona MBB record and understanding the possible influence of cryptotephra on the M-B record in the Sulmona Basin,we performed more detailed sampling and analyses of overlapping standard and smaller samples from a 50 cm-long block that spans the MBB. The new data indicate that (i) the MBB is even sharper than previously reported and occurs ∼2.5 cm below tephra SUL2-18, in agreement with the previous study; (ii) the MBB coincides with the rise of an intensity peak of the natural remanent magnetization (NRM) intensity, which extends across SUL2-18; (iii) except for a 2-cm-thick interval just above tephra SUL2-18, the rock magnetic parameters (k, ARM, Mr, Ms, Bc, Bcr) indicate exactly the same magnetic mineralogy throughout the sampled sequence. We conclude that either SUL2-18 resulted in the remagnetization of an interval of about 6 cm (i.e. during the NRM intensity peak spanning ∼260 ± 110 yr, according to the estimated local sedimentation rate), and thus the detailed MBB record is lost because it is overprinted, or the MBB is well recorded, occurred abruptly about 2.5 cm below SUL2-18 and lasted less than 13 ± 6 yr. Both hypotheses challenge our understanding of the geomagnetic field behaviour during a polarity transition and/or of the NRM acquisition process in the Sulmona lacustrine sediment.314 82