Authigenic Be-10/Be-9 ratio signature of the Matuyama-Brunhes boundary in the Montalbano Jonico marine succession

作者：Simon Quentin; Bourles Didier L; Bassinot Franck; Nomade Sebastien; Marino Maria; Ciaranfi Neri; Girone Angela; Maiorano Patrizia; Thouveny Nicolas; Choy Sandrine; Dewilde Fabien; Scao Vincent; Isguder Gulay; Blamart Dominique

来源：Earth and Planetary Science Letters, 2017, 460: 255-267.

DOI：10.1016/j.epsl.2016.11.052

• Be-10 cosmogenic nuclide
• authigenic Be-10/Be-9 ratio
• Matuyama Brunhes Boundary (MBB)
• high-resolution oxygen isotope stratigraphy
• MIS 19
• GSSP stratotype

Geomagnetic dipole moment (GDM) lows associated with polarity reversals or geomagnetic excursions induce significant modulation of the cosmogenic nuclide Beryllium-10 (Be-10) production. Hence, the reconstruction of atmospheric Be-10 production rates from natural archives such as marine sedimentary sequences or ice cores constitutes a complementary approach, independent from paleomagnetic measurements, to decipher past GDM fluctuations. This is particularly important in the Montalbano Jonico succession (South Italy) since it is candidate to host the Global Stratotype Section and Point of the Middle Pleistocene Stage but where the magnetostratigraphic positioning of the Matuyama-Brunhes boundary (MBB) has not been available up to now. This study presents (1) original authigenic Be-10 cosmogenic nuclide and Be stable isotope results, and (2) new high-resolution benthic oxygen isotope record covering termination IX and Marine Isotope Stage (MIS) 19. A robust chronological framework is established on the basis of (i) our oxygen isotope stratigraphy, using the strong analogies between MIS 1 and MIS 19c in terms of orbital forcing and CO2 level, and (ii) one precise Ar-40/Ar-39 date obtained in the tephra layer V4. The authigenic Be-10/Be-9 ratio record marks the atmospheric Be-10 overproduction linked to the dipole low accompanying the MBB transition, with a characteristic twofold increase of the Be-10 production at the end of MIS 19c and early MIS 19b. This signature is similar to those described in both marine and ice core records. The detailed chronostratigraphy constrained by a radiometrically-dated tephra layer (773.9 +/- 1.3 ka) within the MBB interval, makes it possible to discuss the structure and to assess the timing of the Be-10-production changes, and thus the MBB geomagnetic variations, with an unprecedented accuracy for a marine archive (sedimentation rates similar to 80 cm/ka). These new cosmogenic nuclide production signatures provide the only missing constraint required for retaining the Montalbano Jonico succession as a global-scale correlation reference section for the Early-Middle Pleistocene boundary.

• 出版日期2017-2-15
• 单位中国地震局