MAGNETOSTRATIGRAPHY AND ASTRONOMICAL CALIBRATION OF THE LAST 1.1 MYR FROM AN EASTERN MEDITERRANEAN PISTON CORE AND DATING OF SHORT EVENTS IN THE BRUNHES

A 37 m long piston core (KC-01B) was collected from the Calabrian Ridg e in the Ionian Sea. Astronomical calibration of sapropels and saprope lic signals-based on rock-magnetic and geochemical properties-yields a very accurate time-frame for the last 1.1 Myr, with the exception of the interval (650-850 ka) straddling the Brunhes/Matuyama boundary. We used the oxygen isotope data as an additional constraint on our age m odel. We arrive at an age of 812 ka for the Brunhes/Matuyama boundary, which indicates that its position is determined by delayed acquisitio n of NRM by some 40 kyr. The age of the top of Jaramillo subchron (100 1 +/- 3 ka) is slightly older than that of Shackleton, Berger & Peltie r (1990); that of its bottom (1072 +/- 5 ka) concurs with their estima te. In the Brunhes Chron, four short reversal excursions (CR0-3) were found and dated (CRO 261 +/- 3 ka, CR1 318 +/- 3 ka, CR2 515 +/- 3 ka, CR3 573 +/- 3 ka). In all cases, a high-coercivity reversed component is overlapped to a varying degree with a low-coercivity normal compon ent. Three of the reversal excursions (CR1-3) occur in zones where dia genetic processes were shown to be minimal. The fourth (CRO), in which a very large coercivity overlap occurs, is not well expressed and is found in a zone where some dissolution of magnetic minerals has occurr ed. The existing literature on reversal excursions is reviewed, and so me of the older records with an oxygen isotope or sapropel record have been redated. CRO could correspond to one of the Fram Strait excursio ns (Nowaczyk et al. 1994). CR3 corresponds to the Emperor, which is sh own to be equivalent to the Big Lost reversal excursion. For CR1 and C R2 we propose the names Calabrian Ridge 1 and Calabrian Ridge 2, since correlation with existing reversal excursions is uncertain. The Blake was not detected because extensive diagenesis has occurred in the cor responding interval. All reversal excursions observed in KC-01B corres pond to periods of minimal (relative) palaeointensity in the independe ntly dated record of Valet & Meynadier (1993). This seems to imply tha t reversal excursions are more likely to occur in periods with a relat ively large non-dipole field contribution.