CORRELATIONS OF HAUTERIVIAN AND BARREMIAN (EARLY CRETACEOUS) STAGE BOUNDARIES TO POLARITY CHRONS

Recent ammonite finds in Italian Maiolica limestones allow direct corr elation of Hauterivian and Barremian ammonite zones (stage boundaries) to polarity chrons. At Laghetto and Alpetto (Lombardy, Italy), Lower Aptian ammonites occur just above polarity zone M0 and below the Selli Level, and Upper Barremian ammonites occur in polarity zone M1n. Thes e correlations are consistent with the Barremian/Aptian boundary being close to older boundary of (polarity chron) CM0. The uppermost Hauter ivian ammonite (Faraoni) guide level has been correlated to CM4 at Bos so (Umbria-Marche), confirming the recent correlation of the Hauterivi an/Barremian boundary to CM4. At Monte Acute (Umbria-Marche), ammonite s spanning the Valanginian/Hauterivian boundary interval, and the last appearance of the nannofossil T. verenae, occur close to the CM11/CM 11n boundary. The Valanginian/Hauterivian boundary has previously been placed between the first appearance of L. bollii and the last appeara nce of T. verenae, or between CM10 and CM11. The published Polaveno (L ombardy) magnetostratigraphy for the CM3-CM11 interval has now been ex tended to CM16. This 260 m section, recording the CM3-CM16 interval, i s the most complete single-section record of Cretaceous M-sequence pol arity chrons. No diagnostic ammonites have been found in this section; however, the correlations of nannofossil and calpionellid events to p olarity chrons are consistent with previous studies.