Correlations of Hauterivian and Barremian (Early Cretaceous) stage boundaries to polarity chrons

Abstract Recent ammonite finds in Italian Maiolica limestones allow direct correlation 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. These correlations are consistent with the Barremian/Aptian boundary being close to older boundary of (polarity chron) CM0. The uppermost Hauterivian ammonite (Faraoni) guide level has been correlated to CM4 at Bosso (Umbria-Marche), confirming the recent correlation of the Hauterivian/Barremian boundary to CM4. At Monte Acuto (Umbria-Marche), ammonites spanning the Valanginian/Hauterivian boundary interval, and the last appearance of the nannofossil T. verenae , occur close to the CM11/CM11n boundary. The Valanginian/Hauterivian boundary has previously been placed between the first appearance of L. bollii and the last appearance of T. verenae , or between CM10 and CM11. The published Polaveno (Lombardy) magnetostratigraphy for the CM3–CM11 interval has now extended to CM16. This 260 m section, recording the CM3–CM16 interval, is the most complete single-section record of Cretaceous M-sequence polarity chrons. No diagnostic ammonites have been found in this section; however, the correlations of nannofossil and calpionellid events to polarity chrons are consistent with previous studies.