The sequence of polarity zones established by Alvarez and others for the Cretaceous and Paleocene in the Scaglia Formation in the Bottaccione Gorge at Gubbio has now been extended through the uppermost Paleocene into the upper Eocene Globigerinatheka semiinvoluta zone (= anomaly 18). The relationships between the standard Paleogene foraminiferal zones and the sea-floor anomalies are defined, with the exception of the mid-Eocene zones of Morozovella lehneri, Orbulinoides beckmanni, and the base of the Truncorota-loides rohri zone, which are obscured by inadequate preservation and a fault gap. The base of the Eocene lies above anomaly 25; the lower to middle Eocene contact (base Lutetian) lies in the upper part of anomaly 22; the base of the Bartonian lies below the base of anomaly 18; and the base of the Priabonian (upper Eocene) lies within anomaly 18. Radiometric ages appear to diverge systematically from a geochronology based on steady sea-floor-spreading rates, suggesting that spreading may have been as much as a factor of 3 slower in the Paleocene and the late Eocene than in the early and middle Eocene.

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