Magnetostratigraphy, nannofossil stratigraphy and apparent polar wander for Adria-Africa in the Jurassic-Cretaceous boundary interval

Existing correlations of Early Cretaceous nannofossil events to polarity zones in Italian pelagic limestones are the basis for correlation of polarity chrons to geologic stages, and hence calibration of the Early Cretaceous geomagnetic polarity timescale. Here, we present correlations of nannofossil events to polarity chrons for the Late Jurassic and Jurassic/Cretaceous boundary interval from the Southern Alps, making the case for revisions of current geologic timescales in this interval. The Jurassic/Cretaceous and Kimmeridgian/Tithonian boundaries can be usefully defined at the onsets of polarity chrons CM18R and CM22R, respectively. The Oxfordian/Kimmeridgian boundary can be assigned to CM25. An apparent polar wander path (APWP) for the Southern Alps, derived from, and time-calibrated by bio-magnetostratigraphic data, is similar to, and provides a proxy for, the African APWP in the absence of adequate African data of this age. The Southern Alpine APWP is characterized by a cusp (hairpin) at similar to 30 degrees N/270 degrees E at a time close to the Oxfordian/Kimmeridgian boundary (polarity chron CM25, similar to 154 Ma), rapid APWP from high latitude (>60 degrees N) in the preceding middle Jurassic (Bajocian-Oxfordian) interval coincident with the onset of Central Atlantic/Ligurian oceanic rifting, and a return to high latitudes during the Cretaceous. Early Jurassic poles at high latitudes (>60 degrees N) are evident for Sinemurian to Toarcian-Aalenian time (175-195 Ma). An APWP for this time interval with this level of temporal calibration cannot be constructed using data from Africa itself, or from other Atlantic-bordering continents by rotation to African coordinates. (C) 2010 Elsevier B.V. All rights reserved.