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Implications of a combined biostratigraphic and palaeomagnetic study of the Umbrian Maiolica Formation
Authors:Simonetta Cirilli  Péter Márton  Luigi Vigli
Institution:1. c/o Istituto di Geologia, Universita di Perugia, Perugia (Italy);2. Geophysics Department, L. Eötvös University, H - 1083 Budapest, Kun Béla tér 2. (Hungary);3. c/o Istituto di Geologia Marina, C.N.R., Bologna (Italy)
Abstract:The study of a 275.5 m thick section of white, pelagic limestones occupying the valley of the Fonte del Giordano river on the southern slope of Mt. Montagnola has yielded a biostratigraphically controlled clear magnetic reversal pattern after thermal cleaning. The magnetic stratigraphy of the lower 131 m of the section (Calpionellid zones) is correlatable with the M-sequence of oceanic magnetic anomalies between M-19 and M-14. The reversal stratigraphy of the upper 81.5 m of the section (Radiolaria zone) has also been tied to the oceanic polarity time scale by making linear interpolation for a missing 63 m thickness underneath it.Besides the Fonte del Giordano section two Berriasian outcrops each with a different bedding attitude were studied at Gubbio and near Cagli for tectonic tilt test giving positive results. The mean palaeomagnetic pole position for the Late Jurassic/Early Cretaceous after bedding correction is: Φ = 19.1°, Λ = 288.2°, k = 148.7, α95 = 10.2° (N = 3), confirming the presence of a large swing in the polar path, a common behaviour of apparent polar wandering for the peri-Adriatic region during this time.
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