Implications of a combined biostratigraphic and palaeomagnetic study of the Umbrian Maiolica Formation     

Simonetta Cirilli  Péter Márton  Luigi Vigli 《Earth and Planetary Science Letters》1984,69(1):203-214

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.  相似文献   

Microbial–serpulid build-ups in the Norian–Rhaetian of the Western Mediterranean area: ecological response of shelf margin communities to stressed environments     

Cirilli  Iannace  Jadoul  & Zamparelli 《地学学报》1999,11(5):195-202

Microbial–serpulid communities are the main reef-builders of most Norian–Rhaetian carbonate platforms of Italy. They represent minor, yet significant communities in the shallow western Tethys, in contrast with the highly diversified sponge- and coral-dominated Dachstein reefs widespread from Eastern Alps to Australia. The microbial–serpulid build-ups are systematically associated with narrow intraplatform troughs and developed on the outer margin–upper slope area under marine conditions unsuitable for the development of coralgal reefs. The development of these settings can be related to transtensional tectonics affecting an elongate belt which was roughly parallel to the Piedmont–Ligurian Ocean spreading axis during the Jurassic. Dysoxic and mesosaline waters are the main cause of the success of the Norian microbial–serpulid build-ups; whereas, from the late Norian to the Rhaetian, eutrophication and climate change control their distribution. These environments acted during Norian–Rhaetian times as refuges, where opportunitistic organisms could survive and build frameworks during a period otherwise dominated by coralgal reefs.  相似文献