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Geological Society, London, Special Publications; 2004; v. 222; p. 115-134;
DOI: 10.1144/GSL.SP.2004.222.01.07
© 2004 Geological Society of London

Factors controlling foredeep turbidite deposition: the case of Northern Apennines (Oligocene-Miocene, Italy)

U. Cibin1, A. Di Giulio2, L. Martelli1, R. Catanzariti3, S. Poccianti1, C. Rosselli1 & F. Sani4

1 Servizio Geologico, Sismico e dei Suoli, Regione Emilia-Romagna, V. le Silvani 4/3, Bologna, Italy
2 Dipartimento di Scienze della Terra, Via Ferrata 1, Pavia, Italy digiulio{at}unipv.it
3 CNR-Centro di Studio per la Geologia Strutturale e Dinamica dell’Appennino, Via S. Maria 53, Pisa, Italy
4 Dipartimento di Scienze della Terra, Via La Pira 4, Firenze, Italy

Three major controlling factors affect turbidite deposition in foredeep basins: tectonics in the source area, tectonics in the belt-basin system, and variations of sea-level (local or global). These factors are expected to have different effects on the volume, grain size, provenance and distribution of clastic sediments during the evolution of the basin. The interplay of these factors is investigated for the latest Oligocene-Middle Miocene Northern Appennines Foredeep turbidite wedges by means of turbidite-system-based lithostratigraphy and field mapping, integrated with nannoplankton biostratigraphy and sedimentary petrography. Almost all recognized turbidite systems, unless tectonically truncated, show an overall stacking pattern formed by a lower sand-rich, thickly bedded stage (depocentre stage) passing upward into mud-rich, thinly bedded stages, eventually grading up to mostly mudstone units (abandonment stage). This rhythmically repeated pattern is interpreted as the result of the abrupt switching on and off of coarse-grained input, coupled with an alternating increase/decrease of depositional rate recorded in all detected systems. Biostratigraphy makes it possible to distinguish the switching-off of turbidite systems due to depocentre migration (a new system is switched on basinward) from that due to a regional decrease of clastic input. Sandstone petrography records the compositional variation related to tectonically induced source reorganization. In the latest Oligocene-Middle Miocene NAF foredeep wedges, this integrated dataset allows us to recognize: two different phases of source tectonics in the latest Oligocene and the middle Burdigalian; two major episodes of basin tectonics and related depocentre shift in the latest Oligocene and the Langhian, plus a minor middle Aquitanian phase; and three intervals of reduced regional turbidite deposition during the Late Aquitanian, Middle Burdigalian and Early Serravallian, possibly linked to sea-level rises.