FACIES AND STRATIGRAPHIC ARCHITECTURE OF SUPERPOSED, COARSE-GRAINED TURBIDITE SYSTEMS, THE COLLE MONTARONE CONGLOMERATES (PLIOCENE), NOTARESCO, CENTRAL ITALY.

The Periadriatic foreland basin is a north-south oriented trough located immediately east of the Apennines fold-thrust belt. During the Pliocene, gravel- and sand-grade sediments originated from the uplifting Apennines were abundantly supplied to the deepwater basin by a series of transverse submarine conduits. In the rock record these conduits are preserved as large, coarse-grained canyon fills encased within a thick succession of hemipelagic mudstones. The aim of this study is to document the depositional facies, architectural elements, internal organisation and degree of stratigraphic variability of one of these erosionally-confined turbidite systems exposed at Colle Montarone, in the vicinity of Notaresco (central Italy). These strata have been analysed employing the hierarchical architectural element scheme developed by Ghosh & Lowe (1993) for deep-water sediment gravity flow strata; detailed geological mapping at the scale of third-order (lithofacies) elements and sedimentary logging were used to define both architecture and sedimentological characteristics. Following this approach, these late Pliocene deep-water strata can be described in terms of five orders of architectural elements and their bounding surfaces. Third-order architectural elements are comprised of stacks of similar sedimentation units and correspond to mappable lithofacies. Four types of decametre-scale lithofacies form the basic units of this study, each characterised by a unique combination of facies assemblage, internal geometry, and bounding surfaces: (i) conglomerates; (ii) thin-bedded sandstones; (iii) pebbly mudstones and chaotically bedded mudstones (debrite complexes); (iv) very thinly-bedded mudstones. Fourth-order architectural elements are characterized by cyclically stacked, genetically related third-order elements. Clusters of fourth-order elements are separated by fifth-order surfaces having tens of metres of topographic relief and represent fifth-order elements (turbidite systems). The studied succession can be subdivided into four discrete fifth-order architectural elements, designated Montarone I, Montarone II and Montarone III, Montarone IV, which show a pronounced cyclic stacking pattern.