Rend. Online Soc. Geol. It., Vol. 21 (2012), pp. 889-890. © Società Geologica Italiana, Roma 2012 889 Key words: Lower Messinian turbidite systems, facies association, architectural style, channel, channel-lobe transition deposits, Laga Basin, central Apennine. INTRODUCTION AND GEOLOGICAL SETTING Turbidite channels represent the main ways through which gravity flows transport large volumes of sand and mud in deep- water basins. Most of researchers carried out in the last years have been addressed to define mechanisms of formation and filling of sinuous channels typical of fine-grained mud-rich turbidite systems, while little is known about mode of formation and filling of the channels developed in coarse- grained sand-rich turbidite systems. The data presented here want to contribute to better define the main features of the channels developed in coarse-grained sand-rich turbidite systems as those occurring within the Laga Basin (central Apennine, Italy). Our analysis is based on field data and on the measure of several stratigraphic-sedimentological sections for a total thickness of about 13,000 m. The aim is to describe the channelform geometry and the channel hierarchy, the mode of their formation and filling, and how the features of channel deposits vary from up- to downstream along the depositional profile. The lower Messinian Laga turbidite basin developed since the late Tortonian, when the ensuing propagation of the Apennine compressive thrust-front led to the progressive fragmentation, reorganization and closure of the Marnoso- arenacea foreland basin system. Causing this the Laga Basin shows the typical features of a confined basin where thrust propagation controlled shape, dimension, and topography of the basin as well as the geometry of the deposits and resulting facies. STRATIGRAPHIC AND SEDIMENTOLOGICAL DATA The turbidite deposits of Laga Basin constitute a turbidite complex forming a third-order composite depositional sequence (Laga Depositional Sequence, LDS) made up of several turbidite systems in which it is possible to recognize, from up to down current (i.e., from NW to SE) a channel complex zone, a channel-lobe transition zone, and a lobe zone. Facies analysis allowed to construct two possible facies tracts showing the genetic relationships among channel, channel-lobe transition, and lobe zones. These facies tracts highlight the close physical relationships among these three zones and allow, together with others stratigraphic and sedimentological considerations, to attribute the turbidite depositional systems of LDS to type II systems by MUTTI (1992). Channelized deposits of LDS form a complex hierarchy of sandstone bodies reflecting deposition of turbidity currents at different spatial and temporal scales. Field analysis based on the measure of several stratigraphic-sedimentological sections and detailed correlation panels, allowed to recognize several facies and a channelform hierarchy ranging from single channels, composite channels, and channel complexes. The surfaces bounding the single channels represent diachronous surfaces forming through the passage of several turbidite currents. On the other hand, surfaces bounding composite channels and channel complexes represent the envelopment of several erosional surfaces formed by the migration of single channels. Single channel exhibit facies change from channel axis to channel margin, and a vertical stack of often amalgamated bedsets formed through the migration of 3D bedforms. Ripples and dunes document the movement of sediment bedload and constitute the building blocks of compound and composite dune, approximately from 1 to 3-4 meters thick and several tens of meters long. The life of a single channel is mainly dependent on its stability in a given sector of the fan, a factor that is strongly influenced by the interaction between flows and topography. This interaction can lead to avulsion processes enabling migration of the single channels and the formation of composite channels. Finally, channel complexes represent the channelized sectors of the turbidite systems and are internally characterized by a hierarchy of channel bodies reflecting i) the lateral migration of composite channels driven by avulsion, and ii) the back-filling processes of the system. Unlike for single and composite channels, such mechanisms are under the control of allocyclic factors, such as climate and tectonics, which in turn control the variations in sediment supply. The plan geometry reconstruction of single channels indicates for these architectural elements a funnel-shape geometry, having a narrower section upstream and a wider section downstream, a Architectural style and facies distribution of channel and channel- lobe transition zone in the Lower Messinian turbidite systems of Laga Basin (central Apennines, Italy) DOMENICO CANNATA (*), SALVATORE MILLI (*) & MASSIMILIANO MOSCATELLI (**) _________________________ (*) Dipartimento di Scienze della Terra, SAPIENZA Università di Roma, domenico.cannata@uniroma1.it; salvatore.milli@uniroma1.it. (**) Istituto di Geologia Ambientale e Geoingegneria, CNR, massimiliano.moscatelli@igag.cnr.it.