Abstract The possibility of inferring paleoflow conditions of the Messinian turbidites from the Laga Formation (Central Apennines, Italy) is here analyzed by solving an inverse problem. This inverse problem is solved for elucidating the condition for flow ignition for current velocity, height, and sediment concentration by comparing field data with an analytical solution for the change in bed elevation, related to net-depositional turbidity currents. The obtained layer-averaged values are 2–5 m/s for current velocities, 40–100 m for current thicknesses, and 0.1–2% for sediment volume concentrations. Moreover, the duration time of these flows has been also estimated. Results show values from 1 to 15 hours, depending on the energy of the turbidity currents. This variability in the hydrodynamic conditions also provides some insight into the high-order cyclicity observed into the Laga turbidite deposits. A brief discussion on the vertical structure of a net depositional turbidity current is finally presented. The hydrodynamic conditions of a three-layer turbidity current are inferred from classical tank experiments. The behavior of each layer during the net-depositional phase of a realistic turbidity current is consequently described by using layer-averaged results of the inverse problem, as a function of the Richardson number and the Reynolds number. Results confirm subcritical turbulent behavior of the thin basal layer, a middle layer with a reduced turbulence, and an upper layer with a turbulent cloud where the mean kinetic energy is smaller than the turbulent kinetic energy. External Controls on Deep-Water Depositional Systems SEPM Special Publication No. 92 (CD version), Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-200-8, p. 347–362.

In the central Apennines, interacting siliciclastic and carbonate marine clastic wedges filled the foreland basin system during the late Miocene. Conjunction of collisional thrust tectonics and prethrusting normal faults generated a complex foredeep with intrabasinal structural highs that represented additional source areas to the basin. Detrital modes of the late Miocene central Apennines orogenic system range in composition from intrabasinal carbonate to quartzofeldspatholithic and calclithite arenites. The external zone of the foredeep is characterized by hemipelagic deposits, called the Orbulina Marl. Their arenite beds are composed by intrabasinal carbonate, with dominant bioclasts and minor intraclasts, and glauconite derived from an active shallow-marine carbonate source. These hemipelagic deposits are partly coeval with and partly overlain by siliciclastic turbidites of the Frosinone and the Argilloso-Arenacea Formations, and they represent deposition within local foredeep depocenters. Siliciclastic turbidite sandstones are quartzofeldspatholithic, which documents provenances from metamorphic, plutonic, ophiolitic, and sedimentary rocks. Carbonate intrabasinal structural highs were the main source for carbonate breccias, intrabasinal arenites, and calclithites of the Brecce della Renga Formation, the deposits of which are locally interbedded with the coeval siliciclastic turbidite sandstones. Evolution of late Miocene sandstone detrital modes reflected the changing nature of the central Apennines thrust belt through time and the complex architecture of the foreland basin system; it records the history of accretion, deformation of the foredeep, and progressive areal reduction of carbonate-producing areas along with the sedimentary and structural evolution of local intrabasinal highs.