Sedimentology and physical stratigraphy of the Messinian turbidite deposits of the Laga Basin (central Apennines, Italy)

This work investigates the physical stratigraphy and the sedimentological characters of the Messinian turbidites of the Laga Formation, central Apennines. In particular, the study concerns the lower Messinian portion of the Laga siliciclastic turbidites cropping out between the Mts. Sibillini and the Montagna dei Fiori-Montagnone anticline. The turbidite succession of the Laga basin was subdivided into three main allounits, Laga 1, Laga 2, and Laga 3, bounded by three unconformities and their correlative conformity surfaces, named I1, I2, and I3. Each of the three units show a fining and thinning-upward trend and they are stacked to form a succession with a clear forestepping pattern, reflecting the eastward migration of the basin depocentre induced by the Apennine thrust propagation. The sequence-stratigraphic interpretation of these deposits has allowed the three units to be framed in terms of 3rd- and 4th-order depositional sequences. Two 3rd-order sequences, namely Laga Depositional Sequence (LDS; uppermost upper Tortonian-lowerMessinian) and Cellino Depositional Sequence (CDS; upper Messinian- lower Pliocene), were recognized. The evolution of both the sequences was controlled by tectonic activity and climatic changes, and records an increased thrust activity followed by a slowdown of thrust motion and by a subsequent re-acceleration of the process. This work describes, in particular, the depositional and stratigraphic features of the LDS, which constitutes a thick turbidite complex where the main architectural elements of a fan can be recognized: from slope to basin floor passing through a channelized sector. Two main processes were considered as responsible for the generation of the turbidite flows: fluvial floods and submarine failures of variable volume. Both these processes were closely related to development of shelf margin deltas migrating basinward and landward, in connection to relative sea-level fluctuations forced by a variable combination of tectonics and climate changes.