Depositional and tectonic evolution of the lower–middle Messinian Laga Basin (central Apennines, Italy): controls on channel–lobe relationships in a structurally confined turbidite basin

This study presents an integrated synthesis of the sedimentological, stratigraphic, and compositional characteristics, as well as the tectono-sedimentary evolution, of the lower–middle Messinian deep-water turbidite successions of the Southern Laga Basin (SLB), representing the final depocenter of the Marnoso-arenacea foredeep in the central Apennines. The analysis is based on the integration of previous datasets with new stratigraphic-sedimentological surveys (more than 100 sections for a total thickness of ~20 km) and correlation panels, allowing the reconstruction of the depositional architecture of a 3000 m thick turbidite complex that represents the deep-water sedimentation of a high-rank composite depositional sequence named the Laga Depositional Sequence (LDS). The latter consists of five low-rank sequences (Laga 1a, b, c, d, and Laga 2), organized into lowstand, transgressive, and highstand systems tracts, that in turn are characterized by the presence of several turbidite systems organized in forestepping and backstepping stacking patterns. The turbidite architecture elements include channels, channel–lobe transition zones, and basin-floor lobes, whose distribution and geometry are primarily controlled by depositional gradient, variations in sediment supply, and tectonic activity. The results highlight that, in tectonically active margin settings such as Apennine foreland basins, stratigraphic cyclicity and turbidite sedimentation are predominantly controlled by allogenic factors, such as tectonic and climate. The analysis of sedimentation and subsidence rates indicates comparable values (≈0.9–1.5 mm yr-1), with systematic variations between channel and lobe zones and among different systems tracts, reflecting changes in sediment supply, subsidence, and paleobathymetry. Basin evolution shows a progressive reduction in water depth and a transition from confined to semi-confined conditions, ultimately leading to basin infilling. From a tectonic perspective, basin configuration and evolution are strongly controlled by the propagation of thrust systems, which generated a complex seafloor topography and influenced both stratigraphic organization and facies distribution. The result of this study is significant because it describes an example of an internally deformed wedge recording the transition from a foredeep to a wedge-top depozone. It also provides a high-resolution, basin-scale stratigraphic dataset, which is uncommon for complex turbidite systems and demonstrates that classical sequence stratigraphic models, largely based on eustatic controls, are insufficient along tectonically active margins. It also contributes to a better understanding of confined turbidite systems, which are inherently more complex and less predictable than those of continental passive margins.