FACIES ARCHITECTURE AND LATE QUATERNARY PALEOGEOGRAPHY OF THE SINGLE-CHANNEL, LOW-SINUOSITY RENO RIVER (PO PLAIN, ITALY): IMPLICATIONS FOR LIQUEFACTION PROCESSES

Alluvial plains are highly sensitive to changes in sediment discharge and accommodation space and record a complex depositional history that reflects allogenic processes, including climate and base-level changes, and local autocyclic processes. This complexity is expressed by a high vertical and lateral facies variability and results in significant textural and compositional heterogeneity of the deposits. As a result, the development of reliable models to reconstruct the ancient stratigraphic architecture of alluvial plains is often difficult. In this regard, late Quaternary depositional systems offer well-preserved stratigraphic archives that allow for high-resolution stratigraphic reconstructions. In this study, we provide a detailed subsurface model from a selected sector of the southern Po Plain, along the single-channel low-sinuosity Reno River, which was affected by widespread liquefaction processes triggered by the 2012 Emilia-Romagna seismic crisis. We report a comprehensive sedimentological and CPT-based characterization of the subsoil, and investigate how the stratigraphy controls earthquake induced liquefaction phenomena. The facies associations composing the alluvial subsoil are represented by tabular-layered floodplain mud and peat, channelled coarse-grained sand, and wedge-shaped fine-grained sand and silt (levee), which constitute respectively the basic elements of the liquefaction system: host, source, and sedimentary cap. The subsurface distribution of facies associations suggests that vertical and lateral changes in stratigraphy control mode and location of liquefaction evidence at the surface. In particular, the relative thickness of fluvial channel bodies vs. channel levee deposits (source-seal couplet), and the discontinuities within source layers appear to control the severity of sand ejection.