Terminal Distributary Channel Deposits in the Modern-Age Po Delta lobes, Adriatic Sea

River dominated deltas are characterised by a high degree of river channel and mouth switching, which tends to form several coeval or slightly diachronous delta lobes. An open question is weather the distinct spatial organization of distributary channels and their subaqueous counterparts affect the geometry of subaqueous delta lobes. We took advantage of the extremely high sediment supply of the Modern-Age Po delta system and of the good chronological control on its evolution to analyze in detail the delta lobe geometry and the presence of multiple terminal distributary channels. The very rapid outbuilding of the Modern-Age Po delta (up to 129 m/yr) occurred since the onset of Little Ice Age (ca. 1450 - 1850 AD) under anthropogenic forcing on the river regime and increasing supply driven by colder climatic conditions. A detailed reconstruction of the delta lobe evolution compiled using a dense grid of VHR Chirp-sonar profiles and historical maps allowed to identify two different types of depositional styles in the prodelta: a) shingled depositional delta lobes characterised by laterally-continuous seismic reflectors and showing evidence of variably-preserved flood deposits; and b) lobes with more pronounced mound shape on shore-parallel sections, and bi-directional downlap of internal reflectors, hosting a network of terminal distributary channels filled by massive sediment. The Po delle Tolle lobe outbuilding in the late XIX Century provides the best example of a network of partially preserved shallow-water terminal distributary channels extending to water depths of as much as 25 m. The channel-like features have erosional base, acoustically-transparent and lithologically homogenous fill and likely reflect multiple stages of reactivation. These features occur isolated or in clusters with individual channel widths ranging from 100-300 m and depths up to 4 m. The short-lived episodes of cut-and-fill are hypothetically attributed to episodic events of catastrophic reactivation of distinctive Po river branches driven by sudden increases in river discharge of natural or artificial origin.