| dc.description.abstract | Quantification of the interaction between river discharge and tides is vital to characterize
fluvio-deltaic systems, to identify diagnostic elements of tidal signatures in the rock record,
and to reconstruct paleogeographies. In modern systems, even microtides can significantly
influence delta morphodynamics; yet, many fundamental processes, particularly in prodeltaic
settings, remain elusive. Here, by combining a unique process-product data set acquired
during a flood event of the Po River (Italy) with numerical modeling, we show that tidal signatures
are recorded in the open-water prodelta zone of a microtidal system. Based on the
analyses of box-cores collected before and after a flood off the main distributary channel, we
interpreted storm beds, tide-modulated flood strata of alternating normal and inverse graded
beds, and rapid bioturbation. Modeling of the river discharge indicates that, at the peak of
the flood, the steepening of the water-surface profile forced by 0.15 m lowering of sea level
during low tides generated an 8% increase in river flow velocity. The alternation of profile
steepness and associated cyclicity in flow strength during consecutive tidal cycles controlled
the sediment load of the plume and, consequently, led to the deposition of tidal-modulated
strata. Formation of microtidal signals appears to be enhanced in fluvio-deltaic successions
characterized by multiple distributaries and in basins where river floods are out of phase
with storm-wave activity. Bioturbation of sediment, which can start during the waning stage
of the flow, and erosion by storm waves hamper the preservation of tidal signals, unless rapid
burial occurs. The recognition of tidal-modulated strata in river-dominated settings may facilitate
the characterization of mudstone reservoirs and reconstruction of paleogeographic
conditions during deposition. | en_US |
