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TitleTidal modulation of river-flood deposits: how low can you go?
AuthorMaselli, V; Normandeau, AORCID logo; Nones, M; Tesi, T; Langone, L; Trincardi, F; Bohacs, K M
SourceGeology 2020 p. 1-5, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190549
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
AreaPo River; Italy
Lat/Long WENS 11.6000 12.7000 45.2000 44.5000
Subjectssurficial geology/geomorphology; sedimentology; stratigraphy; fossil fuels; Nature and Environment; Science and Technology; fluvial systems; tides; tidal deposits; tidal environments; deltas; fluvial deposits; fluvial processes; discharge rates; floods; modelling; core samples; graded bedding; bioturbation; flow velocities; depositional cycles; storm deposits; paleogeography; petroleum resources; reservoir rocks; mudstones; depositional environment; hydrography; sediment transport; stratigraphic analyses; alluvial sediments
Illustrationslocation maps; satellite images; time series; profiles; geophysical images; plots; models
Released2020 04 17
AbstractQuantification 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.
Summary(Plain Language Summary, not published)
We combined a unique process-product dataset acquired during a flood event of the Po River (Italy) with numerical modeling. Low tides

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