Abstract
Whether or not one can detect relict signatures of the past imprinted in current landscapes is a question of the utmost theoretical and practical relevance for meandering tidal channels, owing to their influence on the morphodynamic evolution of tidal landscapes, a critically fragile environment, especially in face of expected climatic changes. Unravelling the sedimentary patterns of ancient channels is an expensive process that usually requires high resolution sediment coring. Here we use a novel inversion process of multi-frequency electromagnetic measurements to reveal the signature and characterize the dynamics of a salt-marsh paleo-meander in the Venice Lagoon. We show that the ancient meander migrated laterally while vertically aggrading, developing a peculiar bar geometry which is less common in analogous fluvial meanders. The observed point-bar dynamics and the associated architectural geometry are consistent with remote sensing and borehole data and contrast with current assessments of tidal meander morphodynamics mediated from classical fluvial theories. In addition, the proposed technique, rapid and non-invasive, bears important consequences for detecting buried stratal geometries and reconstructing the spatial distribution of ancient sedimentary bodies, providing quantitative data for the description of landscape evolution in time.
Highlights
Branching and meandering tidal channel networks cut through salt-marsh landscapes and drive the exchange of water, nutrients and sediments within these landscapes
We show that the use a multi-frequency conductivity meter and the application of an innovative inversion technique of multi-frequency electromagnetic data allow one to unravel the geometry of a buried tidal point bar and related channel, which cut through a salt-marsh platform in the Venice lagoon (Italy), where saline soils are extremely conductive, representing a very challenging environment
Similar features and behaviors can hardly be appreciable in the fluvial setting, where lateral migration rates can be more than one order of magnitude larger than those documented for salt-marsh meanders[20,22,26,38,39], and only aggradation rates higher than 1.0 cm/yr are suggested to influence depositional dynamics[34]
Summary
Branching and meandering tidal channel networks cut through salt-marsh landscapes and drive the exchange of water, nutrients and sediments within these landscapes. The dynamics of salt-marsh platforms and of their channel networks are tightly intertwined e.g.3–6 while the channels drain and feed the marsh during the tidal cycle, governing water and sediment fluxes over the platform, the elevation of the marsh in the tidal frame, together with its extension, controls channel growth, maintenance, size and evolution[7,8,9,10,11]. Despite their importance in landscape evolution, tidal networks have received less attention than fluvial ones[12] in terms of the main morphometric characteristics of tidal meanders that are commonly studied following theories developed for their fluvial counterparts[13,14,15,16,17]. A possible approach, both fast and accurate, is provided by electromagnetic techniques that allow one to perform contactless measurements[31]
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