Geophysical investigations unravel the vestiges of ancient meandering channels and their dynamics in tidal landscapes

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.

Tidal currents and wind waves controlling sediment distribution in a subtidal point bar of the Venice Lagoon (Italy)

“…B) suggests that lateral shift of the channel occurred under aggradational conditions (cf. Brivio et al ., ; Boaga et al ., ), that allowed the bar brink to rise upward of about 1·0 m over a lateral shift of ca 45·0 m. Lateral migration of the channel was, therefore, associated with a progressive growth of its cross‐sectional area, which adapted to the increased tidal prism (cf. Rieu et al ., ; D'Alpaos et al ., ; Stefanon et al ., ), that affected the area over the last two centuries (D'Alpaos et al ., ).…”

Point-bar brink and channel thalweg trajectories depicting interaction between vertical and lateral shifts of microtidal channels in the Venice Lagoon (Italy)

“…cm/yr) marshes host a complex network of slowly-migrating (i.e. cm to dm/yr) meandering channels (Allen, 2000;Fagherazzi et al, 2004;Gabet, 1998;Garofalo, 1980;Hughes, 2012;Marani et al, 2002), whose sedimentary and architectural features are still relatively unexplored (Boaga et al, 2018;D'Alpaos et al, 2017;Ghinassi et al, 2018a). The present work focuses on meander bends of the Venice Lagoon providing the first description of different styles of bar brink and channel thalweg trajectories in order to improve our understanding of tidal point-bar evolution and architecture.…”

Inversion of Multiconfiguration Complex EMI Data with Minimum Gradient Support Regularization: A Case Study

“…Introduction. Frequency-domain electromagnetic induction (EMI) methods have been used extensively for near-surface characterization [23,32,30,29,25,45,4]. The typical measuring device is composed of two electric coils (the transmitter and the receiver) that are separated by a fixed distance and placed at a known height above the ground.…”

“…Recent devices are endowed with multiple receivers (multicoil) or use alternating currents at different frequencies as probe signals (multifrequency). Because of their availability, and with the development of efficient inversion algorithms and powerful computers, EMI data are increasingly used for reliable (pseudo) three-and four-dimensional quantitative assessment of the spatial and temporal variability of the electrical conductivity in the subsurface [4,11]. These data are usually collected with both ground-based and airborne systems [26], and they have begun to be used not only to infer the soil conductivity but also to determine its magnetic permeability [14,10,7].…”