From electromagnetic to sediment textural maps: an integrated approach to unravel the intra-point-bar variability of sediment properties

Abstract

Sedimentary sand bodies that originated by the evolution of meandering channels such as point bars, host surficial aquifers, providing preferential pathways for groundwater flow in mud-dominated floodplains. These aquifers are a major source of freshwater, yet they can suffer from different environmental issues such as pollution and salt-water intrusion, which can critically damage agriculture and socio-economical activities. Understanding the internal architecture of point-bar bodies is essential to plan proper aquifer management and address environmental issues in coastal plains. To provide a spatially extensive, cost-effective characterization of point-bar body architecture, this work proposes a multidisciplinary approach to investigate geophysical and sedimentological data through statistical analyses, with an application to two palaeo-meanders in the Venetian Plain, Italy. In this setting, point-bar deposits mainly consist of fine to coarse sand and display lower electromagnetic conductivity values compared to the surrounding muddy overbank deposits. Statistical multivariate analyses on sedimentological and geophysical properties overcome the qualitative direct dependence of electromagnetic conductivity on sediment grain size alone, highlighting a stronger relationship with sediment sorting. By calibrating this relationship on a reasonable number of samples representative of the different depositional bodies, this methodology finally provides maps of sediment textural properties at the meander scale.