Impact of genesis and abandonment processes of a fluvial meander on geometry and grain-size distribution of the associated point bar (Venetian Plain, Italy)

Abstract

Sedimentary sand bodies originated by Holocene meandering fluvial channels are widespread in modern alluvial plains, and their planform morphometry and evolution can be easily detected from satellite images. Results from the combination of different approaches, including remote sensing, geophysical investigations and sedimentary cores contribute to understanding sedimentary facies distribution and reservoir connectivity of these deposits and provide a crucial contribution for developing models predicting fluid migration within them, with relevant implications for reservoir development and management. The present study focuses on a Late-Holocene meander bend of the southern Venetian Plain (Italy) and aims to analyse depositional patterns and grain-size variability of the related sedimentary bodies by integrating morphological evidence with geophysical and sedimentological investigations.The investigated paleomeander has a sinuosity of about 2.2 and is associated with a 15–20 m wide paleochannel. Electromagnetic surveys coupled with sedimentary core description allow depicting a 3D stratigraphy of the related point-bar that is characterised by low conductivity values (i.e., 0–40 mS/m) compared to the surrounding overbank deposits (i.e., 80–250 mS/m). Point-bar deposits form an arcuate shape, which started accreting from a newly-formed sinuous channel. Sedimentary cores revealed that point-bar deposits mainly consist of sands, with minimal vertical and lateral grain-size changes. Channel-fill deposits are mainly sandy and document a gradual abandonment of the channel, which caused a progressive decrease of the channel width. The residual channel is detectable from satellite images and appears to be disproportionally narrow in comparison with other morphometric features of the bend. Such a disproportion can be used to predict infill styles of meandering channels from aerial images. This work highlights how the genesis and abandonment processes of a fluvial meander bend can impact the geometry and sediment properties of the associated point-bar body.