Chrono-spatial modelling of deltaic progradation: timing the evolution of the Po delta Spina lobe (ca. 750 BCE–700 CE)

Deltaic progradation, the seaward extension of deltaic landforms, is a highly complex geomorphological process shaped by interacting natural and anthropogenic drivers throughout the late Holocene. Deciphering the temporal dynamics of deltaic evolution is essential not only for reconstructing past environments but also for assessing coastal risks and predicting future responses to climate change and human pressures. Focusing on the Po Delta, this study presents a detailed chronological analysis of progradation during the first millennium BCE, a period marked by profound environmental and cultural transformations across the Mediterranean. To achieve this, we developed an innovative Chrono-Spatial Modelling (CSM) approach, which integrates high-resolution geomorphological and archaeological datasets with Bayesian age-distance modelling. This method enabled the identification of five distinct progradational systems and the precise dating of 176 beach ridges, revealing a progressive acceleration in progradation rates from the early Roman period (ca. 300 BCE–476 CE). Notably, this temporal shift aligns with escalating anthropogenic pressures, including widespread deforestation, agricultural intensification, and hydrological modifications in the Po River basin, suggesting a gradual yet decisive transition toward a human-dominated sedimentation regime, though natural factors remained influential. Beyond refining existing palaeoenvironmental hypotheses, our approach provides unprecedented spatial resolution of ancient deltaic systems and new perspectives on human-environment interactions in antiquity. Moreover, the CSM framework is readily transferable to other deltaic systems worldwide, offering a powerful tool for quantifying progradation rates and disentangling the relative contributions of natural and anthropogenic forcing over time.