Geoheritage, Sedimentary Controls and Shoreline Change in the Somone Lagoon–Estuary Complex (Senegal): Remote-Sensing and Machine-Learning Projections to 2050

Lagoon–estuary complexes are dynamic sedimentary archives in which shoreline mobility and human pressure affect both coastal function and geoheritage. We integrate 14 sediment cores, a quantitative assessment of seven geosites (Brilha method), eight Landsat and Sentinel-2 shorelines (1984–2025) analyzed with the Digital Shoreline Analysis System (DSAS), and a Gradient Boosting machine-learning model for the Somone lagoon–estuary complex, Senegal. Four compartments were distinguished: sector A (southern coastal spit) shows accretion, sector B (tidal inlet and main-channel margins) critical erosion, sector C (mangrove-fringed lagoon banks) rates within measurement uncertainty, and sector D (northern open coast at Guéréo), moderate erosion. The model, validated by five-fold cross-validation grouped by transect, yields a mean absolute error of 0.59 m yr−1 and a coefficient of determination of 0.54. Its 2025–2050 baseline projects continued accretion in sector A and retreat in sectors B and D, with sector B the main retreat hotspot. A sea-level sensitivity layer based on Shared Socioeconomic Pathways (SSP2-4.5, SSP5-8.5) and the Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC AR6) provides conditional screening, not deterministic forecasts. Shoreline exposure, degradation risk and anthropogenic pressure are kept separate, to support geosite conservation planning.