<p>This study aims to evaluate the geoheritage potential of the Karacabey Floodplain Forest (Longoz), located in the Marmara Region of Türkiye, through paleoecological and geochemical archive data. As the largest floodplain forest in the country, Karacabey Longoz represents a typical delta–lagoon–flooded forest system and stands out as a rare wetland ecosystem that chronologically records both natural and anthropogenic processes in its stratified sediments. A 24&#xa0;cm sediment core extracted from Poyraz Lagoon was analyzed for pollen content, revealing ~ 250-year vegetation and climate change record from a paleoenvironmental perspective. Surface sediment samples from Dalyan Lagoon were examined for heavy metal concentrations and environmental risk indices, indicating significant pollution pressure from industrial and agricultural sources. Using the layered assessment framework developed by Semeniuk and Semeniuk (<i>Hydrobiologia</i>, 708(1), 45–67,&#xa0;<CitationRef CitationID="CR26">2013</CitationRef>), (<i>Australian Journal of Earth Sciences</i>, 66 (6),&#xa0;<CitationRef CitationID="CR27">2019</CitationRef>) for wetland geoheritage evaluation, the site was qualitatively analyzed across five criteria: representativeness, rarity, diversity, archival value, and conservation potential. Findings demonstrate that Karacabey Longoz should be preserved not only for its biological diversity but also as a geoheritage archive documenting environmental and cultural transformations.</p>