Comprehensive analysis of gastropod species in the loess-paleosol sequence of Sa’dabad-3, Gorgan, Iran

Through the examination of land snail shells embedded in the loess-paleosol succession of Sa’dabad-3, this research provides a valuable perspective on past environmental changes and contributes to a better understanding of Quaternary climatic fluctuations in northern Iran. A total of 12,910 mollusk shell specimens were collected from 230 samples taken at 10 cm intervals along the 23-meter-thick Sa’dabad-3 loess–paleosol section, and identified to species level via morphological examination. Although no direct geochronology was performed, the undated Sa’dabad-3 sequence was correlated with dated loess-paleosol sections at Now Deh and Agh Band to establish an approximate chronological framework. In total, 37 land snail species were identified, 16 of which are newly recorded for Golestan Province. Seven malacological zones were distinguished based on stratigraphic variations in mollusk abundance and diversity, reflecting alternating glacial (loess deposition) and interglacial (paleosol formation) intervals. Paleosol layers generally yielded richer assemblages, with a higher proportion of hygrophilous (moisture-loving) species, indicative of relatively warm, humid climates, whereas loess layers mostly contained fewer shells and reflect colder, drier conditions. However, a few exceptions to this pattern were observed, likely due to local taphonomic or microenvironmental factors. By correlation with regional loess records, the Sa’dabad-3 succession is inferred to span from Marine Isotope Stage 7 (~250–300 ka). The Sa’dabad-3 land snail shell assemblages represent valuable proxies for Quaternary climate reconstruction in northern Iran. These findings demonstrate the effectiveness of land snails as paleoenvironmental indicators and underscore the importance of integrating malacological data into multi-proxy climate studies.