A representative mollusc fauna attributed to the late phase of the Karginian Interstadial (MIS 3) has been found in the Bol'shoj Naryn Palaeolithic site (Fore-Baikal region). The general organization of the strata at the Bol'shoj Naryn site has been established through excavations realized during the previous field seasons. It shows a modern soil made of sandy loess deposits 1m thick, dated from the Sartan glacial stage, and underlined by a high viscosity paleosol layers which is up to 1m thick developed during the Karginian Interstadial. The "cultural layer" has been correlated with the upper Karginian soil contains numerous stone tools and animal fossils. This paper focus on the mollusc assemblage attributed to the upper Karginian sediment.The mollusc assemblage (2460 determined specimens) consists of six species and five genera of terrestrial molluscs. Succinella oblonga, Pupilla muscorum and Vallonia tenuilabris are the best represented species. The molluscs suggest the existence of landscapes corresponding with humid meadows and forests located in the relief depressions or along banks of the river. Molluscs of the Bol'shoj Naryn site have been compared with equivalent mollusc complexes from Siberian and Southern Fore-Uralian localities. They display a distinctive poverty in the species composition and show similarity with the complex of the Gornovo locality (Southern Fore-Urals region). Comparison of the mollusc complex from the Bol'shoj Naryn locality with molluscs from the last glacial period also showed similarity with the complex of the Gornovo locality (Kudashevo period in the Southern Urals - last phase of the Late Valdai equivalent MIS 2). The climatic conditions which prevailed in the surroundings of the Bol'shoj Naryn locality during the late phase of the Karginian interglacial period (32-25kaBP) of the Fore-Baikal region were cooler than those existing at the same time in Europe and Southern Urals. Correlation between the data obtained after malacological investigations and other paleontological data obtained from palynology and vertebrate records suggest a moderate cold and humid climate in the Fore-Baikal region during the second part of MIS 3, with predominance of open landscapes of steppes and relatively limited taiga forest, tundra, and wetlands.
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