The objects of the study are massive ice bodies studied in the Mordyakha River valley and on the terrace of Seyakha River (Mutnaya) in the central part of Yamal Peninsula. The first site is located in the center of Yamal Peninsula (68°11ʹ18ʺ N, 68°51ʹ39ʺ E), at absolute elevation of 66-70 m, the second one is located 5 km to the north-west of the Bovanenkovo settlement (70°23.4 N, 68°19.4 E) at absolute elevation of 87 m near the Khanikosito lake. Stable isotope composition, ion composition, pollen and spores content were analyzed in detail. The main findings of the study are: a). The studied massive ice are of intra-ground type; b). One of the main sources of water, from which the massive ice was formed, were lake water and the water of the talik; c). During the formation of massive ice, there was a significant isotope fractionation, which led to the formation of layers with an isotope composition heavier than the original lake water.

Data was submitted and proofread by Yurij K Vasil'chuk and Lyubov Bludushkina at the faculty of Geography, department of Geochemistry of Landscapes and Geography of Soils, Lomonosov Moscow State University.