Rubble-gravel yedoma with rock debris inclusions and penetrated of large syngenetic ice wedges in sections Phoenix and Utinoye, Magadan Region

The aim of this work is to study the rubbly yedoma, which contains rock debris inclusions and large syngenetic ice wedges, in the Phoenix and Utinoye sections in the Magadan region. These deposits are located in the southeastern part of the Polousnensky-Verkhnekolymsky mountain range. In the area there is a sharply dissected low-mountain relief with absolute peaks ranging from 700 to 1,000 meters and relative heights of 200 to 500 meters above the valley floors. Terraces with heights of 4-6, 10-15, 20-25, and 35-40 meters are in the valleys. The geological structure includes rocky and clastic rocks of the Permian, Triassic, and Jurassic ages. The bedrock consists of clayey and sandstone-clay slates, and tuff with pyritized quartz veins. This area belongs to the North Okhotsk Province of the Boreal Floristic Region. The primary forest-forming species in the area is the Dahurian larch (Larix gmelinii). Other species that are present include Siberian dwarf pine, various species of alder, dwarf Arctic birch, and Siberian juniper. The soil cover is predominantly composed of light and dark podburs on gravelly-clay eluvial slate. The larch forests are characterized by taiga peat-humus soils, cryosoils, and mollisols situated within a zone of permafrost that has a thickness of at least 100-200 meters. Within these deposits and adjacent areas, layers of permafrost up to 15 meters or more have been found. These layers are composed of gravelly-bouldery sandy loams and clays with thick ice wedges. The ice complexes that were uncovered in the Phoenix and Utinoye sections started to form between 45 and 40 ka BP and completed their accumulation around 12.9 ka BP. The δ¹⁸O values in the late Pleistocene syngenetic ice from the upper part of the Phoenix section range from −30.4 to −32.6‰, while in the lower part of this section and the Utinoye section, these values are significantly higher, ranging from −25.7 to −27.7‰ and −24.9 to −29.3‰, respectively. This finding suggests steep winter temperature drop during the final stages of the formation of the rubble-yedoma with rock debris inclusions and large syngenetic ice wedges in the Phoenix and Utinoye sections in the Magadan region.