Earth’s Cryosphere, 2011, Vol. XV, No. 3, p. 20-30
ANCIENT ALAS COMPLEXES OF NORTHERN YAKUTIA (PART 2)
T.N. Kaplina
Industrial and Research Institute for Engeneering Survey in Construction, 105187, Moscow, Okruzhnoi pr., 18, Russia, tatianakaplina@mail.ru
The ancient buried Alas Complex in cross-sections of the high Yedoma level on the shores of the Dmitri Laptev Strait is described. This Complex is compared to earlier described Alas Complexes in cross-sections of Duvanny Yar on Kolyma and Achchagyi–Allaikha on the left bank of the Indigirka river. The ancient Alas Complexes possess common structural features. The taberal formations are commonly found at the base of the sections while the alas accumulations occur in the upper part of Alas Complexes. Systems of pseudomorphs of ice wedges are commonly found along the boundaries of these formations. Thus, the structure of the ancient Alas Complexes is similar to the structure of the Holocene Alas Complexes. The ancient Alas Complexes as well as the Holocene Ice Complexes have resulted from the lake thermokarst followed by sedimentation in the alases. In all considered cases the emergence of the ancient Alas Complexes was associated with dramatic environmental changes indicated by the transformation of vegetation from tundra-steppe into humid tundra and even into taiga. This environmental transformation was primarily caused both by some temperature rise and by replacement of a regime of insufficient precipitation by one of excessive humidity. The question of the age of the reviewed ancient Alas Complexes cannot be considered resolved. The most likely intervals of Alas formation and accumulation of deposits in these Alases are the early-karginsky (MIS-3, Duvannyi Yar) and the kazantsevsky (MIS-5, Allaikha and the Dmitri Laptev Strait).
Key words: Northern Yakutia, Pleistocene, ancient Ice Complex, thermokarst, ancient Alas Complex.