Reconstruction of Mamontov – Baraniy Valley-Gully System Development (Bratsk Reservoir): First Results
O. A. Mazaeva, A. A. Rybchenko, E. A. Kozyreva, V. A. Pellinen, A. A. Svetlakov, Y. S. Tarasova
The study is aimed to distinguish the of erosion and accumulation stages in primary erosion forms in the periglacial zone. Mamontov – Baraniy valley-gully system located on the right bank of the Unga bay in forest-steppe territory of Lena-Angara plateau. The gullies cut interbedding loess-like loams and sandy loams of 5–10 meters.
The research is based on detailed stratigraphic research of deluvial-proluvial sediments in the 3 sections of bottom gullies combined with AMS radiocarbon dating of buried soil horizons and faunal remains. The intervals were identified, where the composition, microstructure and sediment properties (particle size analysis, the content of aggregates, organic carbon, carbonates, water-soluble salts, and etc. are different or change dramatically. Change in the content of particle-size fractions in the section also evidences of changes in the conditions of sedimentation, and the presence of buried soil horizons speaks of process stabilisation.
Mamontov – Baraniy valley was formed in Karginsky or Sartan age. By the Atlantic time, a new gully erosion incision had cut (had formed in) through the deluvial-proluvial sediments of the primary valley of Mamontov gully and then it began being filled. There were distinguished 5 cycles of erosion- accumulation processes, dating to the Late Atlantic and Suboreal time.
Two stages of soil formation were distinguished by filling the primary valley of Mamontov gully: the top of the lower soil layer is dated 14 382±771 years ago (NskA-00856 uncal).
In deluvial-proluvial sediments of the Baraniy gully, one soil horizon was exposured, which bottom at the depth of 1,85 m is dated 25 993±503 years ago (NskA-00860 uncal).
bottom gully, deluvial-proluvial sediments, erosion-accumulation cycles, radiocarbon dating
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