The stratigraphic position of archaeological sites in the Angara valley (territory of flooding by the Boguchany Dam reservoir)

The extensive work of the Boguchany archaeological expedition at the inundated territory of the Angara River valley with the water storage reservoir of the Boguchany Dam (360-km zone from the dam of Kodinsk) made it possible to carry out geoarchaeological and paleontologic-stratigraphic investigation in 2009-2012. The resultant information indicated that the sections of the low above-floodplain terraces (AFT) were represented by alluvium, aeolian deposits, and formations of the colluvial genetic series: solifluctional, defluctional, deluvium, landslides, taluses, and rockfalls. Artifacts often occur among disorganized rock blocks: large-sized seismogenic rockfalls onto the floodplain or onto the AFT. Almost all sites (over 20) are confined to the first and second (the upper part) AFT of the Angara, thus allowing to date the most part of cultural layers to the Holocene. The detailed section descriptions and the geomorphological analysis allowed stating that in the studied area the relative height of the first AFT is from ~ 7 to 9 m. The representative sections are situated at the following sites: Derevnya Pashina, Bolshaya Pelenda 1 and Igrenkina Shivera. The transition to the overlying geomorphological level is expressed as a scarp in the relief (4 - 5 m). The relative height of the second AFT is from 12 to 20 m (on the average, ~ 14 m). Such a variation is explained by the fact that the edge part of the second AFT is significantly eroded, and its surface is often complicated by large dunes. The representative sections are situated at the sites Shivera Prospikhino and Medvezhiy Utyos. The wide occurrence of the second AFT allows considering its subaerial stratum as perspective for searching the stone industries of the final Paleolithic. The correlation of the studied sections is complicated by the fact that the surfaces of the coeval AFT may be located at different relative heights. This is connected with the hydrological regime, aeolian activity, permafrost degradation, and neotectonic movements along the faults intersecting the Angara valley. Certain evened platforms of seismogravitational formations can be mistaken for AFT. The separation of these bodies from the terrace complex presents a vital problem in spite of the fact that in the Angara valley, there are known massive and giant seismic rockfalls, blocky landslides and seismites, i.e. the secondary seismogenic deformations of the vibration type. All the aforesaid bears witness to the high seismicity of the region at the end of the Pleistocene - Holocene, when the conditions were developing for the formation of stony dams and dammed lake basins. These natural water reservoirs formed sustained levels of the local sedimentation basins resembling the AFT. The problem of the ancient people's settlement of the Angara basin is directly linked with the reconstruction of ecological connections (both biotic and abiotic). The high neotectonic activity and the geologic structure as a whole define the favorable usefulness of the geochemical landscapes of the studied territory. This seems to explain the multiplicity of archaeological sites and the simultaneous absence of large sites of the Pleistocene megafauna.

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