Intense and quick land relief transformation in the Little Ice Age: The age of accumulative fan deposits in Serteyka River Valley (Western East European Plain).

In the rich of archaeological sites dated from the late Palaeolithic to the Modern Period region of the Serteyka River, deposits of an extensive accumulative fan were studied in detail. In the lower sector of the present-day Serteyka River valley, the strict chronology and depositional conditions of an extensive accumulative fan deposits were studied in detail. An important part of the project has been also: a checking of usefulness of luminescence, radiocarbon and lead methods of dating in determination of the age of inorganic deposits accumulation The 14C, optically stimulated luminescence (OSL), and 210Pb dating methods were used to determine the fan's deposition age. Then, we discussed the depositional conditions of the accumulative fan by the textural, geochemical, and palaeoecological analysis. The use of 14C and 210Pb methods of dating allows for elaboration of a reliable model of the evolution of slope processes occurring from the 2nd half of 17th c. AD to 2nd half of 19th c. AD (i.e. during the younger part of the Little Ice Age). It was a period of human induced deforestation, as confirmed by the first results of palaeobotanical analyses. In addition, four OSL dates have been obtained, but the acquired age significantly exceeded previous expectations. Three dates indicate the Neolithic period, and a chronological inversion of OSL dates can be seen. This may be due to incomplete bleaching of the sand grains during transport, which indicates that the material being transported had a relatively large volume. The lower deluvium of the accumulation fan is formed by the drainage of hydrated sediment (mudflows). Summarizing, slope sediments can be extremely difficult material for absolute dating. This may be due to the redeposition of the material, the hiatuses in deposition and incomplete bleaching of quartz grains. In the case of 14C (AMS) dating, the dependence is on the presence of plant macroremains within the studied material. In the case of slope deposits, there is a very high probability of the redeposition of organic material. Lead dating, on the other hand, has a small chronological range. Moreover, the dating of inorganic sediments with this method poses many problems, including of a methodological nature. In the tested accumulative fan, as a result of insufficient grain whitening and the short chronological range of the 210Pb method, the 14C method was the main analysis determining the age of inorganic sediments. [ABSTRACT FROM AUTHOR]