OSL Chronology And Stratigraphic Subdivision Of Loess-Paleosol Sequences In The Azov Region Of Russia Since Late Quaternary

Extensive distribution and continuous deposition of the Quaternary loess in areas of Eurasia are suitable for reflecting changes in the global palaeoenvironment and evolution of the palaeoclimate.Research on the loess chronology and stratigraphy in this region is conducive to understand the process of environmental evolution in different geological periods under the background of westerly wind circulation.Across the widespread Eurasian loess belt,particular interest and much attention have been given to the Sea of Azov because of its special geographic location and unique sedimentary environment,making it ideal for research of the Quaternary palaeoclimate and palaeoenvironment.However,using various climatic proxies,such as rodent fauna,pollen and polarity changes in the Earth's magnetic field,the stratigraphic subdivision and chronological framework in the Azov region are to some extent based on the correlation of relative chronology.High resolution and detailed dating studies have rarely been used to obtain a systematic chronology sequence in this area.It is exactly that the scarcity of chronologies across the Sea of Azov has limited the interpretation of climatic and environmental information in the East European Plain.As a result,the establishment of a detailed and systematic chronology have become particularly important.For these reasons,the aim of this study is to establish a reliable and systematic chronological framework for two loess-palaeosol sequences(Beglitsa and Chumbur-Kosa)in the Sea of Azov using optically stimulated luminescence(OSL)dating techniques and multi-proxies.With the aid of these OSL dates and various climatic proxies(magnetic susceptibility,grain size,soil color index,calcium carbonates and total organic carbon),the stratigraphic subdivision of two loess-paleosol sequences in the Azov region of Russia since late Quaternary has been implemented.On these basis,a comparison of the stratigraphic composite of the Beglitsa and Chumbur-Kosa section has also been made with other sections around the Azov region.Finally,a succession of palaeoenvironments over the last interglacial-glacial macrocycle in the Sea of Azov has been revealed.Here we present the main conclusions of this study:The optically stimulated luminescence dating of medium-grained quartz could be used to obtain a set of chronologies and is suitable for establish an independent time scale since late Pleistocene in the Sea of Azov loess.Results showed that the single-aliquot regenerative-dose with the standard growth curve protocol performed well in the sensitivity correction and avoided the effects of signal accumulation caused by irradiation,heat and measurement procedures on the signal aliquot.Furthermore,a series of tests and internal checks,such as preteat plateau and dose recovery test,have indicated that the SAR protocol is appropriate,giving confidence in the reliability of measured OSL ages.With a span ranging from 5.4±0.4 to 203.8±18.0 ka of the Beglitsa section and 22.2±1.9 to 76.0±6.4 ka of the Chumbur-Kosa section,deposition of the Azov loess may have begun at least during the last interglacial-glacial macrocycle.OSL ages are stratigraphically consistent with lithological units and no age inversions were apparent,and most of the dates make sense within their local stratigraphic contexts and show a good consisitency.However,due to some ages beyond the maximum age of quartz OSL dating,these dates should be treated with caution for any further explanation in future research.At least the older age estimates should probably be regarded as only minimum ages in case of the occurrence of age underestimation.Further methodological studies should be conducted in the future.A integrated investigation of luminescence dating and climate proxies has given us the confidence to conduct the stratigraphic subdivision of loess-paleosol sequences in the Azov region of Russia since late Quaternary.We briefly presented the stratigraphic compositions of these two section here: depth 9~5.5 m of the Beglitsa section and 4.8~2.8 m of the Chumbur-Kosa section belong to the last interglacial paleosol S1,depth 5.5~1.2 m of the Beglitsa section and 2.8~1.4 m of the Chumbur-Kosa section is the last glacial loess L1.Moreover,the Holocene paleosol S0 accounts for the depth 1.2~0 m of the Beglitsa section and 1.4~0 m of the Chumbur-Kosa section,respectively.Based on a comparative analysis of the stratigraphic composite,the sedimentary thickness differences between sections during the last interglacial-glacial macrocycle in the Azov region were likely affected by the local topography and the section location.As a whole,a general trend is characterized by the warm and wet climate transiting to the cold and dry climate from the earlier towards later stages of the late Quaternary in the Sea of Azov.