INTEGRATION OF DIFFERENT STRATIGRAPHIC METHODS APPLIED TO CLOSED BASINS (FROM THE EXAMPLE OF QUATERNARY CASPIAN SEA)

The difference of opinions concerning the location of stratigraphic divisions boundaries brings the necessity to use integration approach to stratification of sedimentary series. Particularly it is topical for closed basins like Quaternary Caspian Sea having an extremely unstable sea level response to short-term climatic changes. It led to frequent variations of qualitative, quantitative and substantial composition of paleobiocoenosis through the time. High-frequency sea level fluctuations have also been reflected in formation of high order depositional sequences that makes very important the application of sequence stratigraphy principles to Caspian Sea Quaternary sedimentary series. Present research combined the results of bio-, sequence-, chemo- and biogeochemostratigraphic methods applied to Quaternary deposits of the Caspian Sea. Analysis of 18O/16O values in molluscs shells shows the distinct difference in oxygen isotope composition of fossils from different stratigraphic units. These values are divided into three groups clearly coinciding with the Lower, Middle and Upper Pleistocene. Detail stratification of Pleistocene-Holocene deposits have been obtained from microelemental composition of fossils and enclosing them sediments. It has been established a good correlation between biostratigraphic and chemostratigraphic boundaries, which are confined to contact zones of Pleistocene horizons. Data of trace elements contents also allowed to stratify more detail some offshore sections of Quaternary sediments, that was not possible on the base of results of paleontological investigations. Studies of Pleistocene-Holocene deposits in different areas of the Caspian region give an opportunity to distinguish depositional successions of different order and define the chronostratigraphic boundaries. One can distinguish one sequence of forth order and seven small scale sequences, which are good corresponded to biostratigraphic units. From the example of Quaternary deposits of the Caspian Sea it is possible to say about a good correlation of various startigraphic methods applied to closed basins. Such regularity comes from strong climatic dependence both the changes of biocoenosis composition and rapid sea level fluctuations accompanied by formation of sedimentary series.