BARASH M.S., DMITRENKO O.B., KAZARINA G.Kh., KRUGLIKOVA S.B.,MUKHINA V.V.,
STRATIGRAPHY OF QUATERNARY OCEANIC DEPOSITS
Quaternary oceanic deposits is the most suitable object for perform¬ing Quaternary stratigraphy as they often contain continuous record of all environmental changes. For this purpose several methods are used: paleomagnetic, oxygen-isotope, micropaleontological climate ... [Show full abstract] stratigraphic and paleotemperature, and also age estimates and zona- tion subdivision on the basis of evolutionary changes in fauna and flora composition. Magnetic-reversal scale distinguishes only five levels the upper one (the Bruhnes boundary, 0.73 m.y.) often being beyond stratigraphic limits of analysed cores. Oxygen-isotope and all climate stratigraphic methods, including micropaleontological paleotemperature one, can be used only for complete sequences with high sedimentation rates and good reservation of micropaleontological
units, without redeposition, with high frequency of sampling. In case one of the requirements is not observed considerable stratigraphic errors cam occur.
Evolutionary changes in oceanic microplankton composition - appear¬ance and extinction of species - correlated with geochronological scale allow to detect datum levels. 140 datum levels, migration including, are recognized in four microplankton groups (foraminifera, coccolithophorids, diatoms and radiolarians) for 2 my. Correlation is established between changes and geomagnetic field inversions. The greatest frequency of changes is recorded at the base of the Olduvai event (23 levels /0.1 m.y.) and at the base of the Bruhnes epoch (17 levels /0.1 m.y.) which supports the position of the Pliocene- Quaternary boundary at the base of the Olduvai and supports the division of the Quaternary into two parts. Datum levels are limited in space and, probably, globally diachronous. The accuracy of bio- stratigraphic zonation (usually, hundreds of thousands years) is not sufficient for the Quaternary which is characterized by strong and short changes in the environment.
Despite distinct achievements in methods of stratigraphical division of Quaternary oceanic deposits each of them is considerably limited. Further progress in Quaternary stratigraphy is possible only in case all methods are developed and used comprehensively.