PROSPECTS FOR THE INFRAZONAL (MICROSTRATIGRAPHIC) SUBDIVISION OF SEDIMENTARY STRATA

Recent stratigraphic investigations imply that the microstratigraphic or infrazonal subdivision of ancient strata is feasible in the nearest future. Intrazonal markers of short-term events of the past include b iotic, paleomagnetic, lithologic, paleoecologic, paleoclimatic, cyclic , and eustatic ones. These markers constitute a system of stratigraphi cally interchangeable markers (SIM), which allow us to subdivide zones into finer units of a different (usually regional and, in some cases, subglobal) scale. Their duration is estimated at tens or hundreds of thousands of years. A hierarchy and a nomenclature for the microstrati graphic units are suggested. Some examples of infrazonal subdivision ( in particular, Cenozoic studies of the North Pacific) are given.