Miejsce i rola litologicznych poziomów przewodnich w lito- i chronostratygrafii

Abstract

THE PLACE AND ROLE OF MARKER LITHOLOGICAL HORIZONS IN LITHO- AND CHRONOSTRATIGRAPHY Summary The process of replacement of the traditional uniform stratigraphical classification by the Hedbergian one is accompanied some adaptation difficulties. One class of these difficulties concerns the use of lithological markers for age correlation. Two examples are presented, both from the flysch of the Outer Carpathians. A recent proposal regards the Inoceramus Beds in the Skole unit as the Ropianka Formation, composed of four members. The member boundaries are accepted along isochronous marker beds, regardless of lateral changes in the lithological content of the members. Consequently, in some areas a boundary is placed where no lithological change occurs in the section. The members do not represent lithosomes and are chronostratigraphical, rather than lithostratigraphical, units. Marker limestone horizons in the Oligocene strata proved isochronous over great areas. Each horizon is distinguished by several thin limestone layers clustered in a very restricted stratigraphical interval. Within each horizon the limestone is subordinate with respect to its host rocks, which represent different facies in different areas. The importance of the limestone horizons in regional correlations provoked proposals of involving them in lithostratigraphical divisions as beds, members or member boundaries. However, the horizons are neither single beds, nor other lithosomes, nor do they separate lithosomes; they are instead chronohorizons. The misuses reflect the strong need for rock units with boundaries precisely correlatable in age over large areas regardless of the units' lithological and fossil contents. The ailing chronostratigraphy could recuperate by accepting regional and local marker-bounded units in. addition to the major global divisions, elegant but with boundaries hardly recognizable away of their stratotypes.