A framework of ichthyofaunal ecostratigraphy of the Oligocene-Early Miocene strata of the Polish Outer Carpathian basin

Podstawa ekostratygrafii ichtiofaunistycznej osadow oligocenu-wczesnego miocenu basenu zewnetrznych Karpat Polskich The paper presents the results of an analysis of ichthyofaunal variability throughout the section of the Menilite-Krosno Series (MKS) in the Outer Carpathians of Poland. The studied tanathocoenoses were formed at the bottom of a more than 2,000 m deep northern basin of the Tethys, being largely represented by the continental rise and bottoms of its narrow furrows, and - to a lesser degree - the continental slope and slopes of a submarine high. Lateral variability of statististically representative assemblages of tanathocoenoses hosted in thin, isochro- nous horizons is interpreted as a result of both local changes of ichthyocoenoses and the influence of post-mortem relocation of fishes that mainly dwelled the shelf and upper continental slope. Vertical variability, in turn, is considered as a resulting from changeable conditions of the ecological environment, the input and outflow of taxa whose evolution proceeded in the Indo-Pacific area, and the species extinction. Changeability of ichthyofauna within a ca. 16-m.y.-long interval made it possible to document and formally describe 9 zones and 4 subzones of ichthyofauna of ecostratigraphic character. These zones comprise index, representative and accompanying taxa that belong to different ecological groups. Conceptual models of the origin of ichthyofaunal assemblages of individual zones are presented. It is suggested that the origin of assemblage differentiation resulted from the appearance and disappearance of the oxygen minimum zone in the water column, global and local sea level changes, topography of the basin bottom, as well as final basin infilling by sediments of submarine fans. The described and preserved collection of fossil Carpathian fishes, housed at the Department of Palaeozoology of the University of Wroclaw, requires further specialized palaeontological studies in order to reconstruct a more complete composition of the Oligocene-Early Miocene ichthyofauna.