Ambiguities in conchostracan biostratigraphy : a case study of the Permian–Triassic boundary

In recent years, conchostracan biostratigraphy has become a popular tool for the recognition of the Permian–Triassic boundary and for the chronostratigraphic subdivision of the Triassic in intracontinental settings, including also the bone-bearing Keuper strata of Poland. The ambiguous nature of the new bio-chronostratigraphic approach was characterized in a case study of the Permian–Triassic boundary interval. The most important problems were: (1) the lack of documentation of the index species, (2) the indirect correlation with the conodont stratigraphy in marine reference sections through the sporomorph spectra, (3) the lack of definition and documen- tation of supporting palynologic zones, and (4) difficulties in reliable taxonomic determination of Conchostraca. Testing and, if necessary, revision of the zonation by several independent research groups is suggested.