The•Silurian biostratigraphy of Poland based on graptolites

Abstract

The present state of knowledge of deposits of the SiIurian system in Poland is reported, mainly on borehole data, while their biostratigraphy is based on graptolites. The descriptions of the Silurian deposits follow the regional subdivision of Poland into the particular structural units. The rich graptolite fauna they contain permits the whole Silurian system of Poland to be subdivided into zones. These have been defined according to the binding rules. A total! number of 42 zones has been distinguished in the Polish Silurian. Out of these 12 belong to the Velentian, the youngest of them being separated into two subzones; 8 zones characterize the Wenlockian; 13 the Ludlovian, 4 of them forming one index horizon; 9 the Post-ludlovian, with one horizon which can be more accurately defined after its graptolite fauna has been worked out in greater detail. The standard subdivision of the Silurian system, including tone Ludlovian, used in the present paper, follows the international rules. Deposits younger than the Ludlovian but older than the Gedinnian, without an officially recognized stratotytpe or name, are here referred to under the name of Postludlovian. The correlation of the Polish Silurian deposits with other, but only neighboring areas, shows that the Polish profiles contain a complete stratigraphic sequence, particularly in the graptolite fades. Here and there it even passes into the Lower Devonian (Gedinnian) and this makes Poland a region of paramount importance in the study of the evolution of graptolite faunas.