Biostratygrafia i zasięg form przewodnich górnej kredy w Polsce

Abstract

BIOSTRATIGRAPHY AND EXTENT OF INDEX FORMS OF THE UPPER CRETACEOUS IN POLAND

The subject of this paper is the stratigraphy of the Upper Cretaceous in Poland, on the basis of material obtained from bore holes, here are presented the most important only, and the most frequently encountered index forms, on which the stratigraphy in the investigated bore holes has been based.

The chief purpose of this paper is, besides presenting index forms, to call attention to the intertonguing of individual species representing different stratigraphical horizons. The author points out that sharply cut faunal boundaries between such horizons are found only, when a change in fauna takes place or a break in sedimentation occurs. However, where no change is observed, the fauna is clearly intertonguing. This symptom the author succeeded in ascertaining in a number of bore hole profiles.

In Poland, sharply defined boundaries have been found between the Albian and the Cenomanian, since almost on the entire area of Poland facial changes are being observed on this boundary. Similarly, fairly distinct is the boundary between the Cenomanian and the Turonian, since at this period too there may be observed, on littoral shallow areas, a marked shallowing of the sea and a partial change of facies. However, difficult to establish, on the basis of its fauna, is the boundary; between the Turonian and the Coniacian, since the Turonian and the Coniacian forms are distinctly intertonguing. Difficult too to define are the boundaries between the Coniacian and Santonian, Santonian and Campanian or campanian and Maestrichtian, owing to the fact that everywhere we are faced by a distinct inter-tonguing of index forms as presented in the attached table. Clearly defined is the upper boundary of the Cretaceous between the Maestrichtian and the Danian since at many localities we note changes of facies. At this boundary there abruptly disappear the belemnites, ammonites and inocerams.