Występowanie tufitów w kredzie pod Siedlcami

Abstract

OCCURRENCE OF TUFFITES IN THE CHALK NEAR SIEDLCE

The occurrence of tuffites in deposits of writing chalk in the bore hole at Żebrak near Siedlce is the first instance of these sediments being discovered in the Polish Lowland. The stratigraphical position of this tuffite intercalation has been based on its foraminifer fauna. In view of both appearance and extent of individual species and complete associations of foraminifers, the authors ascertained that this tuffite appears in the top part of the Lower Maestrichtian. The principal form charactering this horizon is Pseudovalvulineria gracilis. The lower boundary of the Lower Maestrichtian is defined by forms terminating their extent in the highest Campanian, i. e. Stensiöina annae and Stensiöina exsculpta.

On the basis of their preliminary observations the authors assume that the tuffite has here been formed by sedimentation and by submarine weathering of pyroclastic material which might have been airborne from even far distances.

The occurrence of tuffites in bore hole Żebrak near Siedlce should not be looked upon as a separate occurrence; such deposits are likely to have a wider spread although, at present, there is no evidence of it.

Deposits of volcanic origin are also known from Southern and Central Poland, in Poland they appear within the range from the Campanian to the Danian - Palaeocene.

Thus, in view of the status of investigations of tuffites , heretofore carried out in the Cretaceous of Poland, it is not advisable to utilize these intercalations at stratigraphical index horizons.