Kimeryd i bonon z wierceń w Zarzęcinie

Abstract

KIMMERlDGIAN AND BONON IN IN BORE-HOLES AT ZARZĘCIN (TOMASZÓW BASIN)

The present authors have investigated the ammonite stratigraphy of the Upper Jurassic sediments pierced in the bore-holes Zarzęcin 1 and Zarzęcin 3 (south-western flank of the Tomaszów Mazowiecki syncline, Central Poland).

In the sediments of the upper Kimmeridgian (Aulacostephanus pseudomuta bilis zone) there occur: Aulacostephanus sp., ? Torquatisphinctes sp:, and subordi-nately, Haplacerataceae. In the strata having about 2 m in thickness, a little below and a little above the highest point of occurrence of Aulacostephanus sp., the Virgataxioceras sp. form appears.

In the lower Bononian sediments occurs Subplanites sp., and, subordinately Haplocerataceae, as well. Moreover, several fragments of ammonites have been found here, probably belonging to the genus Pseudovirgatites.

Within the lower part of the middle Bononian two subzones have been distinguished. In the lower subzone there occur ammonites resembling the form Perisphinctes miatschkoviensis of A. Michalski (1890, Plate 9, Fig. 10) and forms of the species Zaraiskites scythicus (Vischn.), the virgatotome ribs of which disclose but three pairs of secondaries.

In the upper subzone, Z. zaraiskensis (M i ch.), Z. quenstedti (R o u i l l.) and forms of the species Z. scythicus occur, the virgatotome ribs of which have 3, 4 and ,5 pairs of secondaries. In addition, one fragment of ammonite has been found, probably belonging to the genus Wheatleyites.

The upper boundary of sediments being referred to the lower part of· the middle Bononian, is an erosional one. Above this boundary, the Neocomian deposits occur.

When considering the palaeogeographical problems, the authors stressed, inter alia, a marked similarity existing between the upper Kimmeridgian and Bononian ammonite fauna of Poland and the contemporaneous ammonite fauna of Russia.