Wybrane problem statygrafii i sedymentacji liasu między Świnoujściem a Gryficami

Abstract

SELECTED PROBLEMS OF LIASSIC STRATIGRAPHY AND SEDIMENTATION IN THE AREA BETWEEN ŚWINOUJŚCIE AND GRYFICE (NORTH-WEST POLAND)

Summary

A lot of new drillings made in the area of the Odra river mouth (Fig. 1) have yielded interesting data on the stratigraphy and sedimentation of the Liassic deposits, mainly of the Pliensbachian ones. These deposits are found in an area which was a fragment of the central furrow of the basin, and of the south-western margin of this furrow. Both the development of these deposits and the location of ammonite fauna sites are shown in Fig. 2.

The ammonites evidence some zones and subzones of Carixian and Domerian (Tab. 1). In the Carixian there are found, beyond a doubt, the following subzones: Uptonia jamesoni sensu stricto, Beaniceras luridum, Acanthopleuroceras valdani, in the Domerian, in turn - of the subzone Pleuroceras apyrernum. Conditienally, there are noted the subzones Platypleuroceras brevispina and Polymorphites polymorphus. There is a lack of faunistic evidences for the subzones Phricodecaras taylori and Tropidoceras masseanum and for the zones Prodactylioceras davoei and Amaltheus margaritatus. In the Upper Carixian there are found numerous foraminifers, subordinately also ostracods and pelecypods. The precisely not determined pelecypod-foraminifer assemblages probably point to the Lower Domerian. The Upper Domerian is characterized by a considerably differentiated assemblage of foraminifers and ostracods.

The section of bore hole Wolin (Fig. 2) distinguishes itself by the most complete development of marine deposits in the Polish Lowland area. Here Domerian ammonites have for the first time been encountered, and brackish-marine development of the whole Sinemurian deposits has been noted. East of this section the Domerian deposits pass from marine facies, through brackish fades to freshwater one, the Upper Sinemurian – from brackish-marine to freshwater facies. On the other hand, westwards the complex is characterized by a reduced thickness and can disclose some stratigraphical gaps. Due to this lateral change the relation between the local lithostratigraphical division and the universal chronostratigraphical division is fairly complicated (Fig; 3).

The Carixian marine ingression (zone Uptonia jamesoni) covered at first the area which was a fragment of the central furrow of the basin, i.e. the Wolin and Gryfice blocks (Fig. 1). Only late in the Middle Carixian the sea crossed a palaeomorphological barrier which runs along the Świnoujście dislocation zone, invading the Uznam block in the peripheral part of the furrow. At the Domerian time the sea with drew latest from the areas situated within the western, part of the Wolin block

(bore holes Wolin and Warnowo – Fig. 1).

During the sedimentation the basin bottom was subject to vertical movements of various intensity. This is proved by considerable changes in thickness, even in the nearby situated sections (Fig. 1 Tab. 2). Most significant are here local changes that are shown in Tab. 3, where deviations from mean thicknesses calculated for the entire area are given in percentages. There are found also areas of local reduction and of local increase in thickness. It is possible to investigate this differentiation of subsidence in time (Tabs. 2 and 3). The movements of the sea bottom took place both along the planes of synsedimentary faults and due to the displacement of the Zechstein salts (areas of thickness reduction above the salt pillows – Fig. 1).