Stratygrafia portlandu niecki mogileńskiej na podstawie otwornic i małżoraczków

Abstract

STRATIGRAPHY OF PORTLANDIAN IN THE MOGILNO TROUGH DETERMINED ON FORAMINIFERS AND OSTRACODS

Summary

Within the Mogilno trough area the Lower Portlandian beds are developed in a siltstone-marly facies and contain fairly poor microfauna assemblage (Fig. 3). For the most part these are foraminifers that occur in an interval Kimmeridgian- Portlandian. Sporadically, there are found Portlandian species like Nodoaria striatojurensis K l ä h n, Saracenaria pravoslavlevi F u r s. P o l e n., or Citharina brevis (F u r s., P o l e n.) or even C. rariocostata (F u r s., P o l e n.) and among ostracods – Cytherella nota L u b. and C. tortuosa L u b.
In their rower part, the Middle Portlandian deposits are represented by marly or siltstone-marly series, in their upper part – by limestones. The microfauna assemblage is much richer (Fig. 4), and may be subdivided into three groups. The first group is represented by the species known from the Upper Kimmeridgian and Portlandian, the second group – by the species which appear at the close of the Kimmeridgian time and proceed still in the Portlandian, and the third group – by the species characteristic mainly of the Middle Portlandian. To these belong: Quinqueloculina egmontensis L l o y, Spiroloculina subpanda L l o y, Ammobacultes haplophragmoides F u r s. P o l e n., Lenticulina (L.) dofleini (K a s a n z.). L (L.) magna M j a t l., L. (Planularia) poljenovae K u s n., Citharina brevis (F u r s., Po l en.), C. rariocostata (F u r s., P o l e n.) C. virgatis (F u r s., P o l e n.,), Nodosaria internotata C h a p m., N. osynkensis M j a t l., N. striatojurensis K l ä h n; and among ostracods: Macrodentina dictyota M a l z, M. maculata M a l z, Galliaecytheridea punctilataeformis (L u b.), G. cf. spinosa K i 1 e n y i and some others.The Uppex Portlandian deposits have been distinguished on the basis of both lithological and microfaunistic criteria. Within the Mogilno trough there occur all ostracod horizons, from F horizon to B horizon. F horizon, developed as limestones, makes a transition bed from the Middle to the Upper Portlandian. As a rule, this horizon is poor in microfauna, frequently lacking any microfauna completely. As far as its age is concerned it corresponds to the marls from Münder.
E and D horizons correspond to the carbonate-anhydrite-gypsum series, or to the limestone-marly series. These horizons may be compared with the upper part of the marls from Münder. Both horizons cannot always be distinguished precisely.
To the characteristic ostracods belong here: Cypridea inversa M a r t., C. lata M a r t., C. valdensis praecursor O e r t i, Mantelliana purbeckensis (F o r b.), Klieana alata M a r t. At the horizon D there appear Scabriculocypris trapezoides A n d e r s and locally Cypridea cf. granulosa S o w; in O e r t i.
C horizon of the Mogilno trough area can distinctly be visible. It is built up of clay-marly deposits with Cyrena shell intercalations. To the type ostracods belong here: Cypridea binodosa M a r t., C. dunkeri J o n e s, C. alta W o l b., Damonella cf. ellipsoidea (W o 1 b.), Dicrortygma groenwali C h r i s t. and numerous representatives of Klieana alata M a r t. This horizon corresponds to the lower part of the marls from Münder .
B horizon is, in the Mogilno trough area, strongly reduced. Lithologically, it is developed like the horizon C, but it contains a different assemblage of ostracods.Klieana kujaviana B i e l, S z t e i n, which does not occur in the lower horizon, is a characteristic species here. The from Klieana alata M a r t. does not appear at all.