Mikrofauna dolnokredowa na wale kujawskim w świetle nowych badań

Abstract

LOWER CRETAOEUS MICROFAUNA OF THE KUJAWY SWELL AREA IN THE LIGHT OF RECENT EXAMINATIONSSummaryIn the area of the Kujawy swell the Neocomian deposits contain microfauna of Riasanian (Berriasian), Valanginian and Hauterivian age. The microfauna is relatively abundant, revealing numerous species and specimens of foraminifers and ostracods (Table 1). The microfaunistic regions are not distinctly expressed since, throughout the area here considered, the microfauna is almost identical. It should, however, be added here that in the north-western part of the area, where the sand content in the deposits is somewhat greater, the microfauna assemblage slightly changes. Calcareous foraminifers are less abundant, and certain species of these foraminifers disappear. The following are two different foraminifer assemblages distinguished in the Lower Cretaceous (Fig. 1): 1 - Lenticulina – Haplophragmoides – Ammobaculites assemblage that occurs in the Riasanian and Lower Valanginian deposits, and 2 - Epistomina -Lenticulina assemblage, characteristic of the Upper Valanginian and Lower Hauterivian deposits. Despite the fact that in the Kujawy swell area the Middle Valanginian is a period of sea shallowing, the microfauna has been found to occur over the entire area in study. In the Riasanian (Berriasian), the following index microfauna has been distinguished: Protocythere pseudopropria emslandensis Bart., Burri, P. praetriplicata Bart., Brand subsp. Infravalangiensis Sztejn as well as Epistomin caracolla anterior Bart., Brand. The microfauna representatives of the Riasanian (Berriasian) and the Lower Valanginian are fairly similar, the following forms have not, however, been encountered in the Lower Valanginian: Protocythere pseudopropria emslandensis Bart., Burri, P. praetriplicata Bart., Brand subsp. infravalangiensis Sztejn. Index microfauna has not been found in the Middle Valanginian deposits, as well. The microfauna encountered in both Lower Valaginian and Upper Hauterivian, within the deposits of similar type, is highly uniform. To the index forms of these sub-stages can, among others, be referred: Epistomina caracolla caracolla (Roem.), Citharina seitzi Bart., Brand, Marginulina pyramidalis Koch, Mandocythere (Costacythere) frankei (Trieb.). In the Neocomian deposits of the Kujawy swell are found both Boreal and Mediteranean species of foraminifers and ostracods; the representatives of the former prevail. There is noted a concurrence of the results of the researches on foraminifers and on spores. The researches on both foraminifers and sporomorphs allow us to draw conclusions as to the climate that governed at the Lower Cretaceous time in the Polish Lowland area.