Stratygrafia podłoża podoligoceńskiego na obszarze Białobrzegi - Jedlińsk – Głowaczów

Abstract

STRATIGRAPHY OF SUB-OLIGOCENE BASEMENT IN THE AREA BIAŁOBRZEGI-JEDLIŃSK-GŁOWACZÓWSummaryForaminider fauna allowed the present author to determine the age of the beds found to occur under the Oligocene pierced by 31 bore holes made in the vicinity of Białobrzegi, within the southern part of the marginal synclinorium. Sixty five rock samples have been taken from the beds that immediately underlain the Oligocene, and fifty four species of foraminifers have been determined. On the basis of index species or index assemblages (Fig. 3) the following Upper Cretaceous and Lower Tertiary members have been determined (Fig. 1): Turonian β, Lower Campanian, Upper Campanian, Lower Maestrichtian, Upper Maestrichtian and Palaeocene (Montian). The lithology of these members is as follows: the Turonian is built of white marls with flints, lacking quartz, glauconite and macrofauna. In the upper members (Santonian, Campanian and Maestrichtian) abundant terrigenous material may be observed. Here are found white-grey brittle marly sandstones and light grey arenaceous marls with glauconite and scarce pelecypod fauna (Pecten sp.) and moluscs. North-east of the line Białobrzegi - Siekluki (Fig. 1) the arenaceous marls pass into marly limestones, marls and marly opokas (Upper Maestrichtian) with pelecypod, gastropod and ammonite fauna, determined by A. Błaszkiewicz as Haploscaphites constrictus vulgaris Nowak, and with Belemnitella archalgenskyi (Jeletzky). Palaeocene (Montian) is developed as marly opoka with an admixture of arenaceous material. In these deposits an echinus has been encountered, referred, according to S. Mączyńska, to the group of the Tertiary echinoids. The Upper Cretaceous and Palaeocene (Montian) deposits are overlain with the dark-grey non-calcareous deposits, strongly arenaceous and with abundant glauconite, or with the clay-siltstone deposits, 0.30-0.80 m in thickness. Locally, there are found white-grey decalcified opokas. These beds lack any foraminifers. Higher up there are grey and grey-green sands of Oligocene age. Foraminifer fauna of the deposits examined is fairly abundant. Two stratigraphical assemblages may be observed here of the genus Globotruncana: assemblage 1 (Turonian β - Lower Santonian) with Globotruncana lapparenti var. lapparenti Brotz., G. lapparenti var. coronata Bolli, G. lapparenti var. bulloides Vögl., G. lapparenti var. tricarinata (Quer.), G. globigerinoides Brotz., G. marginata Reuss, and assemblage 2 (Upper Santonian - Maestrichtian) with Globotruncana lapparenti var. tricarinata, G. lapparenti var. bulloides, G. globigerinoides, G. marginata, G. fornicata, G. arca. These assemblages correspond to the 2. and 3. assemblages distinguished by W. Pożaryski and E. Witwicka (1956) in the Cretaceous deposits of the central area of Poland. Two foraminifer assemblages have been found to occur in the Upper Maestrichtian deposits. The first assemblage is characterized by the occurrence of the Upper Cretaceous benthonic species of the genera Bolivina, Bolivinoides and Stensiöina, of the individual planctonic species of the genus Globotruncana, and of the first representatives of the Tertiary (Palaeocene) foraminifers (Fig. 3). The second assemblage reveals en impoverishment of the Upper Cretaceous foraminifers in favour of the Palaeocene species (Fig. 3). The occurrence of the two foraminifer assemblages within the Upper Maestrichtian deposits may point to the presence of two, lower and upper, horizons, different in age. The Upper Maestrichtian has been documented (in some bore holes, Fig. 3) by Haploscaphites constrictus vulgaris Nowak and Belemnitella archangelskyi (J e l e t z k y), which determines the upper horizon of the Upper Maestrichtian, i.e. the horizon Belemnitella kasimiroviensis.