Osady trzeciorzędowe SW części niecki warszawskiej na przykładzie profilu z Kaczorówka

Maria Danuta Baraniecka

Abstract


Podano szczegółowy opis osadów trzeciorzędowych na przykładzie profilu wiercenia Kaczorówek, w którym osady te występują na głęb. 54,3-282,7 m. W spągu profilu trzeciorzędu występują wapienie margliste i margle z fauną należące do montu, na co wskazuje bogata mikrofauna. Wyżej położona jest seria piasków z wkładkami humusowymi i nielicznymi fosforytami; którą na podstawie badań palinologicznych uznać można najprawdopodobniej za eoceńską. Do niedawna nie była ona oddzielana od wyżej występującej serii glaukonitowej; stwierdzona została podczas sporządzania szczegółowych map geologicznych okolic Grójca i Otwocka. W artykule po raz pierwszy podaje się zasady wyodrębnienia i skład tej serii. Powyżej leży seria glaukonitowa: mułki oraz piaski ze żwirami kwarcowymi i fosforytami, z rozpoznanymi morskimi poziomami transgresywnymi i recesyjnymi. Poprzednio seria ta uważana była za oligoceńską, ostatnio gromadzone są dane przemawiające za wiekiem eoceńskim. W Kaczorówku występują przewodnie gatunki otwornic eoceńskich. Utwory mioceńskie zawierają dwa poziomy węgli brunatnych. Ponad dolnym poziomem występują brekcje i spływy osadów Oligoceńskich na wtórnym złożu. Seria pstrych iłów zaliczonych do pliocenu wykazuje sedymentację cykliczną. Strop osadów trzeciorzędowych datowany jest od góry czwartorzędowymi spągowymi warstwami osadów preglacjalnych, które na podstawie nawiązania do klasycznych profili holenderskich należą do tegelenu, a w środkowej Polsce znajdują odpowiednik w interglacjale ponurzyckim.

TERTIARY'DEPOSITS IN SW PART OF THE WARSAW BASIN AT THE EXAMPLE OF BOREHOLE COLUMN KACZOROWEK

The data presented here were gathered in the ,course or preparation of detailed geological map of the Grójec area (about 50 km south of Warsaw). In that area, Tertiary deposits have been penetrated by one of drillings made for construction of a geological cross-section (Figs. 1, 2). The borehole Kaczorówek recorded Tertiary deposits at depths from 54.3 to 282.7 m. The deposits, resting on Cretaceous marls, belong to the infill of the Warsaw Basin.

At Kaczor6wek, Tertiary sequence begins with marly limestones and organodetrital marls with numerous fragments of bivalve shells (255.0-282.7 m). They are dated at the Montian on the basis of rich assemblage of typicall microfauna (E. Gawor-Biedowa, 1977). The lowermost Tertiary deposits hitherto known in the Warsaw Basin were those from the Sachaczew area in its western part, developed in sandy and calcareous limestone facies (J. Łyczewska, 1951; M. Różkowska, 1955; F. Brotzen, K., Pożaryska, 1957; R. Kongiel, 1958; K. Pożaryska 1965, 1967). It follows that the Kaczorówek locality is a new one for that stratigraphic horizon, representative for SW part of the basin and development of relevant strata in different facies.

In SW part of the Warsaw Basin, marly deposits are overlain by clastics. According to the hitherto accepted views and-descriptions of borehole columns, the clastic deposits were beginning with marine glauconitic sands referred to the Oligocene. However, two series essentially differing from one another have been encountered at Kaczor6wek: lower, possibly of an inland basin or lagoon, and upper, glauconitic marine. Both series presumably belong to the Eocene.

The lower series - sands with humus intercalations - was recorded at depths from 229.4 to 255.0 m (Fig. 3). It comprises sands with .intercalations of humus matter or clays rich in humus. Palynological analysis (Table I) showed that these deposits most probably belong to the Eocene (I. Grabowska, 1976; H. Majchrzak, 1977). Similar deposits, also assumed to be of Eocene age, are known from the base of the Tertiary in Warsaw (Z. Sujkowski, S.Z. Różycki, 1934) and Otwock (A. Łuniewski, 1940). The series of sands with humus intercalations is here divided into units t, 2,3 and 4 (form the base upwards).

The upper, glauconitic series (196.3 - 229.4 m) comprises sands and, throughout marked part of the section, glauconitic silts with some gravel horizons, corresponding to marine transgressions and regressions (fig. 4). The series displays a few horizons of phosphatic and sandstone-ferruginous nodules. Microfauna was found to be innumerous in the studied samples (over a dozen in number) but it comprises single but undoubtful representatives of guide Eocene foraminifer species such as Uvigerina spinicostata C u s h m a n  et  J a r v i s and Lenticulina radiata B o r n e m a n (see E. Odrzywolska-Bieńkowa, 1977). Glauconitic deposits referred to the Upper or, eventually, Upper and Middle Eocene were recently described from eastern part of the Warsaw Basin by T. Uberna (1974) and J. Nowak and T. Uberna (1976). The glauconitic series m here subdivided into units 1, 2, 3, 4 and 5 (from the base upwards).

In the studies section, marine Tertiary deposits are overlain by Miocene series (163.4-196.3 m - see Fig. 5), known throughout the Warsaw Basin. The latter comprises deposits of inland reservoirs: sands and some silts and clays with two horizons of brown coals. Coals of lower horizon ate squeezed and compact, being accompanied by hard, compact and stratified shale-like clays. That horizon is dated at the Lower Miocene (Table 2) on the basis of palynological data (I. Grabowska, 1976). The squeezing of brown coals and the presence of shale-like clays may be related to some tectonic activity.

The squeezed Lower Miocene deposits are overlain by redeposited glauconitic ones. Lower part of the latter displays breccias structure which may also evidence some tectonic movements. Upwards, the redeposited glauconitic deposits display sedimentary flow structures and they interfinge with Miocene sands. The Miocene series is here subdivided into units 1, 2 and 3 (from the base upwards).

Top part of Tertiary comprises series of so-called mottled clays (54.3-163.4 m), represented by faunistically and floristically barren clays and subordinate intercalations of silts and fine-grained sands. It is here subdivided into 3 sets of layers: 1, 2 and 3 (from the base upwards), and assigned to the Pliocene. The series displays varying but cyclic sedimentation, resembling that from the vicinities of Otwock in SE part of the Warsaw Basin (M.D. Baraniecka, 1974). Paleomagnetic studies of Pliocene deposits showed differentiated polarity of magnetic inclination (P. Tucholka, E. Niedziółka-Król, 1978). Successive sets of layers differ in polarity, presumably corresponding to epochs Gilbert (reversed, negative polarity), Gauss (normal, positive polarity) and Matuyama (reversed, negative polarity) paleomagnetic epochs. The present, Brunhes epoch is represented by Quaternary deposits.

The top of Tertiary deposits is fairly well dated by those of relatively the oldest units of the Quaternary, i.e. Preglacial. Lower part of the latter belongs to the telegene A (L. Stuchlik, 1978) as it follows from correlations with sections of the lowermost Quaternary in the Netherlands. In the subdivision of the Preglacial, established for the adjoining Otwock area, these deposits would correspond to the Ponurzyca Interglacial (M.D. Baraniecka, 1975; L. Stuchlik, 1975).

The Kaczorówek section may serve as a reference for correlations of Tertiary deposits in wide areas.


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