Litostratigrafia osadów jury górnej na obszarze IubeIskim

Abstract

LITHOSTRATIGRAPHY OF UPPER JURASSIC DEPOSITS IN THE LUBLIN-RADOM AREA

SUMMARY

The present paper offers a characteristic of lithological formations occurring in the Lublin-Radom area, prepared according to the Code of the Polish stratigraphic classification, terminology and nomenclature. The author has distinguished eleven formations (fm); their stratotypes are based on boreholes with completely (in 100%) cored Jurassic deposits. The established formations were referred to the local biostratigraphy (Niemczycka 1976) and correlated with the accepted ammonite subdivisions (Table 1). 

THE KRAŚNIK FORMATION
Deposits of this formation are represented by sponge organodetritic limestones.
In their lower parts there occur dolomites in the form of euhedral crystals, whereas their upper layers are distinctly silicated and reveal no doIomitization.
The following ammonites can be found in the lower part of the Kraśnik Fm.: Campylites cf. delmontanum Opp., Euaspidoceras perarmatum (Sow.) and Taramelliceras cf. bukowskii Siem.; this allows to estimate its age as Lower Oxfordian – Cardioceras excavatum and Cardioceras bukowskii Zones (Table 1).
The higher part of the formation contains a faunal assemblage of brachiopods and foraminifers, which suggests its Middle Oxfordian age (Table 1).

THE JASIENIEC FORMATION
The formation is composed of organodetric limestones containing mainly trochites. There occur aIso scarcely remnants of pelecypods, brachiopod end gastropods, as well as echinus spicules and algae.
The recognized assemblge of brachiopods and the microfauna (Table 1) points to the Middle Oxfordian age of the formation.

THE BEŁŻYCE FORMATION
Within this formation there occur two main rock types, that is, white pelite Iimestones and grainy limestones, as well as several mixed types.
Gastropods and a certain foraminifer assemblage (Table 1) are representatives of the fauna. The age of the formation cannot be exactly determined; most probably it may be assigned as Upper Oxfordian.

THE GŁOWACZÓW FORMATION
The main rocks of that formation are pelite marls and marly limestones; partly organodetritic coarse-grained and dolomitic in some places. In the whole profile there occur hard grounds and connected with them intraformational conglomerates and calcareous breccias.
The fauna is represented by different Mytilus species and a characteristic microfaunal assemblage (Table 1).
Similar deposits containing an ammonite fauna are know from the Mesozoic surrounding of the Świętokrzyskie Mts and the Polish Lowland. By analogy the age of the Głowaczów Fm. may be estimated as Kimmeridgian.

THE URZĘDÓW FORMATION
The formation is represented by dolomites, marly dolomites, limy dolomites and; secondarily, by grey dolomitic Iimestones. Average CaMg(CO₃)₂ contens in deposits vary from 76 to 99.8%. Quartz and glaukonite grains occur but in inconsiderable amounts.
The fauna is represented mainly y pelecypods; brachiopods and gastropods are less frequent. Its assemblage is similar to that of the Głowaczów Fm. A characteristic microfaunal assemblage is, however different (Table 1).
The age of the formation to be Upper Kimmeridgian (Niemczycka 1976).

THE ZAKRZEW FORMATION (fm)
It is represented by sandy dolomites with detritus of the carbonized and pyritized flora, scrarps of coal and grey-blue cherts. Those deposits are indistinctly horizontally laminated with carbon material in which detritic quartz contents reach 30% layers of brown sandstones with carbonized flora occur scarcely. In their lower parts remants of Echinodermata may be occasionally observed.
In particular boreholes deposits of this formation are somewhat different in a degree of dolomitization and in sand quantities.
No fauna has been documented from deposits of the discussed formation.
However, sedimentological and paleontological considerations allow to estimate ita age as Lower and Middle Oxfordian.

THE BASZNIA FORMATlON
It is represented by glauconite-chlorite marls and marly limestones with layers of mudstones and siltstones and also of calcareous conglomerates. Anhydrite inclusions and detritus of dolomitic rocks occur among them. There was documented the presence of Pseudocyclammina jaccardi (Schrodt.) foraminifers and Vernoniella sequana Oertli ostracods.
On the basis of the microfauna and the facial-paleogeographic analysis the deposits of the Basznia Formation may be determined as Upper Oxfordian.

THE JARCZÓW FORMATION
Its main deposits are nodular dark-grey siltstones and non-calcareous mudstones with abundant carbonized flora, rizoidal structures and detritus of quartz, gneisses and quartz porphyrites.
No fauna has been found in those deposits. Their age may be determined from their position in the lithological profile, between the Kraśnik and the Ruda Lubycka formations, as Upper Oxfordian (Table 1, Fig. 1).

THE TYSZOWCE FORMATION
It is represented by characteristic, veriegated, cherry-green-grey sandstones, mudstones and siltstones, with intercalations of sandy-mudy conglomerates and dolomitic marls. The deposits show a cyclic sedimentation. In the dolomitic doeposits Ammodiscus sp. was found.
There is no sufficient faunistic documentation for deposits of the Tyszowce Formation. Their age has been determination as Upper Oxfordian.

THE RUDA LUBYCKA FORMATION
It is represented by dolomites with anhydrite alternations. Mudstones and dolomitic marls occur less frequently, and limestones and dolomitic limestones are rare.
Stratigraphically important fauna has not been found in the stratotype profile as well as in the adjacent boreholes. Only few remnants of gastropods or pelecypods and single Ammodiscus sp. foraminifers were recorded in calcareous fragments of the profile.

THE BABCZYN FORMATION
In the stratotype profile it is represented by white or beige grainy limestones, oolithic-onkolithic-nodular lumpy or pelite limestones. Algal limestones with corbules are fairIy abundant. Gastropods end ostracods present in deposits of this formation suggest their Portlandian age.