O wynikach czterech wierceń geologicznych w okolicy Korytkowa Dużego koło Biłgoraja

Abstract

ON GEOLOGICAL RESULTS OF FOUR DRILLINGS MADE IN THE VICINITY OF KORYTKÓW DUŻY, NEAR BIŁGORAJSummaryThe present author discusses the geological results of the drillings made in a period from 1948 to 1954 in the area of Korytków Duży, near Biłgoraj, in the south-eastern area of Poland. The first geological and drilling works were begun at the suggestion of J. Czarnocki to recognize the geological structure recorded in gravimetric picture, as a large anomaly of Biłgoraj. In the vicinity of Korytków Duży four bore holes have been made, the most complete section being obtained in bore hole Korytków Duży 4 (Fig. 1). The elaboration of the Miocene deposits pierced by the bore holes at Korytków was published by K. Kowalewski (1959). The present paper comprises the discussion on the Old Palaeozoic (Cambrian), Middle Jurassic and Upper Jurassic formations pierced in bore hole No 4, and the description of the tectonics in the area considered. Cambrian. The Old Palaeozoic substratum that rests under the Jurassic deposits has been encountered in bore hole Korytków 4. It has been found that at a depth of 584 m the Middle Jurassic formations directly rest on the Cambrian. The Cambrian formations are built up of alternating clay-quartzite deposits that dip under an angle of about 70-80°. These deposits do not reveal any organic remains. On the basis of a lithological analogy with the palaeontologically evidenced Palaeozoic deposits found by the neighbouring bore holes (Dyle), the age of the deposits considered may be estimated as Upper Cambrian. Middle Jurassic. The Middle Jurassic formations have been encountered in bore hole Korytków 4, at an interval from 546 to 584 m. They consists of arenaceous-dolomitic deposits that contain abundant pyritized wood remains and fragments of badly preserved pelecypods. The deposits rest with a considerable gap transgressively on the Cambrian formations. The badly preserved fragments of pelecypods and non-typical microfauna do not allow us to determine the age of these deposits more in detail. Upper Jurassic. As it results from the lithological, palaeontological and palaeogeographical analyses, a fairly complete sequence of the upper Jurassic formations is developed mainly in a direction from south to north. The Jurassic formations from Korytków are characterized by poor macrofauna and microfauna. On account of a lack of ammonites and brachiopods the stratigraphy of these formations could not have been determined according to classic schemes and, consequently, the following lithological complexes have been distinguished: Scyphia complex, marly complex, dolomitic complex and oolitic complex. These deposits, 332 m in thickness (Korytków 4), can, according to the terminological recommendations of the Luxemburg Colloquy, be referred to the Oxfordian sensu lato. In the Polish text a list of fauna is given, determined in the individual complexes, and the thicknesses of these complexes are given. The deposits younger than the Oxfordian - (Lower?) Kimmeridgian have been encountered only in bore hole Korytków 2. As compared with the Oxfordian, the Kimmeridgian formations are characterized by a considerable amount of marls, and by the presence of characteristic shell-oyster agglomerates. In addition, there occurs here a monotonous pelecypod fauna, the list of which is given in the Polish text according to the elaboration made by H. Gościniak. To the characteristic features of the Jurassic deposits from Korytków belong: arenaceous-carbonate development of transgressive Middle Jurassic deposits, considerable development of the Scyphia series in the Upper Jurassic, and, as compared for example, with Dyle, a slightly visible participation of the deposits of chemical facies. The Jurassic deposits found to occur in the vicinity of Korytków have been laid down in the marginal zone of the Jurassic sea, nearby the southern boundary of its extent. Tectonics. In the neighbourhood of Korytków, the tectonics is complicated and several coinciding cycles may be distinguished here, beginning from the Sandomirian orogeny, through the Laramie activity, to the Young Alpine one. The Upper Cambrian deposits are steeply dipping, folded, slickensided and contorted. In relation to the Cambrian, the Jurassic deposits are transgressive and discordant, also fairly strongly disturbed tectonically. The tectonical development of the Jurassic deposits, observed at Korytków, may be related to an elevation of these deposits along the huge dislocation line that runs from Mogielnica to Cieszanów. Korytków is situated on the north-western side of this dislocation, within an elevated Jurassic area that is in a contact with the Creataceous deposits, along the dislocation line mentioned above. The post-Cretaceous tectonics is affected later by the processes of Young Alpine orogeny that is responsible for the formation of the Miocene foredeep supported in the north by a hard threshold built up of siliceous-calcareous Jurassic rocks.