Uwagi o rozwoju triasu na obszarze południowo-wschodniej Polski.

Abstract

REMARKS ON THE DEVELOPMENT OF TRIASSIC DEPOSITS IN SOUTH-EAST POLAND

Summary

The authors discuss the Triassic formations found to occur in the area of the Carpathian foreland and in the south-eastern part of the Miechów trough, considering mainly the development and palaeogeographic-tectonical relations of the area in study. The elaboration is based on the results obtained from several bore holes. The correlation of the formations has been supported by both electric and radiometric measurements made in these bore holes. Triassic deposits that occur in the area of study begin with Buntsandstein to Rhaetic inclusive. Both the Lower and the Middle Buntsandstein are in a sedimentary continuity with the Zechstein that may be found here, at places. It is developed analogously to the Buntsandstein. So far, it has been distinguishes from the Buntsandstein deposits in the bore hole Liplas 2 only, where index foraminifers of Zechstein age have been encountered. In the other bore holes, the Roethian is underlain with a variegated series that comprises the Middle and the Lower Buntsandstein and/or Zechstein. Both the Zechstein formation and the Triassic one rest on the Carboniferous, Devonian or pre-Cambrian. The variegated series is developed as claystones, siltstones, sandstones and conglomerates. The sandstones and conglomerates dominate mainly m the lower part, whereas the clays tones and siltstones - in the upper part. Gypsum and anhydrite intercalations are numerous. The thickness of this series amounts to from a feather edge to over 1000 m. Both Roethian and Muschelkalk are developed as carbonate series: limestones, marls, dolomites, frequently with anhydrite interbeddings, as well as sandstones and siltstones. The total thickness of these formations reaches, at places, up to 250 metres. Keuper and Rhaetic are represented by detrital formations, mainly of variegated nature. In the lowermost part of the Keuper, there occurs a series of clay-coals, developed as dark claystones and siltstones, as well as glauconite sandstones, subordinately with the limestone intercalations, and with flora and fauna remains. The total maximum thickness of the Keuper and Rhaetic deposits amounts here to 400 m. It results from the previous data that during the Variscan orogeny, the area was elevated and considerably differentiated morphologically. In the most depressed areas that, at places, resemble grabens, Zechstein and then Buntsandstein deposits were laid down within the shallow water basins. At the Middle Buntsandstein time, a lowering of the northern part of the area took place, and the sea invaded from a SE direction. In that period, the south-western part was elevated and partly eroded. In the north-eastern part, in turn, the sea persisted until the Muschelkalk inclusive. At the boundary with the Keuper, the connection with the open sea was broken, maybe due to the movements of the Labinian (Saxonian) phase, and the area changed into a basin of brackish type. The Keuper deposits are known to occur at a few sites only, since they had almost entirely been eroded before the Rhaetic deposits were laid down. At that time, both Muschelkalk and Roethian deposits were destroyed, as well. At present, the Keuper deposits are represented by the Lower Keuper deposits only. The Upper Keuper deposits have been ascertained doubtlessly. After the Keuper time, this area was elevated and eroded owing the Eo-Cimmerian orogeny. The Rhaetic deposits rest transgressively on various members of the Older Triassic. Most probably, they were laid down in the same zone as the Roethian and Muschelkalk formation. After the Triassic time, the area was uplifted and eroded again. This resulted in a disappearance of the Rhaetic and partly of the older Triassic formations. At present, the Triassic is overlain with the Middle or Upper Jurassic deposits. In the basal conglomerates of Bathonian are found rocks of Muschelkalk age.