Podział geologiczny Polski

Józef Oberc

Abstract


GEOLOGICAL DIVISION OF POLAND

Summary

Two vast Pre-Cambrian crystalline regions occur in the areas of Poland: Fennosarmatian crystalline basement. in the north and east, and crystalline basement of the Bohemian mass folded together with the younger formations, and smaller crystalline region of the Central Carpathians in the south-west. Between them a large synclinorium occurs, filled in with the deposits from Eocambrian to Recent in age. In its central portions the Middle Polish anticlinorium of Laramie phase is situated, running in a SE–NW direction. Pre-Cambrian formations of the Lower San River, hidden under the Tertiary deposits, and a fragment of the Caledonian -Variscan basement, represented by the Palaeozoic of the Świętokrzyskie Mts that distinguished by its oblique (NNW­–ESE) course in relation to the Laramie folds, constitute here a most elevated region. The continuation of the fold zone of the Świętokrzyskie Mts. is hidden under a Permian-Mesozoic series. The Laramie structure is obliquely cut by the margin of the Carpathian part of the Alpides that, bending towards SW, separates on the surface the crystalline basement of the Bohemian Massif from that of the Internal Carpathians.
So far, geological divisions of Poland, particularly of the lowland area, have usually been based on the units of the Permo-Mesozoic cover. However, drilling and geophysical materials allow to-day to distinguish some structural units that appear deeper. A systematic, geological division of the area of Poland, proposed by the present author, embraces: (1) a subdivision into sedimentary units and structural stages (vertical division – Table 1), and (2) a subdivision into tectonic units of higher rank within the individual structural stages. It is also proposed to take into consideration all geological formations, together with the unfolded sedimentary covers of Tertiary and Quaternary age.
1. The following is a systematic scheme, proposed by the present author to sedimentary units: geosynclines, intracratonic basins (geosynclines), fore deeps and covers. Geosynclines and basins may be connected with the areas of different type of sedimentation, e.g. with covers, but in this case they must be characterized by a more intense subsidence. After the pre-orogenic flysch stage, the geosynclines may pass into basins that are distinguished by polyfacial molasse.
A notion concerning structural stage· is closely connected with that of sedimentary unit. The individual stages are separated by regional unconformable surfaces. If the appearance of an un conformity is preceded by some feeble local movements, it is possible to distinguish structural substages, which are of smaller extent than that of stages. For stages and substages tectonic names are proposed by the author, i.e. names of orogenic phases or of orogenies, which are responsible for the formation of a structural stage or substage. The Zechstein stage makes here an exception particularly as concerns the areas where, due to the phenomena of non-tectonical halokinesis, it developed slowly, throughout a long time span, partly during tectonic inactivity. Therefore, name concerning a determined orogenic phase cannot be used for it. Name of the Young Alpine stage subdivided into numerous substages, is proposed for Tertiary and Quaternary deposits that occur beyond the Carpathian Mts. and the Fore-Carpathian areas, usually in horizontal strata, and for Younger Tertiary deposits found in the intramountain depressions. For some intervals of this stage, the deposits of which are folded glacitectonically, the author proposes to use the name of a stage, and to call it by applying an age symbol of the glaciation that is responsible for this glacitectonics.
Large intrusions make here separate structural stages determined by the age of the movements that are responsible for these intrusions: autochthonous granites belong to a stage, at the cost of which they have been formed.
A systematic review of sedimentary units and of structural stages is shown in Table 1. Structural stages constitute tectonic units of the highest order. Since they are of a wide regional extent, we must subdivide them into several units of smaller horizontal extensions. Dislocations, overthrusts, limbs of folds and flexural bends constitute the boundaries between them. Since the main development of tectonic units follows the process of sedimentation, tectonic names (not connected with sedimentary events) are applied for these units as follows: orogen, nappe, fold, anticline, syncline, anticlinorium, synclinorium, dome, diapir, flexure, horst, graben, uplifting (of the basement within a platform area), monocline (limb of a gentle anticline whose bend has been eroded), intrusion, intramountain depression, a.o.
The following are structural elements· distinguished in the north-eastern area of the country: Sphaecofennian folds, Karelian folds, acid intrusions and basic intrusions. The feebly folded Jotnian stage, and the horizontally resting Eocambrian of this area could not have so far been subdivided into separate units. Similarly is in the Lower Silesia area, where a fragment of the Moldanubian basement, i.e. gneisses of the Sowie Mts., the boundaries of which are younger than the orogeny, cannot be subdivided into smaller units of Moldanubian age. On the other hand, the Orlica-Izera branch, Śnieżnik (eastern) branch, and Fore-Sudetic (northern) branch are distinguished in the Old-Assynthian stage as units of this stage. Due to the later intrusions and to a synclinal folding together with younger series, the units of the Old-Assynthian stage have been divided into several subordinate ones (crystalline basements). A small fragment of the Young Assynthian structure, represented in the area of Poland by the Lusatia greywackes, cannot be subdivided in more detail.
To the Caledonian units belong: probably the Kaczawa Mts. and the Kłodzko areas, as well as a small area west of Kamienna Góra, connected with the series of the Bohemian Caledonides of the southern Karkonosze Mts. Several units built up of the Caledonian-Variscan series, without any visible Caledonian folding movements are found in the Lusatia region, the Bardo Mts., and the Łysogóry Mts.
Some units slightly deformed during the Caledonian orogeny and strongly deformed during the Variscan movements, are found east and west of the Świętokrzyskie Mts. (Lublin folds and folds of the southern area of Great Poland, as well as a bundle of Cracow folds). The Variscan units comprise the granite and porphyry massifs of Sudetes and Tatra Mts., basic intrusion in the vicinities of Cracow, Świebodzice (Nassau) structure, Eastern Sudetes (Reuss – an internal part, and Asturian – an external part of this basement, together with the Upper Silesian Coal Basin). The structures built up of the Permo-Mesozoic formations within the Polish Lowland area, as well as North Sudetic and Intra-Sudetic synclinoria, are of Laramie provenance.
In the Carpathians, the Sub-Hercynian stage is subdivided into High-Tatric and Sub-Tatric folds; the Pieniny Klippes Belt with the Sub-Hercynian and Laramie substages belongs to the Sawian stage. The Sawian stage embraces flysch nappes, the Carpathian stage (movements having taken place between the Lower and Upper Tortonian – Carpathian phase) – the internal part of the Carpathian foredeep. Just at the time the flysch was overthrust on the foredeep. Within the lowland area several stages connected with glacitectionic movements, visible in the zones Mużaków–Żary, Mosty–Mirosławice, Zielona Góra, Konin and Włoclawek (stage VI), are distinguished within the Young Alpine stage. In the Carpathian Mts. This stage is represented by the Miocene and Pliocene deposits found in the intramountain depressions.


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