Charakterystyka starokimeryjskich i laramijskich struktur blokowych monokliny przedsudeckiej

Zbigniew Deczkowski, Irena Gajewska

Abstract


W artykule podano charakterystykę tensyjnych i kompresyjnych blokowych struktur klinowych monokliny przedsudeckiej, uformowanych w czasie fazy ruchów starokimeryjskich, przypadających na przełom kajpru i retyku, oraz fazy ruchów laramijskich, zaznaczających się na przełomie kredy i trzeciorzędu. Omówiono wybrane struktury, które rozpoznano głębokimi otworami wiertniczymi.

THE CHARACTERISTICS OF LATE CIMMEBIAN AND LABAMIE BLOCK STRUCTURES OF THE FORE-SUDETIC MONOCLINE

The studies covering the area of the Fore-Sudetic Monocline in south-western Poland have shown that the Late Cimmerian movements from the turn of the Keuper and Rhaetian resulted in tension and compression leading to origin of wide-radius deformations and block structures. Tensional structures from that area are built of one or several blocks delineated by longitudinal normal faults converging towards their bases (Fig. 1). Structures of such type are commonly also cut by transversal faults resulting in small-scale horizontal ,translocations of neighbouring blocks. The structures of the wedge type end in the main plane of disturbance of beds which is presumably related to a deeper-seated fracture·zone. Horizontal tension acting in upper layers resulted in origin of compressional stresses in substratum of the structures which, in turn, resulted in certain warping of rocks forming the structures as well as overlying Permian rocks.

Zones of accelerated subsidence from the Early Jurassic times (Fig. 2) developed within structures of this type in NE parts of the Fore-Sudetic Monocline. The thickness of the Lower Jurassic within the area of such structures increases two or even three times which evidences compensation of subsidence by accelerated sedimentation in these times.

Laramie tensional structures are genetically and morphologically similar to tensional Early Cimmeriian structures (Fig. 12).

Early Cimmerian and Laramie block structures shaped by compressional stresses are similar to one another in genesis and shape. Laramie structures of this type from the Fore-Sudetic monocline were more accurately recognized by drillings. The analysis of the drilling data has shown that compressional block structures are delineated by two longitudinal reversed faults which may bifurcate towards the surface (Figs. 6, 7 and 9). Vertical translocation of some blocks may be fairly large and the blocks may be torn-off from their deeper-seated extensions. The vertical translocations of layers gradually disappeared towards the base of the structure, i.e. towards the place where faults converge into a single plane of disturbation of beds. The structures are additionally complicated by several normal transversal faults.


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