Rola aulakogenów w tektonice platform
Abstract
THE ROLE OF AULACOGENS IN DEVELOPMENT OF PLATFORM
Summary
The finding of relations between oil and gas fields and the system of great synsedimentary troughs of the North Sea has focused attention on other troughs of that type. The main kinds of synsedimentary troughs accepted in the literature include aulacogens, grabens or intercontinental rifts of the Upper Rhinne type and rifts genetically related to continental break-up and sea-floor spreading. In the latest interpretations carried out in the terms of plate tectonics (4-5, 8, 11) it is possible to note a trend to differentiate two trough types only: failed arm rifts (incliuding aulacogens), genetically related to continental •break-up, and impactogens related to continental collision (5). However, the analysis carried out by the authors has shown that the origin of typical aulacogens of the East-European Platftorm (Pachelma and Dnepr-Donetz aulacogens) had not been related to continental break-up but rather to collisions. The analysis has also given support to the concept of the aulacogenic stage as the earliest in evolution of platforms (6, 15). This stage, previously differentiated in evolution of epi-Gothian East-European Platform, may be also recognized in the case of the epi-Alpine, epi-Variscan and even epi-Caledonian platforms of the central and western Europe. In turn, the maximum intensity of processes leading to formation of failed arm rifts corresponds to the time of opening of an ocean, e.g. the Atlantic.
The role of aulacogens in evolution of platforms is mainly connected with formation of sedimentary cover. On the one hand, we are dealing here with regional isostatic adjustment to the load infilling the trough, leading to elastic or viscoelastic downwarp of lithosphere and, therefore, a depression (sedimentary basin) much wider than the trough (2-3), and on the other hand - extension of fractures delineating the trough, leading to its extension and, at the same time, cutting off fragments of a platform.
Summary
The finding of relations between oil and gas fields and the system of great synsedimentary troughs of the North Sea has focused attention on other troughs of that type. The main kinds of synsedimentary troughs accepted in the literature include aulacogens, grabens or intercontinental rifts of the Upper Rhinne type and rifts genetically related to continental break-up and sea-floor spreading. In the latest interpretations carried out in the terms of plate tectonics (4-5, 8, 11) it is possible to note a trend to differentiate two trough types only: failed arm rifts (incliuding aulacogens), genetically related to continental •break-up, and impactogens related to continental collision (5). However, the analysis carried out by the authors has shown that the origin of typical aulacogens of the East-European Platftorm (Pachelma and Dnepr-Donetz aulacogens) had not been related to continental break-up but rather to collisions. The analysis has also given support to the concept of the aulacogenic stage as the earliest in evolution of platforms (6, 15). This stage, previously differentiated in evolution of epi-Gothian East-European Platform, may be also recognized in the case of the epi-Alpine, epi-Variscan and even epi-Caledonian platforms of the central and western Europe. In turn, the maximum intensity of processes leading to formation of failed arm rifts corresponds to the time of opening of an ocean, e.g. the Atlantic.
The role of aulacogens in evolution of platforms is mainly connected with formation of sedimentary cover. On the one hand, we are dealing here with regional isostatic adjustment to the load infilling the trough, leading to elastic or viscoelastic downwarp of lithosphere and, therefore, a depression (sedimentary basin) much wider than the trough (2-3), and on the other hand - extension of fractures delineating the trough, leading to its extension and, at the same time, cutting off fragments of a platform.