Rozwój triasu na obszarze centralnej części Niecki Nidziańskiej

Abstract

DEVELOPMENT OF THE TRIASSIC IN THE CENTRAL AREA OF THE NIDA TROUGHSummaryThe area in study (Fig. 1) comprises the central part of the Nida Trough, beginning with the Kodrąb  horst as far as the line Książ Wielki – Brzegi. Here 18 deep drillings pierced the Mesozoic and partly, completely, the Palaeozoic formations. The materials obtained from these dillings allowed the author to explain the lithological development of the Triassic formations (Figs 4, 5 and 10) and to reconstruct the conditions of their sedimentation.The Lower Triassic is represented here by the Buntsandstein deposits markedly differentiated, but characterized by the similar lithological development in the individual areas pierced by the bore holes considered. The Lower and Middle Buntsandstein rests here, with slight sedimentary gap, on the Upper Zechstein deposits. The best development of these stages can be observed in the north-western part of the Nida. Trough, as shown by bore holes Pągów, Milanów, Gidle and Granice.Here can be distinguished four complexes (Fig. 4) of various lithology which more or less are correlated with the similar, but strongly, reduced complexes of the Lower Triassic encountered in the following bore holes: Secemin, Węgleszyn and Brzegi (Fig. 4). In the remaining bore holes (Fig. 2) the Lower and Middle Buntsandstein deposits are absent, the Roethian formations resting immediately on various Palaeozoic members (Fig.5). The Roethian is developed in carbonate facies, at least with two evaporite intercalations in the north-western, area whereas in the south-eastern region the higher Roethian members as a rule begin with the basal conglomerate. Such a development of the Roethian deposits proves a gradual transgression which approached from north-west towards the south-eastern areas.In the Muschelkalk, carbonate deposits predominate, probably resting, except for the section at Jaronowice, in a sedimentary continuity with the Roethian. At Jaronowice the Muschelkalk rest on the Eifelian beds. At the end of the Muschelkalk sedimentation the basin became shallower, and at some places the sedimentation even ceased, thus being responsible for the lack of the uppermost part of the Muschelkalk considered, and partly of the Lower Keuper.The Keuper in this area is characterized by various thickness (Figs 7 and 8) and marked lithological differentiation. In the Lower Keuper (Fig. 7) are found arenaceous deposits with intercalations of dark shales with abundant flora remains.The Upper Keuper is developed in an arenaceous-siltstone facies and day facies, with gypsum and anhydrite interbeddings. It revels a distinct tripartition into the lower gypsum series, the reed sandstone and the upper gypsum series.In the south-eastern area of the central part of the Nida Trough the Keuper deposits are absent (bore hole Węgrzynów and Książ Wielki), the Rhaetic deposits immediately covering the Muschelkalk ones. It should be supposed that these deposits were completely eroded still before the Rhaetic period. In bore holes Jaronowice and Potok Mały the Keuper is strongly reduced. For the most part its lower parts are not visible; this can be explained by both tectonic conditions and restriction in sedimentation.The Rheatic deposits are developed within the entire area considered, in the arenaceous-siltstone-day facies, frequently with the intraformational conglomerates. Their thickness is fairly consiederable, but strongly decreasing from north-west (Fig. 9). A slight lithologilcal differentiation and a lack of palaeontological evidences do not allow the Rhaetic to be stratigraphically divided in more detail.