Cechy powierzchni ziarn kwarcu z jurajskich wapieni pienińskiego pasa skałkowego

Abstract

Opisano cechy powierzchni ziarn kwarcu: plastry krzemionkowe i siateczkę krzemionkową powstałe w warunkach diagenezy wapieni pienińskiego pasa skałkowego. Niski stopień przeobrażeń tych powierzchni pozwolił na przeprowadzenie rekonstrukcji środowiskowej obszarów źródłowych, którymi były grzbiety geantyklinalne. Był to łańcuch wysp o wąskiej strefie brzegowej i stokach gwałtownie opadających ku głębiom morskim. QUARTZ GRAIN SURFACE FEATURES FROM JURASSIC LIMESTONES IN THE PIENINY KLIPPEN BELT The analysis covered samples form 10 localities in Polish part of the Pieniny Klippen Belt (Fig. 1). Generalized section of the studied rocks includes crinoid limestones: Smolegowa Limestone Formation-  Middle-Upper Bajocian, Krupianka Limestone Formation - Upper Bajocian-Bathonian – Callovian ?, nodular limestones: Czorsztyn Limestone Formation - Callovain-Kimmeridgian, Niedzica Limestone Formation - Upper Bajocian-Callovian, radiolarites: Czajakowa Radiolarite Formation Oxfordian, and Calpionella Limestones: Korowa Limestone Member - Tithonian, Sobótka Limestone Member - Lower and Middle Tithonian. Quartz grains are especially numerous in crinoid limestones and lower part of nodular ones. Sources of quartz material are seen in hypothetical geanticlinal crests, delineating geosynclinal basin of the Pieniny Klippen Belt in the north and south. Two features of surface of quartz grains, originating in the course of diagenesis of limestones – silica plastering and polygonal siliceous network – are described in the paper. Silica plastering (Table I, Fig. 8) is represented by thin silica plates, about a dozen micrometers in diameter, set oblique to grain surface. Table I, Fig. 9 shows development of polygonal siliceous network. Both structures originated in result of precipitation of poorly ordered silica at grain surface. No correlation between the degree of crystallinity of silica in radiolarites and nature of diagenetic alterations of quartz grain surface was found. The grains were subdivided into groups on the basis of differences in size and surface features (Fig. 2). Figure 3 shows surface features of grains from each group. There were differentiated four environments in which an equilibrium between environmental agents and quartz grain surface has been established: eolian environment (groups 6, 7); marine, nearshore environment with low-energy of mechanic action (groups 4 and presumably 5); water environment with low to high energy of mechanic action (group 3); zone of weathering of rocks yielding quartz grains (groups 1, 2, 8 and 9). The analysis of surface of quartz grains made possible preliminary reconstruction of conditions predominating in areas of geoanticlinal crests, i.e. source areas of the grains. The ridges were marked in paleomorphology in the form of an arc of islands in part built of weakly diagenesed sandstones. Grains with cracks in siliceous cover (Table III, Fig. 19) indicate hot climate with high temperature oscillations. Coastal zone was narrow and characterized by high-energy waving. Slopes of the islands were very steeply dipping towards sea deeps. The presence of grains with features of the groups 4 and 5 evidences that “quiet” embayments were also present.