Skład mineralny osadów moreny czołowej lodowca Gas (Spitsbergen) z uwzględnieniem analizy powierzchni ziarn kwarcu w SEM

Abstract

Przeprowadzono badania próbek z powierzchni wału morenowego w zachodniej części strefy marginalnej lodowca Gas. Przeważają skały osadowe, tj. wapienie białe, czarne oraz kalcyt, mniej liczne są okruchy skał metamorficznych - fyllity i łupki, a udział kwarcu jest znikomy. Osad jest przeważnie gruboziarnisty. Na podstawie badań w SEM ziarn kwarcu frakcji 1,0-0,5 mm oraz 0,5-0,25 mm wykazano, że udział wielkoskalowych przełamów muszlowych charakterystycznych dla środowiska glacjalnego jest niewielki. Dominują ziarna zaokrąglone o powierzchni zniszczonej procesami chemicznymi na skutek rozpuszczania i wytrącania krzemionki. Stąd wniosek, że środowisko glacjalne cechowało prawdopodobnie dość znaczne nasilenie procesów diagenetycznych.

MINERAL COMPOSITION OF DEPOSITS OF GAS GLACIER FRONTAL MORAINE

(SPITSBERGEN) WITH REFERENCE TO SEM ANALYSIS OF QUARTZ GRAIN SURFACE

Petrographic composition of 8 samples of moraine deposits of the Gas Glacier is determined by composition of surrounding rocks. That is why debris of sedimentary rocks (white and black limestones and calcite) predominates here and fragments of metamorphic rocks (black phyllites, green schists and especially quartzites) arc much less common. The share of quartz derived from crystalline rocks is negligible. The shape of rock fragments of the sand size appears to be specific, determined by mineral composition. Large grains, especially of black limestone, are generally more angular than the small, and their margins are sharper.

Granulometric analyses showed that the deposits are generally various-grained, mostly coarse. Samples no. 3. 4 and 5 represent deposit similar to till mainly consisting of coarse grains but also of some of the clay- and silt-size ones. Samples no. 1, 2 and 6 and 7 represent sandy-gravel with small share of silt and sample no. 8 the most homogeneous sandy deposit, mainly consisting of fine- and medium-grained sand.

The studies carried out with the use of scanning electron microscope comprised 10 quartz grains of the fractions 1.0 – 0.5 and 0.5 – 0.25 mm. Tables I – X show that large-scale conchoidal fractures, regarded as typical of the glacial environment, are fairly rare here. The grains are often somewhat rounded, with surface strongly destroyed by chemical processes. From beneath the surface, pyramidended quartz growth crystals sometimes appear (Table II L Fig. 6). Rounded grains often display both obliterated traces of old fractures and surface strongly destroyed due to mechanical collisions. In the latter case, the surface is covered with V-shaped depressions. It should be noted that other parts of the same grain may display surface changed in result of silica solution or precipitation processes. Destruction of grain surface of the exfoliation type is also noted. It is connected with scalying of chips or minor fragment of quartz from grain surface presumably due to the action of frost. accompanied by some chemical processes. The resulting chips may be often found in various places throughout the surface.

Conchoidal fractures of various size arc most often found on angular grains: They are often accompanied by various step-or ridge-like forms with smooth surface. The studied glacial environment was probably characterized by fairly high intensity of diagenetic processes and their quantitative predominance among those effecting the quartz grains.