Egzoskopia ziarn kwarcu z osadów czerwonego spągowca rejonu Poznania w elektronowym mikroskopie skanningowym

Abstract

Przeprowadzono badania powierzchni ziarn kwarcu skał piaszczystych dolnego czerwonego spągowca z rejonu Poznania w elektronowym mikroskopie skaningowym. Na podstawie pokroju ziarn, stopnia ich obtoczenia, charakteru urzeźbienia powierzchni oraz rodzaju i sposobu wykształcenia powłok diagenetycznych określono procesy zachodzące podczas transportu, sedymentacji i diagenezy.  EXOSCOPY OF QUARTZ GRAINS FROM THE ROTLIEGENDES OF THE POZNAŃAREA IN THE SCANNING ELECTRON MICROSCOPE Quartz grains from detrital rocks of the Obrzycko Series (Autunian) and terrigenous rocks of the Saxonian (J. Pokorski, 1976) were studied with the use of scanning electron microscope. The analysis· covered core samples from the Obrzycko 1, Września IG 1 and Pniewy IG 1 boreholes.The studies were aimed at identification of agents responsible for transportation of detrital material as well as reconstruction of sedimentary environments. Attention was paid to the shape of grains, degree of roundness, surface relief and the mode of development of diagenetic coatings. Both single grains and rock fragments were analysed.The studies made it possible to state that: 1. In Autunian rocks, quartz grains are sharp-edged, with conchoidal fractures and diversified surface (Table I, Figs. 1, 2; Table II, Fig 3). Terrigenous grains appear to be fairly common in tuffites.Smoothened and semi-rounded grains with strongly levelled surface implicate fluvial transportation (Table V, Fig. 9). Detrital grains with rough, mat surface with marked traces of flaking implicate long-lasting eolization under arid desert conditions (Table III, Figs. 5–6).2. In Saxonian rocks, almost exclusively terrigenous grains are present (Table VI, Fig. 11; Table VIII, Fig. 16). Numerous forms of relief: often overlapping one another, may be noted at their surface. They evidence different transportation media and sedimentary environments. Roundness and smoothening of grains presumably resulted from fluvial transport, whereas surfaces subjected to secondary smoothening dispay traces of activity of mechanical and chemica1 processes which could have taken place in desert environment (Table IX, Fig. 18).3. Autunian and Saxonian rocks are cemented with siliceous-clay material which also forms diagenetic coatings on grains (Table II, Fig 4; Table VII, Fig. 13; Table VIII, Fig. 15; Table IX, Fig. 17).Neogenic quartz is infilling space between grains (Table V, Fig. 10; Table X, Fig. 19). Forms idiomorphic in outline and resembling authigenic clay minerals, are occasionally found (Table X, Fig. 20).