Profil glin morenowych w Wólce Pietkowskiej (Nizina Podlaska) w świetle analiz litologicznych i mikroskopii elektronowej

Abstract

MORAINE TILL SECTION AT WÓLKA PIETKOWSKA (PODLASIE LOWLAND) IN THE LIGHT OF LITHOLOGICAL ANALYSES AND ELECTRON MICROSCOPY Summary The paper presents lithological characteristics of four horizons of tills assigned to the South-Polish Glaciation (P1 and P3) and the maximum and North-Masovian (Wkra) stages of the Mid-Polish Glaciation (Ś1 and Ś3, respectively). From the point of view of granulometry the tills represent silty-sandy or silty-clay sediments with poorly sorted clastic material. Paleozoic limestones predominate on crystalline rocks in their petrographic composition. The share of dolomites is also significant, and local rocks are mainly represented by Upper Cretaceous mudstones. Heavy mineral assemblage mainly comprises garnets, amphiboles, and epidotes but the share of chlorites is also significant. Content of calcium carbonate is equal 15% at the average, and pH is varying from 8.2 to 8.5. Table III shows results of studies on frequency of microstructures at surface of the analysed quartz grains. Surface of quartz grains from Pleistocene tills appears markedly more diversified than that of those from Oligocene bedrock. Rounded grains from tills most often display the following microstructures: irregular fractures varying in size and form and sometimes passing into arcuate crack-offs, V-shaped depressions varying in size, and conchoidal breakages (but the latter are here relatively rare, small and with gentle margins). Angular grains are mainly characterized by microstructures of mechanical origin, especially those of the conchoidal breakage type. Block fractures are also common, being sometimes represented by fractures of the microblock type. Moreover, there occur same V-shaped depressions. Microstuctures of the diagenetic type (e.g. those from precipitation of silica) are generally scarcer on angular grains from tills than on those from modern moraine sediments. The analysis of surface of quartz grains from the whole section showed that diagenetic features are mare common on grains coming from top parts of the till horizons.