Charakterystyka petrograficzna fosforytonośnych iłów ornatowych z Regulic i obszarów przyległych

Abstract

PETROGRAPHIC CHARACTERISTICS OF PHOSPHORITE-BEARING ORNATUS CLAYS REGULICE AND FROM ADJACENT AREAS (CRACOW VOIVODESHIP)

Summary

The paper deals with the general geological conditions and the occurrence of phosphorite-bearing strata in the Upper Jurassic deposits (Callovian, Divesian and Neuvizyan) within the zone of their outcrops that stretch through Oblaszki, Regulice, Grojec and Rudno (Fig. 1). There are given results of petrographic, mainly of microscope examinations of grey Ornatus clays and of marls connected with them. Besides phosphorites, these deposits disclose numerous fossils, particularly rostra of beillemnites, shells of ammonites .(Tables I and III) as well as pebbles and fragments of older limestones and sandstones. At places, the clays contain much calcium carbonate, passing into sandy marls, light-grey or brownish in colour. Some of them reveal abundant quartz and glauconite, whereas other contain only small amounts of these minerals.
Here are distinguished phosphorites formed at the same time, as marls and clays, or almost contemporaneously, i.e. syngenetic phosphorites and those brought into the deposits from the earlier eroded strata. In some places, the earlier (displaced) phosphorites were absorbed by syngenetic ones, or were mixed with them.
Both the syngenetic and the earlier phosphorites contain the same detrital minerals, but in various amounts. Moreover, here are found also the same phosphate substances of (mainly) kolophane and francolite types.
Among the syngenetic phosphorites there occur phosphorite concretions characterized by rough surfaces, with large amounts of arenaceous material, first of all, quartz and glauconite grains and fine calcite fragments, as well as fossil casts and few pseudomorphs with relatively small amounts of arenaceous substance. The displaced, earlier phosphorites are distinguished mainly by their polished surfaces, oval shapes, weathering rinds, as well as by a considerable amount of arenaceous substance.
Both the syngenetic and the displaced phosphorites were formed under similar conditions. Later on, they underwent silification, the traces of which, however, can hardly be observed at present.
More visible are calcitization phenomena, particularly as concerns those from the period following the formation of the phosphorites. In the later period, calcium carbonate was removed from the phosphorites, probably also from their neighbouhrood. After removing, ooids characterized by various shape were formed, frequently reflecting the outlines of the rests of organisms.
The amount of P₂O₅ in the phosphorites varies and reaches up to 27.5% in casts. Because of their low contents in 1 m³, the phosphorites here considered do not present any industrial value.