Zmiany facjalne skał żelazistych w ordowiku podłoża północno-wschodniej Polski

Abstract

FACIES CHANGES IN FERRIFEROUS DEPOSITS IN THE ORDOVICIAN OF NORTH-EAST POLAND

The author performed a petrographic study of glauconitic rocks and limestons with chamosite oolites from the Ordovician from north-east Poland. Special attention was given to changes in the microscopic aspect of the rocks connected with the transition, from a glauconite to a chamosite facies. This transition may be seen in chamosite rims occurring around glauconite grains, and in glauconite relics found in cores of chamosite oolites. Both minerals may be associated as infillings in crinoidal remains. The author discusses the opinions of different investigators concerning the influence of oxidation-reduction conditions on the formation of glauconite and chamosite. She considers the diagram of Krumbein, and Garrels (1952) which presents a classification of chemical sediments is terms of pH and Eh conditions and which in some points gives a new opinion as. to the paragenetic associations of iron minerals. The author concludes that some of her observations are in agreement with the scheme of Krumbein and Garrels, but supposes that the Eh conditions suitable for glauconite and chamosite are rather similar. The formation of glauconite is, however, furthered by a supply of terrigenous material rich in potassium and it is replaced by chamosite, when this supply is gradually exhausted. In the authors opinion the small concentration of iron in the investigated sediments is the result of undisturbed sedimentation, not interrupted by intraformational erosion and redeposition. This supposition is collaborated by the lack of intraformational fragments and by the absence of distorted oolites in the investigated sediments.