Geneza dolomitów cechsztyńskich
Abstract
ON THE ORIGIN OF ZECHSTEIN DOLOMITES Summary Zechstein dolomites belong to a large group of dolomites both physically and genetically related to evaporites. The studies showed that they originated in resulted mixing of fresh and marine water as well as polyphase reflux. A low content of strontium, very well ordered structure and stechiometric composition of the dolomites are typical of those formed in result of mixing of fresh and marine water and reflux in time of deposition of carbonate sediments. Differentiation of the two types of dolomites is possible after detailed analysis of evolution of sedimentary and diagenetic environment, in which dolomitization has taken place. Dolomites originating in result of reflux in time of sedimentation of sulfate and salt deposits are characterized by increased content of strontium, poorly ordered structure and nonstechiometric dolomite ratio. The results of studies showed that the Zechstein dolomites may vary in origin even within a single carbonate horizon and often within a given paleogeographic zone. This makes it necessary to analyse each case separately. In the past, attempts were made to explain all the features of dolomites related to evaporites in terms of a single mechanism, which resulted in questioning index value of some features of these rocks (e.g. composition and degree of ordering of structure) for reconstruction of conditions of dolomitization. In peripheral part of the Zechstein and elevations in its central part, dolomitization was primarily related to reflux from time of sedimentation of carbonates, mixing of fresh and marine water, as well as deposition of sulfates in the sebkha environment, and in the central part - to reflux related to sedimentation of salt in the playa environment. The regularities may be assumed to be typical of all the dolomites related to evaporites.Downloads
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Geochemia, mineralogia, petrologia
