ON THE ORIGIN OF SEDIMENTARY DOLOMITES

The author sets forth his ideas about the formation of dolomite rocks, according to prolonged mineralogical and petrographic investigations and in accordance with experimental physical and chemical data received by 0. K. Yanatyeva. It is shown that formation of dolomites may take place in various ways,' and that means of dolomitization by replacement are diverse, it being known that phenomena Of lime sediment replacement are predominant. Basic characteristics of primary chemical and of replacement dolomites belonging to the period of sediment diagenesis- are established. Six principal cases of the formation of replacement dolomites after, CaCO₃ limes are distinguished. During the Precambrian and the Paleozoic CO₂ in the atmosphere was much higher than at present; according to the author this contributed to the broadness- of the “field of dolomite formations” at that time. In most cases the increase in salinity to a Certain limit favors the formation of dolomites equalizing the solubilities of dolomite and of calcite. This work contains also some criticism of N. M. Strakhov's ideas stated in an article entitled “Facts and Hypothesis in the Problem of Dolomite Rock Formations” (Izvestiya, U. S. S. R. Academy of Sciences, Geology series, no., 6, 1958) giving a fallacious interpretation of the principal questions raised. The relation of the overwhelming majority of fossil dolomites to seas and lagoons is shown in the article: The vast development in nature — particularly in Paleozoic sediments — of primary sulfate-dolomite and of dolomite sulfate rocks, as well as the dolomite content of most anhydrite and gypsum confirms the ideas of the author about the frequent formation of dolomite in saline lagoons involving MgCO₃, not in cases however of high MgCO₃ concentration in the solution. — Author's English summary