Bor w osadach ilastych górnego wendu lubelskiego skłonu platformy wschodnioeuropejskiej

Maria Wichrowska



The paper presents the use of boron as an index of salinity of Upper Vendian clay deposits occurring in the vicinities of Radzyń, Kaplonosy and Białopole, eastern Poland. Boron is primarily accumulated in illites so the hulk of analyses were carried out on clay fraction comprising grains below 2 μm in size (fraction A). Some identifications of boron in whole rock samples and the fraction 2-5 μm (fraction B) were also made (Tables 1 - 3). The content of boron was found to be over 200 ppm in the studied clay fractions, showing marine origin of the relevant rocks (Fig. 5b). "Adjustment" of boron content by taking into account the content of K2O in illite appears to be important for appropriate correlation of deposits (Fig. 5a). Mineral composition of illite-kaolinite-chlorite suggests that the studied rocks are related to acid crystalline ones (Figs. 1-4).
Authigenic illite is an ideal index of salinity as detrital illite may yield boron either carring from parent rocks or absorbed in the course of transportation. The analysis of geochemical facies indices of alimentary environment (V, Cr, Ba) showed that material deposited in Vendian sedimentary reservoir in NE Poland was coming from weathering covers of granitoid rocks in the Mazury - Suwałki elevation and Podlasie metamorphic complex (M. Wichrowska, 1978). When this is the case, there is no reason to assume that the studied illites originally yielded any significant quantities of boron. Thus it may be accepted that the recorded content of boron is the function of salinity of sedimentary reservoir and its use as a salinity index seems justified in the case of these deposits. The analysis of mineral composition and concentration of boron in the studied samples showed that the deposits were originating in marine reservoir characterized by increased salinity (Walker 1968). The recorded slight differentiation in mineralogy and geochemistry may be explained by nonuniform advancement of transformation processes, facilitated by long-lasting, stable hydrodynamic conditions in the basin, e.g. in the Białopole area, or temporary deepening (e.g. in the case of the Siemiatycze Series deposits in the Radzyń area). Mineral composition of samples from the borehole column Radzyń IG-1 corresponds to that of almost pure illite, suggesting negligible supply of terrigenous material and quiet sedimentation in a deep zone of the basin.

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