Gley catagenesis of Devonian red-colored rocks on the Middle Timan

Abstract

Research subject. The article presents the results of morphological, mineralogical, and geochemical studies into gley zones in the Devonian red-colored sediments of the Middle Timan. Aim. Determination of the timing of gleization processes in the formation history of the Devonian sedimentary strata; identification of morphological, mineralogical and geochemical features of gley zones. Methods. A macroscopic study of the morphology of gley zones in successive sections of the sediments was carried out in field conditions. Thin sections were studied using a Nikon eclipse LV100 ND polarization microscope with a Nikon DS Fi2 camera; polished samples were characterized using a TESCAN electron microscope VEGA3 with an Oxford instruments X-Max energy dispersion attachment; the chemical composition was determined by an X-ray fluorescent silicate method on a MESA-500W spectrometer; X-ray diffraction analysis was performed using a Shimadzu XRD-6000 diffractometer under the CuKα radiation. Results. In terms of size and morphological features, the gley zones under study are divided into four types: point, veined, lens-shaped, and bed-shaped. The similarity between the forms of gley zones and core organics fragments was established both in plan and vertically. The lithological heterogeneity of rocks (stratification) does not have any effect on the development of gley processes. Changes in the content of rock-forming elements during gleization are confined to intensive iron removal and a slight decrease in the potassium content; the silica content remains almost unchanged. An increase in the content of aluminum, titanium, and magnesium was observed. Among the contents of microelements, trends towards accumulation of Y and Yb, removal of Ga, V, Co, Ni are noticeable. Conclusions. Gleization processes proceeded for a very long time until the sedimentary sequence was completely formed and compacted; the main mechanism of chemical element migration was diffusion.