TRANSFORMATIONS OF HIGH-CHARGED SWELLING MINERALS DURING EARLY DIAGENESIS IN RECENT SEDIMENTS OF GDANSK BAY (BALTIC SEA)

The aim of the study was to recognize early diagenetic transformations of clay minerals likely taking place in brackish environment of Gdańsk Bay (Baltic Sea). Vistula River loads and sediments of Vistula prodelta (collected from seafloor and from two cores) were studied. pH was determined for 1:1 sediment-water slurry. Clay fraction was separated using Jackson’s procedure (1969). X-ray diffraction patterns were collected for oriented mounts of Na⁺-, K⁺-, Li⁺- saturated samples. Layer charge locations in swelling clays were determined by Green-Kelly test. The charge values were measured using OD method (Kuligiewicz et al., 2015). Relative contents of major cations in studied clays was analyzed using SEM-EDS.

The Vistula River and seafloor sediments were characterized by pH values 6.7-8.42. In studied cores below the seafloor pH decreased down to 2.5. Dioctahedral smectite (montmorillonite), mica, and kaolinite were main constituents of the clay fractions from Vistula loads. Traces of chlorite and hydroxyinterlayerd minerals (HIM) were also identified in the loads. The seafloor sediments also contained smectite, mica, and kaolinite. Clay fractions from the cores were significantly depleted in smectite and enriched in chlorite relative to the clays from the seafloor and the Vistula loads. Layer charges of swelling clays in all studied samples were from 0.46 to 0.56 per formula unit which indicated that the clay fractions were dominated by high-charged smectites. Clay fractions from the Vistula prodelta were enriched in K₂O, MgO, and Fe₂O₃ relative to the clays separated from the loads.

Selective absorption of magnesium and/or iron and the hydroxylation are likely reactions leading to formation of chlorite at the expanse of smectite during early diagenesis in the Gdańsk Bay sediments. The process has to be taken into consideration in sedimentary basin studies.

Acknowledgments:

This study was financed by National Science Centre, Poland [grant number: UMO-2016/23/N/ST10/01388].

Jackson, M L, 1969. Soil Chemical Analysis. Advanced Course, 2nd edition. Published by the author, Madison, Wisconsin.

Kuligiewicz A, et al., 2015. Measuring the layer charge of dioctahedral smectite by O-D vibrational spectroscopy. Clay Clay Miner. 63, 443–456.