Grain-size distribution of sediments in Lake Munozero (Baltic Sea drainage basin)

Bottom sediments have archived a continuum of information about past and recent natural events. Seeking to learn more about the deglaciation process in the Onega ice lake basin, we studied bottom sediments from Lake Munozero situated in North-west Russia (Republic of Karelia). The lake has a tectonic basin; the water surface area is 0.144 km², the elevation above sea level is 79 m. Three sediment cores up to 4.80 m thick were exposed and their lithostratigraphy was described. Visually, the sediment column in the studied 6.00-9.00 m core can be divided into two intervals: sediment in the 6.00-8.86 m interval, made up of beige, greenish-brown gyttja formed during the Holocene; sediment in the 8.86-9.00 interval – greenish-gray clayey silt formed during the Pleistocene.

Analysis of the grain-size distribution in sediments in the 8.00-9.00 m interval revealed the paleohydrodynamic environment for sedimentation in Lake Munozero during deglaciation. Studies have demonstrated that the water dynamic regimes changed at least twice during the transition from a nival to a humid climate. In the 8.00-8.30 m depth interval the sand fraction prevails with 81% to 87%, while the silt fraction contributes 13% to 19%; at the 8.46-8.66 m depth the sand fraction constitutes 87% and 88%, and the silt fraction 12% and 13%; in the 8.80-9.00 m layer the sand fraction declines from 63% to 11%, while the silt fraction grows from 36% to 78%. The share of the clay fraction at 8.00-9.00 m depth is minor, 3% on average. The highest clay content is found in the 8.88-8.90 m interval (13%).

The research was funded from the federal budget under state assignment to KarRC RAS (Northern Water Problems Institute KarRC RAS) and partially funded by RSF grant #18-17-00176.