The Holocene sedimentation history of Lake Võrtsjärv, central Estonia

Lake Võrtsjärv is one of the biggest lakes in Eastern Europe and possesses a complex geological history. Bottom deposits consist mostly of fine sand and silt, accompanied with sapropel (up to 9 m thick) and lake marl (up to 8 m thick). In places, especially in the northern part where the bottom deposits are absent, varved clay or till are exposed in the lake basin. In the southern part of the lake the deposits are much thicker, indicating a gradual rise of water-level. Like the majority of lakes in the Northern Hemisphere, Lake Võrtsjärv possesses a more open eastern and a more swampy and overgrown western bank. Shore types and the lithological composition of shore sediments are varied and highly controlled by the bedrock and glacial deposits. Long-shore transport of sediments is limited. The mineral composition of bottom sediments shows great qualitative and quantitative variability which relates to the grain-size and petrography of the parent deposits. Organic-rich sapropel can be used in agriculture and evidently also for medicinal purposes.