- Last Updated on Wednesday, 30 November 2011 06:08
The uppermost part of the Earth crust in Lithuania has been formed during the youngest geological period – Quaternary (alias as Anthropogenic period) – that began about 1.8 billion years ago. The biggest part of thickness of Quaternary deposits has been formed by glaciers; they where born in Scandinavia and a few times covered territory of Lithuania during the Pleistocene, the first and longest stage of Quaternary. The warmer period spans named as interglacials existed between glaciations, when sedimentation generally took part in the lakes, rivers and bogs. The thickness of Quaternary deposits in Lithuania is very irregular: from a few meters in the North Lithuania until 200 and more meters in the heights of Žemaitija, Medininkai or Vištytis; in the largest part of country predominate thickness of Quaternary is about 80-120 meters. The thickest Quaternary deposits (314.2 meters) are detected in the borehole near to Vembutai settlement, in the Žemaitija Height.
The main geomorphologic features of Lithuanian’s relief have been formed by glaciers and their meltwater. The biggest geomorphologic complexes of recent relief have been formed by Last (or so called Nemunas) Glaciation. Only a small south-eastern part of Lithuania – Plateau of Eišiškės and Medininkai Height – is as relict of previous glaciation. The highest point of Lithuania – Aukštojo Hill (293.8 m above sea level) – is dislocated in this height. All heights of Lithuania are as result of processes of glacial erosion, glaciotectonic and accumulation. The moraine ridges marks the margins of former glacial lobes or tongues; the moraine lowlands prevail in the inner parts of mentioned glacial forms. Much primary moraine lowlands have been reworked by meltwater streams and shielded by glaciafluvial deposits, or damped and covered by glaciolacustrine sediments. After the draying of basins, the latter sediments have been drifted into the dunes in many areas. The resent network of rivers was originated by meltwater streams during the later stage of deglaciation of territory.
The last stage of Quaternary – Holocene – started about 10 thousand years ago, when the climate become significantly warmer and relicts of the glacier finally melted. The intensive sedimentation started in the rivers and lakes. Big thickness of gyttja was sedimented in the lakes; as a result significant amount of lakes overgrow, transmute into the marshes. In Holocene the Curonian Spit was formed due to intensive processes of abrasion, transportation and sedimentation on the Baltic Sea shore. The processes of erosion, which continues until the preset day, left the bright marks on the resent relief: the slopes of hills and valleys was furrowed by ravines and gullies or covered by slides.
At a present day the Quaternary deposits of Lithuania is an object of intensive human activity. For example, about 60% amount of fresh underground water that we are using for centralized water supply is extracted from Quaternary thickness; there are about 98% prospected resources of sand, gravel and clay. Quaternary thickness is an important sphere from geoecological point of view: permeability and physical-mechanical properties of deposits, natural groundwater protection from surface pollution, quality of soils, variety of landscape, and etc. are determinated by composition and peculiarities of geological structure of Quaternary deposits. Thus, geological investigations and geological mapping of Quaternary deposits is one of the main tasks of Lithuanian Geological Survey (q. v. Quaternary Geological Map of Lithuania). The other important direction of investigations – geochemical mapping of Lithuanian soils (q. v. Geochemical Atlas of Lithuania) which enable to estimate as natural composition of geochemical elements, as well as character and scale of anthropogenic pollution. Mentioned information is very important for solution different problems of agriculture, groundwater protection, human health, etc.