Pre-Quaternary

From the geological point of view the area of Lithuania is located in the south-western part of the East European Craton (EEC). More than 1.5 Ga geological history is recorded in the sedimentary cover of Lithuania. Deeply submerging Phanerozoic sedimentary succession, overlying the crystalline basement is represented by the Riphean-Vendian and all the systems of the Phanerozoic to Quaternary, pointing to the persistent subsidence throughout the time (Fig. 1). The structural pattern of the area mostly reflects the configuration of the underlying crystalline basement and features of the Caledonian orogeny. The strongly faulted, displaced by steps and elevations Precambrian crystalline basement gradually submerges to the southwest, from depths of 200 m to 2300 m (Fig. 3). The basement is composed of magmatic and metamorphic rocks, such as granite, gneiss, quartzite, amphibolite etc. The thickness of the earth’s crust in the territory of Lithuania varies in a range of 40–55 km.

Subsidence prevailed during the Paleozoic with occasional short-term uplift events, while non deposition environment prevailed throughout Latest Paleozoic-Cenozoic time span interrupted by shorter sedimentation events. In the most of territory the Cambrian and younger sediments overlie the deeply eroded surface of crystalline basement. The most complete geological section is recorded in the western Lithuania, where the thickness of the sedimentary cover exceeds 2 km, gradually attenuating to the east towards the Mazury-Belarus High. The Paleozoic, Mesozoic and Cenozoic successions are everywhere covered by 0.5-10 to 300 m thick (~ 150 m in average) Quaternary sediments. The Phanerozoic succession is mostly composed of shales, marl, limestone, evaporite, clayey-sandy and calcareous sediments deposited in deep marine, shelf, lagoonal and continental environments. Only the upper part of the sedimentary section, e.g. Quaternary, Neogene, Cretaceous, Jurassic and Devonian sediments crops out at the surface. The older Silurian and Devonian sediments are distributed in the east, while youngest Neogene-Paleogene strata were mapped in the SW part of Lithuania.

Sub-Quaternary relief of the area is highly dissected by palaeoincisions (Fig. 2). The altitudes of the sub-Quaternary surface vary from 90-100 m above sea level to nearly 30-70 m below sea level. The relative depth of paloeincisions reaches 100-150 m and locally even exceeds 200 m.

The tectonic structure of the territory of Lithuania is defined by features within the underlying Precambrian crystalline basement. Several major structural units are distinguished within the territory based on the structure of the crystalline basement, thickness and stratigraphic completeness of the sedimentary cover and the facial distribution. These units include the Baltic Syneclise, the Latvian Saddle, the slope of the Mazury-Belarus High and the Polish-Lithuanian Depression (Suveizdis, 1979; Paškevičius, 1997).

The Baltic Syneclise is the largest traverse structure on the western edge of the EEC. It’s an area of uneven crystalline basement formed of Proterozoic rocks overlain by sedimentary succession. The surface of the basement rocks subsides from 300-500 to 1200 – 1400 (4000) m, and the monoclinal pattern exhibits only rare and small anti- and syn-form structures. The steepest slope of the Syneclise dips in 15-20 m/km in SE part of the area. The Mazury-Belarus High edges the territory of Lithuania from the east and the south. The thickness of the sedimentary cover is less than 500-800 m due to syn-depositional and post-depositional (erosional) wedging of most strata. The most intense uplift of the high occurred during the latter part of the Hercynian time (more than 1 km). The Polish-Lithuanian Depression is represented in the south-westernmost part of Lithuania only by its eastern edge. It is the deepest of the tectonic features within the study area, and depth to crystalline basement reaches 2 km. The Latvian Saddle is the gently dipping area stretching in longitudinal and latitudinal directions. The crystalline basement occurs at the depth of 400-1050 m below sea level and the inclination of the surface is around 2-6.5 m/km. The sedimentary cover is composed of Vendian-Devonian strata. Some Triassic, Permian and Devonian deposits are exposed in the quarries.

The sedimentary succession of Lithuania is subdivided into four major structural-sedimentary complexes: Baikalian, Caledonian, Hercynian and Alpine, based on the tectonic events in the region. Structural-sedimentary complexes differ by their geological composition and inconsiderably by the structural pattern. All of the complexes are separated by unconformities within the sedimentary succession that represents periods of non-deposition and erosion.

Baikalian and Caledonian complexes gradually submerge to the NW following the dip of the crystalline basement. The major structural elements of these two complexes are all defined by features within the underlying Precambrian crystalline basement. The thickness of the Baikalian complex varies from 30 to 265 m. It is represented by volcanomictic gravellite, sandstones and shales.

The thickness of Caledonian varies from 400 m in the eastern part of the Baltic Syneclise to 2500 m to the SW. A 50–250 m thick the Lower-Middle Cambrian sandy succession occurs at the base of the complex. These strata are covered by 35–250 m thick Ordovician shales and carbonates, passing to 200–1260 m Silurian graptolitic shales (Paškevičius, 1997). The Lower Devonian terrigenous sediments reach up to 250 m in the SW.

The structural setting of the Hercynian complex differs considerably from the underlying complexes as well from the structural pattern of the crystalline basement. The top of the Hercynian complex is dipping northwards; thickness reaches up to 800 m (Paškevičius, 1997). The complex is represented by a clastic-carbonate succession mostly of the Devonian age. The uppermost 50–450 m of the Devonian strata were eroded during the Carboniferous uplift. The Carboniferous strata of a few dozens of meters thick occur only on the NW part of the area. The Lower Permian succession attains up to 55 m of thickness.

The Alpine complex includes Late Permian carbonate-evaporitic complex and a mixed Mesozoic and Cenozoic succession with total thickness reaching up to 600–1500 m (Suveizdis, 1997). The complex occurs mainly in the S and SW of the Baltic Syneclise. The thickness of the Permian strata ranges from 20 m to 270 m. 100–500 m thick Lower Triassic red beds are overlain by 170 m thick Jurassic sediments. The Cretaceous terrigenous and carbonate succession, up to 220 m thick, occurs in the SE of the area. The sedimentary cover is crowned by several dozens meters thick glacial Quaternary deposits.

The crystalline basement of Lithuania is strongly dissected by tectonic faulting (Fig. 2). Two major types of faults prevail in the region, i.e. the oldest pre-platform and younger platform features. The former are defined in the crystalline basement and do not dissect the sedimentary cover, whereas the latter penetrate into the sediments overlying the crystalline basement. The faults detecting the sedimentary cover are oriented N-S, W-E, NW-SE and NE-SW predominantly.

The territory of Lithuania was commonly regarded as tectonically inactive at present time. Still, available data show that the vertical movements were rather active in Lithuanian territory during the neotectonic period. According to some instrumental measurements, the Baltic area is affected by NW-SE tectonic compression which might initiate seismic shocks along numerous neotectonic fault zones mapped in Lithuania (Šliaupa, 1998, 1999). Vertical movements of the Earth’s crust are related to the activity of the tectonic blocks, bounded by faults of the crystalline basement and sedimentary cover. The modern vertical movements are of different intensity and trend over Lithuania. The present activity of some faults is verified by high-accuracy geodetic measurements in Ignalina geodynamic polygon.

The sedimentary succession of Lithuania is subdivided into four major structural-sedimentary complexes: Baikalian, Caledonian, Hercynian and Alpine, based on the tectonic events in the region. Structural-sedimentary complexes differ by their geological composition and inconsiderably by the structural pattern. All of the complexes are separated by unconformities within the sedimentary succession that represents periods of non-deposition and erosion.

Rocks and fluids - e. g. the structural elements of the Earth’s underground - are comprising an important part of environment we are living in. Geological and tectonic structure and composition of the crystalline basement and sedimentary cover, magnetic and gravitational fields of Earth etc. are crucial factors, determining the distribution of mineral recourses, influencing the stability of territory and evolution of various geological processes. That’s why the knowledge about the Pre-Quaternary succession is while taking solutions, related with extraction of mineral resources and its environmental impact, protection of environment, implementation of new raw materials and sources of energy, prognosis, forecast and mitigation of geological hazards and utilization of underground storages. Thus, comprehensive investigations of the pre-Quaternary succession of Lithuania and the pre-Quaternary mapping at the different scales (Pre-Quaternary geological map of Lithuania and adjacent territories, Map of relief of sub-Quaternary surface of Lithuania, Structural map of the top of the Crystalline basement of Lithuania) are one of the basic targets of the Lithuanian Geological Survey. Regional geological and geophysical investigations are carried out by the Department of Bedrock Geology, aimed to study the structure and composition of the crystalline basement and pre-Quaternary sedimentary cover, properties of sedimentary rocks, tectonics, geodynamic and seismic processes occurring in the Earth underground. Processing, interpretation and modelling of seismic, magnetic and gravity, geoelectric, deep seismic reflection and well-log data ensures comprehensive analysis of the pre-Quaternary succession.

Detail information about the geological structure of Lithuania can be obtained from:

  • Geological Reports,
  • Publications of LGS,
  • Maps.


Fig. 1. Pre-Quaternary geological map of Lithuania and adjacent territories.

Fig. 2. Map of relief of sub-Quaternary surface of Lithuania.
 

Fig. 3. Structural map of the top of the Crystalline basement of Lithuania.