The geology of Slovakia is structurally complex, with a highly varied array of mountain ranges and belts largely formed during the Alpine orogeny in Mesozoic and Cenozoic eras and with relicts of older Variscan structures of Paleozoic age.[1][2] The internal zones of the West Carpathian orogen collapsed during Paleogene forming the Central Carpathian Paleogne Basin and later in Miocene the Pannonian Basin and Carpathian volcanic chain were formed.[3][4]
Most of Slovakia is situated within the West Carpathian orogenic belt, except for the east of the country which is in the East Carpathians. However, the geological boundary does not coincide with the geographical one. A large area in the southern part of Slovakia is covered with Miocene sediments of the Pannonian Basin system. The West Carpathians are Mesozoic to Cenozoic in age. The internal zones were formed on the collapsed Variscan crust during Late Paleozoic and Mesozoic extension.
The Outer Carpathians represent a externides of the Inner Carpathian crustal scale thick-skinned nappes.
Important nappe stacking of the Internal Western Carpathians occurred gradually since the early Cretaceous. With peak metamorphism in the core of the internal zones of the orogen at approx. 120 - 80 million years ago.[12]
In the zone surrounding the Pieniny Klippen Belt, sedimentation was not interrupted and continued from the Late Cretaceous to Paleocene in Gosau type basins, forming the Myjava-Hričov Group including the Súľov Paleogene. Conglomerates, marlstones as well as the Kambühel Limestone were deposited in this period.[19]
Another marine transgression flooded the region from the vicinity of the Flysch Belt into the area of the Internal West Carpathians during the middle Eocene represented by the Sub-Tatra (or Podtatranská) Group or the Central Carpathian Paleogene Basin. Paleogene sediments are found in the Orava, Liptov, Spiš, Žilina and Podhale depressions. Conglomerates are common as the bottom of the succession, overlain by flysch (alternating sandstones and claystones).[20] At the edge of the subducting Flysch Belt, sedimentary rocks are up to four kilometers thick. The Central Carpathian Paleogene Basin rocks are usually not folded, however, local backthrusting was documented.[21]
Molasse deposits laid down in the Oligocene span into southern Slovakia from the Pannonian Basin in Hungary. The back-arc molasse formed several large basins, including the Vienna Basin, Danube Basin, South Slovak Basin and East Slovak Basin in the Neogene (the Danube, South Slovak and East Slovak are all subdivisions of the larger Pannonian Basin).[22] The basins are filled with the sediments associated with the Paratethys Ocean, up to five kilometers thick. Shales and marls are particularly common, intercalated with sandstone, tuff, conglomerate and algal limestones. Sediments became brackish over time as the Paratethys was isolated from the rest of the world's oceans since Sarmatian to Panonian. Overall, the basins are split up by numerous faults and small grabens, such as the Trenčín, Ilava, Horná Nitra Basin, Turiec Basin, Žiar Basin and Orava Basin, often filled with lake sediments.[4]
The volcanic activity was important in the Miocene especially in the Central and Eastern Slovakia.[23] Geophysical research and boreholes have shed light also on the buried volcanic rocks in the Danube Basin. The buried centers were at Šurany or Kráľová.[24] The volcanic rocks are found throughout the Central Western Carpathians and eastern Slovakia. The volcanism was related to the subduction of the Flysch Belt and back-arc extension of the Pannonian Basin.[10] The main phase of volcanism occurred in Badenian and Sarmatian.[25] It is represented by andesite, dacite and rhyolite.[26] Intrusion of granodiorite is known in the area of Hodruša and Banská Štiavnica.[27] Youngest late Miocene/Pliocene to Quaternary volcanic activity was represented by alkaline basalts to basanites.
A swarm of andesite dikes is also documented in the Pieniny Klippen Belt, however, the Cenozoic volcanic activity was negligible compared to the aforementioned.
In the Upper Pliocene, prior to the Quaternary glaciations Slovakia had a subtropical climate akin to Mediterranean climate.[28]
The Quaternary glaciations identified in Slovakia are, from oldest to youngest: Donau, Günz, Mindel, Riss and Würm.[28] During these glaciations glaciers extender downhill from the High Tatras and nonglaciated uplands were subject to frost weathering and solifluction.[28] Deflation of soils is also evident in mountaineous locations.[28]
Peat, eolian wind-blown sands, fluvial sand and gravel and loess are all typical Quaternary sediments, formed in the past 2.5 million years old and dominating the surface of Slovak lowlands.[29] The loess sheets of Slovakia are named, from the lowest to the highest W1, W2 and W3. In between W1 and W2 lies a layer of black-earth soil and between W2 and W3 lies an incipient soil which in parts is gleyed or cryoturbated.[28]
The Váh River has up to seven terraces of sand and gravel. Travertine and tufa is also common, including travertine which preserved a cranial mold of a Neanderthal from Gánovce. Moraine formations remain in the high mountains from the Pleistocene glaciations.[29]
The moderately metamorphosed Spišsko-gemerské rudohorie Mts. formed by Paleozoic rocks of Gemericum hosts veins of siderite, chalcopyrite and tetrahedrite along with the Veitsch-type magnesite (Hnúšťa, Jelšava and Lubeník).[30] Permian rocks often hold uranium ore.[31]
The Kremnica and Štiavnica Mountains formed by the Miocene volcanic rocks have polymetallic lead, zinc, copper, gold and silver veins. Similar, however, less extensive ore veins are found in the Vihorlat and Slanské vrchy Mountains in Eastern Slovakia. Iron skarn related to Miocene volcanism is known in the Muránka planina Plateau.[30]
Salt is found in the Neogene East Slovak Basin and brown coal is extracted from both the Handlová-Nováky Basin and the Modrý Kameň-Potor Basin. There are small deposits of natural gas and oil in the Neogene strata of the Vienna Basin together with older Triassic rocks.[32]