We can admire picturesque views while travelling in the Carpathian Mountains: at the beginning, when we move from the north to the south, there is an area of delicate waves (foothills) which are next transformed into higher and higher mountains separated with valleys and structural basins. The landscape of this type can be admired nowadays. However, it is worth to be conscious that this territory didn’t always look like this. Once, in a relatively recent geological history, this territory was covered with a sea full of life. The Carpathian Mountains belong to so-called alpine belt that are mountain chains formed during recent large-scale mountain forming movements – Alpine Orogeny. The Carpathian Mountains formation should be connected with slow journey of the African continent towards north and its stress on the Eurasian continent.
From about 150 to 20 millions of years ago on the territory of the present-day Carpathian Mountains there was the Tethys Ocean, which formed an enormous sedimentary basin. The Tethys Ocean was separated with longitudinal elevations of territory of more or less parallel arrangement – so-called cordilleras. As a result of e.g. seismic shakings, various crushed pieces of rocks were thrown into the sea from the cordilleras’ slopes: clay, silt, sands and gravels. Next, thanks to turbidity currents the crushed rocks material was moved to the sea’s bed. Due to its weight and place of sedimentation, the material was subject to sorting. This material, due to the lithification process was transformed into rocks. Gravels formed conglomerates, grains of sand formed sandstones, clay formed claystone, silt formed mudstone. This process was repeated several times. In this manner, the so-called flysh sediments were formed.
As a result of the African tectonic plate’s movement towards north, the Tethys Ocean was reduced and the sediments in the sea were subject to squashing. About 25 millions of years ago, at the turn of Palaeogene and Neogene, the sediments were uplifted and corrugated. The rock mass was detached from the bedrock and it was moved in the form of nappes towards north, to the sediment of the collapse formed in front of the Carpathian Mountains. Gathered flysh sediments created characteristic, alternating strata mainly of sandstone and mudstone. All the Outer Carpathian Mountains are formed of this type of rocks – this is the territory to the north of the Pieniny Klippen Belt.
The process presented above describing the formation of the Carpathian flysh is very general and it only provides an outline of the subject. Processes leading to the formation of the flysh Carpathian Mountains were very complicated and long-lasting. It is worth mentioning that in those formations there were various types of sediment and tectonic structures formed which can be nowadays observed in the rocks; thanks to them geologists are capable of reconstructing the history of the Carpathian Mountains. Finding and providing names for those structures can surely turn into a pleasurable game during walks in the mountains. In the pictures below only few of them are presented.
Sedimentation structures are formed in various ways. They can be divided into primary, that is created during the sedimentation of the material or prior to its lithification, and secondary, usually diagenetic. Primary forms are more widespread and they can be divided due to the processes which contributed to their creation. There are the following structures: depositive, erosive, biogenic and deformative.
Tectonic structures are such forms which are created as a result of various and variable in time areas of stress. In the simplest way, tectonic structures can be divided into two types: continuous and non-continuous. Among the continuous structures there are mainly the plaid and flexure. Depending on the degree of the plaid gradient, the following can be distinguished among others: standing plaids, inclined plaids, inverted plaids and lying plaids (picture). Basic non-continuous structures are among others fault. It is characterized by dislocation of the rock strata along the line of cracks. Depending on the angle and the direction of dislocation there are various types distinguished: strike-slip, thrust fault, normal (picture).