Kokořínsko Protected Landscape Area

Geology and Geomorphology

The Kokořínsko PLA territory occupies the southern section of the Ralská pahorkatina hilly land geomorphological unit and occupies most of the Polomené hory district. The south and south–east of the territory also belong to the Dolní Pojizeří table unit.

The georelief of Kokořínsko PLA can be described as an erosional – denudational relief and its formation was largely due to the lithological character of Cretaceous, Tertiary and Quaternary rocks. We can find a structured series of levels (steps) broken by an extensive network of canyon-like valleys. The majority of the PLA territory is covered by calcareous sediments – sandstones of the Jizera Formation (Middle, and partly Upper Turonian in age). Three lithological units can be determined and these are inverse, upwards – coarsening cycles. In the lowest of these units marlstones pass to siltstones and these calcareous clayey, calcareous, and finally quartzose sandstones coarsening upwards. The following sedimentary cycle has fine-grained calcareous clayey to calcareous sandstone at its base and coarser and coarser quartzose sandstones and granule conglomerates as we move upwards. The highest sequence usually begins with fine-grained silty sandstones transforming into quartzose sandstone and finally into coarse-grained gravelly sandstones as we move upwards. In the south–east of the territory the lime component of the sediments is higher and quartzose sandstone is replaced by calcareous sandstones to limestones. The quartzose sandstones of the lower and middle cycles also contain elements of poor silty-clayey or calcareous matrix. In the middle and upper sequences small upward-coarsening cycles and cross-bedded intervals are found in places (migration of submarine sand ridges).

The permeability of the quartzose sandstones and their jointing led to the formation of a dense network of canyon-like valleys and small complexes of castellated rocks (near Mšeno, Vojtěchov and Bukovec), among which the temperature inversion results in a reverse of the vegetation zones with montane species growing on the valley floors and thermophilous species higher up (vegetation inversion). The capstones (known locally as Pokličky or little lids) which can be seen at the mouth of the Močidla canyon in Kokořínský důl and between Vojtěchov and Jestřebice were formed by selective weathering of the ferruginous sandstones and conglomerates. Rock formations of similar origin are the rock arches (at the mouth of the Kaninský důl canyon and on the edge of the Rač plateau), rock windows, tors and ledges. Pseudokarst phenomena are represented by cavities, rock niches, rock-shelters (Krápník, Tisícový kámen) and caves which have been deepened and extended by human hands (Klemperka, Partyzánská jeskyně, Obraznice, Kostelíček, Nedamy etc.), karren and pitted surfaces on the surface of the sandstones (Husa Nature Monument).

The sandstones of the Jizera Formation are an important source of underground water. The drainage effect of the joint systems is reflected by the resurgences (springs) found in some of the deeply carved valleys, but mostly through the hidden groundwater issues under the alluvial plains.

In the Late Turonian to Coniacian periods, partly silicified marlstones were laid down followed by limestone (Inoceramus opokas) or more rarely calcareous claystones of the Teplice Formation, which form the denudation remnants in the Vysoká area and between Nebužely and Kanina and landslips often happen on them. The Coniac calcareous claystones with siltstone and sandstone intercalations (Březno Formation) are represented in deep layers in the České středohoří Fault (locally called Úštěk Fault) between Blíževedla and Litice as well as on the slopes of Ronov hill (552 m). This fault of Tertiary age is characterised by the subsidence of northern blocks. Only small faults are found in other sections of the PLA territory and together with the jointing systems led to the formation of valleys, ravines, castellated rocks and other phenomena.

The Tertiary period is only represented by the neovolcanic rocks (subvolcanic rocks) which are concentrated around Dubé and to the north of Mšeno and were important in forming the landscape. The best-known is the sodalite trachyte of Vrátenská hora mountain (507 m), the sodalite phonolite of Mt. Vlhošť (613 m) and the trachytic rock on Nedvězí hill (458 m). Basaltic rocks are represented by the olivine-free nephelinite of the Velký Beškovský kopec (474 m) and Špičák (378 m), the olivine sodalitite of Koňský vrch hill (429 m), the sodalite of Dubová hora (397 m) and the bodies of subvolcanic breccia - Supí hora (433 m) and on the slopes of Mt. Ronov (552 m), the peak of which is formed of nepheline basanite.

The most extensive areas with Quaternary sediments are covered with Upper Pleistocene loesses and loess loams with colluvio-eolian sediments found on the steeper slopes. In places the foot of the slope is covered with colluvial sediment. The youngest elements from the Holocene are the fluvial loam and sand dominated floodplain sediments and the lithologically similar colluvio-fluvial sediments in valleys of morphological importance. Hidden groundwater issues on the valley floodplains resulted in the formation of marshlands and marshy meadows.