site 37

Where is the site located?

GPS: 49° 44′ 41.91″ N, 15° 44′ 39.57″ E

The area lies in the southern extension of the Iron Mountains National Geopark, on southwestern slopes of the Iron Mountains which progressively descend to the Doubrava Basin with the winding Doubrava River. The nothern vicinity of the Kladruby u Libice village provides important sources of groundwater, and displays a sinking stream.

What is the geological position of the site?

The site is located in the Bohemian Massif, in the southeastern part of the Bohemian Cretaceous Basin. The basin fill has been preserved along the whole southwestern slope of the Iron Mountains in a structure called “the Long Furrow Cretaceous”. Upper Cretaceous sediments were modelled by subsequent geological processes, creating a structure very favourable for the accumulation and utilization of groundwater.

What happened at this site in the past?

– 95 million years

In the course of the Mesozoic, the supercontinent of Pangea was falling apart into separate lithospheric plates, which drifted atop the elastic asthenosphere. In the latest Mesozoic, this area was lying on the Northern Hemisphere, becoming a part of the Eurasian Plate. The climate was very warm, controlled by the greenhouse effect which induced a rise of global sea level. Flooding occurred over large portions of dry land. In the Late Cretaceous (a part of the last period of the Mesozoic), this site was a shallow sea passage, progressively flooded by warm sea waters. It was located in a shallow near-shore zone, locally dominated by sand, abundantly colonized by bivalves, gastropods, crustaceans and fish. With prolonged flooding, progressive deepening of the depositional area occurred.

What does the site display today?

This site is built by sediments of Upper Cretaceous age, which constitute the extension of the Bohemian Cretaceous Basin elongated along the southwestern slope of the Iron Mountains in the form of the Cretaceous of the “Long Furrow”. They comprise formations of largely marine sediments, originally unconsolidated, which were subjected to diagenetic changes (hardening) through geological time. The lowermost unit is the Peruc-Korycany Formation formed by sandstone and claystone, some 50 to 60 m thick. It is Cenomanian in age (Cenomanian is the first age of Upper Cretaceous). They are overlain by a ca. 30 m thick succession of marlstone and sandy marlstone of the Bílá hora Formation, deposited in the Early Turonian (the oldest part of the second age of Upper Cretaceous). The Jizera Formation lies the closest to the earth surface and consists of harder silty marlstone with spongilitic admixture. It is 50–70 m thick and was deposited in Mid Turonian (the middle part of the second age of Upper Cretaceous). The original almost horizontally lying formations left behind by Late Cretaceous sea were later affected by tectonic forces, which are responsible for their present position. The pile of sediments was divided into separate blocks, and mutual movements of these blocks occurred along faults. The largest displacement occurred at the Železné hory Fault, along which the block of the Iron Mountains was uplifted by several hundred metres. Most of the sediments have been removed by erosion. The remaining strata are somewhat bent, forming an asymmetrical concave-upward structure limited by the Železné hory Fault against the Iron Mountains. Upper Cretaceous sediments in this area display favourable characteristics for the accumulation and transport of groundwater. The individual formations contain rocks with aquifer properties, more or less naturally separated from each other by rocks with sealing properties, almost impermeable for groundwater. As such, they constitute a multi-aquifer hydraulic system. The lowermost aquifer A is bound to sandstones of Cenomanian age, followed by aquifer B formed in sandy siltstones of Lower Turonian age, and by the topmost aquifer C associated with silty marlstones of Middle Turonian age. Groundwater flow is strongly controlled by faults: each block of Upper Cretaceous sediments has an independent regime of groundwater circulation. The Kladruby Block has been defined in the Kladruby area. A certain proportion of groundwater in this block is derived from the adjacent crystalline rocks along, being transported to this block along faults. In this case, the Upper Cretaceous sediments swallow waters of a whole stream coming from the top of the Iron Mountains. Drainage of groundwater in this area was mediated primarily by strata-bound springs and/or overflow springs.

What was affected by man?

The spring issues have been noted by our ancestors already. In the latter half of the 20th century, water from local springs started to be used for communal water supply. Spring reservoirs were constructed in this area, making use of gravity for water distribution. In the 1980s, these sources were boosted by drilled wells approximately 80 m deep. Water from these wells cannot be distributed without pumping.

What was discovered?

This withdrawal area provides high-quality groundwater, used for the water-supply system covering the Chotěboř and Havlíčkův Brod areas.

“The Iron Mountains – a geologically significant region” project of 2014

An information panel was manufactured within the project of “The Iron Mountains – a geologically significant region”. It was installed in the centre of the Kladruby village, by the access road in the proximity of the local information booth. The spring area is located some 500 m northeast of the panel. The withdrawal area is closed to the public; any access is permitted only when accompanied by the operating company staff.