Skuteč – Přibylov


site 30

Where is the site located?

GPS: 49° 51′ 39.92″ N, 15° 58′ 59.99″ E

The area lies in the eastern part of the Iron Mountains National Geopark. Here, the Iron Mountains stretching towards the Skuteč area in the southwest, pass into the curved margin of the East Bohemian Table in the northwestern vicinity of Přibylov.

What is the geological position of the site?

The site is located in the Bohemian Massif, in the marginal area of the Bohemian Cretaceous Basin. The text below will focus on rocks preserved here after the last flooding of the landscape in the Late Cretaceous at the end of the Mesozoic.

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 tectonic 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 progressive rise of global sea level. Flooding occurred over large portions of dry land, first by freshwaters of rivers and lakes. Later on, a large part of the Bohemian Massif became a part of a shallow sea passage. This site was located in a shallow near-shore zone, colonized by ancient vegetation both on dry land and in water. Waters were dominated by the representatives of molluscs and fish.

What does the site display today?

Geological footwall in the Přibylov area is formed by Upper Cretaceous sediments of the Bohemian Cretaceous Basin. The basin fill in this area is represented by marine sediments of the Bílá hora Formation. They were deposited in Early Turonian (Lower Turonian is the second age of Upper Cretaceous). They are underlain by older, sand-dominated sediments of the Korycany Member of Cenomanian age (Cenomanian is the first age of Upper Cretaceous). These are exposed primarily in the valley of the Svatoanenský Stream.
The Bílá hora Formation is composed of hard, light yellow to greyish-yellow sandy marlstone, silicified in places, showing distinct jointing and bedding. It is traditionally called opoka by the stonemasons.

Opoka is fine sediment which originated from clay, quartz and calcite below sea level. Through geological ages, it became consolidated. Its marine origin is corroborated by greenish mineral glauconite, which is present in the form of minute green grains.
Upper Cretaceous sediments play a significant role in the creation and accumulation of groundwater. A two-aquifer hydraulic system can be recognized in this area because two almost independently functioning horizons of groundwater are developed here.

The first aquifer is a deeper-lying one, associated with older, sand-dominated sediments of Cenomanian age. They hold water in pores among individual sand grains. The second aquifer developed in opokas of the Bílá hora Formation which are fed with water from a system of joints. The two aquifers are separated from each other by an interval of clay-dominated sediments. They function independently, unless deformed with subsequent faulting.
The principal aquifer used for water-supply purposes in this area is the sand-dominated Cenomanian aquifer. Water is withdrawn from the Svatoanenské Valley, where the Cenomanian aquifer was previously naturally drained by a system of springs.

What was affected by man?

The history of extraction of the Přibylov opoka dates to the earliest 19th century. The quarries at Přibylov then provided jobs to masons and navvies, who even built their houses here to avoid long journey to work. The biggest boom of quarrying dates to years 1870–1910. Local stone was valued as good building stone, and it was also used for the production of tiles and troughs. Its use for church artefacts, such as altars, has been equally reported. Most of the quarries were abandoned after World War II.

Operation of the pit quarry at Přibylov was re-started in 1974. Its stone is used for rough stonemason products, such as masonry. The products include, among others, wall and paving panels, masonry ashlars and stripe wall linings. For its excellent qualities, the stone is used for restoration purposes in monument reconstructions. For example, it was used in the reconstruction of the Romanesque rotunda at Říp Hill.

With its yellowish colour, the stone earned its name “golden opokaˮ.

What was discovered?

Exposed quarry faces provide a view of geological sedimentary phenomena like the layered structure of the sediment, bedding planes and their dip angles. Thick beds of hard opoka alternate with thinner and less resistant beds, which are prone to weathering. To make a distinction among fine Cretaceous sediments of different consistency, the early 20th century stonemasons used the following terms: hard, compact marlstone was called “opokaˮ, softer and less consistent portions were called “slínovkaˮ, and very soft marlstone, rapidly disintegrating into scales, were called “shnilotinaˮ (rotten stuff).

Deeper parts of opokas from Přibylov contained concretions (aggregates of alien material of different colour); those as big as a head were called “peckyˮ (fruit stones) by the stonemasons.
As stone extraction progressed, fossil remains after the original marine life or rather rare traces after the activity of organisms were revealed. Finds of plant remains were documented, such as twigs of sequoia-like conifers or remains of wood and bark of trees. This evidences the proximity of seashore.
Finds of marine fauna included compressed echinoids, fish scales and bones, oyster shells and elongated shells of the genus Inoceramus – a typical Upper Cretaceous bivalve.

“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 placed to the centre of the Přibylov village, next to Road 358 between Chrast and Skuteč, near a bus stop. The quarry is located about 150 m south of the information panel. It is an active one, accessible only after a prior consent by the company operating the quarry.

A fossil fish from Cretaceous marlstones from the Chrast area (Daniel Smutek)