Where is the site located?
GPS: 49°53’33.44″ N, 15°51’47.42″ E
The area lies in the central part of the Iron Mountains National Geopark, near its northern border. Its relief drops into the flat East Bohemian Table towards the Chrudim area in the south, and a slope of the Iron Mountains rises towards the Nasavrky area in the north. The rocky outcrop of the “Na Syslíchˮ site makes an attractive background to the local sporting-recreational facility. It lies within the Farář Nature Monument (Farář is a reservoir with a valuable occurrence of plant Water Chestnut – Trapa natans).
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 as witnesses of progressive flooding of the landscape, culminating by the last sea flooding of this area 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 fell 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 a large portion 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 fishes.
What does the site display today?
Geological basement at Bítovany is composed of two essential rock units. The basement is formed by older (Paleozoic) magmatic rocks of the Železné hory plutonic complex, represented here by the northern margin of the Nasavrky pluton. The latter body consists of granite of the so-called Žumberk type. It is a reddish rock, which is extracted in the near quarries around Žumberk. The basement is overlain by Upper Cretaceous sediments of the Bohemian Cretaceous Basin. The basin is filled with sediments deposited by the Cretaceous sea in northern, central and eastern Bohemia, i.e. in the region which subsided along faults of the so-called Elbe Zone.
Sediments at this site are of Cenomanian age (Cenomanian is the first age of Upper Cretaceous). Their oldest unit is the Peruc Member, represented by an interval of basal conglomerate ca. 2.5 m thick, and by strongly sandy claystone, locally with minute intercalations of carbonaceous matter, preserved in a low depression at the right side of the outcrop. These sediments are still of freshwater origin. They are overlain by the Korycany Member, displaying glauconitic sandstone of the Quadersandstein (pillar-jointed) type. Greenish grains of glauconite (a mineral of the silicate group) point to their marine origin.
What was affected by man?
The present outcrop was mostly created by natural forces, most notably by the erosional capacity of the local stream, now called Ležák.
This outcrop was noted already in the earliest 20th century by our ancestors. It was described in the unique book on natural conditions of the Chrudim and Nasavrky areas. This book was
authored by teachers of science led by Prof. P. Vepřek, the County School Inspector, and published in Chrudim in 1906. Among others, the book documents that sandstone from the Bítovany area was exploited at several sites and used as sand for casting moulds in the near brickyard. Alternatively, it was quarried for the production of whetstone).
Later, geologists initiated the establishment of a nature geological reserve (its existence was declared by Dr. J. Vodička of the Geological Survey in Prague in 1960). In 1990, the outcrop was included in the Farář Nature Monument, also covering the Farář Reservoir and its vicinity. A comparison of photos from the 1960s with the present situation clearly documents a rapid overgrowing of the section by vegetation.
What was discovered?
The outcrop provides the geologists with an important study section. At the same time, it is very suitable for education and demonstration of geological phenomena to the public. Such phenomena are well visible and easily accessible at this site.
The basement is formed by fossil-weathered kaolinized granite of the Žumberk type. The word “fossilˮ means that weathering took place at times prior to Late Cretaceous. The original red rock turned into light grey: it was subjected to chemical weathering under warm subtropical climate, to the so-called kaolinization. In this process, one of the main components of granite – feldspar – became altered to produce kaolinite (a clay mineral). Kaolinite is used as an essential component in ceramic industry.
Granite is overlain by basal conglomerate, about 2.5 m in thickness. This rock comprises pebbles of various sizes, documenting that the streams had energy enough for the transport of coarse material. In contrast, the right part of the outcrop shows signs of low-energy deposition: fine freshwater sediments having the character of grey sandy siltstone with coalified plant remains locally passing to thin, dark grey coal interbeds. These interbeds yielded fossilized remains of leaves of various Upper Cretaceous plants (conifers, palm-like plants), as reported by the authors of the above mentioned book on natural conditions of the Chrudim and Nasavrky areas.
The topmost portion of the outcrop is formed by yellow to yellowish-grey glauconitic sandstones of the Korycany Member. They have the character of pillar-jointed sandstone (called Quadersandstein) and document the sea flooding – transgression – in the Cenomanian. It is composed of quartz grains held together by calcareous cement, and by ferruginous cement in places. It has been shown to contain tiny fossils of marine organisms, especially bivalve shells, as reported already in the book on Bohemian Upper Cretaceous deposits published by Prof. A. Frič in 1870.
“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 erected at the southern limit of the Bítovany village, near a local road in front of the fork to Horní Mlýn (opposite to the football grounds). The geosite is located 200 m east of the panel. A part of the outcrop was cleaned from native woody plants and shrubs (GPS: 49°53’33.44″ N, 15°51’47.42″E).