Klintholm Limestone Quarry
Geosite of international value, showing the boundary between the two geological periods Danian and Selandian - and a significant shift in the marine environment from a subtropical sea to a cold 'polar sea'.
Klintholm Kalkgrav (Klintholm Limestone Quarry) is located alongside the Great Belt about halfway between Nyborg and Svendborg. It is one of a total of 13 abandoned pits from which lime was excavated for use as agricultural lime between 1935 and 1973.
At the edge of one of the water-filled lime pits, a 50-meter-long and five-meter-high geological profile has been cleaned up, showing several million-year-old layers of lime and marl covered by deposits from the last ice age.
Visitors are encouraged not to damage the geological profile by climbing, digging and hammering. Fossils can be collected in the nearby limestone piles in the grassy area above the profile.
Klintholm Limestone Quaary is easily accessible via public roads and there is a parking lot on the edge of the area. From here, footpaths lead to the site. Near the coast there are shelters and a campfire site.
The area is owned by the joint municipal company Klintholm I/S, which takes care of environmentally sound treatment, landfilling and recycling of special types of waste. Today, parts of the landfill area have been transformed into a hilly grassy landscape with footpaths, viewpoints and groups of large stones. On some of the stones, the surface has been ground flat by the glaciers of the Ice Age and even covered in scratches (scour marks) created in the direction of ice flow when stones scraped against each other.
In late spring, you may be lucky enough to hear the rare bell frog, whose croak can be heard up to three kilometers away. The bell frog is an endangered species with only a few habitats in Denmark - including here at Klintholm and a few places in the South Funen Archipelago. The limestone-rich soil also gives rise to an exciting flora, and the vine snail thrives in the area.
Danien-Selandien grænsen. (1) Bryozokalk (2) Kerteminde Mergel.Photo:Søren Skibsted
The white chalk
Below is whitish limestone from the Danian period (66-61.6 million years before present). The limestone consists of the remains of small colony-forming organisms, bryozoans (bryozoans). They have crusty, stalked or shrub-like limestone skeletons and formed 3-5 meters high and 50-75 meters long reef-like banks. Remains of bryozoans, starfish, sea urchins, corals, shark teeth, brachiopods (brachiopods that resemble clams) and sea lilies (belonging to the same animal group as sea urchins) are found in the limestone.
During the Danian period, what we now call Denmark was located at roughly the same latitude as modern-day Switzerland and was covered by a warm subtropical sea at a depth of 50-150 meters. The limestone at Klintholm was deposited in this sea, probably quite close to the coast.
Numerous nodules of dark flint can be seen in the limestone layers. As a by-product of the limestone quarrying, the flint was transported to Odense, where it was burned and crushed and later used for white pigmentation of asphalt. Some of the flint was also shipped to what was then East Germany, where it was used in the production of faience.
The gray marl
The transition to the next period, the Selandian (61.6-59.2 million years before present), saw dramatic changes. Volcanic activity, with lava rising from fissures in the seabed, created a land bridge between Greenland and Britain, cutting off the supply of warm water from the Atlantic Ocean.
The Danish sea area was now only connected to the cold sea between Norway and Greenland. In the cold water, the living conditions for the calcareous organisms ceased to exist. At the same time, land uplift in parts of Scandinavia led to increased erosion on land, causing clay and decomposed chalk to be carried out to sea.
These changes in the marine environment led to the deposition of gray, calcareous clay called Kerteminde Marl. At Klintholm, the marl is poor in visible fossils. The boundary between the Danian limestone and the Selandian marl is clearly visible and it is precisely the 'Danian-Selandian boundary' that makes the Klintholm site unique. The boundary can only be seen in a few places in the world.
At Klintholm, deposits from the youngest part of the Danian and the oldest part of the Selandian are missing. There is thus a 'gap' in the layer series of at least half a million years, during which the area was probably above sea level, at least some of the time.
Deposits from the Ice Age
During the ice ages, the glaciers eroded the older layers, which is why the Kerteminde Marl is missing in several places - including in the eastern part of the profile. Here, the 'planed' surface was covered by material that melted free of the ice in the form of moraine gravel or as floating moraine that slid down the sloping limestone surface.
Later, various meltwater deposits followed before the entire area was overrun by a glacier that deposited the upper moraine clay. All the layers are thought to have been deposited during the last ice age, the Weichselian, within the period 23-17,000 years before present.
Profilskitse af lagene i Klintholm Kalkgrav. Den røde streg markerer Danien-Selandien grænsen. Photo:Søren Skibsted
The landscape in the future
Klintholm is located in a slightly undulating moraine landscape that slopes gently towards the Great Belt. The terrain is intersected by a number of smaller, predominantly east-west erosion valleys that flow along the coast - including the striking stream valley with the stream Stokkebækken, which flows into the Great Belt about a kilometer south of the limestone quarries. In some places, there are also smaller areas of dead topography.
The coast towards the Great Belt is a pebble beach with countless flint stones. Strong easterly storms and high tides often create sea walls or accumulations of sand on the beach. At extremely low tide, the seabed off the coast is exposed as large sandy areas with scattered 'stone reefs' and large blocks of granite and gneiss in particular, which the sea has previously washed out of the ice age deposits. There are no active cliffs below the site and the low slopes are mostly covered in grass and scrub.
The majority of the site's immediate surroundings are of artificial origin - partly in the form of former, more or less restored and/or water-filled or overgrown limestone pits and partly by Klintholm I/S's industrial facilities and large landfill areas.
From a geological perspective, the surrounding glacial landscape is unlikely to change in the foreseeable future. The biggest future changes are therefore considered to be primarily man-made, e.g. in connection with the continued use of the areas around Klintholm I/S, as well as the possible future establishment of more 'toad holes' for bell frogs. Furthermore, maintenance of the grassland areas and periodic cleaning of the geological profile will also be required.
In the future, increased precipitation and rising sea levels could affect the groundwater level and runoff conditions in the area, potentially raising the water level in the already water-filled limestone ditches.
Klintholm is a geosite of international value as it is one of the few locations in the world where the boundary between the Danian and Selandian periods can be studied in an open profile. Furthermore, the site is currently one of the only publicly accessible places in the geopark where visitors can study the subsurface layers - i.e. layers older than the various glacial and interglacial deposits of the Quaternary period. Klintholm is thus of high research, educational and communication value, and the site is well known among fossil collectors.
The area also has recreational value with shelters, fire pits, footpaths, viewpoints and artificially placed groups of large stones.
Klintholm Kalkgrav is classified as Geosite GS 2-2 (representative of the theme 'Danian strata and the border to Selandia') and the National Geological Site of Interest NGI-122. The area is also protected under EU Natura 2000 site no. 118 and habitat area H102 and is home to various biotopes - including §3-protected grassland areas and scrub on calcareous soil that harbor many interesting plant communities. The many ponds are important breeding grounds for the endangered bell frog (Bombina bombina).