The clayey diatomite commonly known as “mo-clay” (Moler) is found only at locations in the western Lim Fjord region in the northwest of Denmark, the largest and most impressive deposits being those on the two islands of Mors and Fur. Smaller seams are found in the surrounding areas of Thy (Silstrup), Salling (Junget) and Himmerland (Ertebølle).
Mo-clay is a very rare sediment composed of diatoms, a type of algae, from the Lower Eocene (56-54 million years ago) bordering onto the Palaeocene Era. The mo-clay contains about 200 distinct layers of volcanic ash correlating to the volcanic provinces of what are now Greenland, the Faeroe Islands and Great Britain, and to the opening of the Atlantic Ocean, which brought about the creation of the map of the world as we know it today.
This landscape of hills and cliffs contains mo-clay deposits 60 metres deep.
The mo-clay and ash layers were displaced and folded by the great glaciers during the latter part of the last ice age, giving rise to an extraordinarily beautiful and dramatic environment. The hills and cliffs stand in contrast to the fjord – with the natural walls of pale yellow clay accentuated by dark bands of volcanic ash.
The region is mostly privately-owned faming land. The coastal zones are under a conservation order which strictly prohibits building and quarrying. Specific landscape features in the area are totally protected, such the cliff of Hanklit, which stands as one of the earliest examples in Denmark of a popular movement to conserve natural heritage. Hanklit is also a designated international geosite. Skarregaard in Hesselbjerg is owned by Morsø Municipality, and managed by the historical museum. The “cape” of Mors, called Feggeklit, is also under full conservation.
Excavation of mo-clay for industrial purposes started in1903, and inevitably left scars in the landscape. In 1983, a working committee representing industry and national, regional and local authorities as well as environmental interest groups was established. The committee was set up to provide evaluation and to plan future excavation. As a result, a number of selected areas have now been reserved for recreational purposes, leaving other parts for utilisation by industry over a term of years, the firms having pledged to restore the landscape beyond the requirements of current legislation. The plans for utilisation and conservation from the early 1980s are still adhered to and meetings of the various stakeholders are held annually.
Universal importance of the region
The mo-clay region is consistent with the World Heritage Convention, art. II, definition of natural heritage: A precisely delineated natural area, geological and physiographical, of outstanding universal value from the point of view of science, conservation and natural beauty.
The mo-clay as a sediment is very rare, if not unique, and occurs only within a small area in the northwest of Jutland, by the Lim Fjord. As a diatomite, it is made up of two-thirds opal frustules and one third minerals and volcanic ash. The mo-clay formation contains some 200 distinct ash layers, representing deposition processes over 1½ million years. This permits both relative and absolute dating of ash layers and hence unusually precise correlations across a vast area of environmental impacts.
The 60-meter deep deposits of mo-clay contain exceptionally large quantities of fossils of a diversity that provides a perfect record of both aquatic and terrestrial life from a period about 10 million years after the massive extinction event that brought about the demise of the dinosaurs:
- Birds – more than 30 species, probably the best fossils in the world with feathers and chromatin.
- Reptiles – snakes and probably the “world’s best turtles”.
- Fishes – representing diverse species, including possibly the earliest truly deep-water fish, with rare and spectacularly large and intact specimens, such as tarpon.
- Crustaceans – of great regional importance, e.g. shrimps.
- Insects – more than 200 species, many with colour spots, eye lenses, including grasshoppers with sound apparatus.
- Plants – flowers, trees (redwood up to nine metres), many seeds and fruits.
- Diatoms – more than 130 species.
The state of preservation is extremely good, with details rarely seen elsewhere, and permitting very reliable palaeobiological reconstruction. Some fossils are in 3D, and many of them are the earliest known representatives of their orders. 60% of the finest Danish fossil specimens were found in the mo-clay area.
Huge pseudomorph crystals (1½ metres) and the Stolleklint clay, corresponding to the short-term temperature optimum, which by definition marks the beginning of the Eocene era, have great significance for theories on ocean bottom temperature, climate and diagenesis and are highly pertinent to the current debate on rapid climate change.
This landscape of land elevations and fjord holds great dramatic beauty, of a kind seen nowhere else in Denmark or even anywhere else in the world. Local residents and visitors, including many artists such as the photographer Kirsten Klein, draw great pleasure and inspiration from this natural heritage.