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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:
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.
It contains "superlative natural phenomena" and "areas of exceptional natural beauty and aesthetic importance". The mo-clay sediments are rare if not wholly unique - occurring only in this special form by the Lim fjord. The mo-clay region certainly comprises unusual landscape features of great aesthetic value. The region comprises unique natural phenomena such as the world's largest series of volcanic ash layers which are readily observed in quarry walls and natural cliffs, together with an abundance of exceptionally well preserved fossils. The glacial tectonic features and stratigraphy are of extraordinary quality.
This region is perhaps the most concentrated and readily accessible site in the world for research in all the major geological disciplines.
The area comprising these unique mo-clay sites and their environs from Thy across Mors, Fur and Salling to Ertebølle is of a sufficient size to comprise all important aspects of this distinctive region.
The geological formations and landscape of the mo-clay region with its hills and cliffs are largely intact. The area covers a total of 200 km2, most of which is used as farming land - a use which does not conflict with the need for conservation. The coastline and cliffs and major features such as Feggeklit, Hanklit and Skarregaard at Mors are under a conservation order, while Hanklit specifically is a designated international geosite.
A small area of the region is affected by industrial exploitation of the mo-clay. The preservation of the region as a whole is however subject to very detailed assessment and planning. Exploitation is confined strictly to specific parts of the region, and monitored closely by local and regional authorities. But in fact, the quarrying that has taken place is precisely what has exposed the diversity of fossils and produced the extensive knowledge of the region's special geology. The landscape affected by industrial use is subsequently restored and parts of the exposed walls are left as they are for research and educational purposes.
Mo-clay, by virtue of the special factors that brought about its creation, its special blend of diatoms, clay and volcanic ash, its specific history of maturation and the extraordinary diversity and volume of its fossils, is unmatched anywhere in the world.
Diatomaceous deposits exist in many other places. There are chalky, marine diatomites in the Mediterranean Region, along with fish fossils, but these are of much earlier date (less than 10 million years old), and their ash series are far less extensive. California has the deepest marine diatomite layer at around 300 metres of the same age at Lompoc, again with many fish fossils but only a few ash layers. None of these so far are World Heritage sites. Small diatomaceous lake deposits are known worldwide, some with limited series of ash layers, many with a low diversity of fish and many insects, and most of them are much more recent than the mo-clay occurrences, and scarcely comparable.
Due to the very extensive series of volcanic ash layers, these constituting the most unusual feature, the deposits of the mo-clay region are difficult to compare with other regions and sites. The uniqueness of the region from a global perspective also derives from the wealth of diverse geological phenomena within such a limited area. This is remarkable and only adds to its scientific and educational potential.