The Smalfjord diamictite, Bigganjargga Tillite or Reusch's Moraine is a

diamictite Diamictite (; from Ancient Greek (): 'through' and (): 'mixed') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that range in size from clay to boulders, suspended ...

Finnmark Finnmark (; ; ; ; ) is a counties of Norway, county in northern Norway. By land, it borders Troms county to the west, Finland's Lapland (Finland), Lapland region to the south, and Russia's Murmansk Oblast to the east, and by water, the Norweg ...

, northern Norway. The rock was first identified as a

tillite image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

by Hans Reusch in 1891, hence its name. The tillite overlies

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

whose contact surface is striated. Reusch's Moraine belongs to the Smalfjord Formation, a geological formation of

Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic geologic eon, eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era an ...

age. The tillite possibly formed during the Sturtian glaciation in connection to a global glaciation. Reusch's Moraine was among the first sites discovered to bear evidence of Precambrian glaciations, being only preceded by findings in Scotland (1871), Australia (1884) and India (1887). The site is remarkably illustrative and Reusch's 1891 sketch has been labeled "iconic" by Paul F. Hoffman. The area has been protected by law at least since the 1960s and it is forbidden to

hammer A hammer is a tool, most often a hand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nail (fastener), nails into wood, to sh ...

the rocks.

Differing interpretations

While the idea that the rocks and striations are of glacial origin have been endorsed by numerous geologists, a few have disagreed. As early as 1900 did A. Dal question the glacial origin. In the 1960s other geologists followed suit and challenged the established interpretation. A 1964 study by J.C. Crowell proposed the diamictite to be a

mudflow A mudflow, also known as mudslide or mud flow, is a form of mass wasting involving fast-moving flow of debris and dirt that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/se ...

deposit and the striations to be caused also by a mudflow. In 1966 Reading and Walker attacked the mudflow interpretation on the grounds that evidence for contemporary deformation, an expected feature of mudflow deposits, is lacking. The glacial origin idea has been aided by the fact that the diamicton deposited during a period when the Earth was subject to a widespread glaciation. New arguments against a glacial origin were put forward in 1996 by Jensen and Wulff. They argued that the underlying sandstone is not substantially older than the diamicton and that it was not fully consolidated when the striations were made. This argument is based on their findings of imprints of diamictite clasts and diamictite clasts within the sandstone. The same authors claim that the fact that the clasts of the diamicton are locally derived argues against a glacial origin. As such Jensen and Wulff concluded the diamictite is a

debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented Rock (geology), rock flow down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. ...

deposit. Countering these argument M.B. Edwards claims that if the sandstone was unconsolidated then the size of the

clast Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks b ...

s seen in the imprints would have formed much deeper grooves during striation. Edwards adds further that tills made up of locally derived clasts are nothing rare in the geological record.

References

Cryogenian Geography of Finnmark Geology of Norway Neoproterozoic Europe Neoproterozoic geology Sedimentary rocks Glacial deposits of Norway {{Geology of Fennoscandia Sturtian glaciation