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

Finnmark Finnmark (; se, Finnmárku ; fkv, Finmarku; fi, Ruija ; russian: Финнмарк) was a county in the northern part of Norway, and it is scheduled to become a county again in 2024. On 1 January 2020, Finnmark was merged with the neighbouri ...

, 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 ...

Hans Reusch Hans Henrik Reusch (5 September 1852 – 27 October 1922) was a Norwegian geologist, geomorphologist and educator. He served as director of the Geological Survey of Norway. Biography Born in Bergen, he was educated at the University of Leipz ...

in 1891, hence its name. The tillite overlies

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

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

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...

age. The tillite possibly formed during the

Sturtian glaciation The Sturtian glaciation was a Snowball Earth glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined, ...

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 Paul Felix Hoffman, FRSC, OC (born March 21, 1941) is a Canadian geologist and Sturgis Hooper Professor Emeritus of Geology at Harvard University. He specializes in the Precambrian era and is widely known for his research on Snowball Earth ...

. 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 nails into wood, to shape metal (as w ...

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 or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...

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

imprint Imprint or imprinting may refer to: Entertainment * ''Imprint'' (TV series), Canadian television series * "Imprint" (''Masters of Horror''), episode of TV show ''Masters of Horror'' * ''Imprint'' (film), a 2007 independent drama/thriller film ...

s 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 rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

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 ...

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 Troms og Finnmark Geology of Norway Neoproterozoic Europe Neoproterozoic geology Sedimentary rocks Glacial deposits of Norway {{Geology of Fennoscandia