DEFINITION OF SVALBARD AND SPITZBERGEN ISLAND

Spitzbergen is the largest island (15,000 square miles; 40,000 km2) of Svalbard,

a territory of Norway located in the Arctic Ocean. The

islands are located on the Barents Shelf and are bounded by

the Greenland Sea on the west and the Arctic Ocean on the

north. The entire Svalbard archipelago was originally referred

to as Spitzbergen, but in 1940 the name was changed to Svalbard,

and the name Spitzbergen was reserved for the largest

island of the archipelago that also includes the islands of

Nordaustlandet, Edgeoya, Barentsoya, Prins Karls Forland,

and many smaller islands. About half of the island of

Spitzbergen is covered by permanent ice and glaciers, and

many deeply incised fiords rise to a level of about 3,200 feet

(1,000 m), reflecting a peneplained erosion surface that has

rebounded since the Cenozoic. Since the entire archipelago

lies so far north between 76°–81°N, the Sun remains above

the horizon from late April through late August, but remains

below the horizon in winter months. The warm Gulf Stream

current has a moderating effect on the climate.

The Svalbard archipelago is well exposed and preserves a

complex history of Archean and younger events. The island

chain is broken into three main terranes separated by northsouth

striking faults. The eastern terrane has a basement of

Archean through Proterozoic gneisses and amphibolites overlain

by psammitic and pelitic schists and marbles that are

approximately 1,750 million years old. These are overlain by

pelites, psammites, and felsic volcanics that are about 970

million years old, overlain by 900–800-million-year-old

quartzites, silts, and limestones. A Vendian group of pelites

and glacial tillites formed during the Varanger glaciation.

These are overlain by Cambro-Ordovician carbonates, correlated

with similar rocks of eastern Greenland. Mid-Paleozoic

tectonism is related to the closure of the Iapetus Ocean during

the Caledonian orogeny, known locally as the Friesland orogeny.

West-vergent fold and thrust structures formed in the Mid-

dle and Late Ordovician, whereas late tectonic batholiths

intruded in the Silurian through Early Devonian. North-south

striking mylonite zones are concentrated on the western side

of the terrane and indicate sinistral transpressive strains.

The central terrane contains a basement of mainly Proterozoic

and possible Archean igneous gneisses, overlain by

dolostones and Varanger tillites, overlain by Ediacarian phyllites.

These are followed by Cambro-Ordovician carbonates.

Devonian strata on Svalbard are only exposed in the central

terrane and include Old Red Sandstone facies dated by identification

of fossil fish remains, similar to those of Scotland.

These beds are associated with sinistral transpressive tectonics

with the opening of pull-apart basins, and the deposition

of conglomerates, sandstones, and shales in fluvial systems in

these basins. Devonian and Mesozoic strata are folded and

show eastward vergence.

The western terrane has a gneissic Proterozoic basement,

overlain by Varanger tillites interbedded with mafic volcanics

and overlain by Ediacarian fauna. It is thought that this terrane

correlates more with sequences on Ellsemere Island than

in the rest of Svalbard or Greenland, so it was probably

brought in later by strike-slip faulting. Deformation in Early

Ordovician times in the western terrane is linked with subduction

tectonics, which may have continued to the Late

Ordovician. Later deformation occurred in the Devonian,

possibly associated with the Ellsemerian orogeny.

Some models for the tectonic evolution of Svalbard

invoke more than 600 miles (1,000 km) of sinistral strike-slip

displacements in the Silurian–Late Devonian on the northsouth

faults, bringing the eastern terrane into juxtaposition

with central Greenland. This motion is associated with the

formation of the pull-apart basins filled by the Old Red Sandstone

in the central terrane.

In the Carboniferous through Early Eocene, most of

Svalbard was relatively stable and experienced platform sedimentation,

continuous with that of northern Greenland and

the Sverdrup basin of northern Canada. Early Carboniferous

anhydrites, breccias, conglomerates, sabkha deposits and carbonates

form the basal 3,000 feet (1,000 m) of the section,

and these grade up into 1,500 feet (450 m) of fine-grained

siliciclastic rocks, cherts, and glauconitic sandstones. Mesozoic

strata include more than 8,000 feet (2,500 m) of

interbedded deltaic and marine deposits. A Late Cretaceous

period of non-deposition was followed by the deposition of

nearly 5,000 feet (1,500 m) of deltaic sandstones, shales, and

marine beds in the Paleocene and Early Eocene.

In the Eocene, western Spitzbergen collided in a dextral

transpressional event with the northeast margin of Greenland,

forming folds, thrusts, and later normal faults along the

western coast of the island. Small pull-apart basins formed

during this event and are filled by sediments derived from the

contemporaneous uplifted fold belt. Erosion and peneplaination

in the Oligocene through Holocene formed the flat surface

evident across the archipelago today, with Quaternary

glaciations depressing the crust. Postglacial rebound plus

thermal uplift were associated with the opening of the Arctic

Ocean and the Norwegian and Greenland basins. Quaternary

flood basalts in the northern part of Svalbard are associated

with these extensional basin-forming events.

syncline See FOLD; STRUCTURAL GEOLOGY.

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