GEOLOGY OF SVALBARD

SVALEX 2009 Arild Andresen

A Window into the Barents Sea Hydrocarbon Province

Svalbard- An uplifted part of the Barents Sea• The Barents

Sea/Svalbard is

– bordered to the N by a rifted margin

– bordered to the SW by a sheared or transtensional margin

Spre

ading

ridge

• Svalbard represents the uplifted and exhumed part of the Barents Sea

• Post-Devonian rocks on Svalbard can be considered as field analogues for many of the source and reservoir rocks in the deeper part of the Barents Sea

Svalbard

Barents Sea

Bjørnøya

Norway

Simplified W-E profile across central Spitsbergen and the Olga Basin, Western Barents Sea

Seismic data in the fjords of Svalbard

SVALEX cruises in 2006

Geology of Svalbard• Pre-Devonian Hecla Hoek

Basement, variably reworked during the Caledonian orogeny

• Devonian continental deposits (Old Red Sandstone)

• Early/mid-Carboniferous rift deposits

• Mid Carboniferous- Permian shelf carbonates

• Mesozoic silisiclastic deposits

• Tertiary deposits, including foreland basin deposits

Opening of the Fram Strait illustrating movement of Spitsbergen past NE Greenland

Pre-Devonian Basement

Devonian deposits• Strike-slip

movement on major fault zones

• Fault -bounded basins (Pull apart basins?)

• ”Old Red Continent” deposits

• The deposits are dominated by conglomerates and sandstones

Devonian sedimentation and deformation

• Deposition of continental sediments in fault-bounded basins

EastWest

• Combined strike-slip and reverse movement (transpression) along the Billefjorden Fault Zone results in folding of the Devonian deposits (“Svalbardian Phase”)

Early- to Mid-CarboniferousWest East

• Deposition of Early Carboniferous coal-bearing (pre-rift) fluvial deposits

• Mid-Carboniferous syn-rift marginal marine deposits, including conglomerate, sandstone, anhydrite/gypsum and dolomite, in the Billefjorden and St. Jonsfjorden Troughs

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Billefjorden

Synthetic seismic

SvalSim

Carboniferous deposits

• Pre-rift: Coal-bearing continental deposits

• Syn-rift: Alluvial fan and sabkha conditions

• Early post-rift: Marine carbonate platform

• This part of the stratigraphy will be studied in the Billefjorden area

Late Carboniferous and Permian

• Slow thermal subsidence and post-rift deposition• Stable carbonate platform with little influx of clastic

sediments• Deposition of a thick succession of carbonates and

evaporites

Permian• Stable marine carbonate

platform. • Kapp Starostin Formation:

Spiculitic limestone and chert.

Mesozoic• Change from carbonate to

silisiclastic deposition• Continental shelf conditions• The deposits are dominated by

shales and sandstones• Little or no tectonic activity• This part of the stratigraphy will

be studied in the Festningen section

Mesozoic

Festningen

Early? Cretaceous intrusives

• Dolerite intrusives into the Permian Kapp Starostin Fm

Dolerite/diabas dyke

Early Tertiary

• Prior to formation of a transpressional orogen in West Spitsbergen, coal-bearing sediments (black) were deposited in much of the area occupied by Spitsbergen today. This Early Tertiary coal is today mined in Barentsburg, Longyearbyen and Svea

Tertiary• Horisontal shortening of

beds is caused by “space problems” as Spitsbergen moves past NE Greenland

• Compression (transpression) of the region resulted in creation of a foreland basin.

• This basin can now be observed in the Central Basin of Spitsbergen.

Arctic Plate Tectonics and Opening of the North Atlantic Ocean

M10132 Ma

A24B55 Ma

A1333 Ma

Present

Schettino & Scotese (2000)

Transpressional regime when Svalbard was forced around the NE “corner” of Greenland along the DeGeer zone. Svalbard is marked by red triangle

Opening of the Fram Strait illustrating movement of Spitsbergen past NE Greenland

Foreland basin profile

• Right-lateral displacement along the DeGeer Zone in the Paleocene created a transpressional orogen (orogenic belt) in the west and a foreland basin to the East. A perpheral bulge existed most probably further to the east.

Foreland basin analogue

• Formation of a foreland basin (pond) can be compared with the bending of an ice sheet next to a pressure ridge due to increased weight. The lithosphere is likewise elastically bent in front of an orogen.

”Foreland basin”

”Orogenic belt”

Paleocene

Evolutionary model:• The foreland basin starts to develop• Development of a thrust wedge in the west and 3 regionally

extensive dècollement zones in the underlying strata

••

••

Folds in Mesozoicshales and sandstones

Miterhuken

Nordfjorden/Mediumfjellet

Tertiary ”thin-skinned” structures due horisontal shortening

• Duplex associated with the Lower Decollement Zone, Kongsfjorden

Tertiary strata

Foreland basin infill• Infill of the

Tertiary foreland basin

• This section will be studied in the Van Kaulen Fjord.

Tertiary clinoforms at Storvola (right) in Van Keulenfjord, Spitsbergen. The sediments were transported from left (NW) towards right (SE)

Tertiary deposits

Eocene

• Continued shortening of the basin• Basin inversion and deformation along the

Billefjorden and Lomfjorden Fault Zones

Thin-skinned shortening structures

• Local thickening in Triassic shale/siltstone associated with the Middle Decollement Zone (gliding horison).

Loc.: Vendomdalen

Middle Decollement Zone

?

The entire fold in late summer!

Thin-skinned shortening structures

Close-up view of the decollement folds at Midterhuken

Inversion structures along Billefjorden Fault Zone

(Remember that the Billefjorden Fault Zone acted as a left-lateral strike-slipfault in the Devonian, and as a down-to-the-east extensional fault in theMid-Carboniferous)

Summary

• Heckla Hoek : Pre- Devonian, affected by the Caledonian orogeny

• Devonian ”Old Red Sandstone” deposits, fault controlled

• Carboniferous rift basins• Mesozoic silicilastic deposits• Late Paleozoic carbonates• Tertiary foreland basin