Introduction
to the Geology of Svalbard.
H. D. Maher (9/21/98) draft version
Major geologic units: Svalbard has a very
rich, a diverse and long, geologic history that makes it somewhat of a 'mecca'
for geologists, a place where a great variety of geology is on display and
where much can be learned. The richness is partly evident in the outlines
below of major stratigraphic groups and deformation events for Svalbard.
The adjacent simplified map shows the distribution of the four major geologic
units:
- local Tertiary basin sediments (yellow).
- Carboniferous through Cretaceous platform cover sequence
(blue).
- Devonian basin sediments (tan).
- metamorphic basement rocks (pink).
Stratigraphic Groups for post-basement strata: (lines
represent major unconformities)
- Van Mijenfjorden Group: terrestrial and marine siliciclastics
of Tertiary age with basal coal measures. Deposited in various basins the
largest of which is the Central Tertiary basin.
- Adventdalen Group: 950 to 1850 m of Jurassic to Cretaceous marine
black shales overlain by a variety of Lower Cretaceous terrestrial and
near shore clastics. Thicker to the S.
- Kapp Toscana Group: terrestrial and near shore siliciclastics,
with numerous internal discontinuities often forming a condensed section,
with a storm peneplanation deposit. Several meters to 250 m thick.
- Sassendalen Group: Triassic coarsening upwards deltaic and offshore
deposits, with upper hydrocarbon source beds. Overall 250-600 m thick.
- Tempelfjorden Group: spiculitic cherts and intercalated fossiliferous
limestones typically several hundred meters thick.
- Gipshuken Group: transgressive sequence of shallow marine siliciclastics
in local rift basins giving way to carbonate platform conditions with evaporite
and sabkha environments.
- Billefjorden Group: > 650 m thick terrestrial sequence of
mainly quartz arenites with local silts and coally measures.
- Andree Land Group: redbeds representing fluvial systems, common
paleosol development.
- Red Bay Group: coarser fluvial system redbeds.
- great variety of basement units, mainly metasediments, but with some
granites in the NW.
Deformational episodes (from
most recent to oldest):
- Recent glacial rebound.
- Isostatic response to glacial denudation (Blythe and Kleinsphen, 1998).
- Quaternary volcanism in the northwest part of the islands.
- Tertiary transtension, offshore basin and continental margin formation.
- Tertiary transpression (65-38 Ma), polyphase development of variably
decoupled transpressional welt (Maher & others, 1995).
- Late Cretaceous broad uplift and unconformity formation, related to
the High Arctic LIP.
- Late Carboniferous rift basin development (e.g. Billefjorden trough,
Steel & Worsley, 1984).
- Local Serpukhovian folding and thrusting (Adriabukta event, of Birkenmajer,
1981).
- Late Devonian Svalbardian contractional phase (Lamar and others, 1986).
- Devonian basin development (gravitational collapse basins?).
- Polyphase Caledonian mountain building (from 550-350), including extensive
nappe formation, and emplacement of blueschists and eclogites, possible
terrane juxtapositioning.
- Grenvillian nappe formation and subsequent development of regional
angular unconformity, with limited magmatism (Bjornerud, 1990).
- link to reference list:
Tertiary fold-thrust belt:
A primary research interest of mine is in the deformation that effects the
cover sequence and Tertiary strata. The most obvious manifestation of this
event is a fold-thrust belt that parallels the western coast and is responsible
for the uplift, erosion, and exposure of basement rocks along the west coast.
A line demarcating the eastern edge of where these fold-thrust structures
are most obvious is shown in the map below. However, Tertiary deformation
also exists along the E side of the major central Tertiary basin, and along
the large faults in the NE part of the island, basically spanning the width
of Spitsbergen.
Tertiary plate
setting: Similarities in stratigraphy and reconstructions of
plate configurations prior to the development of the Norwegian-Greenland
and Arctic oceanic basins clearly indicate Svalbard, on the NW corner of
the Barents Shelf, was connected to the Wandel Hav basin of NE Greenland.
Opening of the two oceanic basins was linked by a intracontinental, dextral
transform from roughly 65 to 38 Ma, the time of formation of the fold-thrust
belt (Maher & others, 1995). Thus, this orogen was linked to the opening
of oceanic basins as part of a transpressional welt (Harland, 1969) that
developed within a continental platform setting. The concept of decoupling
(Fitch, 1972), that orogen-parallel and orogen perpendicular components
of oblique plate motions were partitioned into different zones to different
degrees, is crucial to understanding this orogen.
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Introduction
to the Geology of Svalbard.