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Abstract

Four main periods in the geologic history of Spitsbergen are the early Precambrian géosynclinal period, the Riphean-early Paleozoic miogeosynclinal period, the Devonian postgeosynclinal (orogenic) period, and the late Paleozoic-Cenozoic platform period.

In the pre-Riphean period, intensive downwarping was followed by subaqueous flows (mostly mafic) and then by inversion of the géosynclinal troughs.

The early Riphean stage is characterized by flyschlike sedimentation. In the middle-late Riphean stage, a complete sedimentary cycle was developed, ending with pre-Paleozoic uplift and peneplanation. At the end of this stage, the slow downwarping which had compensated the general uplift of the archipelago was replaced by smaller-scale uplift and downwarp. In the early Paleozoic stage, a basin developed in Spitsbergen, and shallow-marine sedimentation took place. In the late Ordovician-Silurian stage, the Caledonian geosyncline developed into a complex fold area, the crystalline basement blocks of the Caledonides were “rejuvenated,” and granite and subalkalic intrusions were emplaced.

In the Devonian postgeosynclinal period, horsts and grabens were formed. Orogenic processes were accompanied by development of superimposed basins that were filled with molassic terrigenous deposits up to 6,500 m thick. During the same period, lamprophyre dikes were emplaced.

The late Paleozoic-Cenozoic period included four stages of platform development. In the late Paleozoic stage, terrigenous and carbonate deposits about 2 km thick were formed. Quiet conditions in the Early Car-boniferous were followed by intense block movements in the Bashkirian Age. At the end of the Late Carboniferous, the complex of uplifts and depressions became a single basin, and total uplift at the end of the Permian completed the stage. In the Mesozoic, mainly terrigenous sediments 3 km thick accumulated in a great basin. Total uplift in Late Cretaceous time ended this stage. Intensified block movements localized early Cenozoic basins, which were filled with coal-bearing and conglomerate formations 1.5-4 km thick. The early Cenozoic stage ended with the inversion of the sedimentary troughs, followed by faulting and overthrusting. In the late Cenozoic stage, intense differential motion was renewed along preexisting faults. Uplift was greatest in the inverted mobile zone of the Vestspitsbergen trough. At the end of the stage the center of uplift migrated eastward, and uplift decreased in the Holocene. The Holocene was characterized by volcanic activity and a possible increase in seismicity.

Spitsbergen is now characterized by platform development. The basement of the platform contains two Caledonian fold systems, which frame the Precambrian stable region. The Caledonides of Spitsbergen and Greenland are very similar, but probably were not directly connected to the British-Scandinavian-Sever-naya Zemlyan Caledonides.

Main tendencies of Spitsbergen's post-Caledonian history are an increase in mobility at the western edge of the platform and steady uplift of the northern part.

Analysis of Spitsbergen's structural history allows a positive prognosis for oil and gas prospects in the southern part of the archipelago and the adjoining shelf.

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