The geological evolution of Bjørnøya, Arctic Norway: Implications for the Barents Shelf

David Worsley, Torleiv Agdestein, John G. Gjelberg, Knut Kirkemo, Atle Mørk, Inger Nilsson, Snorre Olaussen, Ron J. Steel, Lars Stemmerik

Publikation: Bidrag til tidsskriftArtikelForskningpeer review

56 Citationer (Scopus)

Abstrakt

The small island of Bjørnøya ("Bear Island"), situated in the Barents Sea almost midway between northern Norway and Spitsbergen, displays a Precambrian to Triassic succession in a continuous series of spectacular cliff exposures. These exposures provide a key not only to the evolution of the Stappen High (on which Bjørnøya rests) but also to the development of analogous structures along the major lineaments that subsequently contributed to the formation of both the Norwegian-Greenland Sea and the Arctic Ocean.

Precambrian to Ordovician dolomites, limestones, quartzites and shales form the basement on which the Upper Palaeozoic succession of Bjørnøya was deposited. In latest Devonian and early Carboniferous times the area subsided asymmetrically, probably in response to NE-SW extension; a southwestwards downtilted half-graben developed over the present-day island, with the basinal axis dipping gently NNW. Some 600 m of sandstones, coals and shales are preserved in two upward coarsening sequences. These represent the repeated progradations of sandy fan systems over floodplains with lakes and northward meandering river channels. Mid-Carboniferous (Serpukhovian) uplift was followed by renewed rifting and the same western hinterland again shed debris over its faulted eastern margins. A shift from humid to a semi-arid climate is reflected by the predominantly red colouration of the resultant 200 m thick succession of conglomerates, sandstones and shales, with caliche horizons. Penecontemporaneous regional sea level rise resulted in the gradual replacement of the alluvial floodbasin deposits by shallow marine siliciclastics and carbonates of shoreline, tidal flat and shallow shelf origin. Continued transgression through the Moscovian, perhaps also with decreasing subsidence rates and only intermittent tectonism, is indicated by the gradual change to a marine carbonate-dominated succession, with cherty biomicrites reflecting the establishment of an open carbonate shelf over the entire area.

A marked rejuvenation of tectonic activity in the late Moscovian established a different depositional mosaic-faulting affected exposures on the present island along N-S to NE-SW lineaments, with differential subsidence down to the west. This produced erosion of earlier deposits over the eastern part of Bjørnøya and deposition of conglomerates, sandstones, shales and dolomites in alluvial gully, coastal and shallow shelf environments to the west. A 200 m thick succession is preserved in western areas and eroded remnants are also preserved as outliers elsewhere on the island. Conglomerate clasts indicate derivation by successive stripping and redeposition of mid-Carboniferous to uppermost Devonian and then basement strata. By the latest Carboniferous the region had again stabilized and platform carbonate deposition resumed, with the development of paleoaplysinid carbonate build-ups. Early Permian flexuring, uplift and peneplanation followed, probably with some transpressive movements. The highly condensed mid- to Upper Permian marine succession of mixed siliciclastics and carbonates oversteps all older strata. The Stappen High then remained a positive feature through to the late Triassic, the youngest beds preserved being of Carnian age. The high subsequently subsided significantly during the Mesozoic, but it again became a positive feature as a result of one or more phases of uplift during the Cenozoic.

Much of the Carboniferous succession of Bjørnøya, with non-marine rifted sequences giving way in the mid-Carboniferous to a marine carbonate shelf development, mirrors time-equivalent successions throughout the Barents Shelf, northeastern Greenland and the Sverdrup Basin. Late Carboniferous and early Permian faulting, flexuring and uplift, and the development of overlying, condensed and stratigraphically incomplete Upper Permian/Lower Triassic platform sequences are however atypical features - only found on local structural highs which together form elements of a major circum-Arctic fault complex along which Paleogene continental separation took place. A hetter understanding of the late Palaeozoic evolution of these highs may contribute significantly to further hydrocarbon exploration in this fron tier petroleum province.
OriginalsprogEngelsk
Sider (fra-til)195-234
Antal sider40
TidsskriftNorsk Geologisk Tidsskrift
Vol/bind81
Udgave nummer3
StatusUdgivet - 2001

Programområde

  • Programområde 3: Energiressourcer

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