The Vøring Basin is a rift basin with a long tectonic history from the late Paleozoic through to the Neogene. Rifting began soon after the end of the Caledonian Orogeny in the Devonian, leading eventually to break-up at the end of the Paleocene, with the onset of seafloor spreading along the northern part of the Mid-Atlantic Ridge. It is an area of active hydrocarbon exploration with numerous oil and gas discoveries.
Structural elements edit
The Vøring Basin consists of a number of terraces, basins and intervening intrabasinal highs between the Vøring Marginal High to the northwest and the Trøndelag Platform to the southeast.[1]
Geological history edit
The geological history of the Vøring Basin has been determined from the rocks exposed onshore in central Norway and particularly in East Greenland where a full sedimentary sequence is found from Devonian through to Paleocene. Most of the other information has come from the results of hydrocarbon exploration, both well data and seismic reflection data.
Caledonian orogeny edit
The basement to the sedimentary sequence of the Vøring Basin was formed during the Caledonian Orogeny, which culminated in the final continental collision between Baltica and Laurentia at the end of the Silurian, in the Scandian phase. At the end of the orogeny the area was occupied by a mountain chain of Himalayan proportions formed by a series of thrust sheets derived from the two continental margins and intervening island arcs and oceanic crust. The leading edge of the Baltic plate had been partially subducted, and eclogites were formed, giving unusually dense areas of basement.
Devonian extension edit
During the Devonian period the mountain belt began to collapse and extend with the formation of major extensional detachments. The extension direction associated with these detachments varies from nearly orthogonal to the Caledonian mountain chain, as in the Fjord Region detachment of East Greenland and the Eidsfjord detachment in Nordland, to strongly oblique in the case of the Høybakken, Kolstraumen and Nesna detachments of south and north Trøndelag. It has been proposed that these detachments have had a major influence on the development of later rift structures.
Carboniferous and Permian edit
During the Late Carboniferous and Permian period the basin is inferred to have undergone continued rifting, from interpretation of the sequences that outcrop in East Greenland.[2]
Triassic rifting edit
Early Triassic rifting is recognised onshore in East Greenland.[2] Late Triassic rifting has been proven within the Vøring Basin, based on well sequences and seismic reflection data. The Late Triassic synrift contains two thick evaporite layers, typically developed as halite, that has affected the geometry of all later faulting. The Triassic salt layers are known from the Trøndelag Platform and Halten and Donna terrace areas and may extend into the main part of the basin towards the northwest, but remain unproven.
Jurassic rifting edit
Following a short hiatus during the early part of the early Jurassic, rifting recommenced, mainly reactivating the Late Triassic rift faults. This rift phase continued until the start of the Late Jurassic. The Late Jurassic marks the main rift phase that formed the Vøring Basin, creating large-scale rift topography, with highly rotated fault blocks. The main sub-basins and intrabasinal highs were formed at this time, including the Træna, Rås, Vigrid and Någrind basins and the Utgard, Vigra and highs. Several large fault zones were also formed during this rift phase including the Revfjallet and Bremstein fault complexes that throw the Halten and Donna terraces down from the Trondelag Platform and the Klakk Fault Zone which formed the boundary between the terraces and the deep basinal areas to the west. The timing of end of this rift event is uncertain with some suggesting that the end of the Jurassic marked the end of active rifting while others suggest that rifting continued to the end of the Early Cretaceous.
Late Cretaceous to Paleocene rifting edit
This major rift phase affects the northwestern parts of the basin and is interpreted to represent the initial stages of break-up. Two distinct phases are recognised withn the overall rift event. The earlier beginning during the Turonian and finishing in the mid-Maastrichtian, the later starting in the late Maastrichtian, finishing at the end of the Danian. The Fles fault zone and Gjallar Ridge fault blocks were active throughout this period. The Nyk fault blocks formed during the second phase.
Break-up rifting and magmatism edit
Towards the end of the Paleocene, the Vøring Basin was strongly affected by magmatism that formed part of the North Atlantic Igneous Province. The Vigrid and Någrind synclines and Fenris and Hel grabens are affected by large sill complexes. These sills were emplaced mainly within thick Cretaceous mudstone sequences at two main times, at about 57 Ma during the Late Paleocene and at 55 Ma at the end of the Paleocene, synchronous with the north Atlantic break-up. Towards the margin small lava flows have been interpreted, forming an area known as the inner flows. Further outboard the main lava sequence forms a large escarpment, the edge of the outer flows. This escarpment continues to the southwest, running most of the way to the Faeroe-Shetland Basin. It is interpreted to be the final part of a long-lived lava delta, with earlier positions of the delta front being visible on seismic reflection data.
Passive margin edit
From the start of the Eocene, the basin became part of the passive margin formed along the southeastern side of the newly created north Atlantic. The passive margin sequence records the continuing subsidence of the basin and the uplift of Scandinavia.
Inversion edit
Towards the end of the Eocene several large inversion anticlines started to form. They had two main phases of growth, Eocene-Oligocene and Miocene. They are mostly orientated north-south and are only rarely associated with clear reversal of older extensional faults. The origin of the inversion is uncertain.
Stratigraphy edit
The proven stratigraphy of the Vøring Basin ranges from Upper Permian to the Quaternary.
Permian edit
A few wells, such as 6608/8-1,[3] have penetrated a sequence of Upper Permian carbonates. The top of this sequence forms a prominent seismic reflector in the Halten Terrace to Nordland Ridge area.
Triassic edit
The Triassic sequence is divided informally into the 'Red Beds' and 'Grey Beds' based on their colour.[4] In well 6507/12-2 two layers of salt were found with a combined thickness of 800m, separated by over 500m of claystones. The uppermost Triassic (Rhaetian) sequence forms the lowermost part of the Åre Formation, part of the Båt Group.[4]
Jurassic edit
The Jurassic sequence is divided into the Båt, Fangst and Viking Groups.[4]
Båt Group edit
The Åre Formation extends in age up to the Pliensbachian. It consists of interbedded sandstone, claystone and coals, with some coal beds reaching 8 m in thickness. It was deposited in a coastal plain to deltaic environment. The overlying Tilje Formation consists of sandstones with interbedded claystones and siltstones, deposited in a nearshore to inter-tidal environment.[4]
Fangst Group edit
The Fangst Group consists of two sandstone units, the Garn and Ile Formations, separate by a thick claystone, the Ror Formation. The Garn sandstones are typically coarser than the older Ile sandstones.[4]
Viking Group edit
The Viking group are mainly claystones, with the lower Melke Formation being somewhat calcareous and the overlying organic-rich Spekk Formation.[4]
Cretaceous edit
The Cretaceous of the Vøring Basin is dominated by claystones, divided into the Cromer Knoll and Shetland Groups. Important sandstone units are locally developed at several levels within the sequence. The Lange Formation includes various Lower Cretaceous sandstones, developed over the Halten and Donna terraces.[4] The Lysing sandstones are of Late Cenomanian to Turonian/Coniacian age and are known from the Halten and Donna terraces,[4] and in the Vigrid syncline as proved by the 6605/8-1 well.[5] The Nise sandstones are Santonian to Campanian in age and are particularly well-developed in the northern part of the basin.[4] Springar sandstones are of Campanian to Maastrichtian in age.
Hydrocarbon exploration and production edit
References edit
- ^ Blystad, P. (1995). "Structural elements of the Norwegian continental shelf Part II: The Norwegian Sea Region" (PDF). NPD-Bulletin. 8. Norwegian Petroleum Directorate: 34–36. Retrieved 15 January 2012.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b Surlyk, F. (1990). "Timing, style and sedimentary evolution of Late Palaeozoic-Mesozoic extensional basins of East Greenland". Special Publications. Vol. 55. London: Geological Society. pp. 107–125. ISBN 9780903317559 http://sp.lyellcollection.org/content/55/1/107.abstract. Retrieved 5 February 2011.
{{cite book}}: Missing or empty|title=(help) - ^ NPD. "General information for 6608/8-1". Norwegian Petroleum Directorate. Retrieved 14 January 2012.
- ^ a b c d e f g h i NPD. "Fact Pages Norwegian Petroleum Directorate". Norwegian Petroleum Directorate. Retrieved 15 January 2012.(Note: to access the stratigraphy section, click on the 'Stratigraphy' button on the menu bar and follow links to lithostratigraphy and then the relevant group or formation)
- ^ NPD. "General information for 6605/8-1". Retrieved 15 January 2012.