Barents Shelf Research Articles

The last deglaciation of Svalbard

Svalbard has been completely covered by an extensive ice sheet at least once, but not in the Late Weichselian (max. 18,000–20,000 years ago). Areas in the western and northwestern parts of Svalbard have been ice‐free for more than 40,000 years. The extension and time of a Barents Shelf glaciation are questions still open for discussion. For most of the Svalbard area we do not know when the last deglaciation started, geographically and in time. The oldest datings for the interval 15,000 to 10,000 years B.P. have an age of about 12,600 years, and datings from between 11,000 and 10,000 years B.P. are rather frequent in the western and northern parts of Spitsbergen. No moraines from Younger Dryas have been found in Svalbard and the glaciers were probably less extensive 10,000 years ago than today. The maximum extension of glaciers in the Holocene took place only a few hundred years ago.

Contributions to the tectonic history of the Innuitian Province, Arctic Canada

The Innuitian Tectonic Province contains the record of a Phanerozoic mobile belt in northern Greenland and the Canadian Arctic Archipelago. Two fundamentally different phases in its development were separated by the Devonian–Carboniferous Ellesmerian Orogeny. The first contribution focuses on the early Paleozoic history of a key area, the second summarizes the Carboniferous to Cenozoic history of most of the Canadian part of the province.(1) The early Paleozoic architecture of the mobile belt is apparent only in Ellesmere Island, where exposures extend from the Canadian Shield through Arctic Platform and Franklinian basin into the Pearya orogenic welt. The Franklinian basin comprised the deep but ensulic Hazen Trough and two unstable shelves bordering it on the northwest and southeast. The northwestern shelf was a site of felsic to intermediate volcanism, mainly in the Ordovician Period. Pearya, a site of granitic plutonism in the Devonian Period, supplied much of the clastic basin fill. Its core consisted of a metamorphic complex, about 1.0 Ga old, exposed in basement uplifts in nor thernmost Ellesmere Island. Both basin and welt essentially formed part of the North American Plate, although rifting, evident from mafic and ultramafic intrusions, probably occurred in Early Devonian (or latest Silurian) time. The history of this part of the province is tentatively interpreted as response to the opening and closure of an ocean, connected with lapetus, that separated northern Ellesmere Island and Greenland from the sialic crust of the present Lomonosov Ridge and Barents Shelf. The Lomonosov Ridge still seems to be attached to the shelf off northeasternmost Ellesmere Island.(2) Deep subsidence and filling of Sverdrup Basin dominated the Innuitian region from Early Carboniferous through Late Cretaceous time. Large halokinetic diapirs and mafic dikes and sills intruded axial parts of the basin succession through Mesozoic time. Steep faults along the northwestern margin of the basin are Middle Cretaceous and older. Part of the northwestern rim of Sverdrup Basin sagged in latest Cretaceous time, becomingpart of the Arctic continental terrace. In the Late Cretaceous and early Tertiary a system of large grabens developed through the southern part of the Innuitian region, linking Canada Basin with Baffin Bay; about the same time, uplift formed some large arches in the northeastern part of the region. Middle Eocene and older rocks were laterally compressed by a phase of pre-Miocene folding and faulting. Some uplift took place in Oligocene or Miocene time on Axel Heiberg Island. The distribution of recent earth quakes does not indicate the presence of modern active plate margins.

Glacial history of the Spitsbergen archipelago and the problem of a Barents Shelf ice sheet

The popular concept of a Late Weichselian ice sheet covering the Barents Shelf and confluent with the Scandinavian and Russian ice sheets is based primarily on the 6500 B.P. isobase which rises to the east over Spitsbergen, and to the west over Franz Joseph Land. Analysis of uplift curves from the Spitsbergen archipelago shows, however, that the strongest early Holocene uplift occurs over northeastern Spitsbergen and eastern Nordaustlandet, falling both to east and west, and that the centre of uplift migrates to the southeast during the Holocene. Direct evidence of glacier fluctuation indicates an important Billefjorden Stage of glaciation at about 11,000 to 10,000 B.P., part of whose extent can be defined by moraines and by abrupt changes in the marine limit. The dominant ice masses of the Billefjorden Stage seem to have formed over eastern Spitsbergen, Edgeøya, Barentsøya and southern Hinlopenstretet, and it is the decay of this ice mass which is primarily responsible for the pattern of early Holocene uplift.Stratigraphic evidence suggests the absence of an important glacial event at 18,000–20,000 B.P., but an important phase of Spitsbergen‐centred glaciation at about 40,000 B.P., and a glacial phase at 80,000–120,000 B.P. It is suggested that many raised beach sequences outside the Billefjorden readvance show an upper sequence related to deglaciation at about 40,000 B.P., and a lower, Holocene sequence related to decay of the Billefjorden ice. The anomalous pattern of late Holocene uplift may be related to restrained rebound produced by regeneration of ice on the main islands of the archipelago and unrestrained rebound on Hopen and Kong Karls Land, which were incapable of sustaining large ice masses of their own.A pattern of LateGlacial climatic circulation which may have produced ice masses on the east coast of Spitsbergen, west coast of Novaya Zemlya and north coast of Russia is suggested. It is also suggested that this pattern of glaciation produced features which have been wrongly interpreted as evidence of a Barents ice sheet.

Sandstone in Lower Cretaceous Helvetiafjellet Formation, Svalbard: Bearing on Reservoir Potential of Barents Shelf

The Helvetiafjellet Formation consists of 50 to 100 m of largely fluvial sandstones and shales deposited throughout Svalbard during a major regression. Sandstones consist chiefly of monocrystalline and polycrystalline quartz, feldspar, chert, and volcanic (basaltic) rock fragments in (1) quartz and quartzose arenites, (2) quartzose lithic arenites, and (3) volcanic arenites. Quartz and quartzose arenites dominate in western Spitsbergen and were derived from a mixed sedimentary-metamorphic terrane in the west. Volcanic arenites are present in Kong Karls Land in the east, and are intercalated with basaltic lava flows which are considered to be the major source for the sandstones. Quartzose lithic arenites in southeast Spitsbergen are a mixture of quartz sands derived from the west and reworked volcanic sands transported from the east. Cementing minerals are variably developed in these sandstones. Quartz overgrowths are dominant in quartz and quartzose arenites. Kaolinite is present in many feldspar-bearing quartz and quartzose arenites, whereas illite is rare. Chlorite is common, together with calcite, in quartzose lithic arenites. Abundant smectite and calcite with minor zeolites are present in the volcanic arenites, which suggests a strong relation between mineralogy of the detrital grains and that of associated cements. Unstable detrital grains released ions to pore waters, which subsequently precipitated clay and calcite cements. Induration increases and maximum porosity decreases from east to west across Svalbard, owing both to higher temperature, caused by progressively greater burial depth and steeper geothe mal gradients, and to tectonic stress in westernmost areas. Early Cretaceous volcanic activity may have provided abundant chemically unstable detritus to basins in the southern part of the Barents Shelf. As a major consequence, clay cements could form during diagenesis, adversely affecting sandstone reservoir parameters. However, the development of secondary dissolution porosity could improve reservoir characteristics of those sandstones which contain chemically unstable minerals such as feldspar grains and calcite cement.

Barents Sea continental margin sonobuoy data

Results from 68 closely spaced sonobuoys obtained aboard R/V Bartlett are combined with 30 published sonobuoy results obtained aboard R/V Vema to provide about 300 velocity solutions from the Barents Sea area and its western continental margin. Sections have been compiled from the closely spaced Bartlett stations, and statistical regressions of sediment sound velocity versus depth were made with all the available data. It was found that distinct geologic provinces from this region can be characterized with five separate velocity-depth curves, based on the regressions. The very low velocity gradient in the thick Tertiary wedge of sediments just west of the Barents shelf probably indicates rapid, deltaic deposition. More than 9 km of subbottom penetration was achieved in this Tertiary wedge.

Fossil Mammals and Early Eocene North Atlantic Land Continuity

Until recently American vertebrate paleontologists, particularly students of fossil mammals, have not generally accepted the concept of a former continuous land area around the north end of the Atlantic, connecting western Europe with North America. G. G. Simpson developed biological arguments based on fossil mammals supporting the existence of a corridor (Simpson, 1953 and references cited there) topologically connecting western Europe with North America in the early Eocene, but Simpson was influenced by the stabilistic geologic rationale of the times when he located the, position of the corridor in Asia because of supposed permanence of the Atlantic oceanic barrier during all of Tertiary time. He did not take into account the epicontinental Turgai Straits sea barrier in Asia that lay athwart his corridor in the early Tertiary. The plate tectonic geophysical synthesis of the history of the North Atlantic and Arctic Oceans is in accord with the mammalian timing evidence that a former Euramerican landmass as well as a biota was severed about 49 m.y. ago and that Holarctic land dispersal since that time has been via Asia alone, becoming possible again with Europe in the midTertiary. Earlier, starting about 70 m.y. ago, a continental collision whose site is now within northeastern Siberia created land continuity between what were then Asia and North America and by the Oligocene the Turgai Straits had finally dried, giving the Holarctic corridor essentially its present configuration. Shallow epicontinental waters have on several occasions crossed Beringia, as at present. Thus the land surface of Holarctica has been rearranged substantially since 70 m.y. ago, North America as a land surface having shifted its allegiance from Europe to Asia. Recently published geological and geophysical information also suggests that, in addition to early Eocene land continuity in the Greenland-Barents Shelf area, a subaerial dispersal route crossing the volcanic Wyville Thompson Ridge from southeastern Greenland to the Faeroes and then to Great Britain and Ireland may also have been possible for a time in the early Tertiary. This latter route is the long familiar but hypothetical Thulean Bridge, now given a new lease on life by geophysical studies of hot spots. Aside from the time-honored and romantic concept of Atlantis, a rationale for a former North Atlantic land area connecting western Europe all the way to the North American mainland can be traced back at least to the 1850's. The concept reached a high level of credibility among biogeographers such as Scharff (1907, 1909, 1911) and geologists such as Arldt (1917), and the connection was usually thought of as operating up until rather late in the Cenozoic. It should be recalled that until Nansen's historic voyage in the Fram in 1893-1896 it was generally believed that the Arctic Ocean was shallow and that a significant amount of unknown land still lurked in those waters-land that might somehow have been a terrestrial dispersal route in pre-glacial times. In its extreme form, the idea of a transatlantic late Cenozoic land bridge in the north is still with us (e.g., Strauch, 1970), although the postulated locale is regarded as Iceland rather than farther poleward. On the other hand various authors, for instance Simpson (1953, 1965), Schwarzbach & Pflug (1957), and Schwarzbach (1959), have claimed that no connection between Iceland and the British Isles existed after the Eocene or that none existed at all during the whole Cenozoic Era. Still other authors have sug1 Department of Vertebrate Paleontology, The American Museum of Natural History, and Department of Geological Sciences, Columbia University. ANN. MissouRi BOT. GARD. 62: 335-353. 1975. This content downloaded from 157.55.39.203 on Thu, 20 Oct 2016 04:19:19 UTC All use subject to http://about.jstor.org/terms 336 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. (32 gested that an Eocene and earlier route was possible in the far north between Greenland and the now mostly submerged Barents Shelf. A few timid souls have hedged their bets by suggesting that both a faar northern and an Icelandic route

Structure of the Barents Sea from seismic refraction

The Barents Sea is underlain by a thick (up to 5 km) sedimentary basin. Seismic refraction has outlined four main velocity discontinuities which have been correlated with geological units on the basis of the geological history of the region. The basin is underlain by a crystalline basement, the nature of which cannot be determined on the basis of seismic velocity alone. Metamorphosed Paleozoic units (velocities around 5–4 km/sec) lie over this basement. Their thickness is not well established but appears to reach 1 or 2 km in some cases. A very distinct and thick (up to 2.5 km) layer (4.1 km/sec) is found almost everywhere and is thought to correspond to a major discontinuity at the end ot the Paleozoic. This discontinuity is followed by a variable velocity layer (2.4–4 km/sec, up to 1.2 km thick) which includes Mesozoic and Cenozoic sediments and is limited to the south of the Barents Sea. The absence of thick Tertiary deposits support the idea that the Barents shelf was emergent at that time. Recent low-velocity sediments are found close to the shelf edge. Gravity anomaly trends reflect a series of depressions of the 5.4-km/sec layer isobath map and suggest that the deeper part of the basin is made of a succession of faulted blocks or intense folds.

Seismic refraction and reflection measurements in the southern Barents Sea

Seismic refraction and continuous reflection measurements were made in the southern Barents Sea. On the basis of these investigations and earlier data from the area, the total thickness of sediments and thickness of the semiconsolidated section have been mapped. The main part of the investigated area consists of Mesozoic and Paleozoic sediments, while the areas near the shelf edge show a westward increasing wedge of Cenozoic deposits above the same sediments found to the east. Along the Norwegian coast and in the areas southwest of Bjørnøya a rapid increase of sediments is noted, while a much more gentle westward growth is found in the main part of the Barents shelf. The data suggest the southern flank of Bjørnøyrenna is an area of structural deformation. Structures that can be associated with salt diapirs are recorded in a limited area on Tromsøflaket.

Marine geophysical survey in the southwestern Barents Sea

A marine geophysical survey in the southwestern Barents Sea reveals an over-all sequence of layered sediments. In the main part of this area relatively high seismic velocities (2.5–3.0 km/sec) occur near the sea floor, but a low-velocity (1.85–2.2 km/sec) sedimentary wedge exists near the shelf edge. The low-velocity section is believed to consist of material deposited during the Cenozoic when the Barents shelf was uplifted. However, the main portion of the sediments seem to be consolidated, of Mesozoic and Paleozoic age. Magnetic and gravity data suggest an irregular basement relief in the west and a smoother and probably deeper basement toward the east. The latter is associated with the Riphean structural complex, whereas the western area may reflect a continuation of the Caledonides.

Transform Faulting along the De Geer Line

DE GEER1 in 1926 first referred to the existence of a physiographic lineament following the western continental slope of the Barents Shelf from Norway to Svalbard, then running along the north-eastern continental slope of Greenland and Canada. Subsequent authors2,3 suggested that extensive dextral strike slip movements had occurred along this line during the continental drift of Greenland and North America away from Eurasia.

Tectonic Evolution of Barents Shelf and Related Plates: ABSTRACT

In this paper an attempt has been made to reconstruct successively earlier configurations of lithosphere plates and their constituent parts, as related to the Barents Shelf. This involved a brief investigation of some possible past relations between Spitsbergen and the northwestern Eurasian plates, Greenland, the Canadian Arctic Islands, and the intervening seas and ocean basins. The restoration of observed crustal strains from structural and geophysical evidence were tested in each case for stratigraphical consistency of the implied reconstructions. Working backward in time the study begins by reversing the late Phanerozoic spreading of the Norwegian and Greenland Sea basins of the Atlantic Ocean and the Eurasian basin of the Arctic Ocean. This leads to familiar reconstructions of Triassic/Permian paleogeology, with Spitsbergen adjacent to North Greenland and Ellesmere Island. There are some alternative reconstructions which have been rejected. The restoration of Paleozoic displacements depend mainly on different interpretations of the Caledonides (especially the amount of closing and the amount of sinistral transcurrence involved). Relations between these structures, the North Greenland and Innuitian fold belts, the Lomonsov Ridge, and the Uralides, for instance, are critical. There are more speculative possibilities for unravelling late Precambrian movements. The development of End_Page 2484------------------------------ the North Atlantic geosyncline, in relation both to alternative models for a proto-Atlantic Ocean basin, and to late pre-Cambrian diastrophism as variously inferred has been considered. End_of_Article - Last_Page 2485------------

The main features of the tectonic structure of Spitsbergen

The Spitsbergen archipelago is situated in the north-westernmost part of the Barents Shelf. The structural position of the archipelago and the variety of its geological complexes make this region very important for understanding the tectonic history of the Atlantic sector of the Arctic.

The Geology of Isis Point, North-East Land (Spitsbergen)

Summary Isis Point, a rocky island-promontory among the ice-cliffs forming the east coast of North-East Land, consists entirely of igneous and metamorphic rocks. On the north coast, as already known, metamorphosed sediments are intimately invaded by a grey granite; at Isis Point amphibolites are prominent among the metamorphic rocks and the stressed grey granite occurs. Quartz-diorites, scarcely known elsewhere in North-East Land, occur as dykes and veins in the complex and are younger than it. Granodiorites, the now wellknown red and pink “granites” of North-East Land, have field relations similar to those of the diorites; aplite and pegmatite associated with the granodiorites cut the diorites. The granodiorites are younger than, or in part coeval with, the diorites; both are usually unstressed. Evidence based on morainic material from Isis Point suggests that Upper Carboniferous rocks rest directly on the igneous and metamorphic complex nearby, overstepping the sediments of the Hecla Hoek Formation from west to east. Some of the rocks of Isis Point outcrop on the coast farther north and in Great Island and White Island to the north-east; it is logical to associate them with the “Archaean” basement of Barents Shelf. Eastward, the Upper Carboniferous sediments occur in Victoria Island. The paper is a sequel to that by the author published in 1950. I. Introduction Two earlier papers describe rocks collected at Isis Point (Sandford 1926, 1950). The first mentions (p. 620) an isolated diorite, of which a specimen was brought back by a member of the 1924 Oxford expedition (Binney