bluuebunny/crossref_metadata_2025 huggingface dataset:
Summary and Remaining Problems
Authors: Trettin H.P.
Published: April 2015

This concluding chapter provides a brief, interpretative overview of the geological history of Innuitian Orogen and Arctic Platform with emphasis on unsolved major problems, and a summary of their resources. References quoted in previous chapters will not be repeated; for geographic names, see Figure 1 (in pocket).

The northern part of the Canadian Shield (including Greenland) consists of a number of relatively small continental plates of Archean age that were welded together into a single supercontinent in a series of Early Proterozoic orogenies. The outlines of the Archean cratons and intervening Early Proterozoic orogenic belts have not yet been established for the High Arctic, but an orogen 1.91.95 Ga old is recognized in southeastern Ellesmere Island and adjacent parts of Greenland (Chapter 6).

An extensive late Middle Proterozoic rifting event is indicated by mafic volcanic and intrusive rocks and associated coarse clastic sediments exposed on Melville Peninsula (Fury and Hecla Basin), northern Baffin Island and Bylot Island (Borden Basin), southeastern Ellesmere Island and adjacent parts of West Greenland (Thule Basin), and northeastern Greenland (Chapter 6). Radiometric ages suggest correlation with the extensive Mackenzie dyke swarm of the eastern Cordillera, dated at about 1.2 Ga. The rift deposits are succeeded by shallow marine clastic and carbonate sediments that also are represented on Victoria Island (Shaler Group). Age and correlation of the sedimentary units are problematic. Lithological relationships suggest that the sedimentary units in the Borden and Thule basins are correlative, but the former have yielded late Middle Proterozoic paleomagnetic ages, whereas
Geophysical Characteristics
Authors: Sobczak L. W.
Published: April 2015

The first measurements of gravity in Arctic Canada were made on Melville Island in 1819-1820 (Sabine, 1821). Gravity measurements in the Arctic did not resume until 1957 when five gravity control stations were established by the Canadian Government (Bancroft, 1958), and in 1958 about 200 gravity observations were made over Gilman Glacier in northeastern Ellesmere Island (Weber, 1961). The same year, as a contribution to the International Geophysical Year (IGY), a subtense bar and gravity traverse was carried out from Clements Markham Inlet on the Arctic coast across the United States Range to Archer Fiord on Kennedy Channel (Weber, 1961). In 1958 the Polar Continental Shelf Project (PCSP) was established, in the then Department of Mines and Technical Surveys, to coordinate most of the scientific studies carried out in the Arctic by the Canadian Government.

From 1960, under the aegis of the PCSP, systematic gravity surveys have been carried out in the Arctic by the Dominion Observatory (later renamed the Earth Physics Branch [EPB], of the Department of Energy, Mines and Resources, and now part of the Geological Survey of Canada) primarily over the relatively flat areas of the Innuitian Region and adjacent continental margin (Sobczak, 1963; Sobczak et al., 1963; Picklyk, 1969; Sobczak and Weber, 1970; Sobczak and Stephens, 1974; Sobczak and Sweeney, 1978). Except for small areas completed in the southern, central, and northern parts of Ellesmere Island, gravity surveys of the mountainous areas of Axel Heiberg and Ellesmere islands have been deferred until reliable elevations can be
Gravity from 64°N to the North Pole
Authors: Sobczak L. W. , Hearty D. B. , Forsberg R. , Kristoffersen Y. , Eldholm O. , May S. D.
Published: April 2015

Although gravity observations were made prior to 1960, systematic regional gravity coverage in the Arctic began in earnest in the early 1960s on land and sea ice with the advent of helicopters and reliable portable gravimeters, and was extended in the 1970s over the oceans with ships and reliable marine gravimeters. As a result, about half of the polar area north of 64°N latitude is now covered with regional (spacings 12 km or less) gravity observations for which the data are readily available to the public. Permanently ice-covered regions of the Arctic Ocean, as well as mountainous and glacier-covered areas, are still largely unmapped. Except for a few pre-World War II gravity stations from regions within the Soviet Union (USSR), no gravity data from the USSR are displayed on Plate 3.

The observed gravity field of the whole Arctic region north of 60°N was first discussed by Sobczak (1978), who presented maps (scale 1:7,500,000) showing the gravity field derived from mean values based on observed (1/2° latitude × 2° longitude) and predicted (1° latitude × 1° longitude) free-air anomalies and a residual gravity field derived by removing the satellite gravity field (Goddard Earth Model 8, GEM 8) from the observed and predicted fields. These maps indicate anomalous gravitational features of wavelengths in excess of 100 km.

Bowin and others (1982) presented a comprehensive free-air gravity anomaly atlas of the world, including a map of the Arctic region north of 70° at a scale of about 1:14,000,000.

The intent of the present
Magnetic anomalies
Authors: Coles R. L. , Taylor P. T.
Published: April 2015

Extensive magnetic surveys have been made over the Arctic Ocean since 1946. The survey techniques have varied, as have the methods and forms of data presentation. This chapter reviews the magnetic anomaly information from the Arctic Ocean region and discusses the significant contributions made by magnetic surveys to the understanding of this region of the earth’s crust. The magnetic anomaly field is the only geophysical parameter in the Arctic that has been reasonably uniformly measured. It is critical to the study of Arctic structure and evolution.
Geothermal observations in the Arctic region
Authors: Langseth M. G. , Lachenbruch A. H. , Marshall B. V.
Published: April 2015

A fundamental goal of geothermal studies in the Arctic region is to determine the rate of heat flow from deep in the earth’s crust. Research during the past 25 years has shown heat flux is closely related to the tectonic evolution of a geological province. When combined with other geological and geophysical data, accurate heat-flow measurements can set constraints on crustal temperatures, age and evolution of the lithosphere, and the distribution of radiogenic heat in the crust. At an even more fundamental level, accurate measurements help determine the total rate of heat loss from the Earth and define the global variation of heat flow and its correlation with other long-wavelength geophysical features.

In addition to the fundamental scientific interest, the subsurface thermal regimes of continents and continental margins of the Arctic are of practical concern for natural resource development. Mean annual surface temperatures on land are well below freezing, which results in a permafrost layer hundreds of meters thick in some places; for example Judge and others (1981) reported a permafrost thickness of 726 m on Cameron Island in the Canadian Arctic Archipelago. The ice-bearing permafrost presents many obstacles to the development of resources and the maintenance of facilities in the Arctic, and as a consequence, a considerable effort has been made by the Canadian and United States governments and industry to evaluate the subsurface thermal regime from an engineering perspective. These efforts have provided many drill holes for subsurface temperature and thermal properties data. Many of these holes will provide
Seismic reflection and refraction
Authors: Jackson H. R. , Forsyth D. A. , Hall J. K. , Overton A.
Published: April 2015

The ice cover of the Arctic Ocean restricts research vessels, limiting the number of miles of seismic reflection and refraction lines in the area. Figures 1 and 2 show the distribution of the lines, andTables 1 and 2 provide references keyed to those figures. This paper describes the distribution, collection, and processing of the seismic reflection and refraction data available in the deep basins and major ridges in the Arctic Ocean and briefly discusses the salient geological results by region. In addition, the position of seismic surveys on the continental margins and adjacent landmasses of the North American plate have been compiled for completeness. These peripheral areas are documented with recent review papers Table 1) including Eldholm and others (this volume) and Larsen (this volume).

Most of the seismic reflection information in the Arctic Ocean has been collected on drifting ice stations; thus, the direction of the lines is controlled by the whims of nature. The data set presented here is incomplete due to the inaccessibility of information collected by Soviet scientists. No seismic profiling has been run from the northern margin of Greenland, and only three refraction surveys and one reflection line exist on the Canadian Polar margin from Greenland to the Beaufort Sea. Most of the reflection lines in the Canada Basin were acquired with power sources of insufficient strength to penetrate the sedimentary section. Even with this meager collection of erratically spaced and variable quality information, important trends can be seen, interesting features
The East Greenland Shelf
Authors: Larsen Hans Christian
Published: April 2015

Geologically, the East Greenland Shelf remained virtually unexplored for many years while the onshore East Greenland Mesozoic basin stratigraphy was intensely studied and served as a reference for the interpretation of the offshore East Greenland and northwest European margins. This development was a natural consequence of the excellent onshore basin exposure while polar pack ice is found almost year-around on the East Greenland shelf. The first geophysical information from the East Greenland shelf was published by Vogt (1970), Eldholm and Windisch (1974), Johnson and others (1975a, b), B. Larsen (1975), H. C. Larsen (1975, 1978), Henderson (1976), and Featherstone and others (1977).

Results of the first multichannel reflection seismic surveying on the shelf were reported by Hinz and Schlüter (1978, 1980). On the basis of this information and initial results from an aeromagnetic survey (H. C. Larsen and Thorning, 1979, 1980), a regional geological model for the East Greenland Shelf was proposed by H. C. Larsen (1980). This model involved early Tertiary oceanic crust thought to be present below parts of the outer shelf off central East Greenland and subsided continental crust thought to be present up to approximately 100 km seaward of the shelf break off southeastern Greenland. The actual position of the shelf edge was found to be controlled mainly by post-rift sedimentation rather than deep crustal features (H. C. Larsen, 1980). It was further suggested that Cenozoic basins might dominate the southern half of the shelf while Mesozoic and Paleozoic basins were likely to be present beneath the northern shelf.
The continental margin northwest of the Queen Elizabeth Islands
Authors: Sweeney J. F. , Sobczak L. W. , Forsyth D. A.
Published: April 2015

The polar continental margin described here lies between M’Clure Strait and the Lincoln Sea (Fig. 1). It clearly separates continental sequences of the Queen Elizabeth Islands from presumed oceanic crust beneath the deep Canada Basin and, near Axel Heiberg and Ellesmere Islands, from rocks of the submarine Alpha and Lomonosov Ridges.

Systematic studies in the region began in the late 1940s with Soviet air-lifted spot soundings over the outer continental slope and rise. In the 1950s and 1960s, the Alpha Ridge and adjacent parts of the outer continental shelf and slope were identified by multiparameter measurements from a series of drifting U.S. ice stations. In Canada, onshore geological studies began in 1955, and reconnaissance investigations of the polar shelf and slope were underway by 1960. The reader is referred to Weber (1983) and Weber and Roots (this volume) for further details of early studies.

Comprehensive reviews that include onshore geology adjacent to the polar margin begin with Fortier and others (1963) with later syntheses by Thorsteinsson and Tozer (1970), Trettin and others (1972), Trettin and Balkwill (1979), Hea and others (1980), Miall (1981), and Kerr (1981). Offshore, chiefly geophysical data over the polar shelf and slope are summarized by Trettin and others (1972), Sweeney and others (1978), Vogt and others (1982), Sweeney (1982), and Forsyth and others (1988).

From the information available up to the early 1980s, it was considered that the polar margin formed when the Canada Basin opened in Jurassic or Early Cretaceous time, that the crust
Canadian Beaufort Sea and adjacent land areas
Authors: Dixon J. , Dietrich J. R.
Published: April 2015

The Canadian Beaufort Sea extends from offshore Banks Island to 141 °W longitude (Fig. 1). It is rimmed to the south by the Yukon Coastal Plain, the outer Mackenzie Delta, including Richards Island, and Tuktoyaktuk Peninsula. The narrow coastal plain of northern Yukon is bounded to the south by the British Mountains and the Porcupine Plateau (Fig. 1). The broad Amundsen Gulf separates the Anderson and Horton plains of the Northwest Territories mainland from Banks Island and Victoria Island.

The continental margin beneath the Beaufort Sea can be divided into several physiographic regions. The shallow-water shelf is 50–100 km wide and is characterized by low, uniform slope gradients of 1–2 m/km. An abrupt increase in the sea-floor slope gradient marks the shelf edge. Water depths at the shelf break vary from 60 m near 141°W to almost 500 m west of Banks Island. Two channel-like features cut across the Beaufort shelf. Northeast of Herschel Island, the Mackenzie Trough (formerly Mackenzie Canyon) cuts obliquely across the shelf in a northwesterly direction (Fig. 1). Southwest of Banks Island, the broad Amundsen Gulf channel cuts across the shelf in a northwesterly direction. Both of these bathymetric troughs are 100–500 m deep and are geologically recent in origin. The continental slope seaward of the shelf edge is 20–50 km wide and is characterized by variable slope gradients of 5–30 m/km. The outer continental slope north of the Mackenzie Trough is marked by a steep, sea-floor escarpment with local slope gradients of up to 170 m/km (Fig. 1)
Geology of the Arctic Continental Margin of Alaska
Authors: Grantz Arthur , May S. D. , Hart P. E.
Published: April 2015

Alaska faces the Canada Basin of the Arctic Ocean along an arcuate continental margin, gently concave to the north, that stretches unbroken from the Mackenzie Delta, near 137°W to Northwind Ridge of the Chukchi Borderland near 162°W. (These and other regional geographic features mentioned below can be found in Plates 1 and 11.) This margin, with an arc-length of about 1,050 km, marks one side of a continental rift along which the Canada Basin opened by rotation about a pole in the Mackenzie Delta region during middle Cretaceous time. The rift- margin structures, which lie beneath the inner shelf and coastal plain in the eastern Alaskan Beaufort Shelf and beneath the outer shelf in the western Beaufort and Chukchi Shelf, are now buried by a thick middle Lower Cretaceous to Holocene progradational continental terrace sedimentary prism.

We divide the Arctic continental margin of Alaska into three sectors of strongly contrasting geologic structure and physiographic expression. In the Barter Island sector (see Figs. 3 and 4) the structure is dominated by the effects of Eocene to Holocene convergence and uplift, and the continental slope is upwardly convex; in the Barrow sector the structure is dominated by the effects of middle Early Cretaceous rifting and continental breakup, and the continental slope is upwardly concave; and in the Chukchi sector the structure is controlled by an easterly trending middle Early Cretaceous rift, and the continental slope abuts the Chukchi Borderland.

Physiographically, the Alaska continental margin is expressed by the Alaska continental
The Arctic continental margin of eastern Siberia
Authors: Fujita Kazuya , Cook David B.
Published: April 2015

The Arctic Ocean margin of the North American plate in Asia forms a continental shelf up to 800 km wide, which underlies the East Siberia Sea (Fig. 1). The New Siberian Islands separate the East Siberian Sea from the Laptev Sea on the west, and Wrangel Island (Ostrov Vrangelya) separates the East Siberian Sea from the Chukchi Sea on the east. The area of the East Siberian Sea is about 1,500,000 km2, and it is connected to the Chukchi Sea by Long Strait (Proliv Longa) and to the Laptev Sea by several straits through the New Siberian Islands.

The shelf of the East Siberian Sea is shallow, less than 50 m deep, and flat. The shelf is cut by two valleys, a few tens of meters deeper than the surrounding shelf, which are extensions of the Indigirka and Kolyma rivers (Naugler and others, 1974). The continental slope of the East Siberian Sea is gentle (slope ~1°), and alluvial cones spread out into the adjacent abyssal plain from submarine canyons (Lastochkin, 1980). The shelf appears to be connected to the Arlis Plateau, but is separated from the Lomonosov Ridge by a sediment-filled trough (Dementiskaya and Hunkins, 1971) (Fig. 2).

Since the geology of the East Siberian Shelf is poorly known, most tectonic and geologic models are extrapolations of the geology of the New Siberian Islands. Wrangel Island, and northern Eurasia. Rather than present the details of these speculations, in this chapter we summarize the known geology of
Ridges and basins in the central Arctic Ocean
Authors: Weber J. R. , Sweeney J. F.
Published: April 2015

This chapter describes the physiography plus the geological and geophysical character of the central Arctic. The available information is chiefly from work done on several ice station transits of the area together with aeromagnetic and satellite magnetic investigations. The data provide crude constraints on the nature and ages of the main sea-floor features of the central Arctic Ocean.

The central area of the Arctic Ocean contains abyssal depths that are traversed by two subparallel submarine mountain ranges, the Lomonosov Ridge and the Alpha-Mendeleev Ridge complex. The wedge-shaped Makarov Basin separates these adjacent ranges, which are close to North America and are more than 500 km apart at their junction with the East Siberian continental margin (Fig. 1). Significant difference in overall morphology and geophysical properties between the Lomonosov and Alpha Ridges, despite their juxtaposition near North America, suggests a complex structural evolution for the central Arctic, whose origins are constrained loosely within the late Early Cretaceous-earliest Tertiary interval.
The Norwegian-Greenland Sea
Authors: Eldholm Olav , Skogseid Jakob , Sundvor Eirik , Myhre Annik M.
Published: April 2015

Generation of oceanic crust at the boundary between the Greenland/North American and the northwestern part of the Eurasian plates has created the Norwegian-Greenland Sea. This relatively young ocean comprises a number of separate basins, plateaus, and ridges revealing that the break-up and separation of the two major plates have not, in geological terms, been a simple process.

In this context we define the Norwegian-Greenland Sea as the deep ocean between Europe and Greenland, bounded in the south by the Greenland-Iceland-Faeroe shallow transverse and in the north by the Spitsbergen Fracture Zone (Fig. 1). Geographically, the term Greenland Sea has been used for the ocean between Svalbard and northeast Greenland, but here we have adopted the geologically accepted usage in which it relates to the deep ocean between the Greenland-Senja and Spitsbergen fracture zones.

Passive continental margins consisting of well-developed shelves and slopes separate the Norwegian-Greenland Sea from the adjacent continental masses of Greenland, Svalbard and Fennoscandia. The two adjacent shallow seas, the North Sea and the Barents Sea were, prior to the formation of the deep ocean in early Cenozoic time, part of a much larger contiguous epicontinental sea between the continental masses.

The scientific exploration of the deep ocean, which started late in the last century, was until the 1950s focused on physical oceanography and marine biology. It was not before the mid-1960s that systematic research programs in marine geology and geophysics were initiated. These investigations were pioneered by regional surveys carried out by Lamont-Doherty Geological Observatory
Canada Basin
Authors: Grantz Arthur , May S. D. , Taylor P. T. , Lawver L. A.
Published: April 2015

The Canada Basin, 1,600 km long and 650 to 1,050 km wide, is an extensive area of moderately deep water lying in the Amerasia sector of the Arctic Ocean (Fig. 1 and Plate 1). Unlike many other ocean basins, it is poorly understood. The tectonic processes that formed it are thought to have played an important role in the structural development and configuration of Alaska and the northeastern USSR, and in the development of the large hydrocarbon resources that have been discovered around the margins of the basin.

The borders of the Canada Basin are North America on the east and south and a complex of submarine ridges and plateaus on the north and west that may have diverse origins. The submarine ridge features include the Northwind Ridge and Chukchi Cap of the Chukchi Borderland on the southwest, and the Mendeleev and Alpha Ridges on the northwest and north respectively. Much of the basin has an extensive continental rise that slopes westward from the Canadian Arctic Islands toward the deep Canada Abyssal Plain. This abyssal plain, which underlies the western Canada Basin, is its deepest part. The Mendeleev Abyssal Plain (Fig. 1) lies to the west of the northern part of the Canada Abyssal Plain and is separated from it by a scarp 300 m to more than 500 m high. This scarp and the Northwind Escarpment (the east face of Northwind Ridge) together form the west boundary of the Canada Abyssal Plain; and their continuity may have
Late Mesozoic and Cenozoic paleogeographic and paleoclimatic history of the Arctic Ocean Basin, based on shallow-water marine faunas and terrestrial vertebrates
Authors: Marincovich Louie , Brouwers Elisabeth M. , Hopkins David M. , McKenna Malcolm C.
Published: April 2015

The paleogeography and marine paleoclimate of the Arctic Ocean Basin have evolved considerably during the past 100 million years, since the beginning of the Late Cretaceous. The shallow-water marine faunas that are needed to understand much of this history have recently been found, so that paleontologic studies of the Arctic Ocean Basin and its margins are presently in their early stages. The paleogeographic history of the Arctic Ocean may be divided conveniently into four intervals, each characterized by different marine connections to the world ocean. The first interval extended through most of the Mesozoic, when the Arctic Ocean was a northern gulf of the Pacific Ocean and subsequently developed seaway connections to other oceans. The second interval was during the Late Cretaceous and early Paleogene, when the Arctic Ocean was more or less completely isolated geographically from the world ocean. The third interval lasted from the late Paleogene to the middle Pliocene, during which the Arctic Ocean was connected to the Atlantic but not to the Pacific; and the fourth interval, lasting to the present day, was ushered in at about 3.0–3.5 Ma by the opening of the Bering Strait. The marine paleoclimate of the Arctic Ocean during the Late Cretaceous and early Tertiary was remarkably warm and equable until the onset of gradual cooling that culminated in late Neogene and Pleistocene ice cover.
Late Cenozoic geologic evolution of the Alaskan North Slope and adjacent continental shelves
Authors: Dinter David A. , Carter L. David , Brigham-Grette Julie
Published: April 2015

The Alaskan Arctic Coastal Plain and its submerged extensions to the north and west, the Beaufort and Chukchi continental shelves, are underlain by a broad, low-relief bedrock surface, the North Beringian Marine Abrasion Platform, which dips gently seaward from the Arctic foothills of the Brooks Range northward to the continental shelf break of the Arctic Basin (Fig. 1). During late Cenozoic time the sea repeatedly transgressed and receded across the North Beringian Platform in response to glacioeustatic sea level fluctuations. A thin veneer of unconsolidated, interfingering marine and nonmarine deposits mantles the bedrock surface and records the succession of geologic environments that have prevailed there during the last 3 m.y. All of these unconsolidated deposits are presently assigned to the Gubik Formation, which has a maximum measured thickness of about 60 m onshore, and thickens to perhaps a few hundred meters in places beneath the Beaufort shelf. In this chapter, we summarize and discuss the depositional history of the Gubik Formation and its bearing on the late Cenozoic geologic and climatic history of the Arctic region. The discussion begins with the onshore exposures, which have been studied in detail over many years, and for which a coherent stratigraphic framework has begun to emerge, and then moves to the offshore deposits, which, though thicker and better preserved, have only recently become the target of stratigraphic investigations.

The marine deposits of the Gubik Formation on the Arctic Coastal Plain have intrigued researchers since the early years of this century, when Leffingwell
The late Neogene and Quaternary stratigraphy of the Canadian Beaufort continental shelf
Authors: Blasco S. M. , Fortin G. , Hill P. R. , O’Connor M. J. , Brigham-Grette J.
Published: April 2015

This compilation of the late Neogene and Quaternary geology of the Canadian Beaufort continental shelf is the result of a nine-year cooperative effort between the Geological Survey of Canada and the Canadian Beaufort Sea oil industry. At depths beyond 100 m below seabed the deeper, more generalized stratigraphy is based on the interpretation of the first two seconds of conventional deep multichannel seismic reflection data (on an approximately 5-km grid) correlated with the shallow sections of several exploration wells (Fortin, 1990). The detailed surficial geology of the upper 100 m of sediment below seabed is based on the interpretation of some 15,000 line km of high-resolution, analogue, and shallow digital multichannel seismic reflection data, including boomer, small airgun, airgun array, and Flexichoc sources (Hunter and Blasco, 1980; Quinn and others, 1987). These shallow profiles were correlated with sedimentological, chronological, biostratigraphic and geotechnical analyses of more than 300 sediment cores recovered from the sea floor across the shelf using conventional gravity, piston, and wireline sampling techniques (Le Tirant, 1979). Sampling procedures included both continuous and interval coring, and sampled depths varied from less than 1 m to more than 100 m below seabed. Limited shallow-borehole well-log information, including velocity, density, and resistivity measurements, were also incorporated (Stirbys, 1990).
Sedimentary basins and petroleum resource potential of the Arctic Ocean region
Authors: Haimila N. E. , Kirschner C. E. , Nassichuk W. W. , Ulmichek G. , Procter R. M.
Published: April 2015

This chapter examines the petroleum potential of the sedimentary basins along the continental margins of the North American Plate in the Arctic Ocean region, including those beneath the continent itself and those beneath its fringing continental terraces. Basins within the Canadian Arctic Islands of North America and in the Baffin Bay regions are considered in other volumes of this series. The large petroleum potential of some of the sedimentary basins of the Arctic Ocean margin of the North American Plate, particularly those on the continental shelf, is already well established. The petroleum resource potential of the abyssal plains of the Arctic Ocean is poorly understood but is thought to represent only a minor portion of the total potential of the region.

The basins in the periphery of the Arctic Ocean Basin are mainly continental terrace wedges on foundered passive continental margins and successor basins on extended continental shelves. The Kronprins Christian Basin on the East Greenland Shelf is separated from European basins by the Mid-Atlantic Ridge north of Iceland (Fig. 1). The rest of the basins along the edge of the North American continent area, from east to west, are the Wandel Sea Basin in Greenland, the Lincoln Sea Basin, the various sub-basins of the Canadian Arctic Coastal Plain and Shelf, the Mackenzie Delta–Beaufort Sea Basin in Canada, and the Kaktovik Basin, the Demarcation Subbasin, the Dinkum Graben, and the Nuwuk Basin off Alaska. West of Alaska and north of Siberia the broad continental shelf contains upper Paleozoic-Mesozoic successor
Arctic Ocean ice cover; Geologic history and climatic significance
Authors: Clark David L.
Published: April 2015

The Arctic Ocean is unique among the world’s oceans because of its perennial ice cover. The geologic and climatologic factors that contributed to development of the Arctic Ocean ice cover are understood in a general way, even though the precise mechanism and time during the Cenozoic that the first ice cover formed are not known. Data concerning climatological processes that encouraged development of an Arctic Ocean ice cover have developed from the general understanding of the paleogeographic sequence of events since the last major time of ice-free conditions during the Cretaceous and early Cenozoic. The lack of facts concerning the precise time, and to some extent the mechanism, of ice cover origin is largely the result of an inadequate data base in the Arctic Ocean. For example, no long sediment core with middle Cenozoic sediment that may represent the time of the initial ice-cover development has been collected. Unfortunately, no research ship with capability for recovery of long sediment cores has been designed for work in the area of year-round Arctic pack ice. Therefore, the only sediment record for the central Arctic Ocean is that recovered from drifting ice stations such as the U.S. T-3 program and the Canadian LOREX and CESAR projects. Offshore drilling on the continental slope of Alaska and Canada has penetrated a more complete Cenozoic section. The sediment is largely non marine and, in the shallow Beaufort Sea area, consists of thick deltaic sediment. Detailed paleoclimato- logic study of this sediment has not been accomplished, but
Gas hydrates of the Arctic Ocean region
Authors: Kvenvolden Keith A. , Grantz Arthur
Published: April 2015

Sediments of the Arctic Ocean region may trap enormous quantities of natural gas in and beneath gas hydrates. These solid, ice-like substances, composed mainly of methane and water, are found in two distinct environments: (1) offshore, in sediment of the outer continental margin, and (2) onshore, in and below areas of thick permafrost. Most offshore gas-hydrate occurrences have been inferred from marine seismic-reflection records where an anomalous acoustic reflector correlates with the base of the gashydrate zone. Onshore, most gas-hydrate occurrences have been inferred from well-log responses. In only a few cases have gas hydrates actually been sampled. This chapter focuses on the known and inferred gas hydrates of the North American Arctic and estimates the amount of methane that may be associated with sediments in the Arctic Basin.
Paleomagnetic and plate-tectonic constraints on the evolution of the Alaskan-eastern Siberian Arctic
Authors: Harbert William , Frei Leah , Jarrard Richard , Halgedahl Susan , Engebretson David
Published: April 2015

The tectonic development of the Arctic Basin is constrained by several independent sets of data. These include paleomagnetic Apparent Polar Wander Paths for the North American and Eurasian Plates, paleomagnetic data from Arctic Alaska, and magnetic isochrons in the Arctic, Atlantic, and Pacific Oceans. In this chapter we use each set of data to constrain plate-tectonic models describing the development of the Amerasia Basin, northern Alaska, and the northeast USSR. First, we use Apparent Polar Wander Paths for the Eurasian and North American Plates to show the existence of a gap between these two plates in the Arctic Basin region before the formation of oceanic crust in the North Atlantic and Arctic oceans (the Late Carboniferous to Early Cretaceous, about 310 to 120 Ma). We then review and present new paleomagnetic data from the North Slope of Alaska to constrain the timing and geometry of the opening of the Canada Basin. The new data shows that counterclockwise rotation of -70° has occurred since Barremian time, providing strong evidence supporting a rotational opening of the Canada Basin. Next, we review plate-tectonic models describing rifting in the Arctic and North Atlantic Basins and correlate tectonic events in the Arctic Basin with these motions. We correlate periods of strong convergence between the continental plates from ~70 to ~56 Ma (Maastrichtian to Paleocene) with compressional deformation between the Chukotsk Peninsula and northern Alaska and movement along the Denali Fault. transform motion between these plates from ~56 through 50 to 38 Ma (lower to upper Eocene)
Bathymetry and physiography
Authors: Johnson G. L. , Grantz Arthur , Weber J. R.
Published: April 2015

The oceanic regions located north of the Arctic Circle are the Arctic Ocean, the Norwegian-Greenland Sea, and Baffin Bay (Plate 1). The latter is described in Keen and Williams (1990). Despite the bold isobaths in Plate 1, the bathymetry of the Arctic Ocean is still poorly known. Most of the Norwegian-Greenland Sea, on the other hand, is quite precisely charted. Exceptions are the areas east of Greenland often covered by the pack ice that exits the Arctic Ocean in the East Greenland current.

The names used for the physiographic features in this volume are those shown on Plate 1. Different names that have been applied to these features in the literature are given in Sweeney and others (this volume.)
“Zero-age” variations in the composition of abyssal volcanic rocks along the axial zone of the Mid-Atlantic Ridge
Authors: Melson William G. , O’Hearn Tim
Published: April 2015

The mid-ocean ridge spreading centers mark the zones where the asthenosphere comes closest to the earth’s surface. Such centers are termed accreting plate margins because the oceanic lithosphere forms along these centers. Magmas that have erupted along spreading centers are minimally modified or not modified at all by contamination with older lithosphere, compared to magmas erupted through the thicker lithosphere beneath continents and islands. Thus, their compositions presumably provide us with least-modified mantle-derived liquids. Controversy remains as to the extent that these liquids—which are overwhelmingly basaltic—represent “primitive” liquids (O’Hara, 1982).

One of the most incisive models of accreting margin magma chambers is Cann’s “cocktail-onion” model (1970, 1974). This model (Macdonald, this volume) envisions a permanent magma chamber beneath fast-spreading centers and periodic magma chambers beneath slow, rifted spreading centers. The Mid- Atlantic Ridge (MAR) belongs to the latter, rifted spreading centers.

Initial work on abyssal basalt from spreading centers revealed a remarkable uniformity in composition and their “depleted” character compared to oceanic island basalts (Engel and others, 1965) in regard to elements such as K and the light rare earth elements (LREE). Since that time, a wealth of new analytical data has revealed much more diversity and certain systematic patterns related to such factors as distance from on-ridge volcanic islands, spreading rate, water depth, and broad regional groupings. A breakthrough in this area included the discovery of systematic variations in Sr-isotopic ratios moving south from Iceland along the Reykjanes Ridge, revealing decreasingly less radiogenic ratios southward, with values
Hydrothermal activity in the North Atlantic
Authors: Edmond J. M.
Published: April 2015

One of the major developments in the earth sciences in the last ten years has been the recognition of the importance of hydrothermal circulation in the thermal and chemical evolution of the oceanic crust. Submarine hot springs with exit temperatures as high as 350°C have been located and sampled at several locations on the ridge systems of the Eastern Pacific (Edmond and others, 1982). Hydrothermal deposits of sulphide ores and pavements of pure MnO2 have been recovered by dredging at numerous other sites. Exploration has been facilitated at these medium and fast spreading ridges by the relatively subdued topography. Success has a high probability, given the frequency of intrusive and eruptive events and the permanent presence of shallow magma chambers (Sleep and Rosenthal, 1979). On the Mid-Atlantic Ridge (MAR), none of these circumstances obtain and the results have been correspondingly meagre, with the obvious exception of Iceland. The strongest evidence for current hydrothermal activity on the MAR comes from the TAG area (Trans-Atlantic Geotraverse) at 26°N. While small temperature and 3He anomalies have been observed in the water column in the axial valley, active venting was not observed during subsequent Alvin dives. However, there are abundant indications that hot springs have played an important role in the development of the MAR over the time-span of its existence.

Much of the evidence is for low-temperature activity of the kind observed on the Galapagos Spreading Center (GSC) in the Eastern Pacific (Edmond and others, 1979 a,b). It is known,
Imaging the ocean floor: History and state of the art
Authors: Vogt Peter R. , Tucholke Brian E.
Published: April 2015

Bathymetry is the science and technology of ocean depth measurement. In the narrow and traditional sense, the objective of bathymetry is to define the seafloor topographic surface, h(x, y). Most bathymetric studies also interpret the depth data— usually displayed in contour charts or profiles—in terms of undersea geomorphology and, in concert with other geophysical data, as a constraint on sub-seafloor geologic structure. In many parts of the ocean, bathymetry is about the only type of geological information available. Thus, compared to land, seafloor topography necessarily plays a larger role in geologic interpretations.

The North Atlantic Ocean covers an enormous area (4 × 107km2) with diverse and numerous geomorphic features at many scales. Bathymetric control is very uneven in distribution and quality. Some areas have been surveyed by overlapping swaths of multibeam bathymetry with reliable mapping of features less than 1 km apart, while other areas of 103 or 104km2 have no soundings, particularly in the equatorial latitudes. Unlike many previous studies, this chapter does not offer a systematic guided tour of the submarine topography. (See Holcombe, 1977 for a glossary of ocean-bottom land forms.) Recent syntheses of Atlantic bathymetry include Vogt and Perry (1982) and Emery and Uchupi (1984). Instead, the potential of seafloor “imaging” is evaluated over a large range of spatial scales, approximately ten orders of magnitude from the form of the entire Atlantic basin down to the size of grains in seafloor sediments (Fig. 1). Under “submarine imaging” are included 3-D (stereoscopic) descriptions of bottom
Gravity anomalies in the western North Atlantic Ocean
Authors: Rabinowitz Philip D. , Jung Woo-Yeol
Published: April 2015

The first accurate gravity measurements in the deep ocean were made in 1923 by Vening Meinesz with pendulum apparatus onboard submarines (Vening Meinesz, 1932). Since that time, and up until the late 1950s, many pendulum stations were occupied in order to obtain information about the earth’s gravitational field over the vast oceanic regions. Though these measurements were accurate (generally 3 or 4 mgal; Ewing and others, 1957) and yielded valuable information concerning the earth’s crust, upper mantle, and isostatic processes, the measurements were discrete and separated by large distances. For this reason, the construction of detailed gravity contour maps of large oceanic areas was virtually impossible. In 1958, continuous gravity measurements at sea aboard surface ships were initiated onboard, U.S.S. Compass Island (Worzel, 1959). Subsequently, gravity measurements have been routinely collected by several of the academic oceanographic institutions and industrial and government agencies.

During the 1960s, major technological advances enhanced the reliability of shipboard gravity measurements. These advances included the development of the satellite navigation system (Guier, 1966; Talwani and others, 1966a) to more reliably compute the Eötvös correction and theoretical gravity values, the development of cross-coupling and off-leveling computers to measure errors resulting from shipboard accelerations (Talwani and others, 1966b), the design of reliable temperature control systems for vibrating string instruments (Bowin and others, 1972), and the modification of the LaCoste-Romberg gravity meter for mounting on a stabilized platform (LaCoste, 1967). Accompanying these technological advances, computer systems were developed for rapid
The relationship between depth and age and heat flow and age in the western North Atlantic
Authors: Sclater John G. , Wixon Lewellyn
Published: April 2015

There are two simple models, compatible with the theory of plate tectonics, that can account for the observed relations between depth and age and between heat flow and age for oceanic crust. The first is the cooling plate model (Langseth and others, 1966; McKenzie, 1967; Sclater and others, 1971), which has been best matched to the depth and heat flow observations by Parsons and Sclater (1977). The second is that of a growing boundary layer (Turcotte and Oxburgh, 1967; Parker and Oldenburg, 1973) that has been matched to the depth and heat flow data by Davis and Lister (1974) and Lister (1977). Both models give good agreement with observations in the range 0–80 Ma. At greater ages the observations of average depth and mean heat flow are best matched by the plate model.

The models are similar in that thermal cooling is the dominant mechanism. The difference between them results from concentrating on two different aspects of the observations. In the plate model, emphasis is placed on matching the exponential decay of heat flow and depth at older ages, whereas the boundary layer model was developed to explain the relation between subsidence and the square root of time on young ocean floor. Though the predictions of the plate model best match the average observations there is a problem with this model in that the constant temperature bottom boundary condition is physically unrealistic. Parsons and McKenzie (1978) have reconciled the two models and also developed
Structure of basement and distribution of sediments in the western North Atlantic Ocean
Authors: Tucholke Brian E.
Published: April 2015

During the past 20 years the morphology of the seafloor has become relatively well known along the crest and shallow flanks of the Mid–Atlantic Ridge through echo sounding and seismic reflection profiling (see Plate 2). In this area sediment cover is so thin, rarely more than 50–100 m, that high frequency echo sounding (12 kHz) essentially maps the surface morphology of oceanic crust. Although our knowledge of this crustal morphology still is far from being detailed or complete, the observed patterns and spacing of fracture zones and crustal blocks provide a general model that can be used to understand the basement morphology in more thickly sedimented regions away from the ridge crest. Structure contours on basment for most of the western North Atlantic recently have been compiled by Tucholke and others (1982) and Tucholke and Fry (1985). Their mapping used the crustal “template” of the mid-ocean ridge together with data from all available seismic reflection profiles in the western Atlantic basins. With some additional mapping, I have extended these structure contours to cover the area from the Mid–Atlantic Ridge crest west to the continental margin between about 8°N and 70°N (Plate 5).

Until the basement morphology is completely masked by sediments, it exerts strong control on how sediments are distributed in the ocean basin. Gravity-controlled mass movements such as debris flows and turbidity currents deposit their sediment load in the deepest accessible basins; consequently, thick ponded sediments often are observed in fracture-zone troughs (Plate 5, Profile F; Plate 6,
Subduction of Atlantic lithosphere beneath the Caribbean
Authors: Westbrook G. K. , McCann W. R.
Published: April 2015

The Caribbean Plate lies between the North American and South American plates and moves relatively eastward with respect to them. The interior of the plate is predominantly oceanic in origin, but along its margins there are island arcs and continental fragments. The plate’s boundaries are often diffuse and ill- defined, especially that with South America.

The boundary between the Caribbean and North American plates exhibits great variety. In the Cayman Trough at the western end of the boundary, a small spreading center (Holcombe and others, 1973) links two major systems of transform faults that extend westward along the southern margin of the trough and eastward along its northern margin and also, less clearly, on its southern margin. The eastward transform faults develop into a complex zone of strike-slip faults in the region of Hispaniola which may also have a component of subduction/underthrusting (Bracey and Vogt, 1970), before passing into a zone of oblique subduction at the Puerto Rico Trench (Fig. 1). Some proportion of the motion across the boundary zone is distributed along the southern margin of Hispaniola and Puerto Rico, with associated deformation of sediments in the Muertos Trough (Ladd and Watkins, 1978). As the plate boundary curves round east of the Lesser Antilles island arc, normal subduction becomes predominant, with active volcanism in the Lesser Antilles. Somewhere along the Lesser Antilles segment of the Caribbean plate boundary, probably at about 14N, lies the triple junction between the Caribbean and the North and South American plates.
Plate kinematics of the central Atlantic
Authors: Klitgord Kim D. , Schouten Hans
Published: April 2015

Opening of the central Atlantic Ocean basin during the past 200 Ma separated North America from Africa and created a classic example of plate tectonic divergent motion and associated geologic features (LePichon, 1968; Morgan, 1968). The entire history of relative motion of these two plates is preserved in the fabric of sea-floor spreading (SFS) recorded by magnetic lineation and fracture zone (FZ) patterns (Fig. 1) (Vine and Matthews, 1963; Heezen and Tharp, 1965) on both flanks of the Mid-Atlantic Ridge. Age calibration of the SFS magnetic anomaly pattern (Cox, 1973; Harland and others, 1982; Kent and Gradstein, this volume) enables us to treat SFS lineations as isochrons of sea-floor crustal ages. FZs mark the path of spreading center offsets (transform faults) through time, providing an approximate flowline trace of the motions that separated the North American and African plates.

Reconstruction poles of rotation and stage poles of motion can be determined from the SFS lineation and FZ data sets (Bullard and others, 1965; McKenzie and Parker, 1967; McKenzie and Sclater, 1971; Harrison, 1972). The kinematic history described by these poles provides a framework for examining major tectonic events, anomalous plate behavior, geologic phenomena, paleooceanographic events, etc. (e.g., Vogt and others, 1969; Tarling and Runcorn, 1973; Dewey and others, 1973; Vail and others, 1977; Sclater and others, 1977; Pitman, 1978; Rona and Richardson, 1978; Schwan, 1980; Kerr and Fergusson, 1981;