The Arctic

Environment, People, Policy

Jack D. Ives, Roger G. Barry, Jack D. Ives, Roger G. Barry, Mark Nuttall, Terry V. Callaghan

• Publisher: Taylor & Francis
• Year: 2019
• Print ISBN: 9781032808291
• eBook ISBN: 9781000699005
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Originally published in 2000, The Arctic provides a comprehensive overview of the region's rapidly changing physical and human dimensions, and demonstrates the importance of communication between natural scientists, social scientists, and local stakeholders in response to the tremendous challenges and opportunities facing the Arctic. It is an essential resource for all Arctic researchers, particularly those developing multidisciplinary projects. It provides an overview of key areas of Arctic research by renowned specialists in the field, and each chapter forms a detailed, varied and accessible account of current knowledge. Each author introduces the subject to a specialist readership, while retaining intellectual integrity and relevance for specialists. Overall, the richness of the material presented in this volume reflects the ecological and cultural diversity of this vast and environmentally critical part of the globe.

Part 1
The Physical Structure and Processes of the Arctic

CHAPTER 1
The Geological Development of the Arctic

MAURITS LINDSTRÖM

Geology is an appropriate background to the description and explanation of Arctic environments. Arctic soils are directly dependent on old bedrock because the rocks are less quickly destroyed by chemical weathering than in other climates. The configuration of Arctic seas and continents is understandable in the light of very long-term geological processes. Furthermore, the Arctic abounds in geological resources that hold promises of economic gain, whereas their exploitation poses formidable threats to an exceptionally vulnerable environment.

The early geological history is documented in the bedrock that is particularly well-exposed in the Arctic because of the poverty of higher vegetation, the removal of soils by extensive Quaternary glaciations, and the slow rate of weathering. Because there was not time enough for the formation of solid rock (except for volcanics) during the younger geological development, geologists must look into the history of non-consolidated deposits in order to reconstruct this development. The geomorphology can also be very helpful. However, particularly important and precise information is continually being gained from the study of the deep ocean, oceanic deposits, and the Earth’s crust under the ocean.

In order to clarify the background of all this information, one must outline the theory of Plate Tectonics that has developed in recent decades. Only its broadest, solidly established features can be rendered here. The Earth is surrounded by a 100–150 km thick shell, called the lithosphere, of which the so-called crust is the uppermost part. The lithosphere is rigid, which means that it does not deform readily or rapidly. It is divided into plates that are between a few hundred to several thousand kilometres wide. The jigsaw puzzle formed by the plates, in principle, covers the entire Earth. If the plates had been perfectly rigid and permanent their interlocking pattern would have prevented any major movement. However, there is overwhelming evidence that they have indeed moved great distances in diverse directions. Rates of movement are typically a few cm to 10 cm/year. The continents are the most rigid and permanent portions of the plates to which they belong. They are deformable mainly at their margins, where the old crust thins considerably. Plate movements can occur mainly because the oceanic lithosphere does not share the permanency of the continents. Old oceanic lithosphere founders into the Earth’s mantle and is destroyed at those plate boundaries where the plates collide. Gigantic fractures open along those other boundaries, where plates drift from one another; this process is called rifting. The fractures are filled from below by magma, i.e. molten rock, that solidifies into the building material of new lithosphere. Thus the plates grow from the boundaries, where they glide apart. The plate movements participate in the heat flow from the Earth’s interior. Their precise causes are still not known in every detail, although alternative, plausible explanations do exist.

The Arctic contains some of the oldest known rocks on Earth. The present structure of most of its continental crust was formed during the Proterozoic Era some 2,500–540 Ma (million years) ago. However, the dating of Proterozoic rocks depends mainly on chemical analyses of radioactive isotopes that occur in trace amounts. This is time-consuming, costly, and fraught with sources of error that may render the method difficult.

With the beginning of the Cambrian Period about 540 Ma ago abundant organisms that can be fossilised appeared for the first time. Fossils provide ready means of precise dating that can be calibrated against a reasonable number of quantitative age determinations by radioisotopes. Therefore the knowledge about geological events is incomparably more detailed and reliable for the Phaneorozoic Era that began with the Cambrian, than for the preceding Eras. This chapter will trace, in the broadest of outlines, the Phanerozoic history of the jigsaw puzzle of continental and oceanic terrains of the Arctic. The method of presentation will be, first to identify the parts of the Earth’s crust that are to be followed on their ways to present geographic positions. Then, the principal geological events will be indicated that made these geographic entities what they are now. Their paths of migration across the surface of the globe can then be reconstructed from their histories.

Geological ‘Building Blocks’ of the Arctic

The Arctic continental terrains surround the Arctic Ocean on the margins of which we find northern Greenland, the Canadian Arctic archipelago, the Mackenzie Lowland and Alaska, the Chukchi Sea and the East Siberian Sea, the New Siberian Islands, Severnaya Zemlya, Franz Josef Land, and Svalbard. The Arctic Ocean began to form by sea-floor spreading in the Jurassic period (about 150 Ma ago), so it is a relatively young geological feature.

The continental crust of Greenland formed mainly in the Archean (pre-2,500 Ma) and Proterozoic Eras and has remained coherent since those times. Major zones of younger mountain—building and lithospheric rupture follow the eastern, northern, and western margins of Greenland.

The Innuitain Orogen occupies much of the Arctic archipelago of Canada. It is a zone of tectonically mobile crust that developed along the shared northern margin of Greenland and the Canadian Shield. Its history can be traced back into the late Proterozoic, and deformation continued into the Tertiary. An orogen is a portion of the Earth’s crust, mostly about a thousand to many thousand kilometres across, that has undergone orogeny. Orogeny, which literally means mountain-building, is a process of very strong deformation of the Earth’s crust through constriction at right angles to the long axis of the orogen, accompanied by the injection of hot magma into the deformed crust. Much of the deformed volume of rock has its mineral content thoroughly changed owing to the increased pressure and temperature. This process of change is called metamorphism. The deformation is expressed through folding and the formation of major fractures that are called overthrusts or thrust-faults. Orogenies last millions to several tens of millions of years. They occur at plate boundaries where plates meet one another in collision.

The Canadian Shield is a continental area that has remained tectonically stable, i.e. practically non-deformed, since the Proterozoic. It occupies part of the Arctic archipelago and all of mainland Canada east of the Mackenzie River; it is the northern most part of the North American Craton (a craton is a large stable part of the Earth’s crust or lithosphere which has not been affected by any significant deformation for millions of years) that includes the central USA with which it has remained a coherent unit since the Proterozoic.

The Arctic Alaska Plate consists of northern Alaska (the Brooks Range, the Arctic Platform to the north of it, and much of the Seward Peninsula) and the Chukotka Peninsula, Anadyr Upland, and Wrangel Island in eastern Siberia. This plate is thought to have rotated anti-clockwise about a pivotal point at the present Mackenzie Delta, which is at the eastern end of the plate. The rotation was the beginning of the opening of the Arctic Ocean.

The Central Alaska and Ruby Terranes occupy a roughly 200 km wide northeast-southwest striking belt. (Strike signifies the horizontal direction of an inclined or vertical, planar structure in a rock—such as for instance the platy grain of a gneiss or mica-schist, or the bedding of a sedimentary rock. A belt is the outcropping surface of a very large, regionally extending and elongated body of rocks that have important features in common, such as for instance folding, thrusting, or volcanicity.) To the northwest of Fairbanks; the Kuskokwim Mountains are the most prominent part of this belt. The Terranes have remained moored to the margin of the North American Craton throughout their history but have nevertheless rotated and moved relative to one another.

The Yukon Composite Terrane extends 2,000 km south-eastward from the Fairbanks area, thus occupying the northern part of the Coastal Ranges. It has remained parallel to the margin of the North American craton to which it is now firmly attached; however, in the course of its history there was a considerable excursion from this margin.

Wrangellia, with oceanward strips of complex terrains, forms the Alaskan Peninsula. Northeast of Anchorage it changes from a north-eastward direction, to continue south-eastwards as a 100—150 km wide, about 2,000 km long strip between the Yukon Composite Terrain and the Pacific. Movements of oceanic crustal plates in the Pacific domain drove it against the continental margin from a distant, unknown position.

The Togyak-Koyukuk Arc made a late appearance in the Jurassic as an oceanward structure that paralleled the Arctic Alaska Plate. It was driven toward the latter plate through subduction of an intervening ocean basin. The subsequent rotation of the Arctic Alaska Plate drove it up against Wrangellia. The remains of the Arc now form the basement of areas between the Brooks Range and the Alaskan Peninsula.

The Koryak Terrain consists of the Koryak Mountains and their southward continuation, the Kamchatka Peninsula. The Terrane abuts in the north against the Arctic Alaska Plate. It migrated toward the present Asian continent in the late Mesozoic from an unknown position in the Pacific realm. Its neighbour terrain to the west is the Kolyma Plate that comprises the lowlands of the Kolyma and Indigirka Rivers, the Omsk Mountains, and the very extensive, hilly territory of the Omolon River where the Yukaghir tribes once had their hunting grounds. The giant arc that forms the western boundary of this plate got its present position through pushing westwards into the eastern margin of the Siberian Platform, where the present drainage areas of the Lena and Aldan Rivers are spreading.

The Siberian Platform extends westwards from the Lena drainage to the Ural Mountains. It is the largest crustral unit dealt with here. In addition to the vast land area it also comprises the continental crust underlying the Laptev Sea. The crust is Proterozoic and older. It has not suffered major penetrative deformation during the latest hundreds of million years.

The Barents Platform includes the continental crust of the Barents Sea and the Pechora Lowland. It is separated from the Siberian Platform by the Novaya Zemlya and Taimyr fold belts and from the Baltic Platform by the Timan Range and the Caledonides of northern Norway. Its easternmost lobe is the north-eastern part of the Kara Sea, bordered to the south by Taimyr and to the east by Severnaya Zemlya. The rocks and structure of the core of this unit were formed in the pre-Cambrian Eras.

The Baltic Platform comprises most of Scandinavia, Finland, the Baltic countries, and European Russia south of the Timan Range and the Barents Sea. Its eastern boundary follows the Ural Mountains. To the north and west it is bounded by the Caledonian fold belt. This Platform has remained essentially un-deformed during the latest 700 Ma.

Svalbard and Franz Josef Land are crustal fragments on the very margin of the North Euro...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Original Title
• Original Copyright
• Contents
• List of Figures
• List of Colour Illustrations
• List of Tables
• Preface
• Foreword
• Map
• Introduction
• Part 1 The Physical Structure and Processes of the Arctic
• Part 2 Life Sciences in the Arctic
• Part 3 Social and Political Dimensions of the Arctic
• Part 4 Anthropogenic Impacts on the Arctic Environment: Regional and Global Consequences and Policy Responses
• Index