Opportunities and Priorities in Arctic Geoscience (1991) / Chapter Skim
Currently Skimming:
5 The Next Stage of Arctic Solid-Earth Geoscience Research
5 The Next Stage of Arctic Solid-Earth Geoscience Research
Pages 19-45
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 19... ...
However, this knowledge does provide some guidance in identifying the most productive regions for focusing our limited resources for support of research and in designing appropriate investigations. A meaningful analysis of the geologic framework and tectonic evolution of the Arctic Ocean Basin would require that all the larger basins and ridges that comprise it be individually investigated and that the character of the geologic structures that bound these first-order features and of the continental margins be determined.
|
From page 20... ...
. The committee therefore recommends that the predominant focus of geologic framework and tectonic studies in the Arctic Ocean Basin be the Amerasia Basin, but selected studies in the Eurasia Basin are also recommended.
|
From page 21... ...
, but even less is known about it, at least in the western literature. The two ridges meet at about a 135° angle near Cooperation Gap, near the center of the Arctic Ocean Basin.
|
From page 22... ...
The geometry of such anomalies, if they exist and can be mapped, is basic to plate tectonic reconstructions in the Arctic Ocean Basin. Delineation of these anomalies has proven difficult because the subbasins are relatively small and because they contain terrigenous sedimentary fills as much as 12 km thick that have depressed the subjacent oceanic crust and significantly reduced, and perhaps obscured, the magnetic signal.
|
From page 23... ...
. The geometry, kinematics, and timing of the early evolution of the Fram Strait gateway need to be documented in detail by seismic reflection profiles and sampling, because interconnection of the deep Arctic Ocean Basin with the world ocean was an event of far-reaching oceanographic and climatic influence.
|
From page 24... ...
Continental Margins A diversity of first-order tectonic features that in large part shaped the physiography and geologic framework of the arctic region underlie the continental margins of the Arctic Ocean Basin, and an understanding of their structural character and age is an essential prerequisite for understanding arctic tectonics. The arctic margins include passive margins of Cretaceous and Tertiary age, transform margins of Tertiary and perhaps Cretaceous age, and in the eastern Beaufort Sea, a convergent margin of Cenozoic age.
|
From page 25... ...
25 Tromso-Mackenzie Lineament An alignment of continental margins and fracture zones, the Tromso-Mackenzie lineament, extends for almost 4,000 km along the western Barents, northern Greenland, and Canadian Arctic Islands continental slopes from near Tromso, Norway, to the Mackenzie Delta in Canada. The lineament is the locus of Cenozoic transcurrent transform faulting on the Spitzbergen fracture zone in Pram Strait and probable Jurassic and Cretaceous transcurrent and extensional faulting off the Queen Elizabeth Islands of Arctic Canada (Vogt et al., 1979b)
|
From page 26... ...
All these questions are critical to understanding the plate tectonic development of the Arctic Ocean Basin. Laptev Sea A transition from rifting by seafloor spreading to rifting by crustal extension in continental rocks can be studied at the junction of the slow-spreading Arctic Mid-Ocean Ridge and the
|
From page 27... ...
A rigorous understanding of the kinematics of rifting in the Laptev transition requires knowledge of the geometry and amount of transform motion, if any, between the Lomonosov Ridge and the east Siberian-Laptev Shelf. Special Studies Comparative Studies of Trans-Arctic Geologic Structure and Stratigraphy The character, distribution, and structure of the geologic formations and lithotectonic terranes that encircle the Arctic Ocean Basin provide important constraints on regional plate tectonic models.
|
From page 28... ...
The movement of the major circum-arctic cratons has been defined fairly well from paleomagnetic measurements and seafloor magnetic anomalies, but the motions of the smaller crustal fragments nearer the margins of the Arctic Ocean Basin are largely unconstrained. Because many arctic tectonic models make different predictions concerning plate translations and rotations, they are especially amenable to paleomagnetic testing.
|
From page 29... ...
Such local networks provided important suD~lemen~arv data in northern Alaska and the Canadian Arctic from 1975 to 1982. Structure and Rheology of the Crust and Upper Mantle 29 -- I ~ - ~ -~~ ~ ~~ i A A primary objective of seismological research in the Arctic Ocean Basin is to determine the structure of the crust and upper mantle beneath the basins, ridges, and continental margins of the Amerasia Basin.
|
From page 30... ...
~_ I Neotectonics Pistal compressional effects of Pacific subduction on the overriding plate appears to have extended into the Arctic Ocean Basin in northeastern Alaska, the northern Yukon Territory, and the southeastern Canada Basin (Grantz et al., 1990c)
|
From page 31... ...
Simultaneous acquisition of subbottom seismic reflection profiles and magnetic and gravity data during GLORIA profiling would greatly enhance the information return. Experience in other ocean basins demonstrates that the acquisition of GLORIA imagery for the entire Arctic Ocean Basin would advance understanding of its geology, sedimentation, and oceanography.
|
From page 32... ...
Tracing and understanding the evolution of arctic climate and oceanography since mid-Cretaceous time is therefore a major scientific goal. Fortunately, an abundant lithostratigraphic and biostratigraphic record of this evolution is preserved in three distinct arctic environments: the sediments of the Arctic Ocean Basin (Thiede et al., 1990)
|
From page 33... ...
These events enlarged the Arctic Ocean Basin, established its deep circulation with the North Atlantic, and produced changes in the distribution and height of arctic highlands. The climatic changes that accompanied these shifts increased the pole-toequator temperature gradient and transformed the Arctic from a cool temperate landscape to one of tundra and continental glaciers (Barnosky, 1987~.
|
From page 34... ...
earth geoscience should be to close this gap with sediment samples from both the Arctic Ocean Basin and the arctic rim. Plant fossils in the Beaufort Formation of the western Canadian Arctic Islands record a gradual cooling in Neoprene time in the Arctic.
|
From page 35... ...
It is now known that the warmest postglacial period in the Arctic occurred during the mid-Holocene, when insolation was high and the thickness of the active layer in areas of permafrost increased (Bradley, 1990~. The recognition of this mid-Holocene warm interval in cores and outcrops from the Arctic Ocean Basin and from the arctic shelf and coastal plain, and in ice cores from Greenland and the Canadian Arctic Islands, would establish an important environmental datum.
|
From page 36... ...
An important ancillary question is whether the Arctic Ocean Basin was a site for evolution and adaption of marine life to cooler conditions and, ultimately, sea ice. Arguably, the unique characteristic of the Arctic Ocean is its perennial cover of sea ice (Clark, 1990a)
|
From page 37... ...
How did changes in bottom water formation in the Norwegian and Greenland Seas during glacial/interglacial cycles affect the physical and chemical oceanography of the Arctic Ocean Basin? Ongoing research in the more southerly ocean basins is attempting to address these and similar issues, but these studies would benefit from closer integration with studies of the sedimentary record in the Arctic Ocean Basin and its continental shelves and coastal~plains.
|
From page 38... ...
For example, paleomagnetic chronostratigraphy suggests that prior to approximately 1.5 million years ago, little ice-rafted detritus and virtually no detrital carbonate entered the Arctic Ocean Basin (Jones 1987~. Preliminary data suggest that since that time floods of lithologically distinctive sediment from the Queen Elizabeth Islands entered the Amerasia Basin approximately every 400,000 years.
|
From page 39... ...
The climatic and environmental history embedded in ice cores will be most fully understood when it is supplemented and complemented by evaluation of the sedimentary record preserved in the Arctic Ocean Basin and its continental shelves and bordering lowlands. ARCTIC GEOLOGIC PROCESSES AND ENVIRONMENTAL INDICATORS Knowledge of the influence of glacial and interglacial climates on the chemistry, mineralogy, Ethology, and texture of arctic biogenic and elastic sediments is meager, but recent observations suggest that certain features of the arctic sedimentary record may enable interpretation, and in some cases quantification, of past environmental conditions and processes in the arctic sedimentary record (Thiede et al., 1990~.
|
From page 40... ...
Characterization and quantification of the clastic and biogenic sediment now being contributed to the Arctic Ocean Basin by winds, sea ice, icebergs, and turbidity currents, and by chemical, biological, or biochemical processes in the water column and in the shallow sediments would significantly improve interpretation of the lithostratigraphic record in arctic cores. Sampling of the water column and ice canopy for the clastic and biogenic components by sediment traps, ice coring in different parts of the Arctic Ocean Basin (Barnes et al., 1982; Honjo et al., 1988)
|
From page 41... ...
that may imprint the sedimentary record. Thus, some of the well-laminated sediment in Barrow Sea Valley and the Arctic Ocean Basin may be deposits from brine-charged density currents rather than from turbidity currents.
|
From page 42... ...
The foregoing speculations recognize the importance of ice-rafted deposits in the Arctic Ocean Basin but are based on meager data on sediment in modern sea ice. The significance of sediment in sea ice is indicated by recent investigations suggesting that turbid, sediment-bearing sea ice on the Alaskan Beaufort Shelf may, in some years, transport 16 times more sediment than the yearly input from rivers feeding the same region (Kempema et al., 1989~.
|
From page 43... ...
The first appearance of previously isolated Arctic Ocean taxa in North Atlantic faunas would effectively date the earliest shallow-water connections between the two ocean basins. Integration of the mammalian and marine faunal evidence for the openings and closings of Arctic-North Atlantic seaways would require additional detailed and extensive fieldwork.
|
From page 44... ...
Definitive study of gas hydrate deposits in the Arctic is now technologically feasible, at least in areas that are seasonally ice free. Seismic reflection and refraction methods can be used to map the distribution and thickness of the continental margin hydrate deposits and to define some aspects of their internal structure.
|
From page 45... ...
Seismic surveys, geochemical sampling, and drilling would be less expensive on the inner shelf and coastal plain, and comparatively inexpert sive seismic surveys may be able to identify gas hydrates beneath permafrost. However, well logs, especially mud logs, and direct sampling with pressure core barrels are the only methods now available for reliably identifying and studying gas hydrate deposits within permafrost, although equilibrium borehole temperatures can identify the zones of hydrate stability in the subsurface (Lachenbruch et al., 19879.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.