National Science Foundation Workshop
December 9-12, 2004
Stanford University, Stanford CA

Report from the Arctic Margin Breakout Group

1.  Most important unsolved problem:  How did the Amerasian Basin of the Arctic Ocean form?

The Arctic Ocean, one of the last geologic frontiers, also represents one of the few major unsolved plate tectonic puzzles on earth. Current hypotheses suggests that northern Alaska and part of Arctic Russia belonged to a once-continuous continental mass joining North America and Eurasia across the polar region.  In the most widely accepted model, a piece of this continent, known as the Arctic Alaska-Chukotka microplate, drifted from the North American to Eurasian side of the Arctic during rotational opening of the Amerasian Basin (Lawver et al., 2002). Evidence supporting this model comes mainly from the northern margins of Canada and Alaska where many stratigraphic and structural studies have been undertaken. The model remains virtually untested by data from elsewhere in the Arctic, particularly by data from NE Russia.  There are serious problems with the model when such data are considered and also with the implied overlap of continental crust when the fragments involved are restored to their hypothesized pre-drift location.

2.  Main Contributing Authors:

Elizabeth Miller
Larry Lawver
Art Grantz
Tom Moore
Boris Natalin
Vicky Pease
Andrei Zayonchek
Bob Ferderer (Exxon)
Marianna Tuchkova
Sergei Sokolov
Dennis Thurston (Minerals Management Service, AK)
Mikhail Kosko
Sergei Drachev
Jaime Toro

3.  Scientific Rationale:

The exact timing, mechanism and geometry of rift-related opening of the Amerasian Basin is important because the answers to these questions also affect our understanding and interpretation of all aspects of the continental margins and the landmasses surrounding this basin. 

4. Broader scientific and societal impact: 

Resolution of the plate tectonic puzzle of the Arctic is required to better understand the immense Arctic continental shelves, their basins, sedimentary cover, and the natural resources these may host.  It will also contribute to our knowledge of the modern plate tectonic framework of the region, including where to locate major plate boundaries through time and how these dictate the location and activity along the inferred plate boundaries today, which are poorly defined.

The plate tectonic history that formed the Amerasian Basin is responsible for the present-day distribution, age, and subsidence history of the shallow continental shelves that rim the Arctic, as well as the location and age of deep ocean basins and landmasses of the region.  Consequently, this plate tectonic history controls not only the distribution of natural resources but also the patterns of oceanic circulation through time, climate and human history.

5.  Approach(es) to problem:

D. What kind of data/investigations are necessary?

In order to address the plate tectonic origin of the Amerasian Basin, international research efforts and interdisciplinary approaches are required.  Our workshop discussions helped establish the most important and potentially fruitful types of investigations that should be carried out in order to resolve unanswered questions. Two general sets of data are critical.  The first of these data sets should characterize key aspects of the pre-opening geologic evolution of the region as these data determine the original fit or match between the various plate tectonic fragments.  The second of these data sets should characterize key aspects of the Jurassic and younger history of the region which are directly tied to the initial rifting and formation of the Amerasian Basin and its margins.  Because so much of the continental landmass involved in the opening of the Amerasian Basin lies offshore, marine seismic reflection and refraction, gravity and magnetics are essential to tackling the problem.  Onshore efforts involve targeting key regions, mostly in Russia, for detailed field-based data collection.

B. Methods of data collection and analysis:

Because of the multidisciplinary nature of the problem, the methods of data collection are varied.   The examples given of work in progress (listed below) are representative of the spread of disciplines and types of studies necessary.  All of us were in unanimous agreement about the need for organization and funding to work on and complete the compilation of existing and new tectonic, geologic and geophysical data in a GIS format which will be essential for fluid progress in research and the comparison and sharing of data.  This is especially true because of the international scope of the project.  Zayonchek and others are building such a database for the offshore Arctic margin of NE Russia. Kos’ko and others report on the start of compilation for the Tectonic map of Russian East Arctic Continental Margin, a Russian contribution to the international circum-Arctic maps project. No up-to-date regional geologic/geophysical compilations of onshore geology and tectonics exist that might mesh easily with the above, but we note that the geologic map of NE Russia (compiled by M. Gorodinski, 1980, 1:1,500,000) now exists in GIS format (Akinin and Voroshin, NEISRI, Magadan). There was a stated need to begin compilation of a new regional tectonic map of NE Russia incorporating new data from onshore and offshore.

We also agreed that there are several specific regional tectonic features and important time-spans that need to be better understood in an Arctic-wide sense in order to resolve the problems of formation of the Amerasian Basin.  Ideally both existing data and new data would be compiled in a GIS and relational database.  We describe these briefly below.

Pre-Amerasian Basin:  Precambrian, Paleozoic and Early Mesozoic trends

Precambrian and Paleozoic:Several older orogenic belts traverse Europe and Asia (i.e. the Caledonian and Uralian belts) and disappear into the Arctic region, where they are disrupted and severed by events leading to the formation of the Amerasian Basin.   It is not clear how these orogenic belts continue to the rest of the world and/or interact with what was once the ancient Pacific Ocean plate boundary of NE Russia and the northern Cordillera. This is an outstanding geologic/plate tectonic question that must be addressed in this region, and which is also of central importance in restoring the pieces of the Arctic plate tectonic puzzle.  The most important relationships to compile data on and to study in greater detail include: 1.  The regional extent and nature of the  Precambrian/Cambrian(?)-Ordovician unconformity in the circum-Arctic,  2.  The age of deformation and orogenesis in basement rocks and 3.  The time-span, depositional history and tectonic setting of overlying Paleozoic sequences are key to circum-Arctic correlations and plate tectonic reconstructions.  Known exposures are in the Taimir, Urals, the Arctic Islands on the Eurasian shelf, Wrangel Island, northern Chukotka, Alaska and East Greenland.  In particular, there is the need for modern geochrononologic studies in order to accurately compare the histories of the now-dispersed fragments of these older orogenic belts.  

Early Mesozoic:  In an extremely short time frame, there was an enormous outpouring of basalt during a major rifting event at the end of the Paleozoic and initiation of the Mesozoic.  Although this event has received much attention in some regions (i.e. the Siberian Traps), we must understand the meaning and regional distribution of this Permo-Triassic event and its implications for paleogeographic changes in the circum-Arctic and for the origin of the Arctic basins themselves.  For example, Triassic sequences on the Russian part of the “Arctic Alaska-Chukotka microplate” were deposited in a deep water basin formed by rifting of an upper Paleozoic carbonate platform, while the contiguous portion of the microplate in Alaska exhibits no evidence for this event.  If we knew more about the exact age, regional significance and distribution of structures and magmatism related to this major circum- Arctic event, we could use these relationships to help contrain plate tectonic models for formation of the Arctic basins.  One complicating factor is that Triassic sequences are now variably deformed where they are involved in younger orogenic belts such as the Brooks Range and Chukotka fold belts.  Nonetheless, it will be important to compile existing data and collect new data from all regions that have undergone rifting in the Triassic.  These include the Barents Sea (undeformed by younger events), northern Verkoyansk (thrust-faulted but not penetratively deformed), Chukotka (penetratively deformed), Wrangel Island (thrust-faulted).   Samples from wells obtainable through State of Alaska for the Chukchi Basin (western margin Hannah trough) would be extremely useful in comparing and contrasting the rift-related sequences in Chukotka to the platformal Triassic of northern Alaska.  These may also be compared to the Triassic of the Eurasian shelf (Arctic Islands) (undeformed) and to the undeformed but mostly subsurface data from the Triassic failed rift beneath the West Siberian Basin.  Fingerprinting source areas for Triassic sediments via sedimentologic and geochronologic methods represents a powerful approach to regional correlation in conjunction to compilation of distribution, thicknesses and tectonic setting.

Mid to Late Jurassic:  Based on the analysis of seismic reflection data from the Arctic margins of Alaska and Canada, the age of formation of the Amerasian Basin by rifting is inferred to have occurred in timespan 135-118 Ma (e.g. Lawver et al., 2002).  Immediately prior to this rifting, an important orogenic event occurred along the paleo-Pacific margin.  This event involved regional shortening, collapse of oceanic basins by thrust faulting, the emplacement of ophiolites and the obduction of a Middle Jurassic and older marine island arc.  Similar such events took place at approximately the same time (Middle Jurassic) in the Verkoyansk-Kolyma belt (Alazaya arc, Oxman et al., 1995) and in Alaska (Angayucham terrane, e.g. Mayfield et al., 1988).  Correlative rocks exist along the South Annyui Zone along the southern boundary of the inferred Arctic Alaska-Chukotka plate in NE Russia (e.g. Sokolov et al., 2002). Compilation of the location and extent of this belt, sedimentologic and paleontologic studies on depositional histories and studies of the exact ages of deformation are essential to the plate reconstruction of the Arctic as these oceanic sequences may represent the youngest continuous belt of rocks that was rifted and dispersed by plate motions that formed the Amerasian Basin.   Such studies could establish whether these remarkably similar events took place along strike of a single plate margin or are unrelated to each other.

Syn-Amerasian Basin Mesozoic sedimentary and tectonic history:

Jurassic to Cretaceous Basins:   It is essential to compile the locations and history of Jurassic and Cretaceous basins and their sedimentary histories within a circum-Arctic framework. The orientation of these basins, the nature of bounding faults, age of inception and record of sedimentation through time, and their correlation across the various shelfal and basinal domains of the present Arctic Ocean is key to understanding the origin of the Amerasian Basin by rifting.  Although it is clear that these histories will provide the most insight into the question of the origin of the Amerasian Basin, these data will be the hardest and most expensive to obtain in the near future as acquisition involves offshore seismic reflection studies and drilling in ice conditions.  The aerially extensive Arctic shelf of NE Russian represents the least characterized piece of continental crust involved in Arctic plate reconstructions.  Progress is being made by Russian efforts (see below) and each of these new data sets will have important bearing on the origin of the Amerasian Basin. 

Jurassic to Cretaceous Deformation:  The generally accepted time-span for the rotational rift origin of the Amerasian Basin (135 to 118 MA) (Lawver et al., 2002) may coincide with the age of crustal shortening in the Brooks Range, Alaska, the Chukotka fold belt, Russia, and northern Verkoyansk. The uncertainties in dating these events, however, leave open the question of whether they are, or are not, spatially and temporally linked (for review and comparison of timing from Alaska to Russia see Miller et al. 2002). In terms of understanding the kinematics and driving forces for the rift formation of the Amerasian Basin (for example, Arctic rift push versus Pacific margin pull), better constraints on the timing of deformational events is critical.  This can be accomplished by land-based field work on basins/depocenters, documenting changing source regions through time by stratigraphic, paleontologic, sedimentologic and geochronologic methods and by dating folding and thrust-faulting directly.  Virtually no modern data on the timing of deformational events exists from Chukotka and Wrangel Island.  The Brooks Range, Alaska, is better studied but still incompletely characterized.  Dating and paleomagnetic studies of basalts exposed on Henrietta Island represents another key locality to collect data relevant to the timing of opening and amount of rotation involved.

Investigations in Progress:

U.S.Geological Survey Petroleum Habitat Map (Art Grantz, Tom Moore and others):  This investigation aims to chart the distribution, ages of sedimentary fill, sediment thicknesses and deformational histories of offshore and onshore basins in the circum Arctic region.  When the project is completed, it will be publicly available.

GIS compilation of offshore geophysical data from the Russian Arctic shelves (Andrei Zayoncheck):  A mostly completed set of 1:1,000,000 scale maps that when completed will cover the entire Arctic continental shelf of Russia.

Compilation of the Tectonic Map of Russian East Arctic Continental Margin (Russian contribution to the International Circum-Arctic Maps Project (VNIIOkeangeologia, M. Kos’ko reports).

Seismic profile across Siberian shelf collected by LARGE. Extends from Indigirka Bay to Genetta Island. Published  interpretations exist by S. Drachev. This profile represents new seismic reflection data providing a cross section of a huge region of few data.  Data not available to the public.

Detailed aeromag surveys to be carried out in 2005 from 1.  The continental margin of the Siberian Shelf to the Mendeleev Ridge and 2. From the continental margin of the Siberian Shelf to the Lomonosov Ridge (Andrei Zayonchek).

Deep seismic reflection profile to be carried out in 2005 from north of Wrangell Island to 78°N (Poselov, VNIIOkeangeologia).  This represents the northernmost part of the offshore continuation of the ambitious on land deep crustal seismic reflection profile extending from Magadan on the coast of the Sea of Okhotsk to Wrangel Island (in progress (2004-05) as reported upon at this meeting by Nikolai Goryachev and referred to by meeting participants as “TRACT” )

UTTG sea-ice seismometer deep crustal refraction study to determine crustal structure of plateaus in the Amerasian Basin, including both the Mendeleev Ridge and the Chukchi Borderland.  Seismic reflection data to be collected along the continental margin to investigate basin formation and to look for cross-cutting faulting.  Attempt to tie offshore structure into well data along margin and to tie into continental geology with particular emphasis to TRACT line that ends at Wrangel Island. Scheduled for 2006 (L. Lawver).

Geophysical survey from Barrow to North Pole utilizing chirp system for hi-res imaging of sedimentary cover (Bernard Coakley, Martin Jacobson) scheduled in 2005.

BGR effort to get into international waters near Russian continental margin with the Polar Stern for a multiclient spec shoot. On the NW side of Wrangel Island. 2005

Oden Swedish Icebreaker cruise to Wrangel Island and points on Chukotka Coast, 2005.  (V. Pease, E. Miller and S. Sokolov). Structural geology and geochronology of Wrangel Island and Chukotka:  Ages of basement rocks, timing of folding and thrusting. Parallel land-based effort in summers of 2005 and 2006 pending funding.

Field work in Novaya Zemlya 2004 by V. Pease with CASP and Stat Oil with investigations of Paleozoic sections, Precambrian/Paleozoic unconformity, and structural studies.

Field Work on New Siberian Islands (2000-2004 and in progress) Alexander Kuzmichev:  This field work has provided new data that demonstrates that the ophiolitic rocks that define the southern edge of the Arctic Alaska-Chukotka microplate are present on the New Siberian Islands.

Field work in Chukotka 2003 and 2004 (Elizabeth Miller, Marianna Tuchkova, Jaime Toro, Sergei Katkov and Igor Podorgny) Characterizing and dating deformation in the Chukotka fold belt and sedimentologic study of Triassic and Jura-Cretaceous deposits.

Field work in the South Anuyi Zone (in progress) Sergei Sokolov, Marianna Tuchkova and others.  To characterize age and depositional history of ophiolitic and sedimentary successions and their age of deformation. 

References Cited:

Lawver, L.A., Grantz, A. and Gahagan, L. M., 2002, Plate kinematic evolution of the present Arctic region since the Ordovician, in, Miller, E.L.,, Grantz, A., and Klemperer, S.L., Tectonic Evolution of the Bering Shelf-Chukchi Sea-Arctic Margin and adjacent landmasses, Geological Society of America Special Paper 360, Boulder, CO, p. 333-358.

Mayfield, C.F., Tailleur, I.L., and Ellersieck, I., 1988, Stratigraphy, structure and palinspastic synthesis of the western Brooks Range, northwest Alaska, in Gryc, O., ed., Geology and Exploration of the National Petroleum Reserve in Alaska, 1974-1982.  U.S. Geological Survey Professional Paper 1399, p. 143-186.

Miller, E.L., Gelman, M., Parfenov, L. and Hourigan, J., 2002, Tectonic setting of Mesozoic magmatism:  A comparison between northeastern Russia and the North American Cordillera, in, Miller, E.L.,, Grantz, A., and Klemperer, S.L., Tectonic Evolution of the Bering Shelf-Chukchi Sea-Arctic Margin and adjacent landmasses, Geological Society of America Special Paper 360, Boulder, CO, p. 313-332.

Oxman, V.S., Parfenov, L.M., Prokopiev, A.V., Timofeev, V.F., Tretyakov, F.F., Nedosekin, Y.D., Layer, P.W., and Fujita, K., 1995, The Chersky Range ophiolite belt, Northeastern Russia, Journal of Geology v. 103, p. 539-557.