G. Becker and WK Braun.

Senckenbergiana Lethaea, Vol. 88, No. 1, Jun 2008, pp. 23-35.

The stratigraphical significance, evolutionary pathways and distribution patterns of Devonian (with emphasis on Middle Devonian) ostracods occurring in western Canada are reviewed. The overall faunal appearance is Devonian in aspect. Typical Eifelian-Givetian markers are ascertainable at the generic level, and occasionally resemble known species. Recognised genera mostly comprise cosmopolitan forms indicating (close or loose) faunal connections to both north and south, but also representing either Old World or true New World forms. A "core group", however, shows a particular bauplan giving a unique aspect, mainly discrete palaeocopine genera, provided with particular extradomiciliar dimorphic features and considered to be endemic for the Middle Devonian of western Canada. In terms of palaeozoogeography, faunal relationships inside Canada and to Devonian occurrences overseas are demonstrated. Connections between sedimentary transgressive-regressive and evolutionary cycles are demonstrated in terms of event-stratigraphy. Against the background of plate tectonic analyses, assumed migration paths are considered, probably northward via the Uralian Sea to Siberia, but certainly and on a larger scale southward across the Rheic Ocean to North Africa (southwestern Morocco, central Sahara) and Europe (Eifel region, eastern Thuringia, Holy Cross Mountains). As a result, the faunal relationship to the adjacent Great Lakes region appears to be much closer than originally predicted, while only loose contacts are traceable to the North American Midcontinent region. The North African and central European relationships are revealed by few, but conspicuous genera and, to some extent, this may be true of the Russian Platform and Bashkiria.

Paul F. Hoffman.

International Geological Congress, Abstracts = Congres Geologique International, Resumes, Vol. 33, No. , 2008, pp. @Abstract 1309055.

The glacial theory for Pleistocene tills and associated landforms in northern Europe and North America was proposed by Esmark (1824) in Norway, Venetz (1830) in Switzerland and Bernhardi (1832) in Germany, but was not widely accepted until after the Scottish glacial revival led by Jamieson (1862) and Geikie (1863). Resolution of the glacial controversy was good for geology-How could older strata be understood if those closest to the Recent remain mysterious (James Smith, 1836)-but was more deeply felt in climate physics. Experimental demonstration of the selective absorbtion of infra-red but not visible radiation by certain gases (Tyndall, 1861, 1863) was carried out expressly to account "for all the perturbations of climate that the researches of geology have revealed". Tyndall recognized that although absorbtion by water vapor is "more essential to the vegetable life of England than clothing is to man", it is the atmosphere's variable minor constituents, notably carbon dioxide, that must be responsible for bidirectional climate change of geological magnitude. "Revolutions in the Sea" (Adhemar, 1842) may seem an odd title for an orbital theory of ice ages, but the book is directed at a problem more central to the ice age controversy than most historians admit, the problem of submergence of the land and its slow reemergence after the ice had disappeared. The titles of papers from "On indications of changes in the relative levels of Sea and Land in the West of Scotland" (Smith, 1836) onward refer to the occurrence of marine faunas in the tills and overlying stratified drift, now raised high above the sea. Adhemar (1842) envisioned gigantic polar ice caps, alternating between the hemispheres, which displace the planet's center of mass, causing sea levels to rise toward the glaciated pole and fall toward its opposite. Although Croll (1864) revised Adhemar's theory of climate change, he accepted his ideas on submergence (Croll, 1866, 1875). Croll's writings on submergence were intended to refute the suggestion of Jamieson (1865) that the submergence was due to "the enormous weight of ice laid down upon the land". The latter emerged triumphant, however, based on geological observations insightfully marshalled (Jamieson, 1882), including the development of peripheral bulges and their collapse, causing drowned forests, upon deglaciation. Jamieson, the most creative and original of the Scottish glacial revivalists, deserves to be better known. The identification in 1859 of late Paleozoic tillites in coastal India, in 1870 in southern Africa and later throughout Gondwanaland (ice always flowing onshore) aroused a young German meteorologist. "The Permian ice age poses an unsolvable riddle for all models that do not dare to assume horizontal displacements of the continents" (Wegener, 1912). Closing the Atlantic and Indian oceans "takes everything mysterious away from the problem".

Charles Barker.

Michigan Academician, Vol. 38, No. 4, 2008, pp. 58-59.

Masao Nakada.

Geophysical Journal International, Vol. 175, No. 3, Dec 2008, pp. 1235-1244.

Long-term true polar wander (TPW) of the Earth was examined by taking into account the effects of simplified convective processes in the Earth's mantle and continental drift. The TPW, for a given viscoelastic earth model, is wholly determined by both the magnitude of non-forcing elements of moment of inertia (I sub(11), I sub(22) and I sub(33)) and I sub(12) element of product of inertia, and the rates for forcing elements, dI sub(13)-dt and dI sub(23)-dt. The forcing rates are largely related to time-dependent convective processes in the mantle and also continental drift. In this study, I examined the TPW on a convecting mantle with oscillating moments of inertia, inferred from a convective process of alternating degree-one and degree-two structure changes of mantle convection by Zhong et al. (2007). In the phase for a relatively hydrostatic Earth, corresponding to largely degree-one planform, the predicted TPW is sensitive to the viscosity structure of the mantle, particularly to the lithospheric viscosity structure, and its magnitude may be larger than similar to 30 degree even for the forcing rates with similar to 10 super(30)kgm super(2)Myr super( -1) related to continental drift (Dickman 1979). In the phase for a non-hydrostatic Earth characterized by largely degree-two planform such as for the present-day, however, the TPW is less sensitive to the viscosity structure, and its magnitude may be similar to 10 degree at most. These results may provide quantitative constraints on examining relationship between rheological structure and convective processes in the mantle, continental drift and TPW.

Wolf Uwe Reimold.

South African Journal of Geology, Vol. 110, No. 1, Mar 2007, pp. 1-46.

This is the story of changing paradigms, regarding the understanding of our planet and its position in space--of geocentric and heliocentric views, but mainly in the earth sciences, over the last several centuries. This is also the story of the revolutionaries--Copernicus, Lyell, Hutton, Van Hoff, Wegener and Du Toit, Dietz and Hess, and finally Shoemaker. It is the story that begins with the Babylonian geocentric but flat worldview, moves on to the heliocentric perspective of the Greek philosopher Aristarch, via the geocentric dogma of the pre-Copernican Middle Ages and Copernicus' revision, to the Cataclysm Theory, and then the beginning of Modern Geology in the form of gradualism and actualism, to continental drift that spawned plate tectonics, and finally to Planetary Science. This new view of the universe includes what I would like to call the New Catastrophism, incorporating the catastrophic forces of the important natural catastrophic processes affecting this planet. The nature of impact cratering as a fundamental universal process and the tools for the recognition of impact structures will be examined, and the role of this process since beginning of accretion and planet formation, and leading to the question whether past impact catastrophes have, at times, spurned major mass extinctions in Earth's biological record. This paper addresses Africa's impact crater record and the stratigraphic record of impact cratering, and examines both the challenge that humanity is experiencing from huge extraterrestrial bolides and the benefits that impact has brought. In the end, the conclusion is derived that an integrated geoscientific and planetological science approach has resulted in new tools to address the ultimate questions of Earth's--and our--past and future.

Masao Nakada.

Earth, Planets, and Space, Vol. 59, No. 6, 2007, pp. 513-522.

Long-term true polar wander of the Earth (TPW) has generally been discussed by taking into account convective processes in the mantle such as downgoing slabs and upwelling plumes. Here I examined a relationship between continental drift and TPW on a hypothetical Earth with no such convective processes in the mantle. I evaluated temporal changes in moments of inertia owing to continental drift during a period of ~250 Ma based on a paleogeographic reconstruction, in which I estimated the lateral density heterogeneities by factoring in the observed mean land elevation of continents and average age of the oceanic lithosphere. The predictions for a viscoelastic Earth model with plausible viscosity models indicate that the long-term TPW might have been affected by continental drift throughout Cenozoic and Mesozoic times, which has wholly proceeded by maintaining isostasy at a certain depth, as well as convective processes in the mantle.

I. J. Demhardt.

Polarforschung, Vol. 75, No. 1, 2005, pp. 29-35.

Certainly not the first to notice the obvious key-and-lock shape of Brazil and Africa, in 1911 the meteorologist Alfred Wegener was nevertheless among the first scientists to link hitherto isolated scientific arguments to these empirical observation and develop a hypothesis conclusively explaining the architecture of the Earth's surface which over the years evolved into an intense debate with his adversaries. Although cautioned by his colleague and father-in-law Wladimir Ko?ppen not to interfere with the discussion of geological matters as a meteorologist - and therefore as an outsider - he presented his thoughts to the "Geologische Vereinigung" in Frankfurt am Main on 6 January 1912 and first published them in 'Petermanns Geographische Mitteilungen', one of the leading geographical monthlies of international reputation, in April 1912 in a paper entitled "Die Entstehung der Kontinente" (The Origin of the Continents). In the, at times, highly controversial debate sparked by Wegener's paper in 'Petermanns Geographische Mitteilungen', which for obvious reasons soon after shifted to geological platforms of discussion, it is a lesser known fact that 'Petermanns Geographische Mitteilungen' too mirrored this heated debate over a period of thirty years in eleven major articles of which four (ANDRE?E 1917, NO?LKE 1922, KOBER 1926, SCHUMANN 1936) opposed Wegener's hypothesis and seven defended his benchmark paper. Interestingly Alfred Wegener himself never defended his concept in this journal, but, except for one supportive paper (RUUD 1930), the others defending his interpretation were some sort of 'family backlash' vigorously conducted by Wladimir KO?PPEN (1921a, 1921b, 1925) and Kurt WEGENER (brother, 1925, 1941, 1942).

V. A. Aristov and N. V. Lubnina.

Trudy Geologicheskogo Instituta Rossiiskaya Akademiya Nauk Vol. 516, 2005, pp. 91-113.

Benjamin R. Phillips and H. P. Bunge.

Earth and Planetary Science Letters, Vol. 233, No. 1-2, 30 Apr 2005, pp. 121-135.

Feedback between continents and large-scale mantle flow through thermal blanketing has long been surmised as a mechanism for continental drift and Wilson cycles. Paleomagnetism provides evidence for extensive continental displacements ( approximately 10,000 km) on time scales of 100-200 million years, comparable to an intrinsic overturn in whole mantle convection. Here we model continental motions in vigorous 3D spherical convection models, focusing on the effects of continent size, mantle heating mode, and a strong increase in lower mantle viscosity. Continents covering 30%, 10%, and 3% of Earth's surface (representative of the former supercontinent Pangea, present-day Asia, and Antarctica, respectively) are introduced into simple end member mantle convection models characterized by pure core or internal heating, and uniform or layered mantle viscosity. Supercontinents promote temperature anomalies on the largest scales (spherical harmonic degrees 1 and 2), primarily through the organization of the long-wavelength convective planform inherent in models with a high-viscosity lower mantle. Bottom heating can promote long-wavelength heterogeneity by clustering plumes beneath the continent. However, in isoviscous models small-scale structure persists away from the continent regardless of the heating mode. Supercontinents respond to long-wavelength heterogeneity by following great circle paths with variations in velocity on time scales of 1 billion years. Smaller continents are unable to promote long-wavelength structure, and the resulting motions are governed by bursts in velocity on time scales of the order of 100 million years. Continental velocities are roughly a factor of approximately 3 smaller than those in oceanic regions, an observation that may help explain the observed difference in the speed of predominantly continental or oceanic plates.

Anonymous

Berichte zur Polar- und Meeresforschung = Reports on Polar and Marine Research, Vol. 516, 2005, pp. 421.

R. Chander.

Resonance, Vol. 10, No. 12, 2005, pp. 58-75.

After Wegener, an astronomer by training and meteorologist by profession, visualized that there was once a single very large landmass on the surface of the earth. Gradually it broke up into smaller fragments, which drifted away to form the present continents. In a few cases, the drifting fragments subsequently collided, coalesced and formed larger landmasses again. Wegener could thus explain in a simple way (1) similarities in shapes of continental coast lines separated by wide oceans, (2) similarities in the rocks and fossils occurring on such coasts and in the fauna and flora inhabiting them, (3) the formation of several major mountain ranges of the world and (4) the evidence in rocks on past climates of the earth.

Christopher R. Scotese and Judith Totman (prefacer) Parrish.

Journal of Geology, Vol. 112, No. 6, Nov 2004, pp. 729-741.

Forty-six miniature plate tectonic reconstructions are presented that can be assembled into a "flipbook" that illustrates the movement of the continents since the Late Precambrian, 750 m.yr. ago. Six principal lines of evidence have been used to reconstruct the past positions of the continents: (1) linear magnetic anomalies produced by sea floor spreading, (2) paleomagnetism, (3) hotspot tracks and large igneous provinces, (4) the tectonic fabric of the ocean floor mapped by satellite altimetry, (5) lithologic indicators of climate (e.g., coals, salt deposits, tillites), and (6) the geologic record of plate tectonic history. I discuss the probable uncertainties associated with the plate tectonic reconstructions and give an estimate of the uncertainty in the positions of the continents back through time.

Thomas K. Nielsen and John R. Hopper.

Geochemistry, Geophysics, Geosystems - G (super 3), Vol. 5, No. 7, 30 Jul 2004, pp. 24.

Volcanic rifted margins show a temporal evolution in igneous crustal thickness and thus provide additional insights into mantle dynamics compared to the steady state situation at mid-ocean ridges. Although details between different provinces vary, volcanic rifted margins generally show a short-lived pulse of extreme magmatism that quickly abates to a steady state mid-ocean ridge. The generation of thick igneous crust at volcanic rifted margins requires either melting of hot mantle material to higher degrees than observed at mid-ocean ridges or melting of larger amounts of mantle material than would be the case for plate-driven upwelling. To assess under what conditions buoyantly driven upwelling or small-scale convection at rifting plate boundaries is important, a fluid dynamical model with non-Newtonian viscosity that includes the feedback from melting on the physical properties of the mantle is developed. To generate a pulse of high magmatic production requires a viscosity and density structure that also leads to excessive fluctuations in magmatic productivity or a sustained high productivity that continues long after breakup. A viscosity increase due to dehydration caused by melting effectively suppresses buoyant upwelling above the depth to the dry solidus, thereby restricting shallow flow to plate-driven upwelling. While this stabilizes the time dependence and forces the productivity to values consistent with mid-ocean ridge accretion, it does so at the expense of eliminating the breakup instability. Models that assume an abrupt change in prerift lithospheric thickness suffer from the same deficits. However, including a sublithospheric hot layer leads to a model that can predict the temporal evolution of igneous crustal thickness observed in refraction seismic data from the southeast Greenland volcanic rifted margin.

T. S. Blake, R. Buick, S. J. A. Brown and M. E. Barley.

Precambrian Research, Vol. 133, No. 3-4, 20 Aug 2004, pp. 143-173.

Eleven high precision (+ or -2-5 million years) SHRIMP zircon U-Pb ages have been obtained from felsic rocks within a single stratigraphic section of late Archaean volcanic and sedimentary rocks in the east Pilbara of Western Australia. The stratigraphic succession (Nullagine and Mount Jope Supersequences in sequence-stratigraphic terminology, Fortescue Group in lithostratigraphic terminology) is interpreted to be the rock record of three major geotectonic cycles that formed in an extensional, rift-related environment between about 2772 and 2715 Ma. The geochronology is constrained by a detailed stratigraphic framework based on unconformities and supported by a preliminary magnetostratigraphy. Field mapping, geochemical and petrographic studies have shown that previously unrecognised thin felsic tuff bands are interbedded in subaerial flood basalt piles and mafic tuffs. While flood basalts and proximal felsic volcanic rocks comprise by volume most of the volcanogenic components of the succession, felsic volcanism is now known to have been active periodically through each geotectonic cycle. The succession covers a time period of about 57 million years. The lower approximately 1400 m of a thick ( approximately 1700 m) clastic sedimentary succession from the oldest geotectonic cycle was deposited at a rate of about 100 m per million years over a mean time period of 14 million years. In contrast, a younger approximately 150 m thick cogenetic tuff-basalt unit accumulated in less than 3 million years, and others probably accumulated at similar rates, comparable to those of Phanerozoic flood basalts. Unconformities in the succession are shown to be of variable duration and one unconformity marking the boundary between the first and second geotectonic cycles may represent a time-gap of more than 10 million years. The unconformity-based stratigraphic framework, the new geochronology and palaeomagnetic studies [J. Geophys. Res. 108 (2003) B12, 2551, EMP 2-1 to 2-21] have been combined to determine a possible late Archaean continental drift rate for one part of the succession, implying a period of motion as fast as or up to five times faster than any known from the Phanerozoic.

Eric Buffetaut.

Endeavour, Vol. 27, No. 4, Dec 2003, pp. 171-174.

Contrary to what happened in many other countries in the 1930s and 1940s, Alfred Wegener's theory of continental drift was not generally rejected in Nazi Germany, although several leading German geologists of the time did not accept it. It was actually presented as the modern view of Earth history in books and magazine articles aimed at the general public. Although outlandish geological theories such as Hörbiger's Welteislehre were favoured by some Nazi dignitaries, they were not widely accepted in scientific circles. On the other hand, continental drift received official support under the Third Reich, at a time when it was ignored or ridiculed by most earth scientists outside Germany.

PB Wignall and R. Newton.

Palaios, Vol. 18, No. 2, Apr 2003, pp. 153-167.

Remarkably different Late Permian-Early Triassic marine records are seen in sections from the western deep-water margin of Pangea (Ursula Creek, British Columbia) and the high paleolatitude, southern margin of the Neotethyan Ocean (Selong, South Tibet). The Ursula Creek section reveals the progressive decline of seafloor oxygen values in the Changxingian Stage (loss of bioturbation, authigenic U enrichment, appearance of pyrite framboid populations), followed by the persistent development of euxinic conditions in the latest Changxingian and throughout the Early Triassic; an event that coincides with the disappearance of a siliceous sponge fauna and the loss of diverse radiolarian populations. The Selong section, which was located on a distal passive margin, records regression and erosion in the mid-Changxingian, followed by a phase of deepening that began in the late Changxingian. The boundary interval is associated with a marked diversity increase due to the appearance of equatorial taxa (foraminifera, brachiopods, and sponges), suggesting warming without extinction in marine waters at high southern paleolatitudes. Only in the late Griesbachian Stage are the diverse Permian holdovers eliminated, again at a level showing evidence for dysoxia (thinly-bedded, authigenic U-enriched, pyrite-rich limestone). Thus, the end-Permian mass extinction is seen to be diachronous by half a million years or more, with late Changxingian extinction in Panathalassa coinciding with diversity increase associated the migration of warm-water taxa into the high southerly paleolatitudes regions of Neotethys.

G. Strik, TS Blake, TE Zegers, SH White and CG Langereis.

Journal of Geophysical Research.B.Solid Earth, Vol. 108, No. B12, Dec 2003, pp. .

A late Archaean (circa 2775-2715 Ma) succession of terrestrial continental flood basalts, mafic tuffs, felsic volcanic rocks, and clastic sedimentary rocks in the Nullagine Synclinorium (and Meentheena Centrocline) of the East Pilbara Basin, Western Australia, has been sampled for a palaeomagnetic study. Over 500 oriented, mostly basalt, drill cores were collected from the supracrustal succession and associated dykes. Thermal and alternating field demagnetization revealed two distinct components. Positive fold, conglomerate, and reversal tests confirm that the primary natural remanent magnetization (NRM) is still preserved. The secondary component is interpreted as the record of remagnetization during a major thermal event, possibly in the Early Proterozoic. Analysis of the primary NRM directions results in a magnetostratigraphy and an apparent polar wander path (APWP) for the 60 Myr interval covered by the sampled succession. Assuming a geocentric axial dipole during this time interval, the APWP shows that the Pilbara Craton was drifting during the late Archaean and that drift rates probably varied significantly. In particular, a mean 27.2 degree shift in palaeolatitude is recorded across an unconformity that represents a relatively short time period and that marks a significant change in basalt geochemistry. This study suggests that continents moved horizontally during the late Archaean and that the rates of movement were significantly faster than in the Phanerozoic. In addition, a reversed polarity interval, with a positive reversal test, is recorded. We argue that it documents the oldest known geomagnetic reversals of the geomagnetic field.

Plate Tectonics and Geomagnetic Reversals

Arthur Holmes.

W. H. Freeman Co.; Reprint,

1973

Bryan Isacks, Jack Oliver and Lynn R. Sykes.

Journal of Geophysical Research, Vol. 73, No. 18, 1968, pp. 5855-5899.

A comprehensive study of the observations of seismology provides widely based strong support for the new global tectonics which is founded on the hypotheses of continental drift, sea-floor spreading, transform faults, and underthrusting of the lithosphere at the island arcs. Study of world seismicity shows that most earthquakes are confined to narrow continuous belts that bound large stable areas. In the zones of divergence and strike-slip motion, the activity ismoderate and shallow and consistent with the transform fault hypothesis; in the zones of convergence, activity is normally at shallow depths and includes intermediate and deep shocks that grossly define the present configuration of the down-going slabs of lithosphere.

L. W. Morley and A. Larochelle.

Special Publications - Royal Society of Canada, Vol. 8, 1964, pp. 39-51.

Paleomagnetic evidence for polar wandering allows geologic dating on a coarse time-scale, numerous polarity reversals observed in rocks suggest it may be possible to date their magnetization with an accuracy of the order of one million years, and scatter in magnetization directions observed in penecontemporaneous rocks resulting from secular field variations might permit dating of geological events to about the nearest thousand years. In practice many difficulties, such as incompleteness and inaccuracy of data, are encountered in using any of these approaches. A method for estimating the time span between successive reversals is suggested. Use of scatter in magnetization direction of penecontemporaneous rocks, is not hopeful for rocks older than several thousand years.

F. J. Vine and D. H. Matthews.

Nature (London), Vol. 199, No. 4897, 1963, pp. 947-949.

The pattern of magnetic anomalies observed over oceanic ridges, characteristically consisting of long-period anomalies over the foothills, shorter-period anomalies on the flanks, and a pronounced central anomaly over median valleys, is discussed in the light of current concepts of spreading of ocean floors and periodic reversals in the earth's magnetic field.

Harry Hammond Hess.

Buddington Vol. (Geol. Soc. Am.), 1962

Starting from the premise of an initially waterless, atmosphereless mass and a catastrophic event involving a single-cell convective overturn within the earth shortly after its solidification, which was responsible for segregation of a nickel-iron core, extrusion of the primordial continental sialic material, and development of bilateral asymmetry, formulates a theory of the evolution of ocean basins based on continued multicell convection in the mantle.

2010 Gordon Reseach Conference on Origin of Life, Hotel Galvez, Galveston, TX, 10-15 Jan 2010
Norman Sleep.