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Gathering Recognizes Contributions of Former Section President Eos, Vol. 82, No. 46, November 13, 2001 of the major continents. The emerging picture of Iapetan paleogeography resembles, in many SECTION NEWS ways, the complex tectonics of the SW Pacific. The post-collisional history of these terranes was discussed by Mark Smethurst. Mark's new data from the Silurian of Newfoundland GEOMAGNETISM & only one Neoproterozoic glacial deposit has resolve a long-standing dispute about possible yielded convincing evidence for low-latitude inclination errors contributing to erroneous PALEOM AGNETISM deposition, but, perhaps equally significant, no paleogeographic models, where some units convincing polar glacial deposits have been have yielded paleolatitudes that implied documented. One of the major limitations to a oceanic separation between the terranes better understanding of Neoproterozoic paleo­ persisting into the mid-late Silurian. These geography and a possible Snowball Earth, is the new data confirm that the various Paleozoic scarcity of reliable paleomagnetic data from terranes that make up Newfoundland were several of the major continental blocks. Most assembled in the Silurian, but later underwent Editor: John W. Geissman, University of New reconstructions incorporate, to varying degrees, oroclinal bending by vertical axis rotations. Mexico, Albuquerque, NM 87131 USA; assumptions about the fits between various Vertical axis rotations also featured in other Tel: +1-505-277-3433; Fax: +1-505-277-8843 continental blocks, or use proxy paleomagnetic presentations, notably that of John Geissman, Section President, William Lowrie; Section poles transferred from other continental blocks who presented paleomagnetic data from Secretary, Steven C. Constable on the basis of an assumed fit. Permian and Triassic rocks along the eastern As an example, while the assembly of Gond- margin of the Colorado Plateau. These data wana in the latest Precambrian is generally indicate that small degrees of rotation are viewed as a collision between east and west consistent with the regional pattern of defor­ Gathering Recognizes Gondwana, Joe Meert presented an analysis mation along the margins of the plateau since of the paleomagnetic and geochronologic the mid-Cretaceous. John Stamatakos also Contributions of Former constraints on the assembly, which suggests presented new paleomagnetic evidence for Section President that eastern Gondwana was not an entity vertical axis rotations associated with normal prior to overall Gondwana assembly Any use faulting in the Crater Flat basin, in southwest PAGE 557 of paleomagnetic data from one eastern Nevada. This latter study is of particular signif­ Gondwana block to constrain the position of icance, as they indicate geologically recent To celebrate the sixtieth birthday of Rob Van another is therefore invalid for times predat­ deformation within the region, which has derVoo, AGU's President and President-elect ing Gondwana assembly. been proposed as the site of the U.S. high-level of its Geomagnetism and Paleomagnetism The application of Paleomagnetism to regional nuclear waste repository. Section, 1988-1992, a workshop was recently tectonics was exemplified by a number of pre­ For Mesozoic and younger times tests of held in an intimate conference setting in Ann sentations on a topic that is close to Rob's heart: paleomagnetic reconstructions become easier, Arbor, Michigan. The purpose was to celebrate the paleogeography and evolution of the Paleo­ but no less contentious, given that marine Rob's many contributions to the fields of pale­ zoic Iapetus Ocean. Conall Mac Niocaill pre­ magnetic anomalies and hot-spot tracks omagnetism and tectonics as he reached this sented a synthesis, much of which was based on become available for comparison. Dennis milestone. Some 30 people attended and were original data collected by Rob and co-workers, Kent summarized the results of paleomagnetic treated to 18 presentations, many of which have of terrane accretion histories in the Northern and magnetostratigraphic investigations of recently been published or are currently in Appalachians, which indicates that the Iapetus Triassic red-bed sequences, related to the review for a special issue in his honor. While Ocean contained several geographically distinct early stages of extension in the Atlantic, along great emphasis was placed on paleomagnetism but contemporaneous volcanic arc terranes. the eastern seaboard of North America, and as the only quantitative tool for generating paleo- The evolving picture of Paleozoic paleogeogra­ demonstrated that the paleolatitudes obtained geographic reconstructions for pre-Mesozoic phy is reaching a level of refinement at which from the paleomagnetic studies agree with time, a recurring theme within the meeting was the location of individual terranes is more paleoclimate gradients obtained from the integration of paleomagnetic results with often the subject of dispute than the position lithofacies.Thus, the climate zonation of the those from other disciplines—a hallmark of Rob's research efforts at the University of Michi­ gan. The meeting also provided an opportunity for students and colleagues of Rob's to indulge in more "speculative" ideas, and the presentations were accompanied by wide-ranging and "spirited" discussions during both the "formal" sessions and the highly enjoyable evening social activities. The paleogeography of the late-Neoprotero- zoic and early Paleozoic formed the basis of one session. Paul Hoffman presented some of the evidence for a "Snowball Earth," including the evidence from stable isotope analyses and the occurrence of cap carbonates and the temporal distribution of banded iron formations; and postulated that such an extreme climatic scenario was almost inevitable, given the predominantly equatorial distribution of the major Neoproterozoic continents. There are important uncertainties in the Many of the people who attended the workshop; from left: John Stamatakos, John Geissman, paleogeographic reconstructions, emphasised Trond Torsvik, Ben van der Pluijm, Ray Russo, Doug Elmore, Chris Scotese, Conall Mac Niocaill, in the presentations by Trond Torsvik and Chris Joe Meert, Mark Smethurst, Rob Van der Voo, Darning Wang, Dennis Kent, Jurgen Matzka, Mark Scotese, which bear on the claimed equatorial Dekkers, Elizabeth Eide, Paul Hoffman, Arlo Weil, Donna Jurdy Chad McCabe, Kate Hagstrum, paleolatitudes of the glacial deposits. At present, Dave Rowley, and Jon Hagstrum. Eos, Vol. 82, No. 46, November 13, 2001 early Mesozoic was not that different from order of 3.4 km2 per year, and there is no of secondary minerals, and Mark Dekkers the modern-day zonal variation and climatic evidence for major changes in this rate over illustrated a new method of analysing isother­ indicators present a valuable test of plate the past 180 Ma. mal remanence acquisition curves using reconstructions. A final theme of the meeting was the appli­ cumulative log Gaussian analysis. A cautionary There has been much recent debate as to cation of rock magnetism in helping decipher tale of self-reversal in ocean floor basalts was the fixity of hot-spots, and John Tarduno pre­ the complex paleomagnetic signal carried presented by Jurgen Matzka, which indicates sented a comparison of paleomagnetic data by rocks. Doug Elmore provided an overview that great care must be taken in interpreting from Cretaceous seamounts in the Pacific of a number of possible models for remagneti- the paleointensity and directional magnetic with the Mesozoic hot-spot framework. The zation of rocks, with particular emphasis records of these rocks, and again illuminated results indicate a significant degree of motion on the remagnetization of cratonic strata. the role that careful rock magnetic work can of the hot-spots with respect to the paleo­ Despite more than 20 years of research on play in plate reconstructions. magnetic framework, and indicate that a the phenomenon, a single underlying mecha­ substantial component of hot-spot migration nism that can explain all of the observations Authors took place in the Late Cretaceous, in contrast has not been recognized, although there to models that argue for an enhanced compo­ appears to be a temporal correlations between Conall Mac Niocaill, Department of Earth nent of True Polar wander at this time. Inter­ secondary magnetizations and orogenic Sciences, University of Oxford, U.K.; Ben estingly Dave Rowley noted there is no evidence events, even if the rocks themselves have not van der Pluijm, Department of Geological for any concomitant changes in the history been directly involved in deformation. Sciences, University of Michigan, Ann Arbor, of ridge production. Inversion of area-age rela­ A better understanding of remagnetizations USA; and Trond Torsvik,VISTA, c/o Geological tionships yields ridge production rates of the most likely lies in the identification and genesis Survey of Norway Trondheim trade wind fluctuations over the Atlantic, which is the moisture source for Huascaran. BOOK REVIEWS The most valuable climate information is obtained from the multiple records used by E. Cook and colleagues and M. Mann and colleagues, who show that ENSO teleconnec­ to initial conditions than by misspecification tions have not been stationary in the past, El Nino and the of the sea surface temperature (SST) forcing. an important fact for prediction efforts. Southern Oscillation. The next chapter covers non-ENSO modes of The multi-proxy record of M.Mann et al.also SST variability and their impact on climate. shows that the persistent
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