||January 29, 2004
GSA Release No. 04-04
February Media Highlights: Geology
Boulder, Colo. - The February issue of GEOLOGY covers a wide variety of subjects and includes several newsworthy items. Topics include: a possible early, short-lived dynamo on Mars; new insights into mechanisms whereby methane hydrates are released from the sea floor; analysis of new magma from early explosive activity as a predictor of volcanic eruptions; and evidence linking continental weathering to regulation of atmospheric CO2. In lieu of a science article, the February issue of GSA TODAY contains GSA's 2003 Presidential Address, "New Technology, New Geological Challenges."
Highlights are provided below. Representatives of the media may obtain complimentary copies of articles by contacting Ann Cairns. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Contact Ann Cairns for additional information or other assistance.
Non-media requests for articles may be directed to GSA Sales and Service.
- Thermal evolution of the Martian core: Implications for an early dynamo
Jean-Pierre Williams, University of California, Los Angeles, Earth and Space Sciences, Los Angeles, CA 90095, U.S.A. and Francis Nimmo, University College London, Geological Sciences, Gower St, London, London WC1E 6BT, U.K. Pages 97-100.
- Mars is thought to have possessed a dynamo that ceased ~500 million years after the formation of the planet. A possible, but ad hoc, explanation for this is an early episode of plate tectonics, which drove convection within the liquid core by rapidly cooling the planet's interior, and thus driving a short-lived dynamo. We present an alternative explanation: that after the Martian core formed, it was initially hotter than the overlying mantle, providing an initial high heat flux out of the core. A core initially 150 K (300 °F) hotter than the mantle can explain the early dynamo without requiring plate tectonics. Our results also suggest that core solidification is unlikely to have occurred, because this process would have generated a long-lived (>1 billion year) dynamo. An initially hot core is consistent with geochemical evidence for rapid core formation and incomplete thermal equilibration with the mantle. Thus, the early history of planetary dynamos provides constraints on the processes of planetary formation.
- Three-dimensional seismic characterization of a venting site reveals compelling indications of natural hydraulic fracturing
Lars Zuehlsdorff and Volkhard Spiess, Bremen University, Geosciences, Klagenfurterstrasse, Bremen 28359, Germany. Pages 101-104.
- The release of large volumes of greenhouse gases as methane from thick sedimentary sequences may affect global climate change, but nature and timing of processes controlling fluid migration and entrapment of hydrocarbons are only partly understood. Models explaining the creation of pathways for focused fluid flow often remain unsatisfactory. Three-dimensional seismic images now provide new evidence that fluids at high pressure may locally crack sedimentary seals and help themselves to escape. This, however, is associated with a short-lived heat pulse and a pressure decrease, which may lead to cycles of gas hydrate decomposition, episodic gas release, and re-formation of hydrate. Our findings relate seismic features with natural hydraulic fracturing, fluid migration, and the formation and subsequent dissociation of methane hydrate. They thus provide some kind of missing link between processes and effects previously implied, and a basis for a consistent integration of different types of interdisciplinary observations. The better understanding of physical processes at this pockmark site may in turn renew the discussion on time scales relevant for geochemical processes, impact studies on the biotic communities at the seafloor, and improve the geological interpretation of gas-rich or hydrate-rich sedimentary sections on both active and passive continental margins worldwide.
- The Warakurna large igneous province: A new Mesoproterozoic large igneous province in west-central Australia
Michael Wingate, University of Western Australia, Tectonics Special Research Centre, 35 Stirling Hwy, Crawley, Western Australia 6009, Australia, et al. Pages 105-108.
- Recent studies of the ages, chemistry, and fossil magnetization of volcanic and plutonic rocks in central and western Australia have revealed a large igneous province (LIP) that was formed ca. 1075 million years ago and which covers at least 1.5 million square kilometers. These rocks, named the Warakurna LIP, probably formed above a plume of hot material that ascended through Earth's mantle beneath central Australia. In addition to providing valuable information on the geological evolution of the Australian continent, recognition of the Warakurna LIP has important implications for mineral potential, including nickel, copper, and other base and precious metals.
- Structural expression of oblique seafloor spreading in the Macquarie Island Ophiolite, Southern Ocean
Jeffrey Karson and Peter Rivizzigno,, Duke University, Division of Earth and Ocean Sciences, 103 Old Chemistry Building, Box 90227, Durham, NC 27708-0230, U.S.A. Pages 125-128.
- Macquarie Island is the only uplifted and exposed fragment of oceanic crust on Earth. Geological structures found on the island were created by seafloor spreading, and thus provide a window into processes beneath mid-ocean ridge spreading centers. The structures are interpreted in terms of faulting, volcanic activity, and hydrothermal metamorphism that occurred during the formation of this unique sample of oceanic crust.
- Magmatic precursors to the May 18, 1980 eruption of Mount St. Helens, USA
Kathy Cashman, University of Oregon, Geological Sciences, 1272 University of Oregon, Eugene, Oregon 97403-1272, U.S.A., and Richard Hoblitt, USGS Hawaiian Volcano Observatory, PO Box 51, Hawaii National Park, HI 96718, U.S.A. Pages 141-144.
- Volcanic eruptions rarely occur without warning. Instead, major eruptions are commonly preceded by weeks to months of activity that includes numerous earthquakes, ground deformation, emission of volcanic gases, and small explosions. In theory, volcanologists should be able to use this precursory activity to say exactly when and how a given volcano will erupt. In practice, it is difficult to infer the composition (and eruptive potential) of magma before it reaches the surface. Here we use detailed studies of ash produced by explosions that preceded the May 18, 1980 eruption of Mount St. Helens, USA, to demonstrate that early explosive activity may emit small amounts of new magma in addition to excavating the upper part of the existing edifice. This juvenile material was not previously recognized because the glass contains numerous small crystals, a consequence of magma ascent to shallow levels. We demonstrate that this textural characteristic results only from rapid transport of magma to shallow levels, and may thus be diagnostic. Application of these results to volcanoes around the world could greatly increase the chances of successful mitigation efforts.
- Valanginian Weissert oceanic anoxic event
Elisabetta Erba, University of Milan, Department of Earth Sciences, Via Mangiagalli 34, Milan, 20133, Italy, et al. Pages 149-152.
- A large change in both climate and ocean chemistry has been discovered in ca. 130 million year old sediments of the northwestern Pacific Ocean basin. Most previous evidence for this event comes from southern and central Europe. This discovery demonstrates for the first time the global and deep-sea nature of this oceanic anoxic event, a time when oxygen was severely attenuated in the oceans. The authors suggest that the global perturbation was caused by the release of huge amounts of carbon dioxide associated with the breakup of the Gondwana supercontinent, and more specifically with the eruption of the Parana-Etendeka flood basalts on the then-joined South American and Africa continents during the Valanginian Stage of the Early Cretaceous. Excess carbon dioxide can cause an acceleration of the global hydrologic cycle and induce oceanic fertilization, which leads to oceanic anoxia, and usually, to an increase in global temperature. However, both oxygen isotopes and oceanic nannofossils indicate a global cooling at the climax of this perturbation. This temperature response is poorly understood, but possibly weathering of basalts exposed on land and burial of organic carbon-rich sediments at sea were responsible for a drawdown of atmospheric carbon dioxide and establishment of reversed greenhouse conditions.
- Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering
Anthony Cohen, Open University, Department of Earth Sciences, Walton Hall, Milton Keynes, Buckinghamshire MK7 6AA, U.K., et al. Pages 157-160.
- New scientific evidence shows how Earth underwent and recovered from a sudden episode of severe global warming at the time of the dinosaurs, ca. 180 million years ago in the Early Jurassic. Global warming took place because large amounts of methane gas were suddenly released from the seabed, causing atmospheric CO2 levels to increase by ~400%. As a consequence of global warming, the climate then became much more vigorous and the weathering and erosion of rocks at Earth's surface increased by 400-800%. But the intense rock weathering involved chemical reactions that consumed the atmosphere's extra CO2 in ~100,000 years, putting an effective brake on global warming and helping climate to return to the status quo.
- Fossil whale preservation implies high diatom accumulation rate in the Miocene/Pliocene Pisco Formation of Peru
Leonard Brand, Loma Linda University, Department of Natural Sciences, Loma Linda, CA 92350, U.S.A., et al. Pages 165-168.
- The Miocene/Pliocene Pisco Formation of coastal Peru contains a large number of fossil whales, many of which are very well preserved with articulated skeletons. Some whales have the baleen (feeding filter in their mouth) still preserved, and evidence that other soft tissues were still present at time of burial. The whales in our study section were buried in sediment composed primarily of microscopic skeletons of diatoms. The calculated rate of accumulation of Pisco Formation sediment is centimeters per thousand years, but this rate cannot apply to the diatomaceous, whale-bearing portion of Pisco Formation. Whales buried that slowly would not have been well preserved. Sediment accumulation rates several orders of magnitude faster probably occurred largely because of frequent diatom blooms, with the diatoms and whale carcasses transported and concentrated in shallow bays by tidal and storm currents.
To review the abstracts for these articles, go to www.gsajournals.org.
To review the complete table of contents for the current issue of GEOLOGY, go to www.gsajournals.org/gsaonline/?request=get-current-toc&issn=0091-7613.
Representatives of the media may obtain a complimentary copy of any GEOLOGY article by contacting Ann Cairns.
Non-pressrelated requests should be made to GSA Sales and Service, 1-888-443-4472.