Boulder, CO, USA – GEOLOGY covers a range of topics, including tsunami geomorphology, sag pond deposits, ooids and seawater chemistry, hillslope weathering, volcanoes and the nature of volcanic eruptions, minerals, marine sediments, paleoseismic faults, oxygen isotope records, bolide impact and banded iron formations, trace metal pollution from mining and metallurgy, tidal cycles, and Barchan dunes. The GSA TODAY science article focuses on microbial mats as evidence for early life and the Groundwork article asks key questions about CO2 sequestration.
First in situ observation of crystallization processes in a basaltic-andesitic melt with the moissanite cell
Federica Schiavi et al., Bayerisches Geoinstitut, Universitat Bayreuth, D-95440 Bayreuth, Germany. Pages 963-966.
Shape, size, number, and composition of rock-forming crystals, as well as their mutual relationship in space, vary widely in natural igneous rocks depending on the magma cooling history and the physical and chemical conditions that the magma experiences during ascent toward the Earth's surface. This gives origin to a variety of igneous rock textures. Schiavi et al. show the first real-time optical observation of a crystallizing magma at 900 degrees Celsius, which was achieved with a newly designed moissanite cell. The direct observation of crystal growth mechanisms has enabled Schiavi et al. to investigate their effect on the variation of the number, size, and shape of crystals and on the evolution of the rock texture. The method also allows the direct determination of crystal growth rates. Their results stress the importance of combining information provided by the real-time observation of the sample during the experiment with data obtained from the quantitative analysis of the sample texture in the interpretation of crystallization kinetics.
An Upper Cretaceous sag pond deposit: Implications for recognition of local seismicity and surface rupture along the Kaibab monocline, Utah
E.L. Simpson et al., Dept. of Physical Sciences, Kutztown University of Pennsylvania, Kutztown, Pennsylvania 19530, USA. Pages 967-970.
Sag ponds develop in extensional, down-dropped segments of earthquake-producing faults. In modern systems, such as along the San Andreas fault, sag pond deposits are helpful in chronicling the neotectonic fault histories. However, in ancient consolidated sediments, sag pond deposits are rarely preserved, primarily because of their precarious position in the fault zone. Simpson et al. document sag pond deposits in the Wahweap Formation and reconstruct the Late Cretaceous movement history of a normal fault in Grand Staircase-Escalante National Monument, Utah.
Holocene ooids of Aitutaki Atoll, Cook Islands, South Pacific
Eugene C. Rankey and Stacy Lynn Reeder, Dept. of Geology, 1475 Jayhawk Blvd., 120 Lindley Hall, University of Kansas, Lawrence, Kansas 66045, USA. Pages 971-974.
Ooids are tiny, spherical, calcium carbonate grains with one or more concentric laminations around a nucleus. They have been found in deposits from virtually all geologic periods throughout the world. Besides forming parts of important hydrocarbon and water reservoirs, these grains have provided valuable insights into paleoceanography, oceanic and atmospheric chemistry, and the conditions in which carbonate sediments were deposited. Although ooids occur throughout geologic time and are in great abundance in some areas today, it remained a puzzle as to why they had not been recognized in modern sediments on any atoll in the Pacific Ocean. In this paper, Rankey and Reeder report finding ooids from Aitutaki Atoll of the Cook Islands in the southern Pacific Ocean. The occurrence, distribution, and mineralogy of the ooids on Aitutaki Atoll suggest that their occurrence is more likely under extremely high carbonate supersaturation levels, some of the highest in the Pacific Basin, and under specific hydrodynamic patterns in the lagoon. Rankey and Reeder argue that these findings validate previous inferences of relations between ooids and global changes in seawater chemistry through geologic history.
Climate-driven processes of hillslope weathering
Jean L. Dixon et al., School of Earth and Space Exploration, Arizona State University, 548 Physical Sciences F-wing, Tempe, Arizona 85287, USA. Pages 975-978.
Earth's surface is shaped by chemical and physical processes that erode soil and dissolve rock. Climate likely controls erosion and chemical weathering on soil-mantled landscapes; however, a complete understanding of this relationship remains elusive due to an absence of data that quantifies both the rates of landscape evolution and the mechanisms by which the land surface changes. Dixon et al. explore physical and chemical changes in soils and rock at two sites in the Sierra Nevada of California with different climates. Using cosmogenic nuclide 10Be, and short-lived fallout radio-nuclides 137Cs and 210Pb, they quantify distinct patterns of soil mixing, erosion, and chemical weathering at sites. Furthermore, their data are among the first to quantify the importance of deep bedrock weathering in both expressing the influence of climate and controlling the erosion of overlying soil.
Multiple inflation and deflation events at Kenyan volcanoes, East African Rift
J. Biggs et al., Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Florida 33149, USA. Pages 979-982.
Surface deformation of four active volcanoes captured on Interferometric Synthetic Aperture Radar (InSAR) underscores the possibility for human hazard, and the potential for geothermal resources. The Kenyan volcanoes are part of the Great Rift Valley that extends from Mozambique to Djibouti; their presence in East Africa attests to the existence of magma reservoirs within the Earth's crust. Biggs et al. have detected signs of activity in four of 11 volcanoes in Kenya. Using a decade of satellite radar imagery, they were able to detect small (less than 1 cm) surface displacements at high resolution. From 1997-2000, they discovered that the volcanoes Suswa and Menengai subsided 2-5 cm, and between 2004 and 2006 the Longonot volcano experienced uplift of ~9 cm. However, the most dramatic uplift unfolded at Paka, which had uplift of ~21 cm during a 9 month period in 2006-2007. Overall, the events were short in duration and episodic, similar to a stop valve that is being turned on and off intermittently. The proximity of these volcanoes to a major metropolitan area poses a challenge in terms of a large eruption. Suswa, Menengai, and Longonot volcanoes are located within 100 km of Nairobi. The study also provides insight as to the geothermal potential of the region. Kenya was the first African country to build geothermal plants to generate a renewable, environmentally-friendly form of energy.
Satellite remote sensing of thermal activity at Bezymianny and Kliuchevskoi from 1993 to 1998
Saskia M. van Manen and Jon Dehn, Volcano Dynamics Group, Dept. of Earth and Environmental Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK. Pages 983-986.
Bezymianny and Kliuchevskoi are two of the most dangerous volcanoes on the Kamchatka peninsula because they inject volcanic ash into air traffic routes. van Manen and Dehn have used thermal signals detected by the satellite-based Advanced Very High Resolution Radiometer (AVHRR) to show differences in how these volcanoes operate before and after explosions. Bezymianny showed a thermal signal before every recorded explosion between 1993 and 1998 as well as continued post-explosive activity. Kliuchevskoi showed shorter bursts of thermal activity and exhibited precursors only before the large 1994 explosion. These contrasting characteristics reflect different magma types and eruption styles: Bezymianny's persistent thermal signal and precursory thermal increases are due to the slow ascent of viscous andesitic magma, whereas the more rapid rise, effusion, and cooling of hotter, less viscous, basaltic magmas at Kliuchevskoi gives rise to a discontinuous thermal pattern. These links between satellite data and volcanic processes are important for monitoring and the continued development of early warning techniques.
Lawsonite Lu-Hf geochronology: A new geochronometer for subduction zone processes
Sean R. Mulcahy et al., Dept. of Geoscience, University of Nevada-Las Vegas, Las Vegas, Nevada 89154-4010, USA. Pages 987-990.
Lawsonite is a critical index mineral for high- to ultrahigh-pressure metamorphism associated with subduction, where one lithospheric plate descends beneath another. Lawsonite is an important carrier of water into the mantle, a likely contributor to subduction zone seismicity, and a bearer of trace elements that link metamorphism to arc magmatism. Lawsonite-bearing rocks commonly lack other minerals suitable for radiometric dating, such as garnet, and methods appropriate for dating subduction zone metamorphism have been limited to 40Ar/39Ar geochronology. Dating subduction zone metamorphism by 40Ar/39Ar, however, can be difficult due to the fine grain sizes of low-temperature assemblages, potassium rich inclusions in subduction zone minerals such as glaucophane, and the complex thermal history of subduction-accretion complexes. Mulcahy et al. present a new method of lawsonite geochronology using the Lu-Hf isotope system and multi collector inductively coupled plasma-mass spectrometry. As a demonstration of the method, they have determined a lawsonite Lu-Hf age of 145.5 plus or minus 2.4 Ma for lawsonite blueschist from the Franciscan Complex, California, the type locality of lawsonite. The new method provides a powerful tool to investigate processes and time scales of subduction metamorphism, crust-mantle recycling via subduction, and the geodynamics of convergent margins.
Deposits of flows transitional between turbidity current and debris flow
Esther J. Sumner et al., Dept. of Earth Sciences, University of Bristol, Queen's Road, BS8 1RJ, UK. Pages 991-994.
The relationship between submarine sediment gravity flows and the character of their deposits is poorly understood. Annular flume experiments by Sumner et al. were used to investigate the depositional dynamics and deposits of waning sediment-laden flows. Decelerating fast (greater than 3 m/s) flows with fixed sand content (10 vol. percent) and variable mud content (0-17 vol. percent) resulted in only four deposit types. Clean sand with a mud cap that resembled turbidity current deposit (turbidite) formed if the flow was turbulent when deposition began, or if the muddy fluid had insufficient strength to suspend the sand. The clean sand could contain structures if mud content was low (less than 6%) and the deceleration period was greater than 300 seconds. Ungraded muddy sand with a mud cap that resembled debris flow deposit (debrite) formed if the flow became laminar before sand could deposit. Clean sand overlain by ungraded muddy sand and a mud cap formed either from a transitional flow or by late-stage settling of sand from a muddy suspension. These deposits resemble enigmatic submarine flow deposits called linked debrite-turbidites. The experiments provide a basis for inferring flow type from deposit character for submarine sediment-laden flows.
Tsunami geomorphology: Erosion and deposition from the 15 November 2006 Kuril Island tsunami
Breanyn T. MacInnes et al., Dept. of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA. Pages 995-998.
Understanding how tsunamis alter natural systems is an important component of protecting coastal communities and saving human lives. Quantifying changes caused by tsunamis has been elusive because measurements of a coastline before a tsunami strikes are made by chance. On 15 November 2006, a tsunami hit the remote Kuril Islands in the Russian Far East - the same tsunami caused $9 million damage in Crescent City, California. The tsunami struck the Kuril Islands between field seasons of the Kuril Biocomplexity Project, a National Science Foundation-sponsored study of the interaction of past humans and their environment. Geologists had collected extensive observations and measurements of Kuril coastlines before the tsunami, and returned afterward to survey dramatic tsunami-induced changes up to 20 meters (65 feet) in elevation. In a study by MacInnes et al., before-and-after data show that processes such as stripping beaches and scouring hillsides removed much more sediment from the coastline than was deposited onshore. This study illustrates that steep topography can significantly enhance tsunami erosion and that tsunamis can be an important factor in shaping coastlines.
Direct calculation of rupture depth for an exhumed paleoseismogenic fault from mylonitic pseudotachylyte
D.P. Moecher and M.G. Steltenpohl, Dept. of Earth and Environmental Sciences, University of Kentucky, Lexington, Kentucky 40506, USA. Pages 999-1002.
Earthquakes commonly form as a result of slip on an existing fault when stresses acting across the fault exceed the frictional resistance to slip. Most such earthquakes (the San Andreas fault earthquakes are the classic example) occur at relatively shallow crustal depths (3-15 km below Earth's surface) where the temperature is low enough (300-400 degrees Celsius) that the crust behaves in a brittle manner and deforms by fracturing. However, some earthquakes apparently form in the deepest crust (30-40 km depth) where the temperature should be high enough (more than 500 degrees Celsius) that the rocks behave plastically and flow (like silly putty) under stress rather than fracturing. Eroded analogs of fault zones exhibiting the behavior of the shallow crust are common. However, eroded fault zones that expose ancient faults in the deepest crust are rare. Moecher and Steltenpohl document an example of an exhumed deep crustal fault, provide evidence for precise determination of the depth for earthquake rupture, and explore potential mechanisms for how deep crustal coseismic rupture occurs.
The combined effect of sea level and supply during Milankovitch cyclicity: Evidence from shallow-marine delta-18O records and sequence architecture (Adriatic margin)
D. Ridente et al., Istituto di Geologia Ambientale e Geoingegneria (IGAG-CNR), c/o Dipartimento di Scienze della Terra, Universita Sapienza, Piazzale Moro 5, 00185 Rome, Italy. Pages 1003-1006.
The impact of climate changes on Earth's life and landscape has been intensely studied in the last 50 years. Because marine sediments represent natural archives of the physical and chemical response to significant climate change, marine geology has gained increasing importance in the study of climate. Marine sediments provide a broad spectrum of evidence for unraveling climate cycles. Some evidence envisages the impact of physical changes in the environment (i.e. shoreline retreat and advance), whereas other provides indications about the timing and mechanism of climate change (i.e., frequency and duration of cyclicity and its relation with astronomical causes). Unfortunately, key information is rarely displayed completely by one unique archive: environmental effects are best recorded by shallow continental shelf sedimentation, whereas chronological information is more likely preserved in the deep oceans. Unraveling climate dynamics and climate-driven depositional cycles thus largely relies on indirect comparison of datasets from different areas. Exceptionally, the Adriatic basin has revealed an ideal place where both types of archives can be exploited and directly compared in order to constrain the timing of climate cycles and unravel the interplay of climate-driven factors (sea level, paleogeography, sediment flux, and dispersal) governing the stratigraphic architecture of shelf and slope deposits. These results by Ridente et al. represent unprecedented documentation of how climate-driven cycles may control continental margin construction, and provide useful insights for interpreting and modeling the stratigraphy of Quaternary continental margins.
Timing and structure of the 8.2 kyr B.P. event inferred from delta-18O records of stalagmites from China, Oman, and Brazil
Hai Cheng et al., Dept. of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA. Pages 1007-1010.
In a study by Cheng et al., oxygen isotope records of stalagmites from China and Oman reveal a weak summer monsoon event that started at 8.2 kyr B.P. with a double-plunging structure. An identical but anti-phased pattern is also evident in two stalagmite records from eastern Brazil, indicating the South American Summer Monsoon was intensified during the 8.2 kyr B.P. event. These records demonstrate that the 8.2 kyr B.P. event is of global extent and synchronous within dating errors of less than 50 years. In comparison with recent model simulations, it is plausible that the 8.2 kyr B.P. event can be tied to changes of the Atlantic Meridional Overturning Circulation triggered by a glacial lake draining event. This, in turn, affects North Atlantic climate and latitudinal position of the Intertropical Convergence Zone, which results in the observed low-latitude monsoonal precipitation patterns.
Extraterrestrial demise of banded iron formations 1.85 billion years ago
John F. Slack and William F. Cannon, U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192, USA. Pages 1011-1014.
Banded iron formations are economically valuable because they constitute the major source of iron used in the manufacture of steel. In the Lake Superior region, deposition of most banded iron formations ended abruptly 1.85 billion years ago, coincident with the oceanic impact of a giant extraterrestrial bolide (meteorite or comet) at Sudbury, Ontario. Estimates suggest that this bolide was 10 to 15 kilometers in diameter, making it one of the largest extraterrestrial bolides known to have struck Earth. The Sudbury bolide probably was approximately the same size as the giant meteorite that hit the Yucatan Peninsula of Mexico 65 million years ago, which produced major environmental changes globally, including the likely demise of the dinosaurs. Based on evidence from the Lake Superior region, a new model by Slack and Cannon is proposed in which the impact of the Sudbury bolide produced a fundamental change in the oxygen content of the oceans worldwide. This impact globally mixed shallow oxygenated and deep anoxic waters of the Precambrian ocean, creating a new suboxic state for deep seawater. This suboxic state, containing only small amounts of dissolved oxygen, prevented transport of iron from the deep ocean to continental-margin settings, ending an about 1.1 billion-year-long period of banded iron formation deposition.
The stable isotope altimeter: Do Quaternary pedogenic carbonates predict modern elevations?
Gregory D. Hoke et al., Dept. or Earth and Environmental Sciences, 227 Hutchinson Hall, University of Rochester, Rochester, New York 14627, USA. Pages 1015-1018.
Stable isotope paleoaltimetry is a relatively new method generally relying on carbonate material preserved in ancient soil horizons, or paleosols, to provide quantitative estimates of range elevation. This method has been applied several times in late Cenozoic settings, but never in a modern mountain setting. Hoke et al., use Quaternary deposits to test the quality of soil carbonate accumulations in recording information about the elevation at which they form. This study presents isotopic data from water and carbonate samples of two catchments that drain the high Andes at 33 degrees south latitude. River water samples from small catchments provide an estimate of the rate at which water vapor loses the heavier isotope of oxygen as clouds are lifted over a topographic barrier. The isotopic gradient on both sides of the range is surprisingly similar. Soil carbonate precipitates from soil water, which, isotopically, should reflect rainfall. After estimating the isotopic composition of the soil water based on average annual temperatures, Hoke et al. find that soil carbonates are good recorders of information about elevation. Their analysis shows that uncertainties in the method are on the order of plus or minus 700 m.
Lake-sediment geochemistry reveals 1400 years of evolving extractive metallurgy at Cerro de Pasco, Peruvian Andes
Colin A. Cooke et al., Dept. of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada. Pages 1019-1022.
Lake sediments from the Peruvian Andes reveal 1400 years of trace-metal pollution resulting from mining and metallurgy at Cerro de Pasco. Cerro de Pasco was once the most intensively exploited silver deposit in the world. While Spanish exploitation of the mine began in A.D. 1600, virtually nothing was known of any Incan or pre-Incan mining activities at the site. Using a radiocarbon-dated archive of atmospheric pollution preserved in nearby lake sediments, Cooke et al. reconstructed the history of mining at the mine. The study reveals smelting of silver-bearing ores began a full millennia prior to the Spanish, around A.D. 600. This early mining relied on smelting to extract silver, and the result was significant metal pollution, primarily lead, to the surrounding environment. The Spanish introduced mercury amalgamation at the mine in A.D. 1600, and while amalgamation greatly boosted silver production, it also generated widespread atmospheric mercury emissions. Spanish mercury pollution from the amalgamation process has been hypothesized for years, but never proven conclusively. This study by Cooke et al. represents the first evidence for mercury pollution from amalgamation, and generates a historical timeline of metal extraction from one of the world's most important silver deposits.
Strain localization in vesicular magma: Implications for rheology and fragmentation
Heather M. N. Wright and Roberto F. Weinberg, School of Geosciences, Building 28, Monash University, Clayton, VIC 3800, Australia. Pages 1023-1026.
Highly destructive explosive volcanic eruptions result from the fragmentation of molten rock and magma. The mechanism of magma break-up/fragmentation is not well understood due to the variable phases that can be present in magma, including melt, crystals, and bubbles; and due to the complex dynamics of magma ascent before and during explosions. We know, however, that magma can fragment when flowing very fast, because at these high rates it behaves like a solid glass instead of a liquid. Preserved bubble textures in pumice fragments from explosive eruptions contain narrow trails of strongly stretched, small bubbles that separate patches of numerous round, unstretched, large bubbles. This suggests that when the magma starts to move, most of the flow takes place in the narrow bands, whereas little or no flow takes place in the unstretched areas. In this way, high-velocity streams form within the magma. These bands affect not only how the magma flows but also how and when fragmentation takes place. Wright and Weinberg argue that fragmentation takes place more readily because faster, localized flow leads to glass-like behavior and cracking in the bands, as opposed to slower flow of the entire magma body. These results affect the dynamics and timing of explosive eruption models.
Cellular energy conservation and the rate of microbial sulfate reduction
Qusheng Jin and Craig M. Bethke, Dept. of Earth and Planetary Science, University of California-Berkeley, Berkeley, California 94720, USA. Pages 1027-1030.
In a study by Jin et al., microbial sulfate reduction is subject to a thermodynamic limit arising from the need of microorganisms to save energy for maintenance and growth, and this limit prevents the process from proceeding until the supply of electron donor or sulfate has been consumed, as would be expected from commonly applied kinetic theory. In pure culture experiments, acetotrophic sulfate reduction stops when the energy liberated by the reaction falls to 33 to 43 kilojoule per mole (kJ/m) sulfate, and an overlapping range of 40 to 56 kJ/m sulfate is observed where sulfate reduction has ceased in experiments with microbial consortia, as well as in lacustrine, marine, and aquifer sediments. These observations correspond to a minimum energy requirement of 33 to 47 kJ/m sulfate calculated on the basis of the cellular physiology of sulfate reducers. In sediments underlying Lake Washington, USA, variation of pore water chemistry with depth can be explained by a reactive transport model accounting for cellular energy conservation, whereas the model evaluated neglecting thermodynamics predicts an unrealistic pattern. Energy availability thus constitutes a primary control on the distribution and rate of microbial sulfate reduction in nature, helping resolve apparent contradictions observed in the laboratory and natural environment.
Impacts of late Holocene rapid climate changes as recorded in a macrotidal coastal setting (Mont-Saint-Michel Bay, France)
I. Billeaud et al., Morphodynamique Continentale et Cotiere, Universite de Caen, UMR CNRS 6143, 24 rue des Tilleuls, 14000 Caen, France. Pages 1031-1034.
Modeling the impacts of climate changes on coastal settings is a challenging objective of numerous research projects. The study of past changes and of their record in sediment successions is one key for unraveling the impacts and their recurrence time scale. Such an approach is common in deep-sea or lacustrine successions but still remains rare in high-energy coastal settings. The sediment infilling of the Mont-Saint-Michel Bay (northwest France), worldwide known for its very high tidal range (15 m), was studied using very high-resolution seismic and core data. It is demonstrated that during the past 6000 years, 1500-year periodicity climate changes are recorded in the sedimentary successions that constitute the infill. Sedimentary expressions of these climate changes vary according to the different sub-environments within the bay, and cycles, a few meters-thick, can be correlated throughout the coastal wedge. The various changes reflect an increase in wave dynamics. Radiocarbon dating suggests that these cycles have a millennial time scale, and the wave climate deterioration they record matches the time of the North Atlantic climate fluctuations known as the Bond cold events. In conjunction with these climate changes, long-term (1800-year periodicity) tidal cycles possibly play a significant role in such macrotidal setting.
Timing and magnitude of recent accelerated sea-level rise (North Carolina, United States)
Andrew C. Kemp et al., Sea-Level Research Laboratory, Dept. of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. Pages 1035-1038.
Kemp et al. have shown that sea-level rise, at least in North Carolina, is accelerating. They found 20th-century sea-level rise to be three times higher than the rate of sea-level rise over the past 500 years. The onset of this acceleration occurred between the years A.D. 1879 and 1915, a time of industrial progress that may provide a direct link to human-induced climate change. The rate of relative sea-level rise, or RSLR, during the 20th century was 3.0 to 3.3 mm per year, a full 2 mm higher than the usual rate of 1 mm per year. Furthermore, the timing of the acceleration appears to be consistent with other studies from the Atlantic coast, though the magnitude of the acceleration in North Carolina is larger than at sites further north along the U.S. and Canadian Atlantic coast, and may be indicative of a latitudinal trend related to the melting of the Greenland Ice Sheet. Understanding the timing and magnitude of this acceleration in the rate of RSLR is critical for testing models of global climate change and providing a context for 21st century predictions.
Barchan dunes stabilized under recent climate warming on the northern Great Plains
Stephen A. Wolfe and Christopher H. Hugenholtz, Geological Survey of Canada, Natural Resources Canada, 601 Booth St., Ottawa, Ontario K1A 0E8, Canada. Pages 1039-1042.
Drought is a recurrent hazard on the Great Plains of the United States and Canada, and a study by Wolfe and Hugenholtz reveals that the driest parts of the Canadian prairies experienced desert-like conditions just prior to agricultural settlement. In the Great Sand Hills of southern Saskatchewan, a region used extensively for cattle rangeland today, desert-like "barchan" dunes migrated across sandy, bare inter-dune areas and dry lake basins in the mid-to-late 1700s. Wolfe and Hugenholtz used Light Detection and Radar (LiDAR) to provide an enhanced topographic view of the sand hills, and optical stimulation luminescence (OSL) dating to determine the last time that the sand grains were exposed to sunlight, in order to reconstruct how and when the landscape had changed. Barchan dunes were transformed into vegetation-stabilized parabolic dunes in the early 1800s with increasing moisture availability. Paleo-climatic records from this area suggest that cooler but drier conditions permitted barchan dunes to prevail, and that a warmer, but less arid climate in the last two centuries caused dune transformation and stabilization.
Diverse aqueous environments on ancient Mars revealed in the southern highlands
James J. Wray et al., Dept. of Astronomy, Cornell University, Ithaca, New York 14853, USA. Pages 1043-1046.
In a study by Wray et al., data from NASA's Mars Reconnaissance Orbiter reveal new mineralogic signatures of widespread water during the first billion years of Martian history. The vast southern highlands of Mars are one of the oldest areas of the planet's surface, but few exposures of water-bearing minerals had previously been reported in this region. Higher-resolution mapping now reveals many such exposures, with varying mineralogy and diverse geologic settings, suggesting a range of water chemistries and temperatures. This diversity indicates that numerous distinct and possibly habitable environments may have been present on ancient Mars. These would have provided a range of opportunities for the origin of life on Mars, at approximately the same time that life first appeared on Earth. To fully characterize the habitability of ancient Mars and determine if life ever did evolve, each of these distinct ancient environments should eventually be explored in more detail by a future mission to the planet's surface.
A possible link between the geomagnetic field and catastrophic climate at the Paleocene-Eocene thermal maximum
Youn Soo Lee and Kazuto Kodama, Geological Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, Korea. Pages 1047-1050.
Is it possible that a cataclysmic climate-change event links to the Earth's magnetism? What proxy (precession, obliquity, and eccentricity) is the intrinsic energy source of geomagnetism immediately after the catastrophic event? These are fundamental problems for the understanding of geomagnetism. In a study by Lee and Kodama, the clues are partially provided by detailed paleomagnetic data from the Paleocene-Eocene thermal maximum (PETM, a catastrophic global warming event initiated at 55.0 Ma) section. This Paleocene-Eocene magnetic reversal is confirmed by both an antipodal shift in direction and a major reduction in magnetic intensity during the lower and upper transitions, and is seen at additional sites, indicating that it was primarily acquired by Earth's magnetic field during PETM.
Magnetostratigraphic data on Neogene growth folding in the foreland basin of the southern Tianshan Mountains
Jimin Sun et al., Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P. O. Box 9825, Beijing 100029, China. Pages 1051-1054.
The Tianshan Range is the longest and highest mountain belt of central Asia, stretching east-west for about 2500 km with the highest elevation being more than 7000 m. By now, there have been many different opinions about the timing of uplift of the Tianshan Range. Here, Sun et al. report 3780-m-thick deposits in the piedmont basin of the mountains. Based on detailed geometry studies of the deformed strata and high-resolution age chronology, their new results offer a unique window into the late Cenozoic tectonic deformation of the Tianshan Range. Their new evidence indicates that the tectonic deformation at 6.5 million years ago is one of the significant tectonic events in the foreland basin of the southern Tianshan Range in response to the Cenozoic India-Eurasia collision.
GSA TODAY
Science article
Geobiology: Evidence for early life on Earth and the search for life on other planets
Sherry L. Cady, Portland State University, Dept. of Geology, 1721 SW Broadway, 17 Cramer Hall, Portland, Oregon, USA; and Nora Noffke.
Deciphering biosignatures and evidence of microbial activity in rocks that have experienced up to 3.8 billion years of burial and multiple tectonic-altering processes remains a challenge. Here, authors Sherry Cady and Nora Noffke explore our ability to recognize and identify evidence of ancient life, even when such life is long extinct. Geobiologists use four types of evidence to recognize ancient life forms: (1) bona fide cellular fossils; (2) carbonaceous remnants of microbial cells and their extracellular matrices; (3) microbially influenced sedimentary structures; and (4) chemical fossils (i.e., organic compounds and inorganic phases). A variety of new analytical techniques is available to investigate these remnants of ancient life, including raman spectroscopy, multiple-sulfur isotopic signatures that indicate miocrobial sulfate reduction, and synchrotron-radiation-X-ray-tomographic microscopy of ~700 million-year-old tiny chert nodules, which reveal metazoans, cyanobacteria, multicellular algae, spiny acritarchs, and animal eggs and embryos. Especially tantalizing is the possibility that these studies hold for understanding the origin of life on Earth and the possibility of life in outer space. A wide variety of environmental settings likely supported a diverse range of anaerobic and extremophilic life on early Earth; this in turn suggests the possibility of life forms in extraterrestrial settings. That Mars samples may be returned to Earth in our lifetime provides an impetus to identify and characterize a wide range of biosignatures, even if they are present in minute amounts and altered from their pristine state.
GSA TODAY
Groundwork article
Facing the main challenges in Carbon Capture and Sequestration
Roel Snieder and Terry Young, Colorado School of Mines, Dept. of Geophysics, Golden CO 80401-1887, USA
Capturing CO2 and injecting it into the subsurface is often seen as the main tool to prevent man-made global warming. Professors Snieder and Young from the Colorado School of Mines point out that the following questions must be answered before this process can be used on a scale that actually makes a difference in preventing climate change: (1) How can the cost of this process be reduced from the projected $150 billion per year? (2) How can the capture and injection be up-scaled with a factor 1,000 beyond current capabilities? (3) How can we predict and monitor leakage? They also point out that many alternative steps are likely to be much cheaper and save energy as well.
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Geology