Boulder, Colo., USA - In the late 13th century, Kublai Khan, ruler of the Mongol Empire, launched one of the world's largest armada of its time in an attempt to conquer Japan. Early narratives describe the decimation and dispersal of these fleets by the "Kamikaze" of CE 1274 and CE 1281 -- a pair of intense typhoons divinely sent to protect Japan from invasion.
These historical accounts are prone to exaggeration, and significant questions remain regarding the occurrence and true intensity of these legendary typhoons. For independent insight, we provide a new 2,000 year sedimentary reconstruction of typhoon overwash from a coastal lake near the location of the Mongol invasions. Two prominent storm deposits date to the timing of the Kamikaze typhoons and support them being of significant intensity.
Our new storm reconstruction also indicates that events of this nature were more frequent in the region during the timing of the Mongol invasions. Results support the paired Kamikaze typhoons in having played an important role in preventing the early conquest of Japan by Mongol fleets. In doing so, the events may provide one of the earliest historical cases for the shaping of a major geopolitical boundary by an increased probability of extreme weather due to changing atmospheric and oceanic conditions.
Depositional evidence for the Kamikaze typhoons and links to changes in typhoon climatology
J.D. Woodruff et al., Dept. of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA. Published online ahead of print on 4 Dec. 2014; http://dx.
Other recently posted GEOLOGY articles (see below) cover such topics as
1. Possible asbestos hazard in Mohave County, Arizona, USA;
2. Crust patterns in the Makgadikgadi Salt Pans, Botswana; and
3. The in-vitro "growth" of gold grains.
GEOLOGY articles published online ahead of print can be accessed online at http://geology.
Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in any articles published. Contact Kea Giles for additional information or assistance.
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Genesis and health risk implications of an unusual occurrence of fibrous NaFe3+-amphibole
Rodney V. Metcalf and Brenda J. Buck, Dept. of Geoscience, University of Nevada-Las Vegas, Las Vegas, Nevada 89154-4010, USA. Published online ahead of print on 4 Dec. 2014; http://dx.
As source of naturally occurring asbestos has been discovered associated with the 13.7-million-year-old Wilson Ridge pluton in Mohave County, Arizona, USA. The naturally occurring asbestos minerals are fibrous NaFe3+-amphibole, principally winchite and magnesioriebeckite, that are similar to those found to cause death and disease in Libby, Montana, USA. Potential human exposure pathways are from both natural wind erosion and anthropogenic disturbances that release fibers from soil into the air. These processes are enhanced by the arid climate of the region. Fibrous NaFe3+-amphibole sources include public lands with popular hiking and off-road vehicle trails that are in close proximity to population centers in the greater Las Vegas metropolitan area in southern Nevada. Because naturally occurring asbestos is often disseminated through geologic materials and may not be readily apparent in outcrop, an understanding of the geologic settings where naturally occurring asbestos may occur is critical to mitigating human health risk. The geologic setting and mechanism of formation of the NaFe3+-amphibole at Wilson Ridge is unusual and would not be predicted by current genetic models. This work suggests that fibrous NaFe3+-amphibole may be present in areas not previously considered at risk for naturally occurring asbestos.
The Li isotope response to mountain uplift
Philip A.E. Pogge von Strandmann, Institute of Earth and Planetary Sciences, University College London and Birkbeck College, University of London, Gower Street, London WC1E 6BT, UK; and Gideon M. Henderson, Dept. of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK. Published online ahead of print on 4 Dec. 2014; http://dx.
Chemical weathering of silicate rocks on the continents is the main natural removal mechanism of atmospheric CO2. It has been proposed that the uplift of the Himalayas over the past 40 million years increased weathering, removed CO2, and therefore caused the long-term decline in global temperatures that resulted in the presence of polar ice at the present. We have tested the relationship between mountain uplift and weathering, using South Island, New Zealand, as an example. We find that higher uplift promotes greater dissolution of rock, while areas of lower uplift, such as floodplains, promote clay formation. The formation of clays will inhibit the efficiency of CO2 withdrawal by storing cations in clays and soils. Hence, while the uplift of mountain belts likely enhances weathering and therefore CO2 removal from the atmosphere, the floodplains that form as a result decrease the efficiency of CO2 sequestration. Comparisons with records of weathering through time now suggest that rather than the Himalaya uplift directly influencing cooling, it was the floodplains that formed from the Himalayas that strongly changed climate and ocean chemistry over the past 40 million years.
The dynamism of salt crust patterns on playas
Joanna M. Nield et al., Geography and Environment, University of Southampton, Southampton SO171BJ, UK. Published online ahead of print on 4 Dec. 2014; http://dx.
Playas (also known as dry lakes or salt pans) are commonly found in deserts and produce dust that can be transported by wind into the atmosphere and alter global climate conditions. However, crusts typically form on the surface of these "dry lakes," which reduce dust emission and evaporation rates, and until now we knew very little about the rate at which the crust changed its shape. This study of the Makgadikgadi Salt Pans in Botswana (a significant Southern Hemisphere dust source) is the first to measure crust patterns over weeks, months, and a year with millimeter accuracy. Typically after flooding, a new crust will be flat and continuous. Over time the crust becomes rough with polygonal ridges which eventually degrade forming a flatter dust rich surface. We find that the shapes of these surfaces change considerably (greater than 30 mm/week) and as patterns develop they can change measured aerodynamic roughness of the surface by as much as 3 mm/week. Aerodynamic roughness is important as this can change the wind speed at which the surface produces dust. The dynamic nature of these crusted surfaces must be accounted for in dust entrainment and moisture balance formulae to improve regional and global climate models.
Layered intrusions and traffic jams
Paul D. Bons et al., Mineralogy and Geodynamics, Dept. of Geosciences, Eberhard Karls University Tübingen, Wilhelmstrasse 56, 72074 Tübingen, Germany, http:/dx.doi/org/10.1130/G36276.1.
Layered intrusions are igneous bodies with a rhythmic variation in mineral composition. The origin of this remarkable layering has been debated for decades. We propose that the layering forms the same way as traffic jams on motor ways when traffic gets dense: simultaneously sinking and floating crystals impede each other's movement, leading to "traffic jams" in the cooling magma chamber. The traffic jams of crystals form barriers that crystals formed later have difficulty to pass, which leads to the formation of layers throughout the whole magma chamber as it slowly cools. The process of layer formation by traffic jams was simulated in a numerical model, which made it possible to constrain the conditions where layering can form. If the melt is too liquid and the magma chamber cools too slowly, crystals all manage to sink to the bottom or float to the top of the chamber, and crystal traffic is never dense enough to form traffic jams. This was the case when the moon solidified and buoyant plagioclase crystals could all float to the surface to form the lunar crust.
Flood-flipped boulders: In-situ cosmogenic nuclide modeling of flood deposits in the monsoon tropics of Australia
Toshiyuki Fujioka et al., Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia. Published online ahead of print on 4 Dec. 2014; http://dx.
Records of extreme climatic events (such as cyclones, floods) are generally limited to the last several thousand years, preventing our ability to correlate changes in paleo-hydrology with different climate states. In this paper, in situ cosmogenic nuclides are utilized to date meter-sized, massive flood-generated sandstone boulders in the Durack River, the Kimberley, northern Australia. A simple numerical model has been established to constrain the timing of the boulder's detachment from bedrock channel floor and overturning. The first application of the model successfully determined the early to mid-Holocene flood events (6000 to 10,000 years) as well as ages potentially dating back to the penultimate glacial ages ~250,000 years. Similar early to mid-Holocene major floods have been recorded in other parts of northern Australia, suggesting that such extreme events may have been widespread in the region during the late Quaternary. The present method has potential to extend the study of paleo-flood records to the past two glacial cycles, providing the opportunity to improve our predictions of extreme event frequency in the face of global warming. The model is also applicable to other deposits by extreme events such as paleo-tsunamis.
Fault geometry and permeability contrast control vent temperatures at the Logatchev 1 hydrothermal field, Mid-Atlantic Ridge
Christine Andersen et al., GEOMAR, Helmholtz Centre for Ocean Research, Wischhofstrasse 1-3, 24148 Kiel, Germany. Published online ahead of print on 4 Dec. 2014; http://dx.
Hydrothermal hot springs at slow-spreading mid-ocean ridges that typically are tectonically dominated are apparently consistently linked to fractures and faults in the oceanic crust. While it seems intuitive that hot fluids use faults as preferential pathway, such efficient flow inevitably leads to extensive mixing with cold seawater. This temperature drop is difficult to reconcile with observed high-temperature black smoker activity and formation of associated massive sulfide ore deposits. In our study we have combined newly acquired micro earthquake data from the fault controlled, high-temperature Logatchev 1 hydrothermal field at the Mid-Atlantic Ridge with numerical modeling of hydrothermal flow to solve this apparent contradiction. In our simulations we find that high temperatures in fluids exiting at fault zones at the seafloor can only be reached when a fault zone is not too wide and not too permeable. Permeability and width must be sufficient to redirect hydrothermal fluids into the fault but low enough to prevent the entrainment of cold ambient seawater.
Goethite as a potential source of magnetic nanoparticles in sediments
J.L. Till et al., Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités-UMPC, CNRS UMR 7590, Muséum National d'Histoire Naturelle, IRD UMR 206, 4 Place Jussieu, F-75005 Paris, France; and Institut de Physique du Globe de Paris (IPGP), Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, 75005 Paris, France. Published online ahead of print on 4 Dec. 2014; http://dx.
The oxyhydroxide mineral goethite is an Fe-rich phase commonly found in soils, dust, and sediments. Through a series of laboratory experiments, Till et al. show that the nanocrystalline form of this weakly magnetic mineral rapidly transforms to produce nanoparticles of the highly magnetic Fe-oxide mineral magnetite under reducing conditions via a dehydration and reduction reaction chain. Such reactions may be responsible for the significant increases in soil magnetic properties observed to occur after wildfires. The study also discovered that this alteration reaction can take place at relatively low temperatures, raising the possibility of dramatic changes in rock magnetic properties for goethite-bearing sediments during diagenesis and metamorphosis. The findings suggest that goethite is likely an overlooked source of magnetic nanoparticles in the environment and raises new questions about Fe-cycling and redox reactions in sedimentary systems.
The in-vitro "growth" of gold grains
Jeremiah Shuster and Gordon Southam, School of Earth Sciences, University of Queensland, St. Lucia, Queensland 4072, Australia. Published online ahead of print on 4 Dec. 2014; http://dx.
Gold cycling under near-surface conditions involve primary gold source weathering, secondary gold mineralization and aggregation. Shuster and Southam demonstrate that regeneration of the biosphere, the circle of life, has a profound influence on the biogeochemical cycling of gold. Natural microbiological processes promoting the formation of secondary gold particles were originally hypothesized over 80 years ago. These processes are now known to contribute to the formation of colloids, octahedral platelets, bacteriomorphic structures and foils from soluble gold complexes. Using a simplified laboratory model of a placer environment, sedimentation and physical compaction enhanced the aggregation of secondary gold particles that ultimately led to the formation of grains. These grains possessed smooth surface textures that were characteristic of natural gold grains and delicate nanometer- to micrometer-size secondary gold structures produced by bacteria. By dissolving and precipitating gold, these microorganisms were critical in gold grain formation and could help explain the formation of nuggets -- a structure 1,000,000 times larger than the original colloidal gold!
Lithologic control on the form of soil-mantled hillslopes
Samuel A. Johnstone and George E. Hilley, Dept. of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA. Published online ahead of print on 4 Dec. 2014; http://dx.
For more than a century, scientists have studied soil transport and how these processes shape hillslopes that are covered by soil. Knowledge of soil transport is used to make predictions of landscape change, helping us assess the rates at which landscapes are being uplifted by tectonic activity and the timing of features associated with ancient earthquakes, among other things. On hillslopes covered by soil, we can't see rocks at the surface but we might expect rocks of differing strength to impact the evolution of hillslopes. However, most predictions for rates of soil transport across hillslopes decouple soil transport and hillslope forms from the rocks present in the subsurface. In this study we document a landscape in Central California where rocks are influencing the form of soil-mantled hillslopes. We note that many of the processes responsible for mobilizing soil act throughout the soil column, but are less active or inactive in deeper parts of a soil column. Based on this decay in transport with depth, we propose a new prediction for soil transport that can explain how rock type may influence rates of soil transport and ultimately landscape forms in certain settings.
Near-seafloor magnetics reveal tectonic rotation and deep structure at the TAG (Trans-Atlantic Geotraverse) hydrothermal site (Mid-Atlantic Ridge, 26°N)
Florent Szitkar and Jérôme Dyment, Institut de Physique du Globe de Paris, CNRS UMR 7154, Sorbonne Paris Cité, Université Paris Diderot, 75005 Paris, France. Published online ahead of print on 4 Dec. 2014; http://dx.
The near-seafloor magnetic anomaly at the Trans-Atlantic Geotraverse hydrothermal site (Mid-Atlantic Ridge, 26 degrees N) is revisited taking advantage of geological constraints from Ocean Drilling Program drill holes and high-resolution bathymetry. The dipolar magnetic anomaly associated with the site is better reduced to the pole (i.e., corrected for the effects of non-vertical magnetization and ambient magnetic field vectors) if the magnetization vector is tilted by 34 degrees N, an observation suggesting that the strongly faulted basalt surrounding the site has been rotated by ~53 degrees along an axis parallel to the Mid-Atlantic Ridge as a probable consequence of the detachment tectonics inferred in this area. Magnetic modeling shows that the nonmagnetic stockwork zone (i.e. the deep part of the site made of mineralized veins in a matrix of altered basalt) is a significant contributor to the observed negative reduced-to-the-pole anomaly, the rest being accounted for by a deeper source probably related to thermal demagnetization of an ascending hydrothermal pipe beneath the active part of the site.
Contact: Kea Giles