Magnetic properties of dashing rocks loess at Timaru, South Island, New Zealand

The relationships between magnetic susceptibility and pedogenic development are different in various regions of the world. For example, loess magnetic susceptibility shows a positive correlation with pedogenic development in Chinese Loess Plateau (CLP),

Magnetic Properties and Paleomagnetism of Zebra Rock, Western Australia: Chemical Remanence Acquisition in Hematite Pigment and Ediacaran Geomagnetic Field Behavior

Zebra Rock, a decorative stone remarkable for its unusual pattern of regularly spaced reddish bands and rods with white background, is found within the Neoproterozoic succession in East Kimberley, Western Australia. The unusual pigment distribution suggests that precipitation of hematite, or its precursor phase, occurred in a single episode. Magnetic properties of hematite pigment in Zebra Rock are distinctly different from those of the host shale, with a smaller median particle size and higher degree of structural perfection. The low thermal stability of the Zebra Rock pigment, with onset of thermal alteration at 300°C, suggests that the rocks have not undergone significant metamorphic heating. Stepwise thermal demagnetization reveals multiple magnetization components. Short-range variability in the relative contributions of the components to the total remanence is indicative of the stochastic nature of the hematite pigment growth process. In addition to seven magnetization components with shallow to intermediate inclinations that can be matched to the Paleozoic Australian apparent polar wander path, Zebra Rock samples contain a distinct steeply dipping magnetization that is not observed in the host shales. The steep magnetization appears to be primary, based on its unique association with the Zebra pattern, dissimilarity with younger directions, and evidence for low degree of thermal alteration of the rocks. The steep characteristic remanence contrasts with previous paleomagnetic indications of low Australian Neoproterozoic paleolatitudes. The characteristic Zebra Rock magnetization is the first Australian example of incompatible magnetization directions that have been reported previously from Ediacaran rocks in Laurentia, Baltica, and Africa.We acknowledge the Australian Research Council (ARC) through grant FS100100076 to APR and colleagues that provided a Super Science Fellowship to AA

Hematite (a-Fe2O3) quantification in sedimentary magnetism: limitations of existing proxies and ways forward

Determination of hematite contributions to sedimentary magnetizations is an important but difficult task in quantitative environmental studies. The poorly crystalline and fine-grained nature of hematite nanoparticles makes quantification of their concentrations in natural environments challenging using mineralogical and spectroscopic methods, while the weak magnetization of hematite and often significant superparamagnetic nanoparticle concentrations make quantification difficult using magnetic remanence measurements. We demonstrate here that much-used magnetic parameters, such as the S-ratio and "hard" isothermal remanent magnetization (HIRM), tend to significantly underestimate relative and absolute hematite contents, respectively. Unmixing of isothermal remanent magnetization (IRM) acquisition curves is among the more suitable approaches for defining magnetic mineral contributions, although it has under-appreciated uncertainties that limit hematite quantification. Diffuse reflectance spectroscopy and other methods can enable relative hematite and goethite content quantification under some conditions. Combined use of magnetic, mineralogical, and spectroscopic approaches provides valuable cross-checks on estimated hematite contents; such an integrated approach is recommended here. Further work is also needed to rise to the challenge of developing improved methods for hematite quantification

Tektites as chronostratigraphic markers in Australian regolith

1992), an asteroid or comet impacted in southeast Asia, producing tektites, microtektites and impact debris which are found over more than 10 % of the Earth's surface (Schnetzler & McHone 1996), including much of Australia and surrounding oceans (Figure 1). The distribution, size and concentration of tektites and microtektites indicate a likely impact site somewhere in southern Laos or Thailand, but the location of the impact site has not yet been discovered. Although there has been considerable debate concerning the age of the Australasian tektites, their age is now firmly established through magneto-stratigraphy of deep sea cores in which microtektites occur just prior to the Matuyama/Brunhes polarity transition (Schneider et al. 1992), as well as direct laser fusion 40Ar/39Ar dating of tektite glass (Izett & Obradovich 1992). Previously, a number of field studies supported a Late Pleistocene age in the range 5 to 25 ka (e.g., Gill 1970, Lovering et al. 1972), but these occur-rences are now considered to represent reworking into younger sediments (e.g., Fudali 1993, Shoemaker & Uhlherr 1999). There has long been speculation that the impact may have triggered the Matuyama/Brunhes reversal (e.g., Glass & Heezen 1967). However, the estimated time (12-15 ka) between the impact and the reversal appears to be too long for a causal link between the two events (Schneider et al. 1992). Tektites have been found in abundance at numerous sites acros

Pre-Quaternary landscape inheritance in Australia

Palaeogeographic reconstructions indicate that parts of the Australian continent have been subaerially exposed for hundreds of millions of years. Some landforms and regolith are demonstrated to be at least 300 million years old, but their persistence at or near the surface is inconsistent with long-term denudation rate estimates based on cosmogenic nuclides and apatite fission track thermochronology. Burial and exhumation are suggested as significant preservation factors, in conjunction with prolonged tectonic stability and a shift to more arid climatic regimes in the Cenozoic