First Precambrian palaeomagnetic data from the Mawson Craton (East Antarctica) and tectonic implications

A pilot palaeomagnetic study was conducted on the recently dated with in situ SHRIMP U-Pb method at 1134 ± 9 Ma (U-Pb, zircon and baddeleyite) Bunger Hills dykes of the Mawson Craton (East Antarctica). Of the six dykes sampled, three revealed meaningful results providing the first well-dated Mesoproterozoic palaeopole at 40.5°S, 150.1°E (A95 = 20°) for the Mawson Craton. Discordance between this new pole and two roughly coeval poles from Dronning Maud Land and Coats Land (East Antarctica) demonstrates that these two terranes were not rigidly connected to the Mawson Craton ca. 1134 Ma. Comparison between the new pole and that of the broadly coeval Lakeview dolerite from the North Australian Craton supports the putative ~40° late Neoproterozoic relative rotation between the North Australian Craton and the combined South and West Australian cratons. A mean ca. 1134 Ma pole for the Proto-Australia Craton is calculated by combining our new pole and that of the Lakeview dolerite after restoring the 40° intracontinental rotation. A comparison of this mean pole with the roughly coeval Abitibi dykes pole from Laurentia confirms that the SWEAT reconstruction of Australia and Laurentia was not viable for ca. 1134 Ma

What Constitutes a Natural Fire Regime? Insight from the Ecology and Distribution of Coniferous Forest Birds in North America

Bird species that specialize in the use of burned forest conditions can provide insight into the prehistoric fire regimes associated with the forest types that they have occupied over evolutionary time. The nature of their adaptations reflects the specific post-fire conditions that occurred prior to the unnatural influence of humans after European settlement. Specifically, the post-fire conditions, nest site locations, and social systems of two species (Bachman\u27s sparrow [Aimophila aestivalis] and red-cockaded woodpecker [Picoides borealis]) suggest that, prehistorically, a frequent, low-severity fire regime characterized the southeastern pine system in which they evolved. In contrast, the patterns of distribution and abundance for several other bird species (black-backed woodpecker [Picoides arcticus], buff-breasted flycatcher [Empidonax fulvifrons], Lewis\u27 woodpecker [Melanerpes lewis], northern hawk owl [Surnia ulula], and Kirtland\u27s warbler [Dendroica kirtlandii]) suggest that severe fire has been an important component of the fire regimes with which they evolved. Patterns of habitat use by the latter species indicate that severe fires are important components not only of higher-elevation and high-latitude conifer forest types, which are known to be dominated by such fires, but also of mid-elevation and even low-elevation conifer forest types that are not normally assumed to have had high-severity fire as an integral part of their natural fire regimes. Because plant and animal adaptations can serve as reliable sources of information about what constitutes a natural fire regime, it might be wise to supplement traditional historical methods with careful consideration of information related to plant and animal adaptations when attempting to restore what are thought to be natural fire regimes

Rapid Access Ice Drill for Sampling Antarctic Bedrock

Abstract The Rapid Access Ice Drill (RAID) was designed and built to rapidly drill through the Antarctic ice cap, and then core the ice-rock transition zone and underlying bedrock. The system is designed to be mobile and to operate autonomously near the South Pole at elevations of 3000 to 4000 m and at air temperatures as low as −40°C. The anticipated drilling environment consists of about 100 m of firn that must be cased, followed by 2500 to 3300 m of glacial ice before reaching bedrock. The ice temperature at the surface is about −55°C warming to near 0°C at the base of the ice (warm ice). Previous work has focused on ice drilling and coring, and individual holes have required more than one drilling season. Our objective is to drill and complete a hole in approximately two weeks. Firn will be drilled using a conventional auger system at 177.8 mm diameter until impermeable ice is encountered. Casing of 114.3 mm outer diameter will be placed in the hole and sealed against the ice with an inflatable packer. The next stage of drilling utilizes a 88.9 mm bit and 69.9 mm flush joint NRQ V-wall core rod to drill the ice section with penetration rates of 3 m/minute. The bottom hole assembly includes an outer bit and wireline-retrievable inner bit. After experimenting with a number of designs, we chose an outer bit with steel cutters to optimize penetration through the ice. In order to collect core in the transition zone or bedrock, the inner bit is removed by wireline and replaced with a coring assembly that utilizes an impregnated diamond bit. The drilling system consists of five modules that will be mounted on skis for traversing the ice. These are a Drilling Rig Module, Rod Handling Module, Fluid Recirculation System (FRS) Module, a Power Module and a Shop/Inventory Module. The rig is a Boart Longyear LF-230 that we have modified to operate with an electric prime mover. The drilling fluid is ESTISOL-140 that is recycled through the FRS. The drilling system is powered by a 500 kW diesel generator. Two of these units are mounted in a power module to provide redundancy

Formation of supercontinents linked to increases in atmospheric oxygen

Atmospheric oxygen concentrations in the Earth’s atmosphere rose from negligible levels in the Archaean Era to about 21% in the present day. This increase is thought to have occurred in six steps, 2.65, 2.45, 1.8, 0.6, 0.3 and 0.04 billion years ago, with a possible seventh event identified at 1.2 billion years ago. Here we show that the timing of these steps correlates with the amalgamation of Earth’s land masses into supercontinents. We suggest that the continent–continent collisions required to form supercontinents produced supermountains. In our scenario, these supermountains eroded quickly and released large amounts of nutrients such as iron and phosphorus into the oceans, leading to an explosion of algae and cyanobacteria, and thus a marked increase in photosynthesis, and the photosynthetic production of O2. Enhanced sedimentation during these periods promoted the burial of a high fraction of organic carbon and pyrite, thus preventing their reaction with free oxygen, and leading to sustained increases in atmospheric oxygen

Evidence for a spike in mantle carbon outgassing during the Ediacaran period

© 2017 The Author(s). Long-term cycles in Earth\u27s climate are thought to be primarily controlled by changes in atmospheric CO2 concentrations. Changes in carbon emissions from volcanic activity can create an imbalance in the carbon cycle. Large-scale changes in volcanic activity have been inferred from proxies such as the age abundance of detrital zircons, but the magnitude of carbon emissions depends on the style of volcanism as well as the amount. Here we analyse U-Pb age and trace element data of detrital zircons from Antarctica and compare the results with the global rock record. We identify a spike in CO2-rich carbonatite and alkaline magmatism during the Ediacaran period. Before the Ediacaran, secular cooling of the mantle and the advent of cooler subduction regimes promoted the sequestration of carbon derived from decarbonation of subducting oceanic slabs in the mantle. We infer that subsequent magmatism led to the extensive release of carbon that may at least in part be recorded in the Shuram-Wonoka carbon isotope excursion. We therefore suggest that this pulse of alkaline volcanism reflects a profound reorganization of the Neoproterozoic deep and surface carbon cycles and promoted planetary warming before the Cambrian radiation