Spatiotemporal variation of agricultural patterns in different geomorphologic and climatic environments in the eastern Loess Plateau,north-central China during the late Neolithic and Bronze Ages

Science China Earth Sciences - Human settlement and agricultural development are closely linked to local geomorphological and climatic environments. However, the variation in agricultural systems...     

Joggins,Nova Scotia

Joggins is a famous fossil locality in Nova Scotia, Canada. Hewn by some of the world's highest tides on the Bay of Fundy, these crumbling cliffs shed light on the life and environments of the Carboniferous Coal Age, 315 million years ago. The site has been a magnet for geologists since the early nineteenth century. Charles Lyell described it as the world's best coal‐bearing section and together with his colleague, William Dawson, reported amazing fossil forests and a rich terrestrial fauna. Since that golden age, the rate of new fossil discoveries has hardly diminished and in recognition of its importance, the Joggins Fossil Cliffs was awarded UNESCO World Heritage Status in 2008. Even after many years of study, it remains a tremendous thrill for us to explore this ‘classic locality’ in far‐flung Nova Scotia. Each winter storm, rock fall, and tide brings with it the tantalizing possibility of new fossils and new scientific insights. In this article we share something of our excitement for Joggins and provide an up to date field guide for those wishing to unlock its secrets.     

PAH concentrations in Coquina (Donax spp.) on a sandy beach shoreline impacted by a marine oil spill

The BP MC252 well failure in the Gulf of Mexico, April 2010 caused concern for crude oil and polycyclic aromatic hydrocarbon (PAHs) exposure along the sandy beaches of the Florida Panhandle. We began collections of Coquina clams (Donax spp.) from the surf zone of Florida Panhandle beaches to monitor PAH contamination to compliment analysis of surf zone sand samples. These clams had higher levels of PAHs relative to ambient sand, and this allowed us to continue to monitor PAH levels after sand concentrations fell below limits of detection. PAH levels in the Coquina tissues were highly variable, perhaps indicative of the heterogeneous distribution of oil and tar on the beaches and exposure to tar particles. Overall, PAH levels decreased continuously in both sand and Coquina tissues, reaching limits of detection within one and two years respectively after oil landed on Florida Panhandle beaches. Our work suggests these surf zone molluscs may be used to monitor pollutant exposure along high energy sandy beach shorelines.     

Female newcomers’ adjustment to life in Toronto,Canada: sources of mental stress and their implications for delivering primary mental health care

Stress disorders and other mental ill health may be brought on by the disruption caused by resettlement. We examine female newcomers’ experiences of adjusting to a new place, metropolitan Toronto, Canada and a new health care system. We consider sources of mental stress experienced during adjustment. We frame this adjustment as a process that happens over place and through time. Thematic findings of interviews (n = 35) with female newcomers from five cultural-linguistic groups are reported. Sources of stress in adjusting to life in Toronto include: navigating a new place, personal safety concerns, adapting to a new lifestyle, and finding employment. Sources of stress in adjusting to a new health care system include: learning how to access care, not having access to specialists, and adapting to a new culture of care. We conclude by considering the implications of what newcomers report for the delivery of primary mental health care (i.e. ‘first contact’ care).     

Hosts of hydrogen in Allan Hills 84001: Evidence for hydrous martian salts in the oldest martian meteorite?

Abstract— The martian meteorite, Allan Hills (ALH) 84001, contains D‐rich hydrogen of plausible martian origin (Leshin et al., 1996). The phase identity of the host(s) of this hydrogen are not well known and could include organic matter (McKay et al., 1996), phlogopite (Brearley, 2000), glass (Mittlefehldt, 1994) and/or other unidentified components of this rock. Previous ion microprobe studies indicate that much of the hydrogen in ALH 84001 as texturally associated with concretions of nominally anhydrous carbonates, glass and oxides (Boctor et al., 1998; Sugiura and Hoshino, 2000). We examined the physical and chemical properties of the host(s) of this hydrogen by stepped pyrolysis of variously pre‐treated subsamples. A continuous‐flow method of water reduction and mass spectrometry (Eiler and Kitchen, 2001) was used to permit detailed study of the small amounts of this hydrogen‐poor sample available for study. We find that the host(s) of D‐rich hydrogen released from ALH 84001 at relatively low temperatures (?500 °C) is soluble in orthophosphoric and dilute hydrochloric acids and undergoes near‐complete isotopic exchange with water within hours at temperatures of 200 to 300 °C. These characteristics are most consistent with the carrier phase(s) being a hydrous salt (e.g., carbonate, sulfate or halide); the thermal stability of this material is inconsistent with many examples of such minerals (e.g., gypsum) and instead suggests one or more relatively refractory hydrous carbonates (e.g., hydromagnesite). Hydrous salts (particularly hydrous carbonates) are common on the Earth only in evaporite, sabkha, and hydrocryogenic‐weathering environments; we suggest that much (if not all) of the “martian” hydrogen in ALH 84001 was introduced in analogous environments on or near the martian surface rather than through biological activity or hydrothermal alteration of silicates in the crust.     

Contrasting pyroclast density spectra from subaerial and submarine silicic eruptions in the Kermadec arc: implications for eruption processes and dredge sampling

Pyroclastic deposits from four caldera volcanoes in the Kermadec arc have been sampled from subaerial sections (Raoul and Macauley) and by dredging from the submerged volcano flanks (Macauley, Healy, and the newly discovered Raoul SW). Suites of 16–32?mm sized clasts have been analyzed for density and shape, and larger clasts have been analyzed for major element compositions. Density spectra for subaerial dry-type eruptions on Raoul Island have narrow unimodal distributions peaking at vesicularities of 80–85%, whereas ingress of external water (wet-type eruption) or extended timescales for degassing generate broader distributions, including denser clasts. Submarine-erupted pyroclasts show two different patterns. Healy and Raoul SW dredge samples and Macauley Island subaerial-emplaced samples are dominated by modes at ~80–85%, implying that submarine explosive volcanism at high eruption rates can generate clasts with similar vesicularities to their subaerial counterparts. A minor proportion of Healy and Raoul SW clasts also show a pink oxidation color, suggesting that hot clasts met air despite 0.5 to >1?km of intervening water. In contrast, Macauley dredged samples have a bimodal density spectrum dominated by clasts formed in a submarine-eruptive style that is not highly explosive. Macauley dredged pyroclasts are also the mixed products of multiple eruptions, as shown by pumice major-element chemistry, and the sea-floor deposits reflect complex volcanic and sedimentation histories. The Kermadec calderas are composite features, and wide dispersal of pumice does not require large single eruptions. When coupled with chemical constraints and textural observations, density spectra are useful for interpreting both eruptive style and the diversity of samples collected from the submarine environment.     

Rhenium–osmium systematics of the Mount Isa copper orebody and the Eastern Creek Volcanics,Queensland, Australia: implications for ore genesis

The syn-tectonic breccia-hosted Mount Isa Cu deposit in northwest Queensland is the largest sediment-hosted Cu deposit in Australia. Whole-rock samples of chalcopyrite-rich Cu ore form an isochron with a Re–Os age of 1,372 ± 41 Ma. This age is more than 100 Ma younger than the previously accepted age of Cu ore formation, an Ar–Ar mineral age for biotite separated from the host rocks within the alteration envelope to the Cu orebody. This discrepancy cannot be unequivocally resolved due to a lack of other absolute geochronological constraints for Cu mineralisation or the deformation event associated with Cu emplacement. The 1,372 ± 41 Ma date may reflect (a) the time of Cu deposition, (b) the time of a hydrothermal event that reset the Re–Os signature of the Cu ore or (c) mixing of the Re–Os isotope systematics between the host rocks and Cu-bearing fluids. However, a range of published Ar–Ar and Rb–Sr dates for potassic alteration associated with Cu mineralisation also records an event between 1,350 and 1,400 Ma and these are consistent with the 1,372 Ma Re–Os age. The 1.8 Ga Eastern Creek Volcanics are a series of tholeiitic basalts with a primary magmatic Cu enrichment which occur adjacent to the Mount Isa Cu deposit. The whole-rock Os isotopic signature of the Eastern Creek Volcanics ranges from mantle-like values for the upper Pickwick Member, to more radiogenic/crustal values for the lower Cromwell Member. The Re–Os isotope signature of the Cu ores overlaps with those calculated for the two volcanic members at 1,372 Ma; hence, the Os isotope data are supportive of the concept that the Os in the Cu ores was sourced from the Eastern Creek Volcanics. By inference, it is therefore postulated that the Eastern Creek Volcanics are the source of Cu in the Mount Isa deposit, as both Os and Cu are readily transported by oxidised hydrothermal fluids, such as those that are thought to have formed the Cu orebody. The Pickwick Member yields a Re–Os isochron age of 1,833 ± 51 Ma, which is within error of previously reported age constraints. The initial ¹⁸⁷Os/¹⁸⁸Os isotopic ratio of 0.114 ± 0.067 (γOs = −0.7) is slightly subchondritic, and together with other trace element geochemical constraints, is consistent with a subcontinental lithospheric mantle source. The Pickwick Member records a minimum age of ca. 1.95 Ga for melt depletion in the subcontinental lithospheric mantle beneath the Mount Isa Inlier prior to the extraction of the magmas which formed the Eastern Creek Volcanics. This corresponds with the end of subduction-related magmatism along the eastern margin of the Northern Australian Craton, which included the Mount Isa Inlier.     

A 1900‐year paleohurricane record from Wassaw Island,Georgia, USA

We present here the first paleotempestology record from Wassaw Island on the Georgia Bight, located in the south Atlantic coast of the United States. In the historical period, the Georgia Bight has experienced less frequent hits by hurricanes than other locations along the US Gulf and Atlantic coasts. The 1900‐year record inferred from the overwash sand layers from a back‐barrier marsh on Wassaw Island suggests that the island was directly struck by major storms on nine occasions during this interval. The Wassaw Island record shows alternating regimes, with periods of increased activity from >2000 a BP until ～1100 a BP, and ～100 a BP until the present, sandwiching a quiet period from ～1100 to 250 a BP. Storm deposits from the most recent active period are perhaps amalgamated, indicating that site‐specific conditions may result in event undercounting and suggests that the relative thickness of sand layers in the sedimentary record is not always indicative of hurricane strength. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of forest disturbance legacy effects on dissolved organic matter characteristics in streams at the Hubbard Brook Experimental Forest,New Hampshire

Dissolved organic matter (DOM) source and composition are critical drivers of its reactivity, impact microbial food webs and influence ecosystem functions. It is believed that DOM composition and abundance represent an integrated signal derived from the surrounding watershed. Recent studies have shown that land-use may have a long-term effect on DOM composition. Methods for characterizing DOM, such as those that measure the optical properties and size of the molecules, are increasingly recognized as valuable tools for assessing DOM sources, cycling, and reactivity. In this study we measured DOM optical properties and molecular weight determinations to evaluate whether the legacy of forest disturbance alters the amount and composition of stream DOM. Differences in DOM quantity and composition due to vegetation type and to a greater extent, wetland influence, were more pronounced than effects due to disturbance. Our results suggest that excitation-emission matrix fluorescence with parallel factor analysis is a more sensitive metric of disturbance than the other methods evaluated. Analyses showed that streams draining watersheds that have been clearcut had lower dissolved organic carbon (DOC) concentrations and higher microbially-derived and protein-like fluorescence features compared to reference streams. DOM optical properties in a watershed amended with calcium, were not significantly different than reference watersheds, but had higher concentrations of DOC. Collectively these results improve our understanding of how the legacy of forest disturbances and natural landscape characteristics affect the quantity and chemical composition of DOM in headwater streams, having implications for stream water quality and carbon cycling.     

A comet impact in AD 536?

Emma Rigby, Melissa Symonds and Derek Ward-Thompson review the evidence for the possibility that a comet may have impacted the Earth in historical times, and discuss the size of the putative comet.