The Cu isotopic composition of iron meteorites

Abstract– High‐precision Cu isotopic compositions have been measured for the metal phase of 29 iron meteorites from various groups and for four terrestrial standards. The data are reported as the δ⁶⁵Cu permil deviation of the ⁶⁵Cu/⁶³Cu ratio relative to the NIST SRM 976 standard. Terrestrial mantle rocks have a very narrow range of variations and scatter around zero. In contrast, iron meteorites show δ⁶⁵Cu approximately 2.3‰ variations. Different groups of iron meteorites have distinct δ⁶⁵Cu values. Nonmagmatic IAB‐IIICD iron meteorites have similar δ⁶⁵Cu (0.03 ± 0.08 and 0.12 ± 0.10, respectively), close to terrestrial values (approximately 0). The other group of nonmagmatic irons, IIE, is isotopically distinct (?0.69 ± 0.15). IVB is the iron meteorite group with the strongest elemental depletion in Cu and samples in this group are enriched in the lighter isotope (δ⁶⁵Cu down to ?2.26‰). Evaporation should have produced an enrichment in ⁶⁵Cu over ⁶³Cu (δ⁶⁵Cu >0) and can therefore be ruled out as a mechanism for volatile loss in IVB meteorites. In silicate‐bearing iron meteorites, Δ¹⁷O correlates with δ⁶⁵Cu. This correlation between nonmass‐dependent and mass‐dependent parameters suggests that the Cu isotopic composition of iron meteorites has not been modified by planetary differentiation to a large extent. Therefore, Cu isotopic ratios can be used to confirm genetic links. Cu isotopes thus confirm genetic relationships between groups of iron meteorites (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites). Several genetic connections between iron meteorites groups are confirmed by Cu isotopes, (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites).     

Urbanization of the United States over two centuries: an approach based on a long-term database (1790–2010)

This paper presents an original methodology for the construction of a harmonized database for urban areas in the United States from 1790 to 2010 (a period with a census every 10 years, amounting to 23 dates). Upstream, this method is based on a theoretical choice, the use of a spatio-temporal reference frame to construct urban areas over the long term, defined by a maximum range of one hour’s travel for each period. We used an automatic aggregation from a Reilly model. Urban measures (growth, concentration) derived from this harmonized database are then presented, providing a unified picture of urbanization in the United States over more than two centuries. They are compared with results derived from more classical databases established using the official figures from the Census Bureau, or from other constructions differing from the present system. The results diverge considerably in some instances, which confirms the impact of the method of delineation of geographical areas in measures of growth.     

Discussion on the article “Paleoseismological analysis of an intraplate extensional structure: the Concud fault (Iberian Chain,Eastern Spain)” by P. Lafuente,L. E. Arlegui,C. L. Liesa,and J. L. Simón (Int J Earth Sci)

This discussion is focused on three aspects of the paper published by Lafuente et al. (Int J Earth Sci, doi: 10.1007/s00531-010-0542-1, 2010) on Concud Fault, constitute the fundamental basis to assess the seismic potential of this capable structure: (1) A slip rate estimated for the Concud Fault based on an erroneous displacement value and a questionable correlation, obviating previously published datings, markedly different to those used by the authors. The wrong displacement value introduces an error of more than 25% in the calculated Quaternary slip rate. (2) A new paleoseismological interpretation of the outcrop of Condud Fault at Los Baños, adding two improperly justified paleoearthquakes to the four events previously inferred. (3) The attribution of faults affecting a young terrace to the most recent recorded earthquake on Concud Fault, ruling out implicitly the likely option of a gravitational origin for them, either landsliding or subsidence due to evaporite dissolution.     

Fluid-driven low-grade metamorphism in polydeformed rocks of Avalonia (Arisaig Group, Nova Scotia, Canada)

The Lower Silurian??Lower Devonian Arisaig Group (Antigonish Highlands) in the Canadian Appalachians is a sequence of shallow marine strata deposited after the accretion of Avalonia to Baltica during the closure of the Iapetus Ocean. Deformation of the strata is widely attributed to the Devonian Acadian orogeny and produced shallowly plunging regional folds and a cleavage of varying penetrativity. Phyllosilicate minerals from the finest-grained rocks exhibit very low-grade (diagenetic-anchizone) metamorphic conditions. X-ray diffraction study reveals that the sampled rocks contain quartz, K-white mica, chlorite, and feldspars; illite?Csmectite and chlorite?Csmectite mixed-layers are common but Na?CK mica and kaolinite occur only in some samples. The identification of illite?Csmectite mixed-layers in diagenetic samples, with Kübler Index >0.50 ??°2?? and the highly heterogeneous b-cell dimension of the K-white micas are in agreement with the variable chemical composition of dioctahedral micas, which present low illitic substitution and variable phengitic content. The spatial variation in the above crystal-chemical parameters was plotted along a NW?CSE composite cross section across the regional folds. No correlation was found between the metamorphic conditions and either the stratigraphic depth or the strain values measured by phyllosilicates orientation analyses, as a function of the penetrativity of the cleavage. However, the metamorphic grade generally increases towards the Hollow Fault, and is highest in samples located within a 1?km corridor from the fault surface. Incipient cleavage is observed in the anchizonal samples located in the vicinity of the Hollow Fault and in some of the diagenetic samples, indicating cleavage development under low temperatures (<200?oC). These relationships, together with regional syntheses, suggest low-grade metamorphism post-dated regional folding and was coeval with Late Carboniferous dextral movement along the Hollow Fault. Fluid circulation associated with movement along this major fault may be the driving mechanism for the increasing metamorphism towards it.     

Market-based conservation of the Amazonian forests: Revisiting win–win expectations

Governments and development organisations consider the involvement of poor forest managers in global value chains and markets as a most promising approach for resolving the social and environmental challenges of the Amazon. This paper intends to provide a clearer picture about opportunities and potentials of this market-approach, by analysing integrated forest based development initiatives in the Bolivian, Brazilian, Ecuadorian and Peruvian Amazon. Findings suggest that the externally promoted initiatives seldom correspond to local realities and that they suffer from limited financial viability due to competitive disadvantages of locals in comparison to more capitalized actors. Success stories remain isolated without replication, and depend on external support for continuation. Only a limited number of families provided with privileged support have been able to overcome the technical, institutional and financial hurdles and to benefit from existing market opportunities. In some cases, interventions have generated conflicts and even weakened social organisation. Instead of simply copying the mistakes of the past regarding the emerging markets for environmental services, it is deemed essential to question the current market focus and search for alternatives placing greater emphasis on the interests, cultures and capacities of local people.     

Methodology and applications for the benefit cost analysis of the seismic risk reduction in building portfolios at broadscale

This article presents a methodology for an estimate of the benefit cost ratio of the seismic risk reduction in buildings portfolio at broadscale, for a world region, allowing comparing the results obtained for the countries belonging to that region. This methodology encompasses (1) the generation of a set of random seismic events and the evaluation of the spectral accelerations at the buildings location; (2) the estimation of the buildings built area, the economic value, as well as the classification in structural typologies; (3) the development of vulnerability curves for each typology; (4) the estimation of the annual average loss of the buildings portfolio in the current conditions as well as in the case of a hypothetical structural intervention. The benefit cost ratio is estimated as the difference between the estimates of the present value of these two annual average losses, divided by the retrofitting costs. This methodology has been applied to the portfolio of public schools of 14 countries of Latin America and the Caribbean, for evaluating the feasibility of the seismic risk reduction at a national scale.     

Palaeoenvironmental evolution of Cenote Aktun Ha (Carwash) on the Yucatan Peninsula,Mexico and its response to Holocene sea-level rise

A 61-cm core was obtained from 4 m below the water table in Cenote Aktun Ha, on the Yucatan Peninsula, Mexico. The cenote is 8.6 km from the Caribbean coast and its formation and evolution have been largely affected by sea-level change. The base of the core dates to 6,940–6,740 cal year BP and overlying sediments were deposited rapidly over the subsequent ~200 years. The pollen record shows that the cenote evolved from a marsh dominated by red mangrove (Rhizophora mangle) and fern (Polypodiaceae) to an open-water system. These vegetation changes were controlled by water level and salinity and are thus useful indicators of past sea level. At the base, the δ¹³C_org isotopic ratios reveal the influence of terrestrial vegetation (−29‰ VPDB), but shift to more negative values up-core (−33‰), indicating an influence from particulate matter in the flooded cenote pool. Although microfossil populations were nearly absent through most of the core, the microfossil assemblage in the upper 6 cm of the core is dominated by the juvenile foraminifer Ammonia tepida and the thecamoebian genus Centropyxis. These populations indicate open-water conditions in the cenote and a major environmental shift around 6,600 cal year BP, which is related to sea-level rise in the Caribbean basin. These data fit well with previously established sea-level curves for the Caribbean Sea. Our reconstruction of the environmental history of Cenote Aktun Ha helps elucidate the floral and hydrological history of the region, and highlights the utility of cenote sediments for studying the Holocene sea-level history of the Caribbean Sea.     

Late Holocene palaeoenvironments of the Nutria Mansa 1 archaeological site,Argentina

This paper presents results of interdisciplinary palaeoenvironmental research carried out on a sediment sequence from the Nutria Mansa 1 archaeological site. This late Holocene site is located in the Pampean plains, Argentina. Siliceous microfossils were recorded (i.e. phytoliths, diatoms, chrysophytes, sponges) and micro-charcoal was analyzed. In addition, fauna identified at the site were correlated with regional palaeoclimatic evidence. Based on the microfossil associations, we concluded that the human occupations occurred beside a fluvial and brackish-freshwater lacustrine setting. Grass communities were located on its margins that developed under a warm temperate climate with evidence for dryness and marked seasonality in part of the record. Although some stratigraphic and faunal evidence indicates a possible temperature increase, these fluctuations were not sufficient to extirpate mammals of arid and cold environments.     

Evidence of high‐energy events in shelly layers interbedded in coastal Holocene sands in Cadiz Bay (south‐west Spain)

In some present‐day coastal areas, recent inactive deposits now outside the reach of sea agents can be observed. These deposits, although formed under different climatic and sea level conditions, often show similar facies to current littoral deposits. They are frequently interpreted as old dunes and beach ridges, or as abandoned spit bars, representative of previous dynamic stages. Nevertheless, in coastal areas which have been subjected to highly‐energetic events similar deposits can also be found. When a dynamic event acts on several adjacent environments, the transported and re‐deposited sediments can create homogeneous deposits with similar facies, that are easily confused. In this work, shelly layers interbedded in relict littoral sands located in the La Algaida pinewood, on the edge of the Rio San Pedro tidal channel, in Cadiz Bay (south‐west Spain) have been studied. The main constituents of the shelly beds are Glycimeris valves, organisms which are no longer found as live specimens in the present‐day sea bed of Cadiz Bay. From their appearance, the origin of these shelly beds could be related to sea washovers generated by tidal or storm action, but their disposition and height over the present sea level implies that even higher energy agents were involved in their formation, such as major storms or tsunami waves. The most significant process was the mobilization of the sub‐tidal and littoral sediments and their dispersal and re‐sedimentation, both lengthways and widthways of the coast, giving way to homogeneous sandy deposits in all littoral environments some of which are now outside the reach of current sea agents. The exception is the present‐day shore of the San Pedro tidal channel, where the sediments are being reworked by tidal and small wave action. If the proximity of the study zone to the limit of the African and Iberian plates is considered, where several historical earthquakes and tsunamis have taken place, it is possible to think that these deposits could be a consequence of sporadic and successive washovers, generated by tsunamis occurring between ad 800 and ad 1200. Sedimentological and historical data indicate an increase in seismic and tsunami activity during this period of time, while the shelly layers would be the consequence of the most intense pulses occurring during these high‐energy events. Copyright © 2009 John Wiley & Sons, Ltd.     

Probabilistic sinkhole modelling for hazard assessment

A method for quantitatively assessing sinkhole susceptibility (spatial probability) and hazard (spatio‐temporal probability) has been developed and independently tested in a 50 km² sector of the Ebro Valley evaporite karst. Three genetic types of sinkholes have been mapped in the floodplain and a terrace surface: 947 small cover‐collapse sinkholes (type 1, terrace), large collapse sinkholes (type 2, floodplain) and large subsidence depressions (type 3, floodplain). The type 1 sinkhole inventory includes two temporal populations: 447 sinkholes formed before 24 November 2005, and 500 between that date and 2 November 2006. Sinkhole susceptibility models have been elaborated analysing the statistical relationships between the sinkholes of the 2005 inventory and a set of potential conditioning factors. The independent evaluation (validation) of the susceptibility models by means of several strategies (random, sequentially excluded, and temporal) has allowed us to select the most significant variables for each sinkhole type and assess quantitatively the quality of models; which are reasonable for the three sinkhole types. Validation has also provided information on the contribution of specific variables and the effect of changing their accuracy to the prediction capability of models. Susceptibility models for type 3 sinkholes have been validated satisfactorily with the 2006 sinkhole inventory (temporal validation). The best susceptibility model has been transformed into a hazard map considering the frequency of sinkholes that occurred in each susceptibility class between 2005 and 2006, as well as their average size. The susceptibility and hazard models obtained could be used as an objective basis for the application of mitigation measures, either of preventive or corrective nature. Copyright © 2008 John Wiley & Sons, Ltd.