Differential Late Paleozoic active margin evolution in South-Central Chile (37°S–40°S) – the Lanalhue Fault Zone

The N–S oriented Coastal Cordillera of South Central Chile shows marked lithological contrasts along strike at 38°S. Here, the sinistral NW–SE-striking Lanalhue Fault Zone (nomen novum) juxtaposes Permo-Carboniferous magmatic arc granitoids and associated, frontally accreted metasediments (Eastern Series) in the northeast with a Late Carboniferous to Triassic basal-accretionary forearc wedge complex (Western Series) in the southwest. The fault is interpreted as an initially ductile deformation zone with divergent character, located in the eastern flank of the basally growing, upwarping, and exhuming Western Series. It was later transformed and reactivated as a semiductile to brittle sinistral transform fault. Rb–Sr data and fluid inclusion studies of late-stage fault-related mineralizations revealed Early Permian ages between 280 and 270 Ma for fault activity, with subsequent minor erosion. Regionally, crystallization of arc intrusives and related metamorphism occurred between 306 and 286 Ma, preceded by early increments of convergence-related deformation. Basal Western Series accretion started at >290 Ma and lasted to 250 Ma. North of the Lanalhue fault, Late Paleozoic magmatic arc granitoids are nearly 100 km closer to the present day Andean trench than further south. We hypothesize that this marked difference in paleo-forearc width is due to an Early Permian period of subduction erosion north of 38°S, contrasting with ongoing accretion further south, which kinematically triggered the evolution of the Lanalhue Fault Zone. Permo-Triassic margin segmentation was due to differential forearc accretion and denudation characteristics, and is now expressed in contrasting lithologies and metamorphic signatures in todays Andean forearc region north and south of the Lanalhue Fault Zone.     

Taphonomy and zooarchaeology in the Neotropics: A view from northwestern Patagonian forest and steppe

Modes of faunal exploitation in NW Chubut Province (Patagonia, Argentina) during the last 3500 calibrated years BP are discussed, based on taphonomic and zooarchaeological analyses. Bone assemblages were recovered from archaeological sites of the Sub-Antarctic forests and the extra-Andean Patagonian steppe, where huemul (Hippocamelus bisulcus) and guanaco (Lama guanicoe) were, respectively, the main staple. In the steppe, lesser rhea (Pterocnemia pennata), a medium-sized flightless bird, also was integrated into the hunter-gatherer diet. Rodents, carnivores, flying birds, and fishes also were recovered. Different processes and agents were involved in the accumulation of small vertebrates bone assemblages (e.g. birds of prey, foxes, and small carnivores). In the steppe, only two taxa of small vertebrates—birds and mountain viscacha (Lagidium viscacia)—can be related with human subsistence activities. These two taxa and all large vertebrates reveal fat-oriented carcass processing.Guanaco bone assemblages associated both with ceramic and non-ceramic technologies do not show changes in carcass processing. Moreover, the similarities in bone grease exploitation suggest boiling prior to the appearance of pottery.     

Large-scale moraine deformation at the Athabasca Glacier,Jasper National Park,Alberta, Canada

In this paper the development of a large-scale gravitational deformation involving the eastern lateral moraine of the Athabasca Glacier in Jasper National Park, Alberta, Canada, is described. Interpretation and analysis of sequential aerial photographs indicates that a 540-m-wide segment of the eastern lateral moraine began to deform in the early 1950s; however, significant movement only began in the late 1960s. Since then, the moraine has undergone progressive gravitational deformation leading to a network of fractures, bulging, and the development of a large gap in the moraine crest. Geographic information system analysis of topographic changes between 1967 and 2006 indicates that the displaced volume of the moraine is approximately 9.0 × 10⁵ m³. In the last 39 years, the moraine crest has displaced 55 m (1.4 m yr⁻¹) down towards the glacier. The development of slope instability is linked to a combination of debuttressing from recent glacier recession, deformation of the moraine, as well as the movement of a large, mobile, debris-mantled slope impinging the upslope margin of the lateral moraine. This case study illustrates the importance of glacial conditioning and local geomorphological factors in creating conditions for large-scale moraine instability in recently deglacierized alpine basins.     

How do small-holder farmers understand insurance,and how much do they want it? Evidence from Africa

Innovative micro-insurance schemes can be one tool to help African small-holder farmers cope with climate variability and change. A critical challenge for implementing such risk transfer programs, however, is helping participants understand how insurance operates, and there is evidence that farmers with a poor understanding of insurance are less likely to use it. One of the proposed tools to help farmers understand insurance is a simulation game, through which farmers can gain first-hand experience with a functioning insurance market. This paper reports on the results of experiments in Ethiopia and Malawi, investigating farmers’ understanding and the effectiveness of a role-playing game at improving that understanding. Our results suggest a generally poor understanding of basic insurance concepts, and are consistent with past results in suggesting that better understanding correlates with greater willingness to purchase it. Our results also suggest that role-playing games may be an important tool for improving understanding, but that they do not necessarily out-perform more conventional training practices.     

The last major earthquakes along the Magallanes–Fagnano fault system recorded by disturbed trees (Tierra del Fuego,South America)

Forests situated above active fault zones may record hillslope evolution, thus holding information about recent seismic events. Lenga trees (Nothofagus pumilio) extend across the Magallanes–Fagnano fault system (MFFS), the active transform boundary between the South American and Scotia plates. Coseismic surface ruptures along the fault scarp tilt trees located uphill. During the interseismic period, tree growth curves the trunks. Annual tree rings from the study area show abrupt changes from concentric to asymmetric, allowing the timing of major historical earthquakes to be established. In this case, tree‐ring analysis suggests rupture on the MFFS fault scarp in 1883 ± 5 and 1941 ± 10, coinciding with the February 1, 1879 (Modified Mercalli Scale, VI) and the December 17, 1949 (Ms 7.8) earthquakes in Tierra del Fuego. Our results provide evidence that this fault system was the source of these earthquakes, which has implications for seismic hazard in the study region.     

The rise of the diptera‐microbial mat interactions during the Cenozoic: consequences for the sedimentary record of saline lakes

Shoreline gypsiferous sediments of an inland lake in central Spain furnishes valuable insight into reconstructions of early sedimentary changes related to shore fly–microbial mat interactions in fossil gypsum precipitating saline lake systems. The association of adult and larval forms of Ephydra (Diptera) with microbial matgrounds overlying the lake margin results in the formation of gypsiferous meniscate back‐filled burrows that provide an analogue for recurring, extensively developed trace fossils that occur in Cenozoic, but not older, lacustrine gypsum rocks. In this setting, sediment burrowing by ephydridae hinders significant preservation of microbialites. The overwhelming rise of Diptera at the onset of the Cenozoic resulted in extensive feeding and dwelling activity and contributed to reshape the saline aquatic habitat where microbial mats thrived, thus leading to the formation of specific trace fossils that are illustrative of the existence of microbes in the paleoenvironment.     

Seasonal and annual throughfall and stemflow in Andean temperate rainforests

The partitioning of gross rainfall into throughfall, stemflow, and interception loss and their relationships with forest structure was studied for a period of four years (October 2002–September 2006) and two years (October 2005–September 2007) in seven experimental catchments of temperate rainforest ecosystems located in the Andes of south‐central Chile (39°37′S, 600–925 m a.s.l.). The amount of throughfall, stemflow, and interception loss was correlated with forest structure characteristics such as basal area, canopy cover, mean quadratic diameter (MQD), and tree species characteristics in evergreen and deciduous forests. Annual rainfall ranged from 4061 to 5308 mm at 815 m a.s.l. and from 3453 to 4660 mm at 714 m a.s.l. Throughfall ranged from 64 to 89% of gross rainfall. Stemflow contributed 0·3–3·4% of net precipitation. Interception losses ranged from 11 to 36% of gross rainfall and depended on the amount of rainfall and characteristics as well as on forest structure, particularly the MQD. For evergreen forests, strong correlations were found between stemflow per tree and tree characteristics such as diameter at breast height (R² = 0·92, P < 0·01) and crown projection area (R² = 0·65, P < 0·01). Stemflow per tree was also significantly correlated with epiphyte cover of trunks in the old‐growth evergreen forests (R² = 0·29, P < 0·05). The difference in the proportion of throughfall and interception loss among stands was significant only during winter. The reported relationships between rainfall partitioning and forest structure and composition provide valuable information for management practices, which aimed at producing other ecosystem services in addition to timber in native rainforests of southern Chile. Copyright © 2010 John Wiley & Sons, Ltd.     

Actor and frontier types in the Brazilian Amazon: Assessing interactions and outcomes associated with frontier expansion

This paper analyzes frontier expansion in the Brazilian Amazon as a process that depends on multiple exogenous and endogenous factors operating at diverse scales, but whose trajectory depends on the dominant actor type (smallholders or medium- or large-scale landholders) occupying the frontier landscape. Despite the broad growing trend of pasture expansion for adoption of cattle ranching as the main land use associated with frontier expansion, some differences persist across actor types. In relative terms, medium- and large-scale landholders place most of their cleared forestland under pasture, and in absolute terms, largeholders have deforested more than smallholders because they hold larger tracts of land. Recently, however, deforestation activity has been increasing in frontiers occupied by smallholders who tend to convert a greater proportion of the forestland in their landholdings to agricultural land uses than larger-scale landholders, mainly to expand cattle ranching operations. Furthermore, smallholders tend to maintain higher cattle stocking rates than medium- and large-scale landholders, which tend to adopt extensive systems of cattle production. Both economic and human development indices in each frontier type vary according to actor type. While in absolute terms, higher per capita agricultural income levels are found in frontiers where largeholders predominate, the corresponding incomes are higher in smallholder frontiers when prorated by unit of land under crops and pasture. In addition, the Human Development Index is higher in frontiers with greater presence of large-scale landholdings.