A deeply embedded companion to LKHα198

The region around the Herbig Ae/Be star LkH198 was imaged at 10m with the CAMIRAS camera at the Canada-France-Hawaii Telescope and the Nordic Optical Telescope. We discovered a deeply embedded companion 6 north of LkH198, which may be responsible for most of the far-infrared emission in the region and for driving the molecular flow. LkH198 appears point-like at our resolution (FWHM 1.3), excluding an extended envelope of transiently heated small grains as the dominant origin of the mid-infrared excess in that star.     

Acute Disturbance of Lake Pontchartrain Benthic Communities by Hurricane Katrina

In 2005, Hurricane Katrina produced a distinct, acute ecological disturbance of the benthic invertebrate community of Lake Pontchartrain, LA, USA. The bivalve Rangia cuneata and other community dominants were lost from 50% (815 km²) of the lake bottom. The storm surge directly killed benthic organisms and produced salinity stratification that caused episodes of detrimental low dissolved oxygen concentration at depths >3.7 m. Past disturbance of the bottom by shell dredging and intrusion of higher salinity bottom water through deep shipping channels appears to have contributed to the severity of this impact. Colonization by tolerant opportunistic taxa occurred, but low rainfall after Katrina has slowed the recovery of the typical rangia community. A decrease in water transparency and an increase in turbidity and chlorophyll a were associated with the loss of clam biomass. Other hurricanes may have produced less obvious but similar effects on smaller spatial and temporal scales.     

The invasive Asian green mussel Perna viridis in South Africa: all that is green is not viridis

The Asian green mussel Perna viridis is an invasive Indo-Pacific species recently reported from South African harbours. To verify the invasion, a phylogenetic (and morphological) analysis of green-shelled mussels (n = 39), found in six South African harbours, was conducted using the mitochondrial cytochrome c oxidase subunit I gene (COI). Estimates of genetic distances using the neighbour-joining analysis identified P. viridis only from Durban Harbour. All other green mussels were more than 3.2% divergent from P. viridis and were identified as green-shelled variants of indigenous P. perna. The only reliable morphological differences distinguishing the two species were the poorly developed mantle papillae and the wavy pallial line in P. viridis. The confirmed occurrence of P. viridis in a South African harbour suggests that there is a possible threat of the species becoming established and then spreading onto the open coast and competing with indigenous P. perna.     

Assessing the influence of afforestation with Eucalyptus globulus on hydrological response from a small catchment in northwestern Spain using the HBV hydrological model

Land use change as conversion pasture to forest produces several changes on hydrological cycle. In this paper, we analyse the effects on stream discharge of afforestation of a small watershed devoted to pasture using the HBV hydrological model. Streamflow data obtained over the first 10 years after planting were employed to evaluate the capacity of HBV model to simulate hydrological behaviour of catchment after afforestation. Obtained results indicate that the estimation of streamflow was accurate as reflected by statistics (R² = 0.90, NSC = 0.89 and PBIAS = 0.34). Afterwards, streamflow under pasture land use (if afforestation had not occurred) was simulated using hydrometeorological data collected during the period of study and model parameters optimized previously, together with two parameters, pcorr and cevpfo, that were adjusted for pasture conditions. The HBV model results indicate that afforestation produced a water yield reduction around 2000 mm (22% of total stream discharge) during the first 10 years of planting growth. The differences between forest and pasture land cover are increasing in all seasons year by year. The greatest streamflow reduction was observed in wet period (autumn and winter) with 76% of total reduction. In summer, streamflow reduction represents only 3% of total, however, represents 24.7% of discharge in this season. Streamflow reduction was related to increase of rainfall interception (mainly in wet periods) and the increase of evapotranspiration by plantation in dry periods. Copyright © 2013 John Wiley & Sons, Ltd.     

The Holocene volcanic history of Gran Canaria island: implications for volcanic hazards

Previous published data, combined with our results of 13 new radiocarbon ages and extensive geological fieldwork, indicate that during the past 11 ka 24 monogenetic basaltic eruptions occurred in the north sector of Gran Canaria. These eruptions can be grouped into three periods of eruptive activity: 1900–3200 ¹⁴C a BP; 5700–6000 ¹⁴C a BP; and an older period represented by only one eruption, El Draguillo, dated at 10 610 ± 190 ¹⁴C a BP. Archaeological studies have shown that the more recent eruptions affected prehistoric human settlements on the island. Field studies demonstrate that the eruptions typically built strombolian cones (30–250 m in height) and associated relatively long lava flows (100–10 350 m in length); a few eruptions also produced tephra fall deposits. The total erupted volume of these eruptions is about 0.388 km³ (46.1% as tephra fall, 41.8% as cinder cone deposits and 12.1% as lava flows). The relatively low eruption rate (～0.04 km³ ka^?1) during the past 11 ka is consistent with Gran Canaria's stage of evolution in the regional volcano‐tectonic setting of the Canary Archipelago. The results of our study were used to construct a volcanic hazards map that clearly delimits two sectors in the NE sector of Gran Canaria, where potential future eruptions would pose a substantial risk for densely populated areas. Copyright © 2009 John Wiley & Sons, Ltd.     

History of plains resurfacing in the Scandia region of Mars

We present a preliminary photogeologic map of the Scandia region of Mars with the objective of reconstructing its resurfacing history. The Scandia region includes the lower section of the regional lowland slope of Vastitas Borealis extending about 500–1800 km away from Alba Mons into the Scandia sub-basin below ?4800 m elevation. Twenty mapped geologic units express the diverse stratigraphy of the region. We particularly focus on the materials making up the Vastitas Borealis plains and its Scandia sub-region, where erosional processes have obscured stratigraphic relations and made the reconstruction of the resurfacing history particularly challenging. Geologic mapping implicates the deposition, erosion, and deformation/degradation of geologic units predominantly during Late Hesperian and Early Amazonian time (～3.6–3.3 Ga). During this time, Alba Mons was active, outflow channels were debouching sediments into the northern plains, and basal ice layers of the north polar plateau were accumulating. We identify zones of regional tectonic contraction and extension as well as gradation and mantling. Depressions and scarps within these zones indicate collapse and gradation of Scandia outcrops and surfaces at scales of meters to hundreds of meters. We find that Scandia Tholi display concentric ridges, rugged peaks, irregular depressions, and moats that suggest uplift and tilting of layered plains material by diapirs and extrusion, erosion, and deflation of viscous, sedimentary slurries as previously suggested. These appear to be long-lived features that both pre-date and post-date impact craters. Mesa-forming features may have similar origins and occur along the southern margin of the Scandia region, including near the Phoenix Mars Lander site. Distinctive lobate materials associated with local impact craters suggest impact-induced mobilization of surface materials. We suggest that the formation of the Scandia region features potentially resulted from crustal heating related to Alba Mons volcanism, which acted upon a sequence of lavas, outflow channel sediments, and polar ice deposits centered within the Scandia region. These volatile-enriched sediments may have been in a state of partial volatile melt, resulting in the mobilization of deeply buried ancient materials and their ascent and emergence as sediment and mud breccia diapirs to form tholi features. Similar subsurface instabilities proximal to Alba Mons may have led to surface disruption, as suggested by local and regional scarps, mesas, moats, and knob fields.     

Study of the Cuban fractures

With the help of aerial photographs, satellite photographs and imageries, contour maps, geological and geomorphological information (personal correspondence and unpublished works), geophysical regional data, and field work, it has been possible to map a network of fractures, alignments, and faults in 26 areas (distinguishing them quantitatively and hierarchically). Links with known regional structures were also studied. Interpretation of the linear relief elements confirms the very different density, dimensions, strikes, and function of the fracturation and also, from a microtectonic perspective, explains the activity of some active faults better. It has confirmed some previous results and improved on others; for example, the Oriente fault which is the most active in Cuba with two segments (Western: Cabo Cruz—Santiago de Cuba; Eastern: Santiago de Cuba—Punta de Maisí, the Western fault being the most active); the Nortecubana fault, forming the northern limit of the Cuban megablock, and divided into three segments; and the Cauto—Nipe fault, forming the limit of the neotectonic units, presenting two segments with three seismoactive knots.     

新疆阿尔泰铁木尔特铅锌矿床流体包裹体研究及地质意义

铁木尔特中型铅锌矿是阿尔泰山南缘克兰盆地内的重要VMS型矿床。矿床赋存于上志留统-下泥盆统康布铁堡组上亚组第二岩性段,容矿岩石为大理岩、绿泥石英片岩、变钙质粉砂岩、夕卡岩。矿体呈似层状和透镜状。矿床的形成经历了喷流沉积期、叠加改造期和表生期。石英、长石、方解石和石榴子石中包裹体类型主要为液体包裹体,在石英中另出现了气体包裹体、纯气体包裹体、含子矿物多相包裹体、含液体CO2的三相包裹体和两相CO2包裹体。喷流沉积期成矿流体均一温度变化于150～330℃,其峰值是165℃和285℃,成矿流体盐度(NaCleq)为4%～16%,流体密度为0.77～0.97g/cm3,流体阳离子主要以Na+为主,次之为K+,阴离子以Cl-为主,其次是SO42-,气相成分主要是H2O和CO2。叠加改造期均一温度范围是150～480℃,峰值为285℃,盐度(NaCleq)为2.2%～17.08%和33.93%～47.2%,流体密度变化于0.61～1.03g/cm3之间,流体阳离子主要以Na+为主,次为K+、Mg2+、Ca2+,阴离子以Cl-为主,其次是SO42-,气相成分主要是H2O和CO2,其次为N2、CH4,含有少量C2H6。