The Nui Chua layered peridotite-gabbro complex as manifestation of Permo-Triassic mantle plume in northern Vietnam

New data on the age, composition, formation conditions, and ore-geochemical specialization of the Nui Chua layered peridotite-gabbro complex are reported. They evidence that the complex resulted from the Permo-Triassic mantle plume activity in northern Vietnam (southern framing of the Yangtze Platform). Two series of mafic and ultramafic rocks differing in ore productivity—layered (PGE-Cu-Ni) and pegmatoid (Fe-Ti-V)—have been recognized within the complex. The first estimates of the composition of their parental melts have been obtained.     

Controls on salt marsh accretion: A test in salt marshes of Eastern Canada

We used¹³⁷Cs-dating to determine vertical accretion rates of 15 salt marshes on the Bay of Fundy, the Gulf of St. Lawrence, and the Atlantic coast of Nova Scotia. Accretion rates are compared to a number of factors assumed to influence vertical marsh accretion: rates of relative sea-level rise, climatic parameters (average daily temperatures and degree days) and latitude (related to insolation and day length), sediment characteristics (organic matter inventory, bulk, mineral, and organic matter density), distance of the core site from the nearest source of tidal waters, and the tidal range. Uniques to our study is a consideration of climatic parameters and latitude, which should influence organic matter production, and thus vertical accretion rates. Significant predictors of accretion rates (in order of importance) were found to be organic matter inventory, distance from a creek, and range of mean tides. Contrary to conclusions from previous studies, we found that accretion rates decreased with increasing tidal range, probably because we considered a wider span of tidal ranges, from micro- to macrotidal. Although four marshes with low organic matter inventories also show a deficit in accretion with respect to relative sea-level rise, organic matter is not limiting in two-thirds of the marshes studied, despite shorter growing seasons.     

Selenium-induced teratogenicity in Sacramento splittail (Pogonichthys macrolepidotus)

Selenium is a potent reproductive and teratogenic environmental contaminant and there are concerns over possible reproductive effects of selenium on the Sacramento splittail (Pogonichthys macrolepidotus) population, a threatened species, in California, USA. In this study, the teratogenic effects of selenium were examined in splittail embryos exposed to 0.0, 5.0, and 15.0 mg l(-1) sodium selenite for 48-h at 18.0 degrees C under static conditions, with renewal every 12 h. Embryo development was evaluated daily for abnormalities from initiation of exposure (stage 27) to initiation of exogenous feeding. At the end of evaluation, prelarvae were preserved for histological analysis. There were no significant differences in mortality or hatching success between control and exposed embryos. Exposed fish had pericardial edema and deformities of skeletal tissues (loss of tail, lordosis, scoliosis, and kyphosis). Other histological alterations were limited to dysplasia, hyperplasia and metaplasia of skeletal tissues in the deformed fish. This study showed that a short exposure of embryos during somite development has significant effects on the musculoskeletal development.     

A hybrid Lagrangian-Eulerian numerical model for sea-ice dynamics

A hybrid Lagrangian-Eulerian(HLE) method is developed for sea ice dynamics,which combines the high computational efficiency of finite difference method(FDM) with the high numerical accuracy of smoothed particle hydrodynamics(SPH).In this HLE model,the sea ice cover is represented by a group of Lagrangian ice particles with their own thicknesses and concentrations.These ice variables are interpolated to the Eularian gird nodes using the Gaussian interpolation function.The FDM is used to determine the ice velocities at Eulerian grid nodes,and the velocities of Lagrangian ice particles are interpolated from these grid velocities with the Gaussian function also.The thicknesses and concentrations of ice particles are determined based on their new locations.With the HLE numerical model,the ice ridging process in a rectangular basin is simulated,and the simulated results are validated with the analytical solution.This method is also applied to the simulation of sea ice dynamics in a vortex wind field.At last,this HLE model is applied to the Bohai Sea,and the simulated concentration,thickness and velocity match the satellite images and the field observed data well.     

Sedimentation in the floodplains of the Mekong Delta,Vietnam Part II: deposition and erosion

Deposition and erosion play a key role in the determination of the sediment budget of a river basin, as well as for floodplain sedimentation. Floodplain sedimentation, in turn, is a relevant factor for the design of flood protection measures, productivity of agro‐ecosystems, and for ecological rehabilitation plans. In the Mekong Delta, erosion and deposition are important factors for geomorphological processes like the compensation of deltaic subsidence as well as for agricultural productivity. Floodplain deposition is also counteracting the increasing climate change induced hazard by sea level rise in the delta. Despite this importance, a sediment database of the Mekong Delta is lacking, and the knowledge about erosion and deposition processes is limited. In the Vietnamese part of the Delta, the annually flooded natural floodplains have been replaced by a dense system of channels, dikes, paddy fields, and aquaculture ponds, resulting in floodplain compartments protected by ring dikes. The agricultural productivity depends on the sediment and associated nutrient input to the floodplains by the annual floods. However, no quantitative information regarding their sediment trapping efficiency has been reported yet. The present study investigates deposition and erosion based on intensive field measurements in three consecutive years (2008, 2009, and 2010). Optical backscatter sensors are used in combination with sediment traps for interpreting deposition and erosion processes in different locations. In our study area, the mean calculated deposition rate is 6.86 kg/m² (≈ 6 mm/year). The key parameters for calculating erosion and deposition are estimated, i.e. the critical bed shear stress for deposition and erosion and the surface constant erosion rate. The bulk of the floodplain sediment deposition is found to occur during the initial stage of floodplain inundation. This finding has direct implications on the operation of sluice gates in order to optimize sediment input and distribution in the floodplains. Copyright © 2013 John Wiley & Sons, Ltd.     

Controls of 234Th removal from the oligotrophic ocean by polyuronic acids and modification by microbial activity

To gain new insights into the variability of particulate organic carbon (POC) fluxes and to better understand the factors controlling the POC/²³⁴Th ratios in suspended and sinking particulate matter, we investigated the relationships between POC/²³⁴Th ratios and biochemical composition (uronic acids, URA; total carbohydrates, TCHO; acid polysaccharides, APS; and POC) of suspended and sinking matter from the Gulf of Mexico in 2005 and 2006. Our data show that URA/POC in sediment traps (STs), APS/POC in the suspended particles, and turnover times of particulate ²³⁴Th in the water column and those of bacteria in STs inside eddies usually increased with depth, whereas particulate POC/²³⁴Th (10–50 μm) and the sediment-trap parameters (POC flux, POC/²³⁴Th ratio, bacterial biomass, and bacterial production) decreased with depth. However, this trend was not the case for most biological parameters (e.g., phytoplankton and bacterial biomass) or for the other parameters at the edges of eddies or at coastal-upwelling sites.In general, the following relationships were observed: 1) ²³⁴Th/POC ratios in STs were correlated with APS flux, and these ratios in the 10–50 μm suspended particles also correlated with URA/POC ratios; 2) neither URA fluxes nor URA/POC ratios were significantly related to bacterial biomass; 3) the sum of two uronic acids (G2, glucuronic, and galacturonic acid, which composed most of the URA pool) was positively related to bacterial biomass; and 4) the POC/²³⁴Th ratios in intermediate-sized particles (10–50 μm) were close to those in sinking particles but much lower than those in > 50 μm particles. The results indicate that acid polysaccharides, though a minor fraction (~ 1%) of the organic carbon, act more likely as proxy compound classes that might contain the more refractory ²³⁴Th-binding biopolymer, rather than acting as the original ²³⁴Th “scavenger” compound. Moreover, these acid polysaccharides, which might first be produced by phytoplankton and then modified by bacteria, also influence the on-and-off “piggy-back” processes of organic matter and ²³⁴Th, thus causing additional variability of the POC/²³⁴Th in particles of different sizes.     

越南东北部Cat Ba岛泥盆系-石炭系过渡层的初探

The Pho Han Formation is exposed on southern Cat Ba Island, Hai Phong Province in northeastern Vietnam, and intercalates the Devonian and Carbonif-erous (D-C) boundary (Ta and Doan, 2007; Komatsu et al., 2012). The D-C boundary section consists mainly of limestone beds, numbered from 1 to 167, interca-lated with alternating black organic-rich shales. The limestone yields abundant brachiopods, crinoid-stems and conodonts. Preliminary investigations on strati-graphy (conodont biostratigraphy and δ13C) and sedi-mentology of beds 113-133 were undertaken in this study.     

Analytical Expression for Vertical Stress within an Inclined Mine Stope with Non-parallel Walls

Arching is a phenomenon that occurs in many situations in geotechnical engineering. When underground mine stopes are backfilled, a significant fraction of the self-weight of the backfill is carried by the side walls. As a result, the vertical stress at the bottom of the stope is significantly less than its overburden pressure. Few analytical expressions published in the literature can be used to determine the vertical stresses of stope with parallel walls. The objective of this paper is to extend the analytical solution previously developed by the authors to long plane-strain stopes with non-parallel walls with both slopes leaning to the same side. Different combinations of wall inclination are examined using the new analytical expression developed. To validate the analysis, the proposed results are compared with numerical model results. The results show that the proposed analytical expression is capable of estimating the vertical stress within mine stopes when the inclination of the hangingwall to the horizontal (α) is less than that of footwall (β). An important behavioural trend for the stress distribution is observed, where with the same overburden pressure and base width, the stress magnitude experienced by fill material significantly varies depending on the wall inclination.