How geological origin influences the quality of sand and the environmental impacts of its mining,Bahia state,Northeastern Brazil

The highly increasing demand for sand in Northeastern Brazil, due to governmental economic incentive focused to this region, has necessitated the opening of new extraction mines, generally without adequate environmental control. This study aimed to assess several sand extraction activities in the Recôncavo territory, Bahia state—area with high variability in sedimentary deposits—by evaluating the quality of the sand and the extraction impacts according to the geological basement. The methodology consisted of field research, using satellite images and maps for characterization, application of the environmental and economic impact checklists, and analysis of organic matter, particle size distribution, and salt content in 35 samples from different sand mines. The sands were classified as white sand (from Neossols/weathered aeolian sandstones), brown sand (from mature soils), and river sand. A strong relation between the geological origin and sand type and quality was established. Although the river sand appears to be the best option for extraction with regards to sand quality and low environmental impacts, the white sand derived from Jurassic sandstones is intensively extracted due to easy access, availability of wide deposits, and visual quality and homogeneity. However, the white sand has an inadequate particle distribution due to its poor gradation (aeolian selection of fine particle) and high environmental impacts due to its location in wet tropical ecosystem dominated by the Atlantic forest and the erosion of sandy soils. We demonstrated that the knowledge of lithology is fundamental for mapping new potential sand mines and minimizing the generated impacts.     

The colonisation of leaf litter by Chironomidae (Diptera): The influence of chemical quality and exposure duration in a subtropical stream

This study tested the hypothesis that the community composition of Chironomidae will change according to the duration of the exposure of plant leaves in a subtropical stream. In addition, we expected the chemical quality of the detritus to affect the association of Chironomidae with decaying plant materials. The chironomid colonisation of leaf litter from Campomanesia xanthocarpa and Sebastiania brasiliensis was assessed in a subtropical Atlantic forest stream. Litter bags containing leaves from these two species were incubated in the stream for 22 days. We identified 7245 invertebrates associated with the leaf detritus of both plant species (5110 were Chironomidae, 70.7% of the total). Thirteen genera of Chironomidae were identified, with Rheotanytarsus, Thienemanniella and Corynoneura the most abundant (94% of all Chironomidae collected). Chironomidae assemblages changed with the duration of incubation in the stream. The dissimilarity and the functional composition of the Chironomidae communities were related to the chemical composition of the detritus. The chemical components that best explained the composition of the fauna were tannins, the C:N ratio, calcium, and magnesium. However, the functional feeding groups were explained by the chemical variables organic matter and C:N. This study found that the exposure time of the detritus and therefore its level of degradation and chemical composition are important factors determining the characteristics of the Chironomidae assemblage in subtropical streams.     

Contrasting oxygen fugacity of I- and S-type granites from the Araçuaí orogen,SE Brazil: an approach based on opaque mineral assemblages

Mineralogy and Petrology - This study presents mineralogical characterization of opaque assemblages from I- and S-type granites from the Araçuaí orogen, southeastern Brazil that belong...     

圣安德烈斯断层南段大地震发生的准周期性

圣安德烈斯断层(美国加州)南段最后一次大地震距今已有153年了,而其平均震间间隔却仅为～100年.如果大地震的复发具有周期性,而并非随机发生或群集发生,则这个时间长度是很值得关注的,而且通常意味着概率意义上的地震危险性增大.遗憾的是,多数地震记录都很简单,这就限制了对单条断层上地震复发的分布特征的描述.本文利用加州Wr...