Terrestrial discharge influences microbioerosion and microbioeroder community structure in coral reefs

Microbioerosion rates and microbioeroder community structure were studied in four Kenyan protected coral-reef lagoons using shell fragments of Tridacna giant clams to determine their response to the influence of terrestrial run-off. Fourteen different microbioeroder traces from seven cyanobacteria, three green algae and four fungi species were identified. The river discharge-impacted reef and ‘pristine’ reef showed similar composition but higher microbioeroder abundance and total cyanobacteria- and chlorophyte-bioeroded areas when compared with the other study reefs. Cyanobacteria dominated during the north-east monsoon (NEM) relative to the south-east monsoon (SEM) season, with algae and cyanobacteria being major microbioeroders in the river-impacted and pristine reefs. The rate of microbioerosion varied between 4.3 g CaCO3 m^?2 y^?1 (SEM) and 134.7 g CaCO₃ m^?2 y^?1 (NEM), and was highest in the river-impacted reef (127.6 g CaCO₃ m^?2 y^?1), which was almost double that in the pristine reef (69.5 g CaCO₃ m^?2 y^?1) and the mangrove-fringed reef (56.2 g CaCO₃ m^?2 y^?1). The microbioerosion rates measured in this study may not be high enough to cause concern with regard to the health and net carbonate production of Kenya’s coral reefs. Nevertheless, predicted increases in the frequency and severity of stresses related to global climate change (e.g. increased sea surface temperature, acidification), as well as interactions with local disturbances and their influence on bioerosion, may be increasingly important in the future.     

南海IODP 349航次基底玄武岩中碳酸盐岩脉的岩石学特征*

国际大洋发现计划(International Ocean Discovery Program, IODP)349航次在南海东部次海盆和西南次海盆残留扩张脊附近的U1431和U1433站位首次钻取基底玄武岩, 通过对16块基底玄武岩内的碳酸盐岩脉薄片镜下观察以及激光拉曼光谱分析, 揭示碳酸盐矿物为方解石和文石, 为典型的洋壳低温热液蚀变次生矿物。U1431站位碳酸盐岩脉为独立的方解石脉、文石脉交替出现; 而U1433站位则存在方解石脉、文石脉和方解石-文石共生脉三种情况。此外, U1431站位在基底~42.1m处出现了平行的方解石脉和文石脉, 揭示U1431存在不同来源热液的多期活动, 即可能存在多次或多阶段不同的热液注入。U1431和U1433站位的碳酸岩脉中, 文石的矿物集合体形状基本一致, 呈块状、纤维状和放射纤维状; 而方解石存在差异, U1431的方解石以斑块状、块状、粒状和纤维状出现, 而U1433的方解石仅出现块状。U1431站位的碳酸盐岩脉的丰度明显高于U1433站位。这些均揭示U1431站位的低温热液活动强, 而U1433站位则相对弱。两个站位的热液活动不同很可能是由于区域地质环境的差异造成——U1431附近的巨大海山为其提供了热液补给, 而U1433远离热液的补给/渗漏点。     

颗粒状纳米碳酸钡锶钙的研制

介绍一种气-液相合成技术合成氧化物阴极用三元碳酸盐,研究沉淀温度、浓度及搅拌速率对合成碳酸钡锶钙结晶形貌的影响,分析其结晶过程.通过优化合成溶液温度及合成浓度,控制碳酸盐的成核和生长速率,合成了一种颗粒状纳米三元碳酸盐,并进行直流发射测试.实验表明,这种纳米碳酸盐能明显提高氧化物阴极的发射性能.     

低扩散系数对Pd77 Cu6 Si17合金易非晶化的影响

采用激光熔凝技术,研究了Pd₇₇Cu₆Si₁₇合金快速凝固组织的演变规律.研究表明:随着生长速度的增大,Pd₇₇Cu₆Si₁₇合金晶体生长组织形貌发生了Pd₃Si枝晶+共晶-ξ枝晶+共晶-共晶团簇-规则共晶-非晶的转变;共晶失稳即非晶形成的临界生长速度为6 mm/s,最小层片间距为35 nm.通过与Al-25 wt%Sm,Al-32.7 w     

浙江省衢州市上方镇重钙方解石矿工艺指标影响因素

重质碳酸钙的白度和色相值(Lab)是最重要的工业指标,但影响因素尚不清楚.本文通过扫描电镜、粉晶X射线衍射(XRD)和电感耦合等离子体发射光谱(ICP-OES)等分析手段,对浙江衢州上方镇的重钙方解矿石进行了研究,以期阐明重质碳酸钙白度和色相的影响因素.结果表明,矿石随研磨粒度的减小白度逐渐增加,在100～400目,白...     

Theoretical analyses of acidization dissolution front instability in fluid‐saturated carbonate rocks

This paper presents an instability theory that can be used to understand the fundamental behavior of an acidization dissolution front when it propagates in fluid‐saturated carbonate rocks. The proposed theory includes two fundamental concepts, namely the intrinsic time and length of an acidization dissolution system, and a theoretical criterion that involves the comparison of the Zhao number and its critical value of the acidization dissolution system. The intrinsic time is used to determine the time scale at which the acidization dissolution front is formed, while the intrinsic length is used to determine the length scale at which the instability of the acidization dissolution front can be initiated. Under the assumption that the acidization dissolution reaction is a fast process, the critical Zhao number, which is used to assess the instability likelihood of an acidization dissolution front propagating in fluid‐saturated carbonate rocks, has been derived in a strictly mathematical manner. Based on the proposed instability theory of a propagating acidization dissolution front, it has been theoretically recognized that: (i) the increase of the mineral dissolution ratio can stabilize the acidization dissolution front in fluid‐saturated carbonate rocks; (ii) the increase of the final porosity of the carbonate rock can destabilize the acidization dissolution front, while the increase of the initial porosity can stabilize the acidization dissolution front in fluid‐saturated carbonate rocks; (iii) the increase of the mineral dissolution ratio can cause an increase in the dimensionless propagation speed of the acidization dissolution front; (iv) the increase of the initial porosity can enable the acidization dissolution front to propagate faster, while the increase of the final porosity can enable the acidization dissolution front to propagate slower in the acidization dissolution system. Copyright © 2012 John Wiley & Sons, Ltd.     

我国首次发现的纤碳铀矿

本文报道的纤碳铀矿产于湖南某花岗岩型铀矿床氧化带中。纤碳铀矿是一种铀酰碳酸盐矿物,在中国是首次发现。本文作了系统的矿物研究并与国外资料作了对比。     

Bauxite development in the North Apuseni mountains, western Romania

The stratigraphic and palaeogeomorphologic conditions of bauxite formation in the North Apuseni mountains are related to the geotectonic evolution of western Romania during the Late Jurassic and Early Cretaceous. Bauxitization, accumulation and preservation of the bauxites were directly associated with karst development in the area under study. The petrographic and mineralogic nature of the bauxite deposits reveal superimposed aliagenetic, catagenic and, locally, metamorphic features. A comparative analysis of the principal chemical components of the different bauxite-bearing zones of the North Apuseni mountains are used to show similar development.     

Organic geochemical studies of a recent Inner Great Barrier Reef sediment—I. Assessment of input sources

The concentration of solvent-extractable (SE) and bound hydrocarbons, ketones, alcohols, sterols, monocarboxylic acids, hydroxyacids and α,ω-dicarboxylic acids of a surface sample (0–2.5 cm) from a recent carbonate tropical sediment taken at 60ft (18m) depth north-west of the Low Isles, North Queensland, are reported in detail. n-Alkanes are a minor constituent in the SE and bound hydrocarbon fractions with the major component being unresolved complex hydrocarbon material which is not an anthropogenic input. 6,10,14-Trimethylpentadecan-2-one derived from chlorophyll, as well as phytol, were identified as major components of the ketone and alcohol constituents. No chlorophyll pigments or pigmented degradation products were present, implying degradation before incorporation into the sediment. This conclusion is consistent with evidence for higher-plant input in which all sensitive lipids have been degraded before incorporation. SE and bound fractions have been studied in detail and show considerable differences probably arising from the importance of viable biomass in the SE fraction. Inputs to the sediment are determined as higher plants, algae, bacteria, fungi and meiofauna in descending order of importance.