Mineralogy,opal, and manganese of middle and late quaternary sediments of the Zaire (Congo) deep-sea fan: Origin and climatic variation

X-ray diffraction and X-ray fluorescence measurements on 5 piston cores provided data on the mineralogy and chemistry of sediments of the last 500 000 years. Opal contents are up to 60%. They increase and opal accumulation rates decrease with increasing waterdepth. Downcore opal variations, with maxima in glacial intervals of both contents and accumulation rates, form a combined signal of ocean fertility and opal preservation, and are controlled by climatic variations.XRD measurements, with an internal standard, show parallel distribution patterns of the major minerals. This demonstrates that the components are dominated by varying contributions of hardly detectable poorly crystallized smectites. The supply from the Zaire river consists of kaolinite, poorly crystallized smectite, quartz, and minor amounts of illite and gibbsite. The continental shelf is the source of well crystallized smectite and admixtures of zeolite and cristobalite coming from Tertiary opal-rich layers. The river contribution is largest in interglacial sediments and the shelf contribution in glacial sediments. Illite is indicative of aridity, and its distribution points to expansions of the African deserts during the glacial stages 2 and 4 and the interstadial around 150 000 yBP. A decrease in supply of shelf minerals, coinciding with a general decrease in sedimentation rate ∼ 350 000 yBP, suggests that a long-term climate warming occurred at that time.High smectite crystallinity values and the presence of reworked pyrite in a continental slope core show the occurrence of downslope transport. Turbidites in the upper fan are mainly of river origin, but minor contributions of cristobalite and zeolite originate from shelf transport intercepted by the Zaire canyon. All cores contain authigenic pyrite, the turbidites also reworked pyrite.In the pelagic and hemipelagic cores roughly 60% of the SiO₂ is opal. The remainder forms part of the clay minerals together with Al. Fe and Ti are associated with the clay minerals. Mn is concentrated in subsurface Mn spikes. Fossil spikes occur in a core at 5500 m and were buried by turbidities. Mn burial rates are high in glacial intervals. Among other things this may due to climate controlled variations in the composition of the accumulating sediments, or to increased bioturbation related to increased plankton production. In all core samples of the anaerobic zone small amounts of MnCO₃ are present, in one sample 12% of MnCO₃ was found.     

Status of yam (Dioscorea spp.) in the Democratic Republic of Congo

Yam is an important tuber crop with enormous potential to enhance rural sustenance and livelihood in DRC. However, studies to enhance its genetic improvement are very far from sufficient with only a handful of information available on the crop. Yam has been treated as an orphan crop compared to contemporary crops such as cassava and sweet potato which have adapted to different cropping systems and become widespread in production. The lack of research attention to address the major production challenges has further decreased the value and potential of the crop compared to its contemporaries. These production constraints include lack of adequate quality planting materials, low yield potential, poor resistance/tolerance to yam mosaic and anthracnose diseases and ultimately poor tuber quality attributes focusing on tuber taste, flesh oxidation and dry matter contents of the majority of the farmers preferred varieties. In this review, we evaluated the status of yam in DRC and presented the needful activities to be incorporated for its improvement. Diversity has however been maintained mainly through ennoblement efforts in house gardens and small farmlands using traditional farming methods. Studies from other nations where yam has been successful with prominence in characterization and genetic improvement brought to light the need for DRC to consider yam as a staple carbohydrate food source, even to the extent of modifications in food public policy. Reversal of the yam's current stigma is a challenge to the scientific community and the population in general.     

Oxygen and carbon isotope analyses of a late quaternary core in the Zaire (Congo) fan

The δ¹⁸O of the planktonic foraminifer Globigerinoides ruber reflects both changes in temperature (∼3°C) and in δ¹⁸O water, while the isotope analyses of the benthic species Uvigerina peregrina and Bulimina aculeata predominantly reflect the wax and wane of ice sheets. Therefore, the curve of the benthic species is more smoothed and reached its postglacial minimum later than the curve of Globigerinoides ruber. The early Holocene increase in the δ¹³C occurs earlier in the bottom water species Uvigerina peregrina than in the surface water species Globigerinoides ruber.     

谢君魔芋染色体数目的观察研究

（云南农业大学魔芋研究所,云南昆明 650201）     

贵州蔷薇属一新变种——光枝无子刺梨

报道中国贵州蔷薇科蔷薇属一新变种:光枝无子刺梨(Rosa sterilisS. D. Shi var. leioclada M. T. An,Y. Z. Cheng et M. Zhong)。     

贵州蔷薇属一新变种——光枝无子刺梨

报道中国贵州蔷薇科蔷薇属一新变种:光枝无子刺梨(Rosa sterilis S.D.Shi vat.leioclada M.T.An.Y.Z.Cheng et M.Zhong).