Hydrogeochemistry of two river main floodplain lakes,Hessia, FR Germany

Two lakes, Lake Gänseweiher (LGW) and Lake Fechenheimer Weiher (LFW) occupy groundwater filled abandoned gravel pits which serve as fishing grounds and are part of recreational areas, respectively.Both lakes are cut into a near-surface groundwater aquifer, which is located in the pleistocene River Main gravel terrace t₆. They are sealed at the base by miocene clays and above by overlying flood deposits of the River Main. The latter provide protection from pollutants derived from wet and dry deposition of atmospheric contaminants.Groundwater chemistry determines the pool of dissolved constituents in lake water. The temporal and spatial distribution patterns of chemical compounds in lake water are brought about by endo-biogenic processes, of which the indicators are nitrate-nitrogen and dissolved silica. The latter illustrates an instantaneous response to pulses of diatom blooms.Both lakes are eutrophic (polytrophic) according to the classification guidelines presented in literature.     

Origin of loess-like silt in Northern Jakutia,USSR

Sediments of different lithological composition of a common feature — a relict system of thick syngenetic ice wedges — are called ice complexes. Three types of ice complex are distinguished in N Jakutia, with different topographic roles. They formed in the second part of the Upper Pleistocene. Author found that it is not the matter of transportation that accounts for the formation of the main features of their composition, but the specifics of lithogenesis first of all determined by the conditions of cryogenic weathering.     

Community perception and participation,prospects in management of forests in marginal lands of Sudan

Fuelwood Development for Energy in Sudan project (GCP/SUD/033/NET) is undertaking research to formulate management plans for Sudan ecologically marginal forests. Rawashda and Wad Kabu forests are taken as examples to initiate sound plans. It is believed that the study of socio-economic parameters of forests users is an essential component to achieve such plan. This study is also fundamental for attaining an integrated land use system, as a prime option of natural resource use. This study is, consequently, aiming at:

1. Providing the base line information of the different communities identified in Tab 3 and using the two forests.
2. Examine people's attitude, perception, participation options in maintenance and management of the two forests. Such parameters are also vital for adoption of an integrated land use strategy in the future.
3. Based on (i) and (ii) to outline broadly the most relevant plan of management land use strategy to be adopted, based on community self-generated options of institutions and objectives of use.

The main findings in this context can be summarized in the following:

1. A complex pattern of economic activities (Tab 3) ranging from pure pastoral nomadism to modern mechanized farming, still characterized by combination of related activities of agricultural/livestock breeding, agriculture/forest resource use, etc. This diversity in activities, which is mostly dependent on the natural resource base, gives a sound base for any option of an integrated land use system.
2. Perception and attitude analysis have revealed a growing awareness of the role of the forest resources in the economy as source of grazing, domestic needs and source of income. This awareness is supported by willingness to participate in any integrated land use plan, yet from a different stand point and objective. Preference of self-generated channels is quite evident, but with a specified role of the government.
3. The major finding is that, and among all communities, the situation is mature for action, although at different levels.

Therefore, each community could be approached along relevant lines of action, as an initial phase before attaining a comprehensive land use plan. On-farm trials (OFTs) or in-herd trials seem to be more relevant compared with expert controlled trials. Any plan of action needs to be preceded by revision of present land tenure systems, establishing grass-root institutions, reorientation of concerned government departments, intensive extension programme and careful formulation of projects, execution and follow-up plans. Such steps need to be geared to narrow the ‘Perception gap’ of development between participants or users and planners.     

Compositional variations and reflectance of the common platinum-group minerals

Summary A detailed study of the compositional variations of 22 different platinum-group minerals, of Os-Ir-Ru- and Pt-Fe alloys, Pt-Pd- and Ru-Os-Ir sulfides, RhIr-Pt sulfarsenides and Pd-Pt tellurides from various deposits resulted in verification of extensive solid solution series and element substitution within different mineral groups. On the basis of representative new microprobe analyses and related spectral reflectance curves of the platinum-group minerals investigated significant correlations between chemical composition and reflectance are discussed.

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Chemische Variation und Reflexion der wichtigsten Minerale der Platingruppe

Zusammenfassung Die Untersuchung der chemischen Variation bei 22 Platinmineralen aus der Gruppe der Os-Ir-Ru- und Pt-Fe-Legierungen, Pt-Pd- und Ru-Os-Ir-Sulfide, Rh-Ir-Pt-Sulfarsenide und Pd-Pt-Telluride ergibt signifikante Mischkristallbildung und Element-Substitutionen innerhalb der unterschiedlichen Mineralgruppen. Anhand neuer Mikrosondenanalysen und der zugehörigen spektralen Reflexionskurven der betreffenden Platinminerale werden die Korrelationen zwischen Chemismus und Reflexion diskutiert.

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With 17 Figures

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Contribution to the Ore Mineralogy Symposium (IMA/COM) at the 14th General Meeting of the International Mineralogical Association, at Stanford, California, in July, 1986.     

Water for food production in Sub-Saharan Africa

Water control is an essential requirement if food and energy crises in Africa are to be resolved on a sustainable basis. The paper reviews the problems and prospects associated with the expansion of irrigation in Africa, where experiences with large and medium scale water management have been of comparatively recent origin. The present status of water development and management issues are approached carefully and cautiously, they can make an important and lasting contribution to the resolution of Africa's food crisis.     

The effect of climate on the growth of early maize at Kabba,Nigeria

This study attempts regression/correlation analysis between maize yield and weather variables based on data analysed for the entire growing season and the different physiological stages of the crop's growth for Kabba in the wet sub-humid climate of Nigeria. The implications of the relationships obtained are examined for maize growth at the station.     

The structure of freedite,Pb8Cu(AsO3)2O3Cl5

Summary The structure of freedite, Pb₈Cu(AsO₃)₂O₃Cl₅, [a = 13.578(2),b = 20.099(3),c = 7.465(1)Å; = 105.73(1)°; space group C2/m; Z = 4] was determined by direct methods and Fourier summations. The refinement of the atomic coordinates and thermal parameters-the metal atoms anisotropic, the remaining atoms isotropic-yielded anR value of 0.086 (R _w = 0.061). The five crystallographically independent Pb atoms are each surrounded by three resp. four O atoms and four Cl atoms. The novel feature of this structure are formal [(AsO₃)₂(CuCl)₂(AsO₃)₂] groups, in which the Cu atoms are tetrahedrally coordinated to two Cl and two As atoms [Cu-Cl = 2.43(8)Å2 × , Cu-As = 2.32(1)Å2 ×]. The mineral is considered to contain Cu(I) and As(III) atoms linked together by covalent Cu-As bonds. The formal groups mentioned are bound to the Pb atoms via Cl and O atoms.

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Die Struktur des Freedits, Pb₈Cu(AsO₃)₂O₃Cl₅

Zusammenfassung Die Struktur des Freedits, Pb₈Cu(AsO₃)₂O₃Cl₅, [a = 13,578(2),b = 20,099(3),c = 7,465(1)Å; = 105,73(1); Raumgruppe C2/m;Z = 4] wurde anhand direkter Methoden und Fouriersummationen bestimmt. Die Verfeinerung der Ortskoordinaten und der Temperaturparameter - Metallatome anisotrop, übrige Atome isotrop -ergab einenR-Wert von 0,086 (R _w = 0,061). Die fünf kristallographisch verschiedenen Pb-Atome werden von drei bzw. vier O-Atomen sowie jeweils vier Cl-Atomen umgeben. Ein neues Bauprinzip dieser Struktur sind formale [(AsO₃)₂(CuCl)₂(AsO₃)₂]-Gruppen, in denen die Cu-Atome durch zwei Cl- und zwei As-Atome tetraedrisch umgeben sind [Cu-Cl= 2,43(8)Å2 ×, Cu-As = 2,32(1)Å2 x]. Es wird angenommen, daß in diesem Mineral Cu(I)- und As(III)-Atome vorliegen, die über kovalente Bindungen verknüpft sind. Diese formalen Gruppen sind über die Cl- und O-Atome an die Pb Atome gebunden.

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With 2 Figures     

Metallogenesis of cratonic oolitic ironstone deposits in the Bled el Mass,Azzel Matti,Ahnet and Mouydir basins,Central Sahara,Algeria

The Bled el Mass, Azzel Matti, Ahnet and Mouydir areas are located in the northwest of the Touareg Shield (Central Sahara, Algeria). Within the Devonian sedimentary formations, nine oolitic ironstone occurrences of EXID type (Extensive Ironstone Deposition) are interbedded.Their mineralogical composition is characterized by four different paragenetic associations: P1 (Chamosite — magnetite — maghemite — goethite); P2 (chamosite — hematite — goethite — calcite); P3 (chamosite — hematitegoethite — quartz); and P4 (chamosite — hematite — goethite). Using textural analysis, four main ironstone facies are distinguished: FOD (ooliths scattered in a detrital groundmass); FOND (ooliths scattered in a non detrital groundmass); FOC (cemented ooliths) and FMC (microconglomeratic facies).Primarily developed in calm conditions by intrasedimentary processes within an iron-rich silicated mud, in lagoons or embayments, ooliths subsequently acquired a detrital character.The ironstone deposition seems to be induced by several pulses of sedimentation through the Devonian and is considered as indicator of sedimentary subcycles. Therefore, the oolitic ferriferous sediments indicate a cratonic sedimentation on the borders of a large epicontinental sea. The source of the iron could be a remote southern continent, probably the Pan-African mobile belt of Nigeria and the Congo Shield.The ironstones of the Central Sahara can be considered as an important branch of the North-African Oolitic Ironstone Belt, extending from Rio de Oro to Libya.

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Zusammenfassung Die Gebiete des Bled el Mass, des Azzel Matti, des Ahnet und des Mouydir, liegen im Nordwesten des Touaregschildes (Zentral Sahara, Algerian). Neun eisenoolithische Horizonte sind hier in die devonischen Sedimente eingeschaltet. Ihr Mineralinhalt kann durch vier verschiedene Paragenesen charakterisiert werden:P1=Chamosit + Magnetit + Maghemit + Goethit; P2= Chamosit + Hämatit + Goethit + Kalzit; P3=Chamosit + Hämatit + Goethit + Quartz; P4=Chamosit + Hämatit + Goethit.Vier vererzte Fazies Typen treten auf: FOD: (die Ooide sind in einer detritischen Marix eingelagert); FOND: (die Ooide sind in einer nichtdetritischen Matrix eingelagert); FOC: (die Ooide sind verfestigt); FMC: microkonglomeratische Fazies.Die Ooide entwickeln sich in ruhigen Bedingungen, in Lagunen oder Meerbusen, durch die Bildung von Konkretionen im Sediment aus einem silikatischen und eisenreichen Schlamm; sie werden dann wie detritische Komponenten aufgenommen und transportiert.Die eisenoolitischen Ablagerungen scheinen durch mehrere Sedimentationsphasen während des Devons entstanden zu sein; so können sie als Zeichen von Sedimentmikrozyklen betrachtet werden. Diese oolitischen Sedimente sind charakteristisch für eine Kratonsedimentation am Rand eines breiten, epikontinentalen Meeres.Der Usprung des Eisens ist in einem südlichen Kontinent zu suchen, wahrscheinlich in dem mobilen panafrikanischen Gebirge von Nigeria, oder auf dem kongolesischen Schild.Diese Erze der Zentralsahara können als ein wichtiger Zweig des Eisengürtels betrachtet werden, der sich in Nordafrika von Rio de Oro bis Libyen erstreckt.

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Résumé Les régions du Bled el Mass, de l'Azzel Matti, de l'Ahnet et du Mouydir sont situées au Nord-Ouest du Bouclier Touareg (Sahara Central, Algérie). Neuf niveaux de minerai de fer oolithique sont interstratifiés dans les formations sédimentaires du Dévonien.Quatre différentes paragenèses caractérisent la composition minéralogique de ces minerais. P1 (chamosite — magnétite — maghémite — goethite); P2 (chamosite — hématite — goethite — calcite); P3 (chamosite — hématite — goethite — quartz) et P4 (chamosite — hématite — goethite). Quatre facies minéralisés ont été en évidence: FOD (oolithes dispersées dans une matrice détrìtique); FOND (oolithes dispersées dans une matrice non détritique); FOC (oolithes cimentées) et FMC (faciès microconglomératique).Développées dans des conditions calmes par concrétionnement intrasédimentaire dans une boue silicatée riche en fer, dans des lagons ou des baies, les oolithes vont acquérir par la suite un comportement détritique.Les dépôts de minerai oolithique semblent avoir été induits par plusieurs pulsations sédimentaires durant le Dévonien et peuvent être ainsi considérés comme des marqueurs de microcycles sédimentaires.Ces sédiments oolithiques sont caractéristiques d'une sédimentation cratonique, sur les bords d'une mer épicontinentale étendue. La source du fer est à rechercher dans un continent situé au Sud, probablement dans la chaîne mobile Pan-Africaine du Nigeria et le Bouclier du Congo.Ces minerais de fer oolithiques du Sahara Central peuvent être considérés comme une branche importante de la ceinture ferrifère Nord africaine, qui s'étend du Rio de Oro à la Libye.

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- ( , ) Bled el Mass, Azzel Mati, Ahnet Mouydir. 9 , . :₁= — — — ë; ₂ = — — ë — ; ₃= — ë — ; ₄= — — ë. 4 : DFOD — ; FOND — , ; FOC — ; FMC — . , , , ; . , . , . ., , , , , — , Rio de Oro .

     

Polymetamorphose und Deckenbau der Strand-Halbinsel/SW-Norwegen

Zusammenfassung Die Metamorphite der Halbinsel Strand / SW-Norwegen gehören zu einem Deckensystem präkambrischer Gesteine, das während der kaledonischen Orogenese von NNW her auf den Baltischen Schild geschoben worden ist (Sigmond Kildal 1978). Eine hangende Deckeneinheit umfa\t Metagranite, Melagabbroide und Gneise. Ihr granulitfazieller Mineralbestand (Metamorphosealter 1,5 Milliarden Jahre) wurde wahrscheinlich vor 1,18 Milliarden Jahren grünschieferfaziell retrograd überprägt. Die Decke ist nur noch in kleinen Erosionsinseln vorhanden. Eine liegende Dekkeneinheit besteht aus metasedimentären Gesteinen. Sie weist Mineralbestände der höheren Amphibolitfazies auf, die ebenfalls grünschieferfaziell überprägt wurden. Die Al^VI-Gehalte der bei beiden metamorphen Prozessen gebildeten Amphibole deuten bei Anwendung eines Diagramms vonRaase (1974) an, da\ die retrograde Metamorphose hier bei höheren Drücken ablief als die ältere Metamorphose. Ein Gesamtgesteinsalter von 1,16 Milliarden Jahren scheint für diese grünschieferfazielle Metamorphose das gleiche orogene Ereignis anzuzeigen wie für die hangende Einheit. Produkt der schwachen kaledonischen Metamorphose (400 Millionen Jahre) ist Stilpnomelan, der auch im Grundgebirge des Baltischen Schildes auftritt.

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The Strand Peninsula, Stavanger district, Southwestern Norway, has become well known, when V. M.Goldschmidt (1920) published his hypothesis of regional metasomatism. All rocks of the Strand area were assumed to be situated in autochthonous position. The main point ofGoldschmidt's hypothesis was progarde metamorphism of argillaceous sediments and their transformation to albite schists and plagioclase gneisses by metasomatic solutions given off from intruded trondhjemitic magmas.However, in contrast toGoldschmidt's ideas, the granitoid sill of the Ormakam-Moldhesten area, Strand Peninsula, and its wall rocks, which played an important role inGoldschmidt's discussion, are now found to be parts of a polymetamorphous thrust unit.Granulite facies assemblages, mainly consisting of orthopyroxene +clinopyroxene+plagioclase+hastingsite±orthoclase and quartz, have been partially replaced by lowgrade assemblages. Probably, the high-grade metamorphism has an age of about 1.5 Ga (Andresen &Heier 1975) whereas the age of the greenschist facies event may be conform to an orogenic cycle at about 1.15 Ga (Sigmond Kildal 1978).A lower nappe, covering the Strand Peninsula for its most parts, was subject of a petrologic re-examination using the microscope and the microprobe analyser. Its contacts with the hanging nappe as well as those with the underlying gneissic basement are characterized by thrust planes and horizons of phyllonites and cataclasites inside of the nappe and by local brecciation in the uppermost zones of the basement.The rocks of the lower nappe have been formed a long with the upper amphibolite facies as indicated by the following mineral assemblage: andesine + hastingsite and Mg-hornblende + quartz +biotite.Obviously, an inverse order of temperature regimes is recognizable in the allochthonous units. Maximum temperature of the upper nappe reached 800C (Müller &Herbert 1984) whereas T_max of the lower nappe did not exceed 750C.Using a diagram ofRaase (1974) the Al^VI-contents of the primary hastingsitic hornblendes of the lower nappe rocks indicate pressures which range distinctly below 5 kbars, whereas the secondary pargasitic hornblendes were formed at pressures of about 5 kbars. Probably the thrusting happened before the formation of secondary hornblendes took place. The load pressure in the lower nappe (< 5 kbars) was distinctly increased when the upper nappe was thrusted upon the lower one. Consequently the Al^VI-contents of secondary hornblendes indicate increased pressure ( 5 kbars).In the gneisses of the lower nappe late fractures were filled by stilpnomelane, chlorite and quartz. Very probably this depends on thrust movements during the Caledonian orogeny.Verschure et al. (1980) found a similar stilpnomelane formation in adjacent terrains of the basement and proposed a weak Caledonian metamorphism of about 400 my.

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Résumé Les roches métamorphiques de la presqu'Île de Strand (sud-ouest de la Norvège) appartiennent à un empilement de nappes formées de roches pré-cambriennes et charriées vers le SSE sur le bouclier baltique au cours de l'orogenèse calédonienne (Sigmond Kildal 1978).Une nappe supérieure comprend des métagranites, des mélagabbroÏdes et des gneiss. Leurs paragenèses, du facies des granulites (âge du métamorphisme: 1,5 Ga) ont été rétromorphosées dans le facies des schistes verts il y a probablement 1,18 Ga. Cette nappe ne subsiste qu'en petits fragments épargnés par l'érosion.Une nappe inférieure est composée de roches métasédimentaires. Ces roches présentent des paragenèses du faciès supérieur des amphibolites, également rétromorphosées dans le facies des schistes verts. L'application du diagramme de Raase (1974) aux teneurs en Al^VI des amphiboles formées lors des deux processus métamorphiques indique que la rétromorphose s'est déroulée à une pression supérieure à celle du métamorphisme ancien. Un âge de 1,16 Ga sur roche totale semble indiquer que le mÊme processus orogénique a servi de cadre à la rétromorphose en facies des schistes verts dans les deux nappes.Du stilpnomélane, présent tant dans la nappe inférieure que dans le bouclier baltique autochtone, témoigne d'un métamorphisme calédonien (400 Ma) de faible degré.

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Strand ( ) , NNW (Sigmond KILDAL, 1978). , . - 1,5 , 118 , . . . , . Al^VI , , RAASE (1974) , , . 1,6 , , , . (400 ) , .