Lower riphean low-carbonaceous shales in the southern urals: Raw material for the manufacture of porous rubble

A property of swelling on heating to yield firm lightweight granules has first been revealed for lowcarbonaceous shales (LCS) from the Riphean stratotype in the Bashkirian Megaanticlinorium, Southern Urals. These granules possess all technological properties of “keramzite” or claydite (an artificial, expanded clayey material) and can successfully substitute this material. Moreover, the procedure of their manufacture, analogous to the manufacture of “shungizite” (an artificial carbonaceous-clayey material) from Lower Proterozoic clayey rocks of Karelia, is more economical than that for keramzit. Productive beds of the homogeneous LCS make up extended bodies tens of meters thick. At the present time, they can be used as cover rocks during the exploitation of the Bakal siderite deposits. The LCS represent fine-grained quartz-chlorite-sericite aggregates (with variable relationships between the major components), bearing fine-dispersed shungite in amounts of 0.5–1.0%. High-quality raw material of this kind is characterized by a fine-dispersed admixture of a mixed-layer clayey material bearing montmorillonite and vermiculite. Geological, lithological, mineralogical, and chemical prognostic criteria have been developed for the shungizite raw material. It has been concluded that this construction material, new for the Urals, is promising for industrial use     

A symposium on the genesis of till

A symposium on the genesis of till entitled Till/Sweden-76 was held in Stockholm 16–18 August 1976. This issue of Boreas contains most of the papers presented at the symposium.     

Basalts of unusual composition from the Chyulu Hills,Kenya

Five Ne-normative basalts are unusually rich in Cr, to a lesser degree in Co, and have very high La/Lu ratios and high contents of several excluded trace elements resembling kimberlites in these and other aspects. They seem to represent mantle-derived magmas, only slightly modified by shallow level crystal/liquid fractionation. Cr was apparently excluded from the crystalline phases in equilibrium with these magmas in the upper mantle.The Chyulu rocks differ in several respects from other Gregory Rift basalts, but closely resemble those from Jan Mayen Island near the Mid-Atlantic ridge. The generation of these unusual basalts is therefore not related simply to mantle composition or tectonic setting, but may reflect unusually high-T (1450°C), low-P (15–29 kbars) environments in the zones of last effective equilibration of these magmas with mantle rocks.     

Significance of Europium anomalies in silicate melts and crystal-melt equilibria: a re-evaluation

Although europium speciation in silicate melts partly reflects prevailing oxygen fugacities, melt composition and structure play the major role in determining Eu²⁺/ Eu³⁺ ratios and europium partitioning into mineral phases. Experimental evidence by different investigators on the magnitude of the compositional effect on Eu²⁺/Eu³⁺ provides consistent results only if account is taken of the oxygen buffer system employed in the experiments. The medium-dependent reduction of europium can be understood in terms of the preferential stabilization of Eu²⁺ by a strong aluminosilicate complex in the melt phase, and to a much lesser degree by metasilicate complexes. The stability of these complexes increases as the field strength of the associated cation species decreases. Hence Eu²⁺-aluminosilicate complexes are preferentially stabilized relative to trivalent lanthanides in melts of appropriate composition and their presence minimizes the enthalpy of the melt. The influence of these complexes is particularly pronounced in melts with a high feldspathic component and a strongly polymerized structure. Their petrogenetic influence is best documented through the behaviour of europium relative to the other lanthanides during anhydrous anatexis in high-grade metamorphic terrains and in the anomalous europium partition coefficients of phenocryst phases which formed during the crystallization of highly silicic magmas.     

Pseudoleucite in a Tinguaite from the Bearpaw Mountains, Montana

The article presents chemical analyses of the pseudoleuciteand groundmass of a pseudoleucite tinguaite, chemical analysesof the principal minerals, chemical estimates of the mode ofthe groundmass, and both chemical and micrometric modes of thepseudoleucite. The principal minerals are hedenbergitic acmite,a nepheline containing 2.3 per cent Fe₂O₃ and 7.9 per cent K₂O,and K-feldspar containing a little BaO and very little Na₂O.The micrometric mode of the pseudoleucite, in satisfactory agreementwith the chemical mode, is nepheline 29.8 per cent, K-feldspar66.2 per cent, acmite 3.0 per cent; the chemical mode of thegroundmass is nepheline 26.8 per cent, K-feldspar 46.6 per cent,and acmite 26.7 per cent. A new analysis of a nepheline fromthe Bancroft area, made to test the analytical procedure, isalso included.     

New data on the Albian-Cenomanian radiolarians from the Karai Formation (South India)

Radiolarians from the lower part of the Karai Formation (upper Albian-middle Cenomanian) are studied in detail for the first time. Among over 50 radiolarian species identified in the formation, there are Acaeniotyle amplissima (Foreman), Savaryella novalensis (Squinabol), S. quadra (Foreman), Vitorfus campbelli Pessagno, Archaeodictyomitra montisserei (Squinabol), Holocryptocanium barbui Dumitrica, Pseudoeucyrtis sp. cf. Ps. spinosa (Squinabol), Stichomitra communis Squinabol, Tubilustrionella transmontanum (O’Dogherty), and others. The discovered radiolarians are divided into the Halesium triacanthum-Orbiculiforma nevadaenis (late Albian-early Cenomanian), Crucella latum-Cryptamphorella micropora (late Albian?-early Cenomanian), and Becus sp. B-Godia concava (terminal Albian-middle Cenomanian) assemblages. In general, the Albian-Cenomanian radiolarians of South India are comparatively less diverse than the concurrent assemblages of the Mediterranean region and California. In taxonomic composition and morphological peculiarities, they are comparable with the Aptian-Albian radiolarians of Western Australia (Ellis, 1993). Consequently it can be postulated that sea basins of South India were situated during the Albian-Cenomanian in the temperate latitudes of the Southern Hemisphere.     

Melanterite and szomolnokite as weathering products of pyrite from the Bazhenovo Formation

Weathering of pyrite in the core recovered from black shales of the Bazhenovo Formation (Upper Jurassic-Lower Cretaceous) in the West Siberian marine basin promoted the successive formation of melanterite (FeSO₄ · 7H₂O) and szomolnokite (FeSO₄ · H₂O). Szomolnokite was detected in West Siberia for the first time.