On the variability of the position of the equatorial electrojet axis in India

An examination of day-to-day and monthly mean positions of the electrojet axis in relation to the changes in the apparent solar declination, in the Indian equatorial region shows marked association between the two. For relatively quiet days, significant correlations are observed between the solar declination and each of the parameters, the northernSq focal latitude, the jet axis and the line of maximumSq(H). From the significant mutual association of these parameters, it has been suggested that the equatorial electrojet could be a part of the world-wideSq current system.     

Organochlorine residues,eggshell thickness,and nest success in barn owls from the Chesapeake Bay

Eggs of barn owls (Tyto alba) were collected from 18 nests in offshore duck blinds on the Maryland side of the lower Potomac River estuary in 1972 and 1973 and analyzed for organochlorine residues. DDE was found in 100% of the clutches, PCBs in 89%, and dieldrin in 78%. Eggshell thickness was inversely correlated with concentrations of DDE, DDD, and dieldrin residues. Six of the 18 clutches had mean DDE residues above 5 ppm, and eggshell thickness in these six clutches was significantly less (P<0.001) than in the other 12 clutches. The owls produced 1.7 young per active nest in 1973. This rate is slightly below the reproductive rate needed to maintain a stable population. An estimated 15% of the population carried concentrations of organochlorine residues that may have been detrimental to their reproduction. Passerine birds, taken extensively as food by a small proportion of the population, are believed to have been the source of elevated concentrations of organochlorines in these barn owls.     

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 highstand oolitic sequence and associated facies from a Late Triassic lake basin, south-west England

High energy, lake‐shoreline carbonate sequences are rarely documented in the geological record. However, one example occurs in the Upper Triassic Mercia Mudstone Group (MMG) of southern Britain. The MMG is one of a number of thick, non‐fossiliferous mudstone deposits associated with North Atlantic Mesozoic rift basins. The origin of the MMG mudstones is the subject of current debate, with marine, playa‐lacustrine and alluvial–aeolian models having been proposed. Shoreline features have been documented from the northern margin of the basin, but the rarity of such features elsewhere in the MMG has led many workers to doubt a lacustrine origin for the mudstones. Wave‐dominated, lake‐shoreline deposits have been recognized in several sections from the southern basin margin in the Clevedon area of the Bristol Channel in south‐west England. These deposits provide evidence for the development of a sizeable perennial to semi‐perennial hypersaline lake in which the MMG mudstones accumulated. Shoreline sediments overlie alluvial stream and sheet‐flood deposits, and pass from transgressive gravel–conglomerate beach units with bioclasts, influenced by shore‐normal waves (deposited under semi‐humid conditions), to lower gradient, highstand oolitic sands affected by more varied wave approach (deposited under progressively more arid conditions), which culminated in lowstand, oolitic strand‐plain deposits overlain by a playa‐mudflat unit. Shoreline deposits record a simple shallowing‐upward transgressive–highstand–lowstand sequence. However, a change from a reflective (transgressive) to dissipative (highstand) shoreline is believed to represent a climatically induced change in prevailing wind direction. Shoreline features recognized in the MMG are similar to those of recent playa‐lacustrine basins of the western United States. Ooids display a variety of size, fracture and dissolution features in addition to beachrock fabrics, suggesting that they were originally composed of radial aragonite, similar to modern ooids from the Great Salt Lake, Utah.     

Occurrence of hypogenic caves in a karst region: Examples from central Italy

The caves of the Umbria and Marche regions in central Italy are made up of three-dimensional maze systems that display different general morphologies due to the various geological and structural contexts. At the same time, the internal morphologies of the passages, galleries, and shafts present some similarity, with solutional galleries characterized by cupolas and blind pits, anastamotic passages, roof pendants, and phreatic passages situated at different levels. Some of these caves are still active, as is the case for Frassassi Gorge, Parrano Gorge, and Acquasanta Terme, with galleries that reach the phreatic zone, where there is a rising of highly mineralized water, rich in hydrosulfydric acid, and with erosion of limestone walls and the formation of gypsum. Elsewhere there are fossil caves, such as Monte Cucco and Pozzi della Piana, where large speleothems of gypsum are present 500 m or more above the regional water table. In all of these important karst systems it is possible to recognize basal input points through fracture and intergranular porosity networks at the base of the oxidizing zone in the core of the anticline, where mineralized water rises up from the Triassic evaporitic layers in small hydrogeological circuits. Different underground morphologies can derive from the presence of a water table related to an external stream or from the confined setting of the carbonate rocks, underlying low permeable sedimentary cover, where artesian conditions can occur.     

Soil geochemistry of Mother Lode-type gold deposits in the Hodson mining district, central California, U.S.A.

The Hodson mining district is in the westernmost foothills of the Sierra Nevada in California, about 17 km west of the town of Angels Camp. This district is part of the West Gold Belt, which lies about 12–16 km west of, and generally parallel to, the better known Mother Lode Gold Belt in central California. The district produced several million dollars worth of Au between about 1890 and 1940.     

Kenntnis der Randstrukturen des Witwatersrand-Beckens im nördlichen Oranje-Freistaat-Goldfeld (Südafrika)

Zusammenfassung Eine Analyse der Randstrukturen des Witwatersrand-Beckens im nördlichen Oranje-Freistaat-Goldfeld zeigt, daß das tektonische Bild der Beckenrandregion nacheinander durch verschiedene Deformationsakte von unterschiedlichem Charakter geprägt worden ist. Auf eine Einengungsphase von spät-Witwatersrand-Alter, die zur Bildung einer randlichen Aufrichtungszone und zum Aufreißen eines Systems von 'normalen und antivergenten Aufschiebungen führte, folgte während des Unteren Ventersdorp eine jüngere Zerrungsphase, bei der es zu einem staffeiförmlgen Zerbrechen der ursprünglich eingeengten Scholle kam. Die Zerrung hängt sehr wahrscheinlich mit dem Zerbrechen der Beckenrandregion während oder unmittelbar nach der Extrusion der Unteren Ventersdorp-Laven zusammen. Dabei wurde ein schmaler randparalleler Streifen der Beckenfüllung in einem Graben versenkt ('Odendaalsrus-Graben). Die abgesunkenen Schollenteile sind in sich noch stark zerbrochen und gewöhnlich schiefgestellt. Da der versenkte Streifen durch ein primäres Einmuldungsstadium hindurchgegangen ist, deutet die Grabenbildung offenbar eine Fortsetzung der Beckenbildungsvorgänge 'mit anderen Mitteln an. — Die Bewegungen haben ein Alter von etwa 2,1 Mrd. Jahren; sie fallen somit ins frühe Präkambrium und sind keinesfalls 'intraalgonkisch, wie es noch bis in die jüngste Vergangenheit angenommen wurde.Tektonische Experimente haben ergeben, daß sich die wichtigsten Störungssysteme der realen Beckenrandstrukturen bei entsprechend gewählter Versuchsanordnung auch künstlich erzeugen lassen.

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The Orange Free State goldfield represents the southernmost part of the Witwatersrand Basin (Fig. 1) which is completely buried under a cover of Ventersdorp and Karroo rocks. The pre-Karroo geology of this area is characterized by a major rift system trending SSW-NNE ('Odendaalsrus graben), followed to the east by a V-shaped horst and two minor rift blocks (Fig. 2). The main graben is bounded by two principal faults (Border Fault, De Bron Fault, Fig. 4) which are roughly parallel to the western rim of the basin.A tectonic analysis of the basin-edge structures in the northern part of the graben reveals that the basin rim has been subjected to a sequence of deformational acts working over a considerable period of time. A primary compression of the basin-edge region in Upper Witwatersrand times resulted in the formation of a marginal fold; since sedimentation continued, the different stages of the folding process were sometimes preserved by a set of minor unconformities within the youngest sediments (Elsburg A Reefs, Fig. 5). With increasing lateral pressure a couple of reverse faults developed to support the folding (faults No. 10 and 11, Figs. 6 and 7); the minor thrust faults No. 19 and 21 represent the second component of this fault system. A reconstruction of the original depositional plain of the Lower Agglomerate shows that the main thrust faults (No. 10 and 11) are definitely older than the Elsburg A 1 Reef and have been obviously revived after the younger sediments had been laid down (Fig. 8 a).In a later stage compression gave way to tensional forces bringing about a fracturing of the overturned limb of the marginal fold along normal faults (faults No. 4 and 7, Figs. 6 and 7). There is reason to believe that the tensional phase was associated with the incipient rifting during early Ventersdorp times and that these faults were more or less contemporaneous with the general tilting of the basin-edge as displayed to-day (cf. Figs. 3 and 4). Because of the westerly tilt the Boulder Beds dip towards the west, although they must have been originally deposited on a ± horizontal or slightly basinward dipping plain. Faulting was mostly accomplished before deposition of the Ventersdorp sediments and the Upper Ventersdorp Lavas took place; the latter are seldom or only to a small degree affected by the fractures (Figs. 3 and 4). — The age of the tectonics is about 2,1×10⁹ years, i. e. early Precambrian and not Algonkian as formerly supposed.Experimental work aiming at an imitation of the observed basin-edge structures has shown that the principal tectonic features can be produced artificially (Figs. 8 a and b). This refers in particular to the main system of thrust-faults as well as to the younger step-faults caused by tension.

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Résumé Les structures tectoniques au bord du Bassin de Witwatersrand dans le district de mines d'or septentrional de la République d'Orange (Afrique du Sud) ont été analysées. Il s'est montré qu'elles sont déterminées par l'action de plusieurs phases de déformation successives de caractères différents. Une phase de compression d'âge Witwatersrand supérieur a d'abord amené un redressement des couches dans une zone marginale du bassin, avec chevauchements à vergences «normales» et inverses. Elle était suivie pendant le Ventersdorp inférieur d'une phase de traction qui produisit des cassures en gradins dans le secteur primitivement comprimé. La traction est très vraisemblablement en relation avec l'effondrement de la zone marginale du bassin pendant ou peu après l'extrusion des laves inférieures de Ventersdorp. Une bande étroite de sédiments, parallèle au bord du bassin, fut alors affectée d'un affaissement (formation du «graben d'Odendaalsrus») où de nombreuses cassures à l'intérieur des compartiments affaissés ont résulté dans la formation de blocs plus ou moins inclinés. Puisque cette zone a d'abord passé par un stade synclinal, on a l'impression que l'effondrement du graben ne représente que la reprise de l'affaissement général du bassin à l'aide d'une «technique nouvelle». - Les mouvements ont un âge de 2.1 milliards d'années, ils datent par conséquent du Précambrien inférieur et ne sont point «intra-algonkiques» comme il fut encore admis tout récemment.Il a été possible de reproduire artificiellement les systèmes de failles les plus importants de la zone marginale du bassin, si les conditions de l'expériment étaient favorables.

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