Franciscan Complex olistostrome at Crescent City, northern California

An olistostrome and bounding turbidites are exposed within the late Mesozoic Franciscan Complex along the Crescent City (California) coastline. Facies grade in character from Mutti & Ricci Lucchi (1978) mixed facies B, C and D, to F (the olistostrome), to mixed A, B and E, progressing upwards within the Franciscan stratigraphic section. The facies F unit outcrop is up to 600 m thick and extends 12 km along strike. It consists of oblate to tabular blocks, up to 200 m in maximum dimension, of greenstone, tonalite, radiolarian chert, limestone, phyllite and greywacke dispersed in a scaly argillite matrix. The olistostromal origin of the unit is indicated by depositional contacts with bounding turbidites, by the presence of abundant recycled sedimentary clasts within the unit, and by the presence of sedimentary breccias and associated dismembered, slump-folded turbidites both within the olistostrome and among subjacent turbidites. Sandstones are chiefly feldspathic litharenites that were very likely derived from the partially dissected, late Mesozoic Sierran-Klamath magmatic are. Franciscan rocks record an early pervasive, layer-parallel flattening strain in such features as extensional faults, necking and pinch-and-swell structures. Several scales of extensional faulting account for the juxtaposition of turbidites of different facies and/or with varying degrees of stratal disruption, the formation of sandstone lozenges, and the formation of scaly foliation in the olistostrome matrix. The latter resulted from the juxtaposition of lenticles with varying concentrations of silt and clay. These were ultimately derived from the finer divisions of turbidite beds that were incorporated into the olistostrome. The presence of gradational contacts between some sandstone olistoliths and the olistostrome matrix, and of sandstone dykes that intrude fractures and associated drag-folded turbidite beds indicate that Franciscan sediments were not lithified during their early deformation. These sediments were deposited in either a trench or trench slope basin, and were first deformed either by gravity collapse of the trench slope cover or, less likely, by vertical loading beneath the toe of the accretionary wedge. They later were folded during internal shortening of the growing Franciscan accretionary prism.     

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.     

Dielectric constants of BeO,MgO, and CaO using the two-terminal method

Using fused SiO₂, CaF₂, and SrF₂ samples with accurately known dielectric constants, we have evaluated the accuracy and precision of two-terminal dielectric constant measurements on small single crystals using empirically determined edge corrections. Values of κ′ at 1 MHz of 3.836±0.05 for silica, 6.814±0.07 for CaF₂ and 6.463±0.09 for SrF₂ indicate an accuracy and precision of 1.0–1.5% for samples having areas of 0.05–1.0 cm². Dielectric constants of BeO, MgO, and CaO measured by this technique are: BeO, κ′_a=6.87 and κ′_c=7.74; MgO, κ′= 9.90; and CaO, κ′=11.95 where κ′_a and κ′_c are the dielectric constants parallel to the a and c axes, respectively. Dielectric loss measurements on CaO in vacuum between 5–400 K at 10–10⁵ Hz indicate significant dispersion at temperatures higher than 300 K, but the effect of the losses on the dielectric constant is less than 1% at 1 MHz and 300 K.     

Seismic and sedimentologic features of Oxfordian-Kimmeridgian syn-rift sediments on the eastern margin of the Lusitanian Basin

Following deposition of widespread middle Oxfordian lacustrine carbonates and evaporites, the Lusitanian Basin was differentiated into a number of sub-basins. The Arruda sub-basin is a half graben basin situated some 30 km north of Lisbon. It accumulated over 2.5 km of Kimmeridgian siliciclastic sediments, and is bounded to the east by the Vila Franca de Xira fault zone. Carbonate deposition persisted over horsts along the fault zone from the Oxfordian to the early Kimmeridgian, and in places to the late Kimmeridgian, and shows a pronounced west-east facies zonation, with higher energy framestones and grainstones accumulating along the exposed western margins. Seismic data indicate a major gap between the horst blocks that acted as a conduit through which basement derived siliciclastics were fed westwards into the sub-basin to form a submarine fan system. The presence of large blocks of framestone carbonates encased in siliciclastics indicates that carbonate sedimentation occurred in abandoned parts of the fan system. The rapid changes of sediment thicknesses and facies types along the eastern margin of the Arruda sub-basin are indicative of contemporaneous strike-slip movements.

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Zusammenfassung Nach der weitverbreiteten Ablagerung mitteloxfordischer Seenkarbonate und Evaporite differenzierte sich das Lusitanische Becken in verschiedene Sub-Becken. Das Arruda Sub-Becken befindet sich ca. 30 km nördlich Lissabon und entspricht einem Halbgraben, in dem über 2.5 km mächtige Siliziklastika des Kimmeridgium zur Ablagerung kamen. Das Sub-Becken wird durch die Störungszone von Vila Franca de Xira nach Osten begrenzt. Auf Horststrukturen entlang der Störungszone wurden im Oxfordium und Unterkimmeridgium, z. T. auch bis ins Oberkimmeridgium Karbonate sedimentiert. Diese Karbonatschelfe weisen eine ausgeprägte Fazieszonierung von West nach Ost auf. Die westlichen Schelfränder sind durch höherenergetische Riffkalke (framestones) und Karbonatsande (grainstones) charakterisiert. Seismische Profile lassen eine große Lücke zwischen den Horstblöcken erkennen, durch welche Siliziklastika aus dem Hinterland ins Sub-Becken gelangten, wo sie einen submarinen Fächer aufbauten. Große Riffkalkblöcke innerhalb der Siliziklastika weisen auf Karbonatsedimentation in verlassenen Fächerbereichen hin. Die schnellen Mächtigkeits- und Fazieswechsel entlang des Ostrandes des Arruda Sub-Beckens sind durch synsedimentäre tektonische Bewegungen zu erklären, welche oftmals eine Dominanz der Lateralkomponente aufweisen.

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Resumo Depois da sedimentação dos calcários lacustres e depósitos evaporíticos da idade Oxfordiano médio, a Bacia Lusitánica diferenciou-se em várias sub-bacias. A sub-bacia de Arruda está situada ca. de 30 km ao norte de Lisboa e corresponde a uma estrutura «half-graben» em que mais do que 2.5 km de sedimentos foram acumulados. Para leste, a sub-bacia é limitada pela zona das falhas de Vila Franca de Xira. Entre o Oxfordiano e o Kimeridgiano, calcários desenvolveram-se em cima dos blocos elevados (horsts) ao longo da zona de falhas. Estes calcários de tipo plataforma exibem uma distincta zonação de facies de oeste a leste. As margens occidentals das plataformas pequenas são caracterisadas por sedimentos recifais e areníticos. Cortes sísmicos indicam uma abertura grande entre os blocos elevados, pelo quai sedimentos siliciclásticos passaram de hinterland à sub-bacia formando um fan submarino. Grandes blocos recifais situados dentro dos depósitos siliciclásticos são evidências para sedimentação carbonática em várias áreas abandonadas dentro do fan. Mudanças rápidas das espessuras e das fácies dos sedimentos ao longo da margem oriental da sub-bacia de Arruda podiam ser explicadas por uma tectónica sinsedimentária dominada por movimentos horizontais.

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Geochemistry of Tertiary tholeiites and picrites from Qeqertarssuaq (Disko Island) and Nuussuaq, West Greenland with implications for the mineral potential of comagmatic intrusions

Tertiary continental flood basalts on Qeqertarssuaq and Nuussuaq in West Greenland contain ～3?km of picrites and variably contaminated tholeiites. The picrites are in the Naujánguit member of the Vaïgat Formation and they have 7–29?wt% MgO, La/Sm?=?0.9–2.1, and ¹⁴³Nd/¹⁴⁴Nd?=?0.51263–0.51307. They appear to have crystallised from high-Mg parental magmas (14.4–16.4?wt% MgO) with isotope and trace element ratios similar to recent Icelandic picrites. Discrete horizons of tholeiites, including the Asûk and?Kûgánguaq, have elevated SiO₂ (50–58 wt%), La/Sm?=?3–7, ⁸⁷Sr/⁸⁶Sr?=?0.70550–0.71224, and low ¹⁴³Nd/¹⁴⁴Nd?=?0.51234–0.51174. These lavas have low Cu and Ni abundances (typically 10–50?ppm Ni or Cu), and in the case of the Asûk on Qeqertarssuaq, they contain droplets of native iron. The low Cu and Ni contents are attributed to scavenging by magmatic sulphides formed in response to crustal contamination of picritic magmas. Two contamination trends are recognised, one to a sediment end-member with high Th/Nb and Archaean model Nd ages, and the other to a meta-igneous component with high La/Sm, low Th/Nb and Rb/Nb, and Proterozoic source ages. Overall, ²⁰⁶Pb/²⁰⁴Pb varies from 16.47–21.68. Both contamination trends are associated with low Cu and Ni, and high SiO₂, and it is argued that the magmatic sulphides were triggered by the increases in silica, rather than simply by the introduction of additional crustal-derived sulphur. Geochemically, the Asûk and Kûgánguaq rocks resemble the most contaminated Nadezhdinsky lavas of the Siberian Trap, which are widely regarded as the source of the Ni and Cu mineralisation in the giant Noril'sk deposits. Mass balance considerations indicate that the parental liquids to the contaminated magmas contained sufficient Ni, Cu, S and platinum group elements to form substantial magmatic sulphide deposits. However, unlike the lavas at Noril'sk, the contaminated (low Cu and Ni) West Greenland basalts are in isolated units with no evidence for a gradual recovery in Ni and Cu abundances with height in the lava column. Comparison with Noril'sk suggests that although significant quantities of metals were scavenged by sulphides in West Greenland, the metal contents of the sulphides may not have been upgraded by continued interaction with subsequent magma batches.     

Seismic Hazard Studies in the U.K.: Source Specification Problems of Intraplate Seismicity

Although the U.K. is in an area of only low to moderate seismicity, the seismic hazard is sufficient to pose a threat to sensitive structures such as chemical plants and nuclear facilities. In quantifying the level of hazard by conventional probabilistic methodology, however, some problems arise in attempting to interpret earthquake data in terms of geological structure and faults. In the U.K., not only is it impossible to identify any demonstrably active faults, but also it is extremely difficult to discern any relationship between the pattern of seismicity and local or regional geological structure.This study discusses the use of two zonation approaches which complement each other in such a way that the general character and trend of seismicity is preserved. In one approach, the zonation is informed by the structural geology, where possible; geological zonation is avoided if it produces sources with heterogeneous seismicity. In the other approach, the record of past earthquakes is divided up into very small zones around individual epicentres or groups of epicentres, the size of each zone usually being proportional to the uncertainty in the epicentral determination of the appropriate event. This zonation preserves an observed tendency of some British earthquakes to repeat themselves. It is suggested that, in intraplate areas such as the U.K., it is often inappropriate to attempt to model individual fault sources. No faults in the U.K. are provably active. Because an earthquake of moderate size can occur on a very short fault segment, it is impractical to restrict fault modelling to major features. Even the two largest U.K. faults, suspected to be active, pose problems in attributing historical seismicity to them as distinct features.     

Geography in a restructuring world?

In those parts of their discipline which can be categorised as spatial analysis, geographers have focused attention on distance as a key variable, and have paid little attention to bounded spaces and territoriality strategies. In a rapidly restructuring world, in which distance is becoming increasingly irrelevant as an influence on many forms of behaviour, territoriality remains an important aspect of the manipulation of space for economic, social, political and cultural purposes: in the terminology of Hagerstrands classic model, while the coupling and capability constraints on interaction are weakening, the authority constraint remains strong.     

Electrokinetic remediation of metal contaminated glacial tills

This paper presents the results of an experimental investigation which studied the feasibility of using the electrokinetic process to remediate contaminated clays of glacial origin, otherwise known as glacial tills. An overview of the electrokinetic phenomena, as well as previously performed laboratory and field investigations, is first presented. The methodology of the electrokinetic experiments which were conducted to investigate the removal of metals from a glacial till is then described. A total of 16 experiments were conducted using glacial till samples obtained from a project site near Chicago. Sodium and calcium were used as the surrogate cationic metallic contaminants. These experiments demonstrated that ion transport during the electrokinetic process occurs due to both electro-osmosis and electromigration, but that due to electromigration is significantly higher than that due to electro-osmosis. Unlike other clays such as kaolinite, the glacial till used for this investigation possessed high buffering capacity because of its high carbonate content which prevented the acid front migration from the anode to the cathode during the electrokinetic process. The ion removal efficiency of the electrokinetic process was found to increase when: (1) the voltage gradient applied to the soil was increased, (2) the initial concentration of the contaminants was increased, and (3) the duration of the treatment process was increased. The ion removal efficiency was also greater for smaller ions which possess less ionic charge and when the ions existed independently in the soil as compared to when they coexisted. This investigation suggests that the electrokinetic process has significant potential for remediating glacial tills contaminated with metals. However, the properties of Na and Ca are not representative of contaminants, such as heavy metals, so further investigations are needed.