A holocene zinc orebody formed by supergene replacement of mosses     

Ian R. Jonasson  Lionel E. Jackson  Donald F. Sangster 《Journal of Geochemical Exploration》1983,18(3):189-194

An extensive deposit of secondary zinc minerals has been formed at Howard's Pass, Yukon by replacement of mosses and as a cement within talus. The deposits are of Holocene age (younger than 9610 yr. B.P.) and occur in blanket peat bogs percolated by zinc-rich springwaters. Buried moss strata undergo cell by cell replacement forming zincian clacite, smithsonite and hemimorphite. The last is the most important secondary mineral in both mosses and talus.  相似文献   

Closed-system marine burial diagenesis: isotopic data from the Austin Chalk and its components     

LANA ANN CZERNIAKOWSKI  KYGER C. LOHMANN  JAMES LEE  WILSON 《Sedimentology》1984,31(6):863-877

ABSTRACT
The carbon and oxygen isotopic composition of the Austin Chalk was examined in cores representing a range of depths from surface to 3000 m in order to document the effects of burial diagenesis on carbon and oxygen isotopic composition. Low magnesium calcite oysters were separated (from 500 um wide areas) and analysed to estimate the starting composition of Cretaceous marine sediment. These gave an average value of -2·5%δ¹⁸O; + 2·0%δ¹³C (PDB). The compositions of micrite, intergranular cement, and fracture cement were analysed, and their deviation from this original marine composition was evaluated to document the progression of chalk diagenesis. Interestingly, micrite exhibits only minor variation in composition from marine values despite present burial depth ranges in excess of 3000 m. The average deviation from δ18O marine is less than 1·5. Furthermore, intergranular cement and particularly fracture cements, which occur only in the deepest cores and which clearly post-date micrite lithification, are generally indistinguishable from micrite in composition. Isotopic compositions exhibit no correlation with depth of burial despite abundant petrographic evidence of deep burial diagenesis. This uniformity in composition is interpreted as reflecting a closed, rock-dominated diagenetic system in which the compositions of precipitated carbonate cements were controlled by the composition of dissolving carbonates during lithification. As such, the composition of burial cement is not representative of the rock-water temperatures during precipitation.
Thus, in the context of isotopic analyses from other carbonate systems, unless the degree of openness of the diagenetic system is known, oxygen isotopic signatures of cements cannot directly be converted to the rock-water temperatures at which they were precipitated unless the composition of the ambient porefluid is also known.  相似文献   

Trace Element Data (1966-1977) for the Six "NIMROC" Reference Samples     

T. W. STEELE  A. WILSON  R. GOUDVIS  P. J. ELLIS  A. J. RADFORD 《Geostandards and Geoanalytical Research》1978,2(1):71-106

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Igneous Petrology of the Synorogenic Fongen-Hyllingen Layered Basic Complex, South-Central Scandinavian Caledonides     

WILSON  J. RICHARD; ESBENSEN  KIM H.; THY  PETER 《Journal of Petrology》1981,22(4):584-627

The 160 km² Caledonian Fongen-Hyllingen complex is an extremelydifferentiated, layered, basic intrusion, synorogenically emplacedat 5–6 kb in the allochthonous Trondheim nappe complex,situated in the Trondheim region of Norway. A zone of gabbroic rocks without rythmic layering usually occursalong the margin and a supposed feeder to at least part of thecomplex is preserved. A wide variety of magmatic sedimentarystructures are present in the c. 10,000 m thick sequence ofrhythmically layered rocks which vary from olivine-picotitecumulates at the base to quartz-bearing ferrosyenites at thetop. Mineral compositions, fractionation trends, and the compositionof feeder rocks suggest a tholeiitic parent. Mineral compositions cover extreme ranges. Olivine varies fromFo_86·2 to Fo_0·2 with a hiatus between about Fo₇₁and Fo₆₁. Plagioclase ranges from An_79·5 to An_1·5,albite coexisting with orthoclase microperthite in the finaldifferentiates. Cumulus Ca-poor pyroxene (Wo_2.4En_66.8Fs_30.8-Wo_2·0En_17·0Fs_81·0)first shows sporadic inversion from pigeonite at the Fe-richcomposition of Fs₆₇ and the final Ca-poor pyroxenes are replacedby magmatic grunerite which reaches an Mg: Fe ratio of 12:88.Ca-rich pyroxenes (Wo_44·7En_43·8Fs_11·5-Wo_47·0En₀Fs_53·0)are highly calcic and have a slight Ca-minimum in the earlystages, unrelated to the disappearance of Ca-poor pyroxene.Calcic amphibole, a constant intercumulus phase in most of thecomplex, becomes a cumulus phase in the later stages and variesfrom titanian-pargasite to ferro-edenite. Magnetite and ilmenitejoin the cumulate assemblage at Fo₅₅ and ilmenite persists intothe final quartz-bearing ferrosyenite where it shows replacementby sphene. Apatite, biotite, zircon, quartz, K-feldspar andallanite join the final extreme differentiates in the namedsequence. The fractionation trend is, in many respects, transitionalbetween those typical of the tholeiitic and calc-alkaline series,and is interpreted as reflecting crystallization under moderate,increasing P_H2O. Cryptic layering shows several reversals to higher temperatureassemblages with increasing stratigraphic height. Successivereversals are to irregular compositions and measured in termsof olivine composition, can be up to about 30 mole per centFo. The minimum stratigraphic thickness to include the entirefractionation range is reduced to about 2200 m after ‘removal’of the compositional overlaps due to the reversals. Thus roughlythree-quarters of the present cumulate stratigraphic sequencerepresents magma replenishment. A mechanism involving the mixingof fresh magma batches with the residual, differentiated magmafrom the previous influx, is envisaged. The periodic influxof fresh magma took place into a chamber which was probablyclosed to the exit of material.  相似文献   

Dynamics of a confined lava flow on Kilauea volcano,Hawaii     

Sally E. Heslop  Lionel Wilson  Harry Pinkerton  James W. Head III 《Bulletin of Volcanology》1989,51(6):415-432

This paper presents a new method of analysing lava flow deposits which allows the velocity, discharge rate and rheological properties of channelled moving lavas to be calculated. The theory is applied to a lava flow which was erupted on Kilauea in July 1974. This flow came from a line of fissures on the edge of the caldera and was confined to a pre-existing gully within 50 m of leaving the vent. The lava drained onto the floor of the caldera when the activity stopped, but left wall and floor deposits which showed that the lava banked up as it flowed around each of the bends. Field surveys established the radius of curvature of each bend and the associated lava levels, and these data, together with related field and laboratory measurements, are used to study the rheology of the lava. The results show the flow to have been fast moving but still laminar, with a mean velocity of just over 8 m s^–1; the lava had a low or negligible yield strength and viscosities in the range 85–140 Pa s. An extension of the basic method is considered, and the possibility of supercritical flow discussed.  相似文献   

Emplacement of the Cleveland Dyke: Evidence from Geochemistry, Mineralogy, and Physical Modelling   总被引：2，自引：0，他引：2  

MACDONALD  R.; WILSON  L.; THORPE  R. S.; MARTIN  A. 《Journal of Petrology》1988,29(3):559-583

The igneous rocks of the British Tertiary Volcanic Province(BTVP) comprise intrusive central complexes and associated lavafields in northwest Scotland and northern Ireland. These centresare associated with linear dyke swarms which are radial aroundthe major central complexes. The most extensive dyke swarm isrelated to the Mull intrusive complex and includes the Clevelanddyke, which appears to extend some 430 km from Mull throughthe Scottish Midland Valley (SMV) to the coast of northeastEngland. The dyke may have been emplaced by lateral magma migrationfrom Mull, by vertical magma migration, or by a combinationof these processes associated with the emplacement of the Mullcentre and the presence of a regional stress field in northernBritain. Petrographic, mineralogical, and geochemical data for samplescollected across and along the Cleveland dyke have been usedto evaluate its petrogenesis and emplacement mechanism. Thesegment of the dyke north of, and along, the Southern UplandsFault, the southern boundary of the SMV, is not comagmatic withthat to the south, which is now defined as the Cleveland dykesensu stricto. The Cleveland dyke is an olivine-free, plagioclase-and pyroxene-phyric basaltic andesite. Plagioclase mineralogyand bulk composition indicate that it experienced a complexmagmatic history involving polybaric fractional crystallizationand minor crustal contamination. Despite this complex evolution,the dyke magma is relatively homogeneous and shows chemicalcharacteristics closely similar to tholeiitic rocks from Mull.The data substantiate lateral emplacement from this BVTP centre,rather than by vertical emplacement through heterogeneous lithosphere. Numerical modelling of dyke dynamics is consistent with emplacementof the Cleveland dyke as a single pulse of magma from the Mullcentre, flowing in a manner transitional between laminar andturbulent conditions. According to this model, the dyke (volumec. 85 km³ was initiated in a large magma chamber below Mullsubject to a small excess magmatic pressure. Lateral migrationat relatively high velocity (1–5 ms^–1) caused emplacementof the dyke in 1–5 days. Following emplacement, minorvertical ascent of magma may have contributed to the local enechelon distribution of dyke segments.  相似文献   

Impact of diagenesis on reservoir quality in a sedimentary geothermal play: a case study in the Cooper Basin,South Australia          下载免费PDF全文

Antoine Dillinger  Ludovic P. Ricard  Cameron Huddlestone‐Holmes  Lionel Esteban 《Basin Research》2016,28(2):252-272

Geothermal resources hosted within sedimentary basins with high natural permeability have been targeted for the production of energy in Australia. The Hutton Sandstone (Cooper‐Eromanga Basin) – a prolific oil and gas producer known to have good reservoir quality and high reservoir volume – was recently tested for its geothermal potential in the Cooper Region. However, recent exploratory drilling did not produce the anticipated flow rates, raising the question of the impact of diagenesis on the reservoir quality of this sedimentary formation. The combined characterization of the petrology, diagenesis and petrophysical properties of the Hutton Sandstone at Celsius‐1 and other surrounding wells indicates variable reservoir properties in the Cooper Region. This integrated study demonstrates that low formation permeability occurs at geothermal target depth and explains the negligible flow rates obtained at Celsius‐1. These low permeabilities are the results of the preservation of widespread detrital clayey matrix and the extensive occurrence of authigenic kaolinite, illite and silica cements at the top and base of the Hutton Sandstone. This aspect is confirmed by NMR T₂ transversal relaxation time becoming shorter at similar depths. Petrography analysis also reveals that sandstones are affected by diagenetic processes of the eogenetic and mesogenetic phases. However, the Hutton Sandstone at Celsius‐1 is presently at pressure‐temperature conditions that are below the mesogenetic conditions, which suggests a late episode of uplift and cooling from maximum palaeotemperatures.  相似文献   

Vent geometry and eruption conditions of the mixed rhyolite–basalt Námshraun lava flow,Iceland     

Lionel Wilson  Sarah A. Fagents  Linda E. Robshaw  Evelyn D. Scott 《Journal of Volcanology and Geothermal Research》2007

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The Liuchiu Hsu island offshore SW Taiwan: tectonic versus diapiric anticline development and comparisons with onshore structures     

Olivier Lacombe  Jacques Angelier  Frédéric Mouthereau  Hao-Tsu Chu  Benoı̂t Deffontaines  Jian-Cheng Lee  Muriel Rocher  Rou-Fei Chen  Lionel Siame 《Comptes Rendus Geoscience》2004,336(9):815-825

A structural and microtectonic analysis performed in the Liuchiu Hsu island demonstrates that its Plio-Pleistocene tectonic evolution was dominated by alternating NW–SE shortening and local radial extension caused by mud diapirism. Previous models based on seismic data considering both the formation of the Liuchiu Hsu island and the fold development in SW Taiwan as mainly driven by mud diapirism, fail to account for both the asymmetry of the west vergent thrust-related anticlines onshore and the elongated character of the ridges formed by diapir alignments offshore, which rather argue in favour of a tectonic origin. To cite this article: O. Lacombe et al., C. R. Geoscience 336 (2004).  相似文献   

"They Changed the Rules": Farm Family Responses to Agricultural Deregulation in Southland, New Zealand     

OLIVIA WILSON 《New Zealand geographer》1994,50(1):3-13

Agricultural deregulation in the mid-1980s altered the economic and political climate in which farm families in New Zealand operate. The results of a survey of sheep/beef farmers in Southland shows that the main response to the new conditions and the rural downturn was to 'self exploit'. Impacts varied, depending on farm finances at the start of the downturn. Farming practices and farmers' attitudes changed… but only partly because of deregulation.  相似文献