Empirical behavior of Chayes' null model

Chayes' t″-test for closure correlations is developed from various approximations and assumptions. The empirical behavior of this test is observed through the use of random-sampling number matrices of order to thirteen. The experiments demonstrate a lower limit for the reliability of Chayes' model of about 91/100. That is, about one chance in ten remains that an error due to the statistical testing is committed on some product-moment correlations in a given matrix of correlation, given a confidence level of 90 percent. With increase in the number of variables, the test for departure from zero correlation can be used provided the sample size remains small.     

When are relative variograms useful in geostatistics?

The relative variogram has been employed as a tool for correcting a simple kind of nonstationarity, namely that in which local variance is proportional to local mean squared. In the past, this has been linked in a vague way to the lognormal distribution, although if {Z_t; t D}is strongly stationary and normal over a domain D,then clearly {exp (Z_t); t D}will stillbe stationary, but lognormal. The appropriate link is made in this article through a universal transformation principle. More general situations are considered, leading to the use of a scaled variogram.     

A method for determining the reversibility of a Markov sequence

This paper describes, given a tally matrix with strictly positive entries, a method to determine whether the associated Markov process is reversible, and (for reversible Markov processes) methods to compute the reversibility matrix from the tally matrix. If the tally matrixN is symmetric, then it is shown that the Markov process must be reversible and the reversibility matrixC equalss (R ^–1NR^–1), whereR is the diagonal matrix whosei ^th diagonal entry is the sum of the entries of thei ^th row ofN (for everyi) ands denotes the sum of all the entries ofN. Because a symmetric tally matrix is of special importance in applications, a ² test is proposed for determining, in the presence of experimental errors, whether such a matrix is symmetric.     

Chi-square tests for markov chain analysis

Markov chain analysis has become a popular and useful technique for the evaluation of stratigraphic information. Field data on frequencies of facies transitions are first assembled in a transition count matrix. Observed frequencies can be compared statistically with frequencies expected if no order, or memory, exists in the stratigraphic sequence. Two chi-square (²) tests have been proposed for this purpose. One of the previously proposed ² tests was observed to give anomalously large values of the test statistic during another study. This unsatisfactory behavior is verified here. Limiting values of the two ² tests (from tables) are compared with the distribution of values for both test statistics obtained by analyzing many random matrices generated by a simple computer program. In all cases, the logarithmic ² test, suggested by several previous authors, fails to provide any meaningful assessment of the presence or absence of order in stratigraphic sequences evaluated. Further use of this test should therefore be avoided.     

Tests for quasi-independence of embedded markov chains

This paper introduces the concept of quasi-independence into embedded Markov chains and identifies the maximum likelihood frequency estimates to be used with ² tests of the null hypothesis of quasi-independence within an embedded Markov chain.     

Vibrational spectroscopy of beta-eucryptite (LiAlSiO<Subscript>4</Subscript>): optical phonons and phase transition(s)

The structural behavior of -eucryptite (LiAlSiO₄) has been investigated using infrared (IR) spectroscopy over a temperature range of 20 to 900 K and FT-Raman spectroscopy at room temperature. IR reflectance measurements show that -eucryptite possesses high reflectivity in the far-IR region, as is consistent with its reported superionic conductivity along the c-axis. On heating, the Li-related IR bands near 246 and 300 cm^–1 (with A₂ symmetry) broadened and weakened dramatically, presumably as a result of Li⁺ positional disordering along the structural channels parallel to c. The disordering process appears to induce a framework distortion, as is evidenced by the broadening of some vibrations of Si(Al)–O with increasing temperature. A change in slope in the temperature dependence of the phonon frequency near 300 cm^–1 and the linewidth of the 760 cm^–1 band at 715 K indicates that Li becomes completely disordered above this temperature. In addition, the temperature dependence of the linewidth for the 760 cm^–1 band exhibits an additional change in slope at 780 K, implying the existence of an intermediate state within this temperature range. The detailed structure of this intermediate phase, however, needs further study. Our IR data provide no indication of structural changes between room temperature and 20 K.     

Isotope geochemistry of the Tieluping silver-lead deposit, Henan, China: A case study of orogenic silver-dominated deposits and related tectonic setting

The Tieluping silver deposit, which is sited along NE-trending faults within the high-grade metamorphic basement of the Xionger Terrane in the Qinling orogenic belt, is part of an important, recently discovered Mesozoic orogenic-type Ag-Pb belt. Ore formation includes three stages: an early barren quartz-pyrite stage (E), an intermediate polymetallic sulfide ore stage (M), and a late barren carbonate stage (L). Carbon, sulfur and lead isotope systematics indicate that the E-stage fluids are deeply sourced; the L-stage fluids are shallow-sourced meteoric water; whereas the M-stage fluids are a mix of deep-sourced and shallow-sourced fluids. Sulfur and lead isotope data show that the ore-forming fluids must have originated from a source with elevated radiogenic lead and low ³⁴S values, that differs significantly from exposed geologic units in the Xionger Terrane, the lower crust and the mantle. This supports the view that the carbonate-shale-chert sequences of the Guandaokou and Luanchuan Groups south of the Machaoying fault might be the favorable sources, although little is known about their isotopic compositions. A tectonic model that combines collisional orogeny, metallogeny and hydrothermal fluid flow is proposed to explain the formation of the Tieluping silver deposit. During the Mesozoic collision between the North China Craton and South China Block (Early-Mid Triassic Indosinian Orogeny), crustal slabs containing the carbonate-shale-chert sequences of the Guandaokou and Luanchuan Groups, locally rich in organic matter (carbonaceous shale), were thrust northwards beneath the Xionger Terrane along the Machaoying fault. Metamorphic devolatilisation of this underthrust slab probably provided the ore-forming fluids to develop the Ag-Pb ore belt, which includes the Tieluping silver deposit. Fluids and magmas were emplaced during extensional stages related to the Jurassic-Cretaceous Yanshanian Orogeny.Editorial Handling: B. Lehmann     

Some problems of interpreting the correlations between the modal variables in granitic rocks

Correlation coefficients of modal variables from several suites of granitic rocks have been calculated and tested for significance using the Chayes-Kruskal and Chayes methods. The results show that although Chayes' remaining-space transformation does, in general, weaken the original proportion correlations, the positive and low-negative original proportion correlations tend to increase in absolute value because of a tendency of positive increment of the covariance by such transformation. However, no satisfactory procedure for choosing the variable to be transformed (V₂)could be determined, and testing of the significance of remaining-space correlations is found to be highly problematic. It is shown also that the Vistelius-Sarmanov procedure of calculation of correlation coefficients from closed-table data does not effectively eliminate the closure effect. It is concluded that assigning statistical significance to the correlation coefficients between modal variables is, in general, unsatisfactory, except where the number of variables 8,the sample size is large (say, 30),and there is no negative element in the variance vector of the corresponding open variables.     

High-resolution magnetostratigraphy and micropalaeontology across the J/K boundary strata at Brodno near ilina, western Slovakia: summary of results

This study summarizes the final results of magnetostratigraphic and micropalaeontological investigations of the Tithonian/Berriasian boundary (J/K) limestones at the locality of Brodno near ilina, Western Carpathians, West Slovakia. The aim is to prepare the background for correlation of a Late Tithonian and Early Berriasian biostratigraphic zonation with global magnetoevents (manifested in detailed magnetostratigraphic profiles) between the Tethyan realm and other regions, particularly the Boreal and Pacific realms. Suitable physical properties of the limestones studied, a favourable geological setting and rich microfossil assemblages (calpionellids) at Brodno (magnetozones M21r to M18r) allowed a systematic collection of new data on the original synoptic section, which now has the character of a high-resolution profile across the J/K boundary. Two reverse subzones detected within magnetozones M20n and M19n are named ‘Kysuca Subzone’ and ‘Brodno Subzone’, respectively. Both can be correlated with analogous subzones in the M-sequence of marine anomalies. Their existence can also be confirmed in the Bosso Valley section in Umbria, central Italy. A detailed study of the interval between magnetozones M20n and M17r in the Bosso Valley profile is presently in its final stage. Both magnetostratigraphic profiles, from the Brodno and Bosso Valley localities, were thoroughly investigated in the intervals close to the J/K boundary and are still unique among continent-based profiles in the detection and precise definition of both reverse subzones within M20n and M19n. Samples collected from the boundary strata of the reverse Kysuca Subzone at Brodno indicated a transition from N (R) to R (N) polarity of the Earth's palaeomagnetic field within a time interval of c. ±5 ka. Limestone samples (total number N=368) were subjected to progressive thermal demagnetization in 10–12 thermal fields and to subsequent multi-component analysis of remanence. The C-component, as the carrier of palaeomagnetic directions, was determined in the temperature interval of 300° to 540°, or possibly 580°C. Magnetomineralogical analyses of pilot samples and unblocking temperatures determined for all samples showed that magnetite is the carrier of remanent magnetization. The positions of the individual events of calpionellid stratigraphy relative to the global magnetic polarity timescale are precisely defined. The base of the Calpionella Standard Zone, which is considered a provisional J/K boundary indicator in ammonite-free sections in the Tethyan realm, lies within magnetozone M19n at the level of 35% of its local thickness. None of the boundaries in the calpionellid zonation coincides precisely with any of those in the palaeomagnetic zonation, but the first appearance ofCalpionella grandalpina , indicating the base of the Intermedia Subzone, lies in close proximity to the base of magnetozone M19r.     

Space group and hydrogen sites of δ-AlOOH and implications for a hypothetical high-pressure form of Mg(OH)<Subscript>2</Subscript>

The space group and hydrogen positions of -(Al_0.84Mg_0.07Si_0.09)OOH are investigated using a single crystal synthesized using a multi-anvil apparatus under conditions of 1000 °C and 21 GPa. The space group determined by single-crystal X-ray diffraction is to Pnn2, with unit-cell parameters of a=4.6975(8) Å, b= 4.2060(6) Å, c=2.8327(4) Å, and V=55.97(1) ų. Partial occupancy of the Al site by Mg and Si suggests the possibility of a limited solid solution between -AlOOH, stishovite, and a hypothetical CaCl₂-type Mg(OH)₂ that is 16% denser than brucite. Difference-Fourier maps reveal two small but significant Fourier peaks attributable to hydrogen atoms. Atomic distances and angles around the first peak indicate a hydrogen bond with O···O distances of 2.511 Å, while those around the second peak are suggestive of a bifurcated hydrogen bond with O···O distances of 2.743 and 2.743 Å.     

Static compression of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>: linear incompressibility of lattice parameters and high-pressure transformations

The high-pressure behavior of -Fe₂O₃ has been studied under static compression up to 60 GPa, using a laser-heated diamond anvil cell. Synchrotron-based angular-dispersive X-ray diffraction shows that the sample remains in the corundum structure up to 50 GPa, but with the appearance of coexisting diffraction lines from a high-pressure phase at pressures above 45 GPa. A least-squares fit of low-pressure phase data to an Eulerian finite-strain equation of state yields linear incompressibilities of K _{a 0}=749.5 (± 18.4) GPa and K _{c 0}= 455.7 (± 21.4) GPa, differing by a factor of 1.6 along the two directions. The enhanced compressibility of the c axis may lead to breaking of vertex- or edge-sharing bonds between octahedra, inducing the high-pressure phase transformation at 50 GPa. Analysis of linear compressibilities suggests that the high-pressure phase above 50 GPa is of the Rh₂O₃ (II) structure. Continuous laser heating reveals a new structural phase transformation of -Fe₂O₃ at 22 GPa, to an orthorhombic structure with a=7.305(3) Å, b=7.850(3) Å, and c=12.877(14) Å, different from the Rh₂O₃ (II) structure.     

Selenium fractionation and speciation in rocks, soils, waters and plants in polluted surface mine environment

A fractionation and speciation was performed to determine the distribution of selenium (Se) species in major components of quartzite surface mine environment (rocks, mine tailings, soils, stream sediments, surface waters and plants) in obov, Slovakia. A three-step sequential extraction procedure was utilised for the fractionation of Se in mine tailings and soils. The first extractant in order to evaluate the soluble and ligand exchangeable fraction of Se (0.1 mol/l K₂HPO₄ + KH₂PO₄ at pH 7.0) solubilized up to 15% of total Se content. The second step (0.1 mol/l K₂S₂O₈ at 90°C) which extracted Se associated or occluded with organic matter released 13 – 45% of total selenium. The decomposition of the residue (HNO₃ + H₂SO₄ 1+1) was used to solubilize the remaining 35–88% of total Se as the final step. The recovery of the procedure was between 97 and 106%. Selenate predominated in natural river and lake waters about pH 7.0 (>95%) but in acid mine leakings up to 40% of selenite was found. In the plants (birch leaves, grass leaves and roots) collected from the area acidified by mine leakings no significant accumulation of selenium was observed. The correlation between total Se and S in the rocks from the mine gives an evidence of the common origin of these elements in the studied area.     

Volcanic and Scientific Activity at Kick ’em Jenny Submarine Volcano 2001–2002: Implications for Volcanic Hazard in the Southern Grenadines,Lesser Antilles

Kick em Jenny submarine volcano, ~8 km north of Grenada, has erupted at least 12 times since it was first discovered in 1939, making it the most frequently active volcano in the Lesser Antilles arc. The volcano lies in shallow water close to significant population centres and directly beneath a major shipping route, and as a consequence an understanding of the eruptive behaviour and potential hazards at the volcano is critical. The most recent eruption at Kick em Jenny occurred on December 4 2001, and differed significantly from past eruptions in that it was preceded by an intensive volcanic earthquake swarm. In March 2002 a multi-beam bathymetric survey of the volcano and its surroundings was carried out by the NOAA ship Ronald H Brown. This survey provided detailed three-dimensional images of the volcano, revealing the detailed morphology of the summit area. The volcano is capped by a summit crater which is breached to the northeast and which varies in diameter from 300 to 370 m. The depth to the summit (highest point on the crater rim) is 185 m and the depth to the lowest point inside the crater is 264 m. No dome is present within the crater. The crater and summit region of Kick em Jenny are located at the top of an asymmetrical cone which is about 1300 m from top to bottom on its western side. It lies within what appear to be the remnants of a much larger arcuate collapse structure. An evaluation of the morphology, bathymetry and eruptive history of the volcano indicates that the threat of eruption-generated tsunamis is considerably lower than previously thought, mainly because the volcano is no longer thought to be growing towards the surface. Of more major and immediate concern are the direct hazards associated with the volcano, such as ballistic ejecta, water disturbances and lowered water density due to degassing.     

Valent state and coordination of cobalt Ions in beryl and chrysoberyl crystals

We have studied the polarized optical absorption and EPR spectra of Co-doped beryls grown by hydrothermal, flux, and gas-transport methods, and chrysoberyl grown by the Czochralski method. In beryls three groups of bands, belonging to three various Co centers, were distinguished by analysis of the absorption band intensities. The first group, bands with maxima at 22 220 (E c), 17 730 (E c), and 9090 (E c), 7520 (E c) cm^–1 are due to Co²⁺ in octahedral site of Al³⁺. The second group is bands at 18 940, 18 250, 17 700 (E c), 18 300, 17 700, 17 000 (E c) and 8830 (E c), 7350 (E c) cm^–1 and 5320 (E c), 3880 (E c) cm^–1, which are caused by Co²⁺ in tetrahedral site of Be²⁺. A weak wide band in flux and gas-transport beryl in the region of 12 500–8300 cm^–1 (E , c) is related to Co³⁺ in octahedral Al³⁺ site. In hydrothermal beryl, bands 13 200 (E c), 10 900 (E c), and 8500 (E c) cm^–1 are caused by an uncontrolled impurity of Cu²⁺ ions. For Co-doped chrysoberyl one type of center of Co has been established: Co²⁺ in the octahedral site of Al³⁺. In the approximation of the trigonal field with regard to Trees correction, the energy levels of Co²⁺ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is explained well in terms of the spin-orbit interaction.     

Âges KAr des roches magmatiques du fossé de Garoua (Cameroun) : leur place dans le cadre de la « Ligne du Cameroun »

KAr analyses on whole rock and minerals are reported for the Kokoumi anorogenic pluton and alkaline volcanics of the Benue valley, west of Garoua (northern Cameroon), which belong to the northern part of the ‘Cameroon Line’. The two formations yield similar ages of 39 and 37 Ma, respectively. These values likely correspond to the time of emplacement. They are in agreement with the interpretation considering the ‘Cameroon Line’ as a huge lithospheric crack tapping a hot deep asthenospheric zone. To cite this article: R. Montigny et al., C. R. Geoscience 336 (2004).     

Geochronology and geochemistry of eclogites from the Mariánské Lázně Complex,Czech Republic: Implications for Variscan orogenesis

The Mariánské Lázn complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calcsilicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377±7, and 367±4 Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated _Nd values and initial ⁸⁷Sr/⁸⁶Sr ratios. Five of the eight eclogite samples have high _Nd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower _Nd values (+ 5.4 to –0.8) and widely variable ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7096). Such low _Nd values are inconsistent with derivation from a MORB, source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension.     

Diagenesis of vascular plant organic matter components during burial in lake sediments

Diagenetic changes are difficult to distinguish from variations in sources of organic matter to sediments. Organic geochemical comparisons of samples of wood, bark, and needles from a white spruce (Picea glauca) living today and one buried for 10,000 years in lake sediments have been used to identify the effects of diagenesis on vascular plant matter. Important biogeochemical changes are evident in the aged spruce components, even though the cellular structures of the samples are well preserved. Concentrations of total fatty acids dramatically diminish; unsaturated and shorter chainlength components are preferentially lost from the molecular distributions. Concentrations of total alcohols are similar in the modern and 10,000-year-old wood and bark but markedly lowered in the aged needles. Hydrocarbon concentrations and distributions show little diagenetic change in the 10,000-year-old plant materials. Cellulose components in the wood decrease relative to lignin components, although both types of materials remain in high concentration in comparison to other organic components. Aromatization of abietic acid proceeds more rapidly in buried spruce wood than in bark; retene is the dominant polyaromatic hydrocarbon in the aged wood. In contrast to the variety of changes evident in molecular compositions, neither ¹³C values nor C/N ratios differ significantly in the bulk organic matter of modern and aged spruce components.     

Counting statistics of f −β fluctuations: a new method for analysis of earthquake data

In a variety of biological and physical phenomena, temporal fluctuations are found, which are not explainable as consequences of statistically independent random events. If these fluctuations are characterized by a power spectrum density S(f) decaying as f ^– at low frequencies, this behaviour is called 1/f noise.Counting statistics applied to earthquake activity data leads to three time scales with different characteristics, represented by the exponent : at interval lengths less than 1 h, the shocks are randomly distributed as in a Poisson process. For medium time intervals (1 day to 3 months), the exponent 1 + is larger (1.4 for M ₀=3), but approaches unity for higher threshold magnitudes M ₀. In longer time ranges the exponent assumes values near 1.55, however, with increasing statistical variation at higher M ₀, due to lower counts.The temporal sequence is different from white noise; thus, it might be fruitful to apply neural network algorithms, because this method allows predictions in some other cases with similar characteristics.