Use of biological marker distributions to study thermal history of the Permian Kupferschiefer of the Lower Rhine Basin

In the Central European Zechstein Basin, the Permian Kupferschiefer has been deposited under marine anoxic conditions. From a lagoon at the southwest border of the Zechstein Sea, today part of the Lower Rhine Basin, 30 core samples have been studied by means of organic geochemical methods. Within the area investigated, the depth of the Kupferschiefer horizon increases from about 350 m in the south to about 1000 m in the north. Furthermore, the Kupferschiefer has been thermally affected in the western part by the intrusive body of the so-called Krefeld High. This geological situation opens the possibility to investigate differences of short term and long term temperature effects on the biological marker distribution within a sediment layer of a largely uniform faciès type. Depth related changes in the hopane, sterane and diasterene/diasterane distributions are compared to those changes induced by the Krefeld High. The composition of aromatic steroid hydrocarbons is used to discuss time-temperature effects. It is shown that depth related values of maturation parameters can only be interpreted by taking into account post-depositional tectonic events. Samples from tectonic horst structures show higher maturation values than one would expect from the present day depth.

---

Zusammenfassung Aus dem Bereich der heutigen Niederrheinischen Bucht wurden an 30 Kernproben des Kupferschiefers organischgeochemische Untersuchungen durchgeführt. Innerhalb des Untersuchungsgebiets nimmt die Teufe des Kupferschieferhorizonts von 350 m im Süden auf über 1000 m im Norden zu. Organisch-geochemische Reifeparameter zeigen an, daß der Kupferschiefer im Westen durch den Intrusivkörper des Krefelder Gewölbes thermisch beeinflußt worden ist. Aufgrund dieser Situation bietet sich die Möglichkeit, Unterschiede im Einfluß von kurzzeitigen und langzeitigen Temperatureinwirkungen auf die Verteilung von Chemofossilien in einem faziell einheitlichen Horizont zu studieren. Teufenabhängige Variationen der Hopan-, Steran-, Diasteran- und Diasterenverteilungen lassen sich mit den zusätzlich durch den Intrusivkörper verursachten Veränderungen vergleichen. Die Verteilungsmuster der aromatischen Steroide werden zur Deutung von Zeit-Temperatur-Effekten im Verlauf der Diagenese herangezogen. Die ermittelten Meßwerte der Reifeparameter lassen sich nur interpretieren, wenn postsedimentäre tektonische Bewegungen nach der Ablagerung des Kupferschiefers in Betracht gezogen werden. Die aus Horsten stammenden Proben zeigen höhere Reifegrade an als entsprechend ihrer heutigen Teufe zu erwarten.

---

Résumé Dans le bassin du Zechstein d'Europe Centrale, les Kupferschiefer permiens ont été déposés dans des conditions marines anoxiques. Dans un paléo-lagon situé à la bordure sud-ouest de la mer du Zechstein, et qui fait partie aujourd'hui du Bassin du Bas-Rhin, 30 échantillons, provenant de carottes, ont fait l'objet d'une étude de géochimie organique. Dans la région ainsi étudiée, la profondeur de l'horizon des Kupferschiefer augmente, du sud au nord, de 350 m à 1.000 m. D'autre part, les Kupferschiefer ont subi, dans leur partie ouest, l'influence thermique du corps intrusif du «Dôme de Krefeld». Cette situation géologique fournit la possibilité d'étudier les effets à long terme et à court terme de la température sur la distribution des marqueurs biologiques au sein d'un niveau sédimentaire de faciès uniforme. Les modifications dans la répartition de l'hopane, du stérane et du diastérène/diasterane en fonction de la profondeur sont comparées à celles qui sont provoquées par le Dôme de Krefeld. Les effets temps-température sont discutés à partir de la composition des hydrocarbures stéroïdes aromatiques. Les auteurs montrent que la valeur des paramètres de maturation liés à la profondeur ne peuvent être interprétés sans que l'on prenne en considération les événements tectoniques postsédimentaires. Des échantillons provenant de structures en horst montrent un degré d'évolution plus élevé que celui auquel on s'attend d'après leur profondeur actuelle.

---

30- - . 350 1000 . , . , , - . , . . - . , , , .

     

Transport properties of rocks from statistics and percolation

Two simplified microstructural models that account for permeability and conductivity of low-porosity rocks are compared. Both models result from statistics and percolation theory. The first model assumes that transport results from the connection of 1D objects or pipes; the second model assumes that transport results from the connection of 2D objects or cracks. In both cases, statistical methods permit calculation of permeability k and conductivity , which are dependent on three independent microvariables: average pipe (crack) length, average pipe radius (crack aperture), and average pipe (crack) spacing. The degree of connection is one aspect of percolation theory. Results show that use of the mathematical concept of percolation and use of the rock physics concept of tortuosity are equivalent. Percolation is used to discuss k and near the threshold where these parameters vanish. Relations between bulk parameters (permeability, conductivity, porosity) are calculated and discussed in terms of microvariables.     

Epirogenese in Nordwestdeutschland im höheren Jura und in der Unterkreide

Zusammenfassung Die epirogenen Vorgänge, die in Nordwestdeutschland im höheren Jura und in der Unterkreide stattgefunden haben, werden in drei Karten dargestellt und im Text erörtert. Vorbedingung hierfür war die Möglichkeit der Trennung des epirogenen und des halokinetischen Anteils an den jeweiligen Bodenbewegungen.

---

Epeirogenic movements, which happened in Northwest-Germany in later Jurassic and in lower Cretaceous time are mapped and discussed. Preliminary condition for this was the possibility of separating the epeirogenic and the halokinetic part of the movements.

---

Résumé Les événements épirogénétiques qui se sont produits dans la partie supérieure du Jurassique et au Crétacé inférieur en Allemagne du Nord-Ouest sont discutés et représentés sous forme de cartes. La condition préliminaire pour cela était la possibilité de séparer les mouvements épirogénétiques et les mouvements halokinétiques.

---

, - . .

     

An objective replacement method for censored geochemical data

Geochemical data are commonly censored, that is, concentrations for some samples are reported as less than or greater than some value. Censored data hampers statistical analysis because certain computational techniques used in statistical analysis require a complete set of uncensored data. We show that the simple substitution method for creating an uncensored dataset, e.g., replacement by3/4 times the detection limit, has serious flaws, and we present an objective method to determine the replacement value. Our basic premise is that the replacement value should equal the mean of the actual values represented by the qualified data. We adapt the maximum likelihood approach (Cohen, 1961) to estimate this mean. This method reproduces the mean and skewness as well or better than a simple substitution method using3/4 of the lower detection limit or3/4 of the upper detection limit. For a small proportion of less than substitutions, a simple-substitution replacement factor of 0.55 is preferable to3/4; for a small proportion of greater than substitutions, a simple-substitution replacement factor of 1.7 is preferable to4/3, provided the resulting replacement value does not exceed 100%. For more than 10% replacement, a mean empirical factor may be used. However, empirically determined simple-substitution replacement factors usually vary among different data sets and are less reliable with more replacements. Therefore, a maximum likelihood method is superior in general. Theoretical and empirical analyses show that true replacement factors for less thans decrease in magnitude with more replacements and larger standard deviation; those for greater thans increase in magnitude with more replacements and larger standard deviation. In contrast to any simple substitution method, the maximum likelihood method reproduces these variations. Using the maximum likelihood method for replacing less thans in our sample data set, correlation coefficients were reasonably accurately estimated in 90% of the cases for as much as 40% replacement and in 60% of the cases for 80% replacement. These results suggest that censored data can be utilized more than is commonly realized.     

Kleintektonische Strukturen am Südwestrand des Tauernfensters und ihre Einbeziehung in großtektonische Konzepte

Zusammenfassung Kleintektonische Strukturdaten wurden gesammelt am Südwestrand des Tauernfensters im Raume Vals über Mühlbach/Südtirol.Aus dem s-Flächen-, Kleinfalten- und Linear-Inventar in ostalpinen Gneisen und der peripheren penninischen Schieferhülle wird ein Partialbewegungssinn der deformierenden Kräfte von N nach S abgeleitet. Der Widerspruch zwischen diesen Geländebeobachtungen und den meisten großtektonischen Konzepten über Aufbau und Entwicklung der Ostalpen wird dargelegt.Die Hypothese einer sekundären Rückkippung zur Erklärung der lokalen Antivergenz scheint nach der tektonischen Analyse nicht glaubhaft. Eine primäre Aberranz zur Generalbewegungstendenz der Ostalpen-Decken wird für diese Region angenommen.

---

Mesoscopic structural dates (planation, minor folds, lineation) of the area of Vals near Mühlbach (Southern Tirol — North Italy, SW-margin of the Tauern window) demonstrate a tendency of the rockdeforming strengths from N towards S. The investigations took place in east-alpine gneisses and in the Upper Penninic mantle.The local tectonic facts appear to be in contradiction to most of the conceptions of structural evolution of the Eastern Alps.The theory of secondary turn-back (caused by accumulation of the Tauern inlier) to explain the local avergence cannot be supported. More applicable seems to be the assumption of primary tectonical exception from the rule of the general northward trend.

---

Résumé Des recherches tectoniques sont faites dans le gneiss austroalpin et dans le Schieferhülle supérieur pennique de la région de Vals près de Mühlbach (Tyrol Sud, cadre SO de la fenêtre des Tauern).Les structures mesoscopiques (planation, plis mineurs, linéations) démontrent tendance de déplacement tectonique partiel du N vers le S. Cette determination semble contredire comme arrangement anormal à plusieurs conceptions sur l'evolution tectonique des Alpes Orientales.Il n'est pas possible de recommander la présomption d'un basculement secondaire (en suite de l'accumulation des Tauern); plus applicable semble l'hypothèse de divergence tectonique primaire et local.

---

- c ( , ). . .

     

Zur Tektonik im Bereich der Brennerlinie

Zusammenfassung Die Verfasser entwickeln aus den Ergebnissen ihrer feldgeologischen und petrographischen Untersuchungen — gestützt auf gesteinsmechanische Überlegungen und tektonische Experimente — ein neues geologisches Konzept für das Tauernwestende.

---

A new concept about the geology of the Brenner region is developed from field observations, petrographic investigations, mechanic considerations and tectonic experiments.

---

Résumé Les auteurs présentent une conception géologique nouvelle de la partie occidentale des Tauern d'après leurs observations géologiques sur le terrain et leurs recherches pétrographiques, en s'appuyant sur des considérations de la mécanique des roches et des expériences tectoniques.

---

- .

---

---

FrauSchmitz-Wiechowski (Wiechowski 1968) hat die Phyllitserie östlich des Brenner untersucht und tektonische Grenzflächen verfolgt.Förster bearbeitete hauptsächlich das Gebiet westlich des Brenner.     

Oxygen isotope variations in granulite-grade iron formations: constraints on oxygen diffusion and retrograde isotopic exchange

The oxygen isotope ratios of various minerals were measured in a granulite-grade iron formation in the Wind River Range, Wyoming. Estimates of temperature and pressure for the terrane using well calibrated geothermometers and geobarometers are 730±50° C and 5.5±0.5 kbar. The mineral constraints on fluid compositions in the iron formation during retrogression require either very CO₂-rich fluids or no fluid at all. In the iron formation, isotopic temperature estimates from quartz-magnetite fractionations are controlled by the proximity to the enclosing granitic gneiss, and range from 500° C ( _{qz – mt}=10.0) within 2–3 meters of the orthogneiss contact to 600° C ( _{qz – mt}=8.0) farther from the contact. Temperature estimates from other isotopic thermometers are in good agreement with those derived from the quartz-magnetite fractionations.During prograde metamorphism, the isotopic composition of the iron formation was lowered by the infiltration of an external fluid. Equilibrium was achieved over tens of meters. Closed-system retrograde exchange is consistent with the nearly constant whole-rock ¹⁸O_wr value of 8.0±0.6. The greater _qz-mt values in the iron formation near the orthogneiss contact are most likely due to a lower oxygen blocking temperature related to greater exchange-ability of deformed minerals at the contact. Cooling rates required to preserve the quartz-magnetite fractionations in the central portion of the iron formation are unreasonably high (800° C/Ma). In order to preserve the 600° C isotopic temperature, the diffusion coefficient D (for -quartz) should be two orders of magnitude lower than the experimentally determined value of 2.5×10^–16 cm²/s at 833 K. There are no values for the activation energy (Q) and pre-exponential diffusion coefficient (D ₀), consistent with the experimentally determined values, that will result in reasonable cooling rates for the Wind River iron formation. The discrepancy between the diffusion coefficient inferred from the Wind River terrane and that measured experimentally is almost certainly due to the enhancement of exchange by the presence of water in the laboratory experiments. Cooling rate estimates were also determined for iron formation retrograded under water-rich conditions. Application of the experimentally determined data to these rocks results in a reasonable cooling rate estimate, supporting the conclusion that the presence of water greatly enhances oxygen diffusion.Contribution 441 from the Mineralogical Laboratory, University of Michigan     

Kohlenstoff- und Sauerstoff-Isotopenuntersuchungen an Karbonatkonkretionen und umgebendem Gestein

The composition of the carbon and oxygen isotopes has been determined in about 40 carbonate concretions and surrounding clays and shales of different geological ages. Two different areas and stratigraphic levels in Northwestern Germany have been sampled: 1. concretions in shales of Lower Cretaceous age fromt he area between Hildesheim and Hannover; 2. concretions in shales of Devonian age from the Harz mountains (and the foreland).While the concretions of Group 1 generally are enriched in the light isotope ¹²C (¹³C values from –3.3 to –43.2 relative to PDB), compared to the surrounding shales (0.9 to –5.3), no significant differences could be observed between concretions and shales of Group 2 (concretions: 2.0 to –7.0; shales: –0.3 to –6.2).The average ¹⁸O/¹⁶O ratios of the Devonian samples are lower than those from the Cretaceous, because the probability of an exchange with light meteoric water in diagenetic reactions increases with geologic age.Formed under special conditions of the microenvironment, such as the presence of organic material and local alkalinity during the early stages of diagenesis, the carbon isotopic composition of concretions will probably have preserved some characteristic properties of this mioroenvironment.It is assumed that concretions with the heavy carbon contain carbon from CO₂ which was in isotope equilibrium with CH₄, both of them liberated during the decay of organic material. The light carbon from concretions of Group 1 is explained as fixed CO₂, originating from microbiological or inorganic oxidation of organic substances, which was not in isotope equilibrium with methane (if this was present at all).After precipitation of the concretionary carbonates, no significant carbon isotope exchange seems to have occurred, otherwise the pattern of a heterogeneous carbon isotope composition found in several concretions could not be explained.Strontium concentrations (see Appendix) range from those of primary calcite precipitated in sea water to diagenetic carbonates formed from solutions with a high Ca/Sr ratio. They indicate that during the formation of concretions in abundant cases the system was closed to ocean water.     

Ergebnisse refraktions-seismischer Messungen im Nordteil der Geotraverse IA

Zusammenfassung Im Nordteil der Ostalpen, hauptsächlich im Gebiet zwischen Salzach und Inn, wurden bei Steinbruch-Sprengungen 11 Profile refraktions-seismisch vermessen. Weil die Geschwindigkeit seismischer Wellen im Bereich dieser Profile auch in lateraler Richtung relativ stark variiert, wurde zur Interpretation der Messungen ein vom Autor entwickeltes Computer-Programm für strahlenseismische Modellrechnungen in zweidimensional inhomogenen Medien verwendet. Für einige der Profile wurden damit Modelle abgeleitet, die als wichtigste Eigenschaft eine Unterlagerung der Kalkalpen bis mindestens 15 km von ihrem Nordrand nach Süden durch eine Schicht von maximal etwa 7 km Mächtigkeit zeigen. Diese Schicht kann nach ihrer Wellengeschwindigkeit aus Molasse und/oder Helvetikum und/oder Flysch bestehen.

---

In the northern part of the Eastern Alps, mainly in the region between Salzach and Inn, 11 seismic refraction profiles were measured using quarry blasts. There are relatively big changes of seismic velocity in this area even in lateral direction, and therefore the measurements were interpreted with a ray tracing method for twodimensional inhomogeneous mediums, the computer program for which was written by the author. Thus there were found models for some of the profiles in which the most important structure is a layer of about 7 km thickness lying under the Northern Calcareous Alps and stretching at least 15 km from their northern margin southwards. From its seismic velocity this layer can consist of Molasse and/or Helveticum and/or Flysch.

---

Résumé Dans la partie nord des Alpes Orientales 11 profils de seismique par réfraction ont été enrégistrés, en utilisant des explosions de carrières. La majorité des profils est située entre la Salzach et l'Inn. Les importantes variations latérales des vitesses de propagation nécessitèrent le développement d'un programme de calcul des rayons séismiques dans un milieu inhomogène à deux dimensions. L'interprétation de plusieurs des profils à l'aide de ce programme indique la présence d'une couche à faible vitesse sous les Alpes Calcaires s'étendant du bord nord des Alpes jusqu'à 15 km au moins vers le sud. L'épaisseur maximale de cette couche est environ de 7 km. Les vitesses indiquent qu'elle peut être composée de matériaux de la Molasse, des couches Helvétiques et du Flysch.

---

- II- , . ., . . . , . , , , 7 , , no- , 15 . , , .

     

Measurement error in compositional data

Compositional data, consisting of vectors of proportions summing to unity such as the geochemical compositions of rocks, have proved difficult to analyze. Recently, the introduction of logistic and logratio transformations between the d-dimensional simplex and Euclidean space has allowed the use of familiar multivariate methods. The problem of how to model and analyze measurement errors in such data is approached through the concept of a perturbation of a composition. Such modeling allows investigation of the role of rescaling, quantification of measurement error, analysis of observor error, and assessment of the effect of measurement error on inferences.     

Hydrothermale Lösungen

Zusammenfassung Das hydrothermale Auflösungsverhalten der vorwiegend als Gangarten auf-tretenden Mineralphasen Fluorit (CaF₂), Baryt (BaSO₄), Cölestin (SrSO₄) und Anglesit (PbSO₄) läßt sich übersichtlich in einem Temperatur-Löslichkeitsdiagramm darstellen und mit dem bekannten, qualitativ ähnlichen System SiO₂-H₂O vergleichen.Gegenüber dem molekulardispers gelösten SiO₂ ergeben sich aber für die in Ionen dissoziierten Lösungen der schwerlöslichen Sulfate und des Fluorits beträchtliche Verschiebungen der Sättigungsgleichgewichte, insbesondere bei Anwesenheit von Elektrolyten als Lösungsgenossen.Diese Beeinflussung, die für die genetischen Verhältnisse der Minerallagerstätten von entscheidender Bedeutung ist, wird für 0,1–2,0 normale NaCl-Lösungen im NaCl-Konzentrations-Löslichkeits-Diagramm der Minerale Fluorit, Baryt, Cölestin und Anglesit isotherm bis zum Siedepunkt der wäßrigen Mischphasen untersucht.Ferner wird das Löslichkeitsverhalten in den ternären Systemen BaSO₄-NaCl-H₂O und SrSO₄-NaCl-H₂O für Baryt und Cölestin gegen 2,0n NaCl-Lösungen entlang der Grenzkurve des Dreiphasengebietes und für die Isochoren 0,326 bis 0,6 bis 600° C und 2000 Bar dargestellt und mit den entsprechenden Verhältnissen der reinen wäßrigen Systeme verglichen.Ein abweichendes inkongruentes Auflösungsverhalten von Alumosilikaten mit Schichtgitterstruktur läßt sich am Beispiel des Muskovits durch die experimentelle Bestimmung der nichtstöchiometrischen Molekularverhältnisse SiO₂/K₂O und SiO₂/Al₂O₃ in den gesättigten Lösungen für den hydrothermalen Existenzbereich des Muskovits nachweisen.

---

The behaviour of solubility for some minerals, which were for the most part found as vein minerals, was determined experimentally and is represented by summarizing diagrams.In the temperature-solubility diagram the hydrothermal solubility of fluorite, barite, celestine and anglesite is compared to the solubility of quartz and muskovite for the boundary curve of the three-phase region and for some isochores. As opposed to SiO₂, which is molecularly dispersed in solution, the ionic solutions of the systems CaF₂-H₂O, BaSO₄-H₂O, SrSO₄-H₂O and PbSO₄-H₂O show considerable displacement of the saturation equilibrium when other components are present in the solution.This influence on the solubility, significant for the genetic relations of mineral deposits, was quantitatively analyzed for 0.1–0.2 n-NaCl solutions. The results are isothermally shown in the NaCl-concentration solubility diagram within the boundaries of room temperature and the boiling point of the aqueous mixed phases.In the tenary systems BaSO₄-NaCl-H₂O and SrSO₄-NaCl-H₂O, the hydro-thermal solubility of barite and celestine in 2.0 n-NaCl solutions is also shown for the range of the boundary curve of the three-phase region and for the isochores 0.326–0.6 up to a temperature of 600° C and a pressure of 2000 bar. These solubilities are then compared with the diagrams of solubility for pure aqueous solutions.The irregular and incongruent behaviour of the solubility of aluminium-silicates of a layered-lattic structure is demonstrated for the system KAl₂(OH)₂-AlSi₂O₁₀-H₂O in the presence of muscovite by experimental determination of the non-stoechiometric molecular proportions of SiO₂K₂O and SiO₂ Al₂O₃. Such determination was conducted in saturated solutions for the hydrothermal range of the existence of muscovite.The geological importance of the knowledge of hydrothermal data of solubility and their application to the process of the hydrothermalmagmatic series and hydrothermalmetamorphosis is discussed.

---

Résumé Le comportement de dissolution expérimentalement déterminé de certains minéraux trouvés surtout en filons est exposé en le résumant par diagrammes.La solubilité hydrothermique de fluorine, barytine, célestine et anglésite est comparée pour la courbe limitante (de la région triphasée) et pour les isochores 0,326–0,6 g.cm³ du diagramme température-solubilité avec le comportement de dissolution du quartz et de la muscovite. Les solutions ioniques des systèmes CaF₂H₂O, BaSO₄-H₂O, SrSO₄-H₂O et PbSO₄-H₂O montrent, comparées au SiO₂ dissous en dispersion moléculaire, de différences importantes d'équilibres de saturation en présence d'associés de solution.Cette influence sur la solubilité qui est d'une importance décisive pour les conditions génétiques des gisements de minéraux, a été examinée quantitativement pour les solutions 0,1–0,2—normales de NaCl. La présentation s'est faite isothermiquement dans le diagramme de concentration-solubilité de NaCl entre la température de chambre et le point d'ébullition des phases mixtes aqueuses.Dans les systèmes ternaires BaSO-NaCl-H₂O et SrSO₄-NaCl-H₂O la solubilité hydrothermique de barytine et de célestine en des solutions 2,0-normales de NaCl est présentée également pour l'espace des courbes limitantes de la région triphase et pour les isochores 0,326–0,6 jusqu'à 600° C et 2000 Bar. Elle est comparée avec les courbes de solubilité de systèmes purement aqueux. Le comportement de dissolution divergeant incongruent des silicates d'alumine à structure stratifiée en treillis est démontré pour le systême KAl₂(OH)₂-AlSi₃O₁₀-H₂O par exemple de la muscovite en déterminant expérimentalement les proportions moléculaires non-stochiométriques SiO₂ K₂O et SiO₂Al₂O₃ dans les solutions saturées pour la domaine d'existence hydrothermique de la muscovite.Importance géologique de la connaissance des dates de solubilité hydrothermique et leur application sur les événements des conséquences hydrothermiques-magmatiques et sur les événements de la métamorphose hydrothermique sont discutées.

---

y 600° 2000 . (CaF₂), ( SO₄), . (SrSO₄) (PbSO₄) - Sio₂-₂.

     

Zur Frage der Geschwindigkeit des Deckenschubes

Zusammenfassung In den folgenden Ausführungen werden Daten über die Geschwindigkeit der Bewegung von Schubdecken in der Hauptbewegungsphase geliefert. Die hierfür verwendeten Beispiele stammen aus den Ostalpen und Westkarpaten. Eine sichere Geschwindigkeits-Bestimmung ist derzeit noch nicht durchführbar. Es können aber Minimalbewegungswerte von etwa 1,5 mm/Jahr errechnet werden. Die reale Transportgeschwindigkeit könnte auch wesentlich höher liegen, vielleicht bei 10–20 mm/Jahr.

---

This paper presents facts pertaining to the velocity of the overthrust of nappes during a tectonical phase by means of examples from the Eastern Alps and the Western Carpathians. An exact determination of this velocity is still not possible. One can calculate minimum values of near 1,5 mm/year. The real velocity of the overthrusts of nappes might be much higher, perhaps 10–20 mm/year.

---

Résumé L'article expose des données sur la vitesse des mouvements des nappes de charriage pendant la phase principale de transport. Les exemples présentés proviennent des Alpes orientales et des Carpathes occidentales. Il n'est pas possible jusqu'à présent de faire une détermination plus exacte de cette vitesse. Mais on peut calculer un minimum de transport d'environ 1,5 mm/an. La vitesse réelle des mouvements de translation pourrait même être nettement plus élevée, et atteindre peut-être 10–20 mm/ an.

---

. . . 1,5 /. , 10–20 /.

     

Conditional Simulation of Random Fields by Successive Residuals

This paper presents a new approach to the LU decomposition method for the simulation of stationary and ergodic random fields. The approach overcomes the size limitations of LU and is suitable for any size simulation. The proposed approach can facilitate fast updating of generated realizations with new data, when appropriate, without repeating the full simulation process. Based on a novel column partitioning of the L matrix, expressed in terms of successive conditional covariance matrices, the approach presented here demonstrates that LU simulation is equivalent to the successive solution of kriging residual estimates plus random terms. Consequently, it can be used for the LU decomposition of matrices of any size. The simulation approach is termed conditional simulation by successive residuals as at each step, a small set (group) of random variables is simulated with a LU decomposition of a matrix of updated conditional covariance of residuals. The simulated group is then used to estimate residuals without the need to solve large systems of equations.     

Geochemical prospecting for lead and zine in Gebel el Rousas,Eastern Desert,Egypt

Gebel El Rousas is an isolated hillock in the Eastern Desert of Egypt. It consists of the Basement Complex (subsurface) which is non-conformably overlain by the Middle Miocene and successively by Pleistocene-Recent terraces. The Miocene strata are mineralized by oxidized hypogene lead-zinc deposits.Geochemical prospecting was attempted for the first time in Gebel El Rousas and for the second time in Egypt. The old terraces of gravels and sands covering the hillock were sampled on a grid pattern of a 30 m spacing. The samples were taken at a depth of 30 cm from the surface. They were sieved to –150 mesh and analyzed for Pb, Zn, Cu, Fe, Mn, and CO₂.Significant contrasts and anomalies resulted for Pb, Zn, and Fe. The main anomalies are parallel and generally coincide with the subsurface mineralized zone which is inferred to cross the area on the same trend. The mineralized zone extends as shown by the geochemical pattern southward, from the known northern part, to a southern district which has not been checked by drilling or any other testing.

---

Zusammenfassung Djebel El Rousas ist ein isolierter Hügel in der Ägyptischen Ostwüste. Er besteht aus dem Basementkomplex, der diskordant von MittelmiozÄn und aufeinanderfolgend von PleistozÄn-HolozÄn-Terrassen überlagert wird. Die MiozÄn-Schichten sind mit oxydischen hypogenen Blei-Zink-Ablagerungen vererzt.Im Djebel El Rousas wurde zum erstenmal der Versuch einer geochemischen Prospektion durchgeführt, für ganz Ägypten ist es das zweite Mal. Gitterförmig wurden im Abstand von 30 m den alten Kies- und Sandterrassen, die den Hügel bedecken, Proben aus einer Tiefe von 30 cm unter der OberflÄche entnommen. Die Proben wurden mit 150 Maschenweite gesiebt und auf Pb, Zn, Cu, Fe, Mn und CO₂ analysiert.Eindeutige Kontraste und Anomalien wurden für Pb, Zn und Fe festgestellt. Die Hauptanomalien sind parallel und fallen normalerweise mit der mineralisierten Zone unter Tage zusammen, die das Gebiet in derselben Richtung durchquert. Wie aus der geochemischen Karte hervorgeht, setzt sich die vererzte Zone nach Süden in ein Gebiet fort, das bisher noch nicht durch Bohrungen untersucht wurde.

---

Résumé Gebel El Rousas est un monticule isolé dans le Désert Oriental de l'égypte. Il se compose de roches du Basement Complex (sous-sol) surmontées en discordance par des terrasses du Miocène Moyen et succéssivement par des terrasses du Pleistocène-Récent. Les couches du Miocène sont mineralisées par des dépÔts hypogènes de plomb et de zinc oxidés.Les prospections géochimiques furent essayées pour la première fois au Gebel El Rousas et pour la seconde fois en égypte. Des échantillons des anciennes terrasses de galets et de sables recouvrant ce monticule furent prises en une carte quadrillé de 30 m. Les échantillons furent prélevés à une profondeur de 30 cm de la surface. Ils furent criblés jusqu'aux mailles de 150 analysées pour la détermination de Pb, Zn, Cu, Fe, Mn, et CO₂.Des contrastes et des anomalies significatifs furent obtenus pour le Pb, Zn, et Fe. Les anomalies essentielles sont parallèles et généralement coincident avec la zone minéralisée du sous-sol qui est supposée traverser la région suivant la mÊme direction. La zone minéralisée s'étend comme l'indique la carte géochimique du Nord au Sud vers un district qui n'a pas été vérifié par forage ou par toute autre méthode éxpérimentale.

---

Djebel El Rousas — , . - . . , . 30 , , 30 . 150 Pb, Zn, u, Fe, n ₂. Pb, Zn Fe. , . , .

     

Models to predict water chemical cluster variables

This study is an attempt to quantify and rank variables of significance to predict mean values of lake pH and related variables (alkalinity, conductivity, hardness, etc.) in small glacial lakes. The work is based on a new and extensive set of data from 95 Swedish lakes and their catchment areas. Several empirical models based on catchment and lake morphometric parameters have been presented. These empirical models can only be used to predict mean values of these variables for lakes of the same type, and these models based on geological map parameters can evidently not be used for highly time-dependent and site-typical predictions. Various hypotheses concerning the factors regulating the mean values of the cluster variables were formulated and tested. Different statistical tests were used to separate random influences from causal. The most important map parameters were: the percent of rocks and open (=cultivated) land in the so-called near area to the lake [as determined with the drainage area zonation (DAZ) method], mean depth, linked to resuspension and the form and size of lakes, relief of the drainage area and lake area. Each of these variables only provides a limited degree of (statistical) explanation of the variability in mean annual values of pH and the water chemical cluster variables among the lakes. The predictability of some of the models can be markedly improved by accounting for the distribution of the characteristics in the drainage area. The variability in mean annual values of pH (and related variables) from other parameters, such as specific anthropogenic load, etc., may then be quantitatively differentiated from the impact of these geological parameters. This paper also gives a simple method to estimate natural, preindustrial reference values of these water chemical variables from the presented models.     

Quantifying and testing differences among means of compositional data suites

Commonly, geological studies compare mean values of two or more compositional data suites in order to determine if, how, and by how much they differ. Simple approaches for evaluating and statistically testing differences in mean values for open data fail for compositional (closed) data. A new parameter, an f-value, therefore has been developed, which correctly quantifies the differences among compositional mean values and allows testing those differences for statistical significance. In general, this parameter quantifies only therelative factor by which compositional variables differ across data suites; however for situations where, arguably, at least one component has neither increased nor decreased, anabsolute f-value can be computed. In situations where the compositional variables have undergone many perturbations, arguments based upon thef-values and the central limit theorem indicate that logratios of compositional variables should be normally distributed.     

Potassic cordierites: characteristic minerals for high-temperature,very low-pressure environments

The mineral chemistry of cordierites from three different sanidinite facies localities-1) volcanic xenoliths from the Eifel, Germany; 1) buchites of the Blaue Kuppe, Germany; 3) paralavas from the Bokaro coalfield, India-is characterized by unusually high potassium contents up to 1.71 wt%, equivalent to 0.22 K atoms per formula unit (p.f.u.) based on 18 oxygens. Significantly, these cordierites are either hexagonal highcordierites (indialites) with =0 or exhibit intermediate -values 0<<0.20 relative to well Al,Si-ordered orthorhombic low-cordierite. Based on microprobe analyses, the predominant substitutional mechanism for alkali incorporation is Alk^[Channel]+Al^[4] for +Si^[4], thus leading to Al/Si-ratios deviating considerably from the value 4:5 in ideal cordierite M₂[Al₄Si₅O₁₈]. The most highly substituted cordierite from Blaue Kuppe is about (K_0.22Na_0.07)^[Ch](Mg_1.33Fe _0.66 ²⁺ )^[6][Al_4.16Si_4.79O₁₈]. Bokaro cordierites are further characterized by obvious (Al+Si)-deficiencies against the ideal value of 9.0 p.f.u., a tendency of which is apparent in most Blaue Kuppe analyses as well. As the tetrahedral deficiencies are often equivalent to excess cations in the octahedra, we assume that ferric iron fills up the remaining tetrahedral sites, again linked with the introduction of potassium according to K+Fe³⁺ for +Si. In comparison with the available experimental data, these natural potassic cordierites are considered stable high-temperature phases regarding their compositions, but not their structural states. Although the substitution KAl for Si in Mg-cordierite is known to lower the maximum -value to be attained, the hexagonal nature of the cordierites must be due to very rapid crystallization and subsequent quenching. The higher -values of the Blaue Kuppe cordierites might be caused by their topotactic origin from preexisting biotite. The complicated twin and domain patterns of the hexagonal Eifel and Bokaro cordierites as observed in thin section could perhaps be attributed to structural modulations as postulated recently for hexagonal cordierite shortly after its growth.     

Wollastonite at the Sterling Hill Fe–Zn–Mn ore body, Ogdensburg, New Jersey

Summary Wollastonite occurs abundantly at the Sterling Hill Fe–Zn–Mn ore deposit, Ogdensburg, New Jersey, one of the few occurrences of wollastonite in regionally metamorphosed rocks; it is absent from the surrounding Franklin marble. Wollastonite occurs in two distinct bands along the inner margins of the synclinal ore deposit. Minerals associated with wollastonite include calcite, grossular-andradite, diopsidic pyroxene, alkali feldspar, and rarely vesuvianite, quartz or bustamite. Assuming the generally accepted values of 750°C at 5kbar at Sterling Hill during metamorphism in the Grenville Orogeny, thermodynamic modeling of reactions involving garnet and wollastonite suggest XCO₂ 0.35 in the wollastonite-bearing rocks. Infiltrating metamorphic fluid rich in H₂O was necessary for the formation of wollastonite; at XCO₂ of 0.35, the calculated minimum volumetric water:rock ratio is 0.51. The source of the water is believed to be the dehydration of water-rich phases in adjacent ores or mafic rocks. The chemical compositions, textures, stratigraphy, and calculated metamorphic conditions show that wollastonite formed from calcite and quartz at the peak of the Grenville Orogeny.Present address: Maryland State Highway AdministrationReceived August 18, 2002; revised version accepted February 5, 2003     

Physico-chemical seasonal variability of a tropical estuary: major and minor elements in water and air

The lower reaches of the Coatzacoalcos River in southeast Mexico is an area of intense industrial development. The physico-chemical characteristics of the area have exhibited differences over the years. Apparently from the associated outcroppings of limestone in the Uxpanapa River Basin, the major elements that are dissolved show higher concentrations of Ca, Mg and HCO₃^– in the waters supplied by this river. The water in the Calzadas River contains high concentrations of Ca, SO₄ and HCO₃^– that are associated with the saline domes crossed by this river. Due to industrial discharges, the sulfate concentration is very high in the water and air during April. Nitrate concentration diminishes with salinity. Higher nitrate as well as nitrite and ammonia levels are present during flood season. Phosphate concentration, associated with high oxygen levels, is higher in January. Zn, Cu and Cr are higher during the dry season (April) when dilution is minimal and low levels of TOC are present. The smaller concentrations of Zn and Cu observed in January are associated with high TOC values in water. The lower levels of Cr present in August are associated with high amounts of suspended matter. Pajaritos Lagoon and Teapa-L, with large industrial discharges, have the highest nutrient and dissolved metal concentrations in the area. Air particles smaller than 2.5 m contain Fe, V, Ti, Cu, Zn, and high amounts of S. These anomalous concentrations of sulfates and metals are attributed to anthropogenic sources.     

Basalt contamination by continental crust: Some experiments and models

Chemical interaction between molten basalt and felsic minerals of the continental crust (quartz, K-feldspar, and oligoclase) was examined in static and dynamic experiments at 1,200°–1,400° C. Under circumstances of continuous stirring at 1,400°, -quartz dissolves in tholeiite melt at a rate of 3.3×10^–6 g/s per cm² of contact area; at 1,300°, the solution rate is 1.5×10^–6 g/cm{cm2}s. The feldspars are molten at the experimental conditions, and interact with contacting basalt melt by diffusion in the liquid state. This is a complex process characterized by rapid initial diffusion of alkalies to establish a distribution between felsic melt and basalt similar to that observed in cases of actual two-liquid equilibrium (both alkalies reach concentrations in the felsic melt 1.5–3 times those in the basalt). Alkali diffusion may be uphill or downhill, depending on which direction of net flux is required to produce a two-liquid type distribution. Once this distribution is attained, subsequent diffusion of all melt species is slow and apparently limited by the diffusivity of SiO₂, which is 10^–9-l0^–10 cm²/s at 1,200° C. Interdiffusion experiments involving molten basalt and synthetic granite confirm the behavior illustrated by the feldspar/basalt results, and give similar SiO₂ diffusivities.The solution rates and interdiffusion data can be used to model basalt contamination processes likely to occur in the continental crust. For the restricted case of solid quartzitic xenoliths, the uptake of SiO₂ in a well-mixed basalt magma is quite fast: appreciable SiO₂ contamination may occur over exposure times of only days to years. If basalt magma induces local melting of crustal rocks, the assimilation process becomes one of liquid-state interdiffusion. In this case, the varying diffusivities of ions and their differing preferences for silicic relative to basaltic melts can produce marked selective contamination effects. Selective contamination of ascending basaltic magmas is particularly likely in the case of K₂O, which may be introduced in substantial amounts even when other elements remain unaffected. The Na₂O content of mantle-derived magmas is buffered against contamination by crustal materials, and K₂O is buffered against further increases once it reaches a level of 1–1.5 wt.%.