The use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual Colorado river discharge

We describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river-water/seawater mixing zone of the Colorado River estuary. Sclerochronological techniques are used to identify tidally-induced, fortnight-scale bundles of daily growth increments within shell cross-sections. These fortnightly markers are used to establish a chronology for samples taken for δ¹⁸O analysis. A composite seasonal δ¹⁸O profile derived from five shells that grew in the absence of river-water flow is used as a baseline against which profiles of river-influenced shells are compared. Because this comparison is between matched fortnights within a year, the temperature of shell growth is likely to be very similar. The difference in δ¹⁸O between the river-influenced shell and the “no-flow” composite shell therefore represents the change in the δ¹⁸O of the water due to the presence of river water in the mixing zone. The river water end-member is also determined within a fortnightly context so that the change in the δ¹⁸O of mixing-zone water can be used to calculate the relative proportions of seawater and fresh-water. The fresh-water end-member is calculated from the δ¹⁸O of bivalves alive prior to the emplacement of dams and water diversions on the Colorado River. The marine end-member is based on direct measurements of the δ¹⁸O of northern Gulf of California water during times of no Colorado River flow. The system has been calibrated to absolute flow amounts using recent releases of known volume and rate.     

Coronal velocity measurements with Ulysses: multi-link correlation studies during two superior conjunctions

A well-known method for studying the solar wind very close to the Sun (heliocentric distances: 4 to 40 solar radii) is by radio sounding between a spacecraft at superior conjunction and the Earth. The Ulysses Solar Corona Experiment was performed at the spacecraft's two solar conjunctions in summer 1991 and winter 1995, during which dual-frequency ranging and Doppler observations were conducted globally on a nearly continuous basis at the NASA Deep Space Network and other ground stations. The dual-frequency Doppler measurements were used to determine coronal plasma velocities by a cross-correlation analysis during those occasions when tracking data were recorded simultaneously at two well-separated ground stations. A filtering technique was developed to suppress noise and enhance the 2-station correlations, a procedure particularly effective at small solar offsets. From the electron content measurements during the two solar conjunctions it was found that regions of higher electron density tend to occur when the two-station correlations yield slower outward flow velocities.     

Die Problematik paläogeographischer Rekonstruktion

Zusammenfassung Mit der heute wohl begründeten Annahme von Lageveränderungen der geotektonischen Großeinheiten während der Erdgeschichte ist die paläogeographische Rekonstruktion problematisch geworden, da sie nicht auf der Basis der heutigen geographischen Lagebeziehungen aufbauen kann. Auf der anderen Seite ist gerade die paläogeographische Rekonstruktion, die unvoreingenommen möglichst alle Einzeldaten der verschiedenen Spezialdisziplinen berücksichtigt, die Voraussetzung für eine kritische Analyse der wechselnden Lagebeziehungen. Gerade seine Problematik macht den paläogeographischen Rekonstruktionsversuch zum unentbehrlichen methodischen Hilfsmittel geologischer und geotektonischer Forschung — unter der Voraussetzung, daß man sich dabei nicht vom heutigen Kartenbild leiten läßt. An den Beispielen des Amazonas-Beckens, des Atlantischen Ozeans und der Paläogeographie Mittelamerikas—Westindiens werden diese Zusammenhänge dargelegt.

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By the well-founded hypothesis of changes in the position of geotectonical major units during earth history, a paleogeographical reconstruction becomes problematical, since it cannot be based on the present geographical situation. On the other hand, it is above all the paleogeographical reconstruction which considers the greatest possible number of single data of the various branches of earth sciences, thus being the presupposition for a critical analysis of the changing position of the geotectonical units. By its complexity, the attempt of paleogeographical reconstruction is an indispensable methodical aid for geological and geotectonical research — under the condition that it is done independently of the actual geographical map. These correlations are demonstrated on the examples of the Amazon basin, the Atlantic Ocean and the paleogeography of Middle America and the West Indies.

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Résumé L'hypothèse bien fondée des changements de position des blocs continentaux pendant l'histoire de la terre, rend problématique la réconstruction paléogéographique, puisque celle-ci ne peut pas se baser sur la situation géographique actuelle. De l'autre coté, c'est surtout la réconstruction paléogéographique qui tient compte des dates individuelles des branches géoscientifiques particulières, étant ainsi le fondement pour une analyse critique des changements de position des éléments tectoniques. Par son caractère problématique, l'essai d'une réconstruction paléogéographique est une aide indispensable pour la recherche géologique et géotectonique — sous la condition qu'on ne regard pas la figure des cartes modernes. L'auteur démontre ces relations par l'exemple du bassin des Amazones, de l'Océan atlantique et de la paléogéographie de l'Amérique centrale et des Indes occidentales.

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Resumo A hipótese é bem fundamentada que, durante a história da terra aconteceram alterações da posiçào dos blocos continentais; em consequência disso a reconstrução palaogeográfica é um pouco problemática; pois não pode basear-se na configuração geográfica atual. Por outro lado, é exatamente a reconstrução paleogeográfica, baseada nas observações e experiências das diversas disciplinas geológicas, que constitui o único fundamento certo de uma análise das alterações consecutivas da posição das unidades geotectônicas. A tentativa da reconstrução paleogeográfica torna-se, dêste modo, um método indispensável para a pesquisa geológica e geotectônica, caso que a reconstrução paleogeográfica é executada independentemente da configuração geográfica atual. Estas relações são demonstradas pelos exemplos do desenvolvimento geológico da bacia do Amazonas, do Ozeano Atlântico e da América Central e das ilhas centralamericanas.

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Laborversuche zum Abbau von Biotit

Zusammenfassung Laborversuche zum Abbau von Biotit und Umbau zu Montmorillonit, Vermiculit oder einer Vermiculit-Chlorit-Wechsellagerung wurden bei pH-Werten von 3,0, 6,0 und 9,8 durchgeführt, wobei sowohl im reduzierenden als auch im oxidierenden Milieu gearbeitet wurde. Aus den Untersuchungsergebnissen kann geschlossen werden, daß durch einen stärkeren Abbau der Oktaeder-Schicht im Verhältnis zum Gesamt-Abbau in saurem Milieu gegenüber basischem die Bildung von Vermiculit bis Chlorit-Vermiculit-Wechsellagerungen gefördert wird. Verstärkt wird dabei die Tendenz zur Chlorit-Bildung durch eine Durchströmung des Biotits. Die Entstehung eines Montmorin-Minerals (eines trioktaedrischen Beidellits) ist nur im basischen Milieu bei stagnierenden Lösungen möglich. Ein Einfluß reduzierender Bedingungen auf den Abbau von Biotit war nur im sauren Bereich festzustellen. In diesem Falle wurde der Abbau erheblich verstärkt. Als eine Hauptursache für die unterschiedliche Auflösung des Biotits unter den verschiedenen Bedingungen kann die Bildung oder das Fehlen einer Eisenhydroxid-Schutzschicht angesehen werden. Durch das Entstehen einer solchen Schicht kann der Abbau behindert werden. Wichtig ist weiterhin die Anwesenheit von Kationen, die den Kalium-Austausch fördern. In verdünnten Lösungen von Ca, Mg und Al konnte in einmonatigen Versuchen aus Hydrobiotit ein Montmorin-Mineral hergestellt werden.Die Ergebnisse der Laboruntersuchungen stimmen gut mit den bisher gemachten Beobachtungen an Biotitumwandlungen in Böden überein.

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Laboratory experiments on weathering phenomena in biotite

Treatment of biotite with solutions of different pH (3.0; 6.0; 9.8) in oxidizing environs showed, that under more acid conditions with good drainage of the solution through the biotite the alteration to vermiculite or even a vermiculite-chlorite interlayer is favoured, while the formation of montmorillonite from biotite can only take place in stagnant basic solutions. An accelerating influence of reducing environs in respect to the dissolution of biotite could only be stated at low pH. The more or less complete formation or the absence of Fe(OH)₃layers, which can help to protect the biotite from being dissolved, is regarded as one reason for the different alterations of biotite.Montmorillonite was easily prepared from hydrobiotite by treatment with 0.02 — n solutions of Ca, Mg and Al.

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Herrn Professor Dr. Dr. hc. C.W. Correns und Herrn Dozent Dr. E. Althaus, Karlsruhe danke ich für Anregungen und Diskussionen. Frau E. Bayer, Karlsruhe, danke ich für die Anfertigung der chemischen Analysen, Herrn Dr. R. Emmermann, Petrographisches Institut der Universität Karlsruhe, für die Überlassung des Biotits aus dem Albtal-Granit mitsamt der chemischen Analyse und Herrn Dr. W. Lücke, Petrographisches Institut der Universität Karlsruhe, für die Atomabsorptions-Bestimmungen.     

Holocene climatic variations—Their pattern and possible cause

In the northeastern St. Elias Mountains in southern Yukon Territory and Alaska, C¹⁴-dated fluctuations of 14 glacier termini show two major intervals of Holocene glacier expansion, the older dating from 3300-2400 calendar yr BP and the younger corresponding to the Little Ice Age of the last several centuries. Both were about equivalent in magnitude. In addition, a less-extensive and short-lived advance occurred about 1250-1050 calendar yr BP (A.D. 700–900). Conversely, glacier recession, commonly accompanied by rise in altitude of spruce tree line, occurred 5975–6175, 4030-3300, 2400-1250, and 1050-460 calendar yr BP, and from A.D. 1920 to the present. Examination of worldwide Holocene glacier fluctuations reinforces this scheme and points to a third major interval of glacier advances about 5800-4900 calendar yrs BP; this interval generally was less intense than the two younger major intervals. Finally, detailed mapping and dating of Holocene moraines fronting 40 glaciers in the Kebnekaise and Sarek Mountains in Swedish Lapland reveals again that the Holocene was punctuated by repeated intervals of glacier expansion that correspond to those found in the St. Elias Mountains and elsewhere. The two youngest intervals, which occurred during the Little Ice Age and again about 2300–3000 calendar yrs BP, were approximately equal in intensity. Advances of the two older intervals, which occurred approximately 5000 and 8000 calendar yr BP, were generally less extensive. Minor glacier fluctuations were superimposed on all four broad expansion intervals; those of the Little Ice Age culminated about A.D. 1500–1640, 1710, 1780, 1850, 1890, and 1916. In the mountains of Swedish Lapland, Holocene mean summer temperature rarely, if ever, was lower than 1°C below the 1931–1960 summer mean and varied by less than 3.5°C over the last two broad intervals of Holocene glacial expansion and contraction.Viewed as a whole, therefore, the Holocene experienced alternating intervals of glacier expansion and contraction that probably were superimposed on the broad climatic trends recognized in pollen profiles and deep-sea cores. Expansion intervals lasted up to 900 yr and contraction intervals up to 1750 yr. Dates of glacial maxima indicate that the major Holocene intervals of expansion peaked at about 200–330, 2800, and 5300 calendar yr BP, suggesting a recurrence of major glacier activity about each 2500 yr. If projected further into the past, this Holocene pattern predicts that alternating glacier expansion-contraction intervals should have been superimposed on the Late-Wisconsin glaciation, with glacier readvances peaking about 7800, 10,300, 12,800, and 15,300 calendar yr BP. These major readvances should have been separated by intervals of general recession, some of which might have been punctuated by short-lived advances. Furthermore, the time scales of Holocene events and their Late-Wisconsin analogues should be comparable. Considering possible errors in C¹⁴ dating, this extended Holocene scheme agrees reasonably well with the chronology and magnitude of such Late-Wisconsin events as the Cochrane-Cockburn readvance (8000–8200 C¹⁴ yr BP), the Pre-Boreal interstadial, the Fennoscandian readvances during the Younger Dryas stadial (10,850-10,050 varve yr BP), the Alleröd interstadial (11,800-10,900 C¹⁴ yr BP), the Port Huron readvance (12,700–13,000 C¹⁴ yr BP), the Cary/Port Huron interstadial (centered about 13,300 C¹⁴ yr BP), and the Cary stadial (14,000–15,000 C¹⁴ yr BP). Moreover, comparison of presumed analogues such as the Little Ice Age and the Younger Dryas, or the Alleröd and the Roman Empire-Middle Ages warm interval, show marked similarities. These results suggest that a recurring pattern of minor climatic variations, with a dominant overprint of cold intervals peaking about each 2500 yr, was superimposed on long-term Holocene and Late-Wisconsin climatic trends. Should this pattern continue to repeat itself, the Little Ice Age will be succeeded within the next few centuries by a long interval of milder climates similar to those of the Roman Empire and Middle Ages.Short-term atmospheric C¹⁴ variations measured from tree rings correlate closely with Holocene glacier and tree-line fluctuations during the last 7000 yr. Such a correspondence, firstly, suggests that the record of short-term C¹⁴ variations may be an empirical indicator of paleoclimates and, secondly, points to a possible cause of Holocene climatic variations. The most prominent explanation of short-term C¹⁴ variations involves modulation of the galactic cosmic-ray flux by varying solar corpuscular activity. If this explanation proves valid and if the solar constant can be shown to vary with corpuscular output, it would suggest that Holocene glacier and climatic fluctuations, because of their close correlation with short-term C¹⁴ variations, were caused by varying solar activity. By extension, this would imply a similar cause for Late-Wisconsin climatic fluctuations such as the Alleröd and Younger Dryas.     

Granate mit Zusammensetzungen zwischen Almandin und Grossular aus den westlichen Hohen Tauern, Österreich

Garnets in epidote-bearing gneisses and mica schists from the western Hohe Tauern, Austria, have been analyzed by optical, x-ray powder diffraction, wet chemical and electron microprobe methods.The garnets frequently show zonal structure and their core compositions are in the range 45–52% grossular, 31–44% almandine, 3–13% spessartine, 0–7% andradite and 0–2% pyrop. The refractive indices n=1.780–1.786 and the lattice parameter a=11.68–11.73 Å likewise are intermediate between almandine and grossular. It is suggested that there is complete solid solution between almandine and grossular, at least under the conditions of greenschist to low-temperature amphibolite facies of regional metamorphism of the Tauern area.

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Prof. Dr. F. Karl starb am 15. 8.1972.

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Dank. Die Mikrosonde wurde von der Stiftung Volkswagenwerk bereitgestellt, und die Probenahme wurde von der Deutschen Forschungsgemeinschaft unterstützt. Wir danken Herrn Dr. P. K. Hörmann (Kiel) für die naßchemische Granatanalyse und Herrn Dr. K. Abraham (Bochum) für die Bereitstellung seines Korrekturprogrammes für Mikrosondenanalysen.     

Das P{\text{ - }}T{\text{ - }}X_{{\text{CO}}_{\text{2}} } Stabilitätsfeld von Lawsonit

At pressures which are expected in the earth's crust, the high temperature border of the lawsonite stability field is marked by reaction lawsonite = zoisite + kyanite/andalusite + pyrophyllite + H₂O. (1a) The equilibrium data of reaction (1a) have been experimentally determined, and the equilibrium curve is characterized by the following P, T-data: 4 kb; 360±20° C; 5 kb; 375 ±20° C; 7kb;410±20° C. In the P, T diagram the equilibrium curve of reaction lawsonite + quartz = zoisite + pyrophyllite + H₂O (6) is very close to the curve of reaction (1a); the distance is smaller than the error stated for curve (1a), i.e. below ±20° C. The stability fields of lawsonite and anorthite + H₂O are not adjacent fields in the P, T diagram. This means that no stable reaction of lawsonite to anorthite + H₂O can exist. Thus, the CaAl-silicate formed by the decomposition of lawsonite is always zoisite. Further, as shown by experimental determination of reaction calcite + pyrophyllite + H₂O = lawsonite + quartz + CO₂, (7) lawsonite can coexist with a gas phase only if the CO₂ content of the gas phase does not exceed 3±2 Mol-%. This means, for metamorphism of lawsonite glaucophane rocks, that the fluid phase that was present during metamorphism has been quite rich in H₂O. Ernst (1971, in press) who applied a different, indirect investigation method when studying the composition of the fluid-attending Franciscan and Sanbagawa metamorphism has come to the result that during metamorphism of lawsonite-glaucophane rocks the fluid phase did not contain more than 1–3 Mol-% of CO₂.     

Stabilitätsbeziehungen von Prehnit- und Pumpellyit-haltigen Paragenesen

This investigation was undertaken to find the typical conditions for the formation of low-grade metamorphic rocks in which prehnite and/or pumpellyite (± actinolite, chlorite, epidote, and quartz) occur as characteristic minerals. In the p, t diagram the slope of the equilibrium curve prehnite + chlorite + H₂O=pumpellyite + actinolite + quartz is negative; the slope of the equilibrium curve pumpellyite + chlorite + quartz=epidote + actinolite + H₂O is positive. The point of intersection of the two equilibrium curves is an invariant point. The relative positions of the six equilibrium curves surrounding the invariant point were found by applying Schreinemakers's analysis.Experimental results show that the paragenesis prehnite-pumpellyite-chlorite-quartz is stable at 2 kb up to 345±20 °C, and at 7 Kb up to 260±20 °C. The paragenesis actinolitechlorite-pumpellyite-quartz occurs only at pressures greater than 2.5±1 kb. It is stable at 7 kb in the strongly pressure-dependent temperature range 260±20 °C to 370±20 °C. The paragenesis actinolite-chlorite-epidote-quartz, typical of the greenschist facies, may occur at pressures of 2–3 kb at temperatures of at least 350±20 °C. This temperature limit is only slightly changed with increasing pressure.

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Herrn Prof. Dr. H. G. F. Winkler möchte ich an dieser Stelle für die kritische Durchsicht des Manuskriptes sowie manche wertvolle Diskussion danken. Ebenso gilt mein Dank Herrn Dr. B. Storre und Herrn Doz. Dr. P. Metz für anregende Diskussionen. Herr Dr. P. Süße besorgte die Übersetzung des Abstracts.

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Außerdem sei den Angestellten der Mineralogischen Anstalten und des Mineralogisch-Petrologischen Instituts gedankt, die zu dieser Arbeit einen Beitrag geleistet haben. Die Deutsche Forschungsgemeinschaft förderte durch apparative Unterstützung wesentlich den experimentellen Teil der vorliegenden Publikation.