Early organic diagenesis: The significance of progressive subsurface oxidation fronts in pelagic sediments

Porewater and solid phase geochemical data at two contrasting NE Atlantic stations are reported. Station 10552, on the Cape Verde abyssal plain, is a site of slow pelagic accumulation (ca. 0.4 cm kyr^?1). Molecular oxygen is present in the sediment column to at least 2 m, and probably much deeper, labile organic-carbon is almost totally consumed in the upper few centimetres of the sediment. By contrast, at station 10554 on the Madeira abyssal plain, the pelagic sequence has been interrupted by the occasional deposition of organic-rich turbidites. Porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic-carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column. This metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time. This phenomenon exerts a controlling influence on the present nutrient profile and redox succession.In a less extreme form, substrate distributions of this latter type are not uncommon in Atlantic sediments. A model has been developed which is controlled by both oxygen and nitrate data. This model permits a vertical profile of metabolic activity to be derived, and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations. About 30% of the total activity at station 10554 is located within the turbidite at the deepening reaction front; this is a non-steady-state condition. In fact, it is found that the integrated metabolic activity at the two stations is not dissimilar (ca. $\text{1–2 × 10}{}^{\mathrm{?13}}\text{moles cm}{}^{\mathrm{?2}}\text{sec}{}^{\mathrm{?1}}$). The striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column.     

Developments in high-resolution solid-state13C NMR spectroscopy of coals

The recent development of “second generation” NMR experiments on coals is discussed in this paper. Such experiments have three aims: (1) To determine the extent to which quantitative aromaticity measurements can be made on coals by cross polarization-magic angle spinning (CP/MAS); (2) To obtain more detailed information on coal structure and reactivity than that given by the simple aromaticity measurements possible at the time; (3) To follow reaction pathways when coal is chemically modified. In this plenary lecture the relevant literature is reviewed, and new experimental work in all three areas outlined above is reported. Experimental evidence is presented which shows that aromaticity measurements on a bituminous coal by cross polarization (CP) or single pulse techniques give identical results. Relaxation data for naphthalene polymers suggest that these structures in coal are seen in CP experiments. Dipolar dephasing experiments suggest that the average size of the coal vitrinite molecule does not increase with increase in coal rank due to aromatic substitution reactions. Various relaxation experiments demonstrate how different carbon types can be distinguished in both¹³C-labelled and unlabelled coals.     

A study of the effect of igneous intrusions on the structure of an Australian high voltage bituminous coal

Samples of heat affected coal taken near two igneous intrusions (dykes) in the Victoria Tunnel Seam of the Newcastle Coalfield have been investigated by chemical analysis, petrography, Fourier transform infrared spectroscopy and solid state¹³C NMR spectroscopy. Visual inspection of the seam near the intrusion showed four distinct zones. These have been called, in order of increasing distance from the dyke, the massive cinder, the banded cinder, heat affected coal and apparently unaffected coal. The samples show an increase in structural change as the distance from the dyke decreases, with the samples taken from the massive cinder nearest the dyke being classified as semicokes.FTIR and¹³C NMR results, together with the results of dipolar dephasing NMR experiments, suggest that the predominant structural change in the heat affected zone is replacement of aromatic ethers and/or phenols with hydrogen, leading to an increase in proton aromaticity. Closer to the intrusion, bond rupture leads to a marked loss of aliphatic groups, while in the most affected region adjacent to the dyke aromatic crosslinking has also occurred to form coke-like material.     

A tritium-exchange method for obsidian hydration shell measurement

A new radiochemical method for measuring the amount of water in the hydrated layer on the surface of obsidians exchanges tritiated water with the water in the layer (20 μl of 5 Ci ml^?1 at 90°C for 10 days) and then back-exchanges it (in 150 ml of water at 35°C for ～ 200 hr.). The activity of the back-exchange water (F) is monitored by liquid scintillation counting of aliquots extracted at known time intervals (t). The activity so measured is then related to the thickness of the hydration rim. A sheet diffusion model shows that the thickness of the hydration shell (l) is inversely proportional to the slope of the F vs.$\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ plot. Comparison of l-values so obtained between obsidians, whose age (x) is inferred from archaeological occupation layers containing radiocarbon-dated wood and charcoal, suggests a relationship between l and x. Implications for New Zealand prehistory are briefly considered. The technique, which is non-destructive, appears particularly applicable to young glasses where the development of hydrated layers may be inadequate for accurate optical measurement.     

The nature of olefins and carboxyl groups in an Australian brown coal resin

The chemical structure of the resin from an Australian soft brown coal (Yallourn) has been investigated by cross-polarization nuclear magnetic resonance spectroscopy with magic angle spinning (¹³C CP MAS NMR). Some additional solution ¹H and ¹³C data were also obtained. Solid-state experiments were performed with and without a delay period before data acquisition. The resulting free induction decays were Fourier transformed with respect to acquisition time and delay period to produce two-dimensional solid-state spectra. Assignments made from the spectra clearly demonstrate that the gross chemical structure of the Yallourn resin is best described as a polymerized diterpenoid with one axial carboxylic group and two double bonds. One double bond is trisubstituted, the other is monosubstituted. After consideration of various mechanisms for polymerization of diterpenoid units during biogenesis and coalification, it was concluded that polymerization occurs at the C₁₅ carbon atoms in the diterpenoids without cyclization of the methylene units at C₈.     

40Ar/39Ar geochronology of a high-grade polymetamorphic terrain,northeastern Strangways Range,Central Australia

Minerals from the northeastern Strangways Range have been dated by ⁴⁰Ar/³⁹Ar total degassing and incremental heating methods. Four periods of metamorphism are indicated: M1 > 1710 Ma, M2 = 1470 Ma, M3 = 700–1050 Ma, and M4 = 326–353 Ma. The two older events are recognised as distinct granulite facies metamorphic episodes, the third event as a complex reheating of the terrain, and the youngest event is the Alice Springs Orogeny.     

Incidence of polychlorinated biphenyls in Clyde seaweed

PCBs accumulate in seaweeds. This survey of concentrations found in fixed algae around the Firth of Clyde reveals a similar pattern of PCB distribution to that found in mussels.     

Plinian eruptions of Nevado de Toluca volcano,Mexico

Zusammenfassung Die Unteren und die Oberen Bimssteine des Toluca sind dacitische air fall-Ablagerungen, die vor etwa 24 500 bzw. 11 600 Jahren gefördert wurden. Der Lower Toluca Pumice bedeckt ungefähr 400 km2 und hat ein Volumen von rund 0,33 km³ (porenfrei gerechnet von 0,16 km³). Nach der 10-cm-Mächtigkeitskurve zeigt er einen nordostgerichteten Verbreitungsfächer. Der Upper Toluca Pumice bedeckt mehr als 2000 km²; sein Volumen beträgt rund 2,3 km³, wenn man die 40-cm-Mächtigkeitskurve zugrundelegt. Das Gesamtvolumen dürfte bei 3,5 km³ (porenfrei gerechnet bei 1,54 km³) liegen. Sein symmetrischer Verbreitungsfächer hat die Richtung N 65° E.Die INMAN-Parameter, Median (Md) und Sortierung (), zusammen mit dem Zerkleinerungs-Index von granulometrischen Analysen aus 23 Bimssteinprofilen zeigen, daß beide Ausbrüche dem plinianischen Typ zuzuordnen sind. Die Korngrößen-Verteilung, verglichen mit einem einfachen mathematischen Modell, gibt einen annähernden Hinweis auf den Ausbruchsverlauf während der Ablagerung der gröbsten Anteile des unteren Teils der Upper Toluca Pumice-Serie. Nach Berechnungen ergibt sich eine Anfangsgeschwindigkeit der Eruption von 500 m/sek aus einem annähernd runden Schlot mit einem Durchmesser von 260 m, sowie eine horizontale Durchschnittswindgeschwindigkeit von 16,2 m/sek und eine Höhe der Eruptionswolke von 40 km. Die freigewordene kinetische Energie betrug rund 6 X 10¹⁹ erg/sek. Die jüngere Eruption dagegen hatte zehnmal mehr kinetische Energie als die ältere.

---

The Lower and Upper Toluca Pumice Formations are dacitic airfall deposits that were erupted about 24,500 yr BP and 11,600 yr BP respectively. The Lower Toluca Pumice covers about 400 km², with a volume of 0.33 km³ (dense rock equivalent 0.16 km³) within the 10 cm isopach, and has a northeast-trending dispersal fan. The Upper Toluca Pumice covers more than 2,000 km², has a volume of 2.3 km³ within the 40 cm isopach, and an estimated total volume of 3.5 km³ (dense rock equivalent 1.54 km³). Its symmetrical dispersal fan trends N 65° E. The Inman parameters, median diameter (Md) and deviation (), together with the fragmentation indices, derived from granulometric studies of samples from 23 pumice sections, show that both eruptions were of Pliniantype. The particle-size distribution, compared with a simple mathematical model of a Plinian eruption, provides an approximate indication of the eruptive conditions during the deposition of the coarsest part of the Lower Member of the Upper Toluca Pumice. Computations give a muzzle velocity of 500 m/sec from a circular vent 260 m in diameter, a mean horizontal windspeed of 16.2 m/sec and an eruptive cloud 40 km high, with a maximum rate of release of kinetic energy of 6 × 10¹⁹ erg/sec. The younger eruption released about ten times more kinetic energy than the older.

---

Resumen Las formaciones »Lower y Upper Toluca Pumice« son depósitos de caida libre, originados hace approximadamente 24,500 y 11,600 años A.P., respectivamente. El depósito »Lower Toluca Pumice« cubre un area de aproximadamente 400 km², y tiene un volumen de 0.33 km³ (0.16 km³ de roca masiva) dentro de la isopaca de 10 cm, y su area de dispersión se prolonga en dirección N.E. El depósito »Upper Toluca Pumice« cubre más de 2,000 km², tiene un volumen de 2.3 km³ dentro de la isopaca de 40 cm, y un volumen total estimado en 3.5 km³ (1.54 km³ de roca masiva); su dirección principal de dispersion es N 65° E. Considerando los parámetres de Inman; es decir, diámetro medio (Md) y desviación estandard (), además de los índices de fragmentatión, derivados todos de estudios granulométricos de muestras tomadas en 23 secciones en el campo, ambos depósitos se deben a erupciones del tipo Pliniano. La distribución de tamaños, comparada con un modelo matemático simple de una erupción tipo Pliniano, muestra los parámetres aproximados de la erupción al momenta de depositarse la fracción más gruesa del miembro inferior del depósito »Upper Toluca Pumice«. Los cálculos dan una velocidad de escape de 500 m/seg de un cráter circular 260 m de diámetro, una velocidad media del viento de 16.2 m/seg y una columna eruptiva de 40 km de altura, con un gasto máximo de energía cinética de 6 × 10¹⁹ ergios/seg. La energía cinética liberada por la última erupción fue diez veces mayor que la primera.

---

Résumé Les formations inférieures et supérieures de Ponce de Toluca sont des dépôts dacitiques d'origine aérienne, qui ont été émis il y a environ 24,500 ans AP et 11,600 ans AP respectivement. Le »Lower Toluca Pumice«, qui couvre environ 400 km², avec un volume de 0.33 km³ (équivalent à 0.16 km³ de roche compacte) dans I'isopaque de Pumice«, couvre plus de 2000 km², a un volume de 2.3 km³ dans l'isopaque de 40 cm, et un volume global estimé à 3.5 km³ (équivalent à 1.54 km³ de roche compacte). Son éventail symétrique de dispersion est dirigé vers N 65° E. Les paramètres Inman, le diamètre médian (Md) et la déviation (), comme aussi les indices de fragmentation tirés des études granulométriques d'échantillons de 23 profils de ponce, montrent que ces deux éruptions étaient du type plinien. La distribution granulométrique des particules comparée à un modèle mathématique simple d'une éruption plinienne, fournit une indication approximative des conditions d'éruption pendant le dépôt de la fraction la plus grossière du membre inférieur du »Upper Toluca Pumice«. Des calculs donnent une vitesse initiale de 500 m/sec à partir d'un évent circulaire de 260 m de diamètre, une vitesse horizontale de vent de 16.2 m/sec et une nuée éruptive de 40 km de hauteur, avec une degré maximum de libération d'énergie cinétique de 6 × 10¹⁹ erg/sec. L'éruption plus récente a libéré environ dix fois plus d'énergie cinétique que l'éruption plus ancienne.

---

, 24500 11600 . «Lower Toluca Pumice» 400 ² 0,33 ³, , — 0,16 ³. 10 , - . «Upper Toluca Pumice» , 2000 ²; 2,3 ³, 40 . 3,5 ³, 1,54 ³. 65°. INMAN, (Md Ø) 23 , . «Upper Toluca Pumica». 500 /, 260 , 16,2 /. 40 . 6&#x0445;10¹⁹ /. 10 , .

     

The magnitude of the paleomagnetic field during a polarity transition: A new technique and its application

Both the magnitude and direction of the paleomagnetic field have been determined during a polarity transition. The results indicate that the geomagnetic field was both strong and stable when the magnetic pole was close to the equator.     

Numerical simulation of particle trajectories in inhomogeneous turbulence,I: Systems with constant turbulent velocity scale

A means of numerical simulation of particle trajectories in inhomogeneous turbulence is described. The method employs a simple coordinate transformation which allows a trajectory in inhomogeneous turbulence to be converted to a corresponding trajectory in homogeneous turbulence. Concentration distributions predicted by the trajectory-simulation method agree precisely with analytical solutions in the special cases of homogeneous turbulence, turbulence with power-law wind and eddy diffusivity profiles, and the neutral atmospheric surface layer.