Sphericity as a characteristic of solids from fossil fuel burning in a Lake Michigan sediment

The property of sphericity is used to identify some anthropogenic particles in a Lake Michigan sediment. Three classes of products from high temperature processes, primarily fossil fuel burning, have been isolated: charcoals, iron oxides and aluminosilicates. The morphologies, structures and surface characteristics are indicative of the combustion process.     

Tungsten in iron meteorites

Tungsten concentrations have been determined by instrumental neutron activation in 104 iron meteorites, and range from 0.07 to 5 μg/g. In individual groups, concentrations vary by factors of between 1.5 and 8, but there are negative W-Ni correlations in 8 groups: IAB, IC, IIAB, IID, IIE, IIIAB, IIICD, and IIIF. The lowest W concentrations are found in groups IAB and IIICD, which also have the smallest slopes on a W-Ni plot. Eighteen anomalous irons have W concentrations between 5 μg/g (Butler) and 0.11 μg/g (Rafrüti). The distribution of W in irons shows similarities to that of other refractory siderophilic elements (except Mo), but is closest to the distribution of Ru and Pt.Assuming that chemical trends in group IIIAB were produced by fractional crystallization, a value of 1.6 can be deduced for the distribution coefficient of W between solid and liquid metal, cf. 0.89 for Mo. Experimental evidence in support of these values is tenuous.     

Some studies of an unusual eucrite: Ibitira

The Ibitira eucrite is remarkable both for its vesicles and its unbrecciated nature. It consists of ~63 vol. % pyroxene (Wo₁₄En₃₈Fs₄₈), 31% plagioclase (An_95–96), ~2% of nickel-iron, troilite, ilmenite, titanian chromite, and 4% of a silica polymorph. It has a mean track density of 1.8 ± 0.3 × 10⁶ cm^?2, mainly due to cosmic rays. Its pre-atmospheric radius must have been at least 10 cm.The absence of complex radiation effects and presence of vesicles place constraints on the thickness of the Ibitira basalt flow. From the freezing time calculations of Provost and Bottinga, it appears that Ibitira came from a flow no less than 2.5 m and probably no more than 10 or 20 m thick. However, this estimate depends strongly on the viscosity of the melt, which is not well known.     

The chemical composition of a Greenland glacier

Chemical analyses on water from dated strata of a south Greenland permanent ice sheet revealed that there is a larger amount of sulfate in samples accumulated during the past decade than in those 60 or more years older. This increase is attributed to combustion of fossil fuel. With the exception of mercury, cadmium and possibly copper, the heavy metal distributions in the glacial waters are similar to those in atmospheric dusts. Previously reported higher mercury values in recently deposited strata were not confirmed.     

Lead-210 and pollen geochronologies on Lake Superior sediments

Rates of sedimentation in two Lake Superior deposits were determined by both ragweed pollen and ²¹⁰Pb geochronologies. The former yields an average rate over the time since the first appearance of enhanced concentrations of the pollen as a consequence of human settlement. Sedimentation rates derived on these two bases can be brought into accord if the first appearance of ragweed pollen in the sediments was around 1830 and if the sedimentation rates have been uniform over the past century.     

Magnetic probing of planetary interiors

The following general question is addressed: what can be learned about a planetary interior from measurements of the global planetary magnetic field at (or near) its surface? The discussion is placed in the context of Earth, for clarity, but the considerations apply to terrestrial planets in general (so long as the observed magnetism is either predominantly of internal origin, or else external source effects can be successfully filtered out of the observations). Attention is given to the idealized but typical situation of a rotating but spherically symmetric planet containing a highly conducting uniform fluid core surrounded by a nearly insulating rigid mantle, whose conductivity, a function of at most radius only, falls monotonically from its largest value at the base of the planetary mantle to zero at the planetary surface; the largest value of mantle conductivity as well as the mean value for the whole mantle and the mantle conductance are assumed small compared to the corresponding values of the core. Exterior to the planet is vacuum in the sense of an electrically uncharged insulator. The core fluid is inviscid, Boussinesq and gravitationally driven.Complete and perfect observations of either the instantaneous internal vector magnetic field together with its secular variation at a single epoch, or more realistically, the instantaneous internal vector magnetic field alone at two separated epochs are presumed available; the time separation between measurement epochs is long compared the Ohmic diffusion time of the planetary mantle, but small compared to that of the liquid core.Under such circumstances we describe how information about each of the following planetary properties can, in principle (though not without practical difficulty) be retrieved from the observations: (1) depth of the core-mantle boundary (a result of Hide); (2) depth to the current and motion sources responsible for the planetary dynamo; (3) presence or absence of small-scale turbulence in the upper reaches of the core; (4) large-scale horizontal fluid motion at the top of the core; (5) strength of horizontal currents, zonal magnetic fields, Coriolis and Lorentz forces at the top of the core; and (6) current system in the mantle and strength of electromagnetic core-mantle coupling.     

Amino-acid racemizarion in Quaternary shell deposits at Willapa Bay,Washington

Extents of racemization ($\text{d}\text{l}$ ratios) of amino acids in fossil Saxidomus giganteus (Deshayes) and Ostrea lurida Carpenter were measured on shell deposits exposed at 21 sites on the east side of Willapa Bay, Washington. Amino acids from Saxidomus show less variability in $\text{d}\text{Spl}$ ratios and, therefore, are of greater use in correlation and age estimation than are amino acids from Ostrea. Shells of two different ages, about 120,000 ± 40,000 yr old and about 190,000 ± 40,000 yr old, are present. These ages correspond to Stages 5 and 7 of the marine isotope record defined by Shackleton and Opdyke in 1973 and hence the shell deposits likely formed during two different high stands of sea level. The stratigraphic record at Willapa Bay is consistent with this interpretation.     

On the kinetics of volatile loss from chondrites

We have re-examined data by Lipschutz and coworkers on thermal release of T1, Bi, In from primitive chondrites, in order to obtain information on the nature and activation energy (E) of the release processes: desorption, volume diffusion, and decomposition of the host phase. Plausible though not definitive choices may be made in some cases. For the Allende C3 chondrite, the main release for Bi and T1 (80 and 86%) between 400 and 700°C appears to be due to desorption of a surface layer, coupled with grain boundary diffusion as the slow step. The main release of In (80%) above 600°C and the small (10–20%) tails of Bi and T1 between 700 and 1000°C probably represent volume diffusion, with activation energies near 30 kcal/mol. The much smaller E's (2–5 kcal/mol) found for this interval by the Purdue group are artifacts, resulting from their failure to correct the initial concentration for the material lost in the preceding peak. Finally, the residual Bi and T1 remaining at 1000°C seem to represent solid solutions in temperature-resistant phases, such as ‘Q’, the principal carrier of planetary noble gases in the meteorite.This distribution—a small amount in solid solution and a large amount in a surface film—qualitatively agrees with that predicted by Larimer (1973, Geochim. Cosmochim. Acta37, 1603–1623) for condensation from the solar nebula, though some of the substrates may have been sulfides rather than metal.Results for Abee and other primitive meteorites are essentially similar, except for a very abrupt 500°C release of T1 from Krymka (81%) and Bi from Tieschitz (70%). This release may represent decomposition of a thermolabile phase in a late condensate, such as organic matter or phyllosilicates. The presence of such a condensate (‘mysterite’) was inferred previously from the apparent overabundance of T1 and Bi in these meteorites.     

The Nazca Group of south-central Peru: Age,source, and regional volcanic and tectonic significance

The Nazca Group, exposed east of Nazca, Peru, consists of a lower part composed of conglomerate and finer-grained clastic strata and an upper part made up of at least seven ash-flow sheets (cooling units or ignimbrites), collectively known as the Nazca Tuff. These tuffs were erupted between about 22 and 18 m.y. ago from a vent area in the vicinity of Pampa Galeras now marked by a collapse caldera. The early Miocene age of the Nazca Tuff provides additional evidence for a major pulse of largely pyroclastic felsic volcanism throughout the central Andes during the early Miocene. Recognition of the Pampa Galeras caldera supports the idea that many of these rocks were erupted from vent areas of the collapse-caldera type located near the eastern margin of the Coastal batholith.The Nazca Group overlies a major erosional surface cut on the Coastal batholith and its envelope that can be traced southward to the Chilean border. This surface is a continuation of the post-Incaic erosional surface to the north, which is overlain by conglomerate and radiometrically dated volcanic rock of late Eocene age. The post-Incaic surface therefore represents a major episode of regional uplift and pedimentation that followed early Tertiary orogeny. The absence of volcanic rocks of late Eocene/early Oligocene age overlying the Coastal batholith near Nazca and in southern Peru may reflect a general absence of post-Incaic volcanism in this portion of the Andes possibly related to differences in the angle of subduction and/or restriction of volcanic and volcaniclastic rocks of this age to depositional basins east of the batholith.