Dielectric anisotropy as a petrofabric indicator

A sensitive instrument for measurement of the angular dependence of dielectric constant in a rotating rock specimen is described and the precautions necessary to obtain meaningful results are summarized. An important problem is the choice of length/diameter ratio for cylindrical specimens, so that complete three-dimensional information can be obtained from a single specimen; this ratio averages 0.86, but is found to be a function of dielectric constant and of electrode geometry. The measurements reported here have been concerned with weakly anisotropic rocks which lack visible fabrics, especially sandstones and basalts. A sandstone was used in a study of the statistical “noise” or scatter in anisotropy axes of a set of 52 similar specimens. The anisotropy was found to be much greater than expected from the finite numbers of grains in a sample. It is concluded that, in spite of careful drying of specimens, the anisotropy is dominated by thin grain coatings which have very high dielectric constants or may even be conducting. A basalt has been found in which the dielectric and magnetic anisotropies have different axes, apparently reflecting different grain alignment events in the history of the rock. However, this is the only example that has been found in which all of the information obtainable from dielectric anisotropy could not have been obtained more easily from magnetic anisotropy.     

The use of the specific interaction model to estimate the partial molal volumes of electrolytes in seawater

The specific interaction model has been used to determine the partial molal volume of electrolytes in 0.725 m NaCl and 35‰ salinity seawater solutions at 25°C. The partial molal volumes of electrolytes (MX) were estimated at a given ionic strength (I) from

$\text{V}\text{(}\text{MX}\text{) =}\text{V}{}^0\text{(}\text{MX}\text{) +}\text{S}{}_{\mathrm{v}}\text{I}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1 + I}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}\text{+ v}{}_{\mathrm{M}}\text{∑}\text{X}\text{B}{}_{\mathrm{<mtext>MX</mtext>}}\text{[X] + v}{}_{\mathrm{X}}\text{∑}\text{M}\text{B}{}_{\mathrm{<mtext>MX</mtext>}}\text{[X]}$

, where S_V is the Debye-Hückel limiting law slope, v_i is the number of ions i formed when MX dissociated, [i] is the total molality of ion i and B_MX is a specific interaction parameter that varies slowly with ionic strength. The values of $\text{V}\text{(}\text{MX}\text{)}$ estimated by using this equation were found to agree very well with experimental values in NaCl and seawater providing there are not strong interactions between M and X. For electrolytes that form ion pairs (i.e. MX°) corrections must be made. Methods are discussed for making these corrections.     

Die Strukturen des „Rogenpyrits“ (Kössener Schichten,Rät) als Beitrag zum Problem der „Vererzten Bakterien“

Zusammenfassung Der Rogenpyrit ist die häufigste Form des Pyrits in den Schlämmrückständen der Kössener Mergel des alpinen Rät. Anschliffuntersuchungen ergaben Strukturen, die mit den Vererzten Bakterien eine nahe Verwandtschaft zeigen und mit einem noch höheren Wahrscheinlichkeitsgrad auf organische Abkunft schließen lassen.Der Rogenpyrit tritt in zwei Typen auf, je nach der Größe der Primärkristalle, den kleinsten Bausteinen. Er wird wie die Vererzten Bakterien als pyritisierte farblose Schwefelbakterien bzw. deren Kolonien gedeutet.Der Rogenpyrit ist ein Faziesindikator: Seine Anwesenheit zusammen mit einer benthonischen Mikrofauna in den Kössener Schichten kennzeichnet diese Mergel als Halbfaulschlamm-Fazies.     

Geologische Beobachtungen an der Küste und auf dem Schelf von Kephallinia (Ionische Inseln)

The largest Ionian island Cephalonia is situated on the edge of the Greek shelf. To the west the slope (20% average) extends to the Ionian fault scarp. This area is characterized by young tectonic activity (last disastrous earthquake in 1953) with dominant N-S and NE-SW fault directions. This paper constitutes the first account of the marine and Quaternary geology of Cephalonia. Late Pleistocene (? Tyrrhen III) red algae-rich limestones - up to 6,5 m thick - with interbedded sand layers transgress steeply folded Plio-Pleistocene and Eocene sediments. In addition, relative sea level changes in Quaternary time are indicated by a submarine platform at ?26 m NN. and 5 elevated shorelines, partly with wave-cut notches and borings, at heights of about 15 m, 45 m, 90 m, 150 m and 190 m, whose correlation with other so-called high-sea-levels of the Mediterranean area is doubtful. Shore- and nearshore sediments mainly consist of eroded coast material and reworked Pliocene which locally crops out on the sea floor, The outer shelf sedimentation is characterized by the deposition of marly foraminiferal ooze which undergoes bioturbation. Because of strong currents the ridge between Cephalonia and Zante is free of recent sediment. A swash mark entirely composed of the tests of sessil foraminiferas (Miniacina miniacea) is described.     

The solubility of calcite and aragonite in seawater of 35%. salinity at 25°C and atmospheric pressure

The solubilities of synthetic, natural and biogenic aragonite and calcite, in natural seawater of 35%. salinity at 25°C and 1 atm pressure, were measured using a closed system technique. Equilibration times ranged up to several months. The apparent solubility constant determined for calcite of 4.39(±0.20) × 10^?7 mol² kg^?2 is in good agreement with other recent solubility measurements and is constant after 5 days equilibration. When we measured aragonite solubility we observed that it decreased with increasing time of equilibration. The value of 6.65(±0.12) × 10^?7 mol² kg^?2, determined for equilibration times in excess of 2 months, is significantly less than that found in other recent measurements, which employed equilibration times of only a few hours to days. No statistically significant difference was found among the synthetic, natural and biogenic material. Solid to solution ratio, contamination of aragonite with up to 10 wt% calcite and recycling of the aragonite made no statistically significant difference in solubility when long equilibration times were used.Measured apparent solubility constants of aragonite and calcite are respectively 22( ± 3)% and 20( ± 2)% less than apparent solubility constants calculated from thermodynamic equilibrium constants and seawater total activity coefficients. These large differences in measured and calculated apparent solubility constants may be the result of the formation of surface layers of lower solubility than the bulk solid.     

Lithic fragments in the Bandelier Tuff, Jemez Mountains, New Mexico

Lithic fragments are a highly varied but significant component of the Bandelier Tuff, Jemez Mountains, New Mexico. Lithic material occurs in concentrations from trace amounts to 30 wt.%, and within the Otowi Member of the tuff has a total volume of 10 km³. Approximately 90% of the fragments are Cenozoic volcanic rocks of the Jemez volcanic field, 10% are Paleozoic sedimentary rocks, and only trace amounts are Precambrian basement. The large volume of lithic material and predominance of shallowly derived fragments requires substantial flaring of the vent near the surface. The cooling effect of ≥ 10 wt.% lithic fragments was sufficient to inhibit welding of the tuff.Many of the basement fragments appear to have been derived from a contact metamorphic zone surrounding the magma chamber. This zone is characterized by shearing and recrystallization, by development of veins of actinolite, augite, and epidote, and by alteration of hornblende to F-rich biotite. Water and fluorine involved in the alteration may have come from the magma chamber.     

The effect of microtopography and vegetation on the catchment of airborne particles measured by remanent magnetism

Measurements of saturation isothermal remanent magnetization (SIRM) for recent ombrotrophic peats show that the rate of deposition of magnetic particulates from the atmosphere varies strongly in response to the persistent, small-scale, spatial changes in vegetation and microtopography characteristic of many raised bogs. Hummock environments may trap over an order of magnitude more magnetic particulates than do Sphagnum lawns and pools. These results, thought to reflect the interception of subhorizontally moving particles by the hummock forming plants, have potentially important implications for studies of pollen deposition (“influx”) rates in peat.     

The role of phytoplankton in the diets of adult and larval shipworms,Lyrodus pedicellatus (Bivalvia: Teredinidae)

The shipwormLyrodus pedicellatus does not feed exclusively on the wood into which it burrows. This paper demonstrates the ability of adults to ingest and incorporate radioactivity from¹⁴C-labelled phytoplankton. The free-swimming larvae of this species, however, do not feed while in the plankton. This is related to their limited ability to delay metamorphosis in the absence of a suitable wood substrate.