Comparison of crude oils and their alteration products

A simple method is proposed for using gas Chromatographic data on the high molecular weight saturated fractions of crude oils to make comparisons of source materials, migration mechanisms and, in particular, alteration processes within reservoirs. The preferential loss of normal alkanes by bacterial attack on a light crude is one of several processes readily followed using this scheme.     

Formation of the Bencubbin polymict meteoritic breccia

The Bencubbin meteorite is a polymict breccia consisting of a host fraction of ~60% metal and ~40% ferromagnesian silicates and a selection of carbonaceous, ordinary and ‘enstatite’ chondritic clasts. Concentrations of 27 elements were determined by neutron activation in replicate samples of the host silicates and the ordinary and carbonaceous chondritic clasts; 12 elements were determined in the host metal. Compositional data for the ordinary chondrite clast indicate a classification of LL4 ± 1. Refractory element data for the carbonaceous chondrite clast indicate that it belongs to the CI-CM-CO clan; its volatile element abundances are intermediate between those of CM and CO chondrites. Abundances of nonvolatile elements in the silicate host are similar to those in the carbonaceous chondrite clast and in CM chondrites; the rare earths are unfractionated. We conclude that it is not achondritic as previously designated, but chondritic and that it is probably related to the CI-CM-CO clan; its volatile abundances are lower than those in CO chondrites. Oxygen isotope data are consistent with these classifications. Host metal in Bencubbin and in the closely related Weatherford meteorite has low abundances of moderately volatile siderophiles; among iron meteorite groups its nearest relative is group IIIF.We suggest that Bencubbin and Weatherford formed as a result of an impact event on a carbonaceous chondrite regolith. The impact generated an ‘instant magma’ that trapped and surrounded regolithic clasts to form the polymict breccia. The parent of this ‘magma’ was probably the regolith itself, perhaps mainly consisting of the so-called ‘enstatite’ chondrite materials. Accretion of such a variety of materials to a small parent body was probably only possible in the asteroid belt.     

Molecular weight distribution of humic and fulvic acids of sediments from a north Florida estuary

The molecular weight distribution of the humic and fulvic acid fractions of two sediments was determined using Amicon ultrafiltrat ion techniques. All fractions of humic substances had a molecular weight range of less than 500 to greater than 300,000. The largest component of humic acids was in the greater than 300,000 molecular weight range, whereas, the largest percentages of fulvic acids were in the less than 500 molecular weight range and the 100,000–300,000 molecular weight range. From this preliminary investigation there appears to be a qualitative relationship between the molecular weight composition of the humic substances in the sediment and the salinity of the overlying water within an estuarine environment.     

The chemistry of orthophosphate uptake from seawater on to calcite and aragonite

The chemistry of orthophosphate uptake from synthetic seawater onto the surfaces of synthetic calcite, aragonite and low-magnesium biogenic calcite has been studied, in order to elucidate the kinetics of the process (generally believed to be the major control of dissolved reactive phosphate in carbonate-rich marine sediments). Our results differ from those obtained by others, who have studied orthophosphate uptake in low ionic strength solutions and at much higher supersaturations relative to apatite.In both ‘free drift’ and chemostat experiments, Mg and F have only a minor effect on the reaction rate. Even at constant solution composition the rate of orthophosphate uptake was found to decrease by 10⁶ over a two week period. The data from the ‘free drift’ experiments can be fitted to the Elovich equation. This indicates that the kinetics observed for this reaction can be explained by an exponential decrease in available surface reaction sites and/or a linear increase in the activation energy associated with chemisorption as the reaction proceeds.     

210Pb balance in Long Island Sound

A material balance is constructed for excess ²¹⁰Pb (relative to ²²⁶Ra) as a test of the retentivity of Long Island Sound for a reactive heavy metal. Excess ²¹⁰Pb is supplied to Long Island Sound chiefly by direct atmospheric deposition [1 ± 0.2(dis·min^?1)cm^?2·yr^?1]. Rivers supply less than 20% of the atmospheric flux, and other inputs, from open ocean waters, ²²⁶Ra decay, groundwater seepage, and sewage discharge, appear to be negligible. The total input of excess ²¹⁰Pb represents approximately the flux required to maintain the inventory of excess ²¹⁰Pb measured in sediment cores from central Long Island Sound; that is, excess ²¹⁰Pb is lost from Long Island Sound chiefly by radioactive decay. The retention of excess ²¹⁰Pb within Long Island Sound is achieved in two steps: a rapid removal of soluble ²¹⁰Pb onto suspended particles and the ongoing entrapment of particles in the basin by the residual bottom-water influx from the east.     

Ferroan calcite replacement indicates former magnesian calcite skeletons

The replacement by ferroan calcite with preservation of the original structures can be used as a new criterion for identifying skeletons originally composed of high-magnesian calcite. This applies to bryozoa, rugose corals, echinoderms, many foraminifera, most ostracods, red algae, and serpulids. On the other hand, skeletons originally composed of low-magnesian calcite were never replaced by ferroan calcite, as shown by belemnites, brachiopods, and most of the pelecypods. Using this criterion, an original low-magnesian calcite composition is inferred for Tentaculites and some ostracods and foraminifera, whereas a previous high-magnesian calcite composition is inferred for trilobites, oligostegina and certain ooids. Chemical instability of high-magnesian calcite is suggested to be the driving force of the replacement by ferroan calcite. In most of the thirty-seven samples investigated, of Oligocene to Devonian age, the ferrous iron concentration of the interstitial fluid increased during diagenesis, as shown by well established sequences of cement A and B and fissure fill. This offers a relative time scale for diagenetic processes. Ferroan calcites contain up to 6 mol % FeCO₃ and up to 5 mol % MgCO₃. In this range of concentration, the distribution coefficients for Fe and Mg between calcite and solution at about 25°C are about 1 to 0-03, respectively, according to experiments. Possible sources of iron are iron oxides and hydroxides as well as clay minerals including glauconite. Though a submarine origin below the sediment surface is conceivable for ferroan calcite, there are serious limiting conditions such as low Eh and, at the same time, lack in sulphate-reducing bacteria. On the other hand, ferroan ‘dedolomite’, compositional zonality in individual ferroan calcite overgrowths, low δ¹⁸C and δ¹⁸O values, and low Mg concentrations point more to a meteoric-phreatic origin of many ferroan calcite occurrences.     

Fair weather and storm sand transport on the Long Island, New York, inner shelf

Both spring-summer and fall-winter sand transport have been observed on the Long Island, New York, inner shelf at water depths of 20-22 m using a radio-isotope sand tracer system. The extent of dispersal of the tagged, fine sand was measured at 3 week intervals in two 70 day experiments. In the late spring and early summer, movement was primarily diffusive in nature, extending 100 m around the line of tracer injection, while late fall-winter patterns had strong advective features, including an ellipsoidal outline extending approximately 1500 m westward of the injection points after the passage of several storms with strong northeasterly winds. Near-bottom current observations made with Savonius rotor sensors identify the event responsible for the bulk of the transport over the 135 day observation period as a storm flow of 2 days duration. Tracer and current observations together suggest that westward winter storm flow along the Long Island shelf is the major mechanism of sand transport at these depths on a yearly time scale. A least-squares fit of several of the observed winter patterns with a plume model yields average sediment mass flux lower bounds of 3.2 × 10^?3 gm/cm/sec and 1.7 × 10^?1 gm/cm/sec for ‘typical’ and extreme winter storm activity.     

The formation and clay mineral reactions of melanoidins

Sugars and amino acids condense readily to form polymers known as melanoidins that closely resemble natural humic substances. In this study melanoidins are formed by reacting glucose with each of three amino acids: glutamic acid, valine and lysine. The basic amino acid, lysine, reacts with glucose at a much greater rate than either of the other two compounds. The chemical properties of the melanoidins are strongly influenced by the amino acid from which they are formed. The nitrogen contents, acidities and electrophoretic behavior of the polymers all reflect functional group distributions inherited from the amino acids. These chemical differences strongly influence the extent of association of the melanoidins with kaolinite and montmorillonite clay minerals. Laboratory simulations suggest that melanoidin formation may be favored in marine environments where basic amino acids should preferentially condense with sugars to form nitrogen-rich polymers that have a great affinity for clay mineral surfaces.