Identification and occurrence of novel C36–C54 3,4-dialkylthiophenes with an unusual carbon skeleton in immature sediments

A series of novel long-chain 3,4-dialkylthiophenes (C₃₆–C₅₄) was identified in a number of sediments ranging from Pleistocene to Cretaceous. The identifications were based on mass spectral characterisation, desulphurisation and mass spectral data of synthesised model compounds. These organic sulphur compounds are probably formed by sulphur incorporation into mid-chain dimethylalkadienes with two methylenic double bonds. These putative precursor lipids are unprecedented and may be considered rather unusual. The distribution of 3,4-dialkylthiophenes in sediments varies considerably with the depositional palaeoenvironment, indicating that these compounds have a potential as molecular markers reflecting changes in palaeoenvironment.     

Geophysical investigations of the Platanares geothermal site, Honduras, Central America

Geophysical studies were carried out in Platanares in Western Honduras, as part of an investigation of the geothermal resource potential of Honduras by Los Alamos National Laboratory in cooperation with the Honduran government and the U.S. Geological Survey. Geological and geochemical studies later followed by exploratory bore-holes indicate this area of rugged topography has the best geothermal potential in Honduras. In order to better understand the geology of the area, gravity, audiomagnetotelluric and telluric surveys were carried out. The site is in a graben of Tertiary volcanics and Cretaceous red beds, with numerous hot springs along faults in the center of the graben. Gravity mapped the thickness of low-density tuffs and the position of associated normal faults. It also indicated the presence of persuasive, shallow, highly silicified, high-density tuffs and gravels. The electrical surveys mapped shallow, high-resistivity silicified zones and faults as low-resistivity zones. The red beds below the tuffs are considered to contain the geothermal reservoir, but their maximum thickness could not be determined by these surveys due to the lack of density contrast and the high surface electrical conductivities. Three geologic cross-sections constructed by others have been re-evaluated using gravity modeling and analysis of eletrical anomalies, showing general agreement but in detail significant differences.     

The alleged kimberlite-carbonatite relationship: evidence from ilmenite and spinel from Premier and Wesselton mines and the Benfontein sill,South Africa

Carbonate-rich, SiO₂-poor residua are developed in some kimberlites solidifying as ocelli, layers, or discrete dikes which satisfy petrographic definitions of carbonatite. Arguments that these rocks have mineralogies, antecedents, and comagmatic rocks differing from those of the carbonatites in alkaline rock complexes, including the specific observation that kimberlites and carbonatites contain ilmenites and spinels of different composition, have been used to refute the alleged kimberlite-carbonatite relationship. New microprobe analyses of ilmenites and spinels from carbonate-rich rocks associated with kimberlites in three South African localities correspond to spinels and ilmenites of carbonatites from alkalic complexes, or have characteristics intermediate between those of carbonatites and kimberlites. The ilmenites are distinguished from kimberlite ilmenites by higher MnO, FeTiO₃, and Nb₂O₅, and by negligible Cr₂O₃. The spinels are distinguished from kimberlite spinels by their Al₂O₃ and Cr₂O₃ contents. There is clearly a genetic relationship between the kimberlites and the carbonate-rich rocks, despite the observation that their ilmenites and spinels are distinctly different, which indicates that the same observation is not a valid argument against a petrogenetic relationship between kimberlites and carbonatites. These rocks are among the diverse products from mantle processes influenced by CO₂, and we believe that the petrogenetic links among them are forged in the upper mantle. We see insufficient justification to deny the name carbonatite to carbonate-rich rocks associated with kimberlites if they satisfy the petrographic definition in terms of major mineralogy.     

Influence of basement structures on the evolution of the major sedimentary basins of Brazil: A case of tectonic heritage

The present study deals with the correlation between the geotectonic features of the basement and the internal structure, shape, geologic evolution, etc. of the major sedimentary basins of the South American platform. The Paraná, Parnaíba and Amazonas basins occupy an area of the order of 3.6 × 10⁶ km², and their sedimentary cratonic sequences were deposited from Silurian to Triassic times. Subsidence rates are estimated around 15 m/Ma in the main depocenters.A geologic study was carried out along the basement features in the surroundings of such basins in order to identify the major structural, geotectonic and geochronological discontinuities. The extension of these basement characteristics towards the interior of the basins are examined. Basement core samples from deep wells were investigated through petrological and geochronological analyses, and pre-existing geophysical and structural maps of those basins were taken again into consideration.It can be concluded that many of the identified basement discontinuities display a direct influence on the depositional history of the basins as well as on their internal subdivisions and external outlines. Basement structures generated during the late Precambrian Brasiliano Cycle turned out to be particularly important.The Paraná and Parnaíba basins are considered to represent cratonic basins, located on rigid lithosphere, tectonically stabilized in the latest Precambrian/early Palaeozoic, and their subsidence is attributed to the establishement of some initial rifted grabens. The Amazonas basin is more complex and includes three large sub-basins with distinct evolutions, each located on a different tectonic segment of the basement.     

Carbohydrates in recent marine sediments—II. Occurrence and fate of carbohydrates in a recent stromatolitic deposit: Solar Lake,Sinai

In a study on the diagenesis of carbohydrates in a recent stromatolitic deposit (Solar Lake, Sinai) monosaccharides are quantitated after mild acid hydrolysis and gas chromatographic analysis as alditol acetates. From the depth profiles of the individual monosaccharides relative to the total organic carbon three categories of carbohydrates can be distinguished. The behaviour of the various categories upon burial is discussed in terms of their potential to become a part of the organic matter that survives geological periods. The distribution patterns of especially the mono-O-methyl monosaccharides at various depths are characteristics for the bacterial communities present in the corresponding parts of the sediment column.     

Belowground productivity of roots and rhizomes in a giant cordgrass marsh

Belowground production of roots and rhizomes in the top 20 cm of soil was 2.2 kg m^?2 yr^?1 based on a maximum minus minimum estimation procedure in a giant cordgrass (Spartina cynosuroides (L.) Roth) marsh in Mississippi. Approximately 1.9 kg m^?2 (86%) of this production occurred in late spring-summer and 0.3 kg m^?2 in late fall. This estimate ignores any production below 20 cm depth and is thus an underestimate. Production values increased to 4.0 kg m^?2 yr^?1 using Smalley’s technique and accounting for decomposition. Aboveground tissues (leaves and stems) were depleted in nitrogen in July which corresponded to peaks in both above- and belowground biomass. The low root/shoot ratio (2.6) on this marsh does not suggest that growth is nutrient limited. Indeed, total productivity (above- and belowground) for this marsh was high (between 4.4 and 6.2 kg m^?2 yr^?1).     

Variations of solar EUV,UV and ionospheric foF2 related to the solar rotation period

Spectral analysis of daily values of various solar indices viz. sunspot number, 10.7-cm flux, H Lyman-<alpha> and -<beta>, specific He, Fe and Mg lines and solar X-rays was carried out for two selected intervals. During interval A (May-August 1978, 123 days) the solar indices showed a prominent periodicity near 27 days, while during interval B (January-May 1979, 151 days) the solar indices showed a prominent periodicity near 13 days. For the same intervals, foF2 (max) and foF2 (average) during 1000–1500 LT were similarly analysed for the locations Cachoeira Paulista, SP, Brazil (23○S, 45○W), and Okinawa (26○N, 128○E) and Kokubunji (36○N, 139○E) in Japan. The 27-day and 13-day periodicities in solar indices were reflected in the foF2 series, but in different relative proportions at the three locations, probably due to the interference of local aerodynamical effects. Some other periodicities were common to solar indices and foF2, while some others were present in the solar indices but not in foF2, or vice versa.     

Seasonal expansion and contraction of stream networks in shallow groundwater systems

Surface water and groundwater are normally closely connected in areas with shallow aquifer systems. Stream systems can thus be considered as the outcrops of associated groundwater flows in areas with a shallow groundwater table and a previous subsurface. This situation prevails in sandy lowland areas where almost all rainfall percolates into the subsurface so that the surplus over evapotranspiration becomes part of a groundwater drainage system before it reappears at the surface in a stream. The stream network, being the interface with the groundwater system, must have the capacity to release the seasonally dependent precipitation surplus through the continuum of ground and surface waters. A river network therefore consists of a hierarchical system of different order and incision depth, of which the discharge-contributing component contracts and expands with the seasonal fluctuation in recharge and water table depth.

Coupling the mathematical expressions for groundwater drainage and stream flow enables development of a conjunctive model which relates the properties of a seasonally contracting and expanding stream network and related groundwater level fluctuation to the seasonal rainfall character for given geological and geomorphological conditions. This model further allows for assessment of drainage network response to a changing environment.     

A study of objective methods for water mass analysis,applied to the Iceland Basin

Ocean Dynamics - Cluster analysis and principal component analysis have been applied to multi-parameter hydrographic data from the Iceland Basin. The results indicate that both objective methods...