High degree spherical harmonic expansion of gravity data

A spherical harmonic expansion of the gravity field up to degree and order 200 was carried out. Free air anomaly data over Canada (1⁰×1⁰ block averages) with a range of 211.1 mgal were used for testing. A low degree expansion (N=30) produced a map with a range of 63.6 mgal with contour patterns that could hardly be correlated with the original hand contoured map. A high degree expansion (N=200) on the other hand resulted in a map with a range of 199.8 mgal which quite faithfully reproduced the original including its local variations. Test computations verify that by monitoring the RMS values and the range of the expansion it is possible to arrive at an optimum degree of expansion for a given data set. It was also verified by the computations, that, since the computed expansions essentially have a zero value outside the domain of the input, it is possible to combine the results of separate non-overlapping expansions. Contribution of the Earth Physics Branch No. 900. Presented at the 1977 Spring Meeting, AGU, May 30–June 3, Washington, D.C.     

Spatial and vertical trends in sediment-phase contaminants in the upper estuary of the St. Lawrence River

The concentration of selected contaminant trace metals and organic contaminants, namely polycyclic aromatic hydrocarbons (PAHs), normal-alkanes, total polychlorinated biphenyls (PCBs), and other organochlorines, was studied in cores from shallow-water fine-grain sediments from both sides of the maximum turbidity zone (MTZ) in the upper estuary of the St. Lawrence. Average trace metal concentrations in the cores were generally lower in downstream sediments, except for Hg and Pb. Hg levels in the cores were very high, exceeding 0.7 μg g^?1 in core C168 (south shore) and 0.19 μg g^?1 in core LE (north shore). Trace metal concentrations in all the cores were highly variable with depth, but after normalization with reference to iron, the trend was remarkably uniform, thus confirming an important inverse relationship with grain size. A similar lack of a well-defined trend was noted in the profiles of the organic components in the modern sediments. Average PAH values for modern sediments at core sites C168 and LO were 1.05 μg g^?1 and 0.44 μg g^?1, respectively (i.e., less than or equal to those in Lake Ontario and upstream in the river). PCB values far exceeded those in upstream sediments (average: 347 ng g^?1 in core LE and 158 ng g^?1 in C168), but were less than in Lake Ontario. Concentrations of chlordane, heachlorobenzene, and mirex were relatively low and uniform in the modern sections of the cores. The vertical uniformity of both the contaminant profiles and those for Cs-137 (C168) suggests that the sediments are relatively young (i.e., definitely less than 35 yr at C168, and probably even less at LE and LO). Therefore no long-term or historical trend is evident.     

Indications of a biological and biochemical evolutionary trend during the archean and early proterozoic

Micropaleontological observations and organic geochemical analyses imply, but certainly do not prove, that life may not have been present ～3,800 Ma ago in Southwestern Greenland; however, physiologically complex prokaryotes flourished by the Early Proterozoic in other locations. It is, of course, also possible that life may have appeared earlier in locations other than Greenland. Investigations of Precambrian biological and biochemical evolutionary trends require interdisciplinary efforts, up-to-date instrumentation and methodology (such as ultramicrochemical analyses of individual microfossils/microstructures), and caution in the interpretation of experimental results.     

Geochemistry, Petrogenesis and Geodynamic Relationships of Miocene Calc-alkaline Volcanic Rocks in the Western Carpathian Arc, Eastern Central Europe

We report major and trace element abundances and Sr, Nd andPb isotopic data for Miocene (16·5–11 Ma) calc-alkalinevolcanic rocks from the western segment of the Carpathian arc.This volcanic suite consists mostly of andesites and dacites;basalts and basaltic andesites as well as rhyolites are rareand occur only at a late stage. Amphibole fractionation bothat high and low pressure played a significant role in magmaticdifferentiation, accompanied by high-pressure garnet fractionationduring the early stages. Sr–Nd–Pb isotopic dataindicate a major role for crustal materials in the petrogenesisof the magmas. The parental mafic magmas could have been generatedfrom an enriched mid-ocean ridge basalt (E-MORB)-type mantlesource, previously metasomatized by fluids derived from subductedsediment. Initially, the mafic magmas ponded beneath the thickcontinental crust and initiated melting in the lower crust.Mixing of mafic magmas with silicic melts from metasedimentarylower crust resulted in relatively Al-rich hybrid dacitic magmas,from which almandine could crystallize at high pressure. Theamount of crustal involvement in the petrogenesis of the magmasdecreased with time as the continental crust thinned. A strikingchange of mantle source occurred at about 13 Ma. The basalticmagmas generated during the later stages of the calc-alkalinemagmatism were derived from a more enriched mantle source, akinto FOZO. An upwelling mantle plume is unlikely to be presentin this area; therefore this mantle component probably residesin the heterogeneous upper mantle. Following the calc-alkalinemagmatism, alkaline mafic magmas erupted that were also generatedfrom an enriched asthenospheric source. We propose that bothtypes of magmatism were related in some way to lithosphericextension of the Pannonian Basin and that subduction playedonly an indirect role in generation of the calc-alkaline magmatism.The calc-alkaline magmas were formed during the peak phase ofextension by melting of metasomatized, enriched lithosphericmantle and were contaminated by various crustal materials, whereasthe alkaline mafic magmas were generated during the post-extensionalstage by low-degree melting of the shallow asthenosphere. Thewestern Carpathian volcanic areas provide an example of long-lastingmagmatism in which magma compositions changed continuously inresponse to changing geodynamic setting. KEY WORDS: Carpathian–Pannonian region; calc-alkaline magmatism; Sr, Nd and Pb isotopes; subduction; lithospheric extension     

Seasonal changes in the composition of the diets of Peary caribou and muskoxen on Banks Island

Caribou and muskoxen are the only ungulate species occupying Arctic tundra environments. We analysed plant fragments found in fresh (< 4 hr old) samples of faecal material to determine the diets of Peary caribou ( Rangifer tarandus pearyi ) and muskoxen ( Ovibos moschatus ) on Banks Island, Canada. Willow was a major component of the diets of both animals, dominating the caribou diet during summer and representing substantial proportions of the muskoxen diet during at least seven months of the year. The diet of caribou was more diverse than that of muskoxen and was dominated by sedge, willow ( Salix arctica ), legume ( Astragalus spp., Oxytropis spp.) and Dryas integrifolia . The diet of muskoxen was dominated by sedge and willow. There was substantial overlap (up to 70%) in the diets of these herbivores with the similarity more pronounced in areas of high muskox density ( ca. 1.65 ani mals/km²). We discuss herbivore diets in relation to foraging behaviour and forage availability.     

A chart for the computation of the gravitational attraction of a right rectangular prism

Summary The gravity effect of a right rectangular prism is calculated by a graphical procedure. The basis of the calculation is an algorithm for the linear combination of readings taken from a chart which has as ordinates and abscissas the body coordinates of the prism normalized with respect to the depth to the top and bottom surfaces.Gravity Division, Earth Physics Branch, Department of Energy, Mines and Resources, Ottawa, Canada. Contribution No. 425.     

Theoretical study of the electrostatic potential of an idealized semi-infinite crystal of talc and vibrational frequencies of an adsorbed proton

The electrostatic potential above a surface of a semi-infinite crystal of talc Mg₃Si₄O₁₀(OH)₂ in the idealized structure (layer group symmetry C2/m) was computed using the electron distribution obtained by a semiempirical INDO/2 calculation of the electron structure of one idealized layer. The potential of the semi-infinite crystal was obtained as the sum of contributions from an infinite number of individual layers. The adsorption enthalpy and the vibrational frequencies of a proton hypothetically adsorbed in vacuo were also computed.     

Evaluating the Performance of Using PPK-GPS Technique in Producing Topographic Contour Map

The Global Positioning System (GPS) is considered as one of the most powerful tools that are used in geodetic works. It is increasingly considered as an alternative tool for conventional surveying techniques. The goal of this research paper is to produce a methodology for generating topographic contour maps using the post-processed kinematic differential GPS technique (PPK-GPS). The performance of this technique is assessed by comparing it with the traditional spirit-leveling technique taking into consideration the accuracy, time, and cost. The study area is located along the Mediterranean coast in the Rosetta area of the middle Delta in Egypt with a total area of about 39 km². The field work includes 14 control points and about 50,000 PPK observations. In addition, 20 check cross sections that extend along the coastal line from Rosetta to El Burullus cities were observed using both spirit-leveling and GPS-PPK techniques. The results of the comparison indicate that the PPK-GPS technique can be used instead of spirit leveling in producing a topographic contour map with an accuracy of about 20 cm in orthometric height. We find that the PPK-GPS technique reduces the estimated time of leveling works in our study area by about 70%.     

Foraminiferal morphogroups in dysoxic shelf deposits from the Jurassic of Spitsbergen

Analysis of benthic foraminiferal assemblages was performed in Bathonian to Kimmeridgian deposits through a section covering the lower half of the Agardhfjellet Formation in central Spitsbergen. The section consists mainly of organic-rich shales, which contain low-diversity agglutinated assemblages. In this foraminiferal succession five morphogroups were differentiated according to shell architecture (general shape, mode of coiling and number of chambers), integrated with the supposed microhabitat (epifaunal, shallow infaunal and deep infaunal) and feeding strategy (suspension-feeder, herbivore, bacterivore, etc.). The environmental evolution of the analysed section is interpreted by using the stratigraphic distribution of morphogroups, combined with species diversities and sedimentary data, in a sequence stratigraphic framework. The section comprises two depositional sequences, which demonstrate that species diversity and relative frequency of morphogroups are correlative with transgressive–regressive trends controlling depth and oxygenation of the water column. In both sequences, the maximum flooding interval is characterized by increased organic carbon content, dominance of the epifaunal morphogroups and reduced species diversity: features reflecting the increased degree of stagnation separating the transgressive phase from the regressive phase.