Laterally constrained inversion of helicopter-borne frequency-domain electromagnetic data     

Bernhard Siemon  Esben Auken  Anders Vest Christiansen 《Journal of Applied Geophysics》2009,67(3):259-268

Helicopter-borne frequency-domain electromagnetic (HEM) surveys are used for fast high-resolution, three-dimensional resistivity mapping. Standard interpretation tools are often based on layered earth inversion procedures which, in general, explain the HEM data sufficiently. As a HEM system is moved while measuring, noise on the data is a common problem. Generally, noisy data will be smoothed prior to inversion using appropriate low-pass filters and consequently information may be lost.For the first time the laterally constrained inversion (LCI) technique has been applied to HEM data combined with the automatic generation of dynamic starting models. The latter is important because it takes the penetration depth of the electromagnetic fields, which can heavily vary in survey areas with different geological settings, into account. The LCI technique, which has been applied to diverse airborne and ground geophysical data sets, has proven to be able to improve the HEM inversion results of layered earth structures. Although single-site 1-D inversion is generally faster and — in case of strong lateral resistivity variations — more flexible, LCI produces resistivity — depth sections which are nearly identical to those derived from noise-free data.The LCI results are compared with standard single-site Marquardt–Levenberg inversion procedures on the basis of synthetic data as well as field data. The model chosen for the generation of synthetic data represents a layered earth structure having an inhomogeneous top layer in order to study the influence of shallow resistivity variations on the resolution of deep horizontal conductors in one-dimensional inversion results. The field data example comprises a wide resistivity range in a sedimentary as well as hard-rock environment.If a sufficient resistivity contrast between air and subsurface exists, the LCI technique is also very useful in correcting for incorrect system altitude measurements by using the altitude as a constrained inversion parameter.  相似文献   

Propagation of the Storegga tsunami into ice‐free lakes along the southern shores of the Barents Sea     

Anders Romundset  Stein Bondevik 《第四纪科学杂志》2011,26(5):457-462

Deposits in coastal lakes in northernmost Norway reveal that the Storegga tsunami propagated well into the Barents Sea ca. 8100–8200 years ago. A tsunami deposit – found in cores from five coastal lakes located near the North Cape in Finnmark – rests on an erosional unconformity and consists of graded sand layers and re‐deposited organic remains. Rip‐up clasts of lake mud, peat and soil suggest strong erosion of the lake floor and neighbouring land. Inundation reached at least 500 m inland and minimum vertical run‐up has been reconstructed to 3–4 m. In this part of the Arctic coastal lakes are usually covered by >1 m of solid lake ice in winter. The significant erosion and deposition of rip‐up clasts indicate that the lakes were ice free and that the ground was probably not frozen. We suggest that the Storegga slide and ensuing tsunami happened sometime in the summer season, between April and October. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Comment: Radiocarbon deglaciation chronology of the Thunder Bay,Ontario area and implications for ice sheet retreat patterns     

Anders E. Carlson  Peter U. Clark  Steven W. Hostetler 《Quaternary Science Reviews》2009,28(23-24):2546-2547

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Population-level genotyping of coat colour polymorphism in woolly mammoth (Mammuthus primigenius)     

Claire Workman  Love Dalen  Sergey Vartanyan  Beth Shapiro  Pavel Kosintsev  Andrei Sher  Anders Gotherstrom  Ian Barnes 《Quaternary Science Reviews》2011,30(17-18):2304-2308

Patterns in the spatial or temporal distribution of genotypes may be indicative of natural selection. Previous work on the woolly mammoth melanocortin-1 receptor (Mc1r) gene identified three polymorphic positions that suggest Pleistocene populations may have harboured both light- and dark-haired mammoths (Rompler et al., 2006, 313: 62). Here, we extend this work and present the first population-level analysis of a functional gene in an extinct species. We genotyped the Mc1r gene in 47 woolly mammoth samples excavated from sites across the central portion of the woolly mammoths’ former range to examine the extent of variation of this polymorphism through time and across space. Only one individual was found to be heterozygous, indicating that the frequency of the ‘light’ mutant allele was very low. We conclude that light-coloured woolly mammoths would have been very rare, and may even have been non-existent if the ‘light’ mutant allele was strongly selected against in its homozygotic form. With the increasing availability of large-scale sequencing technologies, population-level datasets capable of identifying local adaptation will become increasingly attainable.  相似文献   

Abundance of 17 trace elements in carbonaceous chondrites     

Urs Krähenbühl  John W. Morgan  R. Ganapathy  Edward Anders 《Geochimica et cosmochimica acta》1973,37(5):1353-1370

Seventeen trace elements (Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Rb, Re, Sb, Se, Te, Tl, U and Zn) were measured by neutron activation analysis in 8 C1 samples (1 Alais, 3 Ivuna, 4 Orgueil) and in 3 C2 samples (one each of Mighei, Murchison, Murray). The results show far less scatter than earlier literature data. The standard deviation of a single measurement from the mean of 8 C1 samples lies between 2 and 14 per cent, except for the following 4 elements: Au ±18 per cent, Ag ±22 per cent, Rb ±19 per cent and Br ±33 per cent. The first two probably reflect contamination and sample heterogeneity, the last two, analytical error. Apparently C1 chondrites have a far more uniform composition than some authors have claimed.The new data suggest significant revisions in cosmic abundance for the following elements (old values in parentheses): Zn 1250 (1500), Cd 1.51 (2.12), Ir 0.72 (0.43) atoms/10⁶ Si atoms. The Br value is also lower, 6.8 vs 20.6, but may be affected by analytical error.Relative to C1 chondrites, the C2 chondrites Mighei, Murchison and Murray are depleted in volatile elements by a factor of 0.508 ± 0.038, much more constant than indicated by oldor data. Ordinary chondrites also show a more uniform depletion relative to the new C1 data. The mean depletion factor of Sb, F, Cu, Ga, Ge, Sn, S, Se, Te and Ag is 0.227 ± 0.027 in H-chondrites. This constancy further strengthens the case for the two-component model of chondrite formation.  相似文献   

Lunar crater Copernicus: search for debris of impacting body at Apollo 12 site     

John W. Morgan  R. Ganapathy  J.C. Laul  Edward Anders 《Geochimica et cosmochimica acta》1973,37(1):141-154

In an attempt to characterize meteoritic material at the Apollo 12 site, 4 KREEP concentrates from soil 12033 have been analyzed by neutron activation analysis. These contain a meteoritic component in which siderophile Ir, Re and Sb are depleted by about a factor of 2, while volatile Se, Zn, Ag and Bi are depleted by a factor of more than 5 relative to Au. This pattern does not closely resemble any major chondrite or iron meteorite group, but is very similar to that observed in high-alkali samples from Apollo 14. The meteoritic component in KREEP at both sites is therefore predominantly derived from Imbrian ejecta. However, a second, small component of primitive composition seems to be present in Apollo 12 KREEP, judging from the slight, uniform enrichments in Ir, Re, Sb, Se and Zn relative to Au. This component does not seem to be due to micrometeorites. If it is attributed to the Copernican projectile, the crater Copernicus may have been formed by a cometary nucleus, 4 km in diameter, with an impact velocity of 30–40 km/sec. These conclusions depend critically on the assumption that the meteoritic component in Apollo 12 KREEP is representative of the entire impact.  相似文献   

Chemical fractionations in meteorites—VI. Accretion temperatures of H-, LL- and E-chondrites,from abundance of volatile trace elements     

J.C. Laul  R. Ganapathy  Edward Anders  John W. Morgan 《Geochimica et cosmochimica acta》1973,37(2):329-357

Extending our earlier work on 11 L-chondrites, we have measured 9 volatile elements (Ag, Bi, Cs, In, Rb, Tl, Se, Cd, Zn) by neutron activation analysis in 11 LL- and 10 E-chondrites; the first 6 elements also in 22 H-chondrites. The observed fractionation patterns are consistent with theoretical condensation curves and hence were apparently established during condensation from the solar nebula. Ordinary chondrites seem to have accreted between 420 and 500°K at $\text{P ≈ 10}{}^{\mathrm{?5}}$ atm; enstatite chondrites, at 460 to 520°K and P ≈ 5 x? 10^?4 atm. The values for ordinary chondrites agree with O¹⁸-based temperatures by Onuma. et al. (1972) and with other characteristics such as Fe²⁺ content, presence of FeS and absence of Fe₃O₄.A few detailed trends were noted. Seven of the 54 meteorites seem to contain small amounts of a material enriched in Ag, Bi and especially T1; possibly a late condensate from a region depleted in metal. Silver shows considerable scatter, which suggests inhomogeneous distribution in the meteorites. Xenon correlates with In approximately as expected for equilibrium solubility, with some differences (petrologic type 3; E-chondrites) attributable to mineralogical factors. Meteorites of higher petrologic types are slightly deficient in Xe, probably due to gas losses during metamorphism. Cesium also appears to have been redistributed during metamorphism.Various features of the two-component model are critically examined in the light of the latest evidence. Apparently this model still is an adequate approximation of reality.  相似文献   

How well do we know “Cosmic” abundances?     

Edward Anders 《Geochimica et cosmochimica acta》1971

Five lines of evidence suggest that Cl chondrites closely approximate the condensable fraction of primordial solar-system matter: continuity of isotopic and elemental abundance trends, agreement with solar and cosmic-ray abundances, fractionation patterns among chondrites, and absence of chondrules. Maximum differences between Cl abundances and true solar-system abundances are estimated as factors of 2–5 for individual elements and a factor of 1.5 or less for groups of 10 or more elements.  相似文献   

Noble gases in E-chondrites     

Jane Crabb  Edward Anders 《Geochimica et cosmochimica acta》1981,45(12):2443-2464

Noble gas data are reported for 12 E-chondrites. Combined with literature data, they show that K-Ar ages are >4 Æ for 14 out of 18 meteorites, yet U, Th-He ages are often shorter, perhaps due to late, mild reheating. Cosmic-ray exposure ages differ systematically between types 4 and 6, with E4's mostly below 16 Myr and E6's above 30 Myr. This may mean that the E-chondrite parent body contains predominantly a single petrologic type on the (~ 1 km) scale of individual impacts, in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites.The heavy noble gases consist of at least two primordial components: the usual planetary component (${}^{36}\text{Ar}{}^{132}\text{Xe}\text{~ 80}$) and a less fractionated, ‘subsolar’ component ($\text{2700 ≤}{}^{36}\text{Ar}{}^{132}\text{Xe}\text{≤ 3800}$). The latter is found in highest concentration in the E4 chondrite South Oman (³⁶Ar = 760 × 10^?8cc/g, ${}^{36}\text{Ar}{}^{132}\text{Xe}\text{= 2700}$). The isotopic compositions of both components are similar to typical planetary values, indicating that some factor other than mass controlled the noble gas elemental ratios. The heavy Xe isotopes occasionally show some of the lowest ${}^{134}\text{Xe}{}^{132}\text{Xe}$ and ${}^{136}\text{Xe}{}^{132}\text{Xe}$ ratios measured in bulk chondrites, suggestive of nearly fission-free Xe (e.g. ${}^{136}\text{Xe}{}^{132}\text{Xe}\text{= 0.3095 ± 0.0020}$). Amounts of planetary gas in E4 E6 chondrites fall in the range for ordinary chondrites of types 4–6, but, in contrast to the ordinary chondrites. fail to correlate with petrologic type or volatile trace element contents. Another unusual feature of E-chondrites is that primordial Ne is present even in most 4's and 5's (²⁰Ne_p ~ 1 to 7 × 10^?8cc/g). with an isotopic composition consistent with planetary Ne.Analyses of mineral separates show that the planetary gases are concentrated in an HF- and HCl-insoluble mineral similar to phase Q, the poorly characterized, HNO₃-soluble carrier of primordial gases in carbonaceous and ordinary chondrites. The subsolar gases, on the other hand, are located in an HCl- and HNO₃-resistant phase, possibly enstatite or a minor phase included in enstatite. Much of the ¹²⁹Xe_r (50% for E4's, > 70% for E6's) is in HCl-resistant but HF-soluble sites, suggestive of a silicate.A similar subsolar component may be responsible for the high ${}^{36}\text{Ar}{}^{132}\text{Xe}$ ratios of some C3's, unequilibrated ordinary chondrites, and the unique aubrite Shallowater. The planet Venus also has a high $\text{Ar}\text{Kr}$ ratio, well above the planetary range, and hence may have acquired its noble gases from an E-chondrite-like material, similar to South Oman.  相似文献   

Chemical investigations of Atlantis II and discovery brines in the Red Sea     

Lars-Göran Danielsson  David Dyrssen  Anders Granéli 《Geochimica et cosmochimica acta》1980,44(12):2051-2065

Analytical data for the Atlantis II and Discovery deeps in the Red Sea are given. The data were collected in March and June 1976 during the 22nd cruise of R/V Akademik Kurchatov in the Indian Ocean. On board analyses were performed of density, chlorinity, Mg, Ca, Sr and trace elements. The salinity, calculated from the density, is related to the chlorinity by S = 1.67 Cl + 4.02. The Ca-salinity relation is linear for both deeps showing that intermediate waters are formed by mixing of the brines with Red Sea water (RSDW). The hot brine (62°C) in the Atlantis II deep contains approx. 80 mg/kg of Fe and Mn while the warm brine (45°C) in the Discovery deep has a very low concentration of Fe and approx. 50 mg/kg of Mn. Mixing of RSDW containing 2 ml/l of oxygen with the anoxic deep brines causes precipitation of hydrous Mn(IV) and Fe(III) hydroxides. These two processes occur at different depths in the two deeps due to the formation of the warm (48–49°) intermediate brine in the Atlantis II deep. The oxidation-hydrolysis reactions proposed are supported by alkalinity-depth profiles and measurements of pH. These reactions also explain most of the trace element distributions and the composition of the SiO₂-Fe(III) hydroxide slurry recovered by some water samplers in the Atlantis II deep.  相似文献