Field Evaluation of a Slim-Hole Borehole Induction Tool

The Geonics EM-39 borehole induction tool was field tested to evaluate its performance under controlled conditions. The effects of temperature changes and borehole fluids were found to be negligible under most conditions. The instrument can be calibrated in large bodies of water of known electrical conductivity. When properly calibrated, the ± 5 percent accuracy claimed by the manufacturer is obtainable. A geologic unit must be at least 4m thick for the electrical conductivity of the unit to be accurately measured. Geologic units thinner than 4m thick can be detected if the conductivity contrast to adjacent units is sufficiently large.     

Ionospheric convection during the magnetic storm of 20–21 March 1990

We report on the response of high-latitude ionospheric convection during the magnetic storm of March 20–21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric convection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestrom incoherent radars and three digisondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two intervals of particular interest have been identified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes the ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward turning of the IMF in the dusk to midnight local times is found to be approximately half that measured in a similar study at comparable local times during more normal solar wind conditions. Furthermore, this response time is the same as those previously measured on the dayside. An investigation of the expansion of the polar cap during a substorm growth phase based on Faraday’s law suggests that the expansion of the polar cap was nonuniform. A subsequent reconfiguration of the nightside convection pattern was also observed, although it was not possible to distinguish between effects due to possible changes in B_y and effects due to substorm activity. The second interval, 1200–2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the B_z component becoming -10 nT. The response time on the dayside to this change in the IMF at the magnetopause was approximately 15 min to 30 min which is a factor of \sim2 greater than those previously measured at higher latitudes. A movement of the nightside flow reversal, possibly driven by current systems associated with the substorm expansion phases, was observed, implying that the nightside convection pattern can be dominated by substorm activity.     

Formation of ferriolivine and magnesioferrite from Mg — Fe-olivine: Reactions and kinetics of oxidation

Olivine samples (Fa 11) have been oxidized in air (f _O2 = 0.2 atm) at temperatures ranging from 350–700 °C and examined by Mössbauer spectroscopy, transmission electron microscopy, X-ray powder diffraction and thermomagnetic analysis. Oxidation of olivine was found to result in ferriolivine, magnesioferrite (major oxide phase) and magnetite (minor oxide phase) formation. Ferriolivine forms planar (001) precipitates, 0.6 nm in thickness, in the olivine host; the composition is likely to be Mg_0.5 v _0.5(Fe³⁺)_1.0SiO₄. Magnesioferrite MgFe₂O₄ exsolves as fine-grained precipitates (5–6 nm in size) filling interstices between the ferriolivine planar precipitates. Oxidation kinetic data at 700 °C show two stages of oxidation corresponding to formation of ferriolivine in the first stage and magnesioferrite in the second stage. The linear rate law with a rate constant k _Fol = 1.23 · 10^-3 s^-1 was found for the first stage whereas a parabolic rate-law with a constant of k _oxi = 3.28 · 10^-3 s^-1 was determined for the second stage of oxidation. It was found that ferriolivine is not an intermediate metastable phase in the oxidation process, terminated by magnesioferrite formation. The ferriolivine and magnesioferrite are considered to have formed by independent reactions which do not necessarily proceed simultaneously.     

River stabilisation due to changing climate and vegetation during the late Quaternary in western Tasmania, Australia

The Stanley River in western Tasmania, Australia, contains sub-fossil rainforest logs within the channel and floodplain. Of the more than 85 radiocarbon dates obtained, all but 3 date from 17 ka to the present and permit an interpretation of fluvial and related environmental changes over this period. Particular attention is focused on the interactive relationship between the river and its riparian rainforest. Following the Last Glacial Maximum, the Stanley River was a laterally active gravel-load system reworking most of its valley floor in the upstream reaches. With ameliorating conditions at the end of the Pleistocene, climate became less seasonal and flow regimes less energetic. Huon pines already present in the catchment, re-asserted themselves in the form of dense tree cover along the river banks and floodplains with basal floodplain deposition shifting from gravels to coarse sands and granules. By about 3.5 ka, a further change in climate reduced stream discharges substantially. As a result the channel reduced in size, transported finer sediment, became laterally stable, and the floodplain accreted with overbank deposits of sand and silt. Huon pines falling into the channel formed obstructions of woody debris, some surviving for 2 ka. These have reduced stream power and boundary shear stress, further contributing to channel stability. Generational sequences of Huon pines on the river banks, some extending back 1–2 ka, are additional evidence of this stability. Since the Pleistocene, changing climate and the re-establishment of dense riparian rainforest appear to have stabilised the river channels and floodplains of western Tasmania.     

The effect of horizontal resolution on ocean surface heat fluxes in the ECMWF model

Annual mean ocean surface heat fluxes have been studied as a function of horizontal resolution in the ECMWF model (cycle 33) and compared with Oberhuber's COADS (1959–1979) based empirical estimates. The model has been run at resolutions of T21, T42, T63 and T106 for 15 months with prescribed monthly varying climatological SST and sea ice. The T42 simulation was extended to 2 years, which enabled us to determine that many differences between the resolution runs were significant and could not be explained by the fact that individual realizations of an ensemble of years can be expected to give different estimates of the annual mean climate state. In addition to systematic differences between the modeled and the observed fluxes, the simulated fields of surface shortwave and longwave radiation showed much more spatial variability than the observed estimates. In the case of the longwave radiation this may be attributable more to deficiencies in the observations than to errors in the model. The modeled latent and sensible heat fields were in better agreement with observations. The primary conclusion concerning the dependence of ocean surface fluxes on resolution is that the T21 simulation differed significantly from the higher resolution runs, especially in the tropics. Although the differences among the three higher resolution simulations were generally small over most of the world ocean, there were local areas with large differences. It appears, therefore, that in relation to ocean surface heat fluxes, a resolution greater than T42 may not be justified for climate model simulations, although the locally large differences found between the higher resolution runs suggest that convergence has not been achieved everywhere even at T106.     

Quaternary evolution of Cedar Creek alluvial fan, montana

Cedar Creek alluvial fan is a textbook example of an alluvial fan because of its fan shape with smooth, concentric contours and excellent symmetry. Similar planimetric shapes have been used to infer uniform fan deposition; however, Cedar Creek alluvial fan is composed of four fan deposits of Quaternary age, Qf1 (oldest) to Qf4 (youngest), indicating that fan deposition was nonuniform in both time and space. Field studies indicate that deposition of Cedar Creek alluvial fan is related to glaciofluvial outwash activity during the Pleistocene and upper-fan entrenchment and lower-fan deposition during the Holocene.Qf1 and Qf2 deposits are sub-horizontally bedded, clast-supported sandy gravels uniformly imbricated upfan. Comparison of soil profiles developed in these deposits to radiogenically-dated chronosequences within the region indicates that Qf1 and Qf2 are correlative with Bull Lake and Pinedale-age deposits, respectively. These relationships are substantiated by physical correlation of Qf1 and Qf2 with Bull Lake and Pinedale moraines, respectively, in the Cedar Creek drainage basin. The sedimentology and timing of Qf1 and Qf2 indicate deposition in high-energy, proglacial, braided streams. Furthermore, the present morphology of Cedar Creek alluvial fan was established largely during aggradation of Qf1 and Qf2 when sediment supply to the fan was sufficient to activate 60% to greater than 90% of the total fan area. During Bull Lake glaciation, the apex of Qf1 deposition formed the apex of Cedar Creek alluvial fan as Qf1 covered more than 90% of the present fan area. During Pinedale glaciation, Qf2 deposition shifted downfan; Qf2 is inset into Qf1 above the intersection point, but below the intersection point it eroded and/or buried Qf1 as it activated as much as 60% of the fan area.Qf3 and Qf4, comprising 21% of the fan area, are inset into Qf2 in the lower fan area. Soil development in Qf3 and Qf4 deposits indicate episodic deposition and entrenchment beginning in early Holocene and continuing to present. A post-glacial decrease in sediment supply to Cedar Creek alluvial fan is indicated by sediment storage within the Cedar Creek drainage basin. Decreased sediment supply to the fan resulted in upper-fan entrenchment of Qf2 and deposition of Qf3 and Qf4 in the lower-fan area.     

Use of GIS in Optimizing Timber Thinning Strategies in the Eastern Sierra Nevada*

This paper demonstrates the use of a Geographic Information System (GIS) to develop timber thinning strategies on the Kyburz Planning Area of the Tahoe National Forest in northeastern California. The primary criteria used in an assessment of selective thinning potential were forest health and fire hazard ratings. By eliminating environmentally sensitive, economically unfeasible, or low fire hazard areas from consideration, the use of GIS reduced the area that was considered appropriate for thinning by approximately 58%. GIS offers considerable potential for improving resource management strategies.     

国际古植物学1989年研究进展

古植物学是一个日新月异发展着的学科。每年,都有一些新的方法问世,它们结合地质学和生物学方法来研究地史时期植物的生活。其研究广度可以从1989年7月在美国首都华盛顿召开的第28届国际地质大会上明显看出。古植物学家们报告了他们关于“古气候”、“前寒武纪/寒武纪的过渡”、“泥炭和煤的来源”、“适应辐射”、“埋藏过程”、“特异埋藏”及南极地质等方面的研究成果;关于晚石炭世植物群的生物地理方面的文章也很多。 由Gastaldo(1989)编辑的《植物埋藏学——有机沉积过程》论文专辑是将更多的地质