Late Wisconsinan glaciation models of northern Maine and adjacent Canada     

Andrew N. Genes  William A. Newman  Thomas B. Brewer 《Quaternary Research》1981,16(1):48-65

Surficial stratigraphic units of Aroostook County, Maine, have been mapped and formal stratigraphic names for these units are proposed. Evidence exists for at least two distinct glacial phases which are represented by three tills. Two of these tills were deposited penecontemporaneously either as the result of coalescing ice sheets or as the result of the thermal regime existing within a single ice sheet. The oldest till is named the St. Francis and is correlated with the Chaudière Till of southeastern Quebec. The other tills are named the Mars Hill and Van Buren tills, respectively, and are correlated with the Lennoxville till of southeastern Quebec. Interbedded stratified sediments associated with the St. Francis till are correlated with the Gayhurst Formation. Stratified sediments associated with Van Buren and Mars Hill tills are correlated with post Lennoxville sediments of Quebec. Granite-gneiss erratics of Canadian Shield provenance in the Van Buren till indicate advance of the Laurentide ice into northern Maine during late Wisconsinan time. Moraines in southern Aroostook County with associated outwash and eskers record general recession from coastal Maine. Recession occurred after the formation of the Pineo Ridge moraine in Maine and the St. Antonin-Highland Front moraine complex in Quebec. The Caribou-Winterville moraine complex in northern Maine marks the boundary between the penecontemporaneously deposited Van Buren and Mars Hill surface tills and is correlated with the Grand Falls moraine at Grand Falls, New Brunswick.  相似文献   

A review of the braided-river depositional environment   总被引：8，自引：0，他引：8  

Andrew D. Miall 《Earth》1977,13(1):1-62

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Chemical characterization of a “mysterite”-bearing clast from the Supuhee chondrite     

Andrew M. Davis  Lawrence Grossman  R. Ganapathy 《Geochimica et cosmochimica acta》1977,41(7):853-856

Higuchiet al. (1977) proposed the existence of Tl-rich and Tl-poor “mysterite” to explain Tl and Bi contents of dark clasts in the Supuhee H6 chondrite and of bulk Supuhee. They suggested that these two components formed by gas-dust fractionation during condensation. An aliquot of one of the clasts studied by Higuchi et al. and found to contain Tl-poor mysterite was analyzed by instrumental neutron activation in this paper. A complex assortment of element fractionations was found. Data for rare earth and other refractory lithophiles and refractory and moderately volatile siderophiles are consistent with random separation and reunification of gas and dust throughout the condensation sequence. Independent evidence thus exists that processes like those invoked by Higuchi et al. to explain mysterite did occur in the region of the nebula sampled by this clast.  相似文献   

A physiographic approach to land use planning     

Andrew E. Godfrey 《Environmental Geology》1977,2(1):43-50

Physiography has been studied in the United States for more than 75 years, but only recently has it been applied to land use planning. Advantages of a physiographic approach are that it 1) focuses on the problems at the proper scale and conserves energy, effort, and time by selecting the critical parameters, 2) stresses geologic structure and process as factors which should control land use, and 3) presents data in a form which the non-geologically trained planner can easily understand. In 1928 Fenneman delineated and described the provinces and sections of the United States. This paper proposes a classification of smaller physiographic units and presents two examples of how they can be used for planning purposes. Below the section, the units used in this paper are the subsection, the land type, and the topographic element. Subsections delineate areas of distinct geologic structure or process whereas land types delineate ranges in the intensity of those processes. Topographic elements delineate units with distinct ranges of slopes or shapes of slopes, such as concave or convex.  相似文献   

Variation in stable carbon isotopes in organic matter from the Gunflint Iron Formation     

Elso S Barghoorn  Andrew H Knoll  Harry Dembicki  Warren G Meinschein 《Geochimica et cosmochimica acta》1977,41(3):425-430

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Composition of hydrated near-Earth object (100085) 1992 UY4     

Eric L. Volquardsen  Andrew S. Rivkin 《Icarus》2007,187(2):464-468

Near-infrared spectra of the near-Earth object (100085) 1992 UY4 are similar to those of P-type asteroids, providing a fitted geometric albedo of 0.052±0.005 and an effective diameter of 1.68±0.08 km. This object, with a likely outer-belt origin, also exhibits a 3-μm absorption feature with a band depth of 3%±1%, corresponding to a regolithic bulk hydrogen-to-silicon ratio of 0.30±0.05. The bulk of this hydrogen seems to be present in H₂O-dominated minerals.  相似文献   

Mass‐dependent fractionation of nickel isotopes in meteoritic metal     

David L. COOK  Meenakshi WADHWA  Robert N. CLAYTON  Nicolas DAUPHAS  Philip E. JANNEY  Andrew M. DAVIS 《Meteoritics & planetary science》2007,42(12):2067-2077

Abstract— We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC‐ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non‐magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ～0.4‰ amu^?1. The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (～0.0 to ～0.3‰ amu^?1) and chondrites (～0.0 to ～0.2‰ amu^?1) are similar, whereas the range in pallasite metal (～–0.1 to 0.0‰ amu^?1) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (～0.0 to ～0.3‰ amu^?1) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ～0.4‰ amu^?1. In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe‐Ni alloy and the development of the Widmanstätten pattern.  相似文献   

Streambank dewatering for increased stability     

F. Douglas Shields Jr  Andrew Simon  Seth M. Dabney 《水文研究》2009,23(11):1537-1547

Streambank erosion is often the dominant source of sediment leaving modified watersheds. Mass failure of high, steep banks is one of the most serious forms of streambank erosion. The risk of a given bank experiencing mass failure is a function of bank height, angle, and soil strength, which is governed by soil moisture. Two methods for bank dewatering were tested in adjacent sections of streambank bordering a deeply incised channel in northern Mississippi: a low‐cost pump system and subsurface horizontal drains. Pore water pressures (both positive and negative pressures, or matric suction) were continuously monitored for 2 years at the pumped site, at an adjacent untreated control section, and for 1 year at the site stabilized with horizontal drains. Resulting data were used to calculate a time series of the factor of safety using a computer model. Over the course of two wet seasons, average bank retreats for the control and pumped plots were 0·43 and 0·21 m, respectively. More limited monitoring revealed that the site with passive drains retreated about 0·23 m. At the pumped site pore water pressure was 3–4 kPa lower than at the control site during the most critical periods. Accordingly, computed factors of safety were above the failure threshold at the pumped site, but fell below unity at the control site on 11 occasions over the period of observation. Similarly, the drained site displayed generally lower pore water pressure and higher safety factors except for two events when drains were evidently overwhelmed with the volume of local surface and subsurface flows. These results suggest, but do not prove, that bank dewatering promoted lower rates of bank retreat and higher levels of stability since the three sites had slight differences in soils, geometry and boundary conditions. Initial cost of the dewatering treatments were significantly less than orthodox bank stabilization measures, but operation and maintenance requirements may be greater. Published in 2009 by John Wiley & Sons, Ltd.  相似文献   

El Niño Southern Oscillation and Climatic Variability     

Andrew Sturman 《New Zealand geographer》1998,54(1):64-65

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Oligocene uplift of the Western Greater Caucasus: an effect of initial Arabia–Eurasia collision     

Stephen J. Vincent  Andrew C. Morton  Andrew Carter  Samantha Gibbs  Teimuraz G. Barabadze 《地学学报》2007,19(2):160-166

The Greater Caucasus is Europe's largest mountain belt. Significant uncertainties remain over the evolution of the range, largely due to a lack of primary field data. This work demonstrates that depositional systems within the Oligocene–Early Miocene Maykop Series on either side of the Western Greater Caucasus (WGC) display a similar provenance and divergent palaeocurrents away from the range, constraining a minimum age for the subaerial uplift of the range as early Early Oligocene. An Eocene–Oligocene hiatus, basal Oligocene olistostromes and a marked increase in nannofossil reworking also point to initial deformation in the earliest Oligocene. The initial uplift of the WGC occurred during the final assembly of the Tethysides to its south. Uplift commenced after the Late Eocene final suturing of northern Neotethys and during the initial collision of Arabia with the southern accreted margin of Eurasia. This suggests that compressional deformation was rapidly transferred across the collision zone from the indenting Arabian plate to its northern margin.  相似文献