ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Circumglobal transport of aerosolic dust has been traced through radioactive debris, biological material, filtration of air, and oxygen isotope abundance measurements in quartz isolated from dust and from soils and sediments identified as having dust origin. Accretion rates are on the order of a m 106yr-1in Recent times but may have been 100 times as rapid during the Pleistocene. Solar heating in arid areas causes a deep layer of mixing. Dust on the order of 600 μg m-sof air, reaching altitudes of 4 to 10 km, can effect diabatic cooling of the mid-troposphere, and possibly increase subsidence and aridity. A strong momentum source is supplied by large-scale cyclonic storms. Descending air enters the mixed volume, producing gusts of strong wind at the ground which break up larger soil aggregates into silt-sizes that are easily transported. Vertical fluxes of soil material during dust storms reach the order of 10 μg cm-2sec-1. The intensifying pressure gradient moves the dusty air northeastward in the Northern Hemisphere with great speed. For example, Asian dust borne across the Gulf of Alaska, deflected southward along the western boundary of North America, can supply some dust to the Trade Winds reaching Hawaii. Over-grazing of vegetation in arid areas and animal traffic increase dust production. The global significance of aerosols to world climate and to sequestering of air-borne radioactive elements adds impetus to further investigation.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The phenomenon of addition of eolian mineral particles to soils during their genesis modifies the classic concept of soil development from underlying parent materials. Numerous evidences have been reported of the presence in many soils of dust particles that had been transported relatively short or very long distances by wind. Three categories of soils are considered in this paper: (a) soils only slightly modified by eolian increments, (b) soils in which the process of soil genesis has been significantly influenced by eolian additions, and (c) soils developed from two or more strata, always including a thin surface eolian deposit overlying a contrasting substratum.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

A review of literature on the Australian Quaternary suggests that Pleistocene glaciations in the northern hemisphere correlate with pluvial periods in at least the southern higher rainfall areas in Australia. Soil and parent material studies, mainly from southern and southeastern Australia, with age relationships established by stratigraphy, correlation with former sea levels, or by radiocarbon dating show that most differentiated soil profiles are formed on parent materials laid down as colluvial, alluvial or aeolian deposits during the Last (Russ-Würm) Interglacial, or during an interstadial soon after it. These soils are in general noncalcareous in the present day wetter coastal environments, and have calcareous horizons in the more arid inland areas.An important exception to this generalization is the soils of the pre-Quaternary landscapes, associated with ancient shields and platforms. The parent materials of these soils are deeply weathered profiles leached of silica and bases, or deposits derived from them, often considerably modified during the Quaternary.The significance of soil and landscape features in relation to Quaternary environments is briefly discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The genesis of soils formed from volcanic ash is considered in terms of accumulation of humus and the formation and alteration of clay minerals, including the characteristic amorphous allophane. A chronologic frame of reference has been made possible by the dating of ash layers by means of14C determinations on buried organic residues.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Chemical, physical and micromorphological data are given for eight representative pedons from agricultural areas in Afghanistan. An explanation for the genesis of discoidal features is presented. Four soils are classified as Orthids, one as an Agrid, one as an Aquoll, and two as Fluvents.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Calcareous soils developed in widely varying textures of Nile River alluvium of the UAR and the Republic of Sudan during the Quaternary show many physicochemical and mineralogical properties in common, including neutral to alkaline reaction (pH 7 to 8), and about 2 percent organic matter. X-ray diffraction analysis shows that the clay mineralogy is dominated by montmorillonite, with moderate contents of mica, vermiculite, chlorite, and kaolinite. Regularly and irregularly mixed-layer phyllosilicates are abundant. A conspicuous amount of hydroxy (Al, Fe) coatings occur on the montmorillonite layer surfaces. Quantitative analyses of the clay fraction showed a dominance of montmorillonite (40 to 59 percent), with appreciable kaolinite (7 to 18 percent), mica (6 to 13 percent), vermiculite (1 to 11 percent), chlorite (3 to 27 percent), and amorphous material (7 to 12 percent). Quartz and feldspars (0.7 Na feldspar to 0.3 K feldspar) make up 1 to 9 percent and 1 to 6 percent of the clay fraction, respectively. The sand and silt size fractions are dominated by quartz (6 to 65 percent), feldspars (6 to 29 percent), and mica (1 to 19 percent).Weathering of basic volcanic rocks, underlying sandstone and granite in the headwater areas appears to have dominated the mineralogical composition of the alluvium. Detrital minerals wind-carried from the desert appear to have added mica, vermiculite, and quartz to the soils, more vermiculite south of Khartoum and more mica in the delta.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The evolution of concepts of genesis of the present-day Chernozems and of underlying loesses and paleosols is reviewed. Dokuchaev challenged the view that the Chernozems of the Russian Plain were formed in wetlands. He showed them to be in equilibrium with the modern elimate and native vegetation. Recent dating of soil organic matter suggests that the considerable thickness of Chernozems profiles may be a result of loess increments during pedogenesis. The idea that paleosols in the underlying loesses were once Chernozems has been disproved. There is a need for detailed comparison of both modern soils and paleosols of the Russian Plain with their counterparts in North America.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The regional climate of western and northwestern U.S.S.R. is favorable to podzolization, yet Podzols are interspersed with Brown Forest-Lessivé and Brown-Pseudopodzolic soils in the area. These last two soils, commonly classified as subtypes within the type of podzolic soils, have formed because of medium- to fine-textured Quaternary materials in which “geochemical sieves” have been caused by carbonates, or by double layering of somewhat coarse over finer deposits. The processes of lessivage and pseudopodzolization, by which these two soils formed, have altered and translocated materials within the solum, whereas the podzolization process actually sweeps significant quantities of material out of the solum.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The soils of the prairie and adjacent forests of western Washington display features related to the two different vegetational assemblages. Climatic changes during the early part of the Holocene were responsible for the establishment of the prairie within a coniferous biome. The Spanaway soils (prairie) were further affected by infusion of charcoal from burnings induced by Indians. Spanaway should be considered, to an extent, an anthropogenic soil. Total C (14.4 percent), extractable C (8.0 percent), and N (1.10 percent) are all higher in the Spanaway than in the Everett (forest), but C/N ratio is wider in the Everett. Pedogenic Fe is higher in amount and more mobile in the Everett than in the Spanaway. Amorphous Fe reaches a peak in the B horizons of the Everett (Al, 0.49 percent; B2, 1.28 percent) but not in the Spanaway (Al, 0.53 percent; B2, 0.62 percent). Aluminum is preferentially complexed by the organic material of the Spanaway (Al2O322 percent, Al) more than in the Everett (Al2O30.90 percent, Al); pH and clay mineralogy are not apparently afiected by the differences in vegetation.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID