Relict Deep Weathering and Duricrusting in Relation to the Palaeoenvironments of Middle Latitudes

Bibliographic Data

ID4645600
AuthorsG H Dury (corresponding author)
Year1971
Volume137
Issue4
Pages511
Publication date1971-12-01
Peer ReviewedYes
Open AccessNo
TypeARTICLE
VenueGeographical Journal (JOURNAL)
Journal identifiersISSN: 0016-7398 • E-ISSN: 1475-4959
PublisherJSTOR (PUBLISHER)
DOI10.2307/1797147
OpenAlexW2314152844
LanguageEN
Citations received6
References cited6

Relict deep-weathering profiles and duricrusts occur throughout a considerable range of middle latitudes. Chemically, they can probably occupy any position in the fersiallitic range. Palaeoclimatic, palaeobotanical, and palaeogeomorphic evidence indicates that they originated by weathering in conditions that would today be classed as humid-tropical. While such conditions can be reconstructed for middle latitudes for large parts of the Cretaceous, the relict crusts and profiles now exposed at the surface, or buried beneath or in dated basalts, seem to relate mainly to parts of Tertiary time, wherein peak warmth (and on some of the evidence, peak humidity) was recorded during the Eocene, with a sub? sequent warm-humid peak in the middle Miocene. Among relict ferricrusts are those of southwest Wisconsin. Relict silcrusts may include the sarsens of the Marlborough Downs. THERE IS probably no way of defining deep weathering so as to distinguish it completely from shallow or ordinary weathering. However, deep-weathering profiles are commonly associated with surface crusts, whereas shallow-weathering profiles are not. The crusts, often indurated and fully deserving of the title duricrusts (Woolnough, 1927), range widely in physical characteristics and in chemical and mineralogical properties (Maignien, 1965), but very many can be readily classified according to their ternary location in the fersiallitic range (Dury, 1969). Highly ferruginous, highly aluminous, and highly siliceous crusts occupy extreme positions in the classification. Crusts can exceed 12 m in thickness, and complete profiles 80 m or more. In numerous profiles, the pisolitic/slaggy/vermicular or blocky/massive crust is succeeded downward by a mottled zone, wherein clays are blotchily stained by sesquioxides, and where cementation may be pronounced. The mottled zone is succeeded by a pallid zone, wherein white or light-tinted clay minerals can constitute most of the bulk and can be wholly kaolinitic. Alternatively, the whole lower part of the profile is blotched or reddened, constituting the lithomarge of tropical pedology. The means whereby potential crusts are enriched with particular minerals, especially iron, aluminium, and silica, has provoked considerable debate, involving with some writers a postulate of two-stage differential enrichment. There is, however, good agreement that the crusts originate in the shallow subsurface horizons of tropical soils. Concentrations of sesquioxides form the plinthite ofthe Seventh Approximation, ?^ Gr H. Dury is Professor of Geography and Geology at the University of Wisconsin

Geodesy · Latitude · Relation (database · Weathering · Geochemistry and Elemental Analysis · Geological formations and processes · Geology · Geology and Paleoclimatology Research · Paleontology

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