Some Geomorphological Implications of Deep Weathering Patterns in Crystalline Rocks in Nigeria

Bibliographic Data

ID8964327
AuthorsMichael F Thomas (corresponding author)
Year1966
Issue40
Pages173-173
Publication date1966-12-01
Peer ReviewedYes
Open AccessNo
TypeARTICLE
VenueTransactions of the Institute of British Geographers (JOURNAL)
Journal identifiersISSN: 0020-2754 • E-ISSN: 1475-5661
PublisherWiley (PUBLISHER • GB)
DOI10.2307/621576
OpenAlexW2020647920
LanguageEN
Citations received6
References cited2

THE PHENOMENON of deep weathering has received frequent discussion in papers concerned with the geomorphology of terrains developed on crystalline rocks, yet few of these studies show actual depths of weathering except for occasional, isolated locations. This absence of quantitative information obviously weakens arguments based upon the premise that deep weathering occurs widely within a given area or displays particular relationships with surface relief, drainage patterns or individual landforms. This deficiency is explained by the paucity of existing records and the difficulty of obtaining additional data where weathering depths commonly exceed fifty feet. Drilling and portable seismographs are both commonly used by civil engineersl, and the information used in this paper is derived from these sources. It is recognized that such data have certain inherent inadequacies. First the sites are chosen because they appear from surface considerations to be suitable for the ultimate purpose of the project. Most surveys of this kind in Nigeria have been undertaken to determine the suitability of sites for dam foundations. As a result the sites selected are mostly well-defined valleys which usually display frequent fresh rock outcrops. They are not therefore located in areas where weathering depths would be expected to be great. In spite of this limitation there is sufficient variety of site to make the profiles representative of more than one type of terrain. The second difficulty is the lack of uniformity in the terms used to describe the various zones of the weathering profile. Furthermore, subdivision of the profile on the basis of seismic information is not often very accurate. For most of the profiles presented in this study emphasis has therefore been placed only on the recognition of the sound rock line or basal surface of weathering, but there are difficulties even here, for the transition from weathered to fresh rock varies greatly in its characteristics from one borehole to another. There is also the possibility that the upper part of the profile may contain transported material, either sandy wash similar to that recognized for instance by R. V. Ruhe2 or wind blown dust that is well known from Northern Nigeria. Both J. D. Falconer3 and more recently J. Dresch4 have called attention to the role of alluviation in depressions on the interior plains of West Africa. However, it is not thought likely that any serious errors, resulting from the inclusion of transported materials under the heading of in situ weathering products, have been incorporated into the profiles to be described. Seismic traverse information which may be ambiguous in this respect, has been included only from the humid south of Nigeria, where alluvial infilling of the kind envisaged above does not appear to have taken place, and from the Niger valley near Bussa, where a large amount of confirmatory drilling information is

Earth science · Geochemistry · Socioeconomics · Sociology · Southeastern Nigeria · Weathering · Dam Engineering and Safety · Geology · Geophysical and Geoelectrical Methods · Underground infrastructure and sustainability

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