Soil Survey Papers No. 5
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Soil Survey Papers No. 5 ANCIENTDUNE FIELDS AND FLUVIATILE DEPOSITS IN THE RIMA-SOKOTO RIVER BASIN (N.W. NIGERIA) W. G. Sombroek and I. S. Zonneveld Netherlands Soil Survey Institute, Wageningen A/Gr /3TI.O' SOIL SURVEY PAPERS No. 5 ANCIENT DUNE FIELDS AND FLUVIATILE DEPOSITS IN THE RIMA-SOKOTO RIVER BASIN (N.W. NIGERIA) Geomorphologie phenomena in relation to Quaternary changes in climate at the southern edge of the Sahara W. G. Sombroek and I. S. Zonneveld Scanned from original by ISRIC - World Soil Information, as ICSU ! World Data Centre for Soils. The purpose is to make a safe depository for endangered documents and to make the accrued ! information available for consultation, following Fair Use ' Guidelines. Every effort is taken to respect Copyright of the materials within the archives where the identification of the j Copyright holder is clear and, where feasible, to contact the i originators. For questions please contact soil.isricOwur.nl \ indicating the item reference number concerned. ! J SOIL SURVEY INSTITUTE, WAGENINGEN, THE NETHERLANDS — 1971 3TV9 Dr. I. S. Zonneveld was chief of the soils and land evaluation section of the Sokoto valley project and is at present Ass. Professor in Ecology at the International Institute for Aerial Survey and Earth Science (ITC) at Enschede, The Netherlands (P.O. Box 6, Enschede). Dr. W. G. Sombroek was a member of the same soils and evaluation section and is at present Project Manager of the Kenya Soil Survey Project, which is being supported by the Dutch Directorate for International Technical Assistance (P.O. Box 30028, Nairobi). The opinions and conclusions expressed in this publication are the authors' own personal views, and may not be taken as reflecting the official opinion or policies of either the Nigerian Authorities or the Food and Agriculture Organization of the United Nations. CONTENTS Summary 5 Introduction 8 1. General geography of the area 9 2. Methods of study 12 2.1 Geography of the deposits 12 2.2 Granulometry of the deposits 12 2.3 Mineralogy of the deposits 14 2.4 Soil profile morphometry 16 2.5 Vegetation, land use and termite features 18 2.6 Compilation of maps and cross-sections 22 3. Pre-Quaternary geology and geomorphology 23 3.1 Geology 23 3.2 Geomorphology 27 4. The aeolic deposits 31 4.1 Funtua loessic deposits 31 4.2 Sangiwa coversand deposits 31 4.3 Sokoto coversand deposits 32 4.4 Zurmi coversand deposits 39 4.5 Illela coversand deposits 43 5. The older aqueous deposits 44 5.1 Tureta sandy wash-plain deposits 44 5.2 Bakolori loamy high-terrace deposits 45 5.3 Gusau loessic high-terrace deposits 45 5.4 Rabah sandy main-terrace deposits 48 5.5 Talata loamy to clayey main-terrace deposits 49 5.6 Kaura-namoda fine sandy main-terrace deposits 49 5.7 Zazagawa sandy low-terrace deposits 52 5.8 Bagudo loamy low-terrace deposits 53 6. The younger aqueous deposits 54 6.1 Argungu floe deposits 54 6.2 Diggi park deposits 55 6.3 Ambursa central deposits 57 6.4 Tungantudo enclosed deposits 65 6.5 Kurukuru and Gande micaceous deposits 66 7. Geomorphology of the Quaternary deposits and climate 69 7.1 Modes of deposition 69 7.2 Relative age of the deposits 69 7.3 Sources of the deposits 70 7.4 Sketch of the Quaternary sedimentologic history of the area 79 7.5 Periods of geomorphodynamic activity and stability, and related changes in climate 84 8. Comparison with neighbouring areas 91 8.1 The coversands 91 8.2 The river terraces and fioodplain deposits 94 8.3 Regional comparison of absolute ages 97 9. Some applications for land development 99 9.1 Speeding-up of land and soil surveys 99 9.2 Extrapolation of geological and hydrological observations 100 9.3 Facilitation of detailed irrigation and drainage planning . 100 9.4 Guidelines for soil conservation and improvement 101 Acknowledgments 103 References 104 Appendices: 1. Geomorphologie and lithologic features of the Rima-Sokoto river basin, N.W. Nigeria (coloured map 1 : 500 000 and schematic cross-section) 2. Physiography of the Rima-Sokoto floodplains (maps 1 : 20 000 and schematic cross-section) 3. Sketch maps showing the various stages of the Quaternary history of the Rima- Sokoto river basin SUMMARY This paper deals with geomorphologic features in aeolic and aqueous deposits in the northwestern part of Nigeria (Rima-Sokoto river basin), and their relation to climatic changes during the Quaternary. Basic data, expressed on a coloured map 1 : 500,000, have been derived from aerial photographs, descriptions of soil profiles, vegetational and geological studies in the field, and chemical, physical, and mineralogical analyses in the laboratory, all forming part of a UNDP/FAO Soil and Water Resources Survey Project carried out between 1963 and 1966. Kind of deposits There are five different types of deposits of aeolic character. Four of these have a top in the fine sand fraction; they were deposited as dunes and are now partly denudated. Distinguished are: —• Sangiwa coversand formation, originally with transversal parabolic dune forms, — Sokoto and Zurmi coversands with longitudinal dune forms, — Illela coversands with fortress shaped dune forms, —• The fifth aeolic deposit, called Funtua, is a loess. — Most aeolic materials were deposited by ENE winds. There are fourteen different types of aqueous deposits, eight above the present flood- plains, six inside them. Those above flood level are: — High-terrace (Gusau and Bakolori) and sandy wash plain (Tureta) deposits, all three positioned relatively high. — Main-terrace deposits (Rabah, Talata, Kaura-namoda), all three at intermediate level. —• Low-terrace deposits (Zazagawa and Bagudo), both relatively low but above the maximum flood level of the presentday rivers. The sandy wash plain was formed by sheet-flood processes from the Sangiwa sands, the high terrace by a combination of sheet-flood and fluviatile action with loess as an important source of the sediment (especially Gusau). The main-terrace deposits are mainly sandy and were formed by braiding rivers; locally a more meandering river system must have been active as well, resulting in more loamy materials (Talata). The Zazagawa low terrace is a clear sandy braiding river deposit, the loamy Bagudo again shows a bit more meandering river influence. The six aqueous deposits that are in the presentday floodplains are the following: — Argungu floe deposits, sandy deposits with a floe pattern orginated by a braiding river. — Diggi park deposits, meandering river deposits of mainly silty character, at present with a rather high degree of alkalinity, and a park-like vegetative cover. — Ambursa central and Tungantudo enclosed deposits, which have a lacustrine charac ter and are clayey. — Kurukuru and Gande micaceous deposits, having a sedimentology identical to the Diggi park ones, but of recent to sub-recent origin, with little or no alkalinity features, and a strikingly high content of micas. 5 It is apparent that in the early part of the Quaternary there was a rhythmic variation in aeolic and aqueous depositions, only partly separated by downcutting periods, whereas in the latter part there was a rhythmic variation between aqueous deposition and aqueous downcutting, only once interrupted by aeolic deposition. Origin of the deposits A study of the heavy minerals of the sand fractions in combination with the textural and geomorphological features revealed the following about the origin of the deposits. The sandy deposits in the northwestern and central part of the survey area (Sangiwa, Tureta, Sokoto, Rabah, Zazagawa, Argungu and Illela sands) all come from the same original local sources, namely the more or less sandy Cretaceous and Tertiary sediment ary rocks, viz. the Gundumi, Gwandu II + III and particularly Rima formations. It is very likely that these sands developed for a good part one from the other, whether aeolic or fluviatile, the sorting of the sands becoming more and more refined. The fluviatile re-sorting, moreover, led to a gradual coarsening from fine sand to medium sand. Maximum transport distances were 50-75 km, although the distances are usually much less. The sandy deposits in the southeastern subcatchment have also been derived locally; in this case weathering Crystalline basement material was involved, either directly (Zurmi) or indirectly (Kaura-namoda). The very fine sands, loams, and silt-rich clayey deposits occurring both on the river terraces and in the floodplains of the rivers that have their catchment in the Crystalline basement area (Bakolori, Talata, Bagudo, Diggi, Kurukuru and Gande) are all mainly derived, directly or indirectly and by longdistance transport, from weathering Crystalline basement materials. The loessic deposits in the southeastern subcatchment area, however, derived from faraway sources of non-crystalline rocks to the north-east of the survey area, either directly (Funtua) or indirectly (Gusau). The silt-poor clayey deposits in some of the floodplains of the northwestern sub catchment (Ambursa, Tungantudo) are derived from clayey sedimentary ronks mainly in the far north (Sahara), at that time a humid area. Geomorphologie history Absolute dating of the deposits could only be done tentatively, by comparison with neighbouring areas from where some absolute dating has been reported in literature. The following sediment-historical sketch can be given (for details see chapter 7 and 8 and Tables 7 en 8). In a landscape mainly formed by pediplanations during the Early Pleistocene, aeolic sedimentation of poorly sorted sands (Sangiwa) in transversal dunes and loess (Funtua) took place during the Early Weichselien and possibly started already in the Eemien, under desert conditions. This was followed by erosion in a climate with irregular rain fall; a kind of pediplanation process (sheet floods) gave rise to a sandy „wash plain" (Tureta) and fluviatile deposits (Gusau, Bakolori). This period was followed by a return of desert conditions, still during the Weichselien, in which well-sorted sands were deposited as longitudinal dunes (Sokoto, Zurmi).