THE GEOMORPHOLOGY OF SOUTHEAST KENYA A. P. Oosterom STELLINGEN 1. Bij de vorming van de uitgestrekte planatievlakken in Oost-Kenia heeft marine en lacustrine abrasie een belangrijke rol gespeeld. Dit proefschrift. 2. De schaarste aan fossielen van hominiden in Oost-Afrika over de periode van ongeveer 500 000 tot 50 000 jaar BP is schijnbaar. 3. Voor de toepassing van geografische informatiesystemen op bedrijfsniveau in reliefrijke gebieden is het essentieel om programmatuur te ontwikkelen die identificatie van de geologische en geomorfologische positie van een gekozen punt mogelijk maakt. 4. De klink van het Basis- en het Hollandveen is er medeverantwoordelijk voor dat er in Nederland geen aanwijzingen worden gevonden voor hoge holocene zeestanden. 5. De geringschatting van het belang van onderwijs en onderzoek in de geologie en geomorfologie aan de Landbouwuniversiteit te Wageningen is een uiting van onwetenschappelijk doe-het-zelf-denken. 6. Zolang de programmatuur voor het opnemen, opslaan en opvragen van kaarteringsgegevens minder flexibel is dan een veldboekje staat het gebruik van handterminals en veldcomputers vernieuwing in de weg. 7. De betrouwbaarheidsgrens van 25 000 jaar voor de datering van organische carbqnaten met behulp van de 14C-methode is te hoog.. Dit proefschrift. 8. Het woord automatisering wekt onjuiste verwachtingen als het gaat om de invoering en het gebruik van computers. 9. Kerkelijke liedboeken behoren losbladig te zijn. 10. De stelligheid waarmee waarheden worden verdedigd is eerder een maat voor onkunde dan voor inzicht. Stellingen behorende bij het proefschrift: The Geomorphology of Southeast Kenya. A.P. Oosterom Wageningen, 20 april 1988 THE GEOMORPHOLOGY OF SOUTHEAST KENYA Promotoren: Dr. J.D. de Jong, emeritus hoogleraar in de geologie ° ' Dr. H.Th. Verstappen, hoogleraar in de geoniorfologie aan het Internationaal Instituut voor Lucht- en Ruimtekaartering (ITC), Enschede A.P.Oosterom THE GEOMORPHOLOGY OF SOUTHEAST KENYA Proefschrift ter verkrijging van de graad van doctor in de landbouwwetenschappen op gezag van de rector magnificus, dr. C.C. Oosterlee, in het openbaar te verdedigen op woensdag 20 april 1988 des namiddags te vier uur in de aula van de Landbouwuniversiteit te Wageningen 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 Copyright holder is clear and, where feasible, to contact the originators. For questions please contact [email protected] indicating the item reference number concerned. ABSTRACT Oosterom, A.P., 1988. The Geomorphology of Southeast Kenya. Doctoral Thesis, Agricultural University, Wageningen. 227 pp., 34 tbs, 32 figs, 160 refs, English and Dutch summaries, 1 map (1: 500 000). 2 A geomorphological map of an area of 66 500 km in the southeastern part of Kenya has been prepared. In the littoral zone eight major terrace levels occurring between the present shore and approximately 160 m +MSL have been described. Analysis of radiometric datings and uplift rates of the coastal succession suggested that the formation of the terraces extends over the last 1.4 my of the Pleistocene. Soil development indicate a climatic change from humid to savannah conditions at approximately 800 ky BP. Three sedimentary levels occurring in the landward part of the coastal region have been linked with the three highest littoral terraces. In the interior region, the denudation of the vast plains east of the 38 15' meridian was correlated with the deposition of Plio-Pleistocene deposits in the Larau embayment and the coast. To Heleen, Lonneke, Leen, Wimke and Han CURRICULUM VITAE Arie Pieter Oosterom was bom on the 3 October 1952 at Stol wijk, The Netherlands. After obtaining his HBS-b certificate at the Christelijk Lyceum at Gouda, life started his studies in 1970 at the Agricultural University of Wageningen. In 1978 the Ingenieur's degree was obtained with specialization in tropical soil science and geology with soil fertility as additional subject. From 1978 to 1982, he was employed by the Netherlands Organization for Scientific Research (ZWO). During this period he carried out geomorphological field work in southeast Kenya in co-operation with the Department of Geography at the University of Nairobi. From 1982 to 1983 he was associated with the Department of Soil Science and Geology at the University of Wageningen. As a guest researcher, he obtained facilities to prepare a thesis on the geomoiphology of southeast Kenya. Since 1983 he has been employed by the Agricultural University of Wageningen as a university lecturer in the Department of Soil Science and Geology. CONTENTS PREFACE 1 INTRODUCTION 1 2 GENERAL INFORMATION 5 2.1 Geology 5 2.2 Relief 7 2.3 Drainage 11 2.4 Climate and Vegetation 15 3 GEOMORPHOLOGICAL ANALYSIS 17 3.1 Coastal region 17 3.1.1 Littoral zone 18 3.1.1.1 Stratigraphical record 19 3.1.1.2 Morphological structure 27 3.1.1.2.1 Present-day shore 31 3.1.1.2.2 Lower littoral levels 41 3.1.1.2.3 Middle littoral levels 55 3.1.1.2.4 Higher littoral levels 71 3.1.1.3 Origin and development 82 3.1.1.3.1 Sequence of events 84 3.1.1.3.2 Chronological correlation 89 3.1.1.3.3 Tectonic and climatic effects 102 3.1.2 Paralic zone 108 3.1.2.1 Stratigraphical record 109 3.1.2.2/ Morphological structure 113 3.1.2.2.1 Lower paralic levels 114 3.1.2.2.2 Middle paralic levels 120 3.1.2.2.3 Higher paralic levels 129 3.1.2.3 Origin and development 133 3.1.2.3.1 Sequence of events 133 3.1.2.3.2 Chronological correlation 136 3.1.2.3.3 Tectonic and climatic effects 139 3.2 Interior region 140 3.2.1 Denudational areas 140 3.2.1.1 Stratigraphical record 141 3.2.1.2 Morphological structure 143 3.2.1.2.1 Denudational plains 145 3.2.1.2.2 Denudational hills and plateaus 151 3.2.1.3 Origin and development 155 3.2.1.3.1 Sequence of events 156 3.2.1.3.2 Chronological correlation 157 3.2.1.3.3 Tectonic and climatic effects 157 3.2.2 Volcanic and lacustrine areas 159 3.2.2.1 Stratigraphical record 159 3.2.2.2 Morphological structure 159 3.2.2.2.1 Chyulu hills and plateaus 159 3.2.2.2.2 Yatta hills and plateaus 163 3.2.2.3 Origin and development 170 3.2.2.3.1 Sequence of events 170 3.2.2.3.2 Chronological correlation 171 3.1.1.3.3 Tectonic and climatic effects 171 3.2.3 Fluvial areas 172 3.2.3.1 Stratigraphical framework 172 3.2.3.2 Morphological structure 173 3.2.3.2.1 Lower fluvial levels 174 3.2.3.2.2 Middle fluvial levels 179 3.2.3.2.3 Higher fluvial levels 182 3.2.3.3 Origin and development 183 3.2.3.3.1 Sequence of events 183 3.2.3.3.2 Chronological correlation 185 3.2.3.3.3 Tectonic and climatic effects 185 CONCLUSION AND DISCUSSION 187 4.1 Geomorphological history 187 4.1.1 Precrambrian era 187 4.1.2 Paleozoic era 188 4.1.3 Mesozoic era 189 4.1.3.1 Early to Middle Triassic period 189 4.1.3.2 Late Triassic to Early Jurassic period 190 4.1.3.3 Middle Jurassic period 191 4.1.3.4 Late Jurassic to Early Cretaceous period 191 4.1.3.5 Early Cretaceaous period 192 4.1.3.5 Late Cretaceous period 193 4.1.4 Cainozoic era 194 4.1.4.1 Tertiary period 194 4.1.4.2 Quaternary period 197 4.2 Future research 204 SUMMARY 207 SAMENVATTING 211 REFERENCES 215 APPENDICES PREFACE The study of the origin and development of landforms is the work of a geomorphologist. He classifies and describes the nature of the Earth's surface and tries to interpret its genesis. It was my present promotor Professor J.D. de Jong who, through his lectures, attracted my attention to this field of science. He was able to convey to me part of his knowledge and enthusiasm during my study at the Agricultural University of Wageningen. The request to conduct geomorphological research in southeast Kenya meant an unexpected opportunity for further graduation under his supervision. Having come to the end of the study, I wish to express my sincere thanks for his contribution. I look back with pleasure on his yearly field visits and the lively discussions we had. The large number of letters which he wrote from Wageningen witness his continuing interest in the work. The time taken in molding the ideas and field data into a readable account was a strain on both our scientific and personal relationships but it is with honour and respect that I remember his patience and forbearance. I am also grateful to my co-promotor Professor H. Th. Verstappen for his interest, critical remarks and guidance especially during the preparation of this thesis. Among the many others, to whom I am indebted are in the Kenyan authorities in the guise of the Office of the President who permitted the research and gave their full cooperation during the fieldwork. I am grateful to the Netherlands Foundation for the Advancement of Tropical Research (WOTRO) which provided the research funds. I wish particularly to thank Messrs. Schenk, Toet and Vontsteen for their pleasant and accurate handling of the administrative, financial and technical matters.