Zeitschrift Documenta naturae, Band 77 (dn077-1993-1)
München 1993 (1. Auflage); ISBN 3-86544-077-0
Kohring, R. & Schlüter, T. (Hrsg.): Current Research at the Department of Geology, Makarere University, Kampala, Uganda.
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Barifaijo, E., Hampton, C. M., Schlüter, T. & Bethlem, H.: Meteorite Fall at Mbale, Eastern Uganda, 14th August 1992, a preliminary report: 1-5, 2 pls.
Zusammenfassung
On August 14th, 1992, at approximately 15.40 hours East African time, a meteorite fell at Mbale town, E Uganda. About 45
impact localities were traced during a subsequent survey carried out one week later, but their majority was already withont fragments. The collected particles range from 3 g to 20 kg, with
the trend of smaller fragments NWW and larger S of Mbale. Their strewn field indicated a NWW to SEE movement of the meteorite. On the basis of morphology, mineralogy, density and the presence
of chondrules, the Mbale meteorite can be placed in group L of WASSON's classification system, tentatively belonging to the L6 chondrite group, the most common type of meteorite.
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Sinabantu, S.: Variations in Petrography of Rubanda. Chitwe and Masha-Kibaran Granites and its Genetic Significance: 7-13.
Zusammenfassung
Petrographic characteristics of W-bearing, Sn-bearing and barren syn- and posttectonic granites are subtly different. The
minerals present are common for die three types of granites but their modal abundance is variable. The granites consist essentially of quartz, microcline, orthoclase, albitic plagioclase,
biotite and minor muscovite. Accessories include tourmaline, zircon, apatite, and allanite. The secondary minerals are epidote, sericite, chlorite and claH85H86H90H88y minerals. The rocks
have a porphyritic texture and are commonly foliated at die periphery of die plutons. Phenocrysts are mainly K-feldspars. Myrmekitic and perthitic intergrowths are common in die granites The
modal composition of die three types of granite differs. The youngest (W-bearing) granites are mostly alkaline and syenogranite, some tending to quartz granites; Sn-bearing granites vary
between compositions of monzogranite, syenogranite and quartz granite. The oldest barren granites are mostly granodioritic. The difference in age, stages of alteration, modal composition and
type of associated mineralization may indicate different sources of their parent magmas.
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Hampton, C. M.: Unusual Source of Carbonate for Speleothem at Nyakasura, W-Uganda: 15-21.
Zusammenfassung
The speleothems formed at caves near Nyakasura, Fort Portal are unusual in that the carbonate used for their formation
originated from an igneous lava. Estimates of growth rates suggest that die larger speleothems took between 2.000 to 20.000 years to form. The combination of carbonatite lava overlying soft
clay, in close proximity to a stream produce conditions for speleothem formation at Nyallasura, that may be rarely occur at other carbonatite localities.
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Biryabarema, M.: Influence of Geologic Structure and Lithology on the Drainage System of Bunyoro, Western Uganda: 23-30.
Zusammenfassung
Qualitative and limited quantitative drainage analysis of Bunyoro (Masindi and Hoima Districts) was carried out. The
objective was to establish the degree of geological control on the drainage patterns and drainage densities of the area. Data were collected from a drainage map of a scale 1:250,000, compiled
from topographic map sheets of a scale 1:50.000. The geology of the area has appreciably affected the drainage system although the regional slope is still the major controlling factor in flow
directions of the main channels. NE trending geologic structures parallel to the present rift have affected die drainage more than structures in other directions.
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El-Etr, H. & Biryabarema, M.: Statistical Evaluation of Geologic Control of the Shape, Size and Orientation of some Isolated Hills in Southern and Western Uganda:
31-40.
Zusammenfassung
Statistical methods of die student's t-test and azimuth analysis were employed in studying the
influence of geology on die evolution of landforms in W and S Uganda. In the student's t-test comparisons of average hill shape and average hill size were carried out between areas covered by
various rock types to find out whether both or one of the parameters may be directly dependent on the geologic factor. It was found out that the shape of hills in this region is highly
influenced by the geology while size is largely affected by the denudation history of the areas. The azimuth analysis of hills showed striking parallelism between orientation of hills and
structural orientations especially where the denudational history is not very advanced.
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Vaidyanadhan, R., Dixit, P. C. & Schlüter, T.: Geomorphology and Sedimentology of Lake Manyara Environs, Tanzania, East Africa: 41-62, 5 pls.
Zusammenfassung
An area of about 2000 km² around Lake Manyara and Lake Burungi, in NW Tanzania, was geomorphologically mapped using aerial
photographs on a scale of 1:42.250. Field traverses were made to check the interpretation and collect samples of rocks and sediments, with special emphasis on the phosphorites of Minjingu,
ca. 5 km E of Lake Manyara. Lake Manyara is situated along the 5 Part of the Eastern or Gregory Rift in the depression of its W shoulder. The area consists of late Proterozoic metasediments,
Neogene volcanics, and Plio-Pleistocene and Holocene lake beds. There are plateaus, rolling plains, and features like alluvial fans, scree, migrating deltas, besides various others usually
found in a fluvial and lacustrine terrain. A few faults and fractures within the lake beds have been recorded from lineaments on the aerial photographs as well as during the subsequent field
traverses. Also evidence for neotectonics is cited as reflected in the morphological changes of features Associated with stream terraces and lacustrine ridges. Macroscopic and microscopic
studies of rock samples from the lake beds indicate the following rock types: 1. coarse fragmented carbon ate rocks, 2. stromatolitic and oncolitic rocks, 3. oolitic rocks and 4. dolomitic
rocks. Some of them are closely interbedded with volcanic debris. lt. is inferred that the lakes should have occupied a much wider area and periodically shrunk to give rise to sub-parallel
ridges close to the present shorelines; a majority of the sediments is of chemical origin. The phosphorites of Minjingu represent a guano deposit with bone bed features.
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Schlüter, T.: The East African Copal - an almost forgotten Fossiliferous Resin: 63-72, 1 pl.
Zusammenfassung
An extensive exudation of resin from trees of the Leguminosea-species Hymenaea verrucosa is responsible
for die formation of fossil and recent copal in E Africa. A model of its depositional environment is presented: The resin is found in the soils around die particular tree (primary
deposition), in die sandy-clayey soils of an estuarine environment (secondary deposition) or along die coastal shorelines (tertiary deposition). The stratigraphic age of fossil copal in E
Africa is still uncertain, presumably ranging down to the Pliocene. In its abiotic properties die copal shows many similarities with other known fossil resins and ambers. The organic
inclusions are normally in an excellent mode of preservation. Several species of Arachnida, Insecta and Retilia have been described, predominantly already in die beginning of die 20th
century. They indicate a highly diversified paleobiocenosis, most likely not much different from the conditions of today.
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Schlüter, T.: Geological Development and Economic Significance of Lacustrine Phosphate Deposits in Northern Tanzania: 73-79
Zusammenfassung
Phosphate bearing Pliocene or Pleistocene sediments at Minjingu, N Tanzania, host one of the few commercially exploitable
reserves of this essential fertiliser material in E Africa. However, contrary to the formations of large deposits in Morocco, Algeria, Tunisia, Egypt and the Western Sahara, the geological
origin of theses resources in N Tanzia is completely different and locally restricted. The phosphorites of Minjingu are mainly formed by bone fragments of birds (Phalacrocorax
kuehneanus) and fishes (cf. Tilapia sp.), indicating a former lacustrine environment with an increased paleoalkalinity up to 40 meq/l HCO3- + C03--. The reserves of these
phosphorites, commercially exploited since 1983 are limited for approximately 20 years (production target: 100.000 t/y). However, they are one of the overall objectives to advance the
agricultural production in Tanzania by building up its own fertiliser.
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Muwanga, A.: Some Index and Engineering Properties of a Hydrothermally Altered Granite from St. Austell, Cornwall, SW England: 81-89
Zusammenfassung
The results of field and laboratory studies of a hydrothermally granite from St. Austell, Cornwall, SW England, are
presented. The materials are classified into six decomposition grades on the basis of field indices, particularly the N-Schmidt hammer rebound value and the slake test were used.
Interrelationships between N-Schmidt hammer rebound value, point load strength and uniaxial compressive strength are evidently linear. This indicates that N-Schmidt hammer rebound value and
point load strength can form a reliable basis for a quick assessment of material strength.