Geology and paleontology of the Jurassic and Cretaceous beds of southern Tanganyika

Aitken, William G (1959) Geology and paleontology of the Jurassic and Cretaceous beds of southern Tanganyika. PhD thesis, University of Glasgow.

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Part I of the thesis describes the geology of an area of about 400 square miles in the hinterland of Kiswere in the coastal region of southern Tanganyika. More detail is available of the Mandawa-Mahokondo region, where the sequence is most complete, than of the remainder. The greater part of the area is occupied by Mesozoic rocks with marine Paleogene sediments in the extreme east. The exposure of Jurassic and Lover Cretaceous strata is due largely to the erosion of once continuous plateau-forming bus of Upper Aptian age or younger. Unconsolidated continental Neogene sands cap the plateaux and Neogene gravels appear on some of the lower watersheds. The Neogene sediments have not been napped in detail. All stages of the Middle and Upper Jurassic and of the Cretaceous are represented, though the succession is not contimous. The Jurassic and Lower Cretaceous strata (the Mandawa Mahokondo and the Tendagura Series) are largely of littoral or neritic facies and estuarine and continental rooks are present towards the vest. Below the oldest exposed Jurassic bads (the Pindiro Shales), which contain massive gypsum at surface, drilling has proved a thick evaporite series including halite deposits. Thare is a notable easterly thickening of almost all of the individual units of the Jurassic and Lower Cretaceous sedimentary columm. The Tendaguru Beds, which in their type area are only about 400 feet thick, total over 2,500 feet in the north of the Mandawa-Mahokondo area (including about 600 feet of Lower Cretaceous strata) and the total thickness of the Jurassic above the Pladlro shales there approaches 5,000 feet. The marine Upper Aptian occurs in two facies, dominantly calcareous (Kiturika Beds) along the east of the Ngarama Plateau and mixed arenaceous/argillaceous/calcareous to the east of the Mandawa Mahokondo area. The marine Upper Aptian occurs in the west of the area mapped, and the continental Makonde Beds, which have previously been described as equivalent to the Kiturika Beds, cannot be demonstrated to be other than younger than them in the area concerned. The Albion-Senonian sequence forms a series of overstepping, dominantly argillaceous subdivisions, still in part at least of fairly shallow water origin, nowhere extending west of the Upper Aptian limestone outcrop. Below the Callovian, fossils are not abundant or diagnostic but rich fossil horizons occur in the sequence between the Callovian and the Lower Aptian. There is generally a clear palaeontological distinction between the marine horisons of the Jurassic and the Lowor Cretaceous, and palaeontological evidence on the basis of Trigoniids is advanced for correlations within the Kimmeridgian-Tithonian strata. Otherwise, local correlations are in part on lithological grounds. There are two outstanding structures in the area, the Mandawa-Mahokondo and the Makangaga-Ruawa anticlines en echelon, both in part diapiric, of which the axes lie approximately NNW-SSE. To erosion of these is due the exposure of the older Jurassic strata. The former has two distinct culminations. Outside the vicinity of these structures dips generally low. The greater part of the movement, which was to some extent independent in the two structures, was completed by the end of the Jurassic but, locally, faulting and some minor uplift affected Upper Aptian beds. A number of unconformities occur; some are due to local diapiric uplift in the anticlinal areas, but those below the Upper Neocomian and below the Upper Aptian appear to be of widespread significance. The geological history of the axes is outlined and a brief comparison is made of some of the faunas present with others in the Ethiopian Province and elsewhere. Part II of the thesis gives an account of Trigoniids collected during the survey of the Kiswere Hinterland. A total of 11 new species have been named and described and at least a further 5, of which only poor material is available, are also regarded as new. The genera Linotrigonia, Laevitrigonia (as emended by Cox, 1952) and Opisthotrigonia, and the subgenus Pleurotrigonia are reported for the first time from East Africa. of these opisthotrigonia was previously regarded as monotypic. Biometric analysis of variation in communities of Indotrigonia from successive horizons in the Middle Kimmeridgian-Tithonian sequence has been attempted.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: G M Stockley
Keywords: Geology, Paleontology
Date of Award: 1959
Depositing User: Enlighten Team
Unique ID: glathesis:1959-73693
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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