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The Nature of Zeolite Occurrences in Deposits of the Olduvai Basin, Northern Tanzania

Published online by Cambridge University Press:  01 January 2024

Florias Mees ,
Georges Stoops ,
Eric Van Ranst ,
Roland Paepe  and
Elfi Van Overloop
Florias Mees*
Affiliation:
Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, B-9000 Ghent, Belgium
Georges Stoops
Affiliation:
Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, B-9000 Ghent, Belgium
Eric Van Ranst
Affiliation:
Department of Geology and Soil Science, Ghent University, Krijgslaan 281 S8, B-9000 Ghent, Belgium
Roland Paepe
Affiliation:
Geobound International Ltd, Environmental Research Group and Consultants, Doornstraat 27, B-9550 Herzele, Belgium
Elfi Van Overloop
Affiliation:
Geobound International Ltd, Environmental Research Group and Consultants, Doornstraat 27, B-9550 Herzele, Belgium
*
*E-mail address of corresponding author: Florias.Mees@UGent.be
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Abstract

The Plio-Pleistocene deposits of the Olduvai Basin in northern Tanzania consist of a sequence of lacustrine and fluvial sediments. They contain various amounts of zeolite minerals, the formation of which is related to an interaction of volcanic material or detrital clays with saline alkaline lake water and groundwater. Petrographic characteristics of zeolite occurrences provide information about their conditions of formation. They were studied for all four main stratigraphical units that are recognized at Olduvai (Beds I to IV), sampled in the southeastern part of the basin. In the lake-margin deposits of Bed I and the lower part of Bed II, chabazite is the dominant zeolite mineral accompanied by phillipsite and minor amounts of erionite and clinoptilolite. Chabazite commonly occurs as part of altered volcanic rock fragments, characterized by partial or complete dissolution of volcanic glass and the formation of chabazite inside vesicles, following the development of thin smectite coatings. It also formed within the sediment matrix, requiring extended periods of impregnation of the deposits by saline alkaline solutions. Chabazite also occurs extensively as coatings and infillings of pores, developed during periods of subaerial exposure which were characterized by high groundwater levels. Phillipsite formed at a later stage, from more evolved solutions, with higher K/Na ratios than during chabazite formation. The fluvial deposits of Bed IV, Bed III and the upper part of Bed II have a high analcime content. They also contain various amounts of chabazite, phillipsite and natrolite. All zeolite minerals mainly occur in pores. The predominance of analcime indicates a higher salinity and alkalinity than during the preceding period with sedimentation and diagenesis in a lake margin environment. Early development of zeolite occurrences, shortly after the deposits became exposed during breaks in sedimentation, is recorded for some intervals, where zeolites are covered by illuvial clay coatings or by sparitic carbonate cement. In most intervals, however, zeolites mainly formed at a later stage.

Keywords

AnalcimeChabaziteDiagenesisOlduvaiPhillipsiteTanzaniaZeolites

Information

Type
Research Article
Information
Clays and Clay Minerals , Volume 53 , Issue 6 , December 2005 , pp. 659 - 673
Copyright
Copyright © 2005, The Clay Minerals Society

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