Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts
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Oberlin College Honors Theses / OhioLINK
1987
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1415351823 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-oberlin14153518232021-08-03T06:27:27Z Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts Schubel, Kathryn A. Geology Magadi cherts Lake Magadi Kenya Magadi-type The Magadi cherts, inorganic lacustrine deposits from the Lake Magadi area, Kenya, are widely used as a modern analog to explain the origin of ancient inorganic cherts. Formed in a highly alkaline lake, as the result of a transformation from the sodium silicates minerals, magadiite and/or kenyaite, to quartz, the Magadi cherts possess a distinctive set of textural characteristics that allow them to be distinguished from cherts of different origin with only a limited number of samples. Textural characteristics that are diagnostic of the Magadi cherts and that can be used as a test for the occurrence of ancient 'Magadi-type' cherts are: 1) groundmass textures, which lie on a continuum from equigranular mosaics to grid-works, 2) variable concentrations of groundmass inclusions which occur as washes, clots, and fragments, 3) morphology, location, and orientation of cracks, fenestrae, and their filling phases, and 4) crystal molds. The transformation from magadiite to chert is accompanied by a 25% volume loss which is accommodated by the formation of shrinkage cracks, both internal and external, most similar in morphology and infill to subaqueously formed shrinkage cracks in clays and concretions, respectively. Textural and paragenetic criteria appear to be a valid test for the presence of 'Magaditype' cherts. Because important paleoenvironmental interpretations are made based on the presence of 'Magadi-type' cherts, it is important to have diagnostic tests to aid in its recognition. Further field work, and comparisons with lacustrine cherts of intermediate age are clearly needed at this point. 1987 English text Oberlin College Honors Theses / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1415351823 http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1415351823 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Geology Magadi cherts Lake Magadi Kenya Magadi-type |
| spellingShingle |
Geology Magadi cherts Lake Magadi Kenya Magadi-type Schubel, Kathryn A. Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts |
| author |
Schubel, Kathryn A. |
| author_facet |
Schubel, Kathryn A. |
| author_sort |
Schubel, Kathryn A. |
| title |
Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts |
| title_short |
Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts |
| title_full |
Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts |
| title_fullStr |
Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts |
| title_full_unstemmed |
Petrographic Criteria for the Recognition of 'Magadi-Type' Cherts |
| title_sort |
petrographic criteria for the recognition of 'magadi-type' cherts |
| publisher |
Oberlin College Honors Theses / OhioLINK |
| publishDate |
1987 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1415351823 |
| work_keys_str_mv |
AT schubelkathryna petrographiccriteriafortherecognitionofmagaditypecherts |
| _version_ |
1719437189287247872 |