Mineral reactions in the sedimentary deposits of the Lake Magadi region, Kenya

Research Article| December 01, 1976 Mineral reactions in the sedimentary deposits of the Lake Magadi region, Kenya RONALD C. SURDAM; RONALD C. SURDAM 1Department of Geology, University of Wyoming, Laramie, Wyoming 82071 Search for other works by this author on: GSW Google Scholar HANS P. EUGSTER HANS P. EUGSTER 2Department of Earth and Planetary Science, Johns Hopkins University, Baltimore, Maryland 21218 Search for other works by this author on: GSW Google Scholar Author and Article Information RONALD C. SURDAM 1Department of Geology, University of Wyoming, Laramie, Wyoming 82071 HANS P. EUGSTER 2Department of Earth and Planetary Science, Johns Hopkins University, Baltimore, Maryland 21218 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (12): 1739–1752. https://doi.org/10.1130/0016-7606(1976)87<1739:MRITSD>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation RONALD C. SURDAM, HANS P. EUGSTER; Mineral reactions in the sedimentary deposits of the Lake Magadi region, Kenya. GSA Bulletin 1976;; 87 (12): 1739–1752. doi: https://doi.org/10.1130/0016-7606(1976)87<1739:MRITSD>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The authigenic minerals, principally zeolites, in the Pleistocene to Holocene consolidated and unconsolidated sediments of the Magadi basin in the Eastern Rift Valley of Kenya have been investigated. Samples were available from outcrops as well as drill cores. The following reactions can be documented: (1) trachytic glass + H2O → erionite, (2) trachytic glass + Na-rich brine → Na-Al-Si gel, (3) erionite 4- Na+ → analcime + K+ + SiO2 + H2O, (4) Na-Al-Si gel → analcime + H2O, (5) calcite + F-rich brine → fluorite + CO3−−, (6) calcite + Na-rich brine → gaylussite, and (7) magadiite → quartz + Na+ + H2O. Erionite is the most common zeolite present, but minor amounts of chabazite, clinoptilolite, mordenite, and phillipsite were also recognized. Erionite can form directly from trachytic glass by the addition of H2O only. It is characteristic of the Magadi basin because of the low content of alkaline earths in the volcanic glasses and in the solutions interacting with them.Analcime is common in outcrops of the High Magadi and Oloronga Beds. It forms from erionite by a reaction probably initiated by a lowering of the silica activity, which results from the transformation of magadiite to chert. Analcime in the drill-core samples grew at the expense of a Na-Al-Si gel. This gel forms at the lake shore and is washed into the lake during flooding conditions.Fluorite is common in the core samples and can be explained by reaction of the fluoride-rich brines with calcium in the sediments, principally detrital calcite. Authigenic albite and potassium feldspar were not recognized, probably for reasons of reaction kinetics.The presence of authigenic minerals can be accounted for by considering the chemical compositions of the starting materials, mainly volcanic glasses, and the brines they come in contact with. Lake Magadi represents a unique opportunity for studies of diagenesis because authigenic minerals are forming there at the present time and because the evolution of its waters is well known. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.