ELECTRON-MICROSCOPIC EXAMINATION OF NAMURIAN BEDDED CHERTS, NORTH WALES (GREAT BRITAIN) |
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| Authors: | ALAN E OLDERSHAW |
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| Institution: | Department of Geology, University of Toronto, Toronto, Ont. (Canada) |
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| Abstract: | Electron microscopic examination of Namurian bedded cherts in North Wales (Great Britain) has revealed the existence of two dominant surface textures, granular and spongy, with a range of textures intermediate between the two. These textures can be used to differentiate between three principal lithologies within the cherts and between laminae and colour bands within the lithologies. A positive relationship is demonstrated between the presence of spongy texture and a high volume of impurities; there is a gradation, with increasing argillaceous/organic content, from granular through intermediate to spongy surfaces. It is suggested that this gradation reflects an increase in chalcedony over micro-crystalline quartz resulting from: (l) an increase in impurities; (2) an increase in the rate of precipitation of silica. The relationship between surface texture and type of lithology is considered to be consistent with the order of crystallisation for silica put forward by MILLOT (1960). |
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