Abstract
Mineralogical and chemical analyses of fine clay fractions from in and around Lake Abert, Lake County, Oregon, show that the pyroclastic rocks supplying detritus to the lake weather to a suite of layer silicate clay minerals varying from high-charge dioctahedral montmorillonite to montmorillonite/intergrade smectite-chlorite interstratifications. In the lake these clays extract K, Mg, and Si to form authigenic interstratified illite and a trioctahedral, Mg-rich mineral resembling stevensite in composition. Both the neoformed interstratifications contribute little unambiguously to X-ray powder diffraction patterns, which are dominated by the reflections of detrital clays. From limited data it appears that the illite occurs below 0.8 m depth in sediments of a possibly somewhat fresher (brackish) lake and the trioctahedral interstratification between 0.4 and 0.2 m depth in sediments of a lake of about the same size and salinity (about 30–90 g/kg) as that of the present lake.
Резюме
Минералогические и химические анализы мелких фракций глин, взятых изнутри и из окрестности озера Аберт в дистрикте Озеро в Орегоне, указывают, что пирокластические породы (которые доставляют детритус в озеро) выветриваются и образуют слоистые силикатовые глинистые минералы, отличающиеся по составу от заряженных двухоктаэдрических монтмориллонитов до переслаиваний монтмориллонит-смектит-хлорит. В озере эти глины извлекают из воды К, Mg, и Si для образования аутигенных переслаивающихся иллитов и триоктаэдрического, Mg-обогащенного минерала, напоминающего по составу стевенсит. Оба свежеобразованные переслаивания способствуют частично недвусмысленно рентгеновским порошковым диффрактограммам, в которых доминируют отражения детритовых глин. На основании ограниченных данных кажется, что иллит находится ниже глубины 0,8 м в осадках немного пресного озера (солоноватого), а триоктаэдрические переслаивания проявляются на глубине между 0,4 и 0,2 м в осадках озера примерно такого же самого размера и солености (около 30–90 г/кг), как существующего в настоящее время озера. [E.G.]
Resümee
Mineralogische und chemische Analysen von feinen Tonfraktionen aus dem Innern und vom Rand des Lake Abert, Lake County, Oregon, zeigen, daß pyroklastische Gesteine Gesteinsschutt in den See liefern, der zu einer Abfolge von Tonmineralen verwittert, die von stark beladenem dioktaedrischem Montmorillonit bis Montmorillonit/Smektit-bzw. Montmorillonit/Chlorit-Wechsellagerungen variieren. Im See extrahieren diese Tone K, Mg, und Si, um autigene Illit-Wechsellagerungen und ein trioktaedrisches Mg-reiches Mineral, das in der Zusammensetzung mit Stevensit vergleichbar ist, zu bilden. Beide neugebildeten Wechsellagerungen tragen wenig eindeutige Reflexe zur Röntgenpulveraufnahme bei, die vor allem die Reflexe der detritischen Tone zeigt. Aus den begrenzten Daten geht hervor, daß der Illit unter 0,8 m Tiefe in den Sedimenten eines möglicherweise etwas frischeren (brackischen) Sees auftreten und die triok-taedrischen Wechsellagerungen zwischen 0,4 und 0,2 m Tiefe in Sedimenten eines Sees, der etwa die gleiche Größe und die gleiche Salinität aufweist (etwa 30–90 g/kg) wie der gegenwärtige See. [U.W.]
Résumé
Des analyses minéralogiques et chimiques de fractions d’argile fines provenant de l’intérieur et d’autour du Lac Abert, Lake County, Oregon, montrent que les roches pyroclastiques fournissant du détritus au lac s’altèrent en une suite de minéraux argileux silicates variant de montmorillonite dioctaèdrale à haute charge à des interstratifications montmorillonite/smectite-chlorite intergrade. Dans le lac, ces argiles extraient K, Mg, et Si pour former de l’illite authigénique interstratifiée et un minéral riche en Mg ressemblant à la stevensite. Ces deux interstratifications nouvellement formées contribuent peu sans ambiguité aux clichés de diffraction poudrée des rayons-X, qui sont dominés par les réflections des argiles détritiques. A partir de données limitées il semble que l’illite se trouve sous une profondeur de 0,8 m dans les sédiments d’un lac possiblement à eau plus fraîche (saumure), et que l’interstratification trioctaèdrale se trouve entre 0,4 et 0,2 m de profondeur dans les sédiments d’un lac d’à peu près la même taille et de même salinité (~30–90 g/kg) que celles du lac présent. [D.J.]
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Jones, B.F., Weir, A.H. Clay Minerals of Lake Abert, an Alkaline, Saline Lake. Clays Clay Miner. 31, 161–172 (1983). https://doi.org/10.1346/CCMN.1983.0310301
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DOI: https://doi.org/10.1346/CCMN.1983.0310301