Distribution of authigenic albites in a limestone succession of the Helvetic Domain, eastern Switzerland

Abstract

A new occurrence of authigenic albite was found in a Jurassic sedimentary succession of the Glarus Nappe near Walenstadt (eastern Switzerland). The euhedral shape and the chemical purity of these albites are evidence for their authigenic origin. The crystals are irregularly distributed in the sediment, highlighting the importance of the host rock composition for albite authigenesis. The crystals occur exclusively in limestones with a carbonate content higher than 80 wt-%. A diagenetic or hydrothermal origin of albite authigenesis is discussed for the studied region. Clay mineral transformation appears to be an important source of ions for albite formation. RESUME Un nouveau gisement d'albite authigène a été découvert dans une succession sédimentaire du Jurassic, situé dans la nappe de Glaris près de Walenstadt (Est de la Suisse). La pureté chimique et la forme euédrique de ces albites atteste de leur origine authigène. La répartition irrégulière des cristaux dans le sédiment souligne l'importance de la composition de roche hôte pour la formation des albites. Les cristaux sont présents uniquement dans les calcaires contenant plus de 80 %m de carbonate. La possibilité d'une origine diagéné-tique ou hydrothermale est discutée pour la région étudiée. La transformation des minéraux argileux paraît être une source importante d'ions pour la formation de l'albite.

Geochemical evolution of organic-rich shales with increasing maturity: A STXM and TEM study of the Posidonia Shale (Lower Toarcian, northern Germany)

“…Although rarely abundant volumetrically, these albite crystals are widespread within the investigated Harderode and Haddessen samples and no K-or Ca-feldspars have been observed. Based on these characteristics, following Kastner and Siever (1979), Spötl et al (1999), Rais et al (2008) and Bernard et al (2010a), the albite crystals described here might be identified as authigenic feldspars. Not strictly synonymous with diagenesis, authigenesis is commonly used in the literature when referring to minerals that formed in-situ during either high-grade diagenesis or low-grade metamorphism (Kastner and Siever, 1979;Spötl et al, 1999).…”

Low-temperature feldspar and illite formation through bioreduction of Fe(III)-bearing smectite by an alkaliphilic bacterium

“…Motivated by this suggestion, other studies have subsequently documented minor but common occurrence of low-temperature feldspars in carbonate rocks and sandstones (e.g., Hearn and Sutter, 1985;Molenaar and de Jong, 1987;Ramseyer et al, 1993;Spötl et al, 1999;Rais et al, 2008). There have been two models proposed to explain the low-temperature feldspar authigenesis: (a) isochemical transformation (Kastner and Siever, 1979), and (b) the interaction between migrating brine and host rocks (Hearn and Sutter, 1985;Spötl et al, 1999;Rais et al, 2008). In the isochemical transformation model, authigenic feldspar forms through the burial transformation of pre-existing detrital minerals in sediments.…”

“…If the sediment itself serves as the essential donor of all constituents for feldspar authigenesis, authigenic feldspar should be expected to be a common mineral in sedimentary rocks. In contrast, the interaction model between migrating brines and host rocks proposes that the cations (Na, K and Ca) in feldspar are derived from saline fluids, and other constituents of feldspar are supplied from siliciclastic debris (e.g., clay minerals) within host rocks (Rais et al, 2008). However, an experimental study by Small (1994) showed that the formation of feldspar through the reaction between saline solution and smectite required high temperature and pressure (200°C and 50 MPa).…”

“…However, field evidence strongly argues against this model. Specifically, it cannot well explain the restricted occurrence of low-temperature feldspar in regional sedimentary rocks (Rais et al, 2008). If the sediment itself serves as the essential donor of all constituents for feldspar authigenesis, authigenic feldspar should be expected to be a common mineral in sedimentary rocks.…”

A Diagenetic Study of the Wolfcamp Shale, Midland Basin, West Texas

“…Kastner (1971) also cites the importance of ions from sea water in the formation of albite at low temperatures. Kastner (1971) and Rais (2008) linked clay diagenesis to the formation of albite. The albite in the lithoclasts in the Wolfcamp probably formed from internal fluids on the platform before being subaerially exposed and eroded.…”