Sandstone quartz arenite

These unconformity-type deposits are located around the unconformity between the Helikian Athabasca Group sandstones and underlying Archean to early Proterozoic metamorphic basement (Hoeve Sibbald 1978 Hoeve Quirt 1984). The present sandstone cover ranges from 0 to 1500 m in thickness and is dominantly composed of mature coarse-grained quartz arenite with a kaolin-illite clay matrix. 

In the Upper Namur Sandstone the poikilotopic calcite cement is absent in moderately to poorly sorted quartz arenites and feldspathic quartz aren-ites that contain abundant primary porosity and some secondary porosity. Only minor patches of siderite micrite and microspar are observed in these elastics, where euhedral quartz overgrowths are well developed, albeit not volumetrically significant (< 5-10%) (Fig. 14D). The detrital grains are dominated by tangential and long contacts, with rare sutured contacts. 

Based on Folk s (1974) classification scheme, the average sandstone of the Hibernia Field is a sublith-arenite (Qgv 9 F3 g Rg.s). Individual samples are either quartz-arenitic or sublitharenitic, and some are subarkoses (Fig. 7 Table 1). If shale clasts, which are probably predominantly rip-up clasts of intrabasinal origin and do not carry provenance information with respect to terrigenous source areas, are excluded, then the majority of the samples would be classified as quartz arenites. 

Fig. 7. QFR triangular diagram of sandstone petrography of Folk (1974). Q, quartz F, feldspar R, rock fragments. 1, quartz arenite 2, subarkose 3, sublitharenite 4,5, arkose 6,7, litharenite.

In other words, those sandstones with more than 15% matrix were termed wackes. The chief type of wacke is greywacke, which can be subdivided into lithic and feldspathic varieties. Those sandstones with less than 15% matrix were divided into three families. The orthoquartzites or quartz arenites contain 95% or more of quartz 25% or more of the detrital material in arkoses consists of feldspar and in lithic sandstones, 25% or more of the detrital material consists of rock fragments (Fig. 1.20). 

Thin section of Fell Sandstone (a quartz arenite), Lower Carboniferous, Northumberland, England. 

Sandstone Grains are mainly mineral fragments Quartz arenite 95% quartz, voids empty or cemented Arkose 75% quartz, up to 25% feldspar voids empty or cemented... 

The degree of resistance that sandstone offers to weathering depends on its mineraiogicai composition, texture, porosity, amount and type of cement/matrix, and the presence of any planes of weakness. Accordingly, the best type of sandstone for external use for building purposes is a quartz arenite that is well bonded with siliceous cement, has a low porosity and... 

Microlithofacial classification of the sandstones is based on Dott s classification modified by Pettijohn et al. (1972). They are mostly arenites and subarkose and quartz wackes (rare sublithic, sporadically lithic and arkosic). Quartz is the main component of the sandstones (about 60-70 vol. percent). Feldspars (6 vol. percent) are mostly represented by potassium feldspars with plagioclases in lesser amounts. Some micas (muscovite and biotite) and chlorites are observed. Mica content of arenites reaches 3 vol. %, but is higher in the wackes. Heavy minerals present include zircon, sphene, rutile and apatite. Magmatic rocks (volcanic more than Plutonic) are predominant among lithoclasts (about 2 vol. %), but some metamorphic and sedimentary clasts being present too. 

The Carboniferous sandstones in the boreholes in LCB are represented by arenites and wackes, mainly quartz, subarkose and sublithic ... 

There are a few other terms commonly used to describe sandstones. A wacke is a poorly sorted sandstone containing more than 10% argillaceous material (clay). Arenites are well-sorted sandstones having little or no clay in them. An arkose is a sandstone whose particles are derived from plutonic rocks and so consist largely of quartz and feldspar. 

Arenite/wacke Unlike many igneous rocks it is difficult to find a simple relationship between the mineralogy of sandstones and their chemical composition. For this reason the geochemical classification of sandstones does not mimic the conventional mineralogical classification of sandstones based upon quartz-feldspar-lithic fragments. Rather it differentiates between mature and immature sediments. 

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