Detail the general characteristics of quartz arenites and describe an environment where you might expect them to be particularly common.
Arenites contain less than 15% matrix (<15% material that is <30µm). Quartz arenite is a quartz sandstone (>95% quartz) held together by cement precipitated into intergranular pore space. This rock has a high textural and mineralogical maturity, with mostly monocrystalline sand-sized quartz grains and traces of polycrystalline quartz and other heavy, highly-resistant materials like zircon, tourmaline, and rutile. The texture can contain traces of the providence, weathering, and depositional setting, with well-defined bedding, cross-bedding, ripple marks, and lamination. Although usually white or light grey with silica cement, quartz arenite can be stained pink, brown, or red when cemented by iron oxide. Because quartz arenites are composed of only the most resistant grains, they typically form after either extremely vigorous or multiple sequences of weathering and transportation.
In using quartz arenites to interpret geologic history, the key features are:
- Tectonic Setting – The supermature texture and mineralogy indicates that quartz arenite forms in high energy environments with long transportation distances, like beaches or aeolian environments.
- Geometry – Quartz arenite forms in regionally extensive blankets that are metres to hundreds of metres thick.
- Sedimentology – Quartz arenites are frequently vertically and laterally inter-bedded with stable craton margin rocks, like shallow marine mudrock, limestone, or dolomite. When the arenite is deposited by shallow marine or shoreline deposits.
- Fossils – Quartz arenites have rare body fossils, and localized abundant trace fossils.