Siliciclastics
In sediment petrology, the term siliciclastics (plural, singular uncommon) are those clastic sediments and sedimentary rocks whose grain fractions consist mainly of silicate minerals (including quartz ).
The siliciclastics are the most important group within the clastic sediment (it) e. Thus, gravel and conglomerates often sands and sandstones often and clays and shales always siliciclastic. The vast majority of sandstones and siltstones in geological tradition mainly contain grains of quartz ( silicon dioxide , SiO 2 , mineralogically also classified as oxide instead of silicate). Within the "quartz rocks" these quartz-rich siliciclastics are in turn the most important group, ahead of non-clastic sedimentites such as radiolarite (silica schist, lydite) and kieselguhr (diatomite) or diagenetic formations such as flint . Other common minerals in sandstones are feldspars , which belong to the group of aluminosilicates . The finest-grained fraction in poorly sorted sandstones and siltstones and the main component of claystones are clay minerals , above all illite , montmorillonite and (only in a terrestrial environment) kaolinite .
The term "silicon plastic" is mostly used informally as a generic term when a facies or a lithostratigraphic unit is to be described in sediment petrography, which is made up of different types of silicate-rich clastic sedimentary rocks (for example quartz sandstones, arcs , siltstones , mudstones). Typical siliciclastic systems are for example the Kulmfazies ( sub-carbon , marin) of the Central European Varistikums, the red sandstone ( Lower Triassic , Continental) and the Wealden facies ( Lower Cretaceous , continental) Central and Western Europe, which Newark supergroup ( Middle Triassic to Jurassic , Continental) in Eastern North America as well as the Karoo super group ( Upper Carboniferous to Lower Jurassic, predominantly continental) in South Africa .
literature
- Roland Vinx: Rock determination in the field. 4th edition, Springer-Verlag, 2014, ISBN 978-364255418-6 , p. 274 ff.