Item talk:Q161264

Geoscience Ontology Description

Particularly for fine-grained sedimentary rocks, distinction of 'intrabasinal' versus 'clastic' genesis can be very interpretive. In practice the use of clastic mudstone terminology as opposed to carbonate mudstone terminology may be dermined by a priori knowledge about the rock being categorized. If it is associated with other clastic rocks, the clastic categories will be favored, if with cabonate rocks, the carbonate categories will be favored. Carbonate rock subcatgories are defined on two orthogonal dimensions--mineralogy (calcitic vs. dolomitic vs non-carbonate impurities), and texture. The texture categories used here are those of Dunham (1962), and involve grain size (matrix vs. grains/allochems), fabric (matrix vs. grain supported), and genesis (bound, frame, or fragmental). The textural approach used for carbonate rocks is conceptually incompatible with that used for clastic sedimentary rocks, which is solely grain size or mineralogy based. This leads to problems in the vocabulary for rocks of mixed siliclastic/carbonate mineralogy (grainstone vs. sandstone, carbonate mudstone vs. carbonate rich mudstone, how to accomodate marlstone...). Sedimentary rock in which at least 50 percent of the primary and/or recrystallized constituents are composed of one (or more) of the carbonate minerals calcite, aragonite, magnesite or dolomite.