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.
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...).
