Diagenesis, Porosity, and Dolomitization - Microfacies of Carbonate Rocks - page 281

MODIFYING TERMS

Genetic Modifiers Size Modifiers (for regularly-shaped pores < cavern size)

Process Direction of stage Classes mm

256

Solution s Enlarged x Megapore mg large lmg

Cementation c Reduced r 32

Internal sedimentation i Filled f small smg

16

Time of formation Mesopore ms large lms

Primary P Secondary S 1/2

pre-depositional Pp eogenetic Se small sms

depositional Pd mesogenetic Sm 1/16

telogenetic St Micropore mc

Genetic modifiers are combined as follows Use size prefixes with basic porosity types: mesovug -> msVUG;

Process + direction + time small mesomold -> smsMO; microinterparticle -> mcBP

Examples: solution enlarged sx

cement-reduced primary crP Abundance Modifiers : e.g. percent porosity: (15) or ratio of

internal sediment-filled eogenetic ifSe porosity types: (1 : 2) or ratio and percent: (1 : 2) (15%)

Fig. 7.5. Pore types and porosity classification (Choquette and Pray, 1970). After Adams and McKenzie (1998).
Fabric-selective porosity is controlled by primary or secondary fabrics. Primary depositional fabrics include interparticle,
intraparticle, growth framework, fenestral, and shelter pores. Fabric-selective secondary porosity is formed by intercrystal-
line and moldic pores. Nonselective porosity is independent of depositional fabrics and includes fracture, channel, vug and
cavern pores. Breccia, boring, burrow, and shrinkage pores may be fabric-selective or not. These qualitative criteria can be
substantiated by the additional use of genetic, size and abundance modifiers. Note that the definition of micro- and mega- (or
macro-) pores does not always coincide with the limits used by Choquette and Pray. More generalized definitions of
microporosity prefer pore sizes of 1 mm or less (e.g. Pittman 1971). Examples of the use of the Choquette and Pray classifi-
cation are shown on Pl. 29/1 and Pl. 30/1. See Box 7.4 for definitions of pore types.