6 Classifications of Carbonate Rocks Carbonate rocks can be subdivided according to: a) chemical and mineralogical composition, e.g., Chilingar (1960), Pettijohn (1957), or Ftichtbauer (1959), b) fabric features - "groundmass" ( = matrix and/ or cement) and particles, c) special physical parameters, e.g., porosity, Choquette and Pray (1970); see 9.2.1. Almost all the systems of classifications used today are based upon the criteria characterizable either in thin-sections or hand specimens, such as matrix, cement, and particles. Hence, the following discussion of these classifications will emphasize fabric features. 6.1 Principles of Classification Table 36 lists the advantages and disadvantages of some of the modem systems of classification. Dissimilarities in the systems are due less to the different basic concepts than to the consideration of various kinds and quantities of particles types (some authors refer "lumps" to intraclasts; others consider them to be an independent group). Dissimilarities are also due to the various percentages used as boundary values, to a divergent emphasis on size, sorting, and rounding of transported or transportable particles, and to somewhat specialized problems which call for modified systems of classification (e.g., coquina limestones, Schafer, 1970). 6.2 Systems of Classification Important suggestions for systems of classification are found in Classification of Carbonate Rocks, a collection of symposium papers edited by Ham in 1962 (Mem. Amer. Ass. Petrol. Geol. 1). The most commonly used classifications are those of Folk (1959, 1962), Dunham (1962), Leighton and Pendexter (1962) and Bissell and Chilingar (1967, modified by Ftichtbauer, 1974). A discussion of all the suggestions published up to 1967 is found in Baisert (1968). E. Flügel, Microfacies Analysis of Limestones © Springer-Verlag Berlin · Heidelberg 1982 Limestone Classifications: Comparison 367 Table 36. Comparison of the usefulness ofa few modern systems of limestone classification Application Preliminary Advantages Disadvantages Knowledge Dunham Field, Knowledge of Rapid "spot" (1962) hand specimen, texture types identification in thin -section the field Folk Thin-section Knowledge of par- Sensible subdivi- Sometimes too (1959, 1962) ticle types, matrix sion of textural time consuming, spectra some subdivi- sions too artificial Fiichtbauer Field, Knowledge of par- Rapid classifica- Mixture of descrip- (1970) hand specimen, ticle types, matrix, tion tive and genetic thin-section cement criteria Leighton and Field, Knowledge of par- Rapid rock Mixture of descrip- Pendexter hand specimen ticle types, matrix designation tive and genetic (1962) criteria; percent- age boundary values sometimes too rigorous Monty Thin-section Detailed knowledge Well-devised Nomenclature (1963) of particle types scheme systems and terms too complicated; concept similar to Folk Plumley et al. Hand specimen, Knowledge oftex- Rapid classifica- A few basic con- (1962) thin-section ture types, amounts tion of "genetic" cepts somewhat ofinsoluble residues types questionable Todd Thin-section Knowledge of par- Attempt at a Too involved for (1966) ticles, matrix, ce- "comprehensive" facies analyses ment, texture, classification insoluble residues, chemical com- position 6.2.1 Folk Classification (1959,1962) (Table 37, Figs. 52, 53) The system of classification suggested by Folk is based upon the fact that, in principle, carbonate rocks are comparable to sandstones and shales, in regard to sedimentation. I. Major constituents oflimestones are: A. Allochems (carbonate grains or particles): 1) Intraclasts - synsedimentary resediments, e.g., mud pebbles, grapestones, bahamites. 2) Pellets - subrounded, spherical to elliptical grains of micrite, generally devoid of any internal structure. Sizes range between 0.03 mm and 0.15 mm, most commonly 0.04-0.08 mm. These are probably fecal pellets in most cases. 368 Classifications of Carbonate Rocks 3) Ooids. 4) Fossils and skeletal grains. 5) The Folk classification must be modified to include oncoids as terminologically independent particles. The occurrence of more than 10% of oncoids should be marked in the name of the rock type (e.g., oncomicrite or oncosparite); see Table 37. B. Matrix (micrite) C. Sparite Continued p. 371 Plate 31. Classifications of Limestones A=Classification after Folk, 1959 or 1962; B=Classification after Dunham, 1962; C=Energy Index Classification after Plumley et al., 1962; D = Classification after Fuchtbauer, 1974 1. A - pelsparite or sorted pelsparite with echinoderm fragments; B - grainstone or pelletoidal grainstone; C - IV /2; D - cemented pellet-limestone with echinoderms. Lower Cretaceous: mouth of the Rhone, Geneva, Switzerland. Scale is 1 mm 2. A - biomicrite or sparse biomicrite; B - bioclastic wackestone; C - 113; D -limestone rich in skeletal grains or filaments. Late Triassic (Kossen beds): Gaissau near Hallein, Salzburg, Austria. Scale is 10 mm 3. A - oosparite or poorly sorted oosparite with skeletal grains; B - oolith lime grainstone; C - IV /2; D - oolitic limestone. Lower Permian: Forni Avoltri, Carnia, Italy. Scale is 1 mm 4. A - dasycladacean algal biomicrite; B - dasycladacean lime wackestone; C - 11/1; D - fossiliferous limestone rich in matrix. Skeletal grains include Dasycladaceae (Diplopora adnetensis Flugel) as well as echinoderm fragments. This is possibly a "textural inversion" in the sense of Folk (1962), because the dasycladaceans probably did not live in the low energy sedimentary environment indicated by the fine-grained micrite. Late Triassic (Upper Rhaetian limestone): Gruber reef, Feichtenstein, Salzburg, Austria. Scale is I mm 5. A - extraclast-bearing sparite with echinoderms; B - lithiclast lime grain/rudstone; C - V 12; D - detrital fossiliferous limestone. The very well-rounded micritic particles should be regarded as extraclasts. Evidence of this are: high degree of rounding, truncation of the particles in the lithoclasts on the lithoclast boundaries, different cements in and between the pebbles. Lower Carboniferous: Kiicu Tepe near Balya, Anatolia, Turkey. Scale is I mm 6. A - intrasparite; B - lithoclastic grainstone; C - IV /2; D - Sparry lump limestone. Par­ ticles are typical aggregate grains. Dachstein Limestone, Upper Triassic: Dachstein, Styria, Austria. Scale I mm 7. A - biolithite; B - agal-foraminiferal boundstone or framestone; C - V /3; D - reef-lime­ stone. The biogenic framework is composed of the agglutinated foraminifera Haddonia heissigi Hagn (top center), various Corallinaceae (gray and black crusts), corals (bottom and top left, partly bored), and calcareous sponges (top left). At the bottom right Discocyclina sp. Tertiary (Upper Eocene): quarry in the Northeast flank of the Eisenrichterstein peak near Hallthurn, SE Bad Reichenhall, Germany. Scale is I mm 8. A - biopelsparite; B - bioclastic lime grainstone; C - IV /2; D - cemented pellet-lime­ stone with foraminifera. The sections of Galeanella tollmanni (Kristan) are quite conspicuous among the foraminifera. This species is restricted to small cavities in the framework of Upper Triassic reefs. Late Triassic (Dachstein reef limestone): Sauwand near GuBwerk, Styria. Austria. Scale is I mm Limestone Classifications 369 Table 37. Classification of Carbonate Rocks after Folk (1959, 1962), slightly modified Limestones, Partly Dolomitized Limestones, and Primary Dolomites Replacement Dolomites (V) -.lVol o > 10% Allochems < 10% Allochems Allochemical Rocks (I and II) Microcrystalline Rocks (III) Sparry Calcite Microcrystalline 1-10% Allochems <1% Undis- Allochem Ghosts No Cement> Micro- Ooze Matrix > Allo- turbed Allochem crystalline Ooze Sparry Calcite Ce- chems Bioherm Ghosts Matrix ment Rocks (IV) Sparry Allo- Microcrystalline chemical Rocks Allochemical Rocks (I) (II) ~ m'" Intrasparrudite Intramicrudite Intraclasts: Finely Crystal- Medium ~uV)m In traspari te Intramicrite Intraclast-bearing line Intraclastic Crystalline N!:: Micrite Dolomite Dolomite /\ ~ tf? Oosparrudite Oomicrudite Oolites: Coarsely Crys- Finely V);E~ Oosparite Oomicrite Ooli te-bearing •• 0) talline Oolitic Crystalline .~ N ° 0) 'in O)~ /\0 m... Micrite ~.- Dolomite Dolomite °0.. .- ... 6 6'" .-t;.~6 Biosparrudite Biomicrudite 0) Fossils: Aphanocrystal- ° .. ...c: ~o ("'l U -<"') 6 Biosparite Biomicrite u Fossiliferous 0"0 0) line Biogenic ~ 6 o~ /\ .0 ...c: 0) '- '" ° Micrite u Dolomite '" "0 . ~ '" ...c: .g~ :;;c: 0) 0) .9 51 u ~ .n.~ - 0) ;S c '"m m~ <"') "E "'6 :;;c: I>''"' U .. Biopelsparite Biopelmicrite m Pellets: Bo :g Very Finely :;;c: m ~O)~ ° "0 ~ .-"'-0 "E0) §' u !:: -I Pelletiferous Micrite Crystalline ;:::I "0"0 i:E E:!l .. .0 "0 '5 '" ::S'~ - Pellet Dolomite '" 0) .s <"') ~D -, .~ <t: '> ~ -° °'" ~ Q;C'\S ~ etc. °("'l 6 V) "0 :> .... 0 <"') .'= 6 I>' ..=! N .. Pelsparite Pelmicrite '"° ....u ...- V ~ .- 0.. d- ° V) ~ :> -v ~~ ;:::I N °I>' V rD Oncosparite Oncomicrite Oncoids: ~ f1)4-4..9cn Oncosparrudite Oncomicrudite Oncoid -bearing 6°","0 N :::s 0:-::::'0 .. _ '.0 ~ u Micrite ~ ° m ° ~ - :>~ .... o - --'-- Folk Classification 371 ALLOCHEMICAL ROCKS ORTHOCHEMICAL ROCKS SPARITE I MICRITE II III (SPARRY (MICRO­ MICROCRYSTALLINE CALCITE CRYSTALLINE CALCITE LACKING CEMENT) CALCITE MATRIX) PARTICLES is INTRACLASTS. I­ INTRASPARITE INTRAMICRITE MICRITE en o Cl.. :2 OOIDS o u :2 OOSPARITE OOMICRITE DISMI CRITE w (disturbed micrite) :l: Uo ~ FOSSILS ~ (Biogenes) AUTOCHTHONOUS c:x: REEF ROCKS BIOSPARITE BIOM ICRITE IV PELOIDS (pellets) ~ BIOLITHITE PELSPARITE PELMICRITE ~ Sparry Calcite r:;': ::"1 Microcrystalline