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) Vol o-.l > 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 talline Oolitic Crystalline .~ N ° 0) •• 0) 'in ... Micrite O)~ Dolomite Dolomite /\0 m .-~.-... °0.. t;.~ 6 6'" .- 6 Biosparrudite Biomicrudite 0) Fossils: Aphanocrystal- ° .. ...c: ~o ("'l U -<"') 6 Biosparite Biomicrite u Fossiliferous 0"0 0) line Biogenic ~ 6 '" /\ ° .0 ...c: 0) '-o~ Micrite "0 . u Dolomite '" ...c: .g~ :;;c: 0) 0) ~ 51 u ~ .n.~ .9 - ;S c m m~ 0) <"') "E :;;c: I>''"' '" .. Biopelsparite Biopelmicrite m Pellets: "'6 Very Finely :;;c: U ~ Bo :g m O)~ ° "0 "E §' u !:: -I ~ Pelletiferous Micrite .-"'-0 i:E 0) Crystalline E:!l .. ;:::I "0"0 "0 '5 .s '" ::S'~ - .0 ~D Pellet Dolomite '" 0) .~ <"')
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 Calcite Fig. 52. Folk classification (Folk, 1959). Basically carbonate rocks rich in particles (allochemi• cal rocks) and those poor in or devoid of particles (orthochemica1 rocks) as well as autochthonous reef rocks are distinguished. The names are formed by combining terms for matrix (micrite), cement (sparite), and particles (intraclasts, etc.)
II. The rock names obtained from combination with micrite (see Fig. 52), sparite, and particles may be modified by adding the following: A. Grain sizes, terrigenous admixtures, etc. (e.g., "medium biosparrudite" = limestone with bioclasts 4- 16 mm in size; "sandy glauconite foraminifera biosparite" = limestone with more than 10% of foraminifera, more than 10% of siliceous admixtures with glauconite, and carbonate cement); B. Field properties (e.g., "black, hard, massive micrite", "white, hard cross• bedded oosparite").
III. Subdivision according to textural spectra (see Fig. 53): The three main limestone groups can be subdivided after Folk (1962) into 8 groups with textural spectra which reflect the various degrees of water energy during deposition: 372 Classifications of Carbonate Rocks
1. Pure micrite or dismicrite with less than 1 % of particles, e.g., Solnhofen lithographic limestone 2. Micrite or dismicrite with 1 %-10% of particles, e.g. fossiliferous micrite or pellet-bearing micrite 3. Biomicrite, intramicrite, oomicrite and pelmicrite with 10%-15% of particles. The particles are scattered throughout the matrix (sparse biomicrites, etc.) and are loosely packed. See Plate 31/2. 4. Biomicrite, pelmicrite, etc. with more than 50% particles. The particles appear "densely packed" (packed biomicrites, etc.). See Plate 31/4. 5. Poorly washed biosparite with about sub equal micrite and sparite; arises because of weak or changing current intensity. 6. Unsorted biosparite, etc. All or almost all of the micrite is washed out and the poorly sorted particles are cemented with sparite. More than two thirds sparite. See Plates 31/3. 7. Sorted biosparite, etc. The particles are well-sorted but only slightly abraded and rounded. See Plate 3111, 6. 8. Rounded biosparite. The majority of the particles is well-rounded. Generally takes place in the surf zone. These groups may reflect the various carbonate sediments in basinal, shallow shelf, and coastal environments. However, it should be remembered that primary textural inversions are common (e.g., transport of carbonate grains from a reef flat into the carbonate mud lagoons behind it; in this way a sediment corresponding to Group 3 or Group 4 arises, in which the carbonate grains are well-sorted). Oomicrites are formed when carbonate ooids are washed out of a shallow water environment and later deposited into a somewhat deeper protected mud
2/3 LIME MUD MATRIX (Micrite) SUBEQU AL OV ER 2/3 SPARRY CEMENT (Sparite) Percent SPAR AND SORTING SORTING ROUNDED & Particles 0 - 1% 1- 10 % 10- SO % >SO % LIME MUD POOR GOOD ABRADED
Representative MICRITE & FOSSILI- SPARSE PACKED POORLY UNSORTED SORTED ROUNDED Roc k .DISMICRITE FEROUS BIOMICRITE BIOMICRITE WASHED BIOSPARITE BIOSPARITE BIOSPAR ITE T e r m s MICRITE BIOSPARITE
Terminology Folk 1959
Sandy Terrigenous Claystone Clayey or Supermature Analogues Claystone Immature Sand stone Sandstone
• LIME MUD MATRIX ~ SPARRY CALCITE CEMENT
Fig. 53. Textural spectrum of carbonate rocks. In general, "low-energy" sediments on the left, with successively "higher-energy" sediments leading to the right, analogous to a Recent environmental sequence representing the change from a basin up onto a shallow shelf and then to a coastal area. After Folk (1962) Dunham Classification 373 environment. Even bioturbation can lead to a mixture of textural types! Plate 3114 gives an example of textural inversion. A statistical comparison of the Folk system of classification with the distribution of sediment on the Andros platform in the Bahama Banks, done by Imbrie and Purdy (1962), shows that Groups 5-8 are easily recognizable with factor analyses; however, the subdivision of the micritic carbonates into oomicrite, intramicrite, biomicrite, biopelmicrite, and pelmicrite is too finely spun. For instance, in the Bahama Banks only "skeletal mud facies" and a "pellet mud facies" could be differentiated.
6.2.2 Dunham Classification (1962). Expanded by Embry and Klovan (1972) (Table 38)
This subdivision is based on the particle fabric and on the kind of particle binding during sedimentation. In the former a distinction is made between mud-supported and grain-supported fabrics. "Mud support" corresponds to carbonate mud with floating particles which generally do not touch each other (similar to pebbles in a mud puddle) (see Plate 36/2; 46/3). "Grain support" exists then when the particles support each other (similar to grains in a pile of sand). (Plate 32). The particle contacts of a grain support fabric are not always reflected in thin-sections because of the two dimensional perspective. Criteria for "grain supports" are concave-convex particle contacts and a packing index < 2, generally around 1.2 (see Sect. 4.2.3.1), and often sparitic cements. Dunham uses names that combine the names of fabric types with the names of the grain types (e.g., ostracod lime mudstone; ostracod-lithoclast lime wackestone; Crinoid lime packstone; Coated-grain lime packstone; Oolitic lime grainstone). It should be stressed that many limestones can be described more meaningfully by a combination of two names, e.g., bioclastic grain/packstone; a limestone with a predominantly grainstone fabric, but with somewhat densely packed grains. The terms floatstone and rudstone, introduced by Embry and Klovan in connection with the investigation of reef limestones, should be used only for allochthonous limestones in which the significant size of the detrital particles has been caused by erosion and redeposition (e.g., large lithoclasts eroded at the shelf-margin and transported into basins, or fore-reef detritus). There is little point in speaking of "oncolitic rudstones" because the size of algal oncoids is mainly controlled by biological factors and not caused by redeposition. The same holds true for bioclastic limestones with particularly large whole shells (e.g., double-valved pelecypods). Differentiation of autochthonous carbonates (boundstones) is based on the various interactions between sessile organisms and sediments; these interactions are characterized by baffling, binding, and framework building processes. Bafflestones originate in local quiet water environments between intergrown branches of corals or between sponges ("Thecosmilia" in the micrite of Rhaetian K6ssen beds; calcisponges in the reef-core facies of Late Triassic Dachstein limestones, see Plate 43/9). Other organisms, especially algae, but also sessile foraminifera or lamellar stromatoporoids contribute to the formation of binds tones (see Table 23). Table 38. Classification of carbonate rocks according to depositional texture. After Dunham (1962) and Embry and Klovan (1972) ""'-..J +> Original components not bound together during deposition Original components were bound together Original components not during deposition bound together during depo- sition
Generally smaller grains (arenite and silt size) More than 10 percent larger grains (rudite size)
Contains mud ilLacks mud Organisms Organisms Organisms Contains Lacks (micrite matrix) (sparite matrix) act as sediment act as sediment act as frame- mud mud baffiers binders builders (e.g., (micrite (sparite Less than More than (e.g., dendroid (e.g., algal intergrown matrix) matrix) 10 percent 10 percent corals) mats) reef corals) grains grains
Mud-supported Grain -su p ported Matrix- Grain- Boundstone supported supported
Mudstone Wackestone Packstone Grainstone Baffiestone Bindstone Framestone Floatstone Rudstone
Plate 4512 Plate 6/5,1211, Plate 912, 1113, Plate 911, 1711, Plate 24/5, Plate 1311, Plate 23/4, Plate 3912, Plate 4811, 15/6,2612, 20/5,2112, 1712,28/5, 43/5,43/9, 1312, 1411, 3117,4311, 5117 53/3 n 27/3,3114, 21/3,3211, 3111,3116, 4611,48/3 14/3,2912, 43/3,45/5, Pi"
3611,46/3, 3612,37 II, 3212,37/2, 3911,45/3, 4812,5011, ~. ~ 5114,5311 4115,44/5, 3811,4211, 47/5,4911 52/3 (") 4711,47/4 ~ 5013, 5116, o· 5212,5312 en o'"-, n a. o '" '" Indications of algal binding are the existence of pseudostromata, skeletal intergrowth frameworks (e.g., by red algae), constructed voids, laminations contrary to gravity, algal mat laminations, packstone fabric composed of algal-derived particles (algal peloids, etc.) and in situ growth of algae. Typical framestones are formed by closely intergrown primary and secondary reef builders. Examples of the subdivision of the boundstone groups especially important for studies of reef-complexes are found in Embry and Klovan (1972, Devonian of Canada). 6.2.3 Classifications of Leighton and Pendexter (1962), Bissell and Chilingar (1967), and Fiichtbauer (1974) (Plate 31) These classifications are similar with respect to the characteristics used in differentiating rock-types. Differences are represented by the boundaries used for the percentages of grains to micritic material. Leighton and Pendexter suggested that the grain/micrite ratio and the percentage of grains were of value for a textural classification of limestones. The grain/micrite ratio can be calculated as the sum of the percentages of grains divided by the percentage of micrite. The authors distinguish the following particle types: detrital grains (including rock fragments and intraclasts), skeletal grains, pellets, lumps, and coated grains (including ooids, pisoids and algal- or fora• miniferal-encrusted grains). Boundaries used to distinguish the main textural limestone types are 10%, 50%, and 90% grains. The name of the limestone type is formed in the following manner: Oolitic Limestone: Limestone with ooids, and a grain/micrite ratio of 9: 1; oolitic-micritic limestone: grain/micrite ratio of about I: I; micritic-oolitic limestone: grain/micrite ratio 1:9. Other types are called detrital limestones, skeletal limestones, pellet limestones, lump limestones, or algal limestones (if organic framebuilders are of importance). Oolitic limestones correspond to "densely packed oosparites" (Folk) or "oolitic grainstone" (Dunham); oolitic-micritic limestones are "oomicrites" or "oolitic wacke/packstones"; micritic-oolitic limestones can also be called "ooid-bearing micrites" or "ooid-bearing mudstones". Bissell and Chilingar (1967) modified the classification by introducing additional boundaries for the percentages of grains: Six groups are distinguished according to the existence of less than 10% grains (micrite limestone), 10-25% grains ( oolitic-micritic limestone), 25-50% (oolitic-micritic limestone), 50-75% (micritic-oolitic limestone), 75-90% (micritic-oolitic limestone), more than 90% grains (oolitic limestones). The same boundaries were used by Fiichtbauer (1970, 1974) who calls a microcrystalline limestone with no ooids or less than 10% ooids "calcilutite" or "micrite" or "micritic limestone with some ooids"; 10-25% grains: "ooid-bearing limestone"; 25-50% ooids: "limestone rich in ooids"; 50-75% grains: "oolitic limestone rich in matrix"; 75-90% grains: "matrix-bearing oolitic limestone"; more than 90% ooids: "oolitic limestone". Instead of matrix the term cement can be used for sparitic limestones. The existence of several grain types may be indicated by a 376 Classifications of Carbonate Rocks modification of the rock name: A limestone containing 20% ooids and 15% peloids may be described as "rich in ooids and peloids", or "oolitic, peloid-bearing limestone" (if the particles are regarded separately). 6.2.4 Energy Index Classification (Plumley et aI., 1962) (Plate 31) This classification (Table 39) takes into account the fact that different water agitation generates different structures and textural types. Crucial genetic factors are the wave base (water depth below which the movement of the water caused by surface waves does not move the sediment - dependent on wave amplitude, storms, and the bottom topography of the sea). The energy level is a result of the kinetic energy on the sea floor due to wave or current action at the depositional interface and a few feet above; this can be implied from the fabric of the transported particles as well as from the amount of micrite or sparite. It is fundamentally important to recognize the fact that the particles have been transported. Criteria for this may be: a) Fragments of partially indurated sediment (intraclasts) or stratigraphically older rocks (extra clasts) ranging in size from silt to boulders; angular or rounded. b) Rounded fragments of fossils that were not originally round. c) A poorly sorted matrix, e.g., silt grains in a fine-grained matrix (can also be caused by bioturbation!). d) A mixture of carbonate and siliceous particles of the same size e.g., bioclasts and quartz sand. e) A mixture of diverse ecologically incompatible organism assemblages, (e.g., fusulinids in algal biomicrites, dasycladaceans in crinoid biosparites). Plate 32. Limestone Fabrics: Grain-Support in Packstones and Grainstones 1. Echinoderm packstone with abundant echinoderm fragments and some foraminifers. Grain-support fabric is indicated by the dense packing of bioclasts and by the free-standing burrow, which would have collapsed in a mud-supported fabric. Packstones are grain• supported micritic limestones which show properties of sediments deposited in quiet water (micrite) and also properties of sediments deposited in agitated water (grain-support; co-occurrence of sparite and micrite). Overly close packing of particles suggests that grain-support of some packstones was aquired during compaction. Some packstones clearly are of diagenetic origin (e.g., stylobreccias, see Sect. 3.7). Others are of sedimentary origin, as indicated by interstices filled with mud (recording an early or late infiltering of previously deposited mud-free sediment), or by a patchy distribution of micrite in predominantly sparry packstones (due to burrowers which mix originally interbedded sand and mud together). Red nodular Adnet Limestone, Liassic: Adnet near Hallein, Salzburg, Austria 2. Oolitic grainstone with redeposited quiet-water ooids. Grain-support is indicated by the presence of sparry cement and by close packing of the ooids. A quiet-water depositional environment of the ooids can be inferred from the radial microstructure (see Sect. 4.1.3.5), the irregular shape of the ooids, and from the occurrence of broken and abraded grains (indicating a redeposition within a high-energy environment). Lower Cretaceous platform carbonates: Southern Apennines, Italy Scale for both Figures 2 mm Grain-Support 377 Table 39. Energy Index Classification of Limestones (after Plumley et aI., 1962) w-l 00 Limestone Type Limc- Mineralogy Texture Fossil Abundance Characteristic Fossils According to stone and Complexity Fossil Associations Energy Index Sub- Size Sorting Roundness Fossil Preservations Types Quiet Calcite Crinoids; echinoids; bryozoans (fragile branch- I I, Clay (i5 to 50%) Microcrystalline carbonate Matrix: good; Original fossil Barren to moderately ing types); solitary corals; ostracodes; thin- Deposition Detrital quartz « 0.06 mm) or any size fossil Fossils: poor shapes; angular fossiliferous shelled brachiopods, pelecypods, and gastro- in quiet water « 5%) fragments in a microcrystalline fragments if bro- Simple assemblages pods; Fqraminifera; sponge spicules; tubular, carbonate matrix (matrix ken encrusting, and sediment-binding algae; fecal I, < 50%) pellets of bottom scavengers. r---- Calcite (predomi- Common fossil associations are crinoid-bryo- nant) Any size fossil fragments in mi- Matrix: good: Moderately to abun- zoa assemblages, bivalve shell assemblages, Clay « 15%) crocrystalline matrix (matrix Fossils: mod- dantly fossiliferous t:oraminifera assemblages (predominantly I, Detrital quartz <50%) erate to good Simple assemblages planktonic). « 5%) (coquinoid limestone) Many fossils are whole and unbroken and are not mechanically abraded. Any fragmentation of fossil material probably is due to disarticu- lation upon death, to predatory (boring, open- ing, and breaking) activity and scavenger activity, or to solution. Intermittently agi- II, Microcrystalline matrix (> Clastic carbonate Barren to moderately Characteristic fossils and fossil associations are tated Calcite (predomi- 50%), Micrograined to medium- Matrix: good; material subangu- tl1ssiliferolls. Moder- similar to Type I limestones. II nant) grained clastic carbonate and Clastic materi- lar to rounded. ately simple assem- Fossil materials are more fragmental than Deposition alter- Clay « 25%) terrigenous material a I: poor to good Roundness ofter- blages those in Type I limestones and also may be nately in agitated r---- Detrital quartz rigenous clastics is more or less rounded by wave action. Scat- water and in quiet li, « 50%) Microcrystalline matrix (> principally a func- tered fragments of fossils from rougher water (j water 50%), Coarse to very coarse- tion of size. environments may be present. j;;" grained clastic carbonate and Oolites may be C/O ;!l. terrigenous material present is' ~ I'l II, Interbedded microcrystalline Sorting good Barren to moderately g. carbonate and any size clastic. within individu- fossiliferous. Moder- ::s Microscale rhythmic bedding allamina ately complex assem- C/O hlages .....,o ---- ___ 1 __ (j I'l 8- o ::s e;. (1) ~ o R- C/O tTl Slightly III, Micrograined clastic carbonate Clastic material Barren to sparsely [os- Echinoderm, bryozoan, and bivalve shell de- ~ (1) agitated Calcite (predomi- « 0.06 mm) predominates Matrix: good; subrounded to ~iliferous hris; Foraminifera; encrusting algae. ..., III nant) Clastic materi- well rounded. Simple assemhlages Common fossil associations are Foraminifera- ~ Deposition in - Detrital quartz al: moderate to Fine-grained ooli- abraded bivalve shell fragment assemblages. 5" slightly agitated III, (up to 50%) Very fine-grained clastic carbo- good tes may be present Barren to moderately Fossil materials comminuted from larger fossil 0- water nate (0.06 to 0.125 mm) pre- fossiliferous structures are well abraded by wave and cur- (1) :>< dominates Simple assemblages rent action. (j - EO vo Ill, Fine-grained clastic carbonate Matrix: poor; Barren to abundantly vo (0.125 to 0.25 mm) predomi- Clastic materi- fossiliferous 51 nates al: moderate to Simple to moderately e(") good complex assemblages o· ~ Moderately IV, Medium-grained clastic carbo- Matrix: poor; Clastic material Moderately to abun- Crinoids, echinoids, bryozoans, brachiopod agitated Calcite (predomi- nate (0.25 to 0.5 mm) predomi- Clastic materi- subrounded to dantly fossiliferous and pelecypod shell fragments, colonial coral IV nant) nates al: moderate to well rounded. Simple to moderately fragments, stromatoporoid fragments (Silurian Deposition in - Detrital quartz good Oolites may be complex assemblages and Devonian predominantly); tubular algal moderately IV, (up to 50%) Coarse-grained dastic carbonate present fragments, colonial algal fragments (rare), en- agitated water (0.5 to 1.0 mm) predominates crusting algae. - Common fossil associations are similar to as- Very coarse-grained clastic car- Moderately to abun- ,ociations of Types I, II, and III, or they are IV, bonate (1.0 to 2.0 mm) predomi- dantly fossiliferous mixtures of these associations. nates Moderately complex to Fossil materials are generally broken and ab- complex assemblages faded. Strongly agitated Gravel-size clastic carbonate Matrix: poor; Clastic material Sparsely to moderately Crinoids; echinoids; encrusting bryozoans; V V, (rock fragments and fossil mate- Clastic materi- subrounded to fossiliferous thick-shelled brachiopods, pelecypods, and Deposition and rial >2.0 mm) predominates al: poor to well rounded. Pi- Complex assemblages gastropods; colonial coral fragments; stroma- growth in strongly Calcite (predomi- moderate solites may be toporoid fragments (Silurian and Devonian agitated water nan!) • present predominantly); colonial algal fragments; ru- f----- Clay «5%) distid fragments (Cretaceous predominantly). Detrital quartz Gravel-size conglomeratic or Matrix: poor; Clastic material Barren to sparsely fos- Fossil associations are similar to Type IV assa- Y, «25%) brecciated carbonate (>2.0 mm) Clastic materi- angular to well siliferous ciations. Tectonic breccias excluded al: poor rounded Complex assemblages Fossil materials are generally broken and ab- I raded. V, Calcite Not applicable Not applicable Not applicable Abundantly fossilif- Colonial corals, stromatoporoids, colonial al- erous gae (principally the Rhodophyta or red algae Simple assemblages and some genera of the Cyanophyta or blue- (fossil colonial growth green algae). in place) w -0-.J 380 Classifications of Carbonate Rocks f) Ooids (careful! - may originate in agitated waters, but also in quiet waters, see 4.1.3.5). g) Wave-resistant colonial organisms in situ (evaluation of growth forms, e.g., in corals and stromatoporoids as well as Corallinaceae). h) Characteristic sedimentary structures such as small-scale cross-bedding, imbrication structures. This classification generally facilitates a rapid description of the possible water movement at the time of sedimentation. It is difficult to differentiate the proposed subgroups, because the non-carbonate constituents must be known quantitatively - which is not possible in thin-sections. One should be wary of overrating the energy-index classification, for the following reasons: a) The particle sizes are brought into direct dependence on the water movement. These sizes, however, are controlled not only by the water energy but also by the supply available (e.g., size-dependent disintegration of skeletal grains, see Fig. 30); the sizes are also influenced by other factors in the environment (kind and intensity of the cement formation in grapestones; growth rate of algae in oncoids). b) The abundance of detrital quartz is not necessarily dependent upon water energy. Due to eolian transport, carbonate is produced in quiet water environments with up to 50% of quartz - in Plumley et aI. a figure of only 5% is mentioned. c) As in all classifications, the occurrence of microcrystalline matrix does not prove a priori that quiet-water conditions existed, because sediment binding organisms can fix the finest sediment grains even in agitated water. This is especially true of algae. d) The energy ranges given for the individual groups of organisms are too limited. Corals and calcareous algae also occur, for example, in Energy Types I and II. Thus, the fossil assemblages can only be marginally employed in the determination of the energy index. e) The conjectured energy ranges must be checked if possible against observations in hand specimens and outcrops, because current marks, cross-bedding, etc. are often not clearly identifiable in thin-sections. The advantage of the classification is that the vertical and horizontal facies changes can be quickly and simply described. As long as the different energy types are correlated with various water depths (careful!), simplified sedimentation models are produced (examples in Plumley et aI., 1962, and Skupin, 1973 - trochite limestone, German: "Muschelkalk"). A critical evaluation of this classification has been undertaken by Bolliger and Burri (1970) in conjunction with work on the Jurassic limestones in Central Switzerland. Examples for the Energy Indices (EI I-V) are shown in the following Plates I: Plates 3112; 36/l; 45/l II: Plates 12/l; 3114; 32/l; 46/3; 50/3; 5111 III: Plates 35; 5114,6 IV: Plates 1l/3; 2112; 3212; 38/l V: Plates 3117; 37/l; 48/l; 53/3 Consideration of the changes in the minimum and maximum energy indices (EI log min, EI logmax) in profiles makes the recognition and description of the cyclic sedimentation pattern much easier (Catalov, 1972). References: Classification of Carbonate Rocks 381 6.3 Discussion and Examples (Plate 31) In the following checklist for classification, a compilation has been made of the criteria in thin-sections which are important for nomenclature: A. Allochthonous limestones (e.g., "detrital limestones") 1. Which groundmass types occur? - micrite, microsparite, sparite (orthosparite or pseudosparite)? 2. Which of the following particles dominates? Which particles are second in abundance? - fossils or bioclasts, peloids, aggregate grains, oncoids, ooids, cortoids, intraclasts, extraclasts, terrigenous particles? 3. What is the grain/micrite ratio, i.e. grain/sparite ratio? The boundary values 1:9, I: 1, and 9: I are often used. The ratio 9: 1 is hardly ever achieved in nature. Hence, other boundary values such as 3:7,1:1, and 7:3 may be more meaningful (see K. A. Schafer, 1970). 4. Are the particles supported by mud or by other particles? What is the packing index? 5. In which range of sizes do the most abundant particles occur? Siltite, arenite, or rudite? 6. Are those particles, which can be rounded, actually round, or angular? B. Autochthonous carbonates (e.g., "reeflimestones") 1. Do the sessile organisms form relatively flat crusts stacked tightly together or biogenic encrustations (bindstone)? 2. Do the sessile organisms form vertical structures with sediment-filled interstitial spaces (baillestone)? 3. Do the sessile organisms build "framework structures", where the individual colonies are bound together by encrustations of organisms (framestone)? 4. Which groups of organisms are dominant? 5. Are conspicuous communities of organisms present? 6.4 References: Classification of Carbonate Rocks Baisert, H. (1967): Vergleich der Ka1kk1assifikationen. Z. angew. Geol. 12, Berlin Bissell, H. J., Chilingar, G. V. (1967): Classification of sedimentary carbonate rocks. In: Chilingar, G. V., Bissell, H. J. Fairbridge, R. W. (eds.): Carbonate Rocks. Dev. Sed. 9 A, 87-168,16 PIs., Amsterdam: Elsevier Bramkamp, R. A, Powers, R. W. (1958): Classification of Arabian carbonate rocks. Geol. Soc. Amer. Bull. 69,1305-1318, New York Bolliger, W., Burri, P. (1970): see 4.1.7.2 Catalov, G. (1971): Structural-genetic classification of the limestones. Bull. Geol. Inst. Sev. Strat. Lithol. 20,133-156, PIs. 1-6, 1 Tab., Sofia (Bulgarian, English summary) Catalov, G. A. (1972): An attempt at energy index (El) analysis of the Upper Anisian, Ladinian and Carnian carbonate rocks in the Teteven Anticlinorium (Bulgaria). Sed. Geol. 8,159-175,4 PIs., 5 Figs., Amsterdam Chilingar, G. V. (1960): Notes on classification of carbonate rocks on basis of chemical composition. J. Sed. Petrol. 3011, 157-158,3 Tab., Tulsa Choquette, P. W., Pray, L. C. (1970): Geologic nomenclature and classification of porosity in 382 Classifications of Carbonate Rocks sedimentary carbonates. Bull. Amer. Ass. Petrol., Geol. 5412, 107-250, 13 Figs., Littleton, Col. 80121 Dunham, R. J. (1962): Classification of carbonate rocks according to depositional texture. Mem. Amer. Ass. Petrol. Geol.l, 108-121,7 Pis., Tulsa Embry, A. F., Klovan, E. J. (1972): Absolute water depths limits of Late Devonian paleoecological zones. Geol. Rdsch. 6112, 10 Figs., Stuttgart Feray, D. E., Heuer, E., Hewatt, W. G. (1962): Biological, genetic and utilitarian aspects of limestone classification. Mem. Amer. Ass. Petrol. Geol. 1,20-32, 3 Figs., Tulsa Folk, R. L. (1959): Practical petrographical classification of limestones. Amer. Ass. Petrol. Geol. Bull. 4311,1-38,41 Figs., Tulsa Folk, R. L. (1962): Spectral subdivision of limestone types. Amer. Ass. Petrol., Geol. Mem. 1, 62-84, I PI., 7 Figs., Tulsa Fuchtbauer, H. (1959): Zur Nomenklatur der Sedimentgesteine. Erdal u. Kohle 12, 605-613, 7 Figs., Hamburg Fuchtbauer, H. (1974): see 1.4.1 Fuchtbauer, H., Muller, G. (1970): Sedimente und Sedimentgesteine. In: Sediment-Petrologie 3,378 pp., 133 Figs., 55 Tab., Stuttgart: Schweizerbart Grabau, A. W. (1904): On the classification of sedimentary rocks. Amer. Geol. 33, 228-247 Imbrie, J., Purdy, E. G. (1962): Classification of modern Bahamian carbonate sediments. Mem. Amer. Ass. Petrol. Geol. 1,253-272, 13 Figs., Tulsa Leighton, M. W., Pendexter, C. (1962): Carbonate rock types. Mem. Amer. Ass. Petrol. Geol. 1,33-61,9 Pis., 2 Figs., Tulsa Mamet, B. (1961): Reflexions sur la classification des calcaires. Bull. Soc. beIge Geol. Paleont. Hydrol. 70, 48-64, 7 Figs., Bruxelles Misik, M. (1972): Lithologische und fazielle Analyse der mittleren Trias der Kerngebirge der Westkarpaten. Acta Geol. Geogr. Univ. Comenianae, Geol. 22, 5-154, Pis. I-54, 9 Figs., Bratislava Monty, Cl. (1963): Bases d'une nomenclature des roches calcaires marines. Ann. Soc. Geol. Belgique 86,1962163, Mem. 2 B 87-122,1 PI., I Tab., Bruxelles Muller-Jungbluth, W. V., Toschek, P. H. (1969): Karbonatsedimentologische Arbeitsgrund• lagen. 2. Aufl., Veraff. Univ. Innsbruck 8, Alpenkundl. Studien 4,32 pp., 3 PIs., Innsbruck Pettijohn, 1. (1957): see 1.4.1 Pirlet, H. (1965): Classification des Calcaires de la Serie des Areno-Cryptites. Ann. Soc. Geol. Belgique 88,1964/65, Bull. 7-10, B 395-B 410, 2 Figs., I Tab., Bruxelles Plumley, W. 1., Risley, G. A., Graves, R. W., Kaley, M. E. (1962): Energy index for limestone in• terpretation and classification. Mem. Amer. Ass. Petrol., Geol. 1,85-107,4 Pis., 5 Figs., Tulsa Purser, B. H. (1972): Subdivision et interpretation des sequences carbonatees. Mem. Bur. Rech. Geol. Mines 77, 679-698, Paris Robinson, R. B. (1966): Classification of reservoir rocks by surface texture. Bull. Amer. Ass. Petrol. 50, 311, 547-559, Tulsa Rutte, E. (1954): Eine Klassifikation der karbonatischen SuBwassergesteine mit Beispielen aus Sudwestdeutschland. N. Jb. Geol. Palaont. Abh. 100,208-246, Stuttgart Sander, B. (1936): Beitrage zur Kenntnis der Anlagerungsgeflige (rhythmische Kalke und Dolomite aus der Trias). Tschermaks Min. Petrogr., Mitt. 48,112,3/4,27-139, Leipzig Sander, N. J. (1967): Classification of carbonate rocks of marine origin. Bull. Amer. Ass. Petrol. Geol. 52, 311, 325-336, Tulsa Schafer, K. A. (1970): Zur Klassifikation der bioklastischen Karbonatgesteine des Unteren Hauptmuschelkalkes in Baden-Wurttemberg. N. Jb. Geol. Palaont. Mh. 197012, 102-115, 5 Figs., 2 Tab., Stuttgart Skupin, K. (1973): see 4.3.2 Todd, T. W. (1966): Petrogenetic classification of carbonate rocks. J. Sed. Petrol. 3612, 317-340,3 Figs., 10 Tab., Tulsa Wolf, K. H. (1961): An introduction to the classification of limestones. N. Jb. Geol. Palaontol. Mh. 196115,236-250,2 Figs., I Tab., Stuttgart ZuiTa, G. G. (1980): Hybrid arenites: Their composition and classification. 1. Sed. 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