Classification – A Name for Your Sample - Microfacies of Carbonate Rocks

Geology Reference

In-Depth Information

Be aware that micrite and sparite have a priori no ge-

netic significance. The name sparite was designed for

'sparry calcite cement', but the common use also in-

cludes sparry calcite mosaics representing recrystallized

fine-grained matrix.

• While constructing the name of your sample, indi-

cate clearly whether you are strictly following the in-

creasing ranking order proposed by Folk or whether

you prefer the reversed ranking. Imagine for a minute

that about 20% of the particles of your micritic lime-

stone are intraclasts, 75% bioclasts, and 15% peloids -

would you give your sample the name intrapelbio-

micrite or biointrapelmicrite, as many people do?

• If the grains exceed sand-size ranges, use the syl-

lable rud-, e.g. intrasparrudite (a limestone consisting

of millimeter-sized or larger intraclasts occurring within

a sparry groundmass, Pl. 46/5)

• If you prefer a strict guideline leading you to a well-

defined and reproducible name, use the expanded Folk

classification proposed by Strohmenger and Wirsing

(Fig. 8.7).

• Utilize the open-minded character of the original

Folk classification, which allows the rock name to be

combined with additional descriptive characters - e.g.

black, poorly laminated pelmicrite (a common lagoonal

limestone), or red nodular pelagic biomicrite (a com-

mon open-marine deeper-water limestone). Because of

the value of fossils as paleoenvironmental proxies, a

specification of the fossil types is desirable - e.g. dasy-

clad green algal biosparite or pectinid mollusk biomic-

rudite.

• Consider diagenetic alterations in depositional fab-

rics (Pl. 47); Fig. 8.5). The terms proposed by Wright

(1992) are useful, particularly those which character-

ize alterations that have not completely obliterated the

original texture. Try to differentiate between trans-

formed and neoformed fabrics in pedogenic or mete-

oric modified carbonates (Pl. 48).

• Mixed siliciclastic-carbonate rocks require specific

names, e.g. those proposed by Mount (Pl. 49, or by

Folk (1959), who uses adjectives (e.g. clayey, silty,

sandy).

• And read the quotation at the beginning of this chap-

ter again!

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