Page 22 - Carbonate Facies in Geologic History

The Local Origin of Carbonate Particles - Textural Interpretation and Classification 9

Throughout the book, the convenient term bioclast is employed to designate a
fragmental particle derived from breakdown of any sort of calcareous shell, test or
skeleton, regardless of whether the breakdown was mechanical or caused by
organic agents. The term has been restricted by some authors to skeletal debris
resulting only from the latter process. (It was originally defined this way by
Grabau, 1920.) Studies of Holocene carbonate sediments show that much break-
down of organic hard parts is caused by various organisms, but the use of the term
only for this process is considered too interpretative. The term biogenic or bio-
genous is of wider application and is used to refer to biological particles formed in
any fashion, not merely organic debris, but also fecal pellets, peloids caused by
algal rotting ofbioclasts, and grapes tones agglutinated by organisms.
In contrast to bioclasts, ooids and pelletoids are created within preferred size
ranges which probably reflect competence of average currents and waves in very
shallow water (1-10 m); most such particles range from about 0.5 to 1.5 mm in
diameter.

ALLOCHEMICAL ORTHOCHEMICAL
ROCKS ROCKS
I n m
Sparry calcite Microcrystalline Microcrystalline calcite-
cement calcite matrix lacking allochems

Int'adasts •

c Intrasparite Intramicrite Micrite
o
11\
o
a. OOI;toS.
E
o
u
Oosparite Oomicrite Dismicrite
E
CIJ
.c
u FOSS;IS. II
o
< AUTOCHTHONOUS
REEF ROCKS
Biosparite Biomicrite IV
~t~};iii ~
..... . . ,
pellotS. ···•·.•··· .. i
Pelsparite Pelmicrite Biolithite

~ Sparry calcite
I"::".:J Microcrystalline calcite

Fig. 1-3. Graphic classification table oflimestones from Folk (1959, FigA), with permission of
American Association of Petroleum Geologists