Microfacies Data: Matrix and Grains - Microfacies of Carbonate Rocks - page 97

Box 4.4. Microfacies criteria useful for the genetic interpretation of micritic limestones include texture, fabric, and the
preservation and association of fossils. Differences in dominating rock colors are caused by variations in non-carbonate
constituents (e.g. terrigenous input, organic matter, authigenic minerals), pH conditions, and the crystal size of the fine-
grained carbonate matrix. References to settings concern only the more common cases. The numbers refer to the modes
of origin summarized in Fig. 4.1.1.

1 Lime mudstones. Homogeneous very fine-grained ...................................................................................... Pl. 125/1
2 Boundstones, mudstone, wackestones, packstones. Inhomogeneous matrix. Some dark, very fine-grained micrite.
Peloidal, thrombolitic and stromatolitic fabrics. Close association of sponges and in situ microbial structures. Sponge
structures replaced by micropeloidal fabrics. Differentiated microbial fabrics developed at the surface of the sedi-
ment (crusts and vertical pillars, encrusting organisms, bored hardgrounds) or within semi-closed cavities. In situ
peloids and ooids. Gray and dark rock colors within laminae. Common in ramp, deep shelf, mud mound and reef
settings. ........................................................................................................... Pl. 6/5; Pl. 10/1; Pl. 28/1; Pl. 50/1, 2, 4
3 Bindstones, mudstones. Inhomogeneous matrix. Indistinct wavy lamination. Very small peloids exhibiting white
calcite cement rims. Inferred bacterial structures within cavities and voids. Common in ramp, deep shelf and mud
mound settings. Also in non-marine environments. ........................................................ Pl. 8/4-5; Pl. 18/1; Pl. 121/3
4 Bindstones. Very fine-grained matrix (minimicrite). Relicts of cyanobacteria, commonly filaments (Porostromata).
Tidal and shallow subtidal settings. Also in non-marine environments. ........................................... Pl. 7/6; Pl. 124/1
5 Wackestones. Inhomogenous matrix. Abundant fragmented udoteacean calcareous green algae or gymnocodiacean
algae. Shallow-marine subtidal settings, reefs, upper slope. ....................................................................... Pl. 57/3, 6
6 Wackestones containing abundant transported epibionts (foraminifera, serpulids, small mollusks, red algae). Charac-
teristic biotic associations. Spatially restricted lenses consisting of fine-grained carbonates and occurring within
shaly limestones. Tidal and shallow subtidal settings. .................................................................................... Pl. 67/2
7 Fine-bioclastic wackestones and mudstones. Often dark, very fine-grained micrite. Skeletal debris derived from
fragmented and disintegrated shells of invertebrates. Association of debris and large bioclasts and fossils. Dark and
variegated rock colors. Shelf and deeper ramp settings, base-of-slope and basinal settings. Also in non-marine envi-
ronments. ..................................................................................................... Pl. 91/2; Pl. 118/1; Pl. 144/8-9; Pl. 147/4
8 Wackestones, packstones. Abundant micritized grains. Microborings in skeletal and non-skeletal grains. Gray and
dark rock colors. Deep subtidal shelves and ramps. .................................................................................... Pl. 10/3, 5
9 Wackestones, packstones, mudstones. Abundant pelagic microfossils (planktonic foraminifera, calpionellids, 'calci-
spheres') and nannofossils. Light and dark rock-colors. Common in open-marine environments. Deep shelf, slope
and basinal settings. ......................................................... Pl. 29/5; Pl. 73/2, 3, 10; Pl. 76/1, 7, 8; Pl. 77/23; Pl. 99/10
10 Wackestones, packstones. Inhomogeneous calcisiltite matrix. Mixing of silt-sized and larger angular and subrounded
lithoclasts in association with poorly preserved bioclasts and non-carbonate clasts. Various rock colors. Shelf and
ramps as well as slope settings. ..................................................................................................................... Pl. 141/2
11 Common in boundstones. Fine-grained inter- and intragranular calcite cement, dark in transmitted light. Homoge-
neous fabric. Microspar texture. Formed during shallow and deep burial diagenetic environments. Affects marine
and non-marine carbonates (e.g. caliche). ....................................................................................................... Pl. 47/2
12 Patchy recrystallization of micrite to microspar and in places to pseudospar. The recrystallization affects both the
fine-grained matrix and the grains. The crystals of bioclasts (coralline algae, mollusks) may exhibit diminution and
homogenization of size. Formed during shallow and deep burial diagenetic environments. Affects marine and non-
marine carbonates. ....................................................................................................................................... Pl. 38/3, 6

(1969) described a Devonian limestone, using the term
calcisiltite for fine-grained, poorly-sorted carbonates
(grain sizes 5-15 m) which probably resulted from
the breakdown of skeletal material. This fabric origi-
nating from mechanical deposition should not be con-
fused with microspar which describes a diagenetic fab-
ric.
Bioclastic calcisiltites, produced by abrasion and bio-
erosion processes, are common in modern shallow-ma-

rine lime mud environments (Folk and Robles 1964;
Swinchatt 1965; Fütterer 1978). Microbioclastic calci-
siltites, however, also occur in deeper-water ramp, slope
and basinal settings.
Abiogenic or biogenic breakdown of a calcite sub-
strate following the initial diagenesis (microsparit-
ization: Pomar et al. 1975; sparmicritization: Kahle
1977) can produce a 'diagenetic sediment' consisting
of silt-sized crystals. This crystal silt or vadose silt