Classification – A Name for Your Sample - Microfacies of Carbonate Rocks - page 364

8.6 A Name for Your Samples: Some
Practical Advice

the role of the sessile benthic organisms in the forma-
tion of the reef limestone or of the microbialites. Oth-
erwise use the sackname boundstone. Avoid the name
biolithite.
• Integrate into the name the dominant or ecologically
important fossil group, e.g. coral framestone, or more
precisely, branched coral framestone, or, if you have
good taxonomic data, Retiophyllia coral framestone (see
Fig. 8.2).

Which of the two major groups does your sample fit
into? Autochthonous or allochthonous limestone?

Autochthonous limestones: Use the classification pro-
posed by Embry and Klovan (Fig. 8.1A and Fig. 8.5;
Pl. 41 and Pl. 42), if you are sure that you can imagine

Plate 48 Modified Textural Dunham Classification for NonMarine and Palustrine Carbonates

Many non-marine carbonates exhibit specific grains, fabrics and microfacies that are difficult to characterize by
standard classifications developed for marine limestones. The Dunham classification, reflecting hydrodynamic
and biological controls of textures, can be successfully applied to some lacustrine carbonates, e.g. to those
deposited in profundal and infralittoral environments. However, carbonates formed at lake margins as well as
terrestrial carbonates (caliche, tufa, travertines, speleothems) are strongly prone to pedogenesis, meteoric di-
agenesis, and inorganic and microbial carbonate precipitation. Changes in dissolution and reprecipitation by
pCO 2 play an important part. In studying lacustrine carbonates, Arp (1995) developed a modification of the
Dunham classification that indicates pedogenic and early meteoric alterations by adding an interpretative at-
tribute to the descriptive Dunham term. Attributes are transformed, neoformed or derived .
The classification facilitates the description of 'palustrine carbonates' (shallow fresh-water and marsh depos-
its showing evidence of pedogenic modification related to subaqueous deposition and subaerial exposure). The
term is taken from the French word for swampy or marshy. Diagnostic criteria of palustrine carbonates are an
association of shallow-water, bioturbated mudstones and wackestones with a low-salinity biota of ostracods,
gastropods and charophytes, intraclastic grainstones and packstones, and brecciated limestones displaying mot-
tling, root tubules and vertically elongate fenestrae (pseudo-mikrokarst: Freytet and Plaziat 1982). Palustrine
carbonates, originally described from the Late Cretaceous and Early Tertiary (Freytet 1984) have been reported
from a variety of stratigraphic horizons (Carboniferous to Tertiary). The Florida Everglades are taken as a mod-
ern model of the development of palustrine conditions (Platt and Wright 1992).
Examples on this plate are from the Upper Miocene lacustrine carbonates of the Nördlingen Ries impact
crater (southern Germany).

1 Pedogenically transformed skeletal stromatolite (SS). A brownish pedogenic calcite crust (CC) fills up depressions. The
vesicular fabric (VF) is caused by subaerial exposure within the supralittoral. Erect cyanobacteria filaments (F). Ehingen.
2 Pedogenically neoformed 'ooid' pack/floatstone. The pedogenic ooids (OO) were formed in situ around ostracods (O)
and detrital grains. Cladophorites -clast (C) derived from adjacent algal bioherms. The formation of soils in swamps
caused pedogenic circumcrustations around former lacustrine grains. Hainsfarth.
3 Pedogenically neoformed nodule wacke/packstone (top and bottom) with horizontal 'craze planes' (CP) distinctive for
palustrine facies (cracks caused by desiccation, center). The inverse gradation was formed in-situ by alternation of disso-
lution and desiccation. V: Multiple, fibrous and microcrystalline pendant cements and internal sediment in voids. Origin:
Alternating swamp pedogenesis and prolonged meteoric-vadose conditions. Palustrine facies. Ehingen.
4 Pedogenically derived intraclast grainstone. Brownish pedogenic particles with schlieren-like cortices (arrows). Rework-
ing of pedogenically transformed lacustrine grains and redeposition within the wave-exposed eulittoral. Ehingen.
5 Meteorically transformed intraclast rudstone consisting of reworked algal laminites (AL). Meteoric dissolution is indi-
cated by the reduction of particles to flake-like components (black arrow) and partial replacement of micrite by sparite
(white arrows). Note fracturing of meteoric-phreatic cements (FC). CH: Encrusted chiropteran larva. Interpretation: Depo-
sition of coarse carbonate sands within wave-exposed eulittoral followed by meteoric-vadose dissolution during emersions.
Ehingen.
6 Meteorically transformed intraclast wackestone. The vesicular structure (VS) is caused by meteoric dissolution. Root
cavities (RC) have been enlarged by dissolution and filled with drusy calcite. Supralittoral. Ehingen-Belzheim.
7 Meteorically neoformed cement-framestone. The framework consists of laminated, fibrous sinter cements (SC). The
nucleation bases are preserved as a few remnants of microbial micrite (MM). Dendroid sinters (DS) are speleothems.
Interpretation: Alternation of the primary thrombolite fabric by meteoric diagenesis and formation of a new fabric. Cen-
tral part of a spring mound. Ehingen-Belzheim.
-> 1-7: Arp 1995