Page 69 - Carbonate Facies in Geologic History

Chapter III

Outline of Carbonate Petrography

In the history of carbonate geology, progress in understanding limestone and
dolomite as sediments accelerated tremendously as petrographic data were added
to careful field study. There exist various levels of petrographic observation useful
in depositional interpretation. Some require more sophisticated approaches and
more complex techniques than others; the list below progresses from field map-
ping and section measuring to microscopic and geochemical study in the labora-
tory.
1. General lithology.
2. Stratigraphic relations indicating submarine topography, cyclic sequences, fa-
cies changes.
3. Paleontology including paleoecological observations relating organic associa-
tions and sedimentary features.
4. Sedimentary and organic structures, including trace fossils, bedding, direc-
tional properties.
5. Color variations.
6. Microfacies-texture.
7. Microfacies-particle kind identification, mainly biological but including identi-
fication of non-carbonate, acid-insoluble particles.
8. Diagenetic observations; interpretations including consideration of porosity
and permeability measurements.
9. Mineralogical and geochemical laboratory data as needed.
This Chapter reviews most of the above classes of data in outline form, refer-
ring to more comprehensive papers on the subject and the stratigraphic relations
discussed in other Chapters.

Techniques for Examining Carbonate Rocks

Some of the "tricks of the trade," employed in carbonate petrography are briefly
reviewed below. See also Chilingar et al., (1967), Horowitz and Potter (1971), and
Milliman (1974).

Sawing and Polishing

One reason that petrographic study of carbonates lagged far behind that of
sandstones (excepting Sorby, 1879; Cayeux, 1935; Sander, 1936, trans!' 1951), was
that geologists simply could not see enough of limestone fabrics in the field. The
sawing and polishing of slabs and wafers (plaquettes), as well as thin-section