Page 37 - Carbonate Facies in Geologic History

24 The Stratigraphy of Carbonate Deposits

cumbersome, they are purely descriptive and may be accurately employed until
geologists are sufficiently informed in specific cases to be able to replace them
with the parallel descriptive, but partly genetic, terms. As Heckel pointed out,
most major buildups are composites, combining several of the four basic compo-
sitional types.

The Basic Facies Pattern

Chapter I has pointed out that the favored realm of carbonate sedimentation is in
warm shallow water on or bordering shelves in tectonically stable areas. In such
areas sedimentation is mostly autochthonous, the locally produced organic car-
bonate being mainly accumulated close to its site of origin (Shaw, 1964; Ander-
son, 1971, 1974). On a very gently sloping shelf there is a tendency for a seaward,
low energy zone to develop below wave base and a zone of higher wave energy to
be situated somewhat shoreward where waves drag the bottom and where maxi-
mum organic productivity occurs. A third, interior or shoreward low-energy zone
also develops. These three zones may reach a considerable thickness, commonly
forming a prograding or up-building sequence after a period of marine transgres-
sion. Thus they normally form a carbonate ramp or platform. Detailed discussion
of this process follows later in this Chapter.
The hydrologic, climatic, and organic controls exerted on the in situ produc-
tion oflime sediment elaborate this simple trio of environmental belts (basin, shelf
margin, and "backreef') into about nine sub-environments. These are expressed
by a surprisingly regular facies sequence which exists in various tectonic settings
(see below). Its outer belts encircle basins, exist at the edges of major carbonate
banks and form halos around mildly positive areas. It is significant that this
pattern is so persistent: it offers essentially a single model for prediction of geo-
graphic distribution of rock types. It thus becomes a tool for use in practical field
mapping, in designation of rock units for correlation purposes, for depositional
interpretations and in the search for petroleum and for metallic ores such as lead,
zinc, and silver, whose distribution may be facies-controlled. The basic model is
now well known and has been discussed in the several major papers and books
cited below.
The first men to point out the similarity between the Bahama Banks sediments
and facies in the ancient limestones were Maurice Black (1930) and R.M.Field
(1930). About two decades later Thomas Grimsdale, of the Royal Dutch Shell
group, recognized the general application of the pattern in the geologic record.
The Bahama Bank studies of N.D.Newell and students and the publication in
1953 of the book The Permian Reef Complex by Newell et aI., did much to bring
recognition of the usefulness of the pattern. Shortly thereafter, experienced geolo-
gists began to apply the model to Mississippian beds in the Williston basin (Edie,
1958; Shaw, 1964; Irwin, 1965).
Study during the past 20 years has amplified the original three belts very
considerably. (Dooge, 1966; Coogan, 1972; Tyrell and other writers in S.E.P.M.
Spec. Pub. 14, 1969; Wilson, 1970; Armstrong 1974). A brief summary of the
model is presented by Horowitz and Potter (1971).