Page 223 - Carbonate Facies in Geologic History

210 Late Paleozoic Terrigenous-Carbonate Shelf Cycles

P 6. Platy algal mud facies. Lime wackestones (also described in Chapter VI), containing 10-
50% platy algae. These leaf-like (phylloid) forms represent both red and codiacean(?)
algae and occur in well-bedded limestones as well as in mound-shaped buildups. The
plates are delicate and crinkled, in many places broken and somewhat abraded, but are
also found whole. They were calcified only along the cortex; the wall structure is rarely
preserved and mainly as micrite fill of the tubules. Other normal marine organisms may
occur with the plates but the latter dominate; apparently their rapid growth discour-
aged many other organisms. The plates seldom occur together in any regular arrange-
ment and one may conclude that they are partly calcified, light-weight pads, loosely
articulated, and, upon death and decay, easily moved, heaped up, and deposited with
fine sediment. The bedded limestones containing -abundant plates are traceable to
massive lens-shaped bodies. Associated with the algal plates, usually in mounds, are
certain encrusting foraminifera such as Tetratax·is, Tuberatina an.d cornuspirids
Plate XXII).
Environment: Quiet, clear, photic zone water as much as a few tens of meters deep but
possibly much shallower; perhaps at times restricted circulation eliminated many inver-
tebrates.
P7. Flanking beds. Bioclastic, lithoclastic packstones and wackestones with organic debris
derived from growth on tops of slopes and mounds and accumulated in wavy, foreset
beds on depositional slopes.
Depositional dips from a few degrees to as much as 30 degrees, about the angle of
reponse for such debris. Much of the bioclastic debris is worn, broken, and coated.
Previously consolidated or agglutinated sediment is intermixed with finer sediment
which infiltered the coarser framework. Geopetals are common. The biota is believed to
be essentially that of the reef or mound tops. Foraminifera are abundant, particularly
cornuspirid tubular forms, along with broken algal plates and much other bioclastic
matter. Certain indigenous, special communities formed meadows or filled pockets on
the flanks, e.g., crinoids or brachiopods. Environment: moderate wave energy-win-
nowed finer lime-mud sediment depositing it downflank where it was organically pellet-
ed, or occurs as micrite matrix in inter bioherm wackestones. N Qrmal marine circulation
and salinity is indicated by the varied biota. In part, standard microfacies type 5. This
constitutes the example chosen for description and interpretation of carbonate microfa-
cies (Chapter III, Plates I, IV A).
P8. Capping beds of mounds and calcarenite shoals. Grainstones, with coated particles,
ooids, peloids, and rounded and worn, rotted bioclasts. Robust, thick-shelled forms,
such as euomphalid snails and dasycladacean particles, are almost the only nicogniz-
able bioclasts. Often the matrix is calcite mosaic, obscuring or obliterating any original
isopachous and probable marine cement. Extreme compaction caused by early dissolu-
tion of grains may occur in some beds. These beds are rare in the Pennsylvanian-
Wolfcampian but significant; they occur at tops of biohermal strata. They are generally
cross-bedded sands, forming well-defined beds only a few feet thick.
Environment: Very shallow, shoal water with perhaps restricted marine fauna, strong
wave and current action. These beds were often subjected to nonmarine diagenesis after
deposition, having been exposed above sea level during or shortly after deposition.
Standard microfacies type 11.
P9. Caninia-Chaetetes beds. Massive micritic and pure limestone beds common in older
Pennsylvanian strata with many corals. The organisms are not necessarily in growth
position nor are they attached to each other to form boundstone. Probably they grew in
soft, calcareous substrate where they were later buried. Both the colonial Chaetetes and
large solitary Caninia are known in argillaceous sediments as well as in carbonates. If
especially associated organisms exist, these are not known. Environment: Represent
coral rich mud banks or shoals of very shallow water in clear open marine conditions
without clay contamination; relatively quiet water. Standard microfacies type 7 and 8
(Bafflestone ).
P.lO. Onkoidal micrite-algal ball beds, "Osagia-Ottonosia". Thin (1 m) beds of lime mud-
stone or wackestone with rounded nodules, a few cm in diameter. These are masses of
crinkly laminated, presumed stromatolitic algae, intergrown with dark plumose en-