Page 185 - Carbonate Facies in Geologic History

172 Pennsylvanian-Lower Permian Shelf Margin Facies

growth, encrusting habits, and potential for baffling and stabilizing sediment,
must have been considerable. Several paleontologists in the Soviet Union, as well
as in the U.S.A., are specialists in such organisms. The biological assemblages are
described briefly below and illustrated in the Plates. Their preferred ecologic
distributions can be ascertained from examining the diagrams of several buildups
that have been well studied (Figs. VI-5, 7,9, 10).

Algal Plates or Phylloid Algae (Plate XXII)

Study by Wray (1968) and Konishi and Wray (1961) and other specialists has enabled identifi-
cation of abundant thin potato chip-like, irregularly crinkled plates, as probable codiacean
algae with variously shaped cortical tubules and a type of red alga, Archeolithophyllum.
Articulated growth forms with consistent patterns are unknown. The occasionally preserved
cortical layers and orientation of the crystals of internal calcite mosaic indicates that only the
external parts of the pads were calcified in the recognized codiacean(?) genera ( Anchicodium,
Eugonophyllum, Ivanovia). (See Horowitz and Potter, 1971, for taxonomic summary.) The
plates themselves exist generally in a jumbled, brecciated mass in lime mud matrix and are
never articulated-indeed, they may have grown as separate entities and as upright forms.
They occur in horizontally bedded strata but commonly form micritic mounds and presum-
ably were able to form sediment baflles and to trap lime mud. Since they generally become
more abundant higher in the mounds, the mound itself may not have originated by such
trapping, but once it was established, platy algae thrived on it and encouraged its growth.
Their abundant growth possibly choked out other forms of life and they thus appear as a
climax community. The delicate form of the plates, their common association with lime mud
and the thickness of mounds affords evidence of approximate depth ranges for these algae.
Codiaceans flourish today down to 20 m and may range to 70 m in the tropics. The fact that
individual cores of mounds are about 25 m high at most and that these have in places an
encrusting boundstone cap, indicative of wave base, gives an approximate minimum depth
equal to about the mound height for initiation of platy algal growth. The extensive diagenesis
through brecciation and solution alteration of the codiacean plates causes such rock to be
excellent petroleum reservoir.
The algae may also occur in various states of fragmentation. This is commonly seen in
flanking beds of bioherms or in piles of loose algal plates where mud matrix is essentially
absent. Usually the crinkled form of algal plates is better preserved within bioherms or in
beds with considerable micrite matrix. The Archeolithophyllum genus of red algae appears
also in an encrusting habit and presumably grew as irregularly lamellar sheets on top of lime
mud accumulations. It forms flatter lens-shaped structures in Kansas.
Platy or phylloid algae appear early in the Pennsylvanian, both as codiacean(?) forms and
red algae and seem to flourish progressively through Late Pennsylvania. The Late Pennsyl-
vanian beds seem dominated by the codiacean(?) genera Eugonophyllum-Anchicodium, with
larger, more irregular pads. Earlier Pennsylvanian forms seem small, thinner, and appear to
occur in somewhat straighter segments. The Pennsylvanian codiacean(?) genera still flour-
ished in the Wolfcampian but gradually disappeared and are rare or absent in Middle
Permian strata. Boundstone laminated crusts formed presumably by blue-green stromatolitic
algae, may also be part of the algal plate mound facies, most commonly occurring on the tops
of mounds.

Opthalmidid-Calcitornellid Tubular Foraminifera (Plates IVB, XX, XIII B)

(Synonyms or closely related forms (Toomey, 1972) are Apterinella and Cornuspira.)
The foraminifera occur in two basic growth forms:
1. Small masses of such foraminifera coat bioclastic debris of all sorts both within mound
sediment and in normal marine, bedded limestone.