Page 211 - Carbonate Facies in Geologic History

198 Pennsylvanian-Lower Permian Shelf Margin Facies

~ Dosyclod. algae (2) Tubular ·forom.·
8 Rounded cooled porlicles [Q] fusulinid ' foroms '
~ Breccia or congl. clasts ~ Smoll'foroms'
c::J Pellets o Shelly b iodosts
!II Algol plate. ~ Stromololites, Sponge.
[3(J Brecciated fabric
Fig. VI-2S. Idealized Late Paleozoic buildup showing distribution of seven commonly asso-
ciated microfacies: 1. Basal bioclastic micrite pile; 2. Algal plate micrite core; 3. Crestal
boundstone of foraminifera or encrusting algae, Tubiphytes; 4. Organic veneer; S. Flank beds
of tubular foraminiferal debris; 6. Marine talus breccia (rare); 7. Capping bed of shoal grain-
stone with dasycladaceans and gastropod shells. See also Figs.XII-4 and XII-S

Conclusions

Late Paleozoic carbonate buildups display a relationship of facies to growth
history and to a limited extent their tectonic settings. Useful analogies may be
made with some Holocene carbonate mud accumulations. The genesis and partic-
ular characteristics of porosity and permeability in these Late Paleozoic facies
render them particularly important oil reservoirs.

Growth History

Seven stratigraphically significant microfacies in the buildups result when their
normal development is uninterrupted. These are generalized for all shelf buildups
in Chapter XII.
1. The initial accumulation in many places was a basal bioclastic micrite pile
of debris.
2. The algal plate micritic core facies forms as a moundlike accumulation
(baffiestone of Klovan) formed below wave base in quiet water as much as 25 m
deep where the plants trapped lime mud (as determined by the average maximum
height of individual cores).
3. Some mounds of platy algae grew into active wave base where they ac-
quired a crestal boundstone facies of encrusting tubular foraminifera and/or Tubi-
phytes.
4. Mounds in lagoonal or other geographically protected areas developed
only a veneer facies of certain sponges, stromatoporoids and stromatolitic algae
(Parks, 1962).