Geology Reference
In-Depth Information
Plate 83 Paleozoic Coral Groups
The plate displays examples of the two major Paleozoic coral groups and another small group (see Box 10.6 for
definitions).
Rugose corals
(-> 3, 8, 10) are known from the Middle Ordovician to the Late Permian. Rugose corals were
widespread and common by the Silurian and increased in number and diversity in the Devonian. Following a
marked extinction event at the Frasnian-Famennian boundary and at the end of the Devonian, new families with
new morphological features (e.g. complex axial structures, -> 10) arrived in the Early Carboniferous and per-
sisted until the end of the Permian.
Tabulate corals
(-> 1, 4, 7, 9, 11) received their name from horizontal partitions within the corallites, known
as tabulae. The group was common from the Early Ordovician to the Late Permian. Diversification took place at
the end of the Ordovician. Tabulate corals played a significant role in the formation of Silurian and Devonian
reefs. Many tabulate coral taxa disappeared in the Late Devonian. Late Paleozoic tabulates are rare.
Heterocorallia
(-> 2) restricted to the latest Devonian and Early Carboniferous differ from all other corals by
a specific pattern of septa insertion. All these groups apparently had primarily calcitic skeletons.
1
Tabulate corals
. Encrusting colony of
Alveolites
(A)
intergrown with stromatoporoids (S). The colony consists of in-
clined corallites opening obliquely at the surface and appearing rounded polygonal in transverse section. Adjacent coral-
lites are connected by mural pores. Matrix is a peloidal packstone. Reef facies. Late Devonian (Frasnian): Canning
Basin, western Australia.
2
Heterocorals.
The solitary corallites of this small group are characterized by a specific shape and arrangement of the
septa with four axially joined initial septa and later septa forming a Y-shaped pattern. The thin wall consists of microgranular
calcite. Three cross-sections of
Hexaphyllia mirabilis
Duncan. Heterocorals are common fossils of Viséan inner shelf
environments but are also known from the latest Devonian. Matrix is a peloidal micrite with benthic foraminifera (bot-
tom right). Early Carboniferous (Marbella Formation, Late Viséan): Betic Cordillera, southern Spain.
3
Colonial rugose coral.
Cross section of
Argustrea quadrigemina
Crickmay. The walls of adjacent corallites are united,
forming a massive cerioid corallum (coral skeleton). The blister-like elements between the septa are dissepiments corre-
sponding to small convex plates. Middle Devonian (Givetian): Ermberg, Rheinisches Schiefergebirge, Germany.
4
Tabulate corals
. Oblique and longitudinal sections of
Thamnopora
sp., a widely distributed tabulate in Devonian lagoons
or restricted back-reef environments. Note the conspicuously black matrix. This is a common feature of Devonian shelf
carbonates, deposited in protected environments rich in organic matter. Early Devonian (Emsian): Cantabrian Moun-
tains, Spain.
5
Heliolitid coral.
Heteromorph colony of
Pachycanaliculata barrandei
(Penecke). The slender corallites are separated by
a zone (coenosteum) composed of narrow polygonal tubes. Heliolitids have been included within the tabulate corals
because of the existence of tabulae both in broad corallites and narrow tubes, but are now considered to represent a
separate coral group because of the development of distinct equal septa. Middle Devonian (Eifelian): Graz, Austria.
6
Heliolitid coral.
Longitudinal section. Corallites and the smaller tubes of the coenosteum differ in the size and frequency
of the tabulae. Late Devonian (Frasnian): St.Barbe Quarry, Dinant Basin, Belgium.
7
Tabulate coral
. Longitudinal section of
Favosites
styriacus
Penecke. The corallites are subdivided by numerous, evenly
spaced horizontal partitions (tabulae). Adjacent corallites communicate through mural pores (arrows) arranged in rows.
Same locality as -> 5.
8
Colonial rugose coral
. The cross section of
Multimurinus
shows a cerioid growth pattern characterized by corallites that
are touching each other. Note the distinct axial structure (arrow), a common feature of Late Paleozoic Rugosa. Tethyan
Middle and Late Permian bedded shelf sediments often contain intercalated banks consisting of these tens of centimeter-
sized compound corals, which in places can form frame- and bafflestones (Weidlich and H. Flügel 1995). Middle Per-
mian (Wordian): Wadi Aday, southwestern Muscat, Oman.
9
Tabulate corals
. Favositid (F) and thick-walled encrusting auloporid (A) corals. Auloporid corals acted as bafflers, con-
tributing to mound formation. C: Crinoid ossicle, T: Trilobite debris. Late Carboniferous (Kasimovian): Carnic Alps,
Italy.
10
Rugose coral.
The cylindrical corallites of
Siphonodendron
are not in contact and form a fasciculate structure. Note the
peripheral zone formed by dissepiments and the distinct axial structure. The latter is a characteristic feature of Late
Paleozoic rugose corals. Cross section. Early Carboniferous: Western Anatolia, Turkey.
11
Tabulate coral:
Parastriatopora
. The peripheral margins of the coral have been destroyed. This might indicate abrasion
during transport or dissolution within the sediment. Early Devonian (Emsian): Erfoud, Anti-Atlas, Morocco.
