Geology Reference
In-Depth Information
Plate 60 Late Paleozoic Dasyclad Green Algae
Dasyclad algae contributed significantly to the formation of extended algal carbonates (grain- and wackestones)
and the formation of reef mounds and mud mounds in Carboniferous and Permian shelf environments. The plate
displays some globally distributed algal limestones.
Baffling effects of algae with small erect cylindrical thalli were important in the formation of Carboniferous
mounds (-> 1, 2, 5). Some authors consider these algae as dasyclads (Beresellaceae), from which they differ in
a segmentation of the cylinders by horizontal or vertical elements (-> 2); other authors regard them as a separate
green algal group (Palaeosiphonocladales), known from the Devonian to the Early Permian and abundant in the
Middle Carboniferous. The genera
Dvinella, Donezella
and
Beresella,
common in Bashkirian and Moscovian
carbonates
grew in dense low-lying thickets that baffled stabilized sediment, forming large low-relief mud-rich
mounds or banks in relatively quiet normal marine lagoonal settings, landward of grainstone shoal deposits or of
Chaetetes
buildups (Riding 1979; Davies and Nassichuk 1989). Some of the banks and buildups form hydrocar-
bon reservoirs.
Many Carboniferous and Permian platform and ramp carbonates were formed by the accumulation of dasyclad
algae (-> 6) and their reworked and transported fragments (-> 3, 4, 7).
Fig. 10.17.
Distribution of algae and cyano-
bacteria
on an idealized Carboniferous car-
bonate platform. Stacheinacean and soleno-
poracean algae (Pl. 55 and Pl. 56 ) indicate
the deepest habitats in the photic zone.
Higher up in open-marine settings red al-
gae occur together with tubular palaeo-
siphonoclad algae. Shallow shoals and la-
goonal environments are indicated by abun-
dant dasyclads. Dasyclads associated with
palaeosiphonoclads and cyanobacteria mark
a semi-restricted very shallow environment.
Similar associations occur in restricted near-
coastal environments together with algal
cysts (calcispheres, see Sect. 10.2.1.9).
Modified from Mamet (1991)
.
1
Pseudodonezella
boundstone. Middle Carboniferous Beresellacean green algae were important in the formation of bind-
stones and bafflestones as well as of mounds on open-marine carbonate platforms. The algae are characterized by cylin-
drical ramified and constricted thalli (arrows). Middle Carboniferous: Southern Spain.
2
Beresella
boundstone. Beresellids are characterized by a peripheral zone consisting of short, thin, blind-ending cortical
branches, separated by 'clear bands' (arrow) of a non-perforated cortex and an outer cement layer (-> 5). Mid-shelf facies.
Early Permian (Asselian-Sakmarian): Sverdrup Basin, Canadian Archipelago.
3 Coated dasyclad grainstone with
Eovelebitella
(see Pl. 59/1).
The grains exhibit transitions from cortoids to oncoids.
Open-marine platform. Early Carboniferous (Viséan): Spain.
4
Epimastopora
grainstone. The algae are represented by plate-like fragments exhibiting numerous cylindrical or dumbbell-
shaped branches. Epimastoporids are widely distributed in Late Carboniferous and Early Permian outer shelf environ-
ments. Their assignment to dasyclads is a matter of discussion (Flügel and Flügel-Kahler 1980). Early Permian (Asse-
lian): Carnic Alps, Austria.
5
Beresella herminae
Racz. Note continuous calcite layer (arrow) around the thallus, interpreted as carbonate precipitation
within the surficial mucilage sheat of the alga. Middle Carboniferous (Valdeteja Formation): Cantabrian Mountains,
Northern Spain.
6
Mizzia
wackestone. The thalli consist of spherical or cylindrical segments. The branches enlarge in diameter near the
surface, producing a hexagonal pattern in tangential sections (arrows).
Mizzia
limestones were widespread in Middle and
Late Permian shelf and back-reef environments of the tropical Paleotethys. Late Permian: Taurus Mountains, southern
Turkey.
7 Dasyclad spores.
Atractyliopsis carnica
Flügel represents the fertile stage of a dasyclad alga that produced spores of
various sizes and shapes within spherical sporangial cavities (arrows). Calcified spores occur in rock-building frequency
in Late Paleozoic open-marine shelf carbonates. Early Permian: Carnic Alps, Austria.
-> 2: Morin et al. 1994; 5: Eichmüller 1985
