Geology Reference
In-Depth Information
Most
encrusting corallines
(Pl. 54) are dorsoven-
trally organized. They have a basal-most (dorsal) part
(formerly called the hypothallus) near the substrate,
with cells oriented more or less parallel to the substrate,
responsible for the lateral growth, and an outer (ven-
tral) part (formerly called the perithallus) with com-
monly very small cells, developed above and upon the
hypothallus and oriented perpendicular to it, respon-
sible for the plant's thickness. The basal part may con-
sist of multilayered or unilayered filaments (Fig. 10.7B-
E) The cells of the multilayered basal part are described
with regard to size, shape, arrangement of cells into
single, multilayered and arcuate layers (coaxial; Pl. 54/
8; Fig. 10.7 C) or they are non-coaxial (plumose).
A thin surface layer (epithallus) known from mod-
ern corallines is very rarely preserved in fossil algae.
Additional criteria revealed by SEM and ultrathin sec-
tion studies (e.g. connections between contiguous cells)
Plate 54 Corallinacean Red Algae
Tertiary limestones composed predominantly of red algae are important hydrocarbon reservoir rocks, e.g. in
Libya and Indonesia. Corallinacean algae (or coralline algae) are a red algal group characterized by a strongly
calcified tissue exhibiting a fine net-like structure in thin sections. The group is traditionally subdivided into
encrusting (or crustose) corallines and segmented articulate corallines. The former develop millimeter- to centi-
meter-thick crusts, the latter erect, flexible branches consisting of calcified segments and non-calcified parts.
Corallinacean algae are abundant constituents of Cretaceous and Cenozoic shelf and reef carbonates.
The plate shows Tertiary and Cretaceous encrusting corallines forming rigid skeletons. The algal body (thal-
lus) consists of adjacent calcified filaments. Corallinacean algae are most valuable paleoecological markers.
They are used in assessing paleoclimate, paleolatitudes and paleodepths. But note that the occurrence of coralli-
nacean red algae is not
a priori
indicative of a shallow tropical warm-water environment; coralline algae grow in
temperate and cold-water environments as well. In contrast to calcareous green algae, coralline algae flourish
down to several decades of meters even down to about 250 m.
The study of corallines in thin sections needs high magnifications, otherwise algal fragments appear
nonstructured and may be confused with micrite clasts. Similar confusion may exist for the red alga
Marinella
.
This alga (Pl. 136/3, 5), abundant in Late Jurassic and Cretaceous (Barattolo and DelRe (1985) and known until
the Oligocene, is characterized by millimeter-sized thalli composed of extremely fine threads (about < 5 to
15
m). Corallines appear dark in transmitted light and white in hand specimens and polished sections.
1 Red algal nodule (rhodoid) consisting of
Lithothamnion
, a member of the melobesioid coralline algae. Large spar-filled
structures occurring within the thallus are reproductive organs (conceptacles, C). These structures should not be confused
with borings (B). The genus
is characterized by encrusting growth, a multi-layered internal structure and multiporate
conceptacles (black arrows). Interspaces between algal specimens are filled with sediment (peloids, foraminifera). Angu-
lar algal fragments (white arrows) are caused by vadose dissolution and breakage of the algal limestone. The growth form
of the nodules and peloidal infilling indicate restricted water energy within a reef environment. Late Tertiary (Leithakalk,
Miocene): St. Margarethen, Burgenland, Austria.
2 Bioclastic algal debris facies with broken branches of
Lithophyllum
. Note the different cell size of the hypo- and perithallus.
The genus is an important framebuilding coralline alga in Cenozoic reefs. The sample comes from sediments deposited
adjacent to small patch reefs. Late Tertiary (Leithakalk, Miocene): Oslip near Rust, Burgenland, Austria.
3
Sporolithon
(formerly called
Archaeolithothamnium
). The genus is characterized by a multilayered hypothallus and a
thick perithallial tissue with individual sporangia arranged in rows ('sori'; arrow). Late Tertiary (Miocene): Großhöflein
west of Eisenstadt, Burgenland, Austria.
4
Mesophyllum.
Arrows point to conceptacles with a single-pored roof (-> 6). Tertiary (Miocene): Southwestern Turkey.
5
Corallina:
Articulated coralline alga characterized by erect, jointed thalli consisting of segments. The segments consist of
straight central (medullary, M) equant cells and a cortex (C) composed of tiny cells. Quartz-rich algal rudstone. Note the
detrital subangular quartz grains (white). Transgressive near-shore shelf facies (Reijers and Petters 1997). Mid-Creta-
ceous (Mfamosing Limestone, Middle Albian): Calabar Flank, Niger Delta, Southern Nigeria.
6
Lithophyllum
. Conspicuous single-pored conceptacle (arrow). Temperate near-coastal facies. Tertiary (Oligocene):
Pohlkotte, Lower Saxony, Germany.
7
Sporolithon.
Conceptacles are borne in 'sori' (S; compare Pl. 64/12). Same locality as Fig. 6.
8 Rhodoid composed of crustose branches of
Lithophyllum
. Note differences in cell sizes in the basal part (hypothallus, HT)
and the perithallus (PT). Late Tertiary (Miocene): Turkey.
9 Articulated coralline alga.
Subterranophyllum
. Tertiary (Late Oligocene/Early Miocene): Drowned reef complex in the
Sulu Sea south of Palawan, Philippines.
-> 1, 2: Dullo 1983; 5: Oti and Koch 1990; 6, 7: Flügel 1970; 9: Wiedicke 1987
