Geology Reference
In-Depth Information
fossils from calcification of coccoid blue-green algae. - J.
Sed. Petrol.,
54
, 948-971
Riding, R. (1991): Calcified cyanobacteria. - In: Riding, R.
(ed.): Calcareous algae and stromatolites. - 55-87, Berlin
(Springer)
Further reading:
K033, K129-K136
and their appearance in the Late Precambrian has been
explained by a decrease in the Mg
2+
/Ca
2+
ratio near the
Precambrian-Cambrian boundary (Riding 1982), ex-
treme calcium carbonate oversaturation of Precambrian
ocean waters (Knoll et al. 1993), and biological evolu-
tionary controls (Defarge et al. 1994). Calcified fila-
mentous cyanobacteria are common in marine sedi-
ments from the Early Cambrian to the Late Cretaceous.
Calcimicrobes flourished in Cambrian and Ordovician
reefs and open-marine shelf carbonates; they were less
common in Silurian to Permian carbonates, prominent
again in lagoonal and reef environments during Middle
Triassic to Mid-Cretaceous time, but scarce in the Late
Cretaceous. In reefs calcimicrobes acted as frame-build-
ers (e.g. Cambrian and Devonian
Renalcis
; Pl. 82/4. 5)
as well as crypts within cavities (e.g.
Frutexites;
Fig.
10.5). Porostromate calcimicrobes are common con-
stituents of Early Carboniferous ramp deposits (Pl. 53/
5) and Mesozoic inner platform and lagoonal carbon-
ates (Pl. 53/1-4). Depth distribution was not necessar-
ily limited to very shallow environments, as shown by
the occurrence of calcimicrobes in Devonian deeper
forereef positions.
Starting with the Tertiary, the group became prima-
rily limited to nonmarine and transitional environments
(Monty 1973; Pentecost and Riding 1986; Riding 1992).
Records of calcified cyanobacteria from Early Ceno-
zoic and modern shallow-marine carbonate environ-
ments are rare, probably due to the major change in the
preferred biotopes of blue-greens during the Mesozoic.
Starting with the Late Jurassic and Early Cretaceous,
calcified cyanobacteria adapted to marginal-marine and
freshwater conditions, where they become conspicu-
ous carbonate producers in lacustrine and terrestrial en-
vironments.
10.2.1.2 Corallinacean and Peyssoneliacean
Red Algae
Sections 10.2.1.2 to 10.2.1.4 deal with
red algae.
Cal-
cified red algae are common fossils in thin sections of
Phanerozoic limestones (Fig. 10.6). They comprise
some well-defined systematic units (Corallinaceae,
Peyssoneliaceae, Solenoporaceae), Paleozoic fossils in-
terpreted as 'ancestral corallines' (Archaeolithophyl-
laceae), and microfossils attributed to red algae but of
unknown systematic position (Ungdarellaceae, Stach-
einaceae and other Paleozoic groups).
Coralline algae
Definition and calcification:
Corallinacean algae
(also known as coralline algae) are a distinct, exclu-
sively marine group within the Rhodophyta. They rep-
resent the most heavily calcified red algae. Calcifica-
tion occurs intracellularly by High-Mg calcite with
varying amounts of MgCO
3
(up to > 30 vol%). The
stabilization of the High-Mg calcite connected with a
magnesium loss is interpreted as a congruent dissolu-
tion of High-Mg calcite and precipitation of Low-Mg
calcite with a definite textural change (Oti and Müller
1985).
Classification:
Traditionally coralline algae have
been divided according to growth morphology into two
major groups - the non-geniculate (non-articulated)
crustose corallines and the geniculate (articulated) cor-
allines (Fig. 10.7).
Non-geniculate encrusting coral-
lines
comprise crusts, a few microns to several centi-
meter thick, on rocks, coral skeletons, shells, other al-
gae or sea grass. Encrusting corallines vary in size from
thin crusts to massive, nodular or lamellate thalli sev-
eral tens of centimeters in diameter. Some non-genicu-
late corallines are free-living and occur as rhodoids.
Geniculate corallines
are erect branching, tree-like
plants attached to the substrate by crustose or calci-
fied, root-like holdfasts. The plants are flexible owing
to non-calcified sections (genicula) separating longer
calcified segments. Individual segments vary in shape
from cylindrical to flattened. The segments consist of
a central part (medulla) extending upwards to the next
Basics: Calcified cyanobacteria
Dragastan, O., Golubic, S., Richter, D.K. (1996):
Rivularia
haematites:
a case of recent versus fossil morphology.
Taxonomical considerations. - Revista Española de Micro-
paleontologia,
28
, 43-73
Dragastan, O., Richter, D.K., Gielisch, H., Kube, B. (1998):
Environmental siginificance of some Mesozoic 'Poro-
stromata' calcareous algae. - Revista Española de Micro-
paleontologia,
30
, 59-101
Elicki, O. (1999): Palaeoecological significance of calci-
microbial communities during ramp evolution: an exam-
ple from the Lower Cambrian of Germany. - Facies,
41
,
27-40
Fournie, D. (1967): Les Porostromata du Paléozoique. Étude
bibliographique. - Bull. Centre Rech. Pau-SNPA,
1
, 21-45
Merz-Preiss, M. (2000): Calcification in Cyanobacteria. - In:
Riding, R., Awramik, S.M. (eds.): Microbial sediments. -
50-56, Berlin (Springer)
Pia, J. (1927): Thallophyta. - In: Hirmer, M. (ed.): Handbuch
der Paläobotanik. -
1
, 31-136, München (Oldenbourg)
Pratt, B.R. (1984):
Epiphyton
and
Renalcis
- diagenetic micro-
