Geology Reference
In-Depth Information
Fig. 10.59.
Archaeolithoporella
crusts associated with sphinctozoan coralline sponges. The crusts consist of couplets of dark
and light irregular and sometimes disturbed layers without distinct microstructures. Note the difference in the preservation
of the originally aragonitic sponges and
Archaeolithoporella
. Both organisms contributed greatly to the formation of exten-
sive Permian reef structures. Middle Permian (Wordian): Oman. Scale is 1 cm.
Globochaete
is similar to
Gemeridella
Borza and Misik,
but the latter genus displays a petaloid arrangement of
the radial calcitic elements.
Distribution:
The genus is reported from Silurian
to Early Tertiary limestones.
Globochaete
is abundant in open-marine pelagic car-
bonates (e.g. in Late Jurassic deep-water carbonates,
often associated with
Saccocoma
), but also occurs in
shallow-marine environments (Schäfer and Senowbari-
Daryan 1980; Bachmann 1987).
Interpretation:
Originally interpreted as calcified
zoospores of chlorophycean alga
Globochaete
is now
regarded as a planktonic single-celled green alga
(Skompski 1982).
Distribution:
The microproblematicum is abundant
in Late Carboniferous and Permian reef and platform
carbonates.
Interpretation:
Commonly interpreted as calcified
cyanobacterial tube or attributed to green algae.
Lithocodium
Elliott 1956 (Pl. 99/5)
Morphology:
The encrusted partly coiled test ex-
hibits microgranular (calcitic, partly agglutinating) im-
perforate walls that appear dark in transmitted and
brownish in reflected light. The wall has filament-like
alveoli (originally probably containing endosymbionts),
and is covered by a thin epidermal layer. Chambers
show 'bubble-like' structures, originally interpreted as
algal sporangia but now representing cryptic boring
foraminifera.
Distribution:
Anisian to Late Cretaceous.
Often oc-
curring together with
Baccanella irregularis.
The ge-
nus is common in reef limestones.
Lithocodium/Baci-
nella
associations contribute to the formation of mud
mounds through baffling, binding, frame building and
automicrite production (Alsharhan 1987; Neuweiler and
Reitner 1992; Schmid 1996).
Interpretation:
Originally regarded as an encrust-
ing codiacean green alga, the genus is now considered
to be a loftusian foraminifera, probably containing pho-
toautotrophic endosymbiotic algae and boring foramin-
ifera (
Troglotella incrustans
Wernli and Fookes) within
the chambers (Schmid and Leinfelder 1995).
Halysis
Hoeg 1932 (Pl. 98/2)
Morphology:
The genus is characterized by a fan-
shaped structure forming palisades and chains in cross
sections.
Distribution:
Common in Ordovician boundstones
(Munnecke et al. 2001) but also known from Silurian
to Middle Devonian reefs and lagoonal limestones.
Interpretation:
Originally regarded as enigmatic
alga, but now assigned to cyanobacteria.
Koivaella
Chuvashov 1974 (Pl. 98/3)
Morphology:
The genus is characterized by small,
sometimes irregularly shaped tubes with micritic walls
and indications of bifurcations.
