Geology Reference
In-Depth Information
ostracods, serpulids, ostreid pelecypods), but have also
been reported from marine strata. Marine occurrences
were explained by (a) transport of charophytes from
coastal areas to the sea, (b) reworking of nonmarine
beds with charophytes in connection with transgres-
sions, or (c) adaption of some taxa to normal-marine
conditions (e.g. some Devonian genera: Racki and
Racki 1989).
Common microfacies types associated with charo-
phyte-bearing carbonates are ostracod wackestones and
mudstones, lime mudstones with cyanobacteria and
shell fragments, wackestones and grainstones with
charophytes and a mixture of ooids, lithoclasts and skel-
etal grains, and carbonate breccia.
coryne
). Isolated cysts and aggregates of cysts can be
common in limestones. Modern dasyclad cysts are rep-
resented by calcareous, thin-walled spherical hollow
bodies (Marszalek 1975; Berger and Kaever 1992).
Morphologically comparable spheres and aggregates
of spheres and egg-shaped bodies, ranging in size be-
tween 100 and 500
m, are known from Permian, Me-
sozoic and Paleogene carbonates (e.g. Flügel 1966;
Elliott 1986; Pl. 60/7).
Devonian and Carboniferous calcispheres
Hollow spheres with simple or differentiated cal-
citic walls are common constituents of Middle and Late
Devonian restricted lagoonal and back-reef carbonates
as well as early Carboniferous ramps. Sizes between
100 and 500
m. The spheres have been taxonomically
differentiated according to wall structure, ornamenta-
tion and size variation (Pl. 66/1-3).
The
fossils have been regarded as dasyclad algae
(Marszalek 1975) or as planktonic green algae (Volvo-
cales: Kazmierczak 1975), but also as single-chambered
foraminifera. The spheres are commonly associated
with peloids, amphiporid stromatoporoids (Devonian)
or smaller foraminifera (Carboniferous). Paleozoic cal-
cispheres can be used as indicators of paleosalinity.
Basics: Charophyta
Feist, M., Grambard-Fessard, M. (1991): The genus concept
in Charophyta: evidence from Paleozoic to recent. - In:
Riding, R. (ed.): Calcareous algae and stromatolites. - 189-
203, Berlin (Springer)
Mojon, P.O., Strasser, A. (1987): Microfacies, sédimentologie
et micropaléontologie du Purbeckienne de Bienne (Jura
suisse occidental). - Eclogae geol. Helvetiae,
80
, 37-58
Racki, G., Racki, M. (1989): Ecology of the Devonian charo-
phyte algae from the Holy Cross Mts. - Acta Geologica
Polonica,
31
, 213-222
Schudack, M. (1987): Charophytenflora and fazielle Ent-
wicklung der Grenzschichten mariner Jura/Wealden in den
nordwestlichen Iberischen Ketten (mit Vergleich zu Astu-
rien und Kantabrien). - Palaeontographica, B,
204
, 1-180
Schudack, M. E. (1993): Die Charophyten in Oberjura und
Unterkreide Westeuropas. Mit einer phylogenetischen Ana-
lyse der Gesamtgruppe. - Berliner Geowissenschaftliche
Abhandlungen, E,
8
, 209 pp.
Further reading:
K129
Mesozoic and Cenozoic 'calcispheres': Calcified di-
noflagellate algae
Thin sections and SEM studies of Late Jurassic, Cre-
taceous and Tertiary limestones reveal hollow spheri-
cal and ovoid microfossils in rock-building abundance
(Pl. 66/5), often associated with pelagic foraminifera,
calpionellids and radiolarians. The sizes of the spheres
range between about 10 and 100
m, usually about
40
m). The spherical or egg-shaped bodies are char-
acterized by differentiated calcitic walls, with or with-
out openings and pores. Differences in wall microstruc-
ture have been used to distinguish genera (e.g.
Pitho-
nella, Stomiosphaera, Cadosina, Calcisphaerula;
Rehanek and Cecca 1993). SEM studies indicate that
many taxa separated by thin-section criteria represent
diagenetic forms only and that other 'taxa' refer to the
high morphological variation of these fossils.
Many single-layered Mesozoic calcispheres are
cysts of planktonic algae (Calcidinoflagellata: see
Keupp 1981). Calcareous dinoflagellate cysts have ex-
isted probably since the Triassic. Mesozoic calcispheres
exhibit a wide climatic range and were common in tem-
perate regions. They have been found predominantly
in sediments of the deeper shelf to slope and basinal
settings, sometimes in inner shelf environments.
These calcispheres are abundant in association with
other planktonic algae and occur in pelagic upper slope
10.2.1.9 'Calcispheres' and Algal Cysts
Many Paleozoic and Mesozoic shelf limestones yield
small-sized (diameter commonly < 500
m), hollow
spherical microfossils exhibiting calcitic 'walls'. Many
of these fossils, often designated as 'calcispheres', are
interpreted as algal remains, particularly as algal cysts.
True algal spores are very rare in thin sections but red
algal spores have been recorded from Jurassic lime-
stones (Fay and Dirsche 1975).
Paleozoic calcispheres occur in shallow-marine plat-
form and ramp carbonates. Jurassic and Cretaceous
spherical microfossils are predominantly found in pe-
lagic limestones.
Dasyclad cysts
In living, calcifying dasyclads cysts are formed in
reproductive branches or chambers. Some dasyclads
are poorly calcified except around the cysts (e.g.
Hali-
