Geology Reference
In-Depth Information
and basinal carbonates as well as in outer shelf carbon-
ates of low and mid latitudinal settings. The fossils can
be used as bathymetric indicators of shelf margin and
slope environments and in the stratigraphic subdivision
of Late Jurassic to mid-Cretaceous Tethyan and sub-
boreal pelagic carbonates (Borza 1969; Bucur 1992).
the class Rhizopoda. Similar to calcareous algae, fora-
minifera are of prime importance in microfacies analy-
ses. Foraminifera provide time markers for biozona-
tions of shallow and deep marine carbonates, are ex-
cellent environmental proxies and permit ancient depo-
sitional systems to be reconstructed. The shells of
benthic foraminifera have been major constituents of
shelf carbonates at least since the Late Paleozoic and
those of planktonic foraminifera formed pelagic lime-
stones from the Late Mesozoic on. Foraminiferal shelf
limestones are important reservoir rocks for hydrocar-
bons.
Most foraminiferal shells typically range from 0.1
to 1 mm in size, but some groups developed rather large
tests. For study purposes a distinction is made between
smaller foraminifera
and larger foraminifera
(larger
than about 0.6 mm). Smaller foraminifera with test sizes
of approximately 100
m to 600
m form the majority
of benthic foraminifera. They are usually identified by
their external characters, but can be also typified in thin
sections. Larger foraminifera are usually large enough
that geologists can spot them in the field. Their tests
have complex internal structures that need to be stud-
ied in thin sections.
The two major groups of foraminifera are benthic,
living in or on sediments on the sea floor, and plank-
tonic, living in the upper 100 m of the oceans.
Basics: Calcispheres and algal cysts
Dasyclad cysts
Elliott, G.F. (1986): Isolated cysts in the Palaeocene-Lower
Eocene of Kurdistan. - Palaeontology,
29
, 739-741
Flügel, E. (1966): Algen aus dem Perm der Karnischen Alpen.
- Carinthia II, Sonderheft,
25
, 3-76
Marszalek, D.S. (1975): Calcisphere ultrastructure and skel-
etal aragonite from the alga
Acetabularia antillana
. - J.
Sed. Petrol.,
45
, 266-271
Paleozoic calcispheres
Flügel, E. and Hötzl, H. (1971): Foraminiferen, Calcisphären
und Kalkalgen aus dem Schwelmer Kalk (Givet) von
Letmathe im Sauerland. - Neues Jahrbuch für Geologie
und Paläontologie, Abhandlungen,
137
, 358-395
Kazmierczak, J. (1975): Colonial Volvocales (Chloro-
phyta) from the Upper Devonian of Poland and their
paleogeographical significance. - Acta Palaeont. Po-
lonica,
29
, 73-85
Mesozoic calcispheres
Borza, K. (1969): Die Mikrofazies und Mikrofossilien des
Oberjuras und der Unterkreide der Klippenzone der West-
karpaten. - 301 pp., Bratislava (Slov. Akad. Znanosti)
Keupp, H. (1981): Die kalkigen Dinoflagellaten-Zysten der
borealen Unter-Kreide (Unter-Hauterivium bis Unter-
Albium). - Facies,
5
, 1-190
Keupp, H. (1991): Fossil calcareous dinoflagellate cysts. -
In: Riding, R. (ed.): Calcareous algae and stromatolites. -
267-286, Berlin (Springer)
Rehanek, J., Cecca, F. (1993): Calcareous dinoflagellate cysts,
biostratigraphy in Upper Kimmeridgian-Lower Tithonian
pelagic limestones of Marches Apennines (Central Italy).
- Revue de Micropaléontologie,
36
, 143-163,
Villain, J.M. (1977): Les Calcisphaerulidae: Architectures,
calcification de la paroi et phylogenèse. - Palaeonto-
graphica, A,
159
, 139-177
Further reading
: K139, K140
Morphology of foraminifera
The living cell is made up of protoplasma. Exten-
sions of the protoplasma (pseudopodia) protrude
through a single foramen or through minute pores in
the test. Pseudopodia assist in locomotion, capturing
of food, and removal of waste products.
The cell is enclosed by a test consisting of a single
chamber or several chambers each connected by one
or several openings. Most foraminifera are multicham-
bered. The chambers are arranged in whorls. They may
be uniserial (forming a single linear series), or multi-
serial (two or more chambers per whorl). If the test
coils in a single plane around the growth axis, it is called
planispiral. In trochospiral tests the chambers are ar-
ranged in a helical coil. A common arrangement in
which five chambers are visible is called quinque-
loculine. Internally the chambers are separated by walls
called septa. An opening (aperture) in the wall of the
final chamber connects external pseudopodia and in-
ternal endoplasm. The external surface of the tests is
smooth or variously ornamented (e.g. spines and keels).
10.2.2 Foraminifera and other Protozoa
The second prominent category of fossils found in thin
sections of carbonate rocks includes small-sized single-
celled protozoan organisms : foraminifera, radiolarians
and the calpionellids (an extinct group of the ciliates).
10.2.2.1 Foraminifera
Foraminifera are small, predominantly marine het-
erotrophic protists that construct chambered shells
(tests). The group belongs to the phylum Sarcodina and
Diagnostic criteria, classification and major groups
Diagnostic criteria of foraminifera are (1) wall com-
position and microstructure, (2) chamber arrangement
