Geology Reference
In-Depth Information
and their classification. - Vols. 1 and 2, 970 pp., 847 Pls.,
New York (Van Nostrand Reinhold)
Murray, J.W. (1991): Ecology and paleontology of benthic
foraminifera. - 397 pp., London (Longman)
Neumann, M. (1967): Manuel de micropaléontologie des
foraminifères (systématique-stratigraphie). - 297 pp., Paris
(Gauthier-Villars)
Further reading: K111. Relevant papers dealing with fora-
minifera studied in thin sections of Devonian to Tertiary lime-
stones are listed in Box 10.4.
sociated with reworking and redeposition (see Pl. 74/
6, Pl. 118/2). Differences between the infill of worn
foraminiferal sediment and the embedding matrix as
well as rotated geopetals are criteria in assessing trans-
port processes.
Processes leading to the formation of Early Tertiary
grain-, pack- and wackestones with nummulitid fora-
minifera can be derived from the abundance and pro-
portions of large and small tests, their orientation and
the amount of carbonate mud occurring together with
the foraminifera. Large and small tests reflect sexual
and asexual reproduction phases of the life cycle of the
foraminifera.
Assuming that within natural populations small fora-
minifera (A-form, with large initial chambers, megalo-
spheric stage) dominate over large tests (B-form, with
small initial chamber, microspheric phase), four assem-
blages can be differentiated that describe the autoch-
thony or redeposition of the foraminiferal tests:
10.2.2.2 Radiolaria
Radiolarians are single-celled marine planktonic pro-
tozoans that secrete an amorphous (opaline) silica skel-
eton composed of a number of architectural elements
(radial spicules, internal bars, external spines) that are
joined together to form very regular and symmetrical
lattices. The shell has a size of usually less than 2 mm
and commonly between 100 and 250 m across. The
unicellular body is divided by a membrane into an in-
ternal (intracapsular) part (central capsule containing
the endoplasm and the nucleus) and the surrounding
external (extracapsular) part containing the peripheral
cytoplasma. Radiolarians may be solitary or colonial.
1
Relatively undisturbed assemblages: A/B ratio of the
same species 10:1 or more; matrix-support common,
wacke- and mudstones; back-bank environment,
2
Parautochthonous assemblages: A/B average 7:1,
poor sorting, packstones; most fines are removed by
in-situ winnowing caused by wave action; abundant
in bank facies,
Morphology and classification: The shell morphol-
ogy is highly variable but typically corresponds to a
hollow sphere or vase containing one or more bars
across the interior. Some forms consist only of simple
tetraradiate or multiradiate branching needles.
Radiolaria are a subclass of the class Actinopoda that
belong to the subphylum Sarcodina and the phylum Pro-
tista. Modern radiolarians are classified using features
of both the skeleton and the soft parts. Separate classi-
fications have been established for Paleozoic, Meso-
zoic and Cenozoic radiolarians. Recent radiolarians
comprise two major groups: (1) the polycystines, with
solid skeletal elements of opaline silica, and (2) the
phaeodarians with hollow siliceous skeletal elements
connected by organic material, which are rapidly dis-
solved in seawater, and consequently rarely preserved
in the sediments.
The polycystines are subdivided into (1) the basi-
cally spherical-shaped Spumellaria, and (2) the basi-
cally conical-shaped Nassellaria (Fig. 10.29). Some ma-
jor groups of extinct radiolarians differ substantially
from Spumellaria and Nassellaria and are therefore con-
sidered as separate taxonomic units. Spumellarians are
characterized by a pronounced radial symmetry and
single or multiple concentric shells connected by ra-
dial bars. The skeletons have various shapes ranging
from spherical to ellipsoidal to discoidal. Nassellarian
3
Residual assemblages: Layers enriched with B-forms
but A-forms still commonly present; dominance of
imbricated B-forms suggests selective removal of
smaller A-forms and enriching of B-forms, creating
a residual lag,
4
Allochthonous assemblages: Composed of almost
only A-forms, indicating sorting and selective trans-
port.
Basics: Foraminifera
Benthos '86, 3ème Symposium International sur les Foram-
inifères Benthiques (1988). - Revue de Paléobiologie,
Volume spécial, 2 , two volumes, 1005 pp., Genève.
Bolli, H.M., Saunders, J.B., Perch-Nielsen, K. (1985): Plank-
ton stratigraphy. - 1032 pp., Cambridge (University Press)
Haq, B.U., Boersma, A. (1998): Introduction to marine mi-
cropaleontology. 2nd edition. - 376 pp., Amsterdam
(Elsevier)
Hemleben, C., Spindler, M., Anderson, O.R. (1989): Modern
planktonic foraminifera. - 363 pp., New York (Springer)
Jones, R.W. (1995): Micropaleontology in petroleum explo-
ration. - 432 pp, New York (Clarendon Press)
Lee, J.L., Anderson, O.R. (eds., 1991): Biology of foramin-
ifera, 368 pp., Harcourt (Acad. Press)
Loeblich, A.R.Jr., Tappan, H. (1964): Protista 2. Sarcodina
chiefly 'Thecamoebians' and Foraminiferida. - Treatise
on Invertebrate Paleontology, C. - 2 volumes, 900 pp.,
Lawrence (Geological Society of America)
Loeblich, A.R.Jr., Tappan, H. (1988): Foraminiferal genera
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