Geology Reference
In-Depth Information
Basics: Bryozoans
Boardman, R.S., Cheetham, A.H. (1987): Phylum Bryozoa.
- In: Boardman, R.S., Cheetham, A.H., Rowell, A.J. (eds.):
Fossil invertebrates. - 497-549, Palo Alto (Blackwell)
Bone, Y., James, N. (1993): Bryozoans as carbonate sedi-
ment producers on the cool-water Lacepede shelf, south-
ern Australia. - Sedimentary Geology,
86
, 247-271
Brood, K. (1978): Bryozoa. - In: Haq, B.U., Boersma, A.
(eds.): Introduction to marine micropaleontology. - 189-
201, New York (Elsevier)
Conti, S., Serpagli, E. (1988): Bimineralic (calcareous and
phosphatic) skeleton in Late Ordovician bryozoa from
Sardinia: geological implications. - Bolletino della Societa
Paleontologica Italiana,
27
, 129-162
Cuffey, R.J. (1972): The role of bryozoans in modern coral
reefs. - Geologische Rundschau,
61
, 542-550
Gordon, D.P., Smith, A.M., Grant-Mackie, J.A. (eds., 1996):
Bryozoans in space and time. - 442 pp., Wellington (Na-
tional Institute of Water and Atmospheric Research)
Hageman, S.J., Bock, P.E., Bone, Y., McGowran, B. (1998):
Bryozoan growth habits: classification and analysis. - Jour-
nal of Paleontology
, 72
, 418-436
Hageman, S.J., James, N.P., Bone, Y. (2000): Cool-water car-
bonate production from epizoic bryozoans on ephemeral
substrates. - Palaios,
15
, 33-48
McKinney, F.K., Jaklin, A. (2001): Sediment accumulation
in a shallow-water meadow carpeted by a small erect
bryozoa. - Sedimentary Geology,
145
, 397-410
Robison, R.A. (ed., 1983): Bryozoa (revised): introduction,
order Cystoporata, order Cryptoporata. - Treatise on In-
vertebrate Paleontology, 644 pp., Lawrence (Geological
Society of America and University of Kansas)
Scholz, J. (2000): Eine Feldtheorie der Bryozoen, Mikroben-
matten und Sedimentoberflächen. - Abhandlungen der
Senckenbergischen naturforschenden Gesellschaft,
552
,
1-193
Smith, A.M. (1995): Paleoenvironmental interpretation us-
ing bryozoans: a review. - In: Bosence, D.W., Allison,
P.E. (eds.): Marine paleoenvironmental analysis from fos-
sils. - Geological Society of London, Special Publication,
83
, 231-243
Stach, L.W. (1936): Correlation of zooarial form with habi-
tat. - Journal of Geology,
44
, 60-65
Taylor, P.D. (1998): Bryozoan carbonates through time and
space. - Geology,
26
, 459-462
Further reading:
K122
10.2.4 Shells
The fourth part of the discussion of thin-section fossils
deals with shell-bearing organisms characterized by bi-
valved or univalved shells (brachiopods, mollusks, ser-
pulids, ostracods) or by multi-element/multi-plate shells
(trilobites, crustaceans, echinoderms). Most of these
fossils are too large to be included in a standard micro-
facies thin section that will most commonly only ex-
hibit parts or fragments of the skeletons. An identifica-
tion of these bioclasts as to higher systematic levels is
possible when original shell microstructures are still
preserved or unique diagnostic criteria are visible. The
Box 10.7.
Some microstructure types occurring in shells of brachiopods, mollusks, serpulids and ostracods. Definitions
based on Majewske (1969) and Carter (1980).
Complex crossed-lamellar:
Characterized by a disorderly
arrangement of the elements of the crossed-lamellar mi-
crostructure. Found in bivalves and gastropods.
Crossed:
Consisting of elongate structural subunits orga-
nized into adjacent, interdigitating aggregations referred
to as first-order lamellae. Includes crossed-lamellar and
complex crossed-lamellar microstructures. Common in
bivalves and gastropods.
Crossed-lamellar:
Consisting of numerous branching and
wedging lamellae oriented perpendicular or slightly in-
clined to the plane of the shell layer. Each lamella con-
sists of small crystals inclined at a constant angle and
inclined in opposite directions in adjacent lamellae. Most
perfectly developed in aragonitic shells but also occur-
ring in calcitic shells. May constitute all microstruc-
tural layers in mollusk shells or may alternate with other
microstructures. Common in gastropods and bivalves.
Foliated:
Composed of numerous very thin calcite lamel-
lae which may be uniformly oriented over long distances
or randomly oriented over short distances. Common in
brachiopods, some bivalves and gastropods, and some
serpulids.
Homogeneous:
Characterized by orderly arrangement of
uniformly small crystals. Appears bright in transmitted
light and will progressively extinguish under crossed
nicols if the stage is rotated. Common in ostracods and
aragonitic mollusk shells.
Laminar:
Characterized by sheets of strongly flattened
structural units developed uniformly parallel or oblique
to the surface. Includes aragonitic nacreous microstruc-
tures and calcitic foliated microstructures. Brachiopods,
bivalves, gastropods.
Nacreous:
Refers to an orderly arrangement of numerous
thin aragonitic laminae, each separated by thin films of
organic material and uniform orientation ('mother-of-
pearl'). Common in bivalves, gastropods and cephalopods.
Prismatic:
Consisting of closely packed, generally paral-
lel prisms of calcite or aragonite, generally oriented with
their length perpendicular or slightly inclined to the plane
of shell layers. Prism columns are mostly longer than
wide. Common in bivalves.
Spherulitic:
Consisting of densely packed spherical to sub-
spherical aggregates of elongate structural subunits
which radiate in all directions from a central nucleation
site. Rare in aragonitic bivalve shells.
