Geology Reference
In-Depth Information
loid algal sediment is a principal factor in the localiza-
tion of effective porosity and permeable zones.
axis) which bears one or more whorls of lateral branches
(laterals). These primary branches may subdivide dis-
tally forming one to three or more orders of laterals.
Reproductive organs occur on or between branches, or
within the central stem. Aragonite is precipitated around
the stem (or parts of the stem) and between the branches.
As a consequence, fossil dasyclads are represented as
molds in which the area of the stem cell appears as a
spar- or sediment-filled cavity, surrounded by a calci-
fied zone exhibiting the branches as pores. The recog-
nition of the diagnostic criteria is controlled by the ex-
tent of calcification. For major
diagnostic criteria
see
Fig. 10.14.
Basics: Phylloid algae
Cys, J.M. (1985): Lower Permian phylloid algal mounds,
southern Tatum basin, southwestern New Mexico, U.S.A.
- In: Toomey, D.F., Nitecki, M.H. (eds.): Paleoalgology.
Contemporaneous research and applications. - 179-187,
Berlin (Springer)
Kirkland, B.L., Moore, C.H., Jr., Dickson, J.A.D. (1993): Well
preserved, aragonitic phylloid algae (
Eugonophyllum
,
Udoteaceae) from the Pennsylvanian Holder Formation,
Sacramento Mountains, New Mexico. - Palaios,
8
, 111-120
Montgomery, S.L., Chidsey, T.C., Eby, D.J., Lorenz, D.M.,
Culham, W.E. (1999): Pennsylvanian carbonate buildups,
Paradox Basin: increasing reserves in heterogeneous, shal-
low shelf reservoirs. - American Ass. Petrol. Geol., Bull.,
83
, 193-210
Toomey, D.F. (1980): History of a Late Carboniferous phyl-
loid algal bank complex in northeastern New Mexico. -
Lethaia,
13
, 249-267
Toomey, D.F., Winland, H.D. (1973): Rock and biotic facies
associated with a middle Pennsylvanian phylloid algal
buildup, Nena Lucia field, Nolan County, Texas. - Ameri-
can Ass. Petrol. Geol., Bull.,
57
, 1054-1074
Wahlman, G.P. (2002): Upper Carboniferous-Lower Permian
(Bashkirian-Kungurian) mounds and reefs. - In: Kiessling,
W., Flügel, E., Golonka, J. (eds.): Phanerozoic reef pat-
terns. - SEPM Special Publication,
72
, 271-338
Further reading:
K129
(1)
Morphology:
Most dasyclads form unbranched
thalli; only a few form a branched thallus. Unbranched
thalli exhibit various shapes including (a) rod-shaped
(tubelike; e.g.
Macroporella, Gyroporella
,
Velebitella
)
and spherical thalli (e.g.
Mizzia
), (b) clavate thalli
(which increase in size during their development re-
sulting in pear-shaped forms), and (c) stalked thalli with
a spherical or barrel-shaped capitulum (e.g.
Bornetella
)
or a cap formed by whorls of rays (e.g.
Acicularia, Ac-
etabularia
). Most of these types may be unsegmented
or segmented. Branched thalli are represented by di-
chotomous tube-like forms (e.g.
Anthracoporella
) and
articulate forms appearing like beads on a string (e.g.
Cymopolia
).
10.2.1.7 Dasyclad Green Algae
Dasyclads are the most important fossil calcareous al-
gae used in microfacies analyses. These algae appeared
in the Cambrian and were important rock builders dur-
ing the Late Paleozoic, Mesozoic and Early Cenozoic.
Because of their value as palecological proxies and for
stratigraphical zonations, dasyclad algae are key ele-
ments in interpretating of ancient shallow-marine shelf
carbonates. Excellent overviews on the biology of dasy-
clad algae and the methods used in their analysis were
provided by Berger and Kaever (1992) and De Castro
(1997). Deloffre (1988) presented a key for the dis-
tinction of suprageneric taxonomic units.
Most dasyclads are recorded in thin sections as frag-
ments. Generic and specific determinations demand the
reconstruction of the morphology from random cuts and
variously oriented sections (see Fig. 10.2).
(2)
External or internal configuration of the thalli
expressed by undulation and articulation:
Undulation
refers to ring-shaped swellings at the thallus surface,
annulation to ring-like lacing of the thallus surface not
separated from each other (
Neoteutloporella
, Pl. 59/3;
Salpingoporella
, Pl. 62/2), perannulation to pronounced
annular lacings in the calcareous skeleton connected
by noncalcified segments (
Eovelebitella
, Pl. 59/1), and
fissuration to annular fissures in the calcareous skel-
eton. Intusannulation is a term for more or less pro-
nounced undulations of the main axis diameter engraved
into the inner side of the central cylinder.
(3)
Arrangement of laterals (primary branches) at
the main axis:
Aspondyl describes an irregular arrange-
ment at the main axis (
Anthracoporella
, Pl. 59/6;
Teutlo-
porella
, Pl. 61/3), euspondyl a regular arrangement in
whorls like the spokes of a wagon wheel (
Neoteutlo-
porella
, Pl. 59/3;
Salpingoporella
, Pl. 63/2), and
metaspondyl an arrangement of primary branches into
clusters of regular whorls (
Eovelebitella
, Pl. 59/1, Pl.
60/3;
Diplopora
, Pl. 59/2). The arrangement of the lat-
erals is one of the most effective criteria for defining
dasyclad families.
Definition, calcification and morphology:
Dasyclads
are a group of benthic calcified unicellular green al-
gae.
Living dasyclads are mm- to cm-sized, upright grow-
ing plants, which are attached to firm or soft substrates
by rhizoids. Characteristically, the thallus consists of a
long central stem (also called central cylinder or main
Text continued on p. 434
