Geology Reference
In-Depth Information
Fig. 10.58.
Holothurian sclerites.
A
: Thin section exhibiting two differ-
ent sclerites. Early Cretaceous: Sub-
surface, Bahama Bank.
B
: SEM photograph of
Theelia flor-
ida
(Terquem and Bertelin). Early Ju-
rassic: Empede near Hannover, Ger-
many. B: After Fischer et al. (1986).
Scale is 100
m.
Thin sections of
Saccocoma
elements were described
as
Eothrix
and
Lombardia.
Verniory (1955) proved that
these fossils were sections of facetalia and brachialia
of
Saccocoma
and closely related taxa. Characteristic
sections exhibit antler-like shapes (Fig. 10.56; Pl. 96/2,
3).
Echinoidea
Modern echinoids occur in almost every major ma-
rine habitat from intertidal zones to depths of more than
5000 meters, and from the poles to the equator. Regu-
laria are epibenthic detritus feeders living especially
on hard bottoms. Irregularia occur within or on soft
bottoms.
In the Upper Jurassic central European epicontinen-
tal platforms, the
Saccocoma
facies characterizes late
transgressive system tract and highstand deposits.
Within the Tethyan region, the
Saccocoma
facies is com-
mon in deep-marine basinal sequences. Allochthonous
deposition by turbidites on slopes forming
Saccocoma
packstones/wackestones are known from deep-water
settings as well as epicontinental positions (Matys-
zkiewicz 1996).
Morphology and classification:
The skeleton is made
of tightly interlocking plates that form a rigid structure
(test) whose shape ranges from globular to flattened.
Echinoids are traditionally divided into two sub-
groups. The
regular
echinoids
with almost perfect
pentameral symmetry include the Cidaroidea (since
Late Paleozoic) and the Echinoidea s.str. (sea urchins;
Plate 95 Echinoderms
The plate exhibits Paleozoic limestones rich in crinoid plates (-> 1-4) and remains of cystoidean echinoderms
(-> 6) as well as a Triassic limestone with echinoid fragments (-> 5). The figure on this page demonstrates the
morphology of a stalked crinoid (after Black 1988).
1
Crinoid fragments.
Bioclastic wackestone with echinoderms (E; predominantly crinoids) and shells of
pelagic bivalves ('filaments', F). The crinoid sections correspond to the sections A, D and H shown in
Fig. 10.53. The biofabric is characterized by loose and disperse packing and bimodal sorting; see -> 4.
Open-marine deep slope environment. Early Jurassic: Adnet near Salzburg, Austria.
2
Crinoid accumulation
. Crinoid stem plates (columnals) within a tempestite. Some crinoids exhibit
syntaxial cement rims. Most cementation, however, is related to fractures. SMF 12-C
RINO
. Early De-
vonian (Emsian): Erfoud, southern Anti-Atlas, Morocco.
3
Crinoid stem.
Longitudinal section through three columnals. Note grayish color and distinct twin lamel-
lae. Early Carboniferous open-marine carbonate ramp (Viséan): Debnik, Cracov Upland, central-south
Poland.
4
Crinoid packstone.
The columnal (C) is completely recrystallized. Black arrow points to microbor-
ings, white arrows to the serrate boundary between stem plates. B: Bryozoan. The biofabric is densely
packed and well-sorted. The sample is from the deeper part of a carbonate ramp. Mississippian: Turtle
Mountains, Frank Slide, Alberta, Canada.
5
Echinoids.
Bored echinoid plates (EP) and echinoid spines (ES) associated with gastropods (G). White
grains are quartz. Late Triassic: Gurumugl, Mount Hagen, central Papua New Guinea.
6
Cystoid wackestone.
Cystoids were important Early Paleozoic rock builders (Cambrian-Devonian).
The thin section shows broken and eroded plates occurring in a strongly recrystallized limestone rich
in cystoids. Black arrows point to syntaxial overgrowth rim cement. B: Bryozoan. Note the difference
in color between echinoderms (dusty gray) and bryozoans (dark). Late Ordovician (Ashgillian): Cen-
tral Carnic Alps, Austria.
