Geology Reference
In-Depth Information
Fusulinid coquinas (grain- and packstones) may rep-
resent parautochthonous assemblages, allochthonous
downslope accumulations between buildups, concen-
trations through storms, or transgressive deposits dur-
ing times of reduced mud deposition, or they may just
be diagenetic packstones caused by intergranular solu-
tion. Syn- and postsedimentary changes of test shapes
and internal structures (e.g. broken or distorted shells,
shells with breaks of septa) are indications of late di-
agenesis and burial history (see Pl. 36/1, 3).
1988). In contrast to lituolinid foraminifera without wall
differentiation and internal partitions of the chambers,
(Pl. 69/8) which were common in open-marine envi-
ronments, lituolinid foraminifera with complex inner
structures were restricted to warm lagoonal environ-
ments. Widely distributed examples of these Lituolacea
are
Lituosepta
(Early Jurassic),
Orbitopsella
(Early Ju-
rassic),
Haurania
(Early and Middle Jurassic),
Meyen-
dorffina
(Middle Jurassic),
Alveosepta
(Late Jurassic,
Pl. 69/8),
Kurnubia
(Middle and Late Jurassic, Pl. 69/
2, 3, and Middle Jurassic to Early Cretaceous; Pl. 69/
1).
Triassic:
Benthic foraminifera are common in thin
sections of Middle and Late Triassic platform and reef
carbonates (see Pl. 111). Systematic determinations
must consider diagenetic changes of wall structures that
are particularly frequent in involutinid foraminifera
(Hohenegger and Piller 1975). Some taxa are good in-
dex fossils and are used for biozonations (Gazdzicki
1983, Salaj et al. 1983; Fig. 10.27). Open and restricted
platforms as well as different parts of reefs can be dis-
criminated using distinct foraminiferal associations de-
fined by the occurrence or quantitative predominance
of specific taxa (e.g. Schäfer and Senowbari-Daryan
1978; Schott 1983). Examples from various parts of
the Tethys (Alps, Sicily, Greece, Oman) exhibit corre-
sponding association patterns, proving the usefulness
of foraminifera for environmental analysis. Foramin-
iferal distribution was controlled by substrate condi-
tions, specific life behavior, the topography of the depo-
sitional environment and water depth. Common Late
Triassic foraminifera include taxa of Textulariina (Pl.
111/1, 9, 10, 14, 18, 19, 20), Miliolina (Pl. 111/2-8, 15-
17, 22, 23), Rotaliina as well as microgranular fora-
minifera (Pl. 111/21). Note that higher systematic
groups of Late Triassic foraminifera have been differ-
entiated more deliberately using wall structure types
(Hohenegger and Piller 1975, Piller 1978). Involutinid
foraminifera offer the possibility for subdividing re-
stricted and open shelf environments.
Microforaminifera
are linings of juvenile parts of
foraminiferal tests corresponding to chitinous mem-
branes, and often stained red by diagenetic impregna-
tion of Fe-oxides (Stancliffe 1989; Misik and Sotak
1998). These very small fossils (<150
m) are abun-
dant in red Jurassic basinal and deep shelf limestones.
They are known from the Permian to the Quaternary.
Cretaceous:
From the Cretaceous foraminifera
spread into the multitudinous number of niches that they
also occupy today. Thus, by the Cretaceous, environ-
mental factors can be reasonably delimited from fora-
miniferal patterns. Benthic foraminifera are important
index fossils of the extended Cretaceous platform car-
bonates. The evolution of planktonic foraminifera dur-
ing the Cretaceous and in the Cenozoic forms the basis
for excellent biostratigraphic zonations and worldwide
correlations.
Cretaceous benthic foraminifera allow the paleoen-
vironment to be biostratigraphic zoned and parts of plat-
forms and ramps to be differentiated. Stratigraphic sub-
divisions are predominantly based on biozones derived
from the distribution, abundance and ranges of benthic
foraminifera. Oriented sections are important for de-
termining larger foraminifera such as orbitolinids and
orbitoidaceans.
Agglutinated foraminifera (cuneolinids, dicyclinids,
valvulinids and various ataxophragmiaceans; Pl. 71)
are common in lagoonal and shallow inner platform
environments. The agglutinated
orbitolinids
(Orbito-
linacea; Pl. 70) were common in inner and outer plat-
form settings. They permit particularly
Early and
Middle Cretaceous
shallow-water limestones to be
stratigraphically zoned in detail (Schroeder and
Neumann 1985; Velic 1988; Clavel et al. 1994; Becker
1999; Husinec et al. 2000). The time intervals corre-
spond to taxon-range zones and assemblage zones. In
the Tethys a significant spreading took place during lat-
est Barremian to Early Aptian times, associated with
the development of the 'Urgonian' platforms (Masse
1976; Peybernes 1976; Arnaud 1981; Arnaud-Vanneau
Jurassic:
Benthic foraminifera (Pl. 69) and dasyclad
calcareous algae assist in biozonations of Jurassic plat-
form, ramp and upper slope carbonates in the Mediter-
ranean Tethys (Sartoni and Crescenti 1962; Jaffrezo
1980; Sartorio and Venturini 1988; Fig. 10.28A). These
'coenozones' are based on various bioevents (e.g. first
occurrence and disappearance and total range of taxa,
maximum frequency and assemblage patterns; see Sect.
10.3). The first planktonic foraminifera appeared in the
Middle Jurassic (Pl. 69/12).
Particularly common in thin sections of Jurassic plat-
form carbonates are
large lituolinid foraminifera
char-
acterized by complex inner structures (Septfontaine
