Geology Reference
In-Depth Information
fication, number and thickness of beds, lithological
variations (e.g. limestone-marl alternations), carbon-
ate and non-carbonate contents, stable isotopes, main
and minor elements, and rock color (light and dark beds)
reflecting organic carbon content. Sampling within cen-
timeter-scale and the study of planktonic microfossils
both in washed samples and in microfacies thin sec-
tions allow biogenic carbonate productivity to be esti-
mated (e.g. Noé 1993). Important papers dealing with
pelagic cyclic carbonates are listed in Box 16.1.
intraclastic beds with mudstone and limestone clasts
represent lag deposits formed at transgressive surfaces
truncating underlying paleosols (Miller and West 1998).
The microfacies of the overlying limestones is charac-
terized by fossiliferous wackestones and packstones.
An example is shown in Pl. 56/8 and Pl. 118/1.
16.1.1.3 Case Studies: The Lofer Cycle and
the Latemar Cycle (Triassic of the Alps)
Shallowing-upward successions exhibit different
microfacies patterns. Two patterns represented by Tri-
assic carbonates have become key elements in the dis-
cussion of peritidal and diagenetic cycles - the Lofer
or Dachstein cycle of the Austrian Northern Calcare-
ous Alps and the Latemar cycle of the Dolomites in
South Tyrol in Northern Italy. Microfacies and the con-
troversial interpretations of these cycles are the topics
of the following paragraph.
Late Paleozoic cyclothems
The term cyclothem designates the rock record of
cyclic accommodation processes characterized by
coarsening-upward successions, reflecting a passage
from marine sedimentation upwards into terrestrial sedi-
mentation.
The cyclothem concept was developed in the Penn-
sylvanian of the United States and generalized by Weller
in Wanless and Weller (1932) and Moore (1931). At
present, the most widely accepted cyclothem model is
that of the Kansas-cycle cyclothems (Heckel 1977).
Midcontinent cyclothems are dominated by very shal-
low and paralic facies with abundant subaerial expo-
sure surfaces including well-developed paleosols.
Meter-scale shallowing-upward cycles (parasequences)
are common; they are usually capped by subaerial ex-
posure surfaces.
Interpretations of Pennsylvanian cycles include
glacio-eustatic control as well as autocyclic and tec-
tonic controls. Major global sea-level fluctuation docu-
mented by transgressive-regressive depositional pat-
terns and having about 1-3 Ma lasting (3rd-order
cycles) have been recorded from many Late Paleozoic
depositional successions in North America and Europe
(e.g. Russia) and were summarized in sea-level charts
(Ross and Ross 1987, 1988, 1994; Heckel 1986, 1994).
Permian sea-level fluctuation patterns are closely re-
lated to biostratigraphical changes in fossil zonal as-
semblages (e.g. fusulinid zonation). The fossil record
is correlated with deposition during sea-level high-
stands.
Limestone beds are key marker horizons in these
cyclothems. Their interpretation as transgressive or re-
gressive deposits is crucial in the analysis of larger
cyclothems. Microfacies offers key data for evaluating
the paleoenvironment and depositional depths of these
carbonates (significant references are listed in Box 16.1,
Carboniferous and Permian). Cyclothem boundaries
may correspond to prominent marine flooding surfaces
overlain by fossiliferous limestones. Centimeter-scaled
The Lofer (Dachstein) cycle
The cyclic depositional pattern of Alpine Late Tri-
assic carbonates was recognized by Sander (1936) in
the Loferer Steinberge near Lofer, and the Steinernes
Meer, Salzburg, and later investigated by Schwarzacher
(1954) and, in great detail, by A.G. Fischer (1964), who
published a fundamental study on the Lofer cyclothems.
This study had a deep impact on the interpretation of
cyclic carbonate sequences. The cycles of the Late Tri-
assic Dachstein limestone are superbly exposed in huge
mountain cliffs and can be studied over a thickness of
several hundreds of meters (in the Lofer region about
600 m).
Stratal patterns and controlling mechanisms of the
Lofer cycles, however, are still controversial (Gold-
hammer et al. 1990; Satterley and Brandner 1995; Enos
and Samankassou 1998).
Comparable Late Triassic stacked high-frequency
cycles were analyzed in the Southern Alps (Bosellini
and Hardie 1988), Slovenia (Ogorelec and Rothe 1992),
Hungary (Haas 1991, 1994; Balog et al. 1997), Sicily
(Catalano et al. 1974) and Oman (Bernecker 1996;
Weidlich and Bernecker 2003; Fig. 10.40). Lofer-type
cycle patterns are not limited to the Late Triassic as
shown by Liassic successions in Slovenia (Dozet 1993).
Fig. 16.1 shows an idealized Lofer cyclothem illus-
trated by A.G. Fischer (1964) and appearing in many
textbooks and overview articles. Fischer distinguished
an ABC sequence consisting of three members:
