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present (Pl. 140/1). Member A is usually regarded as a
supratidal deposit.
•
Member B
is darker in color, predominantly dolo-
mitic and characterized by distinct lamination struc-
ture (Pl. 140/3; Fig. 16.2C), fenestral fabrics including
shrinkage pores (Pl. 140/2), and intraclasts. The lam-
inites are very often crossed by vertical cracks (prism
cracks, attributed to desiccation). This subtype corre-
sponds to the 'algal mat loferite' described by Fischer
(1964) and to subfacies B1 differentiated by Gold-
hammer et al. (1990). Member B also contains layers
of burrowed, peloidal wackestones and packstones with
restricted fauna consisting of thin-shelled gastropods
and ostracods ('pellet and homogeneous loferites';
subfacies B2). Intercalations of grainstones are com-
mon (Fig. 16.2A, B). Facies B is usually regarded as
an intertidal deposit.
•
Member C
makes up to 85% of the sequence. The
facies comprises <1 m to more than 25 m thick, light
gray massive limestone beds and includes wackestones
and grainstones with submarine hardgrounds. The lime-
stone always contains a large amount of organic de-
bris. Oncoids formed by calcimicrobes are fairly com-
mon. Thick-shelled bivalves (
Megalodon, Conchodon
)
are conspicuous (Pl. 140/4). The bivalves often form
layers and occur in life position. Other common fossils
are gastropods, dasyclad algae, and, approaching the
margin of the platform, corals (Pl. 140/5). Member C
is usually regarded as a subtidal deposit.
The repeated alternation of subtidal and intertidal/
supratidal deposits was explained by sea-level oscilla-
tions. Fischer (1964) favored a transgressive pattern of
the 'Lofer cycle' in which basal intertidal/supratidal
laminites (Member B) pass upward into shallow sub-
tidal units (Member C) recording sea-level rise and a
transgression of the shoreline. Soils capping the sub-
tidal member mark a fall in sea-level. This deepening-
upward interpretation has been opposed by Gold-
hammer et al. (1990) and Satterley (1996) who reinter-
preted the classical Lofer cycles as shallowing-upward
cycles, and Enos and Samankassou (1998), who stress
the possible influence of autocyclic processes and inter-
pret the pattern recorded by the bedded Triassic Dach-
stein limestone as alternating rhythms (...BCBCB...)
rather than regular cycles. The crucial point in the dif-
ferent interpretations is the origin of the red 'soils' of
Member A and the stratigraphic position of this mem-
ber.
Fig. 16.1.
Diagrammatic representation of a Lofer cycle.
The
drawing is by A.G. Fischer (1964), the text is slightly modi-
fied. Following Fischer, an ideal cycle consists of three depo-
sitional units (members or facies) formed under different
environmental conditions. Member A on the top of member C
represents a basal disconformity, subaerial exposure and su-
pratidal conditions. Member B records tidal conditions. Mem-
ber C documents shallow-subtidal deposition. The typical
'loferite' facies characterized by a carbonate sediment riddled
by shrinkage pores (sometimes synonymous with 'birdseyes
limestone') occurs within Member B.
•
Member A
is an unconformity followed by a red-
dish and reddish-greenish or gray argillaceous, gener-
ally thin horizon of reworking with intraformational
mud pebble conglomerates (Pl. 140/2; Fig. 16.2D) and
diagenetic breccias. Associated with facies A are cracks
and solution cavities in the underlying Member C. The
latter is often filled with argillaceous limestone of Mem-
ber A. Some of the solution cavities are aligned paral-
lel to the bedding planes and could represent freshwa-
ter tables formed during the emersion of Member A.
The red matrix is often interpreted as a soil related to
subaerial exposure. Pedogenic structures may be
The
microfacies
of the members forming
Lofer
cyclothems
is highly variable. Common microfacies
types include:
