Page 254 - Carbonate Facies in Geologic History

Organic Composition of Ladinian Wetterstein Limestone 241

The Wetterstein limestone forms major offshore banks like those of the Do-
lomites but is much less dolomitized and has been carefully studied petrographi-
cally in recent years (Ott, 1967; Sarntheim, 1967; Toschek, 1968). The limestone is
hundreds of meters thick (up to 1500 m) and shows generally regular upward
shoaling major facies which also may be traced laterally in belts surrounding a
series of east-west elongate carbonate banks (Fig. VIII-16). The exact distribution
of the several known banks is debated because of tectonic displacements so
common in this Alpine structure belt. The Karwendel bank, forming the high
cliffs north of Innsbruck, is best known. Its boundary is a bioclastic girdle, wider
on the south and perhaps indicating stronger wind waves and currents from that
direction. Its narrow northern boundary is also clearly defined. Other banks are
recognized south of Innsbruck.
All of these banks rise from a platform limestone of Anisian age-termed
Alpine Muschelkalk. Their equivalent basinal facies (Partnach beds) is only 100-
250 m thick and is dark, thin-bedded, slightly bioclastic-spiculitic limestone with
chert nodules and several shale beds. This grades upward into the bank proper
through some thick-bedded, dark gray, bioclastic wackestone with peloids and
abundant crinoid stems, mollusks, and dasycladaceans derived from upslope. No
real forereefbreccia is present (unlike the beds in the Dolomites). The Wetter stein
transition beds instead are a type of basin marginal deeper water limestone (Fa-
cies belt 3 of the author). Texturally, the bank edges consist of poorly sorted
coarse bioclastic debris generally in a sparry matrix but with some bioclastic
micritic infill. Much coarse spar coating is seen. Texture is essentially rudstone to
floatstone. The biota of this bank edge facies includes large crinoids, echinoids,
Solenopora, Daonella bivalves, the brachiopod Rhynchonella, gastropod Euom-
phalus, orthoconic nautiloids, dasycladacean Teutloporella nodosa, some few cor-
als, many segmented or beaded sponges, and encrusting Tubiphytes (Plates XX,
IV B, XXV A, XXVI A).
Ott's careful petrographic study (1967) shows that Tubiphytes is the most
important reef builder. He lists five different finely textured, encrusting growths
with delicate, tiny (2 mm) bushy networks in the sedimentary fabric. Microscopic
study also discerns minute, 1 mm thick, stalks of crystalline calcite and includes
tiny porous pipes in fasciculate or isolated form up to 3 mm in diameter. Those
with nonporous walls are termed H olocoelia. Very delicate fine-branching septate
corals, Calamophyllia, are up to 3 mm in diameter and encrust the epithecae of
other forms. Larger forms are also present. Irregular meshworks and thick stalks
of H olocoelia are present as are fasciculate forms such as "1hecosmilia", M arga-
rosmilia, and Pinacophyllum. The relative abundance of such corals is hard to
estimate. The megafauna is dominated by diverse groups of calcareous sponges.
Inozoa or pharetrones are common but eight genera of columnar, segmented or
beaded forms of Sphinctozoans have been described (Ott, 1967). The sponges
seem to have grown in groups comprised of only a limited number of genera at
one place and to have occupied different ecologic niches from the corals. Hydro-
zoans, both as tiny stalks and as encrusting concentric balls, are present but not
common. Some few encrusting calcareous foraminifera and bryozoans appear to
have been sponge parasites. Calcareous algae are not particularly important;
some blue-green stromatolitic forms may occur as reef binders. The codiacean