Page 257 - Carbonate Facies in Geologic History

244 Permo-Triassic Buildups and Late Triassic Ecologic Reefs

1000 m in the eastern Dolomite trough. These strata contain sparsely fossiliferous
peloidal micrites with sedimentary structures indicative of intertidal and supratid-
al environments. The unit is thoroughly dolomitized and indicates an environ-
mental complex which could easily have contained saline ponds in which evapo-
rites were deposited. Evaporites are not seen but may have been removed by later
weathering. Both the Dolomia Principale and the Raibl might have provided
environments for the generation of dolomitizing fluids (see Chapter X).

Upper Triassic Reef-Lined Banks and Basinal Mounds
of Austria and Bavaria
Introduction and Microfacies

The Upper Triassic of the Northern Limestone Alps may be instructively com-
pared with the older Permo-Triassic carbonate buildups. There is a significant
although gradual development of coral framework construction in the later Trias-
sic reefs. Much the same type of evolution is seen in the progressive development
in size, complexity, and abundance of corals and stromatoporoids from Ordovi-
cian to Devonian time.
Recently, regional interpretative facies studies of Late Triassic strata in the
Northern Limestone Alps have been published both in German and English by
H.Zankl, A.G.Fischer, E.Fltigel, and F.Fabricius. As in the Middle Triassic, the
Hauptdolomit, its limestone equivalent, Dachsteinkalk, and the overlying Rhaetic
limestone were developed as a series of major carbonate banks. These likewise
have been disarranged by northward thrusting. This has been known for many
years for Mojsisovics also studied these strata. General agreement now exists that
thrusting has resulted in a foreshortening of two to three times in the Northern
Limestone Alps, compressing and disarranging the reef rimmed banks. Figure
VIII -12 gives the stratigraphic nomenclature of these beds.
The rock is mostly carbonate. Fltigel (1972) distinguished 12 basic microfacies
types found in Late Triassic strata of the Northern Limestone Alps. The princi-
ples employed by Fltigel in this work serve as the basis for delineating the stan-
dard microfacies types described in Chapter III of this book. Following Fltigel's
letter code, these Late Triassic microfacies are described below using as he did the
Folk classification. Equivalent standard microfacies types are designated SMF.
MF 1. Biomicrite with sessil benthos, generally in life position. Subtypes are based on
(a) preponderance of a certain fossil group, e.g., 7hecosmilia or calcareous sponge
micrite (bafflestone of Klovan), (b) amount of biogenic particles, (c) whether the mi-
critic matrix is bioturbated or pelleted or has biogenic crusts such as algal filaments.
SMF -7 c and SMF -8. (Plates XXIV B, XXVI B).
MF2. Biomicrite with sessile benthos generally in life position but bound by encrusting
organisms. Subtypes are designated according to the type of encrusting organisms.
Sessile foraminifera, alga-foraminifera consortium, calcareous sponges, SMF -7 b,
bindstone of Embry and Klovan (1971). (Plates XXIV A, XXVI A).
MF 3. Biomicrite to biosparite with associated bioclasts of sand to gravel size. Subdivisible
on basis of homogeneity of the bioclastic fraction and on major faunal groups. SMF-
5, bioclastic wackestone-packstone grainstone-floatstone.