Geology Reference
In-Depth Information
Fig. 5.21.
Polymict depositional carbonate breccia.
This mass-flow breccia is part of the Early Permian 'Tarvis breccia' in
the Southern Alps (see Pl. 27/1). The microfacies of the angular and subangular limestone clasts testifies to the erosion and
destruction of different parts of a carbonate platform and platform margins.
Textural criteria of clasts:
Shape angular and variously rounded, high roundness number, low fitting, clast/matrix boundary
sharp, ratio clasts : matrix 3 : 1. Color differences in the clasts correspond partly to differences in microfacies.
Microfacies of clasts:
The numbers refer to microfacies types: The environmental interpretation is based on reference sec-
tions exhibiting the spectrum and the spatial distribution of microfacies types of shelf and shelf margin platform carbonates
(Flügel 1980) and on environment-diagnostic associations of calcareous algae (Flügel and Flügel-Kahler 1980).
1 - bioclastic grainstone with coated skeletal grains, worn fusulinid shells and rounded intraclasts (high-energy shelf lagoon),
2 - bioclastic packstone with dasyclad green algae and smaller foraminifera (protected lagoon), 3 - bioclastic poorly sorted
packstone with various algae, smaller foraminifera and echinoderm fragments (open-marine shelf lagoon), 4 - bioclastic
grainstone with gastropods and dasyclad algae (protected shelf lagoon), 5 - poorly sorted oolitic grainstone with tangential
small ooids, various skeletal grains and cortoids (mixed material derived from ooid shoals and open shelf lagoonal environ-
ments), 6 - lithoclastic packstone with various worn skeletal grains and rounded intraclasts (high-energy shelf lagoon), 7 -
oncoid floatstone with large cyanobacterial oncoids (protected subtidal parts of a shelf lagoon), 8 - boundstone with
Tubi-
phytes
, encrusting sponges and
Archaeolithoporella
, see Pl. 98/8 and Pl. 145 (shelf margin reefs, these boundstones differ in
rock colors and the proportions of encrusting organisms and grains), 9 - small clast of black lime mudstone (probably of
lacustrine origin, compare Pl. 27/1), 10 - bioclastic wackestone with sessile smaller foraminifera (mud mound), 11 - fine-
grained bioclastic grainstone with abundant green algae (protected lagoon), 12 - coated bioclastic grainstone with algae,
foraminifera and other skeletal grains (open-marine shelf lagoon), 13 - fine-grained bioclastic grainstone with skeletal grains
and peloids (protected lagoon), 14 - laminated bindstone (tidal flat). Scale is 1 cm.
The uniform red
matrix
(M) consists of poorly sorted lithoclastic wackestones without fossils. The angular lithoclasts repre-
sent erosional debris infilled together with carbonate mud into interclast voids. Solution voids at the margin of some clasts
and fractures are filled with scalenohedral calcite crystals (CC), subsequent to compaction and pressure solution. White
arrows show penetration of clasts, black arrows indicate surficial solution of some clasts.
