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clasts, representing a mixture of limestone clasts, clay
minerals, iron oxides, quartz silt and isolated bioclasts.
Solution relics ('lithorelics') of the underlying rocks
floating within the matrix. Clasts of variable size within
millimeter and centimeter range. Greatly variable shape,
rarely rounded, but often 'subrounded' due to dissolu-
tion. Extremely poor sorting. Fabric clast-supported.
Fitting often high. Sharp clast/matrix boundary. Circum-
granular cracks around the clasts. Clay-filled fractures
(crypto- and microkarst). Clast/matrix boundary sharp.
Veining common, fracturing uncommon.
Microfacies: Variability of clasts high including lime
mudstones, floatstones and rudstones.
Groundmass : Fine-grained calcitic or dolomitic ma-
trix abundant. Often clayish commonly reddish matrix,
corresponding to the insoluble oxidized residue remain-
ing after the dissolution of underlying limestone. Me-
teoric-vadose and meteoric calcite cements.
Fossils : Rare.
Case studies: Semeniuk 1986; Wright and Tucker
1991.
Solution-evaporite-collapse breccia
Field observations: Thick, discontinuous breccia
bodies. Unstratified or only indistinctly stratified. Some
gravity segregation. Usually proximal to evaporite pri-
Plate 27 Carbonate Breccia: Provenance Analysis of Clasts
Microfacies analysis of the clasts of carbonate breccias has great potential for basin analysis. Compositional
studies of the clasts assist in evaluating intensity and timing of erosion processes and in reconstructing 'lost'
carbonate platforms whose material has been deposited in slope and basin positions (Sect. 16.3). Because the
destruction of shallow-marine platforms depends on changes in water depths caused by sea-level fluctuations,
clast analysis is a promising method in sequence stratigraphy.
The samples shown in this Pl.27/1 and in Fig. 5.21 come from the 'Tarvis breccia', a breccia horizon in Early
Permian sediments of the Southern Alps which can be followed laterally for a distance of several tens of kilometers.
The breccia was studied with regard to the lithologic composition and textural characteristics of the clasts and
the matrix, and with respect to the microfacies types and microfossils (Buggisch and Flügel 1980; Flügel 1980).
The microfacies types of the clasts reflect the erosion of a sequence of shallow-marine platform carbonates
formed in restricted and open shelf lagoons. Platform-margin reef limestones are of subordinate importance.
Most clasts were deposited as mass-flow breccias (Fig. 5.21) and rockfall breccias in mixed carbonate-siliciclastic
settings. Some carbonate clasts are also associated with volcanic material in lacustrine settings (-> 1). Differ-
ences in fitting, size and rounding of the clasts, and the change from carbonate and marly matrix types in the
lower parts of the breccia sequence to predominantly siliciclastic matrix types in the upper part indicate a regres-
sive shift from a shallow-marine to a coastal and continental depositional environment accompanied by syntectonic
events.
1
Lacustrine breccia. The microfacies of the lithoclasts reflects the erosion of shallow-water marine platform carbonates.
The bioclastic grainstone clast (left) with dasyclad green algae ( Connexia carniapulchra , Mizzia sp., Gyroprella sp.) and
fusulinids ( Pseudofusulina ) was derived from carbonates formed in a protected high-energy environment within a shelf-
lagoon. The high primary interparticle porosity was reduced by submarine radiaxial cements. The bioclastic packstone
(right) yields poorly sorted skeletal grains (echinoderms, foraminifera) which underwent selective dolomitization prior to
the erosion and deposition of the lithoclast. Fusulinid foraminifera ( Pseudoschwagerina - center and Pseudofusulina -
right) attest to an Early Permian age. Both clasts were deposited together with volcanic pebbles (VP) within a lacustrine
mud represented by a dark homogeneous micrite with calcite-filled dewatering structures (arrows). During burial the
breccia was affected by strong pressure-solution resulting in distinct penetration of clasts (CP). Early Permian Tarvis
Breccia: Sexten Dolomites, Southern Alps, Italy.
2
Clast-supported forereef breccia. Lithoclast rudstone. Poorly sorted angular, subangular and subrounded clasts of lithi-
fied reef carbonates as well as some isolated reef organisms are cemented by submarine fibrous and radiaxial calcite
cements (RC), characteristic for upper slope deposits. Roundness/sphericity corresponds to the fields B, D, J and K of the
Krumbein visual chart (Fig. 4.30). Reef clasts exhibit diverse microfacies types, indicating erosion in different reef crest
areas. Most limestone clasts were eroded from central parts of the reef, others (bottom right) represent sediments origi-
nally deposited within cryptic environments of reef cavities (indicated by fine-grained peloidal texture and diagnostic
foraminifera). Larger fossils are redeposited sponges ( Cheilosporites - S). Erosion of sediments originally deposited in
low-energy protected environments (deeper reef crest or slope) is indicated by the specific biotic association of sphincto-
zoid sponges (S), spongiomorphid sponges (SP), coral fragments (C) and solenoporacean red algae (SO). Note the micro-
bial coating of frame-building organisms (arrows, cf. Pl. 50/1). Late Triassic (Dachstein Reef Limestone, Norian):
Gosaukamm, Austria.
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