Geology Reference
In-Depth Information
ate conglomerates include (a) storm or swell lags in
shore-face environment (Einsele and Seilacher 1982;
Nemec and Steel 1984; Aigner 1985; Craft and Bridge
1987), (b) lateral accretion lags at the base of tidal chan-
nels (Shinn 1986; Waters et al. 1989), (c) transgressive
lags, originating from a rip-up of underlying older tidal
flat sediments during rises in sea level (Pl. 9/7).
Box 5.9.
Significance of carbonate breccias and con-
glomerates.
Paleoenvironmental proxies
Since the formation of many breccia types is restricted
to specific settings (Fig. 5.20), depositional and non-
depositional breccias assist in the paleoenvironmental
interpretation of non-marine and marine carbonates.
Caliche breccias and karst breccias indicate subaerial
exposure, solution-evaporite-collapse breccias may point
to sea-level lowering (Obrador et al. 1992).
Depositional
patterns
Breccias can mark underlying sequence boundaries
(e.g. Biddle 1984, Garcia-Mondejar 1990) and offer in-
formation on the geometry of carbonate ramps, e.g. dis-
tal steepening.
Reconstruction of provenance areas
Clast analyses of breccias and microfacies studies of
conglomerates provide excellent data which allow de-
tailed reconstructions of the changing sedimentary in-
put into marine or non-marine basins, the provenance of
the material and the climatic and tectonic controls of the
processes involved (see Pl. 27, Fig. 5.21 and 16.3).
Tectonic events
Breccias can indicate the proximity of faults which
may otherwise not be directly detected (e.g. Bosellini
1989; Garcia-Mondejar 1990).
Economic importance
Reservoir rocks:
Fractured carbonate breccias are im-
portant hydrocarbon reservoirs. Of particular interest are
solution breccias (Loucks and Anderson 1985; Miller
1985), debris-flow breccias (Enos 1988) and karst brec-
cias.
Mineralizations:
Breccia-hosted karst and collapse
breccias host Mississippi Valley-type lead-zinc deposits
(Klau and Mostler 1983; Bechstädt et al. 1994; Liaghat
et al. 2000).
Building stones:
Many polymict carbonate conglom-
erates and breccias are used as building and decoration
stones (Pl. 26/3), e.g. 'Nagelfluh' (an interglacial con-
glomerate), or the socalled 'Untersberg marble' (a Cre-
taceous mass-flow breccia) in Austria.
5.3.3.5 Significance of Carbonate Breccias and
Conglomerates
Fig. 5.20 shows the setting of breccias and conglomer-
ates. Box 5.9 summarizes the significance of breccias
and conglomerates for facies analyses and economic
issues.
Basics: Carbonate breccias and conglomerates
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Further reading
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