Geology Reference
In-Depth Information
Fig. 5.19.
Polymict orthoconglomerate
consisting of well-rounded limestone pebbles of different age, quartz pebbles (Q) and
completely rounded fossils (worn and recrystallized colonial coral: top left). Note the strong difference in the microfacies
and the age of the limestone pebbles: Intraclastic grainstone (IG, Triassic), peloidal packstone (PP, Late Cretaceous), argilla-
ceous mudstone (M, Eocene) with some ostracods. The light gray pebbles are dolomite (D, Triassic). The microfacies of the
conglomerate indicates reworking of Northern Alpine rocks, the excellent rounding of the limestones points to a short fluvial
transport distance of the material into the Molasse Basin. Interparticle pores are filled with granular calcite. Penetration of
adjacent clasts (arrows) indicates strong compaction. Early Tertiary (Oberaudorf Formation, Late Eocene): Florianiberg near
Oberaudorf, Bavaria, Germany. Scale is 1 mm.
support or by clasts floating within a sandy matrix. The
clasts of
paraconglomerates
float within a muddy ma-
trix. The main criteria used for the quantification of
conglomerates are clast size and rock types.
The formation of conglomerate is essentially con-
trolled by transport processes. The larger the pebbles
of a conglomerate, the higher is the transport energy.
Conglomerates become better sorted during transport
and the proportion of matrix decreases.
Limestone conglomerates originate in nonmarine
and shallow- and deep-marine environments, and are
common in fluvial and beach settings (Fig. 5.19). Con-
glomerates composed entirely of limestone pebbles
record conditions of rapid erosion and burial, e.g. along
a fault scarp (e.g. erosion of coastal limestone cliffs).
Transgression of an advancing sea in marginal marine
environments can produce limestone conglomerates
consisting of beach gravels. Shallow-marine carbon-
Fig. 5.20.
Environmental setting of depositional carbonate breccias.
A
: Cross section from land - to platform and platform
margin with reefs - to slope and deep swells - down to deep-water basin.
B
: Cross section across a distally steepened ramp.
