Geology Reference
In-Depth Information
Depositional breccias
Mass-flow breccia:
Breccia originating from the downslope transport of shallowmarine and
resulting from the
slope sediments moving under the force of gravity. Includes breccias formed by slumps
deposition of eroded
and slides, debris flows, grain flows, and turbidity flows.
carbonate material)
Submarine rockfall breccia:
Massflow breccia formed by the accumulation of coarse, angular
rock fragments derived by falling from a cliff, escarpment or steep rocky slope.
Peritidal and shallow-marine breccia:
Breccia formed by synsedimentary deposition of eroded
peritidal, shallow subtidal as well as subaerial carbonates, often related to storm events.
Deposition takes place in inter and supratidal settings, and at the beach.
Forereef breccia:
Breccia deposited on the seaward slope of highenergy reefs. Consisting of
eroded reef material and remains of organisms living in the reef or on the foreslope.
Non-depositional
Caliche breccia
: Breccia formed by insitu brecciation in arid and semiarid climates, controlled
breccias
by soilforming processes, and connected with extensive weathering, erosion, solution
(resulting from
and shrinkage.
inplace dissolution)
Solution-evaporite-collapse breccia:
Breccia formed by collapse of beds subsequent to the
removal of soluble material within some beds (e.g. evaporites).
Tectonic breccias
Fissure fill breccia
: Breccia formed within submarine neptunian dikes or subaerial fissure infills
(resulting from
and karst fissures.
internal dislocation
of carbonate rocks)
Internal breccia:
Breccia formed by rupture and fracturing of carbonates near the depositional
surface. These breccias are products of dilation of slightly lithified limestones caused by tec
tonics (e.g. hydraulic fracturing, earthquakes). Internal breccias occur in platform and slope
carbonates which were brecciated shortly after deposition and before final lithification.
Shear breccia
: Breccia caused by brittle deformation associated with thrust and sliding dis
placement.
Diagenetic breccias
Pseudobreccia:
Mottled limestones and dolomites with breccialike textures caused by patchy
(resulting from early
recrystallization and cementation, possibly controlled by the distribution of organic
diagenetic processes)
compounds.
Stylobreccia:
Breccia in which fragments are bound by stylolites. Caused by fracturing of car
bonate rocks, accompanied by pressure solution between the fragments of the breccia.
Fig. 5.16.
Main types of carbonate breccias.
Because many breccias are products of multiple processes, the boundaries
between some categories are transitional. The formation of fissure fill breccias, for example, depends on the existence of a
tectonic framework, but the composition of the breccias is depositionally controlled.
high to moderate, and may include the entire spectrum
of Dunham's texture types (Fig. 5.21). The clasts rep-
resent a mixture of material derived from various shal-
low-water and slope environments and sometimes also
from basinal environments.
Groundmass:
Fine-grained sedimentary matrix (e.g.
pelagic micrite) or matrix brought to the basin together
with the clasts. Depending on the depositional pattern,
the matrix volume is less,than equal to or greater than
that of the clasts. Inter-clast carbonate cements are rela-
tively rare (Pl. 26/3).
Fossils:
Common and abundant in clasts and within
the primary sedimentary matrix (Pl. 9/7), relatively rare
in the allochthonous matrix.
Case studies:
Bektas et al. 1995; Bernoulli et al.
1987; Braithwaite and Heath 1992; Cook 1979; Engel
1970; Flügel et al. 1993; Gawlick 1996; Günther and
Wachsmuth 1969; Leigh and Hartley 1992; Payros et
al. 1999; Peryt 1992; Remane 1970; Ruberti 1993;
Steiger 1981; Stock 1994; Wächter 1987.
Submarine rockfall breccia
Field observations
: Massive or thick-bedded. In-
tercalated in bedded limestones and marl/limestone se-
quences. Thickness ranges between several meters and
some tens of meters. Lateral extension can reach more
than 100 m. The clasts are often eroded from coastal
escarpments or steep submarine slopes.
Clasts:
Lithological composition often polymict.
Limestone clasts may be derived from different litho-
or biostratigraphic units. Fabric clast-supported. Close
packing. Variable shape, angular and subangular clasts
common. Rounded fragments are not caused by abra-
sion during transport but rather to partial dissolution.
