Geology Reference
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Fig. 15.24. Microfacies of boulders of carbonate slope wedges (see Fig. 14.17).
A: Boundstone consisting of microbial crusts. Growth cavities are lined by isopachous fibrous calcite cement (former mag-
nesian calcite cement; white arrow) and filled with early marine botryoidal calcite (originally aragonite) cement. Note throm-
bolitic microfabric (black arrow) characterized by clots of small peloids surrounded by a thin calcite cement rim. The sample
typifies a reef limestone formed at the transition of a platform margin to an upper slope.
B: Polymict breccia consisting of poorly sorted carbonate clasts. Differences in shape, roundness and size of the clasts point
to reworking and redeposition of lithified and semi-lithified material. The clasts are peloidal packstones eroded in platform
interior environments. Arrow points to associated volcaniclastic particles. Rare fossils are an echinoid spine (E) and shells.
Matching boundaries of some clasts point to in-situ brecciation and displacive cement growth subsequent to the mechanical
integration of the allochthonous carbonate (see Blendinger 2001). Middle Triassic (Ladinian): Mahlknecht Cliff, Dolomites,
Italy. After Brandner et al. (1991).
grainstone and packstone) and flat graded grainstones
consisting of redeposited platform-interior and
platform-margin carbonate sands at the toe-of-slope.
Turbidites exhibiting units of the Bouma Sequence
occur in a proximal and distal position. The latter are
characterized by thin grainstone and packstone beds
with skeletal grains and peloids.
The samples shown in Fig. 15.24 are constituents of
foreslope breccias forming platform margin to basin
intercalations within slope sediments (See Fig. 14.17).
Most of the allochthonous material was eroded from
platform and platform-margin limestones. The eroded
material was transported by debris flows and rockfalls
to the slope. Erosion was triggered by sea-level fluc-
tuations. See Pl. 115/2 for another picture of these al-
lochthonous carbonates.
15.7.3.3 Jurassic of Morocco:
PlatformSlopeBasin Transect
A platform-slope-basin system formed during the Late
Jurassic in the Tabas area of eastern central Iran is a
good example of microfacies types of low-angle slope
carbonates (Fürsich et al. 2003; Fig. 15.25). The ex-
port of platform material into the slope and basin is
interpreted as highstand shedding related to relative sea-
level fluctuations. The slope contains a mixture of al-
lochthonous and autochthonous sediments. Autochtho-
nous sediments are oncolitic floatstones and rudstones,
and spiculitic wackestones. Mud flow deposits are char-
acterized by large, fragmented or complete fossils float-
ing in a wackestone to packstone matrix, and by bio-
clastic grainstones (debris flows).
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