Geology Reference
In-Depth Information
Plate 121 Standard Microfacies Types: SMF 16 and SMF 17
SMF 16. Non-laminated peloidal grainstone and packstone and laminated peloidal bindstone
Criteria: Accumulations of very small, grain-supported, subrounded or subangular peloids. Two subtypes are
common: SMF 16N ON LAMINATED , characterized by tiny, equal-sized peloids associated with benthic foramin-
ifera, ostracods or calcispheres. SMF 16L AMINATED is characterized by peloids of different size, forming ir-
regularly distributed fine-grained packstone (pelmicrite), grainstone (pelsparite) and sometimes also packstone
fabrics. An other criterion are wavy micritic laminations. The peloids of SMF 16 are mud peloids, fine-grained
fecal pellets (definitions in Fig. 4.11), and microbial peloids (SMF 16-L AMINATED ). Occurrence: SMF 16-N ON -
LAMINATED is common in shallow platform interiors comprising protected shallow-marine environments with
moderate water circulation (FZ 8) and in inner ramp settings, and may also occur in evaporitic arid platform
interiors (FZ 9A). SMF 16-L AMINATED contributes to the formation of mud mounds and the stabilization of
platform slopes. Additional pictures: Pl. 10/2 (SMF 16-N ON - LAMINATED ), Pl. 66/1 (SMF 16-N ON - LAMINATED ).
SMF 17. Aggregate-grain (grapestone) grainstone
Criteria: Aggregate-grain grainstone. The grainstones and grainstone-rudstones consist predominantly of
arenitic and ruditic lumps and grapestones (see Sect. 4.2.7 for definitions), associated with peloids and some
coated and micritized skeletal grains. Fossils are usually rare, except for a few foraminifera and algae. Occur-
rence: Characteristic for platforms, very rare in ramp settings. FZ 7 and FZ 8 (open and restricted shallow
platforms). Very abundant in isolated platforms of the Bahama type but also occurring in attached platform
settings. Additional pictures: Pl. 15/4, Pl. 15/5, Pl. 15/8, Pl. 43/1.
1
SMF 16N ON LAMINATED . Fine-grained peloid grainstone. Some of the peloids correspond to tiny rounded micrite clasts.
Fossils are very rare except for a few smaller foraminifera. The sample comes from a grainstone bed at the top of a
sedimentary cycle. It represents the shallowest subtidal deposition on a relief formed by algal mounds. Pennsylvanian
(Holder Formation, Virgilian): Alamogordo, Sacramento Mountains, New Mexico, U.S.A.
2
SMF 16N ON LAMINATED . Fine-grained peloidal grainstone. Note the similarity with Fig. 1. Arrows point to 'calcispheres'
(see Sect. 10.2.1.9). The peloids are angular and rounded micrite clasts. The paleoenvironment was a restricted inner
platform lagoon (FZ 8) adjacent to an inner ramp. Early Carboniferous: Belgium.
3
SMF 16L AMINATED . Bindstone consisting of fine-grained laminated peloidal grainstone grading into laminated peloidal
packstone. The sample exhibits distinct alternations of thicker pelsparite layers (PS) and thin pelmicrite (PM) layers
separated by irregular, probably microbial, micrite laminae. This texture is characteristic for mud mounds, slopes, and
protected platform interior environments (FZ 8). Late Jurassic (Oxfordian): High Atlas Mountains, Morocco.
4
SMF 17. Aggregate-grain grainstone. Most grains are micritized aggregate grains (lumps) exhibiting the characteristic
lobate outline. Angular lumps indicate some transport and reworking. The composite grains consist predominantly of
peloids and some bioclasts bound together by microcrystalline calcite. Most grains have rims of thin early-marine cement.
Remaining interparticle pores of the grain-supported fabric were occluded by coarse burial calcite. The sample comes
from a rimmed carbonate platform (FZ 6). This grapestone facies originated within a distance of only a few kilometers
behind the platform edge. Late Triassic (Rhaetian): Steinplatte, Tyrol, Austria.
A
B
Fig. 14.22. Relationship between grapestone facies (SMF 17) and limestone resources. Aggregate grains originate preferentially
in platform settings with moderate but fluctuating water energy, low sedimentation rates and low terrigenous input. The latter
condition and the high amount of interparticle calcite cement are the reason for the formation of chemically high-quality
limestones. The figure shows an example. A: The Late Triassic Dachstein limestones of the Northern Calcareous Alps were
formed on an attached platform (FZ 9 and FZ 8) rimmed by marginal reef complexes (FZ 5, FZ 4, and parts of FZ 7).
Grapestones originated in the back of the reef zone. B: A survey of the Triassic Dachstein limestones revealed that the reef
facies and the grapestone facies have the highest calcium carbonate content, are relatively low in MgCO 3 and contain very
little insoluble residue. These criteria characterize both facies types, particularly the grapestones facies, as targets for the
successful exploration of industrially used pure limestone resources. A and B: Modified from Flügel (1977 and 1981).
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