Geology Reference
In-Depth Information
SMF Types are valuable tools in facies analysis but
do not demand too much from these virtual units. Be
careful in solely using distribution patterns of SMF and
RMF assemblages to recognize and trace facies zones
of shelf-basin transects and
• Discriminate samples showing bindstone/lamination
fabrics, breccia fabrics, shell and echinoderm concen-
trations, and signs of autochthonous reef growths from
other samples.
-- Bindstone and lamination fabrics : These fabrics
characterize the SMF Types SMF 16-L AMINATED (ir-
regular pelmicrite and pelsparite layers consisting
of peloids of different size), SMF 19 (consisting of
couplets of finer micritic laminae and somewhat
coarser pelsparitic laminae), SMF 20 (planar or vari-
ously dome-shaped fine- and coarse-grained lami-
nae), SMF 21 (laminated fenestral spar-filled cavi-
ties within a framework formed by sedimentary and
biogenic grains; note that the fenestral fabrics also
occur in limestones without lamination) and SMF 25
(alternation of fine-crystalline calcimudstone or
dolomicrite layers and evaporitic layers with gyp-
sum or anhydrite).
-- Breccia fabrics are developed in SMF 4 (micro-
breccia consisting of skeletal grains and lithoclasts,
often graded), SMF 5 (fine-grained breccia with a
check your interpretations based on microfacies
types against outcrop criteria (e.g. lithofacies, sedi-
mentary structures),
examine the assignment to specific facies zones in
the context of paleontological and palecological data,
and
do not fit your data to the model instead of doing the
other way round!
14.3.6 Determining Standard Microfacies
Types: A Practical Guide
Having avoided the pitfalls shown in Pl. 127 and dis-
cussed in Sect. 14.3.2, you are ready to determine the
SMF Type of your samples. Take the following steps!
Mudstone Calcisiltite
Wackestone
Floatstone
Packstone
Grainstone
Rudstone
3 Abundant
2 Micro
1 Sponge
5 Densely
1 Sponge
5 Densely packed
4 Microbreccia,
planktonic
bioclastic
spicules, often
packed whole
spicules, often
whole fossils
small bio and
microfossils
peloidal
calcisiltite
fossils and frag
calcisiltite matrix
and fragments,
lithoclasts
23 Micrite or
finegrained
matrix
ments of
4 Microbreccia,
often reef or
5 Densely
microsparite
packstone/
3 Abundant
fossils, often
small bio and
platformderived
packed whole
without
grainstone
planktonic
reefderived
lithoclasts
11 Abundant
fossils, often
fossils
fabric
microfossils
8 Whole fossils,
5 Densely packed coated skeletal
reef or plat
8 Whole fossils,
fine bioclastic
whole fossils
grains
formderived
fine bioclastic
micrite matrix
and fragments,
13 Millimeter to
6 Millimeter to
micrite matrix
22 Millimeter
often reef or
centimetersized
centimeter
9 Abundant frag
to centimeter
platformderived
oncoids with
sized reef
ments of fossils,
sized agglut
10 Abraded
tubelike
derived bio
bioturbation
inated oncoids
and worn
structures
clasts and
10 Abraded and
24 Millimeter
skeletal grains
15-C Ooids with
fossils
worn skeletal
to centimeter
16- N ON LAMINATED
concentric
13 Millimeter
grains
sized litho
Very small
structures
to centimeter
15-M Scattered
clasts
equallysized
15-R Ooids with
sized oncoids
micritic ooids
peloids
radial or radial
with tubelike
22 Millimeter to
18 Abundant
concentric
structures
centimetersized
rockbuilding
structures
24 Millimeter
agglutinated
benthic foramin
16 NON LAMINATED
to centimeter
oncoids
ifera or calcar
Equallysized
sized litho
eous algae
peloids
clasts
21 Sparfilled
17 Abundant
26 Pisoids
voids within a
aggregate grains
micritic or pelmi
18 Abundant rock
critic framework
building benthic
26 Pisoids
foraminifera or
calcareous algae
Box 14.7. Key to the determination of Standard Microfacies Types . The key does not include reef limestones, carbonates with
bindstone/lamination fabrics, and limestones exhibiting concentrations of shells or echinoderms (see text for explanation).
Start with attributing your sample to texture types and continue with the search for SMF Types characterized by adequate
criteria.
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