Geology Reference
In-Depth Information
•
Cell assemblages (e.g.
Bacinella, Ladinella, Thau-
matoporella
)
organic matter.
Archaeolithoporella
also occurs as nod-
ules ('tebagite': Razgallah and Vachard 1991).
Distribution:
Archaeolithoporella
is known from the
Sakmarian to the Latest Permian. The genus is widely
distributed in the western and southwestern Tethys
(Slovenia, Sicily, Greece, Tunisia, Oman), in oceanic
microcontinent settings (Japan, China), and in marginal
basins of Panthalassa (Texas and New Mexico). The
genus is a common constituent of Permian shallow sub-
tidal reefs (e.g. Permian Reef Complex in Texas; Pl.
145/1), often associated with coralline sponges (Fig.
10.59) and with
Tubiphytes
. Together with syngenetic
aragonitic cements,
Archaeolithoporella
formed wave-
resistant structures (Fig. 10.59).
Archaeolithoporella
crusts originated in various settings, including shelf
edge, platform margin, forereef, and upper slope.
Archaeolithoporella
does not seem to be totally depen-
dent on lightened areas, as shown by the occurrence
within syngenetic fissures and cryptic cavities.
Interpretation:
The genus has been interpreted as
red algae, stromatolitic algae, remains of microbial mats
•
Differentiated crusts and plates (e.g.
Lithocodium
,
Palaeoaplysina
).
10.2.6.2 Discussion of Selected
Microproblematica
The following alphabetic discussion of the morphol-
ogy and systematic assignment is restricted to some
microproblematica that are of importance for paleoen-
vironmental and sedimentological interpretations.
Archaeolithoporella
Endo (Pl. 42/1, Pl. 98/8, Pl. 145/1)
Morphology:
Millimeter- to centimeter thick encrus-
tations on hard substrates (fossils, clasts, marine car-
bonate cement) consisting of alternating couplets of
dark micritic layers and slightly thicker layers of fi-
brous or blocky calcite. Micritic layers may contain
Plate 97 Rare ThinSection Fossils
The plate displays fossils which are not common in thin sections of limestones, but, if present, may be important
in microfacies analysis.
1
Placoderm bonebed.
Placoderms are a group of fresh-water and marine fishes with primitive jaws bearing tooth-like
body plates and variously armored heads and bodies. The group appeared in the Late Devonian, flourished in the Devo-
nian and disappeared in the Early Carboniferous. Thin sections of limestones yield bone plates exhibiting characteristic
double-layered microstructures. The sample is a calcareous sandstone. Early Devonian (Odenspieler bed): Bergisches
Land, Germany.
2
Placoderm microstructure.
The placoderm plates are characterized by two layers represented by an inner vesicular (white
arrows) and an outer, more compact finely vesicular structure (black arrows). Same locality as -> 1.
3
Fish scales.
Cross section of numerous thin and flat scales appearing black in transmitted light. The arrows point to
shapes that are characteristic in thin sections. Early Jurassic (Lias epsilon): Hetzles near Erlangen, Germany.
4
Fish tooth
and fish bones
. The black arrow points to a longitudinal section of a tooth of predatory sharks, the white arrow
to oblique sections of fish bones. Shark teeth are characterized by sharply pointed shapes. Late Tertiary (Miocene):
Saykamt, Turkey.
5
Graptolites.
In contrast to the common deposition of graptolites in euxinic basins, graptolites may also accumulate in
shallow-marine pelagic carbonate environments. Silurian (Fluminimaggiore Formation, Wenlock): Southwestern Sardinia,
Italy.
6
Conodonts:
Oblique section of
Polygnathus
. The sample comes from a strongly recrystallized limestone consisting
predominantly of reef debris. Late Devonian: Rugendorf, Frankenwald, Germany.
7
Conodonts morphology.
Free blade (arrow) and platform posterior of
Polygnathus.
The phosphatic conodonts appear
black or brown in transmitted light . The sample is from a pelagic cephalopod limestone. Late Devonian: Elbersreuth,
Frankenwald, Germany.
8
Conodont morphology.
Oblique section of
Polygnathus
ex gr.
P. glabra
. Note carina (ridge with small denticles) and
parts of the platform. Late Devonian (Famennian): Drewer, Sauerland, Germany.
9
Fish scale.
Note distinctive layering (arrow). Middle Triassic (Muschelkalk, Ladinian): Eschenbach, southwestern Ger-
many.
10
Wood.
Length and oblique sections of wood fragments, with a well-defined cellular pattern. Preservation of wood is
facilitated by carbonification or silicification (this example). Small grains within the micritic matrix are terrigenous
quartz. Near-coast mixed siliciclastic-carbonate environment. Middle Jurassic (Bajocian): Morondava Basin, Madagascar.
-> 10: Sample provided by M. Geiger (Bremen)
