Geology Reference
In-Depth Information
Plate 111 Biotic Zonation of ShallowMarine Facies Zones with Benthic Foraminifera: Late Triassic
Platform and Reef Limestones
Reef: Foraminifera of high-growing coral communities
1
Alpinophragmium perforatum
Flügel. The species, known all over the Tethys and from Panthalassan terranes, is charac-
teristic for the central part of Norian and Rhaetian reefs. The fine-agglutinated foraminifer encrusts high-growing corals.
Reef limestone, coral framestone. Triassic (Misfah Formation, Hawasina Group, Norian): Oman Mountains.
Reef: Foraminifera living in millimeter- to centimeter-sized growth cavities and on low-growing reefbuilders (e.g. sphinctozoid
sponges, solenoporacean red algae)
2 Typical reef cavity microfacies with miliolinid foraminifera (1:
Ophthalmidium carinatum
(Leischner);
2:
Galeanella
)
and peloids. Late Rhaetian patch reef: Feichtenstein, Salzburg, Austria.
3 Reef cavity with
Galeanella
(1:
Galeanella
sp.; 2:
Galeanella panticae
Brönnimann et al.) and micrite clasts. This
microfacies occurs in small patch reefs at the margins of intraplatform basins as well as in large platform-marginal reefs.
Same locality as -> 2.
4-5
Galeanella panticae
Brönnimann et al. This miliolinid foraminifer is abundant in protected parts within central reef parts
and occurs also in bioclastic sands deposited in the leeward position of Late Triassic reefs (Facies Zone FZ 7). Norian
(Dachstein reef limestone): Gosaukamm, Austria.
6
'Sigmoilina'
, a common miliolinid foraminifer in the central reef facies. Same locality as -> 4.
7
Ophthalmidium
sp. Common in protected areas between reefbuilders and in mud-rich reefs formed at the upper slope
(Facies Zone FZ 4). Same locality as -> 4.
8
Ophthalmidium triadicum
(Kristan). Oblique section showing the characteristic trumpet-shaped apertura. Common in
boundstones but also in muddy platform areas with reef-derived material (Facies Zone FZ 7). Same locality as -> 5.
9
'Lituosepta'
sp. Common in reef cavitiy sediments and in sediments between reef patches. Rhaetian: Same locality as -> 2.
10
Kaeveria flügeli
(Zaninetti et al.) Common agglutinated foraminifera in protected reef areas. Same locality as -> 4.
Back-reef and near-reef carbonate platform
11 Duostominidae. These foraminifera, characterized by trochospiral tests with microgranular walls, are concentrated in
platform carbonate sands (Facies Zone FZ 7). They are associated with involutinid foraminifera and dasyclad green
algae. Norian (Bedded Dachstein limestone): Dachstein area, Austria.
12 '
Tetrataxis' nanus
Kristan-Tollmann. The genus is most common in platform environments, but also occurs in muddy
shelf limestones (Facies Zone FZ 8). Rhaetian (Kössen beds): Steinplatte, Tyrol, Austria.
13
Glomospira
and
Glomospirella
are difficult to discriminate in thin sections. The genera are characterized by a streptospirally
enrolled second chamber that later becomes planspirally coiled, forming a discoidal test.
Glomospirella
has been re-
garded as agglutinated foraminifera but has now been assigned to the involutinids. Common in platform and backreef
carbonates (FZ 7), associated with other involutinids and dasyclads. Same locality as -> 4.
14 Biserial agglutinated foraminifera, attributed to
Textularia
, are more common in platform sediments than in the reef
facies. Same locality as -> 12.
Platform environments
15
Triasina
grainstone.
Triasina
Majzon is a widely distributed involutinid foraminifer in open-marine far-reef platform
carbonates (FZ 7). Note the different preservation of the primarily aragonitic tests. Late Triassic (Rhaetian): Extraclast
within an Upper Jurassic breccia. Gschöllkopf, Sonnwendgebirge, Northern Alps, Austria.
16
Aulotortus communis
(Kristan-Tollmann), an abundant involutinid foraminifera in grainstones of Late Triassic platforms
(FZ 7). Norian (bedded Dachstein limestone): Gosaukamm, Austria.
17
Aulotortus sinuosus
Weynschenk. Subaxial-axial section. The species occurs in backreef sands as well as in platform
calcarenites and shallow basins. Note the characteristic sickle-shaped chambers. Rhaetian (Kössen beds): Loferbachgraben,
Salzburg, Austria.
Deeper shelf carbonates
18 Encrusting textularinid foraminifera.
Tolypammina gregaria
Wendt. Various attached foraminifera are common constitu-
ents of peloidal muddy carbonates deposited in deeper areas in front of reefs (FZ 4) or in low-energy platform areas
(FZ 8). The foraminifer encrusts bioclasts and acts as binder of sediment grains, sometimes forming oncoids. Rhaetian:
Ehrenreit, Bavaria.
19
Planiinvolutina carinata
Leischner. Attached, probably miliolinid foraminifera. Intraplatform shelf limestone. Same
locality as -> 14.
20
Trochammina alpina
Kristan. The trochospiral tests of this agglutinated foraminifer is most common in micritic lime-
stones (deeper shelf carbonates and protected micritic parts of the inner platform (FZ 8), mud-rich reefs of the upper
slope, FZ 4). Rhaetian: Gruber reef near Hallein, Austria.
21 '
Endothyranella
'. Muddy shallow-basinal limestones. Rhaetian (Kössen beds): Hochalm, Tyrol, Austria.
Far-reef carbonates
22
Agathammina austroalpina
Kristan-Tollmann and Tollmann. This miliolinid or finely agglutinated textulariniid fora-
minifer is abundant in far-reef peloidal muddy settings (FZ 8) and in open-marine inner platform areas (FZ 7). Same
locality as -> 17.
23
Austrocolomia marschalli
Leischner, a lagenid foraminifer. Note the gradually enlarging chambers and wall with costae.
Rhaetian (Kössen beds): Gaissau, Salzburg, Austria.
24 '
Turrispirillina'
sp. Muddy slope (FZ 4) and basinal facies. Norian (Plattenkalk): Gosaukamm, Austria.
