Geology Reference
In-Depth Information
14.2.2 Case Study: Foraminiferal Distribu-
tion in Late Triassic Reefs and Platforms
Benthic foraminifera are common constituents of
Late Triassic platform and reef carbonates. They have
proved to be extremely useful in recognizing facies
zones. Open and restricted platforms (Facies Zones
FZ 7 and FZ 8), platform margins and foreslope envi-
ronments (FZ 6, 5 and 4) as well as individual parts of
reef complexes can be differentiated and subdivided
by distinct foraminiferal assemblages. The concept was
Distributional patterns of benthic foraminifera evalu-
ated in thin sections of shelf carbonates are important
tools in subdividing facies zones of platform, ramp and
reef environments, particularly in Mesozoic and Early
Tertiary sediments.
Fig. 14.13.
Distributional patterns of benthic foraminifera
are successfully used in recognizing and subdividing facies zones
and environments of carbonate platform and reef complexes. The example from the Rötelwand near Adnet (Austria) shows
the distribution of foraminiferal assemblages in a small patch reef formed on a swell within a muddy shallow intraplatform
basin. The facies zones of these Late Triassic limestones are defined by dominating grain types, biota and limestone textures.
The central reef facies is characterized by coralline sponges, scleractinian corals and interstitial reef debris. Note the asymmetric
facies pattern, comprising bioclastic grainstones of a near-reef oncolithic grapestone facies and an algal-foraminiferal facies
at the leeward side, and a mud facies with reef detritus (packstones, wackestones) grading into a marly lime mud facies
(wackestones, mudstones) surrounding the reef. The facies zones are distinguished by specific taxa, assemblage composition
and relative frequency of taxa. Some of the diagnostic foraminifera are depicted in Pl. 111. Length of the section about
1.5 km. Modified from Schäfer and Senowbari-Daryan (1981).
