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Plate 138 Tracing PlatformBasin Relations by Statistical Clusters of Late Triassic Calciturbidites
The plate displays statistically confirmed 'clusters' of calciturbidites occurring within the basinal Norian basinal
Pedata/Pötschen Beds of the Lacke section near the Gosaukamm (Austria). The Pedata/Pötschen limestones are
bedded micritic carbonates with abundant turbidites (packstones and grainstones) and submarine slumping and
sliding structures.
The clusters are defined by cluster analysis and the dominant grain composition and evaluated by factor
analysis and correspondence analysis. The analysis of the total section resulted in the differentiation of seven
clusters. Six clusters (shown in this plate) represent 744 of 747 samples (99.5%). The individual clusters can be
defined by the relative amount of one or more point-count groups compared to the overall means. The source
area of the turbidite grains is deduced from the distribution patterns of platform and reef biota of the Gosaukamm-
Dachstein platform, particularly of foraminifera that are strongly facies-controlled (see Pl. 111).
The grain composition of the calciturbidites indicate alternations of (1) turbidites with predominantly plat-
form-top derived grains (shallow reef, platform interior), and (2) turbidites containing mainly basin-derived
material, planktonic and pseudoplanktonic material in combination with micrite. Factor analysis show that three
factors account for 88% of the total compositional variation. Factor 1 (50% of the total variables) is controlled by
the variable groups representing the open ocean input versus shallow-marine biota and clasts. Factor 2, explain-
ing 27% of the variation, is loaded with clasts and open ocean input. The variation in factor 3 is due to platform
interior material combined with shallow reef biota and micrite. Factors 2 and 3 can be explained as dilution by
mud related to changes in productivity or the supply of grains.
The contrast between the clusters A and B and D, the clusters E and G are best explained as fluctuation
between deep-water sedimentation and platform-derived input, corresponding to pronounced highstand shed-
ding from platforms to deep basins. During the lowstand carbonate productivity was low, and the shallow reef
and platform interior stopped producing carbonate. Sediment deposition was determined by open marine biota
together with material exported from protected and/or somewhat deeper reefs.
1 Cluster A. Calciturbidite characterized by abundant filaments (open-marine biota) and increasing micritic matrix. High
input of open oceanic biota and deep reef biota and low input of shallow reef and platform interior biota. Corresponds to
Standard Microfacies Type SMF 3.
2 Cluster B , characterized by dominance of open-marine biota and low amount of micritic matrix. The arrow points to
Variostoma crassum Kristan, a characteristic foraminifer of the basinal Hallstatt facies. Highest mean input of open ocean
material combined with a minimum of shallow-reef material and non-facies-specific biota. Corresponds to SMF 3.
3 Cluster C. The sediment consists of open ocean originated grains and platform derived grains, embedded in micritic
matrix. Open ocean biota are represented by thin shelled bivalves ('filaments', F) of the Halobia-Posidonia group and the
planktonic alga Globochaete (most tiny globular structures). Platform derived grains are foraminifera (PF). Cluster C
comprises the largest group (399 samples). These turbidites were deposited during the transition from A to B, and D to G.
4 Cluster D. The sediment is characterized by an increase in the input of shallow reef and platform interior material and a
decrease in micritic matrix. Shallow reef material is represented by characteristic reef foraminifera (RF; see Pl. 111) and
peloids reworked from reef cavities. These peloids are characterized by microbially induced calcite rims. Echinoderm (E)
fragments might have had their source area in upper slope environments. Cluster D covers 228 samples. The clusters D, E
and G correspond to SMF 4. Characteristic of high input of shallow-reef and platform interior material and low input of
micritic sediment.
5 Cluster E. As compared with -> 4, the input of platform interior grains is much higher. Note the abundance of platform-
derived foraminifera (PF) and echinoderms (E) associated with shallow-reef foraminifera (RF) a few cemented reef-
derived lithoclasts (LC) and reworked reef crusts (RC). Clusters E and G are dominated by the high input of platform-
originated grains like clasts, platform interior grains and shallow reef biota. Cluster E is more pronounced in that respect
than cluster G.
6 Cluster G . High input of platform derived grains (small peloids), platform interior material (foraminifera) and reef mate-
rial (black fragments). Note the occurrence of fragmented reef biota comprising recrystallized coralline sponges and reef
crusts (RC), and interreef material comprising pseudopunctate brachiopod shells (B) and echinoderms (E). The increase
in grain size from cluster D to G (-> 4 to -> 6) reflects changes in high-energy conditions.
-> 1-6: Reijmer and Everaars (1991)
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