Figure 4.
Model of the benthic community response to hypoxia and anoxia during the late Pliensbachian and early Toarcian.
Community maturity stages: III, undisturbed/climax communities; II, transitional communities; I, pioneer/disturbed communities; 0, grossly disturbed communities. Letters refer to biofacies in Figures 2 and 3. Note: the recovery path from Stage 0 to II is different from the decline from Stage III to 0 because of species extinction after prolonged hypoxia and anoxia. The post-anoxia Stage II community (biofacies L) has a different taxonomic composition from the former ones (E, F: Stage II) due to the origination and immigration of new species in the intervening time period. Figure modified from [3].
Figure 1.
Late Pliensbachian to early Toarcian variations in the alpha diversity of benthic ecosystems of the Cleveland Basin.
(A) Simpson index of diversity (1-d). (B) Taxonomic diversity (Δ) in red and taxonomic distinctness (Δ*) in blue. Each point represents the measured value for each sample; the lines were smoothed using the 3-point moving average function. F = Formation; M = Member. Italics indicate ammonite zones and subzones (see text for details). The white and grey bars delimit ammonite subzones. For more details on the lithology see Figure S2.
Figure 2.
(A) Samples labelled and grouped according to their stratigraphic unit and ammonite subzone (see Figure 1). (B) Samples grouped according to the biofacies identified by the CLUSTER analysis (see text for details). (C) Samples grouped according to lithology. Note, because the scaling and orientation of axes in nMDS are arbitrary, the configuration was rotated to have the greatest variation along the first axis.
Table 1.
ANOSIM pairwise test between samples from consecutive stratigraphic units.
Table 2.
ANOSIM pairwaise test between subzones.
Figure 3.
The CLUSTER analysis, together with the SIMPROF test, identified 12 groups of samples (coloured in grey) which are statistically distinct. The thick black lines indicate at which similarity levels the clusters are grouped together by the SIMPROF test. The 12 groups have been interpreted as different benthic biofacies. Coloured bars and symbols indicate the different stratigraphic units and ammonite subzones each sample belongs to (colours and symbols as in Figure 2A).
Table 3.
SIMPER analysis on biofacies and species life habit information.
Figure 5.
Comparison of relative sealevel, palaeotemperature and nMDS axis 2 sample scores through the studied section.
(A) nMDS axis 2 sample scores, each point represents one sample. Colours refer to the different biofacies. (B) Relative sea level curve compiled from [71] and [72]. (C) δ18O isotope values from belemnites, brachiopods and bivalve calcite interpreted as reflecting relative palaeotemperatures; data from [73]–[75]. Triangles: belemnites, squares: brachiopods and bivalves. Stratigraphy as in Figure 1.