Archaeocyath Sequence Biostratigraphy

Stratigraphic studies of South Australian archaeocyaths (Gravestock 1984; Debrenne and Gravestock 1990; Lafuste et al. 1991; Zhuravlev and Gravestock 1994) and tax-onomic revision of the whole class (Debrenne et al. 1990; Debrenne and Zhuravlev

1992) provide sufficient information to assess the distribution of archaeocyath species within a sequence stratigraphic framework.

The four sequences are depicted in figure 6.4 with a relative sea level curve for the Arrowie and Stansbury basins. Archaeocyath assemblage zones (Zhuravlev and Gravestock 1994) are shown at the base of the figure, and the number of species within each zone is depicted in columns. Older trace and shelly fossil occurrences are also shown. Horizontal scales are arbitrary, as is the relative sea level curve, although de-

Figure 6.4 Arrowie and Stansbury Basin archaeocyath assemblage zones, species diversity, sequences, and relative sea level curve.

piction of increasing water depth through the Early Cambrian (dashed envelope in figure 6.4) is in accord with a generally transgressive setting. This envelope represents a second-order cycle of sea level change from the terminal Proterozoic to late Botoman, an estimated 20-25 m.y.; thus each third-order sequence spanned about 5 m.y.

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