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FIGURE 2
Examples of invertebrate ichnotaxa with biostratigraphic significance in marginal-
marine rocks. (A)
Climactichnites wilsoni
. Upper Cambrian, Postdam Group, slab exhibited
at the Smithsonian Institution. Scale bar
¼
10 cm. (B)
Heimdallia chatwini
. Ordovician, Peninsula
Formation, Table Mountain Group, Matjiesgloof Farm, South Africa. Pencil
¼
14 cm long.
Hagadorn, 2008; Yochelson and Fedonkin, 1993
), though with a highly
restricted paleogeographic distribution (
Jensen et al., in press
). The wall-like
trace
Heimdallia
(
Fig. 2
B) records sophisticated sediment handling and is
apparently restricted to Late Ordovician-Early Carboniferous strata, with
various ichnospecies displaying even more restricted ranges (e.g.,
Heimdallia
zigzag
in the Lower Silurian) (
Seilacher, 2007
). The ichnospecies
Treptichnus
pedum
, indicative of the Proterozoic/Cambrian boundary (see below), is
typical of shallow to fully marine deposits but also has been recorded in
marginal-marine environments (
Geyer and Uchman, 1995; MacNaughton
and Narbonne, 1999
). Similarly, some ichnospecies of
Cruziana
and
Rusophycus
may occur in brackish-water settings, expanding the environ-
mental range of application of
Cruziana
stratigraphy (
M´ngano and
Buatois, 2003
) beyond its more typical shallow-marine application (see
Section 4.2).
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