Microbioerosion - Trace Fossils as Indicators of Sedimentary Environments - page 219

Ordovician ( Pohowsky, 1978 ). Most of these have been established as zootaxa
but often mainly based on the morphology of their traces and thus ichnological
characters (e.g., Pohowsky, 1978 ), leading to taxonomical confusion. This has
partly been resolved by the establishment of respective ichnotaxa such as
Pennatichnus , Iramena ( Fig. 7 F), and Pinaceocladichnus by Boekschoten
(1970) and Mayoral (1988) . Their possibly considerable potential as paleoen-
vironmental indicators has, however, not been explored to date.
4. PALEOENVIRONMENTAL SIGNATURES
4.1 Paleobathymetry
The investigation of microendolithic ichnocoenoses has been shown to be a
strong tool for judging light availability and hence relative bathymetry in both
modern and ancient environmental settings. This is based on the photoautotro-
phic character of many euendoliths and their specific low-light tolerance limit
and light optimum, resulting in a distinct vertical zonation pattern. Cyanobac-
teria dominate the shallow euphotic zone in the supratidal to shallow subtidal
range, chlorophytes are most abundant in the deep euphotic to dysphotic zone,
and exclusively chemotrophs occur in aphotic depths ( Akpan and Farrow, 1984;
Budd and Perkins, 1980; Golubic et al., 1975; G¨nther, 1990; Perkins and
Tsentas, 1976 ). From the intertidal toward the supratidal zone, this distribution
pattern is complemented by a gradual decrease in endolithic biodiversity
governed by the varying ability of the euendoliths to tolerate strong UV fluxes,
partial desiccation, and rainfall ( Hoffman, 1985; Le Campion-Alsumard, 1978;
Radtke et al., 1996 ). This vertical distribution pattern was translated into a set of
bathymetric index ichnocoenoses ( Table 1 ) defined by the co-occurrence of
specific key ichnotaxa and supported by general characteristics of the ichnocoe-
noses ( Glaub, 1994; Glaub et al., 2001; Vogel et al., 1995, 2008 ). For high-
latitude settings, Cavernula pediculata has been suggested as substitute for
the rare Fascichnus acinosus ( Wisshak, 2006 ). In addition, it is desirable to
nominate Rhopalia catenata as a replacement for the problematic “ Paleoconch-
ocelis starmachii ” based on the main occurrence of its producing chlorophyte,
Phaeophila dendroides , in the shallow euphotic III to deep euphotic zone and its
reasonably wide stratigraphic and biogeographic range.
Case studies in various modern tropical to high-latitude settings confirmed a
remarkable consistency in the zonation pattern of the ichnocoenoses despite
considerable latitudinal telescoping leading to a condensed photic zonation
in high latitudes (e.g., Gektidis, 1997; Gektidis et al., 2007; Glaub, 2004; Glaub
et al., 2002; Vogel et al., 2000; Wisshak, 2006; Wisshak et al., 2005, 2011 ). In
parallel, the ichnocoenosis scheme has successfully been applied to a variety of
fossil carbonate factories throughout the Phanerozoic, allowing, for instance, a
comparison of the relative bathymetry of prominent reef occurrences and
corresponding faunal associations in the Silurian, Permian, Triassic, and Juras-
sic (summarized in Vogel et al., 1995, 1999 ). An extensive microbioerosion