Microbioerosion - Trace Fossils as Indicators of Sedimentary Environments - page 220

TABLE 1 The Photic Zonation as Reflected by Specific Index Ichnocoenoses

and General Microborer Distribution Characteristics ( Modified from Glaub,
1994; Glaub et al., 2001 ; and Vogel et al., 2008 )

Photic zonation Index ichnocoenoses General characteristics

Euphotic zone
(

Shallow I
(supratidal)

Not yet defined Dominance of

cyanobacteria with sheath
pigmentation

1% surface
illumination)

>

Shallow II
(intertidal)

Fascichnus acinosus/
Fascichnus dactylus

Dominance of
cyanobacteria, vertical
orientation of borings

Shallow III
(subtidal)

Fascichnus dactylus/
Rhopalia catenata
(replacing
“Paleoconchocelis
starmachii”)

Cyanobacteria abundant
and eukaryotes, change
from vertical to horizontal
orientation

Deep Rhopalia catenata

(replacing
“Paleoconchocelis
starmachii”)/
Ichnoreticulina elegans

Dominance of eukaryotes,
mainly rhodophytes and
chlorophytes, horizontal
orientation, chemotrophs
increasing, maximum
diversity

Dysphotic
zone
(0.01-1%
surface
illumination)

Saccomorpha clava/
Ichnoreticulina elegans

Dominance of
chemotrophs, additionally
Ichnoreticulina elegans
and/or Scolecia filosa

Aphotic zone
(

Saccomorpha clava/
Orthogonum lineare

Only chemotrophs

0.01%
surface
illumination)

<

analysis of Ordovician strata showed that the early emplacement of the first
index ichnocoenoses took place during the Late Ordovician ( Vogel and
Brett, 2009 ) and that the scheme can readily be applied to strata as old as the
Silurian ( Vogel et al., 1999 ).
Since microbioerosion analyses can be based on even few very small shell
fragments, it is a particularly suited approach for paleoenvironmental assess-
ments where only limited sample material is available—such as is the case
in drill-core material. Despite this promising potential, corresponding studies
so far remain scarce. Radtke (1998) was the first to identify and interpret micro-
boring trace fossils from a drill-core in an Oligocene limnic-brackish lake set-
ting of Sieblos/Rh¨n, Germany, and Radtke (2007) revealed salinity trends in a
marine-limnic succession recorded in a core of the Oligocene Pechelbronn