Deep-Sea Fans - Trace Fossils as Indicators of Sedimentary Environments - page 632

channelized parts of depositional lobes, where the “shallow-water” forms can
be still present. Monaco et al. (2010) distinguished five ichnocoenoses in the
Oligocene-Miocene foredeep and piggy-back basins of the Apennines. They
noted that some ichnotaxa are more abundant in certain settings, for example, Sco-
licia in channelized fan lobes and Arthrophycus strictus in the middle part of the
lobes. It is questionable whether similar relationships can be found in other areas
and deposits of different age. Cummings and Hodgson (2011b) considered the
ratios of pre- to post-depositional forms as the most powerful tool in the charac-
terization of the trace-fossil distribution in different parts of the depositional sys-
tem in the Late Cretaceous-Eocene deep-sea fan sediments of the Basque Basin,
northern Spain. They concluded that the higher diversity and intensity of
bioturbation and domination of the pre-depositional forms is typical of marginal
parts of channel environments and lobes, while the axial part of channels displays a
lower diversity of trace-fossil assemblages dominated by post-depositional forms.
In the axial part of lobes, post-depositional forms exclusively occur with a dom-
inance of Ophiomorpha . Moreover, fan fringe deposits are characterized by highly
diverse trace-fossil assemblages with both pre- and post-depositional forms, while
the basin-floor fan is dominated by Zoophycos . Such a picture of trace-fossil
distribution is in general consistence with the so-far published data, showing
the differences between the distal and proximal facies (e.g., Heard and Pickering,
2008; Ksi˛˙kiewicz, 1977, Uchman, 2001 ) and the subichnofacies trends pre-
sented above. Phillips et al. (2011) discovered the highest diversity (but generally
low—less than 10 ichnogenera) in the Eocene/Oligocene heterolithic facies of the
Gr`s d'Annot Basin, SE France, which are interpreted as an accumulation of distal
turbidites on a protected slope or channel filling.
Giannetti and McCann (2010) noted a strong dependence of the trace-fossil
distribution on lithology, substrate consistency, and food supply in the
carbonate-rich turbidite succession of the Upper Paleocene in the Zumaia
section, northern Spain. Giannetti (2010) stressed also fluctuations in the rate
of sedimentation as a controlling factor for the same deposits.
6. TRACE-FOSSIL ASSEMBLAGES
The composition and diversity of deep-sea trace-fossil assemblages can record
paleoenvironmental and ecological conditions. Ekdale (1985) distinguished
between K- and r-selected ichnotaxa. K-selected ichnotaxa are produced by
animals adapted to a stable environment with low or moderate ecological stress;
they usually reproduce slowly. Their diversity is high, but their abundance is
relatively low. Graphoglyptids are the best example. Producers of r-selected
trace fossils, mostly opportunists, are adapted to instability and high environ-
mental stress. The morphology of these trace fossils is often simple and their
diversity is low, but their abundance can be high.
In turbidites, K-selected forms are mostly pre-depositional traces, whereas
r-selected forms are normally among the post-depositional burrows ( Tunis and