Hemipelagic and Pelagic Basin Plains - Trace Fossils as Indicators of Sedimentary Environments - page 653

(e.g., Gage and Tyler, 1991; Lopez et al., 1989; Rex, 1983 ). Concomitantly,
(hemi)pelagic deep-sea deposits were interpreted ecologically, based on their
trace-fossil content ( Ekdale, 1985; Ekdale and Mason, 1988; Leszczy´ski
and Uchman, 1991, 1993; B˛k, 1995; Wetzel and Uchman, 1998a, 2001;
Rodr´guez-Tovar and Uchman, 2004; Rodr´guez-Tovar et al., 2010 ).
Bioturbational structures store information about the ecological conditions
during their production, but in turn, the endobenthic animals disturb the origi-
nally layered sedimentary record. In particular in Pleistocene andHolocene sedi-
ments of the ocean basins, bioturbation has been studied to better understand the
effects of vertical mixing, so as to improve the accuracy of paleoceanographic
and paleoclimatic investigations (e.g., Berger and Heath, 1968; DeMaster
et al., 1991; Smith and Rabouille, 2002; Trauth et al., 1997 ). The analysis of ver-
tical displacement of tracer particles by burrowers led to a better understanding
of the bioturbation process and the behavior of the producers (e.g., Kotake, 1989;
L ¨ wemark and Werner, 2001; Wetzel, 2002 ). Similarly, the preservation poten-
tial of event layers has been addressed (e.g., Bentley et al., 2006; Ruddiman and
Glover, 1982; Wetzel, 2009; Wheatcroft, 1990 ). In these terms, the recoloniza-
tion of the sea floor after event bed deposition or an ecological disaster has been
evaluated (e.g., Ingole et al., 2005; Thiel, 1992 ).
Mixing also enhances the flux of oxygen and water into the sediment and
extends the zone of organic-matter remineralization and hence plays an impor-
tant role with respect to global biogeochemical cycles ( Chester, 2000 ). Thus,
the bioturbational processes affect diagenesis (e.g., Bromley et al., 1975; Savrda
et al., 2010 ). The purpose of this chapter is to give an overview of the ichnology
and the ecological interpretation of hemipelagic and pelagic deposits as well as
to provide examples of the ichnological record of some deep-sea processes and
phenomena.

2. ICHNOLOGY
2.1 Aspects Regarding the Bioturbated Zone
To quantify burrowing activity, bioturbation has been described as a diffusion-
like process comprising an infinite number of small random steps (e.g.,
Boudreau, 1986a ), but also non-local, long-range vertical transport was consid-
ered ( Boudreau, 1986b; Boudreau and Imboden, 1987 ). Within the so-called
surface mixed layer, the sediment is churned by burrowing organisms so effec-
tively that even short-lived radioisotopes exhibit a roughly constant concentra-
tion; below the mixed layer, the radiotracer concentration decreases
exponentially (e.g., DeMaster et al., 1991 ; Fig. 1 ). For modern, stable oceanic
environments, the mean thickness of the mixed layer has been estimated to be in
the range of 9.8 4.5 cm ( Boudreau, 1998 ). At a specific site, however, the

thickness of the mixed layer was found to be related to the flux of organic matter
to the sea floor (e.g., Smith and Rabouille, 2002; Trauth et al., 1997 ). Therefore,