Environmental Engineering Reference
In-Depth Information
3.1 Sediment Types
(Hemi)pelagic sediments may differ regarding their lithology. It is not clear if
the lithology itself is a significant factor influencing burrowing organisms. Bur-
rows are better preserved in calcareous than in muddy sediments (
Berger et al.,
1979
). Radiolarites, made of spiny sediment particles, would theoretically influ-
ence burrowing organisms and display the same trace-fossil content as the other
(hemi)pelagic sediments (e.g.,
Kakuwa, 2004
). The ichnological record is pos-
itively or negatively affected by diagenesis because this process can enhance or
reduce color differences between burrows and host sediment.
Trace fossils can help to distinguish between deep-water and shelf equivalents
of the same (hemi)pelagic facies (e.g.,
Ekdale and Bromley, 1984; Monaco,
1995
). The former authors proposed to distinguish between deep-sea Cretaceous
chalk containing
Zoophycos
and shelf chalk with
Thalassinoides
.
3.2 Sediment Consistency
The margin of burrows stores information about the sediment consistency. In
addition, the porosity of the substrate during trace-fossil production can be esti-
mated by measuring the actual porosity and the compaction-induced deforma-
tion of a trace fossil (
Wetzel and Aigner, 1986
). Direct observations allow
distinction of six categories (
Wetzel and Uchman, 1998b
).
Looseground
:
Tubes within loose grains of sandy substrates are stabi-
lized by a mucus lining (e.g.,
Skolithos
) or by a pellet-armed wall (e.g.,
Ophiomorpha
).
l
Soupground
:
Animals “swim” through the sediment producing biode-
formational structures and produce burrows having characteristic “man-
tle and swirl” appearance in cross section (
Lobza and Schieber, 1999
), or
assemble a “floating pile foundation” in suspension-rich settings (
Wetzel
and Bromley, 1996
).
l
Softground
:
Thin-walled (e.g.,
Palaeophycus
) or pelleted tubes are stable.
l
Stiffground
:
Unlined tunnels are stable (e.g.,
Thalassinoides
,
Zoophycos
).
l
Firmground
:
Animals use body appendages to burrow, and burrow
margins often exhibit a sculptured ornamentation (e.g.,
Spongeliomorpha
).
l
Zoophycos
producer (
Wetzel and Aigner, 1986
). (B) Sand (light) resting on mud (dark); sand has
filled up the open burrows (
Gl
) typical for
Glossifungites
surfaces; the sand has been intensely bio-
turbated. X-ray radiograph (negative). Institute of Geosciences Kiel, Germany, core 16384-2
(61
57.55
0
N, 11
53.15
0
W), 310-320 cm (Late Pleistocene), southern flank of the Iceland-Færø
Ridge at 1255 m water depth. IRD, ice rafted debris;
Th
,
Thalassinoides
;
Sk
,
Skolithos
. (C) Modern
hiatus horizon produced by bottom currents that traverse a seamount chain within the South China
Sea (14
52.4
0
N, 118
35.4
0
E; 3,940 m water depth; core SO 114-16; for details, see
Wetzel, 2008
).
The sediment has been partly eroded and the surface has become stained by Fe- and Mn-oxides.
A stiff sediment consistency is indicated by the numerous open burrows and the ornamentation
of the burrow margins by claw-sculptures (arrow). (D, E) Vertical (D) and horizontal (E) section
through a bottom-current-affected omission surface (Late Cretaceous, Prealpes medianes,
Switzerland); interconnected U-shaped tubes (arrows mark deviations) were produced in a stiffened
substrate; later overprint by pressure solution.
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