Environmental Engineering Reference
In-Depth Information
FIGURE 7
General trace-fossil distribution in glacial environments.
Ar
:
Arenicolites
;
Co
:
Cochlichnus
;
Ch
:
Chondrites
;
Cn
:
Conichnus
;
Di
:
Diplichnites
;
Dc
:
Diplocraterion
;
Dp
:
Diplopodichnus
;
Dt
:
Diopatrichnus
;
Ga
:
Gastrochaenolites
;
Go
:
Gordia
;
Me
:
Mermia
;
Pa
:
Palaeophycus
;
Pl
:
Planolites
;
Rh
:
Rhizocorallium
;
Sk
:
Skolithos
;
Si
:
Siphonichnus
;
Te
:
Teichichnus
;
Th
:
Thalassinoides
;
Un
:
Undichna
.
After
Buatois and Ma´ngano (2011)
.
Table 2 in
http://booksite.elsevier.com/9780444538130
for ichnotaxa and refer-
ences;
Fig. 7
). They generally show a low degree of bioturbation, impoverished
diversity, and diminutive size, when compared with ichnofaunas from normal-
saline environments. These features are typical of brackish-water ichnofaunas
(e.g.,
Buatois et al., 2005
). However, the presence of truly marine, deep-water
ichnogenera (e.g.,
Phymatoderma
,
Zoophycos
) suggest the establishment of
the archetypical
Cruziana
Ichnofacies in deep-water settings, impoverished
due to lowered salinity owing to dilution by glacial meltwaters. The occurrence
of the
Cruziana
Ichnofacies in turbidites, instead of the expected
Nereites
Ichno-
facies, can be explained by the downslope transport of food by turbiditic currents
and mass flows (
Eyles et al., 1992
).
4. ICHNOLOGY OF RECENT GLACIAL ENVIRONMENTS
Little ichnological research has been performed in modern glacial environ-
ments, all of them concentrated in the Arctic regions. The record of bioturbation
in glaciolacustrine and terrestrial environments includes chironomid traces from
sediments of a Norwegian lake in contact with ice (
Duck and McManus, 1984
),
vertebrate and invertebrate traces of a fluvial pointbar in northern Alaska com-
pared to
Treptichnus
,
Cochlichnus
,
Archaeonassa
(
Aulichnites
in
Martin, 2009
),
and
Helminthoidichnites
(
Martin, 2009
), and a low-diversity
Palaeophycus
-
dominated trace-fossil assemblage with rare
Arenicolites
from postglacial
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