Environmental Engineering Reference
In-Depth Information
McCall and Tevesz, 1982; Uchman and
ยด
lvaro, 2000; White and Miller, 2008
).
These vertical to inclined biogenic structures in lacustrine settings do not cor-
respond to the
Mermia
Ichnofacies (
White and Miller, 2008
). In contrast, they
may be best assigned to the continental
Skolithos
Ichnofacies (
Fig. 3
), based on
their morphology and vertical orientation. These diminutive types of
unbranched, branched, and U-shaped vertical burrows were assigned to the
Arenicolites
suite by
Bromley and Asgaard (1979)
, who later erected the
Arenicolites
Ichnofacies (
Bromley and Asgaard, 1991
). However, the differen-
tiation between the
Arenicolites
Ichnofacies and the
Skolithos
Ichnofacies at
present is not possible because the traces are the same morphologically.
With further documentation of case studies from fully lacustrine settings, it
may be possible to define new ichnofacies and/or subdivide the
Mermia
Ichnofacies and to clarify the significance of the diminutive trace types of
the
Skolithos
Ichnofacies in these settings. For instance,
Voigt and Hoppe
(2010)
recognize the mutual exclusion of assemblages of simple grazing trails
from high-density examples of 3D burrow networks in the sublittoral zone of a
freshwater lake. In order to recognize some of the variability within the ichno-
facies most common in lake basins, it is possible to group ichnogenera based on
similarities in their morphology, size, orientation, and preservational style
(
Table 2
). These groups are informal and should not be considered as subdivi-
sions of ichnofacies, but they are useful for comparisons among the dominant
assemblages preserved in different lake types. This approach may also provide a
way to discuss some of the discrepancies between biological and ichnological
data, between modern and fossilized traces in lake basins, and between exam-
ples associated with marginal-marine, freshwater-influenced marine, fully
lacustrine, lake margin and alluvial environments.
FIGURE 3
Box diagram showing the continental
Skolithos
Ichnofacies. The ichnofacies can be
informally grouped by similar morphologies, sizes, and orientations that show common associations
between ichnotaxa (see
Table 2
). Diminutive branched and unbranched vertical burrows (Group 1):
Sk
,
Skolithos
;
Ar
,
Arenicolites
;
Po
,
Polykladichnus
. Medium-sized vertical and U-shaped traces
(Group 2):
Sk
,
Skolithos
;
Ar
,
Arenicolites
; Es, escape traces. Large-sized branched and unbranched
vertical burrows (Group 3):
Sk
,
Skolithos
;
Ps
,
Psilonichnus
.
Search WWH ::
Custom Search