Environmental Engineering Reference
In-Depth Information
FIGURE 2
Box diagram showing common ichnogenera of the
Mermia
Ichnofacies. The ichno-
facies can be informally grouped by similar morphologies, sizes, and orientations that show common
associations between ichnotaxa (see
Table 2
). Surface trails (Group 1):
Me
,
Mermia
;
He
,
Helminthoid-
ichnites
;
Go
,
Gordia
;
Co
,
Cochlichnus
;
Ac
,
Archaeonassa
. Arthropod trails and trackways (Group 2):
Wa
,
Warvichnium
;
Cr
,
Cruziana
. Horizontal infaunal burrows and surface tunnels (Group 3):
Pl
,
Pla-
nolites
;
Pa
,
Palaeophycus; Tr
,
Treptichnus
;
Va
,
Vagorichnus
. Resting and feeding traces (Group 4):
Lo
,
Lockeia
. Fish swim and resting traces (Group 5):
Un
,
Undichna
.
freshwater ponds on alluvial plains (
Buatois and MĀ“ngano, 2002, 2004;
Melchor et al., 2006
), very shallow films of water in low-energy lake margins
(e.g.,
Metz, 1996, 2000
), and littoral zones of hypersaline lakes in regions with
freshwater input (
Scott, 2010
). In permanently subaqueous zones of lakes, this
ichnofacies is typically exclusive of elements of the
Scoyenia
Ichnofacies and is
associated with fine-grained deposits in low-energy sublittoral to profundal
zones. In shallow littoral zones or ephemeral water bodies, the
Mermia
Ichno-
facies may be closely associated with other trace-fossil types (e.g., meniscate-
backfilled burrows, vertebrate footprints), as well as a greater variety of
sedimentary structures (e.g., ripple cross-lamination) and indicators of subaerial
exposure (e.g., desiccation cracks). In these cases, the
Mermia
Ichnofacies sig-
nifies standing or gently flowing water, with traces produced in very shallow
subaqueous to saturated substrates. Some examples show the
Mermia
Ichno-
facies in settings influenced by glacial runoff, both in continental (e.g.,
Benner
et al., 2009; Uchman et al., 2009
) and freshwater-influenced marginal-marine
environments (e.g.,
Buatois et al., 2006, 2010; Netto et al., 2012
).
Bivalve locomotion and resting traces (
Lockeia
) are also produced in littoral
to sublittoral zones of freshwater lakes (e.g.,
McCall and Tevesz, 1982; White
and Miller, 2008
) and are presently included in the
Mermia
Ichnofacies. The
backfilled feeding structures of some modern bivalves, such as
Pisidium
(
White and Miller, 2008
), are as yet undescribed in ichnological terms. Other
trace types that have been recorded in low- to moderate-energy littoral to sub-
littoral and profundal zones include those produced by oligochaetes (incipient
cf.
Polykladichnus
isp. and cf.
Labyrintichnus
isp.) and insects such as chirono-
mid larvae or mayfly nymphs (diminutive
Polykladichnus
,
Skolithos
,
Arenico-
lites
,
Beaconites
) (e.g.,
Charbonneau and Hare, 1998; Gingras et al., 2007;
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