Types of Ichnofacies
The trace fossils have remained in appearance rather constant since Cambrian,
even if their producers might have been different. The trace fossil assemblages
can be divided according the palaeoenvironmental scheme into a number of
ichnofacies named after a characteristic trace fossil. The ichnofacies
indicate a particular sedimentary facies and can be identified on the basis
of its trace fossil assemblage
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The typical position of the major ichnofacies in
marine and continental environments: Cr - Cruziana; G - Glossifungites;
N - Nereites; Ps - Psilonichnus; Sc - Scoyenia; Sk
- Skolithos; Te - Teredolites; Tr - Tripanites; Z - Zoophycos
(after Benton & Harper, 1997)
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Woodground |
Rockground |
Firmground |
Loose- and softground |
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Sedimentology / environment |
Marine |
Freshwater |
Freshwater |
Marine |
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Energy |
Bathymetry |
Grainsize |
Teredolites
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Trypanites
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Glossifungites
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Scoyenia
|
-
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Psilonichnus
|
|
-
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Backshore |
Sand
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Rusophycos?
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Skolithos
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High
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Beach
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Sand
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-
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Arenicolites?
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Arenicolites
|
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Event
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Shelf
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Sand silt
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Fuersichnus?
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Cruziana
|
|
Medium
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Lagoon /
shelf
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Sand, silt
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Mermia
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Nereites
|
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Event
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Slope to
abyssal
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Sand, mud
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Zoophycos
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Low
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Mud
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Scheme indicating relationships of ichnofacies with
environment (after Bromley, 1996).
Nereites Ichnofacies
The Nereites Ichnofacies is recognized by the presence of meandering
pascichnia (Nereites, Neonereites and Helminthoide),
spiral pascichnia (Spirorhaphe), and agrichnia (Paleodictyon
and Spirodesmos). Vertical burrows are almost entirely absent.
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Nereites Ichnofacies viewed in pelagic carbonate
ooze.
(after Benton & Harper, 1997)
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This ichnofacies indicates deep-water environments, including ocean floors
and deep marine basins. The trace fossils occur in muds deposited from
suspension, and in the mudstones and siltstones of distal turbidites.
Zoophycos Ichnofacies
The Zoophycos Ichnofacies is characterized by complex fodinichnia
(Zoophycos, and sometimes other deep traces such as Thalassinoides)
in tiered arrangements.
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(after Benton & Harper, 1997)
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The ichnofacies occurs in a range of water depths between the abyssal zone
and the shallow continental shelf, in normal background conditions of sedimentation.
The Nereites Ichnofacies may be a matching association found at
similar water depths during times of turbidite (event) deposition.
Cruziana Ichnofacies
The Cruziana Ichnofacies shows rich trace fossil diversity, with
horizontal repichnia (Cruziana and Aulichnites), cubichnia
(Rusophycus, Asteriacites and Lockeia), and vertical burrows.
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(after Benton & Harper, 1997)
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This ichnofacies represents mid and distal continental shelf situations,
below normal wave base, but may be affected by storm activity.
Skolithos Ichnofacies
The Skolithos Ichnofacies can be recognized by a low diversity of
abundant vertical domichnia burrows (Skolithos, Diplocraterion
and Arenicolites), fodinichnia (Ophiomorpha), and
fugichnia.
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(after Benton & Harper, 1997)
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All these traces typically indicate intertidal situations where the organisms
have to be able to respond rapidly in stressful conditions. The Skolithos
Ichnofacies was at first seen as occurring only in the intertidal zone,
but it is also typical of other shifting sand environments, such as the
tops of storm sand sheets and the tops of turbidity flows.
Psilonichnus Ichnofacies
The Psilonichnus Ichnofacies shows a low diversity assemblage of
small vertical burrows with basal living chambers (Macanopsis),
narrow sloping T-shaped and Y- shaped burrows (Psilonichnus), root
traces, and vertebrate footprints.
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(after Benton & Harper, 1997)
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This ichnofacies is typical of backshore, dune areas, and supratidal flats
on the coast
Scoyenia Ichnofacies
The Scoyenia Ichnofacies is characterized by a low diversity trace
fossil assemblage, mainly simple horizontal fodinichnia (Scoyenia
and Taenidium), with occasional vertical domichnia (Skolithos)
and repichnia produced by insects or freshwater shrimps (Cruziana,
Isopodichnus).
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(after Benton & Harper, 1997)
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The traces are preserved in fluvial and lacustrine sediments, often in
the silts and sands of redbed sequences. Associated subaerial palaeosoils
and aeolian sands may contain domichnia and repichnia of insects, and dinosaur
and other tetrapod foot-prints.
Glossifungites Ichnofacies
The Glossifungites Ichnofacies is characterized by domichnia
(Glossifungites and Thalassinoides) and sometimes plant root
penetration structures. Other behavioural trace fossil types are rare.
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(after Benton & Harper, 1997)
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The traces occur in firm, but not lithified sediments, such as muds and
silts in marine intertidal and shallow subtidal zones. The firm grounds
may develop in low energy situations such as salt marshes, mud bars, of
high intertidal flats, or in shallow marine environments where erosion
has stripped off superficial unconsolidated layers of sediment.
Trypanites Ichnofacies
The Trypanites Ichnofacies is characterized by domichnial borings
of worms (Trypanites), bivalves (Gostrochaenolites), barnacles
(Rogerella) and sponges (Entobia).
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(after Benton & Harper, 1997)
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These are formed in shoreline rocks or in lithified limestone hard grounds
on the seabed. Bioerosion traces made by gastropods and echinoids are rarely
preserved in ancient cases.
Teredolites Ichnofacies
The Teredolites Ichnofacies is identified by the presence of borings
in wood (especially Teredolites), especially those produced by marine
bivalves such as the modern ship worm, Teredo.
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(after Benton & Harper, 1997)
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