Box The nine ichnofacies

The Nereites ichnofacies (Fig. 19.13a) is recognized by the presence of meandering pascichnia such as Nereites, Neonereites and Helminthoida, spiral pascichnia such as Spirorhaphe, and agrichnia such as Paleodictyon and Spirodesmos. Note that the whole concept of agrichnia is debated: the most commonly quoted example, Paleodictyon, has been interpreted as the mold of a deceased, soft-bodied, colonial-type organism, although others dispute this new view. Vertical burrows are almost entirely absent. This ichnofacies is indicative of deep-water environments, and includes ocean floors and deep marine basins. The trace fossils are found in muds deposited from suspension, and in the mudstones and siltstones of distal turbidites.

The Zoophycos ichnofacies (Fig. 19.13b) is characterized by complex fodinichnia like Zoophycos, and it may contain other deep traces such as Thalassinoides in tiered arrangements. The ichnofacies occurs in a range of water depths between the abyssal zone and the shallow continental shelf, and may be associated with low levels of oxygen. This ichnofacies may occur in normal background conditions of sedimentation, whereas the Nereites ichnofacies may be a matching association found at similar water depths during times of event (turbidite) deposition.

The Cruziana ichnofacies (Fig. 19.13c) shows rich trace fossil diversity, with horizontal repichnia (Cruziana, Aulichnites), cubichnia (Rusophycus, Asteriacites, Lockeia) as well as vertical burrows. This ichnofacies represents mid and distal continental shelf situations that may lie below the normal wave base, but may be much affected by storm activity.

The Skolithos ichnofacies (Fig. 19.13d) is recognized by the presence of a low diversity of abundant vertical burrows, domichnia-like Skolithos, Diplocraterion and Arenicolites, fodinichnia-like Ophiomorpha, and fugichnia. These all typically indicate intertidal situations where sediment is removed and deposited sporadically, and 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 upper reaches of submarine fan systems in deeper water.

The Psilonichnus ichnofacies (Fig. 19.13e) is a low-diversity assemblage, consisting of small vertical burrows with basal living chambers, Macanopsis, narrow sloping J-shaped and Y-shaped burrows, Psilonichnus (a ghost crab burrow), root traces and sometimes vertebrate footprints. It is typical of backshore, dune areas and supratidal flats on the coast.

The Scoyenia ichnofacies (Fig. 19.13f) is typified by a low-diversity trace fossil assemblage, mainly simple horizontal fodinichnia (Scoyenia, Taenidium), with occasional vertical domichnia (Skolithos) and repichnia produced by insects or freshwater shrimps (Cruziana) preserved in fluvial and lacustrine sediments, often in the silts and sands of red-bed sequences. Associated subaerial sediments, such as eolian sands and paleosols, representing unnamed ichnofacies, may contain domichnia and repichnia of insects, and dinosaur and other tetrapod footprints.

The Glossifungites ichnofacies (Fig. 19.13g) is characterized by domichnia such as Glossifungites and Thalassinoides and sometimes plant root penetration structures, but other behavioral trace fossil types are rare. The sediments are firm, but not lithified, and may occur in firm compacted muds and silts in marine intertidal and shallow subtidal zones. The firmgrounds may develop in low-energy situations such as salt marshes, mud bars or high intertidal flats, or in shallow marine environments where erosion has stripped off superficial unconsolidated layers of sediment, exposing firmer beds beneath.

The Trypanites ichnofacies (Fig. 19.13h) is characterized by domichnial borings of worms (Try-panites), bivalves (Gastrochaenolites), barnacles (Rogerella) and sponges (Entobia) formed in shoreline rocks or in lithified limestone hardgrounds on the seabed. In modern examples, bioerosion traces such as feeding scrapings made by gastropods and echinoids may be common, but these are rarely preserved in ancient cases.

The Teredolites ichnofacies (Fig. 19.13i) is identified by the presence of borings in wood (especially Teredolites), mostly produced by marine bivalves such as the modern shipworm, Teredo.

Read more about the key ichnofacies through web sites at http://www.blackwellpublishing.com/ paleobiology/.

1 Spiroraphe

2 Lorenzinia

3 Chondrites

4 Paleodictyon

5 Nereites

6 Cosmorhaphe

Repichnia Cubichnia

Nereites Ichnofacies

1 Phycosiphon

2 Zoophycos

3 Spirophyton

Nereites Ichnofacies

1 Asteriacites

2 Cruziana

3 Rhizocorallium

4 Aulichnites

5 Thalassinoides

6 Chondrites

7 Teichichnus

8 Arenicolites

9 Rosselia

10 Planolite not to scale

Cruziana Ichnofacies

1 Psilonichnus

2 Macanopsis

3 vertebrate footprints

1 Psilonichnus

2 Macanopsis

3 vertebrate footprints

Macanopsis
Psilonichnus Ichnofacies
Zoophycos Ichnofacies
Spirophyton

not to scale

Cruziana Ichnofacies

1 Ophiomorpha

2 Diplocraterion

3 Skolithos

4 Monocraterion

Diplocraterion Trace Fossil

not to scale

Skolithos Ichnofacies not to scale

Skolithos Ichnofacies

1 Scoyenia

2 Ancorichnus

3 Cruziana

4 Skolithos

1 Scoyenia

2 Ancorichnus

3 Cruziana

4 Skolithos

Psilonichnus

not to scale

Scoyenia Ichnofacies not to scale

Scoyenia Ichnofacies

Figure 19.13 Block diagrams showing typical trace fossils of the major ichnofacies: (a) Nereites ichnofacies, viewed as molds on a turbidite bed bottom; (b) Zoophycos ichnofacies;. (c) Cruziana ichnofacies; (d) Skolithos ichnofacies; (e) Psilonichnus ichnofacies; (f) Scoyenia ichnofacies; (g) Glossifungites ichnofacies; (h) Trypanites ichnofacies; and (i) Teredolites ichnofacies, characterized by vertical bulbous burrows of bivalves (Teredolites) and subhorizontal burrows. (Based on Ekdale et al. 1984; Frey et al. 1990, and other sources.)

Thalassinoides

not to scale

Glossifungites Ichnofacies not to scale

Glossifungites Ichnofacies

1 Thalassinoides

2 bivalve boring

3 polychaete burrow

4 Rhizocorallium

5 Psilonichnus

not to scale

Trypanites Ichnofacies

1 echinoid grooves

2 barnacle borings

3 sponge borings

4 polychaete boring

5 bivalve boring

6 sipunculid boring

7 polychaete boring not to scale

Trypanites Ichnofacies

Diplocraterion

Teredolite

Teredolites Ichnofacies

Teredolite

Teredolites Ichnofacies

Figure 19.13 Continued

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Responses

  • andrew
    Where does nereites ichnofacies occur?
    1 year ago

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