Ichnofacies

An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited.

Psilonichnus

Concept

Trace fossil assemblages are far from random; the range of fossils recorded in association is constrained by the environment in which the trace-making organisms dwelt.^[1] Palaeontologist Adolf Seilacher pioneered the concept of ichnofacies, whereby the state of a sedimentary system at its time of deposition could be deduced by noting the trace fossils in association with one another.^[1]

Significance

Ichnofacies can provide information about water depth, salinity, turbidity and energy. In general, traces found in shallower water are vertical, those in deeper water are more horizontal and patterned.^[1] This is partly because of the relative abundance of suspended food particles, such as plankton, in the shallower waters of the photic zone, and partly because vertical burrows are more secure in the turbulent conditions of shallow water. In deeper waters, there is a necessary transition to sediment feeding (extracting nutrients from the mud).^[1] Food availability, hence trace type, is also controlled by energy: high energy environments keep food particles suspended, whereas in lower energy areas, food settles out evenly, and burrows will tend to spread out to cover as much area as economically as possible.^[1]

Ichnofacies have a major advantage over using body fossils to gauge the same factors: body fossils can be transported, but trace fossils are always in situ.^[1]

Recognized invertebrate ichnofacies

Marine Invertebrate Ichnofacies[1][2][3][4]
Name	Common Ichnogenera	Substrate	Inferred Paleoenvironment
Scoyenia[1]	Skolithos, Cruziana, Diplichnites, Rusophycus[5]	Variable - typically sandstones; red beds may be nearby	Diagnostic of terrestrial[1]/freshwater[5] facies.
Psilonichnus[6]	Psilonichnus, Coenobichnus, Cellicalichnus, Macanopsis[4]	Highly variable grain size, sand, soft substrate[6]	Coastal barrier islands, strand plains, delta plains, estuaries, lagoons, and bays.[4][6]
Trypanites[7]	Entobia, Trypanites, Gastrochaenolites, Caulostrepsis, Maeandropolydora, Conchotrema[4]	Hardground, endurated substrates[7]	Coastal cliffs, reefs, beachrock[8]
Teredolites[9][10]	Teredolites, Thalassinoides[4]	Resistant woody and coaly substrates[11]	Driftwood, peat[11]
Glossifungites[1]	Diplocraterion, Skolithos, Spongeliomorpha, Rhizocoralium, Arenicolites, Thalassinoides, Fuersichnus[1][4]	Firmground, dewatered muds[1]	Shallow, marginal marine, deltaic or estuarine erosion surfaces.[1]
Skolithos[1]	Skolithos, Ophiomorpha, Arenicolites, Diplocraterion[1][4]	Unconsolidated littoral sands[1]	Beaches and sandy tidal flats, shallow water, foreshore to upper-shoreface, above wavebase[1][4]
Cruziana[1]	Arthrophycus, Phycodes, Rhizocorallium, Teichichnus, Arenicolites, Rosselia, Bergaueria, Thalassinoides, Lockeia, Protovirgularia, Curvolithus, Dimorphichnus, Cruziana, Rusophycus[1][4]	Sand and silt heterolithic successions and organic detritus[4]	Mid to distal continental shelves. Below normal wave base, but not necessarily below storm wave base[1][4]
Zoophycos[1]	Zoophycos, Phycosiphon, Chondrites[1][4]	Marine softground, impure sands and silts[1]	Deeper water, bottom of shelf; turbidite facies[1]
Nereites[1]	Nereites, Megagrapton, Protopaleodictyon, Spirophycus, Helminthoraphe, Glockerichnus, Spiroraphe, Cosmoraphe, Urohelminthoida, Desmograpton, Paleodictyon, Scolicia[1][4]	Fine-grained muds and clays interbedded with turbidite silts[1][4]	Deep water, pelagic, base-of-slope turbidity systems[1][4]

Recognized vertebrate ichnofacies

Vertebrate Ichnofacies[12][13]
Name	Common Ichnogenera	Substrate	Inferred Paleoenvironment
Chelichnus[13] (Laoporus)[12]	Chelichnus, Brasilichnium[12][13]	Unconsolidated, larger-grained sands	Aeolian sand dunes[13]
Grallator[12]	Grallator, Jindongornipes, Koreanoformis, Avipeda, Brachychirotherium, Rhynchosauroides, Eubrontes[12][13]		Lacustrine shorelines[13]
Brontopodus[13]	Charirichnium, Ceratopsipes, Amblydactylus, Brontopodus[13]	Clastic or carbonate[13]	Coastal plain, marine shoreline[13]
Batrachichnus[13]	Batrachichnus, Limnopus, Amphisauropus, Dromopus, Dimetropus, Gilmoreichnus, Chirotherium		Tidal flat-fluvial plain[13]
Characichnos[13]	Characichnos, Undichna, Lunichnium, Puertollanopus, Serpentichnus, Batrachichnus, Hatcherichnus[13]	Semi-consolidated firmgrounds	Subaqueous lacustrine, estuarine, and deltaic environments[13]

See also

• Trace fossil classification
• Bioturbation