An ichnofacies is an assemblage of trace fossil

Trace fossil

Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...

s that provide an indication of the conditions that their formative organisms inhabited.

The 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. Palaeontologist Adolf Seilacher

Adolf Seilacher

Adolf "Dolf" Seilacher is a German palaeontologist who has made major contributions to evolutionary and ecological palaeobiology in a career stretching over 60 years. He won the Crafoord Prize in 1992, the Paleontological Society Medal in 1994 and the Palaeontological Association's Lapworth Medal...

 pioneered the concept of ichnofacies, whereby the state of a sedimentary system at its time of deposition could be deduced by noting the fossils in association with one another.

Their power

Ichnofacies can provide information about water depth, salinity

Salinity

Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

, turbidity

Turbidity

Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....

 and energy. In general, traces found in shallower water are vertical, those in deeper water are more horizontal and patterned. 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 nutrient

Nutrient

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s from the mud. 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.

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.

Recognised ichnofacies

Ichnofacies
Ichnofacies name	Constituent fossils	Usual matrix	Implied environment
Cruziana Cruziana Cruziana is a trace fossil consisting of elongate, bilobed, approximately bilaterally symmetrical burrows, usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension...	horizontal repichnia and cubichnia; vertical burrows	Well sorted sands and silts	Mid to distal continental shelves. Below normal wave base, but not necessarily below storm wave base
Glossifungites		Omission surfaces	Erosion surfaces on semi-consolidated muds, which suspension feeders dug shelters into. Usually shallow water, but channelisation may allow to occur in deeper water.
Nereites		pelagic muds between turbidites
Psilonichnus
Scoyenia	Skolithos, Cruziana, Diplichnites Diplichnites Diplichnites is an ichnogenus thought to be made by members of the Phylum Arthropoda. It is a fossil trackway showing two parallel lines of feet impressions. The famous terrestrial arthropod genus Arthropleura produces the trace fossil D. cuithensis... , Rusophycus Rusophycus Rusophycus is a trace fossil allied to Cruziana. Rusophycus is the resting trace, recording the outline of the tracemaker; Cruziana is made when the organism moved...	Variable - typically sandstones; red beds may be nearby	Diagnostic of a terrestrial/freshwater facies.
Skolithos Skolithos Skolithos is a common trace fossil ichnogenus whose original form consisted of approximately vertical cylinders. One well-known occurrence of Cambrian trace fossils is the famous 'Pipe Rock' of northwest Scotland...		littoral sands	Shallow water, above wave base (?)
Teredolites
Trypanites Trypanites Trypanites is a narrow, cylindrical, unbranched boring which is one of the most common trace fossils in hard substrates such as rocks, carbonate hardgrounds and shells . It appears first in the Lower Cambrian , was very prominent in the Ordovician Bioerosion Revolution , and is still commonly...
Zoophycos Zoophycos Zoophycos is an ichnogenus thought to be produced by feeding worms.-Occurrence:Zoophycos is found in deep marine muds and sands, often between turbidite beds. It is known from both the fossil record and deep sea sediment cores....		impure sands and silts	Deeper water, bottom of shelf; turbidite facies.