Ichnofacies

Arguably the most important use of trace fossils is their application to paleoenvironmental interpretation. As the behavior of an organism is linked to certain environmental conditions, so the manifestation of this behavior (i.e., the trace fossil) is indicative of particular environments. Different types of trace fossils form distinct groupings that are generally stable through time. Four of the identified ichnofacies are primarily related to energy conditions, water depth, and deposition rates. Other ichnofacies reflect the nature of the substrate. Each ichnofacies is named after a characteristic ichnogenus (Fig. 14.2).

Trypanites ichnofacies

Rather than reflecting water depth and physical energy of the environment this ichnofacies is indicative of substrate. The Trypanites ichnofacies is found in fully lithified substrates, such as rocky coastlines and hard grounds. Organisms bore into the substrate for shelter or rasp the surface for food, which forms the traces

Cambrian Skolithos

Skolithos ichnofacies

This ichnofacies is generally developed in shallow water in the nearshore environment. It is typical of higher energy conditions associated with well-sorted, shifting sands. Deep, vertical, and U-shaped tubular burrows characterize the ichnofacies. The resemblance of Skolithos to organ pipes gave the Cambrian rocks of NW Highland Scotland the name "Pipe Rock". Other traces common in this ichnofacies are Ophiomorpha, which is similar to Thalassinoides but has a larger diameter and bumpy outer wall formed of fecal pellets, and Diplocraterion. All these burrows suggest a substrate that is moving, requiring the animals to dig deep burrows and repeatedly modify them during periods of erosion and deposition

Sea level -200 m

Cruziana ichnofacies

The Cruziana ichnofacies reflects shallow water, with lower energy conditions between the outer edge of the surf zone and storm wave base. It is commonly developed in estuarine, lagoonal, or shelf environments. This is a high diversity ichnofacies with crawling, deposit feeding and shelter traces dominating

Ichnofacies

Sea level -200 m

Fossil Trace Classification

Zoophycos ichnofacies

Typically this ichnofacies indicates deep water environments and is developed from the deep shelf to upper continental slope. Complex feeding traces characterize the ichnofacies. Zoophycos, traditionally thought to reflect deeper water settings, is now considered to be associated with low oxygen environments and the low diversity in this ichnofacies may reflect oxygen-stressed conditions

Nereites ichnofacies

Developed on the abyssal plain, this ichnofacies reflects quiet, moderately well-oxygenated conditions. Most traces are found within the lower surface of beds and show a systematic grazing of the sea floor for food and detritus

Fig. 14.2 Ichnofacies and their main trace fossils: A, Caulostrepsis; B, echinoid borings; C, Entobia; D, Trypanites; E, Skolithos; F, Arenicolites; G, Diplocraterion; H, Thalassinoides; I, Ophiomorpha; J, Phycodes; K, Crossopodia; L, Rhizocorallium; M, Asteriacites; N, Zoophycos; O, Lorenzinia; P, Paleodictyon; Q, Cosmorhaphe; R, Heminthoida; S, Spirorhaphe; T, Taphrhelminthopsis.

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