THE PROBLEM WITH CONTINENTAL ICHNOFACIES MODELS AND PARALLEL CONSTRUCTION WITH MARINE ICHNOFACIES COUNTERPARTS

The erection of continental ichnofacies has been plagued with a multitude of fundamental and constructional problems since the creation of the Scoyenia Ichnofacies by Adolf Seilacher in 1967. He proposed an ichnofacies scheme of trace fossil assemblages recurrent through geologic time that included marine ichnofacies: Skolithos, Glossifungites, Cruziana, Zoophycos, and Nereites. These ichnofacies reflected environmental (facies controlled) and physicochemical conditions that determined the distribution of tracemaking organisms and conditions in which they inhabited. The Scoyenia Ichnofacies encompassed all “nonmarine” redbed environments and was named for the trace fossil Scoyenia, found in Permian fluvial deposits. Since that time, other workers have proposed additional continental ichnofacies, as well as modifying the original ichnofacies and others subsequently proposed. The premise for their construction is purported to be their recurrent, archetypal or representative nature in the geologic record that parallels the construction of Seilacherian ichnofacies, which are based on recurrent facies associations––facies controlled––and related to facies models from which physicochemical conditions are interpreted. This line of inductive reasoning for parallel construction is where “the wheels come off the cart” when proposing continental ichnofacies. First and foremost, the distribution of the vast majority of continental tracemaking organisms is controlled by the groundwater profile. They are NOT facies controlled. Stratal patterns composed of facies associations in continental environments are shaped by sedimentation rate, depositional energy, the frequency, magnitude, and time between depositional events, and hydrology. The distribution of organisms, however, is controlled physicochemically by postdepositional conditions of the environment, which is the groundwater profile, and by extension, climate, and are strongly heterogeneous spatially and temporally. Terrestrial environments are dominated by subaerial exposure and, hence, pedogenesis (soil formation), which can be weak to strong based on depositional environment and climatic settings. Freshwater aquatic environments may appear to be more facies controlled, however, they, too, experience a wide range of groundwater profile, hydrologic, and climatic variability that do not parallel facies associations and, hence, are not facies controlled. Thus, no proposed continental ichnofacies are valid, except for Scoyenia.