Pitfalls of Paleobathymetric Interpretations Based on Trace Fossil Assemblages

Abstract

Trace fossils have been used widely as indicators of original water depth in paleoenvironmental studies, but most paleobathymetric interpretations in ichnology have been based on only a small number of standard ichnofacies. In addition to bathymetry, it is important to recognize that salinity, oxygen concentration, and substrate character also play a major role in controlling the distribution of trace fossils. Several pitfalls of paleobathymetric interpretation based on trace fossils can lead to erroneous paleoenvironmental reconstructions. The most common of these pitfalls, of which historical geologists should be wary, include the following: 1) occurrence of a particular ichnogenus does not necessarily indicate the presence of the ichnofacies of the same name, and a standard ichnofacies may be identified without the presence of the namesake trace fossil; 2) environmental shifts of certain trace fossils have occurred through time, so the paleoenvironmental significance of a particular ichnotaxon may have changed during its histoty; 3) the nine standard ichnofacies that have enjoyed wide use by ichnologists have broad environmental significance that may include, but certainly extends beyond, bathymetry; 4) not all environmental situations are represented in the nine standard ichnofacies, so many trace fossil associations in the real world cannot be easily fit into those categories.