Process ichnology and the elucidation of physico-chemical stress

This paper sets out a philosophical approach to ichnological (trace fossil) analysis, which focuses on the interpretation of trace fossils as sedimentary structures rather than as paleontological entities per se. Using wide-ranging datasets and a large number of observations and interpretations, a “Process Ichnology” framework is proposed. This interpretive framework provides an improved means of estimating the presence and magnitude of various physical and chemical (i.e., physico-chemical) depositional stresses (e.g., water turbidity, sedimentation rates, substrate consistency, salinity, and oxygenation) in ancient sedimentary environments. Ichnological datasets that are considered include: 1) trace-fossil distributions; 2) ethological diversity and the range of diversity; 3) the significance of burrow linings; 4) trace-fossil size; and, 5) post-depositional compaction of trace fossils. From these data, higher-resolution estimates can be made for the determination of sedimentation rates, temporal variation in sedimentation rate, sediment consistency, and aspects of the bottom- and interstitial-water chemistries. Additionally, the character of depositional bypassing of sediment grains can be determined. The methodologies and interpretations herein are intended for use by non-ichnologists in a manner akin to the interpretation of physical sedimentary structures. However, the outlined framework is complementary to other methods of ichnological analysis, such as ichnofacies- or ichnofabric-analysis, and can be applied as such. Indeed, this method is a derivative of these and other earlier techniques, and should be employed where a systematic approach to obtaining high-resolution sedimentological interpretations is a required aspect of the study.