Introduction to Ichnology
Published:January 01, 1984
Geologists recognize a myriad of post-depositional agents, which invariably influence and alter any sediment as soon as it is deposited. Some of these agents are physical (e.g., oscillating waves, transportive currents and compaction phenomena); some are chemical (e.g., oxygen diffusion, mineral dissolution and cementation); and some are biological (e.g., sediment reworking by animals and plants).
In many cases, the effects of biological agents in the sediment overshadow those of physical and chemical agents in producing recognizable features, such as textures, fabrics and sedimentary structures, that aid geologists in their attempts to understand the history of a sedimentary rock. It is very important for sedimentary geologists to recognize and understand primary textures, diagenetic fabrics and physical sedimentary structures; it is equally important for them to recognize and understand biogenic textures, biogenic fabrics and biogenic sedimentary structures.
The study of post-depositional biological effects on sedimentary deposits is known as “ichnology” (from the Greek iknos, meaning “trace or track”, and logos, meaning “word or study”). The field encompasses those aspects of organism-substrate interrelationships that focus on how plants and animals leave a record of their activity in the sediment. Whether it be a trilobite that makes a footprint, a dinosaur that digs a nest, or a dense population of shrimp that thoroughly churns the sea-floor, its record in the rock is something to interest and excite the ichnologist.
Ichnology is truly an interdisciplinary subject, involving important elements of paleontology, paleoecology, sedimentology, stratigraphy and even geochemistry. The subject has a history of inquiry extending
Figures & Tables
Ichnology: The Use of Trace Fossils in Sedimentology and Stratigraphy
Ichnology is a fascinating field of endeavor. As with science in general, it is a process of solving mysteries–in this case, mysteries of fossil behavior. In a very real sense the ichnologist is Sam Spade or Sherlock Holmes–following footprints, searching for traces of dastardly deeds, studying artifacts, attempting to reconstruct a sequence of events from subtle clues, pursuing the identity of someone (or something) long dead. Who was the culprit? What was he/she doing? Where was he/she living, working or going? Not only intellectually intriguing, ichnology also has practical application and economic importance. In today’s frenzied quest for energy and mineral resources, exploration geologists value every tool that aids their search. Ichnologic observations and analyses can help the sedimentologist reconstruct ancient depositional environments, help the stratigrapher correlate sedimentary strata, help the paleontologist determine the nature of fossil communities, and help the geochemist determine the effect of organisms on sediment composition. This publication was written to serve as a comprehensive and intelligible introduction to ichnology for anyone with even rudimentary geologic training, whether or not that person enrolls in a formal course on the subject. The book emphasizes sedimentologic, stratigraphic and paleoecologic al aspects of ichnology.