Recognition of Trace Fossils
Published:January 01, 1984
Trace fossils are very peculiar things. More often than not, the greatest difficulty in dealing with them is simply recognizing that they are trace fossils in the first place! Many a spirited argument has arisen on the outcrop between geologists who take opposing views on the biogenic vs. non-biogenic origin of a particular structure in the rock, and a good share of these arguments go unresolved because of either poor preservation of the structure or lack of clear criteria for distinction between alternative solutions.
We cannot do much about the preservation state, although there are some ways by which we can enhance the visibility of a structure or its component features (see Chapter 4, this volume). We also can seek to develop objective criteria to help us distinguish between biogenic structures and primary (mainly physical) or secondary (mainly chemical) non-biogenic structures. The pitfalls of recognition and identification are many, however, so workers always must proceed with caution and keep their minds open.
If presented with a problematic structure, some criteria which may lead one to consider a biogenic origin include the following items (Table III-1). Be sure to note that the occurrence of one or more of these features may not assure a stamp of certainty on the identification, but at least its (their) occurrence may assist in offering an intelligent guess.
(1) Obvious resemblance of the structure in question to the body form or a body part of an organism. Footprints are a good example of this, because the
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.