Limiting Factors of Bioturbation and Trace Fossil Distribution
Published:January 01, 1984
1984. "Limiting Factors of Bioturbation and Trace Fossil Distribution", Ichnology: The Use of Trace Fossils in Sedimentology and Stratigraphy, A. A. Ekdale, R. G. Bromley, S. G. Pemberton
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If geologists wish to make accurate paleoenvironmental reconstructions based on trace fossil evidence, a clear understanding of the factors that limit trace fossil distribution is essential. Too often we read unqualified statements, such as, “the presence of Ophiomorpha indicates the environment was a beach”, or “the water depth must have been abyssal because of the occurrence of Nereites.” Such interpretations may not be incorrect, but they do imply rather simplistic application of some complex relationships.
Trace fossils represent the presence of particular kinds of behavior patterns in particular habitats, and as such they reflect the paleoecology of the trace-makers. Just as the distribution of animals and plants is influenced directly by a wide variety of physical environmental parameters, so is the trace fossil record they produce (e.g., see papers in Frey, 1975b).
Perhaps the most fundamental aspect to understand about a sedimentary rock is whether it was deposited on land or under water. This is not always easy to discern, and the literature is full of controversies over the origin of specific rock units, which may be interpreted by some workers as subaerial dune deposits and by others as tidal flat deposits, or by some workers as paleosols and by others as lake beds. Perhaps trace fossils can help in such situations.
Paleosols are preserved remnants of ancient soil horizons, which provided stable, although chemically evolving, substrates for organisms. The soils commonly are recognized by characteristic lithic and geochemical sequences, but usually they have a characteristic ichnologic signature as well.
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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.